Tires - slippery when wet...questions

[Guest]

I bought my GS a year and a half or so ago and the tires that are on it are in good shape, not cracked or anything. I do a decent amount of riding in all weather including the rain, and I didn't notice this until riding a friend's bike in the rain - my bike in the rain is like riding on ice, particularly at the rear. Any kind of excessive throttle in any gear will spin the tire. If I ride through a puddle and half the tire is wet and I ride around a corner, the bike will repeatedly slide-grip-slide-grip as the wet and dry parts alternate contact with the road. I'm assuming that although the tires look and feel fine, they are old and that somehow has a major effect on wet-weather grip. Am I right? Every old tire I've come across has been dry rotted as well, and in the 5-7k miles I've put on these, they aren't cracked. Dry weather performance is good enough to drag pegs and has never left me wanting. Is this common at all? The rear tire is getting close to done anyway so I may as well replace it, but if being oldish makes that much difference in the rain, I'll go ahead and do the front too.

[Steve]

Yes, old tires will do that to you.

What are the date codes?

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[gearheadE30]

I'll have to check tomorrow. I decided it wasn't really safe to ride until I get new tires so I'm riding the dirtbike. Guess I got so used to sliding a dirtbike around that I didn't realize the GS wasn't supposed to do that too. I have a hunch it's going to be hilariously old, since the only numbers I can remember when I looked at the sidewall ended in 88...but that can't be right...no way. There's gotta be another number somewhere that I just missed. Guess you can't just trust what they look/feel like to tell the age like you typically can a car tire.

[Steve]

Find the "DOT" number on the sidewall. There will be several letters and numbers, the last group will be in a separate box, and there will be three or four digits. Those three or four digits are the date code. Let us know what the numbers are, we can tell you how old the tire is.

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[gearheadE30]

So I figured out the date codes...both tires were made before 1990. I have 2 new Avon Roadriders on the way that should be a night and day difference. I can't believe I put 3k miles on these tires...

[bonanzadave]

So I figured out the date codes...both tires were made before 1990. I have 2 new Avon Roadriders on the way that should be a night and day difference. I can't believe I put 3k miles on these tires...

You'll love those Avons (if they don't crack ). I was sliding all over on a set of old Dunlop Elite 491's. Night and day difference with the Road Riders.

[gearheadE30]

Yeah, I read about the whole cracking thing... that seems to be a really common issue with a lot of different motorcycle tires right now. I have a Shinko 244 and a 705 on my dirtbike and the moment, and both of those are known to do it, too. Seems to go hand in hand with softer compound tires.

My theory is that a lot of people run these older bikes at the tire pressure that the manual states, which is not really correct anymore. Modern tires are designed to run with more pressure. Lowering the pressure increases deflection in the tire and causes significant internal heat buildup. An inherent property of rubber is that flexture and deformation create an internal temperature that lowers the fatigue life, resulting in crack propogation. Running higher (30+ ish, depending on load and conditions) pressures seems to alleviate the problem, at least somewhat.

At any rate, these old tires have made me feel skittish for a while, but I attributed it to possible wear in other parts of the bike and just rode more sedately. I'm really excited to feel the difference, especially considering that this is the first road bike that I've actually put 'good' tires on.

[Steve]

The old rule of thumb for tire inflation still applies:

"There should be a 10% increase in pressure from cold to hot."

Adjust your tire pressure when cold to an easy number, like 30 psi. Go for a ride. Make it at least 50 miles or so to get the tires nice and warm. Check the pressure, it should be 33 psi. If it is more, the tires flexed too much, warmed the air and increased the pressure. If it is less, the tires did not flex enough to warm the air, so they are over-inflated. Adjust the pressure by the difference to that +10% number. In other words, if your hot pressure was 35 psi, you need to add 2 psi, making your cold pressure 32 psi. Of course, you need to do another ride to warm the tires again, but that's OK. If you regularly carry a passenger, you need to repeat the process with the passenger to determine your 2-up pressures, too.

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[gearheadE30]

coming from the car world, I've never heard that. I always have tuned pressures for handling and rollover/deflection. I'll try that out when I get the new tires on and see where it puts me.

[eil]

Cars are so heavy that they can give you one number that's good all of the time because passenger/cargo weight doesn't make much difference. On a motorcycle, rider/passenger/cargo add a lot of weight relative to the rest of the machine.

[gearheadE30]

Yeah, that's a good point. Tires showed up today! I have exams I should be studying for, but it's going to be so hard to not go swap the tires...

[1980GS1000E]

You won't believe the difference.

[gearheadE30]

Got the new tires on and painted the rims. Holy cow did that make a hell of a difference. I'm still trying to get over my nervousness that resulted from riding on the old crappy tires for so long, but it is sooo much nicer to ride now. Not to mention it feels a lot safer, wet or dry, and doesn't fight my inputs.

Pics:

[greg78gs750]

nice looking bike. i'd like to see a pic of the caprice in your sig, my first car was an olds wagon....enjoy the new shoes!

greg

[Crankthat]

Having new tires will make a huge difference in grip/traction wet conditions.
Having the Roadriders should make for a great improvement period.
I am due for a new set and am liking the profile on those.
Hmm, will have to do some investigating!

I have often wondered if the cracking we hear about in the newer tires is due to people who stunt?
People who stunt their bikes go really low in tire pressure.