Study finds that wide tires + low psi = less rolling resistance off road
- Thread starter Beast
- Start date
why didn't they test 3" gazzoladdis? 
Or those godawful Surly ones?
I think their study, whilst definitely interesting and more than likely quite relevant for XC bikes whilst climbing, is lacking high-speed credibility when DH tyres are considered. The material damping of a thick tyre and tube is pretty significant IMO.
Always thought this was common knowledge?
For the DH forum this is crucial info for newbies and those who don't ever experiment with tires and tire pressure. I think most experienced riders have realized that you should run only as much PSI/bar as you need to avoid pinch flats and rim dings -- beyond that your tire conforms less and you get bounced around more. On the other hand -- too low and your tires can roll off the rim even when you're not getting rim dings or pinch flats. I still remember rolling a Maxxis Minion DHF off my front rim in a hard corner when I tried to run really low PSI... not fun!
For those of us who climb our bikes by pedaling, we have to make compromises. Wider tires = heavier tires, and heavier tires usually are more work to pedal because they weigh more. Usually. There are exceptions, like a big single-ply vs a narrow dual-ply, or a high-volume small tread vs a low volume narrower but chunky tread.
Then again, there's also the tough-guy benefit of getting stronger if you can manage to pedal those bigger tires on a long climb.
For those of us who climb our bikes by pedaling, we have to make compromises. Wider tires = heavier tires, and heavier tires usually are more work to pedal because they weigh more. Usually. There are exceptions, like a big single-ply vs a narrow dual-ply, or a high-volume small tread vs a low volume narrower but chunky tread.
Then again, there's also the tough-guy benefit of getting stronger if you can manage to pedal those bigger tires on a long climb.
During the experiment speed is held as a constant. The speed is measured by the SRM system, which infers speed directly from wheel rotation. A wheel with lower pressure will have a smaller effective diameter and move a shorter distance per rotation than a wheel with more pressure. This will give lower power input results for the wheel with lower pressure (between identical tire models where the computer presumably wasn't re-calibrated).
I don't know if this would negate the results of the test, but it might knock them down an inch.
I don't know if this would negate the results of the test, but it might knock them down an inch.
For that reason I really like my 2.55 Weirwolf LTs (low tread). Big and wide but still roll great. I run them at about 18psi.
18psi? seriously? whenever I used to read about that stuff over at empty beer I would think to myself, "this dude rides slower than a granny on flat, smooth trails."
maybe you're just the smoothest rider on earth, though.
I weigh 150 lbs and I can't get away with less than 23-25psi front, 28-30 psi rear on my trails at my normal riding speeds. probably because I really suck.
Yeah 18psi is pretty damn low! At 200lbs the minimum pressures I need are about 26psi front, 30psi rear (dual ply minions), and even then I rim out pretty hard from time to time. That said, I'm heavy, enjoy a good plow and am not possessed of Sam Hill's smoothness.18psi? seriously? whenever I used to read about that stuff over at empty beer I would think to myself, "this dude rides slower than a granny on flat, smooth trails."
maybe you're just the smoothest rider on earth, though.
I weigh 150 lbs and I can't get away with less than 23-25psi front, 28-30 psi rear on my trails at my normal riding speeds. probably because I really suck.
Depends on the track and rider. On some trails I could get away with as low as 16psi fron when I was 135lbs. Now I tend to run a bit higher pressures and I havent been on a smooth trails for long. Tubeless on ust rims also helps.
To be honest I do question my pump a little. My old Park Tool pump was reading too high but this new pump seems to be in line with a few others I've tried. At any rate they are really low and mold around everything. Really great on wet roots because they mold around the root to the firm ground. Definitely slower on the smooth stuff but around here there is so little of that. I've posted my best times on my informal time trial (rocky xc) with these tires. I do have to be careful with square edge rocks tho. But so far 18-20 seems to be my magic number for not getting pinch flats.
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A digital pressure gauge is the only way to know down to 1psi (.5psi actually), which I like when running sub 35psi. I use Topeak's.
this line of thought brought about the hutchinson python....lower pressure with more knobs gives better traction and equivalent or better rolling resistance.
Not a real big surprise here...but there are so many other factors...knob design, tube thickness/tubelessness, rider weight, etc.
Not a real big surprise here...but there are so many other factors...knob design, tube thickness/tubelessness, rider weight, etc.
top xc pros are running tubular mtb tires around 2.1-2.2 range, and although these tires are small, the tubular tires have a much larger contact area. Word on the street is that they are running somewhere around 24psi because of this "less rolling resistance" factor.
There's gotta be a point of diminishing return or I wouldn't be the only rider on the hill using 2.7s. They sure feel slower than 2.5s but I love the grip and flat protection.