overinflated tires ?

[ieandro]

thanks for all the posts guys and gals.

It still seems like everyone here has a preference on following the recommended tire pressures. I think I will ride it out at 135 at the rear for now. It's been about a month of solid riding and haven't gotten a flat yet .. *crossing fingers*

Scienceiscool .. that bikephysics.com website is too much info. I loved it. You can't really mess with science.

 

[OscarC]

I don't subscribe to this at all. See this. http://www.analyticcycling.com/ForcesTires_Page.html

Most here will argue that because of the higher tire inflations, the tire will actually skip over the road due to the rough surface. And when you are skipping, you lose contact with the ground and hence speed as well. Make sense. How ever I argue that you are not traveling fast enough and that the surface is not really rough enough to where you are skipping. In other words, I don't believe your tires leave the ground unless you truly are traveling over larger crack fills, or larger higher bumps. When a car's shocks are bad you can usually see that tire bouncing up and down dangerously on the freeway, think back you may have seen this. In a less extreme case it is evident that the tires are leaving the groung becuase you see lumpy wear on the tires. I weigh 142 lbs. and ride hard and fast. My pressures are always at 120 psi. If my tires were leaving the ground I believe I would see a lumpy tire wear from the tread rubbing away. The only difference is that my ride will be slightly harsher but I don't care. My carbon bike will absorb some of this. I really don't care how many web sites claim the opposite at this point.
If I'm climbing at 12 mph do you really believe my tires are leaving the ground? If I'm pedaling on a flat at 21-23 mph, are my tires really leaving the ground? I don't think so. Even downhill at 45 mph, the only times my tires are leaving the ground is when I am bunny hopping something or riding over cracks covered with tar.

But they don't! They feel faster, but are actually slower. Also, overinflation can be a big safety hazard. The numbers on the sidewalls are the MAX, not the recommended inflation pressure. Anything more than that and the manufacturer is explicitly telling you that there's a chance the tire will come off the rim. I've never seen anyone roll a clincher during a race and remain upright...

John Swanson
www.bikephysics.com

 

[alienator]

I don't subscribe to this at all. See this. http://www.analyticcycling.com/ForcesTires_Page.html

Most here will argue that because of the higher tire inflations, the tire will actually skip over the road due to the rough surface. And when you are skipping, you lose contact with the ground and hence speed as well. Make sense. How ever I argue that you are not traveling fast enough and that the surface is not really rough enough to where you are skipping. In other words, I don't believe your tires leave the ground unless you truly are traveling over larger crack fills, or larger higher bumps.

The tires don't have to leave the ground for the bad effects of over inflation to manifest. All it takes is for the tire to be deflected in a direction other than the direction of travel. In that case, then, not only is the energy spent deflecting the wheel/tire assembly but energy is then also expended in the extra flexure of the tire casing. It's a scientific fact that this happens. It's not a belief.

 

[dhk2]

I don't subscribe to this at all. See this. http://www.analyticcycling.com/ForcesTires_Page.html

Most here will argue that because of the higher tire inflations, the tire will actually skip over the road due to the rough surface. And when you are skipping, you lose contact with the ground and hence speed as well. Make sense. How ever I argue that you are not traveling fast enough and that the surface is not really rough enough to where you are skipping. In other words, I don't believe your tires leave the ground unless you truly are traveling over larger crack fills, or larger higher bumps. When a car's shocks are bad you can usually see that tire bouncing up and down dangerously on the freeway, think back you may have seen this. In a less extreme case it is evident that the tires are leaving the groung becuase you see lumpy wear on the tires. I weigh 142 lbs. and ride hard and fast. My pressures are always at 120 psi. If my tires were leaving the ground I believe I would see a lumpy tire wear from the tread rubbing away. The only difference is that my ride will be slightly harsher but I don't care. My carbon bike will absorb some of this. I really don't care how many web sites claim the opposite at this point.
If I'm climbing at 12 mph do you really believe my tires are leaving the ground? If I'm pedaling on a flat at 21-23 mph, are my tires really leaving the ground? I don't think so. Even downhill at 45 mph, the only times my tires are leaving the ground is when I am bunny hopping something or riding over cracks covered with tar.

Perhaps you ride only on supersmooth pavement. Around here, your tires will certainly leave the ground on rough-textured 45 mph descents. Tar strips, patches, just small bumps in the road will tend to launch a rider as light as you running max pressures.

At 142 lbs, will bet you could ride faster and safer on 100 psi or less inflation. 120 psi is slowing you down, unless your road surfaces are super-smooth, eg new fine-textured asphalt. When Michelin recommends a range of 87-116 psi on their 23mm ProRace tires, that's to allow for different rider weight and road conditions; not because they want riders to go slow and lose.

Understand it's hard to believe that less pressure will roll faster, but it's true on most normal textured road surfaces. I didn't believe the experts either until I tried it for myself.

 

[otherworld]

Over-inflated tyres slow you down. As Alienator correctly points out, this is a FACT and has nothing to do with what some “believe” or others “feel” etc.

The four factors that govern rolling resistance ar:

1 Total weight of rider and machine.
2 Characteristics of the road or track surface.
3 Characteristics of the tyre itself (sidewall flexibility and response)
4 Inflation pressure.

Whether a tyre is over or under inflated depends on all of the first three factors.

Put simply:
If your tyres are under inflated they will have to flex too much and so cause higher rolling resistance.

If your tyres are over inflated they will flex less but cause more of the entire weight of machine and rider to be lifted over every little bump and crack, again causing higher rolling resistance.

The ideal situation is to have inflation pressure at the point where the tyres can absorb some of the surface irregularity while still remaining within their optimum limits of flexibility and response.

Jay.

 

[OscarC]

No I don't ride only on smooth pavement. There are small sections everyone in a while that are rough but where I do rattle down the road but I don't mind. I've ridden at 100 psi already. I ride faster and roll much longer at higher psi's. I've done timing tests with different tire pressures but I'm always faster at higher pressures.

Perhaps you ride only on supersmooth pavement. Around here, your tires will certainly leave the ground on rough-textured 45 mph descents. Tar strips, patches, just small bumps in the road will tend to launch a rider as light as you running max pressures.

At 142 lbs, will bet you could ride faster and safer on 100 psi or less inflation. 120 psi is slowing you down, unless your road surfaces are super-smooth, eg new fine-textured asphalt. When Michelin recommends a range of 87-116 psi on their 23mm ProRace tires, that's to allow for different rider weight and road conditions; not because they want riders to go slow and lose.

Understand it's hard to believe that less pressure will roll faster, but it's true on most normal textured road surfaces. I didn't believe the experts either until I tried it for myself.

 

[ScienceIsCool]

No I don't ride only on smooth pavement. There are small sections everyone in a while that are rough but where I do rattle down the road but I don't mind. I've ridden at 100 psi already. I ride faster and roll much longer at higher psi's. I've done timing tests with different tire pressures but I'm always faster at higher pressures.

Here's another data point for everyone. Last year I got a chance to work with the neutral support at a large pro race. I was the "mechanic" in the car that was supporting the break. Before the race, the lead mechanic (who has been working races for 20+ years as a career) had me pumping up about 50 sets of neutral support wheels.

I asked him if I should put them up to 120 psi? No no no no!!! Put them up to 105 psi. That is the optimum pressure for the majority of riders you'll service today.

John Swanson
www.bikephysics.com