Author Topic: Suggested MTB air pressures by GEAX (full suspension vs front suspension  (Read 1044 times)

jim-ratliff

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See the link below that Svend sent me in email.  I find it very interesting that they recommend different air pressures for full suspension bikes than for front suspension bikes (though I can manufacture a reason why).  Equally interesting that they don't differentiate between tubed and tubeless tires.

http://www.geax.com/en/technology/?cat=15&prod=79

Examples for Lynn and I.  I weigh 183 with a 27 lb full suspension bike. She weighs 120 with a 26 lb full suspension bike.

J. Full suspension bike, 2.1 tire, 210 lbs combined weight.  Front = 42, rear = 50.  (Front susp:  Front=39, Rear=46)
L. Full suspension bike, 2.1 tire, 150 lbs combined weight.  Front = 33, rear = 41.  (Front susp:  Front=30, Rear=38)
L. Full suspension bike, 1.9 tire, 150 lbs combined weight.  Front = 36, rear = 44.  (Front susp:  Front=33, Rear=41)


B. Full suspension bike, 2.3 tire, 190 lbs combined weight.  Front = 36, rear = 44.  (Front Susp:  Front=33, Rear=40)
« Last Edit: August 12, 2011, 03:30:48 pm by jim-ratliff »
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bushwacka

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they are right that you can run lower pressure on the rear of a FS bike. The suspension make it less likely to pinch the tire(or tube if you still insist on running those things).

With that said I never run much less than these guys, I do run tubeless but noone runs pressures that high even with tubes.

I weigh 166lb and run 24 psi front and 28 psi rear on my FS bike and run 30 psi rear on my SS hardtail.

jim-ratliff

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Bushwacka:

They are saying the opposite, that it's more efficient to run higher pressures front and rear on a full suspension bike.

I'll edit the first entry and post their recommendations for your weight and full suspension. (cause I'm 20 pounds heavier than you.
« Last Edit: August 12, 2011, 03:55:08 pm by jim-ratliff »
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bushwacka

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I have no idea then seems strange.

I would ask their pros before blindly following some website. ask any legit pro XC race guy there pressure and I be surprised to ever hear over 35 most are closer to 20-25. if it wasnt faster they wouldnt do it.

jim-ratliff

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I remember the excellent link you provided of the guys using power meters across uneven terrain. 
But this is interestingly different.  Equally interesting that they broke it down by type of suspension and not for tubeless vs. tubed.
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bushwacka

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yeah I do not find it interesting I find it incredibly flawed and missed leading. I have spent the last half hour trying to find a pro racer who rides Geax tires to no avail.

jim-ratliff

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Here's the logic.  I don't think it's flawed, may be incomplete.

Sheldon Brown's website (a road biker) was the first place I read about the advantages of lowering pressure to let the tire absorb some of the terrain.  Obviously in road bikes, its just minor irregularities.  Every time a bike goes up and over an irregularity, it bleeds enough energy to lift the entire weight of the bike by that amount.  Energy has to come from somewhere, and it comes from pedaling.  And so, while most people ride their bikes with 100+ pounds of air, he recommended 90 or even less and also pointed out that pro riders use considerably less.  This is consistent with the New Zealand power meter tests that you provided the link for.

However, it's like race cars where you reduce the unsprung weight as much as possible (partly for different reasons).  On a hardtail, all of the rear weight (including the rider) is unsprung.  But, if all that has to move to absorb the bump is the suspension, then it's not nearly as much work to lift the rear suspension as to lift the whole bike.

MAYBE.  But GEAX also didn't support their recommendations with power meters or any evidence at all.  And none of this even talks about relative grip. My son is a off-road Jeep fanatic, and they do the same thing.  They air the tires down to 5-10 psi for grip off-road and over rocks even if it requires more horsepower to turn them, and then air them back up for the ride home.  Most hard core jeeps have an aftermarket air compressor under the hood just to air the tires back up for the road.


I would guess that long MTB endurance races run higher pressures than shorter races???
« Last Edit: August 12, 2011, 04:23:21 pm by jim-ratliff »
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Svend

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Jim, it sounds like you are talking yourself into running lower pressure than you are at present  8)  I know that to a veteran road rider like yourself, 30 or 35 psi must sound like a near-flat tire, but it actually works better.  Even with tubes (sorry Josh). 

