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  1. #101
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    just fyi....i was involved in this thread a while ago. after plenty of riding various tire pressures on maxxis high roller 2.5 dh casing tires, i'm at 27 front and 35 rear on my dh bike. any lower and i flat. of course this is one rocky terrain which is at my local bike park. traction and rolling resistance don't mean anything if your ride gets delayed because of flats. a recent trip to downieville showed me i'm right on with my pressures because i didn't have to stop and fix flats like other guys in our group (i ran 28/36 just in case) - it makes a run much more fun when you don't have to fix your bike half way thru it! just sayin'....

  2. #102
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    Quote Originally Posted by mr.niles
    just fyi....i was involved in this thread a while ago. after plenty of riding various tire pressures on maxxis high roller 2.5 dh casing tires, i'm at 27 front and 35 rear on my dh bike. any lower and i flat. of course this is one rocky terrain which is at my local bike park. traction and rolling resistance don't mean anything if your ride gets delayed because of flats. a recent trip to downieville showed me i'm right on with my pressures because i didn't have to stop and fix flats like other guys in our group (i ran 28/36 just in case) - it makes a run much more fun when you don't have to fix your bike half way thru it! just sayin'....
    And if the title of this thread wasn't "Tire pressure for all around XC riding", that would be a good point
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  3. #103
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    Quote Originally Posted by gvs_nz
    Mfg have released snippets of their research over the years which are counter intuitive to the “Physics” as we thought we understood it. XC World Cup podium finishers using 2.4 tires have a little more info at their fingertips than we do.

    When comparing different width tires it's not the size of the contact patch which governs rolling resistance but the shape. It’s related to hysterisis not friction.

    When considering construction of tires and their rolling resistance the physical tread blocks have an affect but are secondary to the underlying tread region of the casing.

    Whether on or off road, there is trend towards wider tires having less rolling resistance. Aerodynamics aside, a 25mm road tire, even at 120 psi, has been shown to have 40% less rolling resistance than 19 mm road tire at the same pressure. A 1.7" tire at 60 psi has the same rolling resistance as a 2.4" tire at 30 psi. The rougher the ground the greater the effect. As much as 50 watts can be gained on rough terrain using the 2.4" tire at 23 psi over the the 1.7" tire at 60 psi.
    I'd be interested in having a look at this research. Do you have any of it?

    Also, for your example of a road tyre, there are no tread blocks to complicate factors. There is certainly compound and construction - which are significant variables - witness pro motorsport. But you can't beat the physics.

  4. #104
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    I'm 230 lbs and run 45 psi rigid or suspension and I never get flats. You should not get flats when you ride. I see so many posts about running 20ish psi and you they always get flats - like it's accepted or something. Yeah, it's a little rougher - my god you're on a MOUNTAIN BIKE. I tried 40 psi the other day and that was ok but I really like to the tight feel of a properly enflated tire.

  5. #105
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    I vary my pressure with the trail and the gang I am with. When I go on trails with very technical climbs and a bunch of good riders I tend to go as low as I think is safe and go 2 psi lower

    I usually do well clearing technical stuff while other sometimes get stumped on a slippery steep uphill section. I'd rather have to fix a flat sometime during the ride but be the only one to clear a tough section cause I was the only one with traction

    I do this cause they usually smoke me when its fast (doh)

    I'm around 140lbs, on FS 30lb GT, Running Nevs 2.1 @ 22-25psi with tubes for fun technical group rides.

    Cheers,
    Paul

  6. #106
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    I was running 50/50 for years on 2.1 tires front and rear. I swapped over to a 2.35 front and dropped psi to 35 front and 45 rear. There's a bit more rolling resistance, really feel it on the ascents but there's also much more bite on the descents and overall I'm pretty happy with the lower psi.

