Off-road 29er tyre pressure survey

[gkmac]

I've had a Schlumpf 29er for about a year now, used for speedy tarmac riding courtesy of the Big Apple tyre. Thanks to a little persuasion from little Roger I bought a "spare" Kenda Klaw XT rear tyre at the same time.

Only now have I just put it on, with the intention to try out my XC routes on fireroads, which up until now I've exclusively tackled with a 24" 2.6" muni, which seems like a tractor for the long routes, capable but rather heavy and slow. There's nothing technical apart from the occasional unavoidable root or so.

But what tyre pressure to put in it? I've done a search on the forums and they all say things like "I've increased/decreased the tyre pressure and it works better"... with no mentions of actual psi numbers.

So what psis does everyone have in their 29er off-road tyres? Replies from Kenda Klaw XT users are preferable, but any other 29er off-road tyre owners would be worth listening to as well.

[johnfoss]

Mostly people don't give numbers because they don't apply to you. For their numbers to be useful to you, you would have to have the same rim, the same tire, the same type of terrain, and live at similar elevations. And then there's the whole thing about how most tire pressure gauges are not that accurate.

Which means, unfortunately, you're going to have to experiment. Rule one, keep the rim from touching the ground. This means more pressure than you may want if there are drops, sharp rocks, etc. Beyond that, you'll have to do some riding and testing. Start with high pressure and work your way down, it's a lot easier than going the other way.

I did this a few weeks ago. It was my first MUni ride after several weeks of prep for the Lake Tahoe (Coker) ride. The tire and seat height just didn't feel right and I did a whole bunch of changes before it felt comfortable. Then I was at the top of the long climb and the rules changed...

[Mikefule]

On my 28" I run the tyre at 130 psi. As yours is a 29" and therefore,
3.5% bigger, that would suggest about 136 psi...

Seriously, the best test is the finger and thumb test. Pump the tyre up, then sqeeze it. If you can squeeze it a bit between finger and thumb, it's probably about right. A bit harder for flat fast road, a bit softer for bumpier stuff.

I don't see any obvious reason why tyre pressure should vary considerably with wheel diameter, rather than tyre section. I run my KH24 at around 20 psi, and that's a 3" section. The Holy Roller is a 2.3" section and runs at a bit more than 20 psi. (The 28 (700c) is a 23mm section.)

[kington99]

I recently got a kenda klaw XT, I've got the pressure way up around 40 psi i think, anything less and the sidewalls balloon out causing major drag as I ride. At this pressure there is little bounce for absorbing drops or putting in rolling hops. However as you know I'm a big guy, and much heavier than I look, I expect several stone heavier than you, so maybe start at 30 and play with it from there. The 29er is such a liberating experience after plodding around on a 24" for years, I was amazed how close the speed was to my N36, infact on the rough stuff I'm pretty sure the 29 was faster than I've previously managed on the 36.

[lowlight]

i dont know what pressure mine is at as ive never looked. The 'giving it a squeeze' test is usually pretty good. Also I find hopping on the spot for a bit gives me a fairly good indication of pressure.

The 29er is such a liberating experience after plodding around on a 24" for years

Agree there. Am struggling to find a use for my 24" now round here

[joemarshall]

Bout 30ish on mine.

Lower if it's technical stuff though.

40ish if I'm riding much road too.

50ish if it's mainly road.

Basically, if you're getting annoyed by it being squelchy and slow, that suggests you need more for the terrain you're riding, if you're annoyed by it knocking you off at the slightest bump, less pressure.

Joe

[rob.northcott]

I can't suggest any actual pressure for a 29er tyre (I run about 18psi in the 26x3 and 28psi in the coker), but I'd say start with it on the hard side to start with and let it down a bit at a time - you don't want to start with it too soft and prang the rim on a rock.

Rob

[mark williamson]

Well, the recommended pressure on the sidewall of the Klaw is something like 40-60psi, right? By default I usually inflate to 40 or so; I tried 60 once and found it a bit hard to handle. I may have just been unused to it, but it did feel easier to control once I'd let some air out.

I've ridden it down to rather low pressures - possibly about 20psi, I think. I did this when it snowed and I got nice surefooted handling out of it. But running that pressure probably put me at risk of blowouts, snakebite punctures and rim damage, so I'm not sure I'd recommend it generally...

Rumours are that in the next year or so we ought to see some DH oriented 29er tyres come onto the market. Hopefully these will run at lower pressures for those who need it.

On the plus side, my Kenda rolls quite nicely on the road During the British "Summer" I may switch back to my BA 2.35 if it stops raining for long enough, but even for purely road based commuting I find the Kenda works quite nicely.

[norry]

KH29 2005 / 150 cranks / Kendra Klaw / 72kg

I've also just do the pinch test with my tire, but today I checked before my ride and it was at 22 PSI. I'd been riding offroad for sometime at this level and it hasn't bothered me. So as I test I upped it to 30 PSI. No difference, at least none that I noticed.

Conditions today were mud / hard packed sandy paths / loose tree bark single track / wet grass / small stones / under 1ft drops

I tend to pump up the tire before riding and if I start bouncing off things too much I lower the pressure, if the tire starts folding sideways on corners etc then I up the pressure.

I'd start high then lower to suit.

[kerosian]

Originally Posted by mark williamson

Rumours are that in the next year or so we ought to see some DH oriented 29er tyres come onto the market. Hopefully these will run at lower pressures for those who need it.

This is true, Kris is riding the '08 WTB stout, and he tells me that it's bigger, better, and higher volume than anything on the market currently. 2008 is supposed to be the year of the 29er!