When I started lowering the pressures on all our bikes, everyone noticed an improvement in grip on the single track.  Rolling resistance on the hard gravel rail trail is much worse, so I pump 'em all back up to 50psi for those rides.  But for rides in the woods, the girls (being slightly lighter than me) are all down to 30 psi, and I run 35 psi on my 29er.  Luckily there are few sharp rocks here to shred sidewalls (mostly glacial moriane sand and gravel deposits here -- nice round rocks) and we don't do big hits to cause pinch flats, so we can get away with that with tubed tires.  At 45 to 50 psi on single track, we were bouncing and slipping all over the place, esp. the three of us riding hardtails.  Not fun.

FWIW, I have not had a pinch flat in about 10 years, since I used Panaracer Smoke which had really thin sidewalls.

So.....why not try it for a ride? Nothing to lose, eh? If you don't like it, take out your pump and puff 'em back up again.  (Er....you did buy a mini-pump to carry along....didn't you?)  :D

« Last Edit: August 12, 2011, 09:39:02 pm by Svend »

jim-ratliff

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 :D


I've been up and down the range of pressures some (pinch flatted with front tire at 35).
Rolling resistance at lower pressures with my tires and bike is noticeably more work.
But "a pressure" is also not apples and apples. A 26" takes more pressure than a 29".  A 2.1 width takes more pressure than a 2.3.  And Jim at 180 takes more pressure than Josh at 165, and Lynn at 120 takes a lot less pressure than Jim.
Tires with stiffer sidewalls require less pressure than tires with really flexible sidewalls.



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bushwacka

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a 26er does not take more pressure than a 29er..... I was able to run even lower on my 26er because I was able to use a wider stiffer tire on a 26er than I can find for a 29er.

remember wider tires roll faster but only at lower pressure, and only with out tubes. If you lower pressures with a tube in it the tube is now flexing with the tire flexing, its also causing friction as they rub on each other. The friction is compounded by such a skinny tire as the contact patch is much longer on the ground than a wide tire.

a ghetto tubeless setup will take a 30 minutes and 30 dollars to set up and can be done on nearly any bike and any wheel combination. Judging by how much time both of you guys are posting on here discussing you slightly lower but still way to high pressure, why not look up how to do it, and just do it. Ill even give my number out so I cna walk you though it.

http://www.tetongravity.com/forums/showthread.php/98811-Ghetto-Tubeless-A-how-to.?highlight=Ghetto%20Tubeless

sorry the pictures are down but really I would just try it, you have nothing to lose.


jim-ratliff

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BW:

Ok, you make my point. For the same tire the 29 will require less pressire than the 26 because the 29er has a larger contact patch (longer). The same is true of a 2.3 tire as opposed to a 2.0 (15% wider contact patch).

I'm 20+ lbs heavier than you (and 35 years older), running a  15% narrower tire than you, and a tire with much less stiff sidewalls than you. It's inconceivable to me that we should be running the same tire pressure.

My tires, with me on the bike, do NOT roll easier at 35 pounds than at 45.

Maybe the problems you had with sidewalls on the SB8 were because you were locked in to a given pressure and they needed 7 pounds more?
« Last Edit: August 13, 2011, 09:09:29 pm by jim-ratliff »
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jim-ratliff

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BW (and everyone):

The fact that I may not choose to totally follow anyone's advice doesn't mean that I don't totally enjoy all of the information that you have brought to the forum.

People like me that are in their 60's are entitled to be a bit obstinate?   ::)   Who knows, I may "discover" the advantages of lower tire pressures in a year or two.

Lynn and I were both wanting to ride 50 miles today.  She got hers, I got a flat after 33 and stopped.
« Last Edit: August 13, 2011, 08:03:03 pm by jim-ratliff »
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bushwacka

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BW:

Ok, you make my point. For the same tire the 29 will require less pressire than the 26 because the 29er has a larger contact patch (longer). The same is true of a 2.3 tire as opposed to a 2.0 (15% wider contact patch).

I'm 20+ lbs heavier than you (and 35 years older), running a  15% narrower tire than you, and a tire with much less stiff sidewalls than you. It's inconceivable to me that we should be running the same tire pressure.

My tires, with me on the bike, do NOT roll easier at 35 pounds than at 45.

