pressure and rolling resistance .- Mtbr.com

# Thread: pressure and rolling resistance .

1. ## pressure and rolling resistance .

Well I've read up an awful lot on this and basically they say (they say a lot !) there's a point to which there isn't any less resistance despite putting a million psi
There comes a point when your bike won't roll any quicker , what do you guys run in your tyres , and what is the max pressure on your tyre wall ?
I did run 85psi in my schwalbe 1.5 city jets and now have 30 psi in my continental race kings which say 45 on the side if I recall .

2. 100 - 110 psi on my Gatorskins. I can tell when they start getting low like in the low 90's as the handling and effort it takes to turn them changes.

3. Second TenSpeeds comment

I run Conti GPs at about 110 and most of my Tufos at 120-30. All in the 700x19 to 700x23 size range.

If they get down to the low 90's I run the risk of pinch flats hitting road debris.

4. Originally Posted by crazee horse
Well I've read up an awful lot on this and basically they say (they say a lot !) there's a point to which there isn't any less resistance despite putting a million psi
There comes a point when your bike won't roll any quicker , what do you guys run in your tyres , and what is the max pressure on your tyre wall ?
I did run 85psi in my schwalbe 1.5 city jets and now have 30 psi in my continental race kings which say 45 on the side if I recall .
There is some science to this:

You need to add tire suppleness to get a working theory.

If your tire has infinite suppleness....ie no energy is required to deform the rubber side walls.....then you just need enough pressure to keep the tire on and provide cornering stablity etc.

If you tire has in not very supple at all... ie lots of energy is required to deform the rubber side walls....then you need enough pressure to minimize the deformation for any given ground condition.

Tire manufactures know this...so the max inflation pressure would only be optimum for rolling resistance on a very smooth track.

Most tires also have a minimum inflation pressure....this pressure is adequate to fully seat and mantain a the bead seat.

Unless I am running tubeless tires in rough conditions...I am always somewhere in the middle...generally pretty close to half way between the two pressures.

On my comutter I just pump to max then ride till I feel the squirm or drag....then pump back up....I am lazy.

5. 105-110 on my 25 and 28c panaracer tservs.

6. Really goes to tire width. my "commuter" bike has 40mm tires that i run about 50. Anything above that, and I can barely tell any difference in resistance, but the bumps hit harder. When I go below 45, I can definately feel increased resistance though.

7. Originally Posted by crazee horse
Well and basically they say (they say a lot !) there's a point to which there isn't any less resistance despite putting a million psi
I think what they generally say is that on smooth surfaces you can go as high as you want - you can run a solid steel wheel from a railroad car if want to.

But when there are imperfections in the road or trail surface a million psi tire bounces up-and-back off of them which slows you down, whereas a softer tire deforms around them.

And the comparison isn't between running the same tire at super-high and super-low pressures, but running a narrow tire at high pressure versus a wider tire at low pressure.

With that being said, I tend to like something like the 15% drop model: Problem Solvers | Optimal Bike Tire Pressure

If nothing else, that encourages people to run a lower pressure upfront.

8. I have a pair of Continental Touring Plus tires on my commuter, I keep them around 90-100 psi. The back is very touchy as I load it with my fat butt and gear, the fronts I usually run at 80ish. I try to keep them pumped up to reduce snakebites too. That's my biggest issue in urban riding.

9. Very low.

I have my 30c slick tires at 35psi, my 2.2 race kings ss mtb tires at 20 psi, and my 2.4 winter tires at 15 psi.

My road bike is still up about 85-90psi since it's not tubeless yet.

10. 40 PSI on basically every tubeless mountain bike tire I've used to commute on. Less for trail use.

On the super skinny (1.5"...who would use a tire narrower than that?) road tires on the 'cross bike, I run 80.

I notice the 2" range tires rolling slower on the road when they drop to around 35. Over 40, I don't notice an improvement. So I've landed on 40 as my commuting sweet spot.

11. On my commuter, I've settled on 50-60psi on my 700x38's as a happy spot.

On my old Stumpy with pretty narrow rims 2.4-2.2's, I run them around 20-24psi. On my Bucksaw with 65mm rims, I like about 15psi for pavement, 9psi for faster hardpack, about 8psi if it's slow and chunky, about 6psi for moist fall/spring conditions or packed snow, and down to about 2-3psi for up to about 6" of fresh snow.

12. I've been happiest running the rear tires 10% or so below the labeled max, and the front around 20% below the rear, on pavement and gravel. Slightly over the minimum labeled pressure in snow or mud.

75- 80 psi rear on Vittoria Hypers (700x 37), with 50 -60 front tire pressure, 50 psi rear and 40 front on Maxxis Ardents (29x 2.35) has been about right for me with all the crap I carry. A lighter rider with fewer groceries etc. would need fewer psi to get the same contact patch and rolling resistance (I think).

At work we have done several studies of draft (power required to pull) wagons with steel, pneumatic, and wooden wheels over varying terrains. On gravel, poor pavement, or hard packed dirt pneumatic tires gave the lowest amount of force required (some of this is from the relatively wider tire), followed by wooden wheels with a steel tire, and wooden wheels with a rubber tire. All steel wheels, the infinitely hard option, were only lower in draft if they were significantly larger in diameter than then other options.

13. I just purchased a Giant Revel 29er and seen the tires say 65psi max ! I ride only on the street and was wondering if you guys think I could bump it up to 75 or 80 psi ! I'm 6'8 and 280 !

14. I would be very cautious about exceeding the recommended tire pressures by that much. Do you know what the recommended max pressure for the rim is?

15. most cheap 2.0/2.1 tires are 60tpi, if that. It would have an awful time withstanding that kind of pressure. 65 is plenty for a tire that size, anyway, even at your weight. I rode a cargo bike with about 380 on it, and still didn't feel like I needed to be all the way maxed out.

@rustedthrough,

The pressure max of most rims drops in proportion to the width of the tire, so a wider tire means a lower max pressure. Mavic prints this stuff on their rims, not sure other manufacturers do.

16. A split rim could ruin your whole morning.

17. Originally Posted by RC51 RIDER
I just purchased a Giant Revel 29er and seen the tires say 65psi max ! I ride only on the street and was wondering if you guys think I could bump it up to 75 or 80 psi ! I'm 6'8 and 280 !
This is a mountain bike correct? Different tire pressure because the bike/tires are designed for off road use. You are going to want to swap to a more road friendly tire if your only plans are to ride on the road with that bike.

18. My thoughts exactly , why would you wanna run such a high psi in an mtb ?

19. Originally Posted by RC51 RIDER
I just purchased a Giant Revel 29er and seen the tires say 65psi max ! I ride only on the street and was wondering if you guys think I could bump it up to 75 or 80 psi ! I'm 6'8 and 280 !
you may split the rim or you may blow the bead....

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