  7. #107
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    Quote Originally Posted by Rum Runner
    I vary my pressure with the trail and the gang I am with. When I go on trails with very technical climbs and a bunch of good riders I tend to go as low as I think is safe and go 2 psi lower

    I usually do well clearing technical stuff while other sometimes get stumped on a slippery steep uphill section. I'd rather have to fix a flat sometime during the ride but be the only one to clear a tough section cause I was the only one with traction

    Cleaning steep techy climbs is under-appreciated by too many riders. I mean, anybody can ride downhill (though some may need to go slower than others). But you make a tough climb, and you know you accomplished something.
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  8. #108
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    Quote Originally Posted by trailville

    Cleaning steep techy climbs is under-appreciated by too many riders. I mean, anybody can ride downhill (though some may need to go slower than others). But you make a tough climb, and you know you accomplished something.
    I agree, going fast down is simply a matter of having a less risk perception to what your doing where as climbing is a partial skill.

  9. #109
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    OK- dumb pressure question, tire selection aside and assuming same tires, same trails, same bike-
    As things get drier and looser on the surface on your usual trails, especially sandy soil riders, do most increase or decrease pressure to gain more traction? What about increased foliage, esp pine needles(aka slippery bastards)?

    I can make a theoretical argument both ways in my head, but it's quite empty in there

  10. #110
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    repeat post

    wouldn't is be nice to be able to delete a post that isn't in the right place in a thread?

  11. #111
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    Quote Originally Posted by Noclutch
    OK- dumb pressure question, tire selection aside and assuming same tires, same trails, same bike-
    As things get drier and looser on the surface on your usual trails, especially sandy soil riders, do most increase or decrease pressure to gain more traction? What about increased foliage, esp pine needles(aka slippery bastards)?

    I can make a theoretical argument both ways in my head, but it's quite empty in there
    General rule is to lose pressure. As you release air, the tyre footprint increases and the bigger contact patch will float more over the loose stuff. Only exception to this rule is for deep mud when the ability to cut through the mud helps traction (hence narrow tyres with sharp knobs).

  12. #112
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    Quote Originally Posted by mtb63
    I'm 230 lbs and run 45 psi rigid or suspension and I never get flats. You should not get flats when you ride. I see so many posts about running 20ish psi and you they always get flats - like it's accepted or something. Yeah, it's a little rougher - my god you're on a MOUNTAIN BIKE. I tried 40 psi the other day and that was ok but I really like to the tight feel of a properly enflated tire.
    With your weight, you must use higher pressures. However, you lose traction with the higher pressures as your contact patch is smaller. Not a big issue downhill (might even help), but uphill, it's not good. In XC also generally slower. However there is a point when you need to add air to go faster....

  13. #113
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    About the "time to leave 1994" comment, many of us are still riding that way -- on a 26" hardtail.

    Currently I'm running 35f 40r on 2.1/1.9" tires. This feels pretty good all around, including the 8-12 road miles each way to/from the trails. If I go lower, I get pinch flats in the rear and the front slips around the rim under braking, threatening to shear off the valve stem.

    Next tires will be 2.2 or 2.4 for sure, now that we can get fast tires in that size (Ralphs, Saguaros, etc.) If they slip I'll glue 'em on, but probably not go tubeless as that's still too fussy for me.

    In the early 90s, Specialized made a 2.5" Ground Control, which we all thought were the cat's pajamas and surely the Next Big Thing. But most riders believed that skinny/light = fast, and few frames could accommodate these tires so they were a non-starter in the marketplace. Same with Ritchey's 2.3" Zmax, and I think Fisher made a 2.5" tire too. The cool kids at the time wouldn't be caught dead on them.

  14. #114
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    Since this thread is about XC pressure and not rocks/technical stuff, I have a ? for you FAST XC guys out there.

    My friends and I that are pretty quick on the trails can NOT run lower pressure than about 30psi in the front without rolling the front tire. The rear does the same at close to the same pressure. Now when I go on a road trip out west in the rock then I run ~24psi no problem. But I'm talking about fast single track that is pretty hard packed and cornering FAST.

    Now I know that there are lots of variables to consider like rim width, tire casing stiffness, size of tire (especially compared to rim width)....etc. I am currently running 819's with a WTB Weirwolf 2.3 UST on the front, Maxxis Advantage LUST 2.1 in the rear. Same results with a few other tires as well. Results are the same with either tubes or UST.

