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

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

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

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 »