Road Cycling - Tire Pressure

I recently bought a pair of Conti Grand Prix's which say max pressure is 120 psi. My LBS says to go ahead and inflate them to 130 psi. to really get em humming. Could this be dangerous or lead to premature wearout? Any thoughts? Thanks

I recently bought a pair of Conti Grand Prix's which say max pressure is 120 psi. My LBS says to go ahead and inflate them to 130 psi. to really get em humming. Could this be dangerous or lead to premature wearout? Any thoughts? Thanks

I wouldn't do it. The max rating is there for a reason. Also, your rims have a max rating ...believe Mavic limit is 130..maybe 140 (?) psi. I used to run max sidewall pressure, but after asking some of the senior riders in the local club, I've lowered the pressure down. Have decided I like the GP 3000s at 95 frt/100 rear psi a lot better. Also, my Michelin Pro Race show a range on the sidewall, from 87-110 psi...believe that's a better recommendation than just a max rating, since it tells you it's fine to lower the pressure.

Believe the ride, roadholding and puncture resistance is better at lower pressures. The contact patch of course is a little bigger, but I don't think that means more rolling resistance on most normal road surfaces.

Your optimum depends somewhat on rider weight of course...I'm 168 lbs. I'm sure you'll get lots of different opinions here. Suggest you experiment for yourself and see what you like.

I would stick to the recommended pressure on the sidewall. Anything over 120 is going to give a rough ride on bitumen. I run 120psi in the rear, and 100psi in the front if the course is downhill and twisty, I find it gives better grip and less bounce over small bumps in the middle of a corner. If the course is flat and straight I run 120 F&R.

CHEERS.

Mark

A few years ago there was an article in Velo News about Michelin tires. As I recall, the Michelin rep said the max pressure was about the performance range, not just how much the tire can safely hold. Above that you sacrifice handling, etc.

has anyone noticed a definite tire deformation when sprinting uphill? I did some standing hill climbs today, and my back tire was making all sorts of rubber squenching sounds...i had this visualization of one of those top-fuel dragsters with their wrinkle-tire slicks...

A few years ago there was an article in Velo News about Michelin tires. As I recall, the Michelin rep said the max pressure was about the performance range, not just how much the tire can safely hold. Above that you sacrifice handling, etc.
this is true with automobile tires as well

It depends on your weight. The weight of the rider and preference will determine the proper psi for your tires.

i weigh between 115 and 125lbs and can usually notice a bit of dragginess if the tires are at or below 100psi (feels like i'm riding through sludge). i tend to run about 120 in all my tires, front and rear, regardless of ratings. that's road and track bikes, mind you.

i usually have 20-30psi in my trials bike (they can go down to like, 12psi and retain their shape when i'm sitting on the bike, i believe) and on my BMX i run 90 for the rear and 60 for the front, which is what both are rated for.

BECARFULL!!

Don't go beyond the max. pressure, i went for just the max pressure, and i think the air pump was vibreate between 120 to 130 PSI, then just..............BOOOOoooooOOOm :D. i lost my tube :( for little inhancement in the performance.

dxb

Max pressure is usually a compromise between the ad men ( who want to use a high figure in the adverts ) and the lawyers who want it low ( product liability ) .
Mind unless you weigh more than 220 lbs you should not need more than 120 psi .
A good test for a worn rim is 200 psi and then if wornout the rim splits ( pros only , don´t try at home ) so if your tyre burst at 130 psi then something was wrong before you started ( rimtape perhaps )

High pressure gives less resistance , less grip , less comfort .
Low pressure gives more grip , more comfort but more risk of puntures ( too low = pinch flats )
Try 120psi and see how it feels , unstable or bouncy then go lower .
ps high pressures may not work as well if very cold or wet ( same reason , lack of heat in the ' tread ' ) , a lower pressure will cause more ' movement ' of the tread and warm the tyre . ( sqeeze a rubber ball and feel the effect )

I agree with el Inglés concerning the compromised inflate to figure. I have been running Conti GP3000s for the last 2 years and have been inflating them at 135 pounds. The ride is more harsh. Fewer flats. The speed is better and I haven't lost any control. If the tire kabooms on you at 130...then there was a pinch or something somewhere. In the winter I run with the GP 4 Seasons and inflate them just like the GP3000s. Never had a problem.

I weigh 240lbs. I run 135psi in the rear and 120 in the front. I do this on every brand of tire on my road bike. On my commuter I run 26x1.50 at 80 psi., because I want a little more plush ride. I took the commuter on a traning ride yesterday over roads that beat me up pretty badly on my road bike and cracks that I feel on the road bike don't even come through on the commuter.

Your Grand prixs. I ran it at 135psi also, and had no problems at all. I experenced no more or no less flats than usual either. The GP seems to be a fast wearing tire no matter how I run it.

