Bicycle Mechanics - Tire Blow Outs!!! (Question about Tire Size & Rim Size)

Hope someone can help,
After replacing tires and the tubes on an old 10 speed with 27" wheels. I had two blow outs in three days. I am convinced that when I put air in the tires the tubes are actually lifting the tires off the rim slowly and when it lifts enough the tube comes out and BANG!!!.

One went BANG while I was eating dinner last night.

The guy at the LBS when selling me the tires showed me two tires one was smaller and lighter and the other was larger and much cheaper. I went with lighter and smaller. I asked him how much air should I put in them. He said just put in what it says on the tire.

Tire: Cyclepro Discovery 27" x 1 1/8. 105 lb.

Tube: Cyclepro on the tube box:
700X28-35C
27x1/8 - 1 1/4

Rim: ARAYA 27 X 1 1/4 W/O HP. Japan

Last night I put just 85 lb's in and this morning I can see a white line starting to show just below the gumwall. With time this white line gets bigger. I am convinced that the tube is actually lifting the tire off the rim even at 85lb's

I asked the guy if it was OK to use tires that say 27"x 1 1/8 when the rim says 27"x 1 1/4 and he said it was fine.

I have attached a picture of the blow out. Both tubes went the same way.


Any thoughts about this?

Thanks for your help,
J B

Most likely it is a problem with the tire's manufacturing tolerances, but there are a couple things to look at before trying a different brand of tire from a different shop.

Before mounting the tire make sure the rim tape or strip is centered in the rim and not riding up the side of the rim. If it is off center it could be keeping the tire bead from fully seating.

When you put the tube under the tire, put in just enough air for the tube to take shape. This will help keep a fold in the tube from lodging under the edge of the bead and keeping the bead from seating.

When you pump up the tire, start out with about 30 psi., maybe even a bit less. Take the wheel and go around both sides of the tire rolling the tire away from you a bit and checking the bead to make sure it is sitting evenly in the groove on the rim and making sure that there is nothing like the rim strip or the tube keeping the tire from sitting in the groove. Also if the bead is sitting too low in the rim on one side it will be sitting too high on the other side and can blow out.

Having said all this, my guess is that the tire is just poorly manufactured and is slightly too large in diameter to sit properly in the rim groove. There are still good quality 27" tire to be had but most LBSs don't stock more than one or two choices.

Almost certainly your problem is that you are using high pressure tires on an old smooth bead rim. You need a new style rim with a ridge on the inside of the sidewalls to prevent the tire bead from slipping off. Either that, or reduce your pressure until you stop blowing tubes.

When your bike was built, the tires were not designed for high pressures and so it wasn't a problem.

+1

http://www.sheldonbrown.com/harris/tires/630.html


Generally, the "rule of thumb" for traditional 630 mm (27 inch) tires is that they should be inflated to 70-75 psi. This shouldn't be a problem with any tire, despite whatever disclaimer the manufacturer puts on the sidewall. However, if you're restricted to this pressure range, you probably shouldn't be running tires narrower than 1 1/8, or preferably 1 1/4, unless you're a very lightweight rider.

Almost certainly your problem is that you are using high pressure tires on an old smooth bead rim. You need a new style rim with a ridge on the inside of the sidewalls to prevent the tire bead from slipping off. Either that, or reduce your pressure until you stop blowing tubes.

When your bike was built, the tires were not designed for high pressures and so it wasn't a problem.


Yes you are correct! These rims are smooth bead rims. They are in perfect condition and I would like to keep them on this bike. Do you think if I lower the pressure around 75lbs the bike will provide the same kind of ride it was capable of when it was new? I don't mind lowering the tire pressure if I don't have to give up original performance. Or would you recommend get the same kind of tires the bike came with (if possible). The original tires are so bad the only thing I can read on it is "High Racer"

Thanks for all the responses,
J B

Wanted to update all of you. Having a hard time reading my old tires but it looks like the recommended tire pressure was 90lbs. I think 90lbs could be to much to ask for the new tires on these rims.

Any other thoughts,
J B

I believe if you go to the page I linked to on Sheldon's site, he says you are likely to be OK with new tires as long as you don't inflate to over 70-75 pounds. Even though the tires say they must be used with hooked rims, this is likely the case because of the higher pressure rating.

I think because of the lower pressure I would go with 27 x 1 1/4 at 70 psi... instead of anything narrower. This should be big enough and high enough pressure to avoid pinch flats. and should ride as well as the bike did originally.

Good luck!

Little Darwin,
Yes I did check out that page and I do agree with you. I would have liked 27 x 1 1/4 but LBS dude says 27 x 1 1/8 would be fine. I do disagree with him. Had these tires for about a week. For some reason I don't think he would be happy with me returning them. Although, I did bring rim /w old tire in for him to look at. At his request.

Are there any vintage tires available for these old bikes these days? Can anyone recommend a good one?

Thanks again,
J B

The width of the tire is probably not the issue. However, you might check harriscyclery.com for narrower 27" tires.

Even though the rims may be in great condition, if they are steel and you plan to ride the bike much, you would be well advised to replace the rims with aluminum. You will get much better braking performance in wet conditions. If you don't wish to have the wheels rebuilt, you might check Harris Cyclery for a set of new 27 inch wheels with freewheel rear hub.

Supcom,
They are aluminum and they are in like new condition. Replacing them at this point is not an option.

Thanks for your response,
J B