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Do Tires Lose Traction With Wear?

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Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Do Tires Lose Traction With Wear?

Old 09-28-18, 12:37 PM
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RFEngineer
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Do Tires Lose Traction With Wear?

I am getting less confidant on some of my descents because I feel like my tires are near the point of losing traction. Mostly, this is happening when I am having to brake hard going down a steep slope into a turn. I am running continental GP4000s and they have ~2000 miles on them. I am not getting flats at all, but I am concerned that maybe with their age, they aren't gripping like the did when new. Is this a thing? Or does traction stay constant over the life of a tire?
Thanks!
Alan
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Old 09-28-18, 12:51 PM
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Yes, tires do get less grippy as the rubber gets thinner. The rubber can also dry out and become less supple if you use them for more than 1 year. Depending on your weight and road conditions, 2000 miles may be nearing the end of life for a GP4000, especially for the rear tire. These tires do have wear indicators; what do they show?
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Old 09-28-18, 02:24 PM
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If you can see the wear indicators, then you're fine. When you can't see them, the tread thickness has worn done past what Continental recommends for safety. I usually get 2-3000 miles out of a set of GP4000. But the wear indicators do sneak up on you. I check them every 10-15 rides and they will disappear in one cycle.
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Old 09-28-18, 04:31 PM
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I think the fronts don't change because they don't change shape. Since 90% of hard braking is from the front, I don't think that's a problem. The rears wear flat in the center, so think they might not do as well in hard corners but should be fine for braking. That said, I've followed street motorcycles cornering hard at high speed. The rear tire sort of folds over, keeping the center flat in contact with the road. A bit disconcerting, but it seems to work OK. I've never bothered to watch the contact patch on the bicycle in front of me while cornering at the limit. Probably not a good idea to do so. On the whole I'd come down on the side of just watch the wear indicators. The rubber should be the same all the way down. I do notice that I start to get more flats before the indicators have gone in the back, and so don't usually wear them down 'til they're gone.
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Old 09-28-18, 04:31 PM
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Thanks! It looks like my wear indicators are still present. Does anyone think the flats (flat spots on the tire) that are created as a tire wears down affect handling?
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Old 09-28-18, 04:50 PM
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Originally Posted by Carbonfiberboy View Post
That said, I've followed street motorcycles cornering hard at high speed. The rear tire sort of folds over, keeping the center flat in contact with the road.
No, when you bank the motorcycle, your contact patch moves toward the shoulder.
The whole point of dual compound tires on sport touring bikes is to put the harder rubber in the center for long wear, and put softer rubber on the shoulders for good grip.
Look at a bikes "chicken strips" and you can see how far it has been leaned into corners.
If the tire was deforming to keep the center in contact with the road, then they could just make them squared off like auto tires, instead of rounded.

A side effect of the contact patch moving toward the shoulder in cornering, is that wider tires require more lean of the bike to keep the CG over the contact patch.

Lots of slo-mo scenes of hard-cornering bikes in here:

Last edited by Shimagnolo; 09-28-18 at 05:13 PM.
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Old 09-28-18, 05:29 PM
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Yes, they lose traction. As well as aging, wearing, there is also UV degradation as well. Sunlight is murder on rubber compounds.
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Old 09-28-18, 05:43 PM
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If the rear tire is "squared" it certainly does effect the handling of the bike. I have had several motorcycles as well and the "square" does change the handling. The bike seems to flop over. With a road bike tire, between 23-25 mm it would have some loss. If you feel it does and I do, that is when it is time for a new tire. And I just love new tires, they always feel so nice. On serious twisties, downhill, it is more about your confidence. And if a new tire make me feel more confident, I can and do go faster. Somewhere between 40 and 50mph, I want all the confidence I can get. There is something about an E-ticket ride, I climbed the darn hill, I want to get as much as I can out of the downhill.

Somewhere between brand new and well used is an great area of grip, which is different for everyone due to riding style, weight and road condition, I weigh 200+ so I probably go through tires a little faster than you. But at 2K for mileage, while not worn out, you got decent life from the tire. I will probably get slammed for that, but my rear tires, get rotated once before they square and I can get a little more out of a set. If I am lazy and don't change them, my front will go 3k and I will definitely need a new one in the rear which will be significantly squared or flat in the center. And U/V is a huge enemy of your tire as has been stated above. Cold and heat will also have some effect on the tire.

That video is awesome! Scares the heck out of me, but awesome!

