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  1. #301
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    the physics on tire contact patch is close enough, but technically doesn't conform exactly to the air pressure calculations, especially on wide rims or when using very stiff, heavy tires like UST.

    the reason is very simple: more than just air is actually bearing the bicycle & rider weight. it's the tire carcass.

    the carcass bears little weight using a 1.8" race-day-only semislick, but it bears a lot when you run a heavy tire on a p35. think about a runflat tire for a car. how does it bear the weight of the car with little to no air pressure?

    anyway, just food for thought. this is another one of the ways people run ultra-low pressure is by using a wide rim and a beefy tire.

  2. #302
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    I am 185# rider and went with the 40# tire pressure and when I was about 8 miles from my truck when I got a pinch on both tires and bent my rear rim. I was on a down hill run with lots of rock. The week be for I was on smooth dirt and more of a flat trail and it worked great. so i think a lot has to do with your riding terrain.

  3. #303
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    The other day, I had a long ride on the paved road with some pretty steep climbs before getting off-road, so I had the tires inflated to about 40#, thinking that this pressure would be low enough to handle sandy surfaces... I quickly realized as I left the pavement and hit a 15% grade, with hard dirt and a thick coat of sand, that I really wanted to have less pressure in the rear tire - it spun out and slipped very badly - but I didn't want to let the air out because I didn't have a lot of time before dark and I had a long ride back on the pavement.

    I've been thinking about getting a compressed-air cartridge-type tire inflator, but I'm not sure which one, and whether there are inflators that you can re-fill... I have DEFINITELY noticed widely varying performance with different tire pressures... Can somebody recommend the best way to quickly inflate/deflate and manage tire pressures while on the trail?

  4. #304
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    it can feel 'funny' when riding on pavement with trail pressure, like you have a flat tire, but it's barely slower if you actually measure your speed and elapsed time. you will lose a lot more time getting off the bike to mess with the air pressure.

    I would get a high volume frame pump if you really insist on doing this.

  5. #305
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    Can't believe I just read this whole thread...

    ...but I didn't read much about bent or dented rims. Are most of you able to go this low without worrying about your rims? I'm constantly thinking about them getting damaged.

  6. #306
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    Quote Originally Posted by mr.niles View Post
    in fact i do have timing device coming in the mail! yeah, it's hard to tell! that's why it's confusing to me. i'm always changing my presuures around to try and figure out what is best. i will try lower pressures, but i'm just not sure where to start. any ideas?
    I can't remember where I read it, but recently I saw a formula for a base tire pressure from which you can adjust, depending upon your tires, trail type, conditions, etc. The formula was to divide your weight with helmet, shoes and backpack by 7. Subtract 1 lb for the front tire and add 2 lbs for the back tire.

  7. #307
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    Quote Originally Posted by dhmoore View Post
    I've been thinking about getting a compressed-air cartridge-type tire inflator, but I'm not sure which one, and whether there are inflators that you can re-fill... I have DEFINITELY noticed widely varying performance with different tire pressures... Can somebody recommend the best way to quickly inflate/deflate and manage tire pressures while on the trail?
    When I need to I carry a mini pump (like 150 grams) and a digital gauge (50 grams). Especially with a new bike/tires combo that I want to play with. Little weight, gives you insurance, reliable. When I ride with buddies one pump in the group is usually enough.

  8. #308
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    Quote Originally Posted by geeter View Post
    I can't remember where I read it, but recently I saw a formula for a base tire pressure from which you can adjust, depending upon your tires, trail type, conditions, etc. The formula was to divide your weight with helmet, shoes and backpack by 7. Subtract 1 lb for the front tire and add 2 lbs for the back tire.

    Hey, that sounds interesting.... I'd like to see this tire-pressure formula. I've been using the caveman method: grab tire and squeeze hard, if going uphill, it okay if very squishy... if going downhill, no want so squishy, especially if have innertubes... if no steep up and downs, make tire hard like rock so bike pedal easier.

  9. #309
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    To all those who are resisting going tubeless as I was for years. I even had tubeless ready wheels and ran tubes, GO TUBELESS and don't look back.
    No More pinch flats. I weight 195 and like to ride technical trails with as much rocks, ruts, roots and jumps as I can find. With tubes I ran 34/36 psi with an occasional pinch flat, tubeless I now run 26/29 on 2.3/2.2 tires with no issues. I have run as low as 21/25 but I feel the sidewall flex too much. As far as trail repairs, carry a spare tube and co2 cartridges with a quality inflator. I also carry a small pressure gauge to check pressure and a small pump just incase.

    Best advice I was give regarding mountain biking was to go tubeless.

  10. #310
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    Quote Originally Posted by dhmoore View Post
    Sounds H


    Hey, that sounds interesting.... I'd like to see this tire-pressure formula.
    It is on Stan's NoTubes site.

  11. #311
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    That formula is linear and as such I doubt it will work well for light and very heavy riders. A 115 pound woman can ride 15F/17R psi, really?

  12. #312
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    Quote Originally Posted by raducanmihai View Post
    It is on Stan's NoTubes site.
    Damn, you beat me to it.

    In my experience, its been closer to (weight/7)+3 in front, and (weight/7)+7 in rear, but I'm also suspicious of the readings on my floor pump. Its 10 years old and I have not found 35 psi from others peoples' pumps to feel like 35 psi from my pump. I end up running 31 f/35 r. Your experiences may vary

    Quote Originally Posted by ColinL View Post
    That formula is linear and as such I doubt it will work well for light and very heavy riders. A 115 pound woman can ride 15F/17R psi, really?
    I'm a 200 lbs Cat 1 SS mtbr, so I think my tires have their work cut out for them .
    Something wrong with your bike? Blame it on super human strength and sleep well at night knowing you are more than a man.