Maybe the problems you had with sidewalls on the SB8 were because you were locked in to a given pressure and they needed 7 pounds more?

the 29er does not have a larger contact patch it does have longer one though.  The deal was to get the SB8 from stop flatting I had to run them at a pressure that exceeded my skill level of bike handling. So being that I like to make things as easy as possible I got rid of the SB8. The Pirannha is just as fast with sidewalls that can withstand 28 psi alot better.

like I have been saying you CAN NOT run a low pressure on a tubed tire and expect it to roll better. It will grip more but it will not roll better. There is a TON of friction between the flexing tire and tube that becomes rolling resistence. You can not understand low pressure and why it rolls faster and grips more untill you ride a tubeless tire.


jim-ratliff

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the 29er does not have a larger contact patch it does have longer one though. 


Contact patch means "area" of the tire (bike or car) in touch with the surface.  Area = length X width.  A "longer" contact patch or a "wider" contact patch both result in a "larger" contact patch.
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jim-ratliff

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Josh:  So give me a summary by answering the following questions.

1. Your new bike.  What size wheel and tire, and what pressures do you run front and rear?

2. Your single speed. What size wheel and tire and what pressures do you run front and rear?


And a counter-point article that maybe hits at the real point, you and I are different riders.
I especially liked his summary:

http://www.downcycles.com/blogs/techtips/2009/05/24/title_1



I recommend tubeless tires to riders who are competitive. Many a race has been lost due to a tube pinch flat. Riders who have a fat wallet and a lot of patience are also good candidates for tubeless. Weekend warriors should stay clear of tubeless. I feel that most riders will suffer with problems with tubeless. Tube systems work pretty well and are pretty easy to work on trail side.
In the long run, most riders will end up running tubes in the tubeless tires. I?ve battled the tubeless system tooth and nail. As of now, I have a leaky tubeless Igniter on the front of my bike and a Cross Mark on the rear with a tube since the tires bead is weak, not enough to bulge the tube, but just enough to leak all the air if set up tubeless.
In other words, I?ve been beaten by tubeless tires. I have surrendered, forced to run tubes inside this sophisticated, brilliantly engineered, tubeless work of art.
« Last Edit: August 15, 2011, 07:30:38 am by jim-ratliff »
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jim-ratliff

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I would ask their pros before blindly following some website. ask any legit pro XC race guy there pressure and I be surprised to ever hear over 35 most are closer to 20-25. if it wasnt faster they wouldnt do it.


Agreed, And you/they have the engine to expend going fast.
For me, faster isn't much of a factor or motivation at all.  The legit "pro race guy" doesn't have any relevance to me.
That would be like me using the same skis that you use -- I don't ski the places that you go and don't place the same demands on my skis, or expect the same performance that you do.   ;D


So the question becomes, for the average rider more than 40 years old (and his family), are tubeless MTB tires simpler, more cost effective, less tiring, and more reliable than tube type tires. 
« Last Edit: August 15, 2011, 02:05:49 pm by jim-ratliff »
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Svend

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So the question becomes, for the average rider more than 40 years old (and his family), are tubeless MTB tires simpler, more cost effective, less tiring, and more reliable than tube type tires. 


A most excellent question, Mr. R! Since my great enthusiasm of yesterday about going tubeless for our entire family's fleet of bikes, I have since tempered that with a mild dose of reality.  I called a few friends and family who are mtn. bike nuts, but of the non-racer persuasion, and also talked to a couple of shop guys, to get some other opinions.  The consensus is split, not surprisingly, among exactly those two groups -- the shop guys (who all race, BTW) said tubeless is great, go for it, etc.; whereas friends/family said it's not worth the all the work for the marginal gain if you're a recreational rider. 

From these conversations, and from reading some objective reviews online, I have decided that I will try tubeless for my bike, because the tires and rims are TLR, as an experiment to see how easy/hard it is to do and how reliable it is with gear that was designed for this.  But for our other three bikes, which do not have TLR rims or tires, I will not be doing it, and for the following reasons: 

-- too much work...with a busy small business to run, and two very active teenage girls at home, I simply don't have time to fuss around with sealants and BMX tubes and keeping on top of leaks -- it's enough work just keeping all four bikes in good running tune....mtn. biking is not my life, but is a fun pastime, and bike maintenance shouldn't take more time than actual riding;

-- I don't have the tools....meaning I don't own an air compressor, and don't intend to buy one just for going tubeless;

-- it's messy....leaking sealant all over our garage floor does not appeal;

-- marginal weight gain....yes tubeless removes the tube, but ghetto tubeless puts half a BMX tube back in again, plus a whole lot of liquid goo; alternatively, if I bought UST tires, they all weigh more to begin with....typically at least 100g more; so either way, I'm not convinced I'd actually be saving much weight at all.