Last edited by GeorgeAz; 09-28-18 at 05:50 PM.
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Old 09-28-18, 05:56 PM
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One qualifier.. I think brand new (less than ~50 miles) tires have less grip than broken-in ones.
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Old 09-28-18, 07:16 PM
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Originally Posted by Rootman View Post
Yes, they lose traction. As well as aging, wearing, there is also UV degradation as well. Sunlight is murder on rubber compounds.
50%, 5%, 0.05%, 0.000000005%? It seems the existence of the effect is a lot less important than the magnitude.
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Old 09-28-18, 07:37 PM
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Originally Posted by asgelle View Post
50%, 5%, 0.05%, 0.000000005%? It seems the existence of the effect is a lot less important than the magnitude.
Magnitude depends on a host of things. Store the bike outside? That's the worst thing. Ride dozens of hours a week in Arizona? That's a lot of UV . Ride in cloudy northern climes for just a few hours a week and store it indoors it's not much of a factor.
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Old 09-29-18, 03:14 PM
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Originally Posted by Shimagnolo View Post
No, when you bank the motorcycle, your contact patch moves toward the shoulder.
The whole point of dual compound tires on sport touring bikes is to put the harder rubber in the center for long wear, and put softer rubber on the shoulders for good grip.
Look at a bikes "chicken strips" and you can see how far it has been leaned into corners.
If the tire was deforming to keep the center in contact with the road, then they could just make them squared off like auto tires, instead of rounded.

A side effect of the contact patch moving toward the shoulder in cornering, is that wider tires require more lean of the bike to keep the CG over the contact patch.

Lots of slo-mo scenes of hard-cornering bikes in here:<snip>
OK. I've never been on one of these newfangled machines. I was referring to my experiences on my 30 DIN HP BMW riding as fast a possible in the Alps, summers of '68, '69, and '70. I was dicing with different bikes with different tires on different wheels. I see almost no tire deflection on these modern tires. I wonder what the inflation pressures might be on those racing bikes? IIRC, I ran 42 lbs. on my 4" rear. I also notice that the rims are almost the same width as the tires. Thinking about bicycles and tire roll, maybe that's why I like the feel of 23mm tires on my 23mm rims and why I really didn't like the feel of 28mm tires on 19mm rims on our tandem. They're OK with 23mm rims, though.

Another interesting thing was that the video noted the well-known fact that friction is independent of surface area. There's no term for area in the friction formula. Yet it's also well known that pro bicycle mechanics reduce tire pressures for wet races. Though, being an engineering type, I never do and I ride in the rain a lot.
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Old 09-29-18, 05:09 PM
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Originally Posted by RFEngineer View Post
Thanks! It looks like my wear indicators are still present. Does anyone think the flats (flat spots on the tire) that are created as a tire wears down affect handling?
Just ride them. They're fine. The mythical "flat spot" is meaningless.
They will deform under your weight to contact the road, regardless of what they look like when not under load.
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Old 09-29-18, 05:29 PM
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Originally Posted by Carbonfiberboy View Post
OK. I've never been on one of these newfangled machines. I was referring to my experiences on my 30 DIN HP BMW riding as fast a possible in the Alps, summers of '68, '69, and '70. I was dicing with different bikes with different tires on different wheels. I see almost no tire deflection on these modern tires. I wonder what the inflation pressures might be on those racing bikes? IIRC, I ran 42 lbs. on my 4" rear. I also notice that the rims are almost the same width as the tires. Thinking about bicycles and tire roll, maybe that's why I like the feel of 23mm tires on my 23mm rims and why I really didn't like the feel of 28mm tires on 19mm rims on our tandem. They're OK with 23mm rims, though.

Another interesting thing was that the video noted the well-known fact that friction is independent of surface area. There's no term for area in the friction formula. Yet it's also well known that pro bicycle mechanics reduce tire pressures for wet races. Though, being an engineering type, I never do and I ride in the rain a lot.
Ahhhh!
There was a huge change in motorcycle tires since then.
In 1987 Michelin introduced radial tires, and they have taken over the bike world.

But radial bike tires are very different from radial auto tires.
The tread extends almost from bead-to-bead with a nearly non-existent sidewall.
Instead of the very flexible sidewall (in auto tires), the sidewall and tread are laterally stiff as hell.
See the attached photo; That is a 50 pound weight on the sidewall, and the tire does not flex at all when I put it on there.

Specs on that tire:
Size: 160/60
Weight: 15#
Width(measured by calipers): ~6"
Tread width(measured along tire with cloth tape): ~7.5"
Sidewall width: 1.375"
Operating pressure: 36psi (on my Kawasaki Versys 650)

Last edited by Shimagnolo; 09-29-18 at 11:37 PM.
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Old 09-30-18, 12:33 AM
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To those saying they lose traction, how do you believe this is happening?
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Old 09-30-18, 12:47 AM
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Resting on cold concrete for extended periods of time will also affect the rubber. Keep it off the floor or riding on the road
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Old 09-30-18, 10:27 AM
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Originally Posted by Shimagnolo View Post
No, when you bank the motorcycle, your contact patch moves toward the shoulder.
The whole point of dual compound tires on sport touring bikes is to put the harder rubber in the center for long wear, and put softer rubber on the shoulders for good grip.
Look at a bikes "chicken strips" and you can see how far it has been leaned into corners.
If the tire was deforming to keep the center in contact with the road, then they could just make them squared off like auto tires, instead of rounded.

A side effect of the contact patch moving toward the shoulder in cornering, is that wider tires require more lean of the bike to keep the CG over the contact patch.
Yea looking at tire wear patterns is sort of the e-wang of sport bikes.
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