  13. #313
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    Here is a cool app by Geax.....Bead seat diameter, tire type, type of riding, rider weight, etc....will calculate the lowest pressures you can run.


    iTire Pressure « Geax.com

  14. #314
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    Thanks raducanmihai n ZXFT... kewl stuff! :]

    Holy COW, ghettocop! Dude! That's a VERY kewl app!

    I was goofing with my pressures on a steep, rocky, ascent the other day and lowered the pressure waaaaaay down so the rims were bumping the rocks (tubless)... SERIOUS improvement in traction and much, much smoother climb... I knew lower pressure was better for climbing, and run low pressure, but not this low - like fifteen pounds! haha did it just to see how low I could go... then put a few more pounds in and climbed some more... then again, and let some out... got it just right, but didn't have a pressGuage with me to record the exact pressure... on the descent I pumped 'em back up again several pounds more for the extra impact and stability at higher speeds... gotta get a guage... as I was riding, I was thinking "yea, one of these days we'll probably have a guage and a controller on the handlebars with a pressure adjustment while riding" wouldn't THAT be kewl!

  15. #315
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    Historically:

    50F/50R
    35F/45R

    Now I'm at 35F/40R. I've found anything less in the rear and the tire distorts too much, I can go a bit less in the front but this combo seems ideal for me for now. I'm 215 loaded up. Picking up a new bike here, a 29", so I'll get to play with PSI again!

  16. #316
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    Quote Originally Posted by ZXFT View Post
    In my experience, its been closer to (weight/7)+3 in front, and (weight/7)+7 in rear, but I'm also suspicious of the readings on my floor pump. Its 10 years old and I have not found 35 psi from others peoples' pumps to feel like 35 psi from my pump. I end up running 31 f/35 r. Your experiences may vary
    Quick update, I tried 29f/32r with a new floor pump (since my old one broke ) and it felt very similar to my previous 31/34. I'll keep messing with pressure and see if I cant get it down to the stans formula.
    Something wrong with your bike? Blame it on super human strength and sleep well at night knowing you are more than a man.

  17. #317
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    Quote Originally Posted by ZXFT View Post
    Quick update, I tried 29f/32r with a new floor pump (since my old one broke ) and it felt very similar to my previous 31/34. I'll keep messing with pressure and see if I cant get it down to the stans formula.
    2 PSI is well in the margin of error of floor pump gauges. Mine pump gauge has 5PSI difference than the other gauges which I believe are more accurate (one mechanical and one digital, both reading within 0.5SPI of each other)

  18. #318
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    So after skimming through this entire thread my head is spinning. I came on here looking for info because during trail riding my rear tire is spinning on steep climbs and the bike is bouncing around too much on descents. Obviously the psi im running is too high.

    Just for clarification...as the tire pressure drops what are you gaining and losing? Does a lower pressure provide more traction/braking or are you going to corner better?

    This thread has been very informative. Thanks!
    Last edited by Criswell; 08-19-2012 at 09:56 PM.

  19. #319
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    Quote Originally Posted by Criswell View Post
    Does a lower pressure provide more traction/braking or are you going to corner better?
    Both. Assuming its not so low that your tire squirms in corners.
    Something wrong with your bike? Blame it on super human strength and sleep well at night knowing you are more than a man.

  20. #320
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    Quote Originally Posted by ghettocop View Post
    Here is a cool app by Geax.....Bead seat diameter, tire type, type of riding, rider weight, etc....will calculate the lowest pressures you can run.
    iTire Pressure « Geax.com
    Muchas Gracias! Great app.(I like no brainer concrete answers, even if it's slightly off )!

  21. #321
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    Quote Originally Posted by Criswell View Post
    So after skimming through this entire thread my head is spinning. I came on here looking for info because during trail riding my rear tire is spinning on steep climbs and the bike is bouncing around too much on descents. Obviously the psi im running is too high.

    Just for clarification...as the tire pressure drops what are you gaining and losing? Does a lower pressure provide more traction/braking or are you going to corner better?

    This thread has been very informative. Thanks!
    Keep in mind rear suspension setup matters too.

  22. #322
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    Generally, with lower pressure:

    Gain traction (cornering, braking, climbing)
    Bike is little more vague
    Bike rides more plush (less bounce, especially on a hard tail)
    Less rolling resistance on rough terrain
    More rolling resistance of flat terrain
    More prone to pinch flats (tubes)
    More prone to rim damage
    More prone to burping and tire rolling off the rim (tubeless)

    I think thats about it?

  23. #323
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    I am a 190-200 pounder excluding the 20 pounds of equipment, water and stuff on me and run 1.6bar soft front and 2 (very stiff) back tubeless onloose sharp rocky track. I need advise on the sort of tyres though since I have shredded two back tyres in the last two months - the last was a Scwalbe Rocket Ron EVO 26" and besides 7 pinky sized holes I fixed an inner and then after some 50K's popped went the sidewall - was this just bad advise from my shop since i run the same in front with no problem in the past year+? I now switched to Continental Speedking 2.2 which apparantly has thicker sidewalls. So far ok besides one small puncture that sealed up quick and Stans leaking small bits all the time from the valve and rim edge. Did not loose much pressure on yesterdays 50K run. I must add that the rim took a knock and bent when I hit a rock but it is almost 98% good but for a small wobble. Should I rather convert my backwheel to downhill rims, hub and tyres? Or will this be SO much heavier?

  24. #324
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    This is a great thread... Except it looks like I wasted $80 on my new set of Geax barro race 2.0s. This is a low volume tire and I weigh 252 or so. I suspect a few of you will tell me to ditch them.

    They're actually very good tires, and def better than my Nanos on the dirt. I've only ridden them twice on the trail tho, and the both rides were muddy - after the rain rides so they've not been fully tested yet. I'm running 28/30 right now, and don't think I should go much lower as I am a big MF-er.

