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pedal me happy
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Discussion Starter · #1 ·
I ride a full rigid sir9 and tubeless crossmark rear with stans sealant. I like to run about
28 to 30 on the trails but on a hardpacked section where I can really put the hammer
down I can get the tire to roll off to the side I dont burp any air but it feels like you just
folded up the rear wheel. Around town when I can't get to the trails and ride some
pavement I have to run close to 40 to keep this from happening. Anybody else have
this same thing. I like the cush of low pressure but when the tire rolls to the side it
is not a good feeling.
 

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Yep, tires flex can be very disconcerting. It doesn't sound like you've ever actually rolled the tire though because that is usually an instant wipe out. Besides pressure, rim width also affects this a lot. Actually, the two are very related. Wider rims provide a larger base because the tire is supported at a point further out towards the full width of the casing. I used a 2.35 Rampage on one of my old bikes that had a 21mm front rim and I had to keep pressure well above 30 off road because the tire was not stable on a rim like that. Even at higher pressures I did roll the tire off the rim once. I've run a Rampage more recently on a much wider 27mm rim and I was able to run the pressure down below 20 without problems (and I weigh 195 btw)

Sidewall construction seems to have an effect as well but I haven't tried a wide enough variety of tires to really see this.
 

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pedal me happy
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202 Posts
Discussion Starter · #3 ·
My rims are 25mm wide and I am sure a thicker side wall would help but I like the light
tires. At first I thought the wheel was flexing so I looked down when I was riding and
could watch the tire rool out to the side it stays on the rim but it is totally over to the
side and only on the left I guess my right foot is stronger and when I pull the bike back
and forth it only does it on that side. I always lube up the bead of the tire and wheel with
stan's and when it dries it really glues the tire in place, when i have dismounted them
it took a little effort to get it loose but this is a plus. Otherwise the pressure thing
is just a comprimise between things I guess.
 

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I've been running 20f/24r with XDX on Flows. 185lbs + gear. Rigid. The tires have gripped better with low pressure than somewhat low pressure. Upper 20's leads to more squirm for me. At the lower pressures it seems to grab more.
 
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