Tubular tire pressure loss

[blkhotrod]

i have been checking air pressure loss in my tubulars and over a 5 hour period, the pressure drops from 150 to 130. i have a 5 hour race and was wondering if the road friction on a 70-80 degree day might compensate for the slight leakage around the valve extension? thanks

 

[daveryanwyoming]

i have been checking air pressure loss in my tubulars and over a 5 hour period, the pressure drops from 150 to 130. i have a 5 hour race and was wondering if the road friction on a 70-80 degree day might compensate for the slight leakage around the valve extension? thanks

If your tube is actually leaking it's not likely to improve while out on the road. Are you sure you're not just seeing the pressure drop over time typical of a latex tube? If you really have a leaky valve stem then I'd change out the tire before your race or at the very least slime the tube to minimize further losses. But riding on a known leak sounds like setting yourself up for trouble out on the course.

And what the heck are you doing running 150 psi for a 5 hour road race? On anything but the smoothest surfaces (like really fast wood tracks) Crr typically increases with very high pressures. It depends on your weight and the road surface, but typical charts for rider plus bike and kit at 80 kg show lowest Crr around 110 to 120 psi on real world roads. Sure a very hard tire bouncing around on all the road irregularities feels really fast, but that don't make it so....

-Dave

 

[alienator]

The rate of pressure drop will be higher at higher pressures. Latex tubes leak substantially faster than butyl tubes. Riders who ride at 150 psi for 5 hours are less fresh than riders who ride at 110 psi for 5 hours.

 

[Peter@vecchios]

i have been checking air pressure loss in my tubulars and over a 5 hour period, the pressure drops from 150 to 130. i have a 5 hour race and was wondering if the road friction on a 70-80 degree day might compensate for the slight leakage around the valve extension? thanks

First, NO reason to ride tubies at a 150 psi. At that pressure you lose most of the benefits of tubulars and no, you don't have significantly lower RR. What you have is a rock hard ride.

I'm guessing you have a teeny hole. Tubies with latex tubes lose about 20 psi in 24 hours, not that much in a few hours.

If it IS the valve being out so as to use a valve expender, then I'll bet at 110-120 psi(still high for a tubular) it won't OR replace the valve guts with the type where you install the valve guts onto the valve extender so you can close the valve. Vittoria makes some.

 

[blkhotrod]

If your tube is actually leaking it's not likely to improve while out on the road. Are you sure you're not just seeing the pressure drop over time typical of a latex tube? If you really have a leaky valve stem then I'd change out the tire before your race or at the very least slime the tube to minimize further losses. But riding on a known leak sounds like setting yourself up for trouble out on the course.

And what the heck are you doing running 150 psi for a 5 hour road race? On anything but the smoothest surfaces (like really fast wood tracks) Crr typically increases with very high pressures. It depends on your weight and the road surface, but typical charts for rider plus bike and kit at 80 kg show lowest Crr around 110 to 120 psi on real world roads. Sure a very hard tire bouncing around on all the road irregularities feels really fast, but that don't make it so....

-Dave

where might i find these charts? rider+bike is more like 70 kg and road is smooth. i appreciate all the input from everyone.