Largest Rear Tire Size I Can Use--'87 GSXR 750 - Sportbike Forum: Sportbike Motorcycle Forums
 
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post #1 of 8 (permalink) Old 04-07-2001, 06:12 PM Thread Starter
 
Join Date: Mar 2001
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Question

My son just bought an '87 Suzuki GSXR 750 with only 1860 original miles on it. Absolutely immaculate condition.
The stock rear tire size is 140/70 VR18.
We would like to put the LARGEST, meatiest size rear tire on it possible (in both width and heighth) using the STOCK rear rim (which we've had powdercoated to match the bike).
The Suzuki dealer is saying we probably shouldn't go any larger than a 150/70/18.

Anyone have any experience with this?? Or advice??
What about a recommended brand of tire?? Looking for something that's a reasonable compromise between "stickiness" and "good mileage wear".
Thanks much for any help.

Lee
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post #2 of 8 (permalink) Old 04-09-2001, 10:43 AM
 
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If my memory serves me well, the rim size is 3.50 x 18. The correct tire is a 140 or possibly a 150. I know of many people that used 170 tires on this model. Unfortunately, you would be shoving a tire on that was made for a much wider rim. I would agree with your dealer and either use a 140 or 150. You are going to have limited selection in your tire choice because 99% of the sport bikes from the last 10 years use 17's.

I know that Metzeler Comp K tires were the choice of many several years ago.

You ABSOLUTELY CAN NOT use a radial tire on this rim EVER!!!
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post #3 of 8 (permalink) Old 04-10-2001, 01:27 PM
 
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large tire

I know a little about this subject. I've stuffed bigger tires on before. The thing to remember is that your changing the geomotry of the bike. The bike was desighned for 140mm tire so thats the way they set up the suspension and ride hieght on that bike.
It dosen't buy you any perfomance only looks.
Hope that was some help.
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post #4 of 8 (permalink) Old 05-14-2001, 09:27 AM
 
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Question Radial Tire help

I see where NitrousFJ6 mentioned that you can't put radials on the rim of the GSXR that was mentioned? Why not? The reason I ask is that I'm restoring a 86 ZX1000 Ninja and about to order radials for it (don't have many choices any more on high quality sport tires) can it take radials? I am sticking with the size the factory recommends. Even