Road Cycling - consequences of overinflation?

Hi, I'm new to road biking, so I've never really used high tire pressures before. I've come up with this cool little road bike -- a 1982 peugeot kid's road bike with 24" wheels. I replaced the original 1 3/8 inch wheels with nicer narrower alloy wheels, which came with 24 x 1 1/8 road tires of unknown age. These tires say "nylon" and "the silver star tire" and give the max pressure as 75 psi. Now I'd like to do more than 75 psi. I've got them about 80 now. Can I go higher? What will happen if I go too high -- tire coming off rim, violent blowout, what? Do I really have to get new tires? Mostly I ride around town, but I am going on a 67-mile mountain jaunt in a few weeks. Cheers!

I have heard that the way the tire people test tires is to inflate them until they blow off of the rim. That is alledgedly at twice the recommended tire pressure.

So sure, you can over inflate your tire.

But on road tires, rolling resistance does go down with more inflation, but the gain above 110 psi is very minor. Also overinflation does hurt the ride making it more bumpy.

With your wide tires, I would think that although you could probably run a fair bit more then 75 psi, you really would not see much effective decrease in rolling resistance above say 85 psi.

Overinflation = BANG!.....simple.

But what pat said.... I would actually trial different pressures and see how they handle, and ride over bumps etc.

Brendon

If they are of unknown age I would be hesitant to over inflate at all, especially if you are going to trust them on a longish ride. Have you checked for cracking in the sidewalls etc.?

Hi, I'm new to road biking, so I've never really used high tire pressures before. I've come up with this cool little road bike -- a 1982 peugeot kid's road bike with 24" wheels. I replaced the original 1 3/8 inch wheels with nicer narrower alloy wheels, which came with 24 x 1 1/8 road tires of unknown age. These tires say "nylon" and "the silver star tire" and give the max pressure as 75 psi. Now I'd like to do more than 75 psi. I've got them about 80 now. Can I go higher? What will happen if I go too high -- tire coming off rim, violent blowout, what? Do I really have to get new tires? Mostly I ride around town, but I am going on a 67-mile mountain jaunt in a few weeks. Cheers!

I've become progressively more cautious about tire pressure through the years. The worst thing that can happen to you is to have a tire blow off of the rim at speed. That does happen in real life. I personally know of two cases, and neither of those individuals was exceeding their tire's rated air pressure. So much for the "you can double the listed air pressure" theory.

Through the years, bike tires and rims have gradually changed. Modern tires and rims have "hook beads" that allow them to stay on the rims while using much higher air pressures than previously. If your tire is rated for 75psi, I doubt it is a hook bead tire so I'd be cautious with it.

The other half of your tire/rim interface is the rim. A 140psi tire on a 110psi rim is only safe up to 110psi. Almost nobody has any idea what the rated pressure for a brand new rim is and, as the brake surface wears, the amount of air pressure a rim will safely contain gradually declines. The failure mode is that air pressure can push the rim flanges away from the centerline and allow the tire to slip off. Modern european rims now have wear indicators designed into them to tell when the brake surface has worn too far for continued use.

thanks for the tips. i never thought about the limits of the rim before -- i just assumed that it would be way above the limit for the tire anyway. the tires aren't cracked, but they do have a slightly stiff dry texture that is not present on new tires. any recommendations for 24" road tires? the only ones i've found on the web are called panaracer tecnova II's.

My exprience with very high inflation of tires is much higher incidence of flats as well as more damage to the tire itself.

They are supposed to blow only at twice the recommended psi?

I think this might apply to MTB tires (even then I'm skeptical), but surely not to road tires. I personally think it will blow way before that... For 110 psi tires, don't go higher than 130 psi...

I only recently found out that Mavic recommend maximum inflation for their rims.
How general are they?


Mountain/Cross Rims

TIRE SIZE...MAXIMUM PRESSURE
inches....psi

1.00....113.00

1.20....103.00

1.50.....88.00

1.75.....76.00

1.90.....69.00

1.95.....66.00

2.00.....63.00

2.10.....59.00

2.20.....55.00

2.30......49.00


Road Rims

TIRE SIZE.....MAXIMUM PRESSURE

mm......psi

19....146.00

23....138.00

25.....131.00

28.....117.00

nutbag, can you share your source?

It's on the Mavic site, but I think there's a different Mavic site for each continent.

http://www.mavic.com/servlet/srt/mavic/road-prod?lg=uk

Click on one of the road rims, and the data should pop up.

thanks for the tips. i never thought about the limits of the rim before -- i just assumed that it would be way above the limit for the tire anyway. the tires aren't cracked, but they do have a slightly stiff dry texture that is not present on new tires. any recommendations for 24" road tires? the only ones i've found on the web are called panaracer tecnova II's.

There are several different 24" tire sizes. It's hard to tell which one you have. I suggest you contact Sheldon Brown at Harris Cyclery. They can get several and he can probably point you in the right direction if you tell him exactly what tires you have, what kind of rims you have, and what kind of bike they are on.

It's on the Mavic site, but I think there's a different Mavic site for each continent.

http://www.mavic.com/servlet/srt/mavic/road-prod?lg=uk

Click on one of the road rims, and the data should pop up.


Thanks. Probably could have guess it, but I appreciate your response with it.

Not only will the tire blow off the rim, but a front blowout at the wrong time, especially in a downhill curve, can be more costly then a new tire and tube. You may end up feild testing your helmet.