I have two sets of rims, the ones I use this time of year have Bontrager hard case 700x23s that say to 100 psi.. I am runing the same 120x135 that I run with Fortezzas in the summer, no problems! The only time I ever blew a tube, was when I didn't have the bead seated on the rim properly. :rolleyes:

I agree with el Inglés concerning the compromised inflate to figure. I have been running Conti GP3000s for the last 2 years and have been inflating them at 135 pounds. The ride is more harsh. Fewer flats. The speed is better and I haven't lost any control. If the tire kabooms on you at 130...then there was a pinch or something somewhere. In the winter I run with the GP 4 Seasons and inflate them just like the GP3000s. Never had a problem.
Love my 4-seasons and 1850 miles with no problems at 120psi,just like it says on the side of the tire. This info isnt on the tire to ignore.

Love my 4-seasons and 1850 miles with no problems at 120psi,just like it says on the side of the tire. This info isnt on the tire to ignore.

But that is the tire's max rated inflation pressure only. It doesn't say "recommended pressure", but "maximum"...on my 3000's anyway. On the Pro Race, the sidewall has the range of recommended pressures, starting at 6 bar (87 psi) up to 8 bar (116). So, Michelin are saying anything in this range ought to be acceptable, depending on your weight, the road surfaces, and the ride feel/grip you like to have.

Recent Leonard Zinn column in VeloNews states that high pressure will actually increase rolling resistance on chip and seal road surfaces vs 90 psi, since the hard tires are putting more vertical energy (vibration) from the road into the frame. http://www.velonews.com/tech/report/articles/5537.0.html

Of course, it's your personal choice what pressure to run. I rode for many years as a "max rated pressure" guy until I switched.

All bicycle tires are built with at least 5% margin for error, in other words it's safe to go 5% above the max pressure BUT you do so at your own risk because the manufactures put that rating there for a reason-so they don't get sued!

Max pressure on a sidewall does not mean that's the only pressure to run them at, it's meaning is based on load just as car tires are. Just as HarryK pointed out with the Velonews article, hard tires may actually hurt performance; but if you weigh 145 and I weigh 245 and we both run a max pressure my handling and stopping and performance on rough roads would actually be better than yours because the load on yours is less. You weighing only 145 may need to put in only 100psi instead of 135 like a 245 pounder would have too. But if you weigh 145 and use 100psi and I weigh 245 and run 100 than I'm going to have issues with more flats etc.

The ideal tire pressure for any one person on any one tire is trial and error. You need to find the pressure that allows you to stop without the rear tire locking up quickly or doesn't skip around sharp turns, or where rough roads prevent good road contact. I only weigh 163 and I run 100 psi in the rear and 90 on the front-I'm also not one of those max pressure guys. The folks at Rivendell would also agree with the Velonews folks.

But that is the tire's max rated inflation pressure only. It doesn't say "recommended pressure", but "maximum"...on my 3000's anyway. On the Pro Race, the sidewall has the range of recommended pressures, starting at 6 bar (87 psi) up to 8 bar (116). So, Michelin are saying anything in this range ought to be acceptable, depending on your weight, the road surfaces, and the ride feel/grip you like to have.

Recent Leonard Zinn column in VeloNews states that high pressure will actually increase rolling resistance on chip and seal road surfaces vs 90 psi, since the hard tires are putting more vertical energy (vibration) from the road into the frame. http://www.velonews.com/tech/report/articles/5537.0.html

Of course, it's your personal choice what pressure to run. I rode for many years as a "max rated pressure" guy until I switched.
And i've read lower psi will ride better on chipped asphalt and doesnt effect the rolling resistance so in the end,nobody knows so run what feel best.One problem people forget are the rims are rated also,in bars i think,max psi. I run 120 and let it go from there for a week and see no difference in ride as the psi decreases but under 100,i am feeling like i'm in mud where others have said i was full of sh$t because they are running 90 and its no different from 120. So i guess you have to do the old what works best for you and dont let others tell you your wrong because they do it different.Small point,wheelset,bike,rider weight,surface riding on will make a difference but we all knew that except for the ones who belive its only their way that works.Sure is a lot of trouble to just pump up and ride,LOL.

Yeah, like a lot of things we hash over, it comes down to personal preference. I live on a fairly steep hill, and rolling out of the driveway every day gives me a 38-39 mph top speed coasting downhill. So far, I can't tell any difference tire pressure makes on this speed. Getting into an aero tuck, and even light winds, matter of course. Want to try more tests in warmer weather...but of course have to climb back 200 ft for every downhill.

