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  1. #1
    Rollin' on 29s!
    Reputation: mikepro's Avatar
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    How much sidewall flex is normal when on bike?

    I know there are lots of tire pressure threads here, but I'm looking for more subjective info. A couple of rides ago, I had the front tire blow out on me. Happened after a tight corner where the front wheel slid out from under me. I think the wheel must have rolled off the rim a bit and the tube got pinched. About 30 feet later she blew, and tire got jammed up in the front fork. Almost caused me to endo.

    I think I was running about 40-45 psi in the tire, according to my pump gauge, and I weigh about 285lbs. Rim is a Bontrager SuperStock Disc 29, tire is a Bontrager Jones XR 29x2.25" (front wheel).

    From some of the threads here, this seemed like an ok pressure. But, I did notice that when I sat on the bike and bounced up and down on it and turned the wheel, that there was a lot of sidewall flex and rippling. I was kind of concerned about that, but since I'm a newb, and from what I had read in other threads, it seemed maybe ok, especially with the 29er big wheels. How much of that flexing is "normal"?

    Now I run closer to 60 psi (according to my pump gauge). That seems really high, but I can still squish them in with my thumb, and when I sit on the bike and bounce, I don't see any alarming ripples in the sidewalls that make me think the tire is going to come off. The tire still bulges out a little from my weight, but it looks about right to me. Is this a good way to subjectively judge if I'm running a good tire pressure?

  2. #2
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    Reputation: EDDIE JONES's Avatar
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    I weigh 285lbs and have never had a tire do that to me. I generally run about 35 psi front/38 psi rear. This was on 26ers and 29ers. Absolutely no problems. I think your problem may be your tires. Try something with a little stiffer sidewall like the Geax Sturdy or the Hutchinson Spider. Pump up the front to 35-38 and the rear 38-40. I think your problems will go away. I am sorry. I didn't catch the fact that you were riding a 29er. I use an Ignitor on my 29er at the moment running 38 psi and have had really great results with it.
    Last edited by EDDIE JONES; 09-18-2007 at 02:33 PM. Reason: I let my ignorance show

  3. #3
    Spring! Spring! Spring!
    Reputation: bear's Avatar
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    Tire design, sidewall strength, etc., certainly a factor.

    Run a heavier duty tire and you can run less pressure, or vice-versa.

    Rim width at the tire bead can also be a factor. Wider rims may help a tire work better for you than the traditional narrow XC style rims sold on bikes (what are not TRULY perfect for Clydes).

    If you can find a heavier-duty tire for your 29er it may help a lot (at the cost of rolling weight, but rolling heavy is better than not rolling and flat).

  4. #4
    Rollin' on 29s!
    Reputation: mikepro's Avatar
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    OK, well after some experimenting today, I think my pump has suddenly taken a crap, and is reading about 20 psi low. I filled up some tires with a shrader valve so I could check them with my hand held gauge. At my pump 63 psi reading, the hand held dial gauge read about 40. So, when I pumped mine up to "45" by my gauge, I was actually running like 25psi!!! That helps explains the flat. I guess I should email Blackburn about my pump...

    So, I think using my calibrated thumb and eyeballing the deflection method, I really filled my tired up to about 40 psi. I think that is pretty good. I may play around with it a bit. I don't think these tires are all that great for traction and cornering. Geez, when I rode my friends Klein with his wide death grip tires, that thing would climb anything. I was thinking the 29er would feel the same, but it feels like less traction to me.

  5. #5
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    Reputation: EDDIE JONES's Avatar
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    With the proper tires and the right psi the 29er WILL climb anything you have the legs for! Try some Nevegals or Rampages and let us know what you think then

  6. #6
    Rollin' on 29s!
    Reputation: mikepro's Avatar
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    Here's another question... I've noticed this bike is a bit squirrely in the corners. Will changing my tire pressure help this? Should I increase or decrease to get better cornering traction? I'm at about 40psi rear now, and it feels like I could definitely go down a bit if it would help. (Then again, maybe it is just my technique, I am a noob)

  7. #7
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    Reputation: EDDIE JONES's Avatar
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    I would go down to about 35-37lbs. It will and should make a big difference.

  8. #8
    Rollin' on 29s!
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    Hey Eddie. Well, I did an experiment, and went up to 50 psi in the rear, and 40 in front. It was definitely bumpier, but seemed to handle much better. I think I can definitely go lower in the front, as most of the load seems to be on the rear. I let some air out of both tires halfway through my ride, (no gauge, but maybe a couple of psi). It smoothed things out a bit, and still seemed ok in the handling department. I guess I will just keep playing, and working my way down in pressure until I find my sweet spot, but I'm starting to think with these tires that that place will be above 40 psi in rear.

  9. #9
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    I actually run about 38lbs on the rear sometimes/35lbs front and at my weight 285lbs, I get great results and no pinchflats. What you try to do is find that magic psi when the tire doesn't roll over and you are not flatting on square edge hits, but almost

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