When to replace a tire?

Question

I was repairing a flat on my rear tire today and noticed that the tire has started developing a flat area on the tread (see the photo below, it is the one on the right). The tire is a Continental Ultra Sport. Comparing the rear with the front there is an obvious band about 10-12 mm wide around the circumference of the tire where it contacts the road. The front tire still has a more tubular shape (little or no flat band).

My goal is to understand what this is telling me about the bike (significantly more load on rear tire?) and how I ride it and also to understand better when the tire needs replacement. For the latter question I'm primarily concerned with the reliability of the bike – a lot of my riding is for transportation and I'd like to minimize flats.

Answer 1

Yes, it is time to change that tire!

Your current front tire looks to be in very good shape so when you purchase a new tire you should put it on the front wheel and then move the old front tire onto the rear wheel.

Continental road tires have helpful wear indicator dots on them that will show you when the tread of the tire has reached its recommended replacement point:

There will be two of these indicators on the tire, one on each side of the tire's center line. Note, they are not always quite this close together. Many other brands will also have such some type of indicator marks on them, especially road tires and other tires with no to light thread patterns.

For other tires there are some general rules you can follow on when to replace a tire:

1. You start experiencing a sudden increase in the number of flats received in a tire and there are not good explanations for the flats.
2. The tire has worn down to the point the casing has started showing through the tire.
3. On bikes where your tires have noticeable tread pattern (mountain bike, cyclocross tires etc.) and the tread pattern has worn down.
4. You have a long, wide flat spot along the centerline of the tire, such as in your photo. At this point you may also notice your speed has dropped of slightly and that cornering may have gotten a little squirrelly.
5. The tire has cracked rubber, either due to the age of the tire or mistreatment such as improper storage or consistently riding on the tire while it was under inflated.

Some people will try to give out general milage estimates of how long a tire should last but these tend to be pretty useless as your tire's longevity depends on the type of tire, your riding style, your riding conditions etc.

It is typical for rear tires to wear more quickly then the front tire. I have always attributed this mainly to the fact all your starting force is applied to the rear wheel hence any wear due to friction while starting and accelerating is experience on the rear tire.

This answer to the question 'why does my back tyre wear so much more quickly than the front?' also postulates increased deformation of the turning rear tire results in more wear due to the sliding of the tire that occurs during the deformation process.

Answer 2

Obviously there is a lot more wear on the back tire than the front -- you're providing power through the back wheel and your weight is mostly over the back tire. If you brake a lot with the rear brake, you'll also increase your tire wear versus using the front brake (you can brake more efficiently with the front brake; this is why you see bigger brakes in the front for cars as well, even on a rear engine rear wheel drive car like a Porsche 911). Skid stops also can wear out the tire more. You can easily wear out a few back tires for each front tire.

If you drive a front wheel drive front engined car, you'll notice a similar thing -- your front tires will wear out quicker than the rears (hence why you do tire rotation). That being said, don't rotate your tires on a bicycle -- you need a better tire in the front since if something happens to the back tire, you can normally control it but recovering from anything happening in the front is much harder.

The general rule for when to replace a tire is when you start getting flats, or the tire's structure is not good anymore (cut tire, fabric showing or damaged, etc.).

Answer 3

Yes - replace the rear if you can afford to. Otherwise be aware that punctures will increase, so ride accordingly.

I suspect the wear issues are partially because the rear carries more of the load than the front, and also perhaps you're braking on the back too much. If you brake equally, the rear wheel looses "downforce" and is more likely to lock and skid a bit. Most braking comes from the front, and the rear is mostly a separate backup system.

On my heavy ebike I managed to wear through the tyre and ended up with a "blister" where the tube poked out the hole. Most of this was braking hard and small skids eating up the rubber.

Remeber that tyres are consumables, just like brake blocks or chains. You've almost consumed this one.

Answer 4

As tires accumulate more miles, they become more prone to puncture. It can be difficult to tell just how much rubber is left. Technically, you can use the tire until the cord shows. However, the rubber could split and the cord will push through. At this point, you'll be lucky to limp to your destination. To insure reliability, replace the tire.