    My question is - would it be a good setup to go with a 2.3 tire in the front and leave the Geax in the rear? I'm not gonna put one of the Nanos back on as it's already been proven that they suck on the loose stuff.
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  25. #325
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    Throwing my experience into the mix.
    I weigh about 160-165# in full gear. I am running 2.25 Nobby Nic front and 2.25 Racing Ralph on back. Both are the TL-Ready, SnakeSkin version. I have put two scoops of Stans in each. They just work. I am running these on 26" XTR Trail wheels.

    I have been riding these tires at between 19-22# F and 20-23# R and did the BC Bike Race at this tire pressure. They were a little soft/squishy on the roads but they just worked.

    I also ride fairly hard on a wide variety of terrain (steeps, rocks, smooth, sandy) with no problems (burps, air loss). That said, I am also fairly good at line selection and we don't have much in the way of sharp exposed rocks in Whitehorse.

    The bead locks onto the rim and it's a bugger to break when I have to replace the Stan's (just did). It literally glues into place.

  26. #326
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    Quote Originally Posted by ewise View Post
    The bead locks onto the rim and it's a bugger to break when I have to replace the Stan's (just did). It literally glues into place.
    What I do is lay the wheel flat on the ground, and step on the tire close to the rim. With all your body weight on it the tire will separate from the rim, so far it worked every time and super easy. Once it separates in one point a tire lever can do the rest, and if not, step again on the trouble spot.

  27. #327
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    my weight is 225lbs i ride a '09 specialized rockhopper expert im new to riding what pressure is recommended for me? im new to all this mountain biking by the way.

  28. #328
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    Quote Originally Posted by mr_z View Post
    my weight is 225lbs i ride a '09 specialized rockhopper expert im new to riding what pressure is recommended for me? im new to all this mountain biking by the way.
    What tires? Size is a major factor.

  29. #329
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    26 x 2.00" specialized fast trak.

  30. #330
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    Quote Originally Posted by mr_z View Post
    26 x 2.00" specialized fast trak.
    Try 30 front, 35 rear. If it feels squirmy (you'll know it when you feel it) or you pinch flat, bump it up 3-5 psi on the tire that is giving you issues until the problem goes away. I am nearly your weight with similar width tires, albeit a different tread style, and that's what I would do.

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  31. #331
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    Quote Originally Posted by geeter View Post
    I can't remember where I read it, but recently I saw a formula for a base tire pressure from which you can adjust, depending upon your tires, trail type, conditions, etc. The formula was to divide your weight with helmet, shoes and backpack by 7. Subtract 1 lb for the front tire and add 2 lbs for the back tire.
    That was helpful. Thanks.

  32. #332
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    I weigh 180 fully loaded with 3L of water in my Camelback. Running Hans Dampf 26x2.35 in front at 24 psi and Racing Ralph 2.25 in the back at 26 psi.

  33. #333
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    I probably weigh 180 lbs loaded up. Still learning about tires. Limits are sliding off roots on a turn due to too high a pressure, 40 lbs or so. Let out air until a finger squeeze dents the side of the tire. Before I went tubeless rims, just converted-tubeless, it was like gaining a gear, rolling friction much better. Squirm on corners is creepy after a couple of gulp flats throw you down. Switched to foldable tubeless on tubeless-clincher rims, a much stiffer tire without squirms or gulps, gaining back some tire friction. Feels solid.

    Bought a tire gauge and decided to run rated minimum of 30 lbs, but tire like a rock slipping on every flat stone and root. Started letting air out to gain secure grip on rocks and roots. Now they look slightly flatter and fatter on the bottom, squeeze test ok. Maybe if I think about it ahead of time I'll pump up on the electric pump at home to cut down on rolling resistance on the long miles, and then when I reach the trail, or large rocks on the road, I'll let out air when I unlock the front shock (w/hardtail), tuning pressure it down until it feels secure. I sure don't want a gulp flat, but those new clinchers really lock in, and I've had no flats, squirms or gulps since I went legit.

    Of course, I've been really cautious about getting too low and have pumped up on the trail when it feels too soft. The last thing I want to do is go down on a gulp in a tight turn (have done) the bruises, road rash and near death experiences are not part of the fun. Part of getting older is slowing down knowing you're not as invulnerable as your glands lead you to believe. Having your life flash before your eyes is not for me now, or later.

    I would like a lower pressure gauge as nothing over 40 lbs is of interest to me, and my 160 lb AccuGauge is not very useful in tuning lower pressures. Got any suggestions? I'll trade you a nice gauge for something easier to read at low pressures.

  34. #334
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    After 20 years of riding tires from 45-65 psi, I finally read this thread. I'm 6'0, 195 lbs with gear. Just got done riding my Spesh Epic 29er EVO with 30psi front and back... life changing. Tearing through rock gardens like a fat kid chasing an ice cream cone. No bottoming or pinch flats.

    Can't wait to try even lower pressure.

  35. #335
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    Quote Originally Posted by Schroedinger View Post
    After 20 years of riding tires from 45-65 psi, I finally read this thread. I'm 6'0, 195 lbs with gear. Just got done riding my Spesh Epic 29er EVO with 30psi front and back... life changing. Tearing through rock gardens like a fat kid chasing an ice cream cone. No bottoming or pinch flats.

    Can't wait to try even lower pressure.
    People like you are rare. Most people if they've been doing it one way for 20 years thats the "right way" to do it. Good job on having an open mind.
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  36. #336
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    I weigh 200 lbs (not including camel back stuffed with tools & water) and run 32 psi front and back on my stumpy fsr. I have never had issues with flats or pinch flats, I tried 30 & 28 on a variety of tires and they felt too squirmy for my weight along with pinch flats.