    So I would like to hear input on guys who can truly corner fast on more hard packed trails. What tire sizes, rim width, and finally what pressure. I you don't know exactly what I mean about the tire rolling then you aren't cornering fast enough to understand.

    thx
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  15. #115
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    Quote Originally Posted by bquinn
    Since this thread is about XC pressure and not rocks/technical stuff, I have a ? for you FAST XC guys out there.
    Since when is rocks/techy stuff not XC?

    Quote Originally Posted by bquinn
    I you don't know exactly what I mean about the tire rolling then you aren't cornering fast enough to understand.
    Good one. Most of my riding is on slower techy singletrack, but if I'm riding somewhere that I know has faster track with turns I'll up the pressure just for that reason (the squirrely feeling you get when your front tire rolls sideways). Every bike setup decision you make is some type of compromise. But it is different for different tires.
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

  16. #116
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    Holy God, you guys run some high pressures...

    I went on a quest to find the fastest rolling tires possible, and first went with Small Block 8's, then tried Gaex Sagauros - which I have both on my 26" and 29'er rigids. Both fanatastic tires and mounted up tubeless with ZERO problems - no burping, even on incredibly rocky terrain - I believe I have 2.35's on both bikes. I ride the trails 5-7 days a week, and I ride to the trails (none of that driving garbage). Sometimes I'll cover 20 miles+ of asphalt on my mountain bike if I want to go explore more.

    I am 210-215lbs and I run 22-26 psi most of the time, usually higher in the rear tire. Before I leave the house, I start at 30psi, and adjust at when I get to the trail. If it's hardpacked and smooth - there's no need for adjustment. When I check it after the ride, I will find I am down to the 22-26 range in most cases.

    On my tubeless 'cross bike, I change the tire pressure depending on the course, but I start at 40psi and go down from there. 'Cross racing is a whole different beast.

    I pretty much ride XC most of the time, but I do throw in the technical stuff almost every ride. Climbing rocks I can definetely feel the difference when I have too high of pressure. Doesn't affect my XC riding, either: whatever that means, but it looks like my rock climbing doesn't including fast XC. Again, I think I found the fastest rolling tires for my trails.

    IMO, it's hard to get a true answer for your situation. I think talking to the local racers in your neck of the woods and asking them their set-up would be the best direction to go, or ask your LBS what the sweet set-up is. IMO, it's very regional specific. I bet my set-up would suck for more humid areas like Florida and in the South. For Nor-Cal, my set-up works like a charm.

  17. #117
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    Quote Originally Posted by Dion
    IMO, it's hard to get a true answer for your situation. I think talking to the local racers in your neck of the woods and asking them their set-up would be the best direction to go, or ask your LBS what the sweet set-up is. IMO, it's very regional specific. I bet my set-up would suck for more humid areas like Florida and in the South. For Nor-Cal, my set-up works like a charm.
    This is a great point Dion. XC means so many different types of terrain depending on the area of the country you live in. I for one have no rocks, no steep technical climbs, just fast single track in the woods that can be very hard packed (sometimes completely solid if it's been dry like all fall here). For that circumstance I can't imagine running mid to low 20's while cornering fast if my tires start rolling at ~29-30lbs.

    My LBS which has some well qualified riders, including the owner which has mounds of race trophies on his walls can't run less than 32lbs or he runs into the rolling issue. Another rider is at 45lbs F/R and neither understand how it would be possible to run the low #'s. I'm sure there are other riders on this board that have hard packed single track and run into this issue and was hoping with some time I would hear from them.

    I didn't mean to be snotty about the 'actually fast' comments, but I've learned over time that many riders that claim to be fast are far from it when cornering, and I need experience/comments from those that truly are.

    thx
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  18. #118
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    Quote Originally Posted by Dion
    Holy God, you guys run some high pressures...

    I went on a quest to find the fastest rolling tires possible, and first went with Small Block 8's, then tried Gaex Sagauros - which I have both on my 26" and 29'er rigids. Both fanatastic tires and mounted up tubeless with ZERO problems - no burping, even on incredibly rocky terrain - I believe I have 2.35's on both bikes. I ride the trails 5-7 days a week, and I ride to the trails (none of that driving garbage). Sometimes I'll cover 20 miles+ of asphalt on my mountain bike if I want to go explore more.

