Tubular question - air pressure loss

[dd74]

My tubular tires (not tubeless) lose a good amount of air when sitting overnight; I'd say 10 pounds of pressure. I don't think there are leaks in the tires. Anyway, is this loss of pressure normal? It makes me wonder if the tires leak air while I ride on them. Any ideas? Thx.

[carpediemracing]

With latex tubes that's normal. Contis generally don't have latex tubes, Vittorias do. Not sure of others. You should look up your tires' specs.

Someone did a leak down test, measuring pressure during some regular interval. I was shocked at how much pressure a latex tubed tubular loses in 5-6 hours.

[dd74]

With latex tubes that's normal. Contis generally don't have latex tubes, Vittorias do. Not sure of others. You should look up your tires' specs.

Someone did a leak down test, measuring pressure during some regular interval. I was shocked at how much pressure a latex tubed tubular loses in 5-6 hours.
So they must lose pressure while being ridden, correct? Like over the course of a five or six-hour ride, there's some pressure loss.

I use Vittoria and Veloflex. The Veloflex don't seem to leak as much. But I've also noticed the air pressure loss is less on an aluminum wheel than a carbon wheel.

[thegunner]

veloflexes lose a fair amount for me over the course of 3 or 4 days -- like 30 psi. i think it's pretty normal, but maybe i'm okay with mediocrity ;)

[saab2000]

Vittorias lose a lot every day. 30-40psi, or more it seems. Veloflexes a bit less. Continentals none at all it seems.

I've never noted adverse loss over a ride but I'm sure it happens. But good tubulars just ride nicer, not slower, with less air in them. So if you start at 100 psi and it drops to 80 over the course of a ride it's not really a bad thing.

But yeah, latex tubes lose pressure far more rapidly than butyl. That said, I've found Vittorias to leak almost too fast. They seem to lose nearly half their pressure over a day.

[christian]

I assume the Vittoria cx tires are butyl-tubed. Mine seem to lose pressure very slowly.

[FlashUNC]

Latex vs. Butyl tubes, basically.

[ultraman6970]

I know this will cause problems with some but anyways...

If you have the bad custom of leaving the tubulars inflated after you are done using the wheels, or if you dont take the air out (some pressure out) of the tubulars after you are done using the wheels then is normal that you can feel those differences, because some valves leak more air than other ones, never knew why unless you have punctures and in that case you have to put the wheel in water (if you dont want to unglue the tubular).

If you take some pressure out the tubulars will last you longer (here is when some will say that im bsing, maybe the super old tubies users wont) and you wil notice that the tubular can stay with months with 40 psi for example.

IMo you have a leaky valve or a puncture, lose half of the air ovenight is too much.

[carpediemracing]

So they must lose pressure while being ridden, correct? Like over the course of a five or six-hour ride, there's some pressure loss.

I use Vittoria and Veloflex. The Veloflex don't seem to leak as much. But I've also noticed the air pressure loss is less on an aluminum wheel than a carbon wheel.

Correct. The "loss curve" flattens out so you don't lose the same amount regardless of starting pressure. If you start high then you lose a lot. Start low and you don't lose as much.

What I found interesting is that pros like Boonen and such run extremely low starting pressures in a long race like Paris Roubaix. I think he started with 56 psi. Although the loss won't be quite so significant if he had started at 100 psi, it's still going to be somewhat significant. This means he's hitting the cobbles at maybe 50 psi, maybe 45 psi, and he may be finishing at 40-45 psi.

The rim shouldn't make a difference since the rim doesn't trap air and the tire casing is basically transparent to air pressure (i.e. casing doesn't have any sealing capacity).

Contis, at least the ones I've had, typically run butyl tubes so they don't lose much pressure in a few hours.

Clinchers have the same issue - use a thin latex tube in your clincher and it'll lose air kind of quickly. Use butyl and it won't.