Seems to me that this would all be for marginal performance gain anyway.  A bit of extra grip and a few ounces lighter really won't make much difference for our bikes or where we ride (easy to intermediate single track, mostly hard clay with a bit of sand, round stones and roots thrown into the mix -- nothing sharp or jagged or rugged).  Let's face it, we are recreational riders, just out for fun, fresh air, camaraderie, and to enjoy the great countryside we live in.  We rarely do rides longer than 2 hours, and are all fit enough to roll a few ounces extra weight for that amount of time.

To put this in a different perspective, all of us -- myself, my wife, and esp. the girls, who are totally new to this sport -- still have a lot of fundamentals to learn (or relearn in mine and my wife's case -- we rode a lot until 16 years ago when our first daughter came along, and are now getting back into the sport).  Balance; using body angles and position for climbing/descending/cornering/jumping/hairpins; gear selection; braking; acceleration......y ou name it....basic good, flowing, riding skills...and gaining confidence at the same time.  Worrying about tubed vs. tubeless is rather low on the list of priorities.  We all have great bikes, and I do keep them well tuned and running silky-smooth.  And there are good tires on all our bikes.  As I've mentioned, I have been running lower pressures in these already -- down to 30 psi for the lighter gals; 35 psi for me -- which all seems to be working fine.  Much better grip than say, 45+ psi, and no pinch flats so far (cross fingers).  When looking at replacement tires, I will choose some that have robust sidewalls that won't be prone to pinch flats, which should continue to keep us out of trouble.

So, Josh, thanks for all the tips and help.  I really appreciate your time to educate us all here about having this option for our bikes.  For the right rider and situation, it looks like a great way to go.  But until I have more time and energy to spend on this sport, and until we all become much more skilled riders and thus more demanding of our equipment, I think I will try tubeless only for my bike.  I would like to shed a bit of weight, as the 29er is not exactly feather-light, and because the tires and rims are already TLR, this seems like a great way to do it.  I'll let you all know how it turns out later.

Cheers!

« Last Edit: August 15, 2011, 06:10:25 pm by Svend »

bushwacka

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the 29er does not have a larger contact patch it does have longer one though. 


Contact patch means "area" of the tire (bike or car) in touch with the surface.  Area = length X width.  A "longer" contact patch or a "wider" contact patch both result in a "larger" contact patch.

you guys spend alot of time typing. In the time since I last left here I could have done a 100 mile bike ride and converted 10 tires to tubeless

contact patch does not change from one bike to one bike.

The only 2 variable in contact patch are

sprung weight
air pressure

wheel size, tire size and bike do not affect contact patch size. they will affect shape but the size. The square centimeters put on the ground would not change on my bike if I though pugsley tire on it or a road tire. Only the shape would be different.

BTW you have unsprung weight totally wrong in an early post, I typed up an explanation but the forum deleted it.


bushwacka

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Josh:  So give me a summary by answering the following questions.

1. Your new bike.  What size wheel and tire, and what pressures do you run front and rear?

2. Your single speed. What size wheel and tire and what pressures do you run front and rear?


And a counter-point article that maybe hits at the real point, you and I are different riders.
I especially liked his summary:

http://www.downcycles.com/blogs/techtips/2009/05/24/title_1



I recommend tubeless tires to riders who are competitive. Many a race has been lost due to a tube pinch flat. Riders who have a fat wallet and a lot of patience are also good candidates for tubeless. Weekend warriors should stay clear of tubeless. I feel that most riders will suffer with problems with tubeless. Tube systems work pretty well and are pretty easy to work on trail side.
In the long run, most riders will end up running tubes in the tubeless tires. I?ve battled the tubeless system tooth and nail. As of now, I have a leaky tubeless Igniter on the front of my bike and a Cross Mark on the rear with a tube since the tires bead is weak, not enough to bulge the tube, but just enough to leak all the air if set up tubeless.
In other words, I?ve been beaten by tubeless tires. I have surrendered, forced to run tubes inside this sophisticated, brilliantly engineered, tubeless work of art.