Yeah, like a lot of things we hash over, it comes down to personal preference. I live on a fairly steep hill, and rolling out of the driveway every day gives me a 38-39 mph top speed coasting downhill. So far, I can't tell any difference tire pressure makes on this speed. Getting into an aero tuck, and even light winds, matter of course. Want to try more tests in warmer weather...but of course have to climb back 200 ft for every downhill.

Over 28 kph the wind resistance is bigger than rolling and funnily enough the difference in rolling resistance UNDER POWER ie pedalling is very little different between the same tyre / pressure be it 20 mm or 23 mm , But the 23 runs softer on the butt .

Good reading! I will have to rethink my tire pressure stratagy! I've been maxing them. Now I think I will try lowering a bit to see what it feels like. My guess is I will also get less fatigue in my hands!!

Bill

A lot depends on the carcus : for example above 120 tpi and you get a softer ride at a given pressure than say 60tpi which cheaper tyres ( and some not so cheap ) tend to have . re TPI ( treads per inch ) this is generally of a the more the merrier type of theory as it also tends to make a tyre more puncture resistant as well as giving more grip .
the combined contact patch of a cycle on 23 mm tyres is , I´m told , about 550 sq mm ( ie bugger all ) and in comparison with a motor bike or car the tyres will contribute far more to the handling and roadholding than any other factor so buying too cheap don´t pay .

Still more...
http://www.sheldonbrown.com/tires.html#pressure
(mostly says what's already been said here)

In my opinion and experience, the Conti GPs can handle it, provided your rims are okay, but I'd be afraid to go much higher. So try it. If you like it, fine. If not use less. Vary pressure for ride conditions.

Best thing I've seen so far in this thread is roadbuzz' suggestion to refer to Sheldon's Website:
http://www.sheldonbrown.com/tires.html#pressure

The way to determine proper inflation for road tires outlined therein, along with the pros and cons of over or under inflation, are nearly universally applicable. It's up to each rider to figure out which are the lesser of the various evils associated with running on tires that are over or under inflated.

Moroever, running clincher tires with 10% - 15% of the sidewall psi numbers are WELL within the safety margins of quality rims and tires, assuming your rim's sidewalls are in good shape and your tire beads properly fit-up to your rim's bead hooks. Moreover, not all tire manufacturers use the sidewall number to indicate "Max" inflation; I believe Vredestein uses the number to indicate at what psi they recommend each tire be operated, e.g., the Fortezza's come with 135, 145, and 150 recommended psi levels, varying with tire diameters.

The clincher tire/rim concept is what limits psi more so than most anything else. You'll note that tubular tires -- which are held to the rim by adhesives and to a certain extent a compressive force from the inflated tire -- are routinely rated for 180 - 200psi.

Tube ruptures or tire blow-offs on clinchers during inflation or shortly thereafter -- as someone else noted -- are almost always caused by having the tube pinched between the tire's bead and the rim.

Just my .02.

Still more...
http://www.sheldonbrown.com/tires.html#pressure
(mostly says what's already been said here)

In my opinion and experience, the Conti GPs can handle it, provided your rims are okay, but I'd be afraid to go much higher. So try it. If you like it, fine. If not use less. Vary pressure for ride conditions.

The one thing that no one has mentioned yet is the inner tube. Be sure to use the correct inner tube size. An inner tube that is 19c in a 23 c tire will stretch and fill the tire, but at high pressure, kaboom is more likely. Even if it doesn't blow when you pump it up, that first pothole could do it in.

The tire sidewalls matter alot! Cotton is supple and nylon tends to be harsh. Look at a nice tubular tire, say a vittoria CX, at high pressure, still feels supple.

High pressure gives less resistance


High pressure only gives less resistance on perfect surfaces (tracks, perfect roads). On rough surfaces (most roads, especially chipseal) you will actually get improved rolling resistance by running less pressure.

High pressure only gives less resistance on perfect surfaces (tracks, perfect roads). On rough surfaces (most roads, especially chipseal) you will actually get improved rolling resistance by running less pressure.
I'm not very smart and thats most likly right,but i have a hard time agreeing with it. Something about softer tires rolling better.What will roll faster,a golf ball or a dough ball?

I'm not very smart and thats most likly right,but i have a hard time agreeing with it. Something about softer tires rolling better.What will roll faster,a golf ball or a dough ball?

Obviously too soft will start to get slow again. :)

The issue is bump absorption. The fastest descender on bumpy roads is a bike with suspension because it absorbs the bumps and keeps steady contact with the road. The next best thing is a little give in the tires. Tires that are too hard for the road will actually bounce (very minutely) causing extra friction each time it hits the road.

This might be up for debate, mind you. But I was glad to see Lennard Zinn agree with me recently.

(See the "How Wide is too wide" section) (http://www.velonews.com/tech/report/articles/5537.0.html)