  37. #337
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    Quote Originally Posted by stumpynerd View Post
    I weigh 200 lbs (not including camel back stuffed with tools & water) and run 32 psi front and back on my stumpy fsr. I have never had issues with flats or pinch flats, I tried 30 & 28 on a variety of tires and they felt too squirmy for my weight along with pinch flats.
    What tires are you using and how wide are they?

    I am currently 215 without gear, running a 2.4 X-King front at 28 psi and a 2.2 Race King rear at 30 psi. I have narrow rims (17 inside) but would like to go lower as I haven't felt any squirm cornering, but the issue is that the tires tend to slide in the rim and tear off valve stems. This is currently remedied with gorilla taped beads but I don't want to push it. Oh how I wish I would have bought wider rims...

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  38. #338
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    Im running 2.2 captains currently with American Classic MTB rims, Im not sure how wide they are but 32 psi works best for me on a wide variety of terrain.

  39. #339
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    I usually ride the rear tire around 20psi. I'm 145 and ride technical single track with a lot of baby heads. I am riding tubeless 2.0 on 29er rims. Up front I run about 23 on 2.2s

  40. #340
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    Quote Originally Posted by Schroedinger View Post
    After 20 years of riding tires from 45-65 psi, I finally read this thread. I'm 6'0, 195 lbs with gear. Just got done riding my Spesh Epic 29er EVO with 30psi front and back... life changing. Tearing through rock gardens like a fat kid chasing an ice cream cone. No bottoming or pinch flats.

    Can't wait to try even lower pressure.
    Yeah, sounds stupid, but I've gotten this old and I am just now toying with pressures on both the Road and MTB, and the results are eye opening.
    I am so old school I still run the Smoke/Dart combo. I am feeling good at 25F/30R and it's been awesome. I may go a little less, just to see. I am going by the rule, 'keep reducing until you snake bite, then add 5'
    We will see.

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  41. #341
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    I weight about 185lbs load up, bike is a 26lbs FS. Currently running 35/35psi ft/rr on Specialized Specialized "Fast Trak" Armadillo 2Bliss ready 26x2.00 ft and Specialized "The Captain" Armadillo 2Bliss ready 26x2.00. Both currently with tubes with sealant. I hate flats.

    Plan is this winter to change to something wider (2.25-2.4) and go tubless. Also will buy an accurate pressure gage. Then I'll experiment with which pressure is the best compromise for the range of surfaces I run on (pavement to lose rock/dirt climbs).
    Last edited by BDozer; 10-27-2012 at 08:16 PM.

  42. #342
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    I have 2.1" tires (I think--It says 26x2.1 on my tires (I'm kinda new to MTBing)) and I weigh 125 lb, so what kind of PSI should I use (or how low could I go)? On the tires it says the min PSI is 40 and the max is 65. I do XC mostly.
    Thanks!
    Also, everyone is saying "keep lowering it until you get pinch flats" but isn't that at all bad for the tire and/or tube to keep puncturing holes in it/them?

  43. #343
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    Quote Originally Posted by Ferrari353 View Post
    ...Also, everyone is saying "keep lowering it until you get pinch flats" but isn't that at all bad for the tire and/or tube to keep puncturing holes in it/them?
    You may ruin a tube but probably won't hurt the tire while figuring it out (you're not going to be pinch flatting every ride over and over). At only 125# I'd start with ~32psi and go from there.

  44. #344
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    Quote Originally Posted by Ferrari353 View Post
    Also, everyone is saying "keep lowering it until you get pinch flats" but isn't that at all bad for the tire and/or tube to keep puncturing holes in it/them?
    I wouldn't say lower until you get pinch flats. There are many other reasons to stop lowering. In my terrain the tires will start to squirm in turns and feel like you are riding on gello before they flat. In a tubeless setup they can also roll off the rim in low pressure. Not to mention flat spotting your rim or getting too many dings and scratches. All are reasons not to go too low.

    But for your original question, after a pinch flat the tube can be toast, because the cuts can be long. Tires seem to care less.

  45. #345
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    Quote Originally Posted by gmcttr View Post
    You may ruin a tube but probably won't hurt the tire while figuring it out (you're not going to be pinch flatting every ride over and over). At only 125# I'd start with ~32psi and go from there.
    That seems like you'd be wasting a lot of patches fixing the pinch flats. I'll try 32 and see how it rides. If it doesn't feel right (or like jello), then I'll raise the PSI.
    Thanks for the advice guys!
    Quote Originally Posted by CrozCountry View Post
    I wouldn't say lower until you get pinch flats. There are many other reasons to stop lowering. In my terrain the tires will start to squirm in turns and feel like you are riding on gello before they flat. In a tubeless setup they can also roll off the rim in low pressure. Not to mention flat spotting your rim or getting too many dings and scratches. All are reasons not to go too low.

    But for your original question, after a pinch flat the tube can be toast, because the cuts can be long. Tires seem to care less.

  46. #346
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    Here's the rule of thumb I've always used. I've never had a accurate gauges on any of my pumps, so I take the tire and "bounce" my weight down on it with the narrow outside of my palm. I should just barely be able to feel the rim when I bottom out on the front wheel. A tiny bit more pressure than that for the back.

    This is for a rigid bike with 2.4" tires, tubes, and rhino lite rims.

  47. #347
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    I am running 29x2.3 Renegades on Crest rims at 15 psi front and rear with tubes, on a HT. I weigh 155. No problems yet, and they don't feel squirmy. When I first got these tires I aired them to 20 psi (which is what I was running my 29x1.95 Renegades at) and they were way too bouncy. Next tried 17 psi which was a bit better, but not quite what I was hoping for. 15 psi pretty much hit the spot. My home trails are relatively rocky, however I have been riding them for years and I am a somewhat smooth rider.

    I'd like to get a separate gauge to confirm these pressures since I would not have guessed that I'd be running them and I am pretty surprised.

  48. #348
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    What I have noticed is that the wider the tire, the lower the pressure I can get away with.