1. New bike there both change quite bit but currently

Front Tire 29x2.25 Maxxis Ardent 24 psi,  Rear Tire Hutchison Tubeless ready Toro 29x2.15 27 psi

2 single Speed

currrently

Front tire 29x2.15 Hutchison Toro Tubeless ready 22 psi, Rear tire Hutchison Tubeless ready 29x2.15 28 psi

I have to be really careful with this rear tire that low because of pinching the tire, but the rear of my SS needs as much grip as I can give it.

The guy can say whatever he wants. He tried it with seemingly really shitty results. I have had tires never flat for 1500-2000 miles.


jim-ratliff

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BW:


Thanks.


And I also understand that his article is just another person's opinion. And his racing may be more downhill or jumps or something else related to HIS riding style. (or maybe your ghetto setup works better than whatever he was doing).
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jim-ratliff

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the 29er does not have a larger contact patch it does have longer one though. 


Contact patch means "area" of the tire (bike or car) in touch with the surface.  Area = length X width.  A "longer" contact patch or a "wider" contact patch both result in a "larger" contact patch.

you guys spend alot of time typing. In the time since I last left here I could have done a 100 mile bike ride and converted 10 tires to tubeless

contact patch does not change from one bike to one bike.

The only 2 variable in contact patch are

sprung weight
air pressure

wheel size, tire size and bike do not affect contact patch size. they will affect shape but the size. The square centimeters put on the ground would not change on my bike if I though pugsley tire on it or a road tire. Only the shape would be different.

BTW you have unsprung weight totally wrong in an early post, I typed up an explanation but the forum deleted it.


OUCH.  Your engineering understanding surprises me sometimes.  You are right about the contact patch.  It's determined by the weight the tire has to support. Wrong thinking on my part. Good catch. 


I type much better than I ride, btw.
« Last Edit: August 16, 2011, 07:39:32 am by jim-ratliff »
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bushwacka

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I would ask their pros before blindly following some website. ask any legit pro XC race guy there pressure and I be surprised to ever hear over 35 most are closer to 20-25. if it wasnt faster they wouldnt do it.


Agreed, And you/they have the engine to expend going fast.
For me, faster isn't much of a factor or motivation at all.  The legit "pro race guy" doesn't have any relevance to me.
That would be like me using the same skis that you use -- I don't ski the places that you go and don't place the same demands on my skis, or expect the same performance that you do.   ;D


So the question becomes, for the average rider more than 40 years old (and his family), are tubeless MTB tires simpler, more cost effective, less tiring, and more reliable than tube type tires.

your still not understanding physics.

the deal is you can measure the decrease in rolling resistance with a SRM if you have a wider tubeless tire.

the first thing you have to understand is a narrow tires roll slower due to these facts.

Contact patch SIZE does not change no matter what tire you put on your bike. If you put a 1.3 inch slick and 2.6 inch knobby, the contact patch will remain the same size. It will not however remain the same shape. The slick will have a longer narrow contact patch and the knobby with have short, and wider contact patch. They will be the same overall size though. You can easily test this and this is fact please do not debate a fact unless you have some new experiment to disprove what many people who are smart know.

Ok so fact number one - Contact patch given the same pressure and over bike/ride weight is the same.

fact number 2 - a shorter contact patch has short lever working against you. where as the longer contact patch has longer lever. translation assuming no friction from a tube,(and no increase in weight) a wider tire is going to roll faster than a narrow tire, because of its shorter lever.

curious how many tubes you guys have replaced this year alone? 5 bucks a tube starts to add up. I have replaced zero on my own bike. When someone use one of my tubes to repair their flat. I take it off of them at the end of the ride. I call it the tube of shame. your tires should never flat while MTBing.

On skis I know your much older than me, but if you were the same age as me. Its the argument of the chicken and the egg aint it? can you not ski the same terrain as me because your not as good as me? or is it because of the better equipment I am using? ME personally I would never want to think that my equipment was ever holding me back. I am the only excuse for not doing something not what i am skiing or riding.


bushwacka

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the 29er does not have a larger contact patch it does have longer one though. 


Contact patch means "area" of the tire (bike or car) in touch with the surface.  Area = length X width.  A "longer" contact patch or a "wider" contact patch both result in a "larger" contact patch.

you guys spend alot of time typing. In the time since I last left here I could have done a 100 mile bike ride and converted 10 tires to tubeless

contact patch does not change from one bike to one bike.

