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Discussion Starter #1 (Edited)
I currently have a 94 Suzuki GS500E. The rear tire is a 130/70/17. I would like to go wider...is that possible? Maybe to a 150/60/17? Dont know if it will clear it, due to the fact of the chain cover and the arm that attaches to the rear caliper. Let me know. Thanks. Reason why I would like to go wider, when I am in a corner at a step lean angle the back end feels as though it is gonna come out from under me. Need more contact area at these type of lean.
 

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you probably could, but the question is why do you want to? I know it looks cool, but more often than not, changing to a wider rear tire on a sportbike (or any bike really) changes the handling in a bad way.
 

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Unless you also go with a wider front tire, you will adversely effect your handling, by going wider out back.
 

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BrianGS500E said:
I currently have a 94 Suzuki GS500E. The rear tire is a 130/70/17. I would like to go wider...is that possible? Maybe to a 150/60/17? Dont know if it will clear it, due to the fact of the chain cover and the arm that attaches to the rear caliper. Let me know. Thanks. Reason why I would like to go wider, when I am in a corner at a step lean angle the back end feels as though it is gonna come out from under me. Need more contact area at these type of lean.
I wouldn't. But when looking at tires it will also usually tell you the smallest rim you should put it on. Now what happens when you don't. I know a friend that did this. He put a 200 on the back of his Gixxer 750. Handling he swears didn't change much; however, within one year he sold his bike and is now not riding.

I'm told that if you do that...it looks kewl..but only for about and hour then the tire looks skinny again to you.
 

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Discussion Starter #5
Just thought I would update you guys, just put a 170-60-17 on the rear and a 120-70-17 on the front, I personally can tell a huge difference. Thanks though for everyones input.
 

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A huge difference in what? I'd have guessed that such a wide tire on such a skinny rim would've given you less contact patch. I'd really like to see some pics. That's pretty extreme.
 

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And shape dictates size. I'd have thought that obvious. They're quite interrelated. Ask a racer.
 

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nope. contact patch SIZE depends on weight of bike on the tire and air pressure in the tire. NOTHING to do with tire SIZE.

if you have a big diameter tire, the patch is long and skinny, but if you have a small diameter tire, the patch is wide and short. same area, though.

i used to race cars, so i'll just ask myself. :p
 

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Motorcycle tires, being round, and their cross-section being determined by both pressure and rim size, have little in common with car tires. You can bet your lug nuts that the changing shape of a tire has a tremendous effect on handling, and the contact patch is a part of that.
 

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Does Size Matter

Squeezing a wide tire onto a narrow rim can be a big mistake. Here's why.

By Andrew Trevitt

Those low-profile 190-series tires sure look gnarly on the back of a sportbike, and we've seen them pinched onto all sizes of rims. But in reality, a 190/50-17 fits properly only on a 6.0-inch rim, and cramming it onto anything smaller severely changes its profile.

As an experiment, we mounted a 190-series Metzeler Rennsport onto our F4i's 5.5-inch rear wheel and took some measurements. Compared to the correctly sized tire on the same rim, the 190's profile closely matches the 180's near the edges of the tread, but is much lower in the center area-equivalent to about a 6mm change in ride height. Effectively, the wider tire will give more rake and trail when the bike is vertical, while keeping close to the original geometry when the bike is leaned over. Accounting for one (by changing ride height) will unduly affect the other.

Following our test with the Metzeler Sportecs, we slipped a 190/50 rear Sportec onto the F4i and rode a portion of the test loop for a practical comparison. With no changes to suspension or geometry, the F4i felt substantially different with the wider tire. With the bike straight up and down, steering was slightly sluggish in comparison, but just off vertical, the F4i was quite tippy and darted into corners. The light, neutral steering of the Sportecs was completely changed and the bike lost its balanced feel. The sensation was very much like riding on a tire squared off from too many freeway miles. At higher lean angles, performance was less affected, although making transitions from side to side was unpredictable. And, contrary to the popular myth that the wider tire puts down a bigger footprint and gives more traction, we felt no improvement in that department from the properly sized tire.

We've experienced similar changes with a 180-series tire on a 5.0-inch rim meant for a 170-series bun. Tire engineers work hard to design and match front and rear profiles for characteristics that we sometimes take for granted. Upsetting that balance is surprisingly easy and you should think twice before sacrificing your tire's performance for appearance's sake.

This story was originally published as part of the tire test in the June 2002 issue of Sport Rider.


And that's only a 10mm increase. He went 40! That tire has to be comically misshapen.
 

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sure, handling would be different, but your statement that the different tires would have a SMALLER CONTACT PATCH is simply flat-out incorrect, no way around it.

example - bike weighs 500 pounds, and distribution is 50/50. so that's 250lbs front and 250lbs rear. tire pressure for example is 36psi front and 42psi rear, so:

250lbs front supported by 36psi = 6.94 square inches contact patch
250lbs rear supported by 42psi = 5.95 square inches contact patch

nowhere in there does the WIDTH of the tire make any difference to the SIZE (area) of the contact patch. nothing at all. doesn't matter if this is a car tire, motorbike, bicycle, or farm tractor.

the SHAPE does change, but it's still the same SIZE, no smaller or bigger.
 

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RowdyRed94 said:
Does Size Matter

Squeezing a wide tire onto a narrow rim can be a big mistake. Here's why.

By Andrew Trevitt

And, contrary to the popular myth that the wider tire puts down a bigger footprint and gives more traction, we felt no improvement in that department from the properly sized tire.


And that's only a 10mm increase. He went 40! That tire has to be comically misshapen.

again, SHAPE is not the same as SIZE. regardless of what tire, the contact patch is THE SAME SIZE.

in fact, your quote CONFIRMS that! :bluethum:
 

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Sorry, but you're oversimplifying this to an absurd degree. You cannot divide weight by pressure and get some area of rubber contact. You're completely ignoring the change in shape of the tire. I don't have the energy to try and make that more clear.
 

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RowdyRed94 said:
Sorry, but you're oversimplifying this to an absurd degree. You cannot divide weight by pressure and get some area of rubber contact. You're completely ignoring the change in shape of the tire. I don't have the energy to try and make that more clear.

WTF? go read a book. pressure is PSI - pounds of weight per square inch. it matters SQUAT what the tire is made of, how wide it is, how blah blah blah.

you CAN and you DO divide weight by pressure to get area. that's how you calculate pressure in the first place! i have a 100 pound weight that is supported by a 1" diameter rod. the pressure at the tip of that rod is 100 pounds DIVIDED BY area of rod (0.78sq.in), giving a pressure of 128psi.

pressure = weight / area

that's pretty fundamental math
 

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narrow != smaller


you keep mixing up size with shape. they are different.


edit - that's nice. i'm a graduate of engineering and have done racing for a few years (autocross / track days). what's your point? there are various reasons for going to a wider or narrower tire, like car guys go, but that doesn't start changing the contact patch and all of a sudden making it twice as big as with OEM tires.
 
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