[ultraman6970]

Well in the PR race they go with 28s tubulars to start with... second you cant go with 100 psi in that race because you need the cushioning. I cant imaigne going 120 psi with 21 mm tubulars in the PR, before the 1st mile of cooblestones you get puctures.

PErsonally doubt the pressure is as low as 55 psi that's too low for him, 80 i believe... 55 will deform too much and will hit the rim big time, 200 pounds ass in here and even when i was 165 back in my racing days with 55 psi I was able to hit the rims... No idea if a light cx tire might not do that but regular 22 mm road tubulars will hit the rim at 55 if you hit a pot or in cobblestones.

As for losing air while riding, thats so debatable because i never felt tubulars lose air while riding unless you have a puncture, specially during the winter because in the summer is clear that you get more pressure due to heat.

[carpediemracing]

I know this will cause problems with some but anyways...

If you have the bad custom of leaving the tubulars inflated after you are done using the wheels, or if you dont take the air out (some pressure out) of the tubulars after you are done using the wheels then is normal that you can feel those differences, because some valves leak more air than other ones, never knew why unless you have punctures and in that case you have to put the wheel in water (if you dont want to unglue the tubular).

If you take some pressure out the tubulars will last you longer (here is when some will say that im bsing, maybe the super old tubies users wont) and you wil notice that the tubular can stay with months with 40 psi for example.

IMo you have a leaky valve or a puncture, lose half of the air ovenight is too much.

With good tubulars it's not necessary to release the pressure, even with the butyl tubed Contis. In the old days, with cheaper or thinner case tires, if you left the tires fully inflated, the casing would stretch. It was comical how large some training tubulars would become in just a month or two - a formerly 21 mm tire might be close to a 28 or 32 mm tire, cracks all over the tread, etc.

After having seen that with a few tires, back in the day, I religiously deflated my tires.

Then I noticed that even after a season or two my tubulars weren't stretching out. My 21 mm tire was still about 21 mm, ditto my 17 mm tires, etc. So I stopped deflating my tires, first starting with the really thick casing tires (Clement Futura) or the nylon casings (Panaracers). I saw that the tires remained about the same size. I stopped deflating my tubulars as a habit.

I keep an eye out for cracks in the tread. Good tubulars feature treads glued onto an inflated casing. Cheaper tubulars have the tread vulcanized (sort of melted) while the casing is not inflated. When you inflate a cheap tubular the tread cracks everywhere. I haven't had one of those tires in forever but those were the tires you had to deflate every time you rode - they usually had cheaper butyl tubes so they held pressure well, and the casing was cheap so it stretched like mad.

The only other tires I had to deflate regularly were silks. They stretched like mad (or else I got them wet by accident, I dunno). After some of the hassle with the mythically better silks I bagged using them.

For the last 20? years I have been using a mix of Vittoria CXs with some Contis thrown in (Sprinters and something else at about that level), and, for the last few years, Bontragers (the two nicer ones). I never deflate them after a race. Except for the lumpy as heck Contis they always need air within a day, and after a week they're so soft they might as well be flat.

[redir]

In theory they lose air after a long ride but in practice you won't notice it unless it's a valve problem. Sorry Ultra but I don't but that letting the air out of the tire helps it last longer. But You didn't present any science behind that idea and I'd be open to any explanation as to why?

[Lionel]

Veloflex carbon at 80 psi will be around 60 psi after 24 hours.

FMB 27mm PR at 55 psi will be around 45 psi after 24 hours.

Boonen is fine.

[Lovetoclimb]

I used to run FMB Competition CX 22mm road tubulars on Campy Boras and they would steadily lose air between race weekends from 100psi down to 30ish.

Even on my clincher tires with latex tubes for cyclocross (both made by challenge) they will drop from 30-35 down to the mid teens in 48 hours or less.

[nighthawk]

So with leakage established as unavoidable.. whats the best state to store glued and mounted tubs, pressure or no pressure?

[thwart]

Boonen is fine.Glad we got that settled. ;)

Good tubies leak air faster than cheaper tubies. Contis may be the exception.