The only 2 variable in contact patch are

sprung weight
air pressure

wheel size, tire size and bike do not affect contact patch size. they will affect shape but the size. The square centimeters put on the ground would not change on my bike if I though pugsley tire on it or a road tire. Only the shape would be different.

BTW you have unsprung weight totally wrong in an early post, I typed up an explanation but the forum deleted it.


OUCH.  Your engineering understanding surprises me sometimes.  You are right about the contact patch.  It's determined by the weight the tire has to support. Wrong thinking on my part. Good catch. 


I type much better than I ride, btw.

sorry for the caps in the lat post....

its the contact patch starting to making sense though now?

the real reason why road bikes have narrow tires has more to do with aerodynamics and weight than rolling resistance.  On MTBs for XC racing almost all the pro run 2.25 front and at least 2.1 rear. Some run as wide as 2.4 fronts and 2.35 rear.

In a perfect world 2.4 would weigh as much a 23c road tire and in that perfect world the 2.4 would for sure roll faster due to its short contact patch. In the real world wider tires do add weight, there is point in time where staight line speed is going to be sacrificed by the added weight, there is also a point in time where the added corning grip is not going to make you any faster.
« Last Edit: August 16, 2011, 07:39:01 am by jim-ratliff »

jim-ratliff

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curious how many tubes you guys have replaced this year alone? 5 bucks a tube starts to add up. I have replaced zero on my own bike. When someone use one of my tubes to repair their flat. I take it off of them at the end of the ride. I call it the tube of shame. your tires should never flat while MTBing.

Tube count for me??

One mtb tube when I lowered the front pressure to 35 and got a flat.  Patched the tube and it's my spare.

One roadbike tube.  I converted to 25c tires this year and had been working my pressure down.  Snakebite Saturday after 30 miles at 95 lbs when the back rolled over a rock or something. I didn't see it, must have swerved over something. Patched the tube and it's now my backup.

I don't think that's at all bad, considering.  And I buy cheap tubes at Performance Bicycle.

« Last Edit: August 15, 2011, 10:35:35 pm by jim-ratliff »
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jim-ratliff

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Unsprung weight??

On cars, unsprung weight are those parts (wheel, tire, brakes, spring, some control arms weight) that move up and down with the road surface and are not isolated from the road surface by the springs.

On my GT, I am sprung weight, but most of the rear triangle and wheel and tire are unsprung as is the front tire/wheel and bottom part of the shock??
« Last Edit: August 16, 2011, 08:21:12 am by jim-ratliff »
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Svend

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curious how many tubes you guys have replaced this year alone? 5 bucks a tube starts to add up. I have replaced zero on my own bike. When someone use one of my tubes to repair their flat. I take it off of them at the end of the ride. I call it the tube of shame. your tires should never flat while MTBing.


Tube count for me = 1 tube, about 12 years ago, when I used a Panaracer Smoke rear tire that had thin sidewalls.  Pinching wore a hole through the sidewall, and the tube too.  Replaced with an exact clone -- the IRC Piranha Pro -- which had the same tread pattern but stiffer sidewalls, and have not had a single flat since.  Nor on any of our other bikes.  As I've said several times, we don't have very rugged terrain here (no sharp rocks and such) so I think that really helps us to run 30 to 35 psi in tubed tires.  No sharp hits on the wheels = no pinch flats.  :)



Ok so fact number one - Contact patch given the same pressure and over bike/ride weight is the same.


Eh? What's that ya say Sonny?   |:-{)~    I can't hear ya!

Gee, if using all capital letters in a post is considered shouting, then what does 24pt font mean? Using a bull horn? No need to yell at us, Josh. ;D  We may be older and obstinate (well, at least Jim is  ;) ) and slow to change our ways at times  ::) ,  but we're not hard of hearing yet.

Cheers!


« Last Edit: August 16, 2011, 03:16:31 pm by jim-ratliff »

Svend

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Getting back to the original post, I was curious about how the Geax table matched with what I am putting in our tires, so I converted the presssures from the table to psi, and then calculated what our pressures should be.  Interestingly, the pressures that I am keeping right now (except for mine), are actually pretty close to what Geax recommends. 