    This leads me to another question - what is the widest tire people are running on Crest rims? I am currently on Nobby Nic 2.25" (at 17 psi) and want to go wider, but don't want problems with squirming...

  49. #349
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    Quote Originally Posted by BigwheelsRbest View Post
    What I have noticed is that the wider the tire, the lower the pressure I can get away with.

    This leads me to another question - what is the widest tire people are running on Crest rims? I am currently on Nobby Nic 2.25" (at 17 psi) and want to go wider, but don't want problems with squirming...
    I think that the Crests are fine with that. I'm pretty sure I came across a Notubes forum question where the Notubes guy said the Crests could definitely handle a 2.3. I'll see if I can find it.

    Crests are 21 inner width, so they're in my opinion and experience pretty suited at running wider tires.

    I had been running 26x2.4 X-king's on my Bontrager RXL's which are the standard 19mm width, and to me, they always felt fine. I also ran those with tubes. They were the first generation Racesports and sealing them up was a PITA so I just gave up and used tubes. Blew my mind how well they rode and how low I could go with the pressure (around 20-21) and changed my mind about running skinnier tires.

    I recently bought some of the X-king's in 29x2.2 in the RTR Protection version. Unpackaged one, put it on an aired it up, and it was way small...smaller than the Renegades at 1.95. Returned 'em. Hoping Conti actually starts delivering that tire in 2.4,

  50. #350
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    rigid/hardtail/full sus variable?

    ~200#'s geared up. I've been running Stan's Flow rims and Panaracer Rampages 2.35's, front and rear, on a rigid steel SS and a Yelli Screamy hardtail.

    As many posters before, I go as low as I can on Pac. NW trails without rim striking or feeling too squirrelly. The low pressure obviously helps with traction, and also with the cush of the ride. I think I'm usually at 18-23 front and 20-25 rear. If I have to ride pavement for a long stretch, I'll inflate.

    Here is my question. I do not think it has been addressed directly yet.
    How does tire inflation and suspension, specifically FS, interface?

    After a season of only having my rigid and HT I have just built a 650 SC Blur XC and am therefore thinking about this.

    Does it make sense to run a bit higher psi with a FS bike, in order to better engage the suspension?
    I imagine that there is an optimal psi where the cush in the tire works in concert with the suspension--where they are balance in the same way we need to balance front and rear suspension in a bike.

    When I had a full suss before (a Rip9) I ran the tires as low as I did on my rigid and HT, but I always wondered about the tire psi/FS relationship.

    Anyone have an opinion?

  51. #351
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    You would run the FS bike at the same pressures for a given tire as the HT bike, like you said. I see a lot of people running huge tires on rigid bikes to get max air volume tires to run them as low pressure as possible, in order to get a better ride. But that's of course nothing like full suspension.

    You may not need higher pressure in a fast-rolling tire on pavement or gravel roads. I have not noticed any real difference between my trail pressure, 25F/27R, and running 5 psi more for the road. This is on a fast tire, a Geax Saguaro 2.2F/2.0R. On other tires, especially slow rolling tires, the difference was more significant.

  52. #352
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    Quote Originally Posted by daniel harvey View Post
    ~200#'s geared up. I've been running Stan's Flow rims and Panaracer Rampages 2.35's, front and rear, on a rigid steel SS and a Yelli Screamy hardtail.

    As many posters before, I go as low as I can on Pac. NW trails without rim striking or feeling too squirrelly. The low pressure obviously helps with traction, and also with the cush of the ride. I think I'm usually at 18-23 front and 20-25 rear. If I have to ride pavement for a long stretch, I'll inflate.

    Here is my question. I do not think it has been addressed directly yet.
    How does tire inflation and suspension, specifically FS, interface?

    After a season of only having my rigid and HT I have just built a 650 SC Blur XC and am therefore thinking about this.

    Does it make sense to run a bit higher psi with a FS bike, in order to better engage the suspension?
    I imagine that there is an optimal psi where the cush in the tire works in concert with the suspension--where they are balance in the same way we need to balance front and rear suspension in a bike.

    When I had a full suss before (a Rip9) I ran the tires as low as I did on my rigid and HT, but I always wondered about the tire psi/FS relationship.

    Anyone have an opinion?
    Tire pressure is part of the setup with suspension, hardtail or fully. I have needed to change tire pressures for suspension bikes compared to what I used on a rigid bike. Change the suspension settings and have found I needed to adjust the tires again. How I changed the pressure varied with the specific tire and the suspension type. With some other tires it does not seem to matter what type of bike they are on.

    I have also used tires that worked terribly on a rigid bike no matter the pressure. Moved them to a suspension bike and they were brilliant.

    All goes back to the basic answer for this thread: you need to experiment and see what works best for you, your terrain, setup and riding style.
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  53. #353
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    Quote Originally Posted by daniel harvey View Post
    Does it make sense to run a bit higher psi with a FS bike, in order to better engage the suspension?
    I imagine that there is an optimal psi where the cush in the tire works in concert with the suspension--where they are balance in the same way we need to balance front and rear suspension in a bike.
    I run a few more PSI on the hardtail rear tire to reduce the chance of pinch flats (comparing to equivalent tire on FS).

  54. #354
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    So I just recently came from a ride here in Las Vegas and this trail has rocks pretty much everywhere. I decided to go tubeless and I think the pressure was at 40-45 on front and back. I am running Nevegal Crossfires 26x2.1 on the back. I got a "burp" riding on the ridge of a boulder, So I go and pump it back up not having a gage I just went by feel. About 2 miles later, I hit a pretty good rock and that was that. I go into my pack and look at my tube, Oh my god...Tube I bought had the wrong valve, I thought I bought a presta valve. My wife who rode with me was pretty pissed, We were 5 miles in , in the middle of the desert, Thank god there was a person that passed me off a 29er tube and I put in on my 26er and rode back safely.
    Now I think it had a lot to do with me being 220lbs. I will stick to tubes till I lose about 25-30 more lbs.