    I am 210-215lbs and I run 22-26 psi most of the time, usually higher in the rear tire. Before I leave the house, I start at 30psi, and adjust at when I get to the trail. If it's hardpacked and smooth - there's no need for adjustment. When I check it after the ride, I will find I am down to the 22-26 range in most cases.

    On my tubeless 'cross bike, I change the tire pressure depending on the course, but I start at 40psi and go down from there. 'Cross racing is a whole different beast.

    I pretty much ride XC most of the time, but I do throw in the technical stuff almost every ride. Climbing rocks I can definetely feel the difference when I have too high of pressure. Doesn't affect my XC riding, either: whatever that means, but it looks like my rock climbing doesn't including fast XC. Again, I think I found the fastest rolling tires for my trails.

    IMO, it's hard to get a true answer for your situation. I think talking to the local racers in your neck of the woods and asking them their set-up would be the best direction to go, or ask your LBS what the sweet set-up is. IMO, it's very regional specific. I bet my set-up would suck for more humid areas like Florida and in the South. For Nor-Cal, my set-up works like a charm.
    Certainly for your type of riding, in fast hard-pack conditions hich pressure is the way to go. Just like road riding, small contact patches are fast when traction is not an issue. I assume that you use low-knob tyres as well? Furious Fred or Small Block8?

  19. #119
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    You must be really fast to roll your tire off your rim on single track with 30 psi. Check the downhill threads and guys are generally running same or lower pressure than you. Or is it just you do night like the feel of the tire squirming?

  20. #120
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    Quote Originally Posted by skiwi
    Certainly for your type of riding, in fast hard-pack conditions hich pressure is the way to go. Just like road riding, small contact patches are fast when traction is not an issue. I assume that you use low-knob tyres as well? Furious Fred or Small Block8?
    I ride Gaex Sagauros on both my 26" and 29er. I ride both bikes rigid and it is very, VERY bumpy and rocky on the trails I ride daily. Baseball sized rocks that will shake a dental filling loose. If it was smoother, I probably would run a bit of a higher pressure - like today I'm riding in Santa Cruz and will inflate my tires a bit.

    Believe-you-me, I've spent a lot of money and fiddling around with tire pressures with lots of different tires and lower pressure/fast rolling small knobs works great for me.

    I doubt it would work as well in other parts of the country, though.

    I run higher pressures on my 'cross bike when I train for racing, understanding I'm not going to be riding on MTB trails and I need a little more speed.

  21. #121
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    I agree it's a personal thing. I use 60psi and roll a lot faster then my friends. In fact, I cost past them while there pedaling.

    Chris.

  22. #122
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    Quote Originally Posted by happydog500
    I agree it's a personal thing. I use 60psi and roll a lot faster then my friends. In fact, I cost past them while there pedaling.

    Chris.
    And how does 60psi work on Devils Gulch? Still faster than your buddies? Able to stay on the trail?
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  23. #123
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    Works supper good!! Twice I hit hard but its fast coming down!! If you go up the gulch (actual trail, not mission creak) you'll spin in a couple areas, but other then that its fast.

    Chris.

  24. #124
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    Quote Originally Posted by happydog500
    I agree it's a personal thing. I use 60psi and roll a lot faster then my friends. In fact, I cost past them while there pedaling.

    Chris.
    You gotta be trolling for a bite. You got one.

    Is this based on experience through using large volume tires at lower pressure and then reverting back to skinny tires at roadie pressures? Coasting at high speed on smooth surfaces has a lot, if more, to do with aerodynamics.

    I can say the same thing about about coasting down trails while on race kings behind guys on skinny tires at ridiculous pressures bouncing all over the place.
    Take a look at some of the current[ not 1990]world cup vids and see if you can see anybody on skinny tires at high pressure. Some are running 2.4's and they are big 2.4's.

    Xmas is coming, do your joints and back a favour by buying a Race king 2.2 and set it just above squirm pressure and feel what smooth speed is, not perceived speed. Do back to back timed tests with your current set up then post back to us. I'd be very surprised if you still stuck to your current set up.

  25. #125
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    60psi, Wow.
    I don't even run 60psi in my 700x35 cross tires on my touring bike.
    Warning: may contain sarcasm and/or crap made up in an attempt to feel important.

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