Here are the recommended pressures for the gal's rides:

T's bike, 26in. hardtail -- front 33; rear 40
M's bike, 26in. hardtail -- front 29; rear 36
A's bike, 26in. full-suss -- front 35; rear 42

For all the above bikes, I am putting in about 30 to 35 psi front and rear, which is about what they recommend.  The difference is for the rear tire, where Geax recommends higher psi than I use.  I find these recommendations useful, and will try upping the rear tire a bit and see what the feedback is from the girls.

As for my bike, Geax has no recommendations for 29in. tires, but if I use the recommended pressures for 26in. tires, here is the outcome:

S's bike, 29in. hardtail -- front 42; rear 51

I'm not sure if this is a realistic correlation from 26in. to 29in., but these pressures are higher than what I am running now.  Personally, I find that 50 psi is too high for me on singletrack, but works perfectly well on hard pack smooth trails.  I will browse the other tires maker's sites and see if I can find a similar table that includes 29in. tires.



« Last Edit: August 16, 2011, 05:39:09 pm by Svend »

bushwacka

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again I think the Geax site is utter bullshit.

You can listen to it but there isnt a single MTBer I know in person that would listen to it.

I really think I am going to have to ride with you guys and give you some wheels to try out.

bushwacka

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http://twentynineinches.com/2007/08/11/geax-saguaro-29-x-220-tires-final-review/

a real rider riding a Geax tire. He is not riding their suggested pressures though......

Leelikesbike agree with me as well

http://www.leelikesbikes.com/22-or-24-specialized-purgatory-front-tire.html

"Rolling resistance ? Definitely slower on smooth surfaces, but that?s not where you ride. On rougher surfaces, bigger tires (with proportionally lower air pressure) tend to roll faster than smaller ones."

again he is only talking tubeless you know the technology thats been around since 1999......
« Last Edit: August 16, 2011, 09:20:54 pm by bushwacka »


jim-ratliff

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OK, I'm convinced.   ::)
« Last Edit: August 17, 2011, 06:49:38 am by jim-ratliff »
"If you're gonna play the game boy, ya gotta learn to play it right."

jim-ratliff

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lighter faster rolling tires are not faster on trail

http://www.leelikesbikes.com/are-freeride-tires-faster-than-xc-race-tires.html

----  when speed, especially speed through corners, is the criteria. (i.e. Racers)

My experience on that same course probably would not be the same, because I'm not going to be pushing the limits of traction in the corners.

"If you're gonna play the game boy, ya gotta learn to play it right."

Svend

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Hey Josh,

Nice review on the Geax Saguaros.  Thanks for finding that, as I've been looking at replacements for my Bontragers for a while, and that one looks like a winner.  As I mentioned, my wife has Geax Arrojo on her bike, and loves them.  They make great tires, and I'm pleased to see a good one of theirs in 29er size.  Might be a great choice for my rig, and for my wife's when the Arrojos wear out.

As for our ongoing pressure debate, I think you are somewhat missing my point.  I have said all along that for single track riding, we all prefer to run our tires at lower pressures than for the hard pack flat trails -- ie. at 30 to 35 psi, even on my bike.  This does not seem overly high to me.  That is about as low as I am comfortable going with tubes, for fear of pinch flats or denting our rims.  For a rider of my weight (220 lbs), 35 psi with tubes is kind of pushing the limit, don't you think?  And yet, I have not had a pinch flat so far. 

So.....it seems that you and I actually agree on something. 

Coincidentally, our pressures happen to agree quite closely with Geax, at least for the lighter girls, but I don't recall you saying that 30 psi was WAY too high, at least for a tubed tire.  Perhaps the Geax tables are not "utter b***sh**" after all, as you so eloquently put it.  So....perhaps we agree on that too?

Believe me, if I could go lower, I would.  But other than on my bike, which is TLR, I am just not willing to go tubeless, meaning that I don't want to go through the hassle of converting non-TLR rims and tires to tubeless, for reasons I've already stated.  I don't think anyone is doubting your assertions that tubeless is better.  I'm sure you are right.  You are a far more experienced rider than we are, and I do believe you.  But you have different demands of your gear, and are willing to put extra time and effort into getting better performance, but I am not.  We are all recreational riders, not professionals or serious racers, and therefore have different expectations of our gear, and limits to the time and money we spend.

Speaking of which.....
a real rider riding a Geax tire......