  55. #355
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    Quote Originally Posted by JoeJITSU View Post
    So I just recently came from a ride here in Las Vegas and this trail has rocks pretty much everywhere. I decided to go tubeless and I think the pressure was at 40-45 on front and back. I am running Nevegal Crossfires 26x2.1 on the back. I got a "burp" riding on the ridge of a boulder, So I go and pump it back up not having a gage I just went by feel. About 2 miles later, I hit a pretty good rock and that was that. I go into my pack and look at my tube, Oh my god...Tube I bought had the wrong valve, I thought I bought a presta valve. My wife who rode with me was pretty pissed, We were 5 miles in , in the middle of the desert, Thank god there was a person that passed me off a 29er tube and I put in on my 26er and rode back safely.
    Now I think it had a lot to do with me being 220lbs. I will stick to tubes till I lose about 25-30 more lbs.
    I am right at 215lbs, run Stan's Arch wheel set, sealant and Nobby Nic tires running between 20 and 30 psi with no issues, it may just be the combo of wheel / tire causing your issue?

    I have also heard of tires blowing off with psi to high, 40 could be to high with your combo, try a lower tire pressure??

    It would suck for me to have to go back to tubes! Good luck....

  56. #356
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    I've read a couple of pages of this thread, but not all of them.

    My new bike is tubeless from the LBS. I went from 35 to 30 psi. Tonight I tried 25 psi. Wow! I could hold tight corners that I used to slide on. I could also keep traction if I ran towards the edges of the trail and accidentally hit duff. So my question: is there any risk of burping tires and having a major blowout if I run lower pressures?

    I'm running Ground Control 2Bliss 2.1s (stock on Speci Carve 29er HT). I weigh probably 190# with all my gear and the bike weighs 26#. Trails are not particularly technical -- mostly slightly damp hardpack with many roots and some mud (not deeper than the tire). On a scale of 1 to 5, 5 being the most technical, I'd rate them a 2.

  57. #357
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    Tire pressure for all around XC riding?

    Lower. And lower.

  58. #358
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    Quote Originally Posted by Gregon2wheels View Post
    Tonight I tried 25 psi. Wow! I could hold tight corners that I used to slide on. I could also keep traction if I ran towards the edges of the trail and accidentally hit duff. So my question: is there any risk of burping tires and having a major blowout if I run lower pressures?

    I'm running Ground Control 2Bliss 2.1s (stock on Speci Carve 29er HT). I weigh probably 190# with all my gear and the bike weighs 26#. Trails are not particularly technical -- mostly slightly damp hardpack with many roots and some mud (not deeper than the tire). On a scale of 1 to 5, 5 being the most technical, I'd rate them a 2.
    Yes there is risk. I rolled a tubeless tire completely off the rim on a bad landing when the front was not straight. There is also a compromise in handling in lower pressure. Looks like you are around your sweet spot. I wouldn't go much lower than that, and always carry a spare tube with you in case it happens. It really depends on the trails and your riding style. Rocks and roots increase the chance of a burp, jumps, drops and high speed turns as well.
    I now run around that pressure and I weigh little less and use fatter tires, after I put a couple of nice dings in the rims.

  59. #359
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  60. #360
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    Great link,could exsplain why i had a front tire blow.

  61. #361
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    I'm back on this "lower pressure" approach after discovering it on my own way back when. This is a good discussion for validation!

    The odd thing I've found in recent years was that many bike shops, tire manufacturers, tire reps, floor pump instructions, etc. recommend the higher pressures -- the range of 35psi to 60psi depending on rider weight! It had made me think that my "lower pressure" approach was amateurish with no scientific basis for a better ride. That it was just psychological.

    Designers of tire tread, I was once told, do not design them for 20psi riding. Not even for 25psi. This is why, I was told, the sidewalls are stamped with the range of something like 35psi to 65psi. And these are 2.1 29" knobby!

  62. #362
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    Quote Originally Posted by malariavalley View Post
    It recommends 30psi front and 33psi rear for me.

  63. #363
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    I'm still searching for optimal pressures on my MTB. On my cyclocrosser on the same tracks, I run 45f/70r on 33mm Maxxis Razes. Racing, that goes down to 40f/60r.
    Those pressures were come across after using Sheldon Brown's tyre pressure page for a baseline. 15% drop when loaded and then tune for the conditions. Which would indicate about 30f/35r for 88kg on 2” tyres as a start point.

  64. #364
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    After having read through all 15 pages of this thread my head is spinning. I am new to mountain biking and am currently doing single-track, technical uphill/downhill through the rocky woods of CT.

    I have a Cannondale Moto2 at 35.5 lbs and my weight w/ gear is almost 160 so full weight on tires is 195.5 lbs.

    I am riding (tubes) Kujo DH 26x2.35" rear and Specialized Clutch SX 26x2.5" in front. I have been riding w/ 30-32psi in both tires but it seems, from what I have read, that I should be lower. I will definitely be adjusting my tires for tomorrow's ride but just would like a ballpark suggestion from some experts here.

  65. #365
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    I'd go 3-4psi lower both ends and work from there.

    I'm not fast at all and weigh 180 odd plus gear and am running 28f/30r on 2.0” tyres.
    Last edited by NordieBoy; 07-30-2013 at 11:19 PM.

  66. #366
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    Time your rides. Sometimes a ride can "feel" fast, but time out slow. I've done this to adjust pressures and it works well over the long term. I have also found that different tires may work better at different pressures even though they are the same size. For example, a UST and "Racesport" version of the same tire at the same size work best at different pressures.

  67. #367
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    Just go by feel. Ride what makes you feel confident, provided you're not burping tires or pinch-flatting. I did it this way and in the end found that my pressures were exactly what the calculator recommended for me.

