Tire Pressure

Hi,

For training use lower pressure, the one you are using now is OK. For racing you could use higher pressure, closer to the limit. Higher pressure makes you faster but decreases the tire life.

Anyway 170 psi is extremely high for a 140 lbs person !
Regards

youhaditcoming said:

Hi,

For training use lower pressure, the one you are using now is OK. For racing you could use higher pressure, closer to the limit. Higher pressure makes you faster but decreases the tire life.

Anyway 170 psi is extremely high for a 140 lbs person !
Regards

Thanks! I have run them at 170 and it is fast but the ride is rough. Perhaps the answer is to not run a pressure higher than your own weight?🙂 Also, never eat anything larger than your own head except of course pizza which is thin.

This is a reasonable guide, but then all tires are different.

http://two-wheels.michelin.com/2w/front/affich.jsp?codeRubrique=8092004154733&lang=EN

Higher pressure does not make you faster. Higher pressure does reduce rolling resistance; however past a certain point (this is dependent on road surface), higher pressures will slow you down. When a tire with too high pressure hits a bump in the road, that tire is deflected upward or even backwards, reducing the energy used to propel the bike forward. You can actually feel this when you go from chip & seal to smooth tarmac: you feel the bike going faster.

alienator said:

Higher pressure does not make you faster. Higher pressure does reduce rolling resistance; however past a certain point (this is dependent on road surface), higher pressures will slow you down. When a tire with too high pressure hits a bump in the road, that tire is deflected upward or even backwards, reducing the energy used to propel the bike forward..

exactly

I've been working on a new analogy. :p

This is an extreme exmaple to make a point: if you pumped the tyres up to 170psi, put a 20lb baby on the bike and roll it down the road, what would happen (assume the baby can keep it straight and not fall off🙂)?
The bike would bounce all over the place. A wheel that is bouncing up is being retarded in its forward motion. So, to a more realistic situation: a 110 pound rider with 170psi in his tyres is still gunna bounce (or at least buzz) around on anything but the smoothest roads

ok, it needs some work 🙂

alienator said:

Higher pressure does not make you faster. Higher pressure does reduce rolling resistance; however past a certain point (this is dependent on road surface), higher pressures will slow you down. When a tire with too high pressure hits a bump in the road, that tire is deflected upward or even backwards, reducing the energy used to propel the bike forward. You can actually feel this when you go from chip & seal to smooth tarmac: you feel the bike going faster.

Hi,

In theory that's sounds ok, however i doubt mechanics can really take all that into account for example in a stage race where wheels are setup everyday for example. Even if they do i don't think there's much difference in calculating all that,

Some new information for the debate, from cyclingnews.com: McEwen (a small-medium size rider) uses Vredestein tubulars that can take up to 200 psi, 14 bar !

Regards
[img]img356.imageshack.us23vredesteintyreskq4.jpgOpen ↗[/img]

youhaditcoming said:

Hi,

In theory that's sounds ok, however i doubt mechanics can really take all that into account for example in a stage race where wheels are setup everyday for example. Even if they do i don't think there's much difference in calculating all that,

Some new information for the debate, from cyclingnews.com: McEwen (a small-medium size rider) uses Vredestein tubulars that can take up to 200 psi, 14 bar !

So? Does McEwen ride the tires with 200 psi in 'em? No. Does that 200psi have anything to do with the correct pressure for riding? No. That 200psi is only a reflection of the pressures at which the tire will blow off the rim, and generally the max pressure is below the blow-off the rim pressure.

alienator said:

Higher pressure does not make you faster. Higher pressure does reduce rolling resistance; however past a certain point (this is dependent on road surface), higher pressures will slow you down. When a tire with too high pressure hits a bump in the road, that tire is deflected upward or even backwards, reducing the energy used to propel the bike forward. You can actually feel this when you go from chip & seal to smooth tarmac: you feel the bike going faster.

youhaditcoming said:

In theory that's sounds ok, however i doubt mechanics can really take all that into account for example in a stage race where wheels are setup everyday for example. Even if they do i don't think there's much difference in calculating all that,

Some new information for the debate, from cyclingnews.com: McEwen (a small-medium size rider) uses Vredestein tubulars that can take up to 200 psi, 14 bar ! .g[/img]

🙂 I'm pretty sure this is more than theory, in fact, it's now generally accepted as a given.

I'd be amazed if any pro had more than 140/150 in his tyres for a mass start stage

A couple of years ago I got the chance to work as a mechanic in a neutral support car for a pro race. Getting everything set up beforehand, I was asked to do the grunt work of inflating all the wheels. What were they set to? 105 psi. No more. No less.