Latex is cool, butyl is not.

[carpediemracing]

Well in the PR race they go with 28s tubulars to start with... second you cant go with 100 psi in that race because you need the cushioning. I cant imaigne going 120 psi with 21 mm tubulars in the PR, before the 1st mile of cooblestones you get puctures.

PErsonally doubt the pressure is as low as 55 psi that's too low for him, 80 i believe... 55 will deform too much and will hit the rim big time, 200 pounds ass in here and even when i was 165 back in my racing days with 55 psi I was able to hit the rims... No idea if a light cx tire might not do that but regular 22 mm road tubulars will hit the rim at 55 if you hit a pot or in cobblestones.

As for losing air while riding, thats so debatable because i never felt tubulars lose air while riding unless you have a puncture, specially during the winter because in the summer is clear that you get more pressure due to heat.

I misspoke on Boonen's pressure - 59/62 psi. Chavanel ran 58/59 psi.
http://velonews.competitor.com/2012/04/bikes-and-tech/what-tires-wheels-and-pressures-were-roubaix-riders-running_212925

I've ridden some allegedly smoother cobbles in races and in training (in northern Belgium). I found that I was good with relatively high pressures on a 21 mm tire. I had no choice - I didn't have any other tires with me - but any issues with race pace were with me, not with my equipment. In training once I got up to about 45-48 kph the cobbles basically disappeared under me; in races the field, in the short time I could stay with them, typically sustained 55-60 kph on the cobble sections. Problem was I couldn't sustain that pace too long, either in training or in races. In the races I was getting shelled and pulled while hitting max speeds, on a flat course, of over 70 kph. The problems, again, were with me, not with my equipment. I highly doubt I could have found, through equipment, another 15-20 kph in average speed in the opening salvos of a kermis.

Personally I run much higher pressures than many riders around me. I think I grew up expecting the tires to be somewhat rigid and it's hard for me to wrap my head around the low pressures. I admit I've run my wide-rim 23c clinchers at 55-60 psi in a pinch (late for a ride) but if I had a choice I'd have pumped them up to 85/90 - 95/100 psi. With regular width rims I used to run 110/115 - 115/120 psi with the same size tires.

In the last three seasons I've weighed from 155 to 200 lbs in races and I ran 120 psi (lighter weight) to 140 psi (heavier weight) in my 21-23 mm tubulars. Since tubulars don't rely on the rim for shape it doesn't matter what rim I have, I need the pressure for the tire to hold the shape I expect it to hold.

The tire pressure leak down post (http://socialcyclists.org/road-racing/tire-pressure-loss/msg63388/#msg63388) content:
i took 6 wheel sets. 5 had latex tubes. 3 used valve extenders (+1 used vittoria's "removable valve"). for the latex tubes, i used PTFE tape on the RVC for one wheel in each wheelset. three tire (tube) manufacturers were represented.

here's what i found:
* pressure decrease in 2h of latex tubes was ~7-8psi; loss was 1-2 for butyl
* decrease after 4h of latex was 10-16psi; 4-5 for butyl
* decrease after 12h was 25-32 for latex, 7-9 for butyl

Personally I'm no super expert with tire pressures - I can't tell within 20 psi if I'm okay or not. I do notice a difference if I'm a bit low on tubulars, like 20-30 psi low; at that point I don't like the way the bike responds in certain situations. I can't tell if a tire loses air over the course of an hour but over the course of a day it seems a lot (like if I pump up my tires early in the morning at a race I promote, then 7 hours later start getting ready for my race, the tires seemed a bit dull, not quite as bright as a just-inflated tire).

Based on the above person's very basic experiment it seems that in a crit there won't be a big difference, after 6 hours there might be, and after a long day there definitely will be.

The person that did the experiment raced the 200 mile USAC-sanctioned RR (LO....something) so for him such tire pressure loss over 10 hours is significant.

For me, a one hour crit guy, not so much. However, based on that guy's experiment I'll top off the tires if I race again later in the day.