    Bonucing off of rocks and roots? Lower the psi.
    Squishy feel, pinch flats or the tire coming off the rim? Raise the psi.

  68. #368
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    Geax Seguaro 2.2's, 29". 24 psi, front and rear. 210 lbs. Works for me, with no issues. Has a nice supple feel, and I do not notice any squishiness.
    "Caught my first tube this morning....sir!"

  69. #369
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    175lb to 180lb, sometimes 185lb. Concrete, just below max rated on both tires. Back, Dirt; 35psi to 45psi, sometimes 50psi, depending on terrain, density of soil and/or mud. Front, dirt; 48psi, unless using 50pis+ on rear--again, dependent on soil conditions--.
    I drive more when the streets need repairs! -'95 ZJ

  70. #370
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    Never more than 33 in the back and 29 out front. I am 180-185 geared up and deal with a good amount of sharp rocks at high speed on every ride. The only flat I have had in the past 4 years was from running over 35 in the back... My strava times have shown me over and over again that low pressures are significantly faster for the areas I frequent. By the way, I use a maxxis freeride tube in the back with a 2.25 exo ardent, and a 2.1-2.4 DH tube up front that came on my slayer with a 2.4 HR2 or sometimes a 2.25 ardent up front. I do ride more AM than XC but the pressure doesn't change between the two I like to set and forget.

  71. #371
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    such a subjective question with too many variables; Tires, tread, tread width, sidewall thickness, rubber durometer, terrain, rider weight, etc.

    Nonetheless I ride tubeless 28 or so rear, 26 or so front. works for me with my local rocks.

  72. #372
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    I was thinking about this whilst switching tyres today. On the sides they had the usual 35-60 psi range and I honestly don't think I've ever ridden with either tyre at even the bottom part of that range for anything other than testing. The only time I ever tend to put 30+psi in my rear tyre is when I know that the trail is going to be without technical sections.

    I did recently try a few loops around a local cycle path and I lost about 5 minutes (over an hour) with higher pressures as I couldn't get the power down properly on the gravelly ascents. Dropping the rear to about 32psi stopped the bike feeling like it was bouncing around (on a relatively flat surface!) and I was definitely quicker.

  73. #373
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    Tire pressure for all around XC riding?

    I run 19 front / 23 rear with 2.35 x 650b tubeless on my hardtail. I weight ~155lbs. Try what Stan's says. Divide your weight by 7 and take off 1-2 psi front and add 1-2 psi in the rear.

  74. #374
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    165 lbs and have been experimenting with a 2.35 Hans Dampf SnakeSkin front and a 2.2 Geax Saguaro TNT rear for snow riding on my rigid 29er, Haven UST rims. 22 psi rear rides well without looking like it is completely flat while 18 psi front is as low as it will go without burping and even lower would be better.

    One thing I've noticed with the Saguaro is that the direction of the tread makes a very noticeable difference. I switched it to the "traction" direction and suddenly the back end slides out sideways much more easily while cornering and using the rear brake.

  75. #375
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    Tire pressure for all around XC riding?

    Running around 18 to 20 front and about 21 to 23 back on 29ers. I weigh 165 geared up.

    I meet a guy running 65 on a 26er the other day and I don't see how he gets any traction. I'll be toast down hill and could climb much either.

  76. #376
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    200lbs 2.4 x-king 18 & 20 psi
    PIVOT

  77. #377
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    That MTB Tech site was pretty helpful. I still run about 2-3psi lower than they say, but I know I am in the zone. I really just go by feel, but make note of the pressure when I hit the sweet spot.

    The site also confirmed my experience which is that low pressure on a 26” is different than a 29”. I have both and run the 26” (tubeless on WTB Frequency i19 rims with Geax Akas) at about 27/28 and it feels great. But I run the 29er a good deal lower at 24/25 to get the same feeling (tubeless on Stan’s Arch rims and Maxxis CrossMark). Overall, I like the feel of the Aka the best, but it wears REALLY quickly.

  78. #378
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    Re: Tire pressure for all around XC riding?

    Quote Originally Posted by wahday View Post
    That MTB Tech site was pretty helpful. I still run about 2-3psi lower than they say, but I know I am in the zone.
    Really? I run about 10psi lower than they say.

  79. #379
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    Quote Originally Posted by NordieBoy View Post
    Really? I run about 10psi lower than they say.
    There are a lot of factors like tubed v. tubeless, tire size and rider weight but I definitely couldn't drop another 10psi from what they recommend. They said 29 or 30 for my 26". I definitely couldn't go down to 19 or 20 on those wheels. Things get squirrelly the closer I get to 25. Similarly, I can't see running my 29er as low as 16 or 17. Though this is a new ride for me and I have been dropping the pressure each day I have been out. 24 is the lowest I have gone on rocky terrain with some good climbing and the extra grip was perfect. But the front end was getting a little unstable in tighter turns on downhill and hardpack. Still figuring it out.

  80. #380
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    Quote Originally Posted by wahday View Post
    There are a lot of factors like tubed v. tubeless, tire size and rider weight but I definitely couldn't drop another 10psi from what they recommend. They said 29 or 30 for my 26". I definitely couldn't go down to 19 or 20 on those wheels. Things get squirrelly the closer I get to 25. Similarly, I can't see running my 29er as low as 16 or 17. Though this is a new ride for me and I have been dropping the pressure each day I have been out. 24 is the lowest I have gone on rocky terrain with some good climbing and the extra grip was perfect. But the front end was getting a little unstable in tighter turns on downhill and hardpack. Still figuring it out.
    Day to day on my fully, I run 24f/29r and for racing on the hard tail, 21f/24r.
    Both with tubes and 180lb rider.

