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mnoutain bkie rdier
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Discussion Starter · #4 · (Edited)
Fakie1999 said:
I follow stans divide your weight by 7 method. 20 rear 18 front for me.
Thanks. You mean?

•Rider weight in pounds divided by 7 = x
•x-1 = Front tire pressure in PSI
•x+2 = Rear tire pressure in PSI

That would put me at Front: 20psi Rear: 23psi (2.1 SB8). Pretty close to what I was doing already...
 

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It really depends on the tire for me. My downhill tires I run 12 psi and my light weight tires I run at 40 psi. For me it depends on how stiff the sidewall is and if I am running tubless or not. I find on my light weight tires (thin sidewall) and if I run them tubeliss I have to run more PSI to keep the sidewalls from rolling in turns, burping and from bottoming out (hitting the rim on the ground). At 40psi tubeless it feels like 35psi with tubes. So for me tubeless is about not getting flats and not about lower tire pressure. Oh all my tires are non-ust.

Is anyone else finding that they need more PSI when tubeless? Or am I the only one.
 

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I hadn't seen the Stan's method of calculating pressure. At 160 lbs, I'd be 22 front, 25 rear. I've been running 28 and perfectly happy, even thought it was soft at first. I might have to try lower. At 28 I'll burp them once or twice a year. Would the lower pressure increase burping chances?
 

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There's no way everyone could use a calculation based only on weight to determine tire pressure. What about tire volume, inner rim width, and tread width? What about calculating a floating point rider weight distribution?

Yes, I'd imagine a set of equations could be devised that everyone could use, but you'd need help from a physicist. What's more, the equations would only be as useful as the desired outcome (rolling resistance vs. grip, contact patch vs. sidewall exposure, etc.). At best you might be able to get a set of variables to plan with, but of course you'd still be the ultimate judge of what works best for conditions/goals.

In other words, you'd still be at the mercy of trial and error.
 

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mnoutain bkie rdier
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Discussion Starter · #9 ·
lassiar said:
There's no way everyone could use a calculation based only on weight to determine tire pressure. What about tire volume, inner rim width, and tread width? What about calculating a floating point rider weight distribution?

Yes, I'd imagine a set of equations could be devised that everyone could use, but you'd need help from a physicist. What's more, the equations would only be as useful as the desired outcome (rolling resistance vs. grip, contact patch vs. sidewall exposure, etc.). At best you might be able to get a set of variables to plan with, but of course you'd still be the ultimate judge of what works best for conditions/goals.

In other words, you'd still be at the mercy of trial and error.
So....what PSI are you running?:p It's not that complex unless you are looking to go as lowwwwwwwwwwwwwwww as possible w/o causing a major problem.
 

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newnan3 said:
Do you guys find that you get rim-strikes occasionally when you have such a low psi?
I trashed my first "tubeless" rear rim from running such low psi.. I've since rebuilt with a flow rim since I've got a bit of caveman in me, but I also don't like the ride when the rear is that low, it gets squirlly so I only ride that low when doing snow rides.
 

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175 lbs, Mavic SLR wheels, Race king 2.2, 25-26 psi front, 29-30 psi rear. I cannot go any lower in the rear because when i venture into the 26-28 psi range the tire wants to roll over on itself in high G curves. I love this setup and will be running it this race season. Lots of grip and give in the tires at these pressures.
 

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rydbyk said:
Thanks. You mean?

•Rider weight in pounds divided by 7 = x
•x-1 = Front tire pressure in PSI
•x+2 = Rear tire pressure in PSI

That would put me at Front: 20psi Rear: 23psi (2.1 SB8). Pretty close to what I was doing already...
yeah. I dont know where I read that either. I suppose I should mention I was running stans olympics with stans ravens 26x2.2 at the time. I switched to racing ralphs in 26x2.25 and ran the same pressure. I feel like they run harder, so, I think I could go even lower on those.

Stans website had a chart on one of the wheel pages, with rider weight and tire size. I cant find it on the new website.
 

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mutaullyassuredsuffering
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higher

I run a bit higher than many here. I'm 170lbs and go with 26 front and 30 rear on my 2.4RR/2.25 RR rigid setup, and 32 front 30 rear on my 2.25RR/2.25RR 100mm setup.

I used to run lower (24psi) until a burp off of a 1.5 foot step followed by a cut tire gave me the opportunity of walking my bike 15 miles in the dark back to my car. I err on the side of caution now.
 

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did a very cold and wet 8 hour solo running my racing ralph 2.25's on my tallboy at about 13 front and 18 rear, I wish I could get away with going that low all the time, this was at trails with a lot of sand below the surface, so great quick drainage, not much mud, lots of wet roots, never been faster over that course, just gotta be very aware where you are placing your rear wheel, a few days later dented the crap out of my rear rim and shredded a tire flying through a section I hadnt ridden in a while and coming up short on hopping a creek crossing at speed and stuck my rear wheel into a square edged rock on the other side instead of landing nicely
 

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mnoutain bkie rdier
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Discussion Starter · #15 ·
LiamC said:
did a very cold and wet 8 hour solo running my racing ralph 2.25's on my tallboy at about 13 front and 18 rear, I wish I could get away with going that low all the time, this was at trails with a lot of sand below the surface, so great quick drainage, not much mud, lots of wet roots, never been faster over that course, just gotta be very aware where you are placing your rear wheel, a few days later dented the crap out of my rear rim and shredded a tire flying through a section I hadnt ridden in a while and coming up short on hopping a creek crossing at speed and stuck my rear wheel into a square edged rock on the other side instead of landing nicely
Thanks, but how did you manage to do 4,294,967,295 posts?:eekster:
 

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7 posts a second....for the past 25 years straight. just picked up a set of this years Schwalbe tubeless ready tires, racing ralph on the back and rocket ron on the front, probably be able to get away with a whole lot less sealant, wonder how low they will go comfortably.
 

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Pump Calibrations

What pumps are being used to set such low numbers?
I have a Park and a Joe Blow .The Park has 2 lb. incrments but starts off at more than zero, it's somewhere like 5 0r 6 lbs.{has seen better days}
The Joe Blow has 4 lb increments , more for roadies ?
I guess i need to find one with 1 lb increments.
Thanks.
 

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mnoutain bkie rdier
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Discussion Starter · #20 ·
RIDESLOW said:
What pumps are being used to set such low numbers?
I have a Park and a Joe Blow .The Park has 2 lb. incrments but starts off at more than zero, it's somewhere like 5 0r 6 lbs.{has seen better days}
The Joe Blow has 4 lb increments , more for roadies ?
I guess i need to find one with 1 lb increments.
Thanks.
I use a Lezyne now. I think that more importantly, the pump needs an accurate PSI guage. My Lezyne has 5lb increments as far as I can recall. I still find it fairly easy to visualize where I am at on the guage though in 1lb increments.

I use an air compressor with presta guage sometimes too..(a must for me when setting up my tubeless tires). They both agree on PSI.

Not sure if it is EXACTLY 21lbs, for example, but it is pretty darn close..
 
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