Not sure what you mean by a "real rider"? What is your definition of real rider? Does that include only racers? Elite mtn. bikers? Am I a "real rider" in your eyes? I hope we have some mutual respect here....with emphasis on mutual.

Regards,
S

bushwacka

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I actually do respect you guys, but would you respect you even more if you tried something before discounting it and did not just say its too tough or to much hassle with out first ever trying any of my methods.

He is a real rider because he is someone who has figured out what pressure and what tires will work best for him. What you guys are doing is like arguing whether a 78mm or 82mm ski is better in powder, when the real answer is neither.

I just hate arguing quantifiable facts about physics.  Its like arguing whether the sky is blue or not, or whether gravity holds us to the earth. The scary thing is we know much more about why the sky is blue, or the rolling resistance/grip of tire than we know about gravity. I do not speak opinions ever.

If I did not respect you guys Id be telling you to run 1.8 at 60 psi because that is the faster way to ride!  ;D


jim-ratliff

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lighter faster rolling tires are not faster on trail

http://www.leelikesbikes.com/are-freeride-tires-faster-than-xc-race-tires.html

This was a pretty good link, and my compliments to Lee's bikes for putting together such an instrumented and objective test. It just doesn't prove your assertion.  On the three mile flat putting out 100W, the cross country was 38 seconds faster.  On the 2 mile 10% climb the XC tire was 19 seconds faster.  On the trail, the lighter faster rolling tire was faster.  On any section that included curves and demanded traction, the freeride tire killed the XC tire. And they clearly say that in their analysis.

My conclusion.  Freeride (wider, low pressure) tires don't roll faster, but what they surrender is more than made up by additional traction for those riders that can take advantage of the traction.  Not my opinion, facts proved in the test. And it certainly highlights why real racers use wider, lower pressure tires.
And, even for me, I'm feeling like we've talked this to death.
« Last Edit: August 17, 2011, 07:18:10 am by jim-ratliff »
"If you're gonna play the game boy, ya gotta learn to play it right."

Svend

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Hey -- thanks Josh.  Good of you to clarify that.  And sorry if I took you on on that one.  I wasn't sure where you were coming from with the "real rider" comment, and just wanted to make sure that you were on the up-n-up.  We have had some people here on this forum who have behaved in a very disrespectful and condescending way to others because we didn't seem to fit their elitist ideals.  So thanks for sorting that out.  I appreciate that.

As for tubeless vs. tubed, high pressure vs. low -- I think we've flogged this one enough.  Please don't get the impression that I am criticizing what you have to say.  I said the following last night.....
As for our ongoing pressure debate, I think you are somewhat missing my point.  I have said all along that for single track riding, we all prefer to run our tires at lower pressures than for the hard pack flat trails -- ie. at 30 to 35 psi, even on my bike.  This does not seem overly high to me.  That is about as low as I am comfortable going with tubes, for fear of pinch flats or denting our rims.  For a rider of my weight (220 lbs), 35 psi with tubes is kind of pushing the limit, don't you think?  And yet, I have not had a pinch flat so far. 

Believe me, if I could go lower, I would.  But other than on my bike, which is TLR, I am just not willing to go tubeless, meaning that I don't want to go through the hassle of converting non-TLR rims and tires to tubeless, for reasons I've already stated.  I don't think anyone is doubting your assertions that tubeless is better.  I'm sure you are right.  You are a far more experienced rider than we are, and I do believe you.  But you have different demands of your gear, and are willing to put extra time and effort into getting better performance, but I am not.  We are all recreational riders, not professionals or serious racers, and therefore have different expectations of our gear, and limits to the time and money we spend.

.....which indicates pretty clearly that I actually agree with you, and would like to try tubeless for my bike.  But that I have other reasons for not going tubeless on the other bikes (ie. I don't own an air compressor, etc.....) that have nothing to do with dismissing your advice or disrespecting what you have to say. 

We do like a good argument around here at times, but no one should take these lively discussions personally.  Sometimes we take a contrary position just to flush out more detail, when the original assertion looked a bit sketchy.  Then we all agree in the end....or not.  But that's OK, ain't it?  This tire pressure debate was great fodder to kill some time until we can argue about ski stuff once the autumn comes.  Speaking of which, what's wrong with using an 82mm ski in powder?

(just kidding..... ;D)

Cheers,
Svend
« Last Edit: August 17, 2011, 07:24:43 am by Svend »