    When I was running tubeless on the fully, most tyres were best for me about 25psi on the rear, except for a Hutchy Python which had a sweet spot around 29psi.

    Lots of figuring out involved...

  81. #381
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    The advice "Lower your pressure until you experience pinch flats" makes sense if you're running tubes. But what if you're tubeless? "Lower your pressure until you destroy a rim" is not a very palatable answer.

    How does one balance the desires to 1) experiment with pressures, and 2) not destroy their expensive rims?

    I'm guessing gently bottoming out isn't a problem, so the key is to learn what that feels like and avoid it?

  82. #382
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    Quote Originally Posted by matto6 View Post
    I'm guessing gently bottoming out isn't a problem, so the key is to learn what that feels like and avoid it?
    That's what I do. If I feel a rim strike or 2 on a ride I know I'm running a couple psi low. Also if it starts feeling squirrly in corners. I haven't damaged any rims due to this, it seems pretty obvious if it's dangerously low.

  83. #383
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    Re: Tire pressure for all around XC riding?

    Quote Originally Posted by matto6 View Post
    The advice "Lower your pressure until you experience pinch flats" makes sense if you're running tubes.
    Not sure this makes any sense at all! The last thing I would want when out on the trail would be a flat to fix and risking a ruined tube. Not good advice in my book.

    I run tubeless between 26-30 psi as the trails I ride are generally more rooty and fast rolling. When I was tubed it would be in the 35-40 psi range.

    Sent from my Nexus 4 using Tapatalk

  84. #384
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    Quote Originally Posted by coxinio View Post
    I run tubeless between 26-30 psi as the trails I ride are generally more rooty and fast rolling. When I was tubed it would be in the 35-40 psi range.

    I used to do that back in the 90's, tires were a lot skinnier and good info was harder to come by then though. 25 psi for me with 2.2/2.3's, and I have yet to pinch flat due to this.

  85. #385
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    Quote Originally Posted by J.B. Weld View Post
    I used to do that back in the 90's, tires were a lot skinnier and good info was harder to come by then though. 25 psi for me with 2.2/2.3's, and I have yet to pinch flat due to this.
    Good advice and old habits die hard, will try lowering pressure next time I'm running a tube.

  86. #386
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    Im 220 on 2.0 tires on my cannondale.whats a good pressure I could run on the trails?

    Jeremy Reed

  87. #387
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    Tire pressure for all around XC riding?

    Quote Originally Posted by jeremyreed View Post
    Im 220 on 2.0 tires on my cannondale.whats a good pressure I could run on the trails?

    Jeremy Reed
    Read this thread. It tells you how to find what works for you.
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  88. #388
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    Quote Originally Posted by shiggy View Post
    Read this thread. It tells you how to find what works for you.
    Good thread, thanks

  89. #389
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    I have mine both at 40 now..rated low is 33psi and high is 55....

    Jeremy Reed

  90. #390
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    Conti XKing 2.2, 175lb, 25f/28r. (tubes)

  91. #391
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    At the moment, on the hard tail, Conti X-King 2.4's (55mm width, with tubes), 17psi front, 21psi rear.
    16f/20r and I got a couple of rear rim strikes when seated.

    87kg, fast(ish) cruise speed, rocks and roots only a couple of cm high.

    On the fully, Hutchy 2.1's, Toro front and Bulldog rear. Both tubed. 20f/24r.
    Last edited by NordieBoy; 09-09-2014 at 02:35 PM.

  92. #392
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    Tire pressure for all around XC riding?

    20 front / 25 rear...tubeless

  93. #393
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    Quote Originally Posted by cnitram View Post
    20 front / 25 rear...tubeless
    What tyres/widths?

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    I run Hans Damf 2.35 Front and NN 2.25 Rear. I weigh 155 with all my gear. I used to run 25 front and 28 rear. After my rear losing traction every now and then, and my current rides getting hotter as the ride progresses, I've lowered my pressures to 21/23 respectively. The air inside the tires expands with the heat and the tires do feel harder after the ride. I find that this is perfect for my riding style, terrain and ability - moderately aggressive/dry, loose gravel/intermediate skills.

  95. #395
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    I think for some people, a flat, a ruined tube, or a dinged rim is a big deal, for others, its just part of the experience; a good explanation why there are such widely ranging ideas of what is the "right" pressure.

  96. #396
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    Tire pressure for all around XC riding?

    220 geared up. Start rides with 25 front, 30 back, but may reduce pressure if conditions dictate (my non scientific system is to do a five count while pressing in the valve which equals roughly 5 psi). Happened yesterday - bone dry here in SD and a lot or the trail was loose rocks and I was bouncing / skipping around and under steering. Using hookless carbon rims, Hans Dampf 2.3 up front, Racing Ralph 2.2 in back. I have to say I much preferred the ride of the lower pressure and even though I was at approx 20 front, 25 back. Unless you are flying off 2 plus foot jumps or are slamming your bike into everything, the lower pressure (tubeless) should be good to go as far as flats.

  97. #397
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    For tubes, run as low as you can without pinch flatting. That'll be your limiting factor. For tubeless, go as low as you can without having the tire roll under while cornering, or without feeling like it's wandering. It'll change on different width rims. I can go lower on 21 mm rims than I can on 17 mm rims with the same exact tire.

  98. #398
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    Guess i have been on road/TT bikes too long... I still have a "mental" issue going below 30psi on my tubeless setup.. All I can think about is rolling resistance.

  99. #399
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    Yep, you have. Different ballgame.

  100. #400
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    Re: Tire pressure for all around XC riding?

    Quote Originally Posted by XTERRAGreg View Post
    Guess i have been on road/TT bikes too long... I still have a "mental" issue going below 30psi on my tubeless setup.. All I can think about is rolling resistance.
    I have a 30psi mental barrier too, but mine is the opposite. If I have to, I'll put 29psi in, but I can't put 30.

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