stupid tire question

[blaine]

I am running 100-90.I tried it at 25psi bike wanted to follow cracks in the road.Increased psi to 30 lbs bike feels alot more stable.I have 17000kms on same tire.Still not down to wear bars.I also run 30psi in the rear.These are CHALLENGER tires.I get good mileage from these tires.

[dhgeyer]

diffluere,

I think you are on the right, common sense track. Here's what I know on this subject, some of which has already been stated. The pressure in the owner's manual is almost always lower than the max pressure on the side of the tire. There was one bike I owned where they were the same, but that was a very heavy bike. The GZ is a very light bike.

As a general rule, ideal handling will be achieved with the pressures listed in the owner's manual. Maximum tread life will be achieved at a pressure somewhat above that, but handling will be affected. A somewhat increased pressure will delay, in particular, "cupping" on the front tire. This is a kind of scalloped pattern that develops on the area between the center and the sides of the tire, and is noisy in turns, and makes the bike not feel "right".

Increasing the pressure will give a bit harder ride, and will tend to make the bike's steering more negative (it will have more of a tendency to want to go straight and pull out of turns requiring a little more countersteering effort). Increased pressure also decreases the contact patch between the tire and the road a little bit, thus decreasing traction slightly. None of these effects are dramatic, and most knowledgeable riders keep their tire pressures somewhat above what is listed in the owner's manual so that they don't have to buy tires as often. Generally, the higher pressure you run them at, the longer they'll last, within the safety limits.

Two cardinal rules are: 1) never go below the pressure listed in the owner's manual, and 2) never go above the max pressure listed on the tire.

Always measure tire pressures cold, before riding. Bear in mind that, as ambient temperatures rise, so does tire pressure - roughly 1 psi per 10 degrees F.

There are dealerships and service centers that inflate motorcycle tires to 40 psi front and rear no matter what the manual says. Other go by the book, others go somewhere in between, so you're not going to get agreement on this even among the "experts".

Knowing the parameters, you make your own choice.

By the way, putting a different size tire on the bike will definitely affect handling, so please go easy until you learn to what degree this has occurred in your case. It may be barely noticeable, or quite pronounced. When I went with a larger diameter tire on my BMW R850R, it required a lot more steering effort. I was quite surprised at the difference.

And it's not a stupid question.

[diffluere]

I've actually had the 120/80 tire since August, I just never thought about the pressure being different until now! I've just been riding around, keeping it at 25psi. I didn't really notice a difference when I got it, but the old tires were OLD (like..original 2002 tires) so they probably didn't feel the best anyway. Plus, I was a brand new rider so I wasn't really used to my bike yet anyway. It feels just fine now, and other people that have ridden my bike haven't mentioned anything weird.

Thanks for the help guys!