This seems to be the optimal balance between rolling resistance and wheel deflection for most people. This assumes that you are roughly "average" and weigh 70 kg. Didn't one of the manufacturers (Continental?) have a chart which showed the optimal pressure versus rider weight?

Anyways. Just a data point to consider.

John Swanson
www.bikephysics.com

ScienceIsCool said:

A couple of years ago I got the chance to work as a mechanic in a neutral support car for a pro race. Getting everything set up beforehand, I was asked to do the grunt work of inflating all the wheels. What were they set to? 105 psi. No more. No less.

This seems to be the optimal balance between rolling resistance and wheel deflection for most people. This assumes that you are roughly "average" and weigh 70 kg. Didn't one of the manufacturers (Continental?) have a chart which showed the optimal pressure versus rider weight?

Anyways. Just a data point to consider.

John Swanson
www.bikephysics.com

Yeah, but the max pressure on thems Vredestein tubies is 200psi. I'll bet you didn't think of that, did you now?

since all of rolling resistance and friction on a bike accumulates to about 1-2% of resistance forward motion i think the ~0.05% or whatever decease in rolling resistance for going from say 110 psi to say 140 psi (which others have demonstated doesn't necessarily translate into actually making it easier to move forward) is going gain you more than the gain of running the lower pressure and reducing vibration related fatigue and much improved handling from the larger contact patch at the lower pressure... being fresher and being able to ride through corners faster count for a lot especially in a crit

higher pressures feel faster because you're bouncing all over the place.. but every time your rear wheel leaves the ground your bike slows down.. every millimeter, but many times a second add up.. a honda civic going 150km/h feels fast but a benz s-class feels much slower at 150km/h

high pressure tire are a measure of the tpi of the tire and tpi are a measure of the suppleness of the tire --> less rolling resistance but because a tire has a high max pressure doesn't mean that's the optimum pressure to run them at.. go to the conti site... don't know if they still have the optimum pressure guide but most of the optimum pressures for tires but the last time i checked most were in the 100-110psi range even though rated to 160-170psi max

tire pressure depend on rider + bike weight... if you can't run the tires at the optimum pressure for the tire (i.e. not the max pressure) you should up the tire width not the tire pressure

EDIT - yep they still have max and recommended... check out the conti sprinters http://www.conti-online.com/generator/www/de/en/continental/bicycle/themes/tires/race/sprinter/sprinter_en.html
some manufactures will try to trick buyers because they know there is this misconception that higher pressure are better, but at least conti has some scruples...

youhaditcoming said:

Hi,

For training use lower pressure, the one you are using now is OK. For racing you could use higher pressure, closer to the limit. Higher pressure makes you faster but decreases the tire life.

Anyway 170 psi is extremely high for a 140 lbs person !
Regards

Higher pressure decreases the tire life? Says who? Take some air out of your car tires and ride for a couple hundred miles and tell me if you get the same mpg as when they're fully inflated (higher pressure). Also, tell me if there is less tire wear.

mrklein said:

I am using the new style (slick) Conti Sprinter 250 tires. Does anyone have thoughts about the best tire pressure to run? They are rated to 170 PSI and I have been runing about 135-140 PSI and they last about 4000 miles so I'm very pleased with the durability and the ride is still good. I have been told that if the pressure is too high in a tire that the rolling resistance will be higher. Is this true? If so is it enough to matter? Certainly too little is no good so what then is "ideal"? I am about 140 lbs if that matters. Thanks for any thoughts.

I think there is an optimum pressure for every tire/rider weight (load) combination. Doesn't matter whether it's a car, bike or wheelbarrow tire. Optimum pressure equalling max tread life and min rolling resistance. The Michelin tire chart (that someone posted) shows that the heavier the rider, the closer to max air pressure the tires should have. I'm guessing this is true for all bike tire manufacturers. Just my 2 cents.

mullerrj said:

Higher pressure decreases the tire life? Says who? Take some air out of your car tires and ride for a couple hundred miles and tell me if you get the same mpg as when they're fully inflated (higher pressure). Also, tell me if there is less tire wear.

Go look at your car tires, and then look at your bike tires. See if you can detect a difference in the way they each operate. I bet if you think about it hard, you can.

mullerrj said:

Higher pressure decreases the tire life? Says who? Take some air out of your car tires and ride for a couple hundred miles and tell me if you get the same mpg as when they're fully inflated (higher pressure). Also, tell me if there is less tire wear.

