So tonight, the 23mm tyre commits suicide...

[BiggJawn]

I was going to take my steel Raleigh out for a fast one tonight, so I pump up the tyres to 100, and while i'm getting changed, the rear one blew off the rim!

I think that bike's screaming for a set of Roly-Polys...

[Longhorn]

1. What are Kevlar tires?

Is that a brand name or something special about what they're made of? I keep reading on the bikeforums.net board about different tire names and wonder about the pros and cons. Thanks!

I'm glad the tire didn't blow in your face! :hi:

[BiggJawn]

2. It's a belt.

There's a Kevlar belt in the tread, and in the case of a folding tyre, the bead is made of Kevlar cord instead of wire. The bead is Kevlar so you can fold up a spare and take it with you, and the belt is for puncture protection.

I have owned a set of Kevlar tyres, and I didn't like 'em because they repeatedly blew off the rim and the rear finally had a sidewall failure. But YMMV...

The one that blew last night had a patched tube in it and it failed at the patch.

[happyslug]

4. A tire is more than Rubber

Basically it is a Steel Frame (called "Belts") which the Rubber (and other compounds) are formed around. The belt gives the tire its shape and form while the Rubber gives a tire its grip, and ability to hold air (Together with the Inner tube in non-tubeless tires, by itself in tubeless tires). Note this is how Automobile tires are also made.

Now the steel can be replaced with other rigid (but flexible) material. Over the last 20 years more and more bicycle tires have gone to Kevlar as the belt (Replacing the Steel belt with a Kevlar Belt). At first this was to make the tire lighter and stronger (Kevlar is stronger than steel, thus you can use less Kevlar and thus make a lighter but stronger tire). Than it was discovered that you can make a Kevlar Tire that folds. Thus a lot of long trippers started to take extra tires with them because they could fold these fold-able tires into their Panniers (Can't do that with a Steel belted tire).

While having a spare tire (as opposed to a spare inner tube) is nice, but the number of time I have had a tire failures in over 20 years of biking is 1, and that was because I forgot to check out the tire on my bike trailer before I went on a 30 mile bike ride, had I looked I would have seen that the tire had worn down to the inner tube, why I left the tire on to that point was just stupid of me, but the only time I have EVER had a problem with a bike TIRE (as opposed to the inner tube).

Now The off-road Bike riders have a lot more tire failures than people who ride on paved roads. Furthermore off road bicycle racing rules say you MUST make any and all repairs to your bike with what you have on you or the bike, this encouraged carrying extra tire in case one blew out (On off road racing states a racer may borrow tools but NOT parts, unlike road bicycle races where you can exchange wheels and even the bicycle if something goes wrong).

My experience with tires is that unless you are going off road, stay with the "slicks" i.e. tires with no thread or knobs. The reason for this slicks provide the maximum surface area to the road and thus the best "grip" on the road. The various treads and knobs seen on bike tires are pattern after similar treads on cars. The problem is car treads are design to minimize the effect of hydroplaning (i.e. what happens when do to rain on the road the car tire is operating on water NOT road surface). Bike tires are so narrow and the speed you are going (even down hill) is so low that you rarely hydroplane on a bicycle.

Hydroplaning is affected by four factors, first is tire area (i.e. the area of the tire in contact with the road.) The wider the tire the more likely that water will be "caught" by the tire and NOT pushed out to the side as the tire goes through water.

The second factor is tire shape. Bicycle tires are "rounded" i.e. have a curve to them as oppose to the flat surfaces of automotive tires. Bicycles tires round shape makes it easier for water to be pushed away from the tire-road surface point.

Third is speed, the faster you are going the more likely that water will be "captured" by the tire. Hydroplaning even in most cars does not start till around 25 mph, most cyclist rarely get that fast except going down hill.

Fourth is tire pressure, the higher the pressure the easier it is for the tire to push the water from its path (With tire pressures over 100 pounds per square inch needing to go over 100 mph for the tire to hydroplane).

As you can see Bicycle tries, unlike Automotive tires, rarely hydroplane. Automotive engineers on the other hand have to plan for hydroplaning given the lower pressure, wider surface area, flatter surface area and general greater speed Automotive tires operate with. Threads on automotive tires are thus designed to minimize hydroplaning by thread design, something NOT NEEDED on Bicycle tires.

Thus why the Threads on Bicycle tire? People are use to seeing tires with threads given their experience with automotive tires, so they expect threads and tire makers give the people want they want.

Now the knobs and threads on off road bikes ARE EFFECTIVE OFF ROAD. But useless on paved roads (During winter I sometimes use knob-ed tires with steel studs for extra traction, I have lost traction on ice and fell one to many times, but as soon as the ice is gone my slicks go back on those wheels, the roll Resistance of the studded tires is immense).

Now the knobs on off road tires word on dirt, for their dig into the dirt, but asphalt and concrete are to hard for they to penetrate so they give you NO traction on paved roads even in the wettest of conditions.

Thus the best tire for general road use is a slick (i.e. a tire with NO knobs or threads). For dirt roads slicks are good enough (Through on paths, cross country tires with knobs are good, and on ice studded tires).

[Kolesar]

3. I have these Vittoria tires with Kevlar "in the tread compound"

It is not layed up like a nylon or aramid belt (or steel for autos), it is part of the rubber. These 700x25 tires have lasted 2500 miles, and they finally are looking like they need replacement. They don't make that model any more.

I have friend who bought the roly-polys and lamented that they start with a round cross section, but turn into a tire with a flat center, so they are squirrelier than any tire he has had. He put it succinctly: "they're junk".