Cars and bikes are of course different in the way they load tires. But, you could try inflating your car tires to the max rated pressure and see how that works. Mine say 44 psi maximum on the sidewall, but I've found roadholding and ride to really go bad at 36 psi, with no apparent improvement in fuel economy. (Yes, I'm one of the geeks that computes and records mileage with every fill up)🙂

Have found that staying close to the car manufacturer recommendations (which are based on speed and load for my car) really works better than the max sidewall rating.

dhk2 said:

Cars and bikes are of course different in the way they load tires. But, you could try inflating your car tires to the max rated pressure and see how that works. Mine say 44 psi maximum on the sidewall, but I've found roadholding and ride to really go bad at 36 psi, with no apparent improvement in fuel economy. (Yes, I'm one of the geeks that computes and records mileage with every fill up)🙂

Have found that staying close to the car manufacturer recommendations (which are based on speed and load for my car) really works better than the max sidewall rating.

Dhk2- your cars road handling and ride is based on more than just your tire pressure, like: tire compound, tire quality, tire tread, wheel alignment, balancing, car load, etc. Just too many variables

I always inflate my car tires to the max rated pressure printed on the tire. With proper alignment, I get the max advertised mileage out of them. If I underinflate the tires even just a little, they'll wear unevenly. (BTW, wear is due to friction/rolling resistance) So, for the most part..whether it be a bike tire or car tire, I almost always inflate them (tires) at or near their max psi rating. For my bike tires, that are rated at 120 psi, I maintain anywhere from 110-120 psi. And, at 180 lbs. I don't get any bounce that some refer to. If you weigh 140 lbs..maybe you do. Until somebody can show me scientific proof stating otherwise (since I'm a geek engineer), I'll continue to inflate the tires (both car and bike) at or near max psi.

mullerrj said:

Dhk2- your cars road handling and ride is based on more than just your tire pressure, like: tire compound, tire quality, tire tread, wheel alignment, balancing, car load, etc. Just too many variables

I always inflate my car tires to the max rated pressure printed on the tire. With proper alignment, I get the max advertised mileage out of them. If I underinflate the tires even just a little, they'll wear unevenly. (BTW, wear is due to friction/rolling resistance) So, for the most part..whether it be a bike tire or car tire, I almost always inflate them (tires) at or near their max psi rating. For my bike tires, that are rated at 120 psi, I maintain anywhere from 110-120 psi. And, at 180 lbs. I don't get any bounce that some refer to. If you weigh 140 lbs..maybe you do. Until somebody can show me scientific proof stating otherwise (since I'm a geek engineer), I'll continue to inflate the tires (both car and bike) at or near max psi.

How do you know you don't get any bounce? The amount of force applied in directions not parallel and of the same sign as the vector defining the direction of travel doesn't have to be so much as to make you feel a "bounce." It can be much more subtle than that.

I can also guarantee that both underinflation and overinflation cause increased wear, worse traction, and thus worse handling. I've seen it first hand and up close on tires that have come off superbikes that I raced.

Being an engineer you'd think you would have thought this through more.

alienator said:

How do you know you don't get any bounce? The amount of force applied in directions not parallel and of the same sign as the vector defining the direction of travel doesn't have to be so much as to make you feel a "bounce." It can be much more subtle than that.

I can also guarantee that both underinflation and overinflation cause increased wear, worse traction, and thus worse handling. I've seen it first hand and up close on tires that have come off superbikes that I raced.

Being an engineer you'd think you would have thought this through more.

I get more "bounce" from an underinflated tire than I do an overinflated tire.

Also, I said nothing about overinflating or underinflating tires. I said I prefer inflating to (or up to) the recommended max pressure printed on the sidewall of the tire. And, until someone gives me a legitimate scientific explanation of why I shouldn't..I'll continue to do so. BTW, your explanation was far from a "scientific" explanation..sorry.

mullerrj said:

I get more "bounce" from an underinflated tire than I do an overinflated tire.

Also, I said nothing about overinflating or underinflating tires. I said I prefer inflating to (or up to) the recommended max pressure printed on the sidewall of the tire. And, until someone gives me a legitimate scientific explanation of why I shouldn't..I'll continue to do so. BTW, your explanation was far from a "scientific" explanation..sorry.

Ah, I see: one of those. Well, then, there's no point in going further then, since it's very unlikely that you would even understand a scientific explanation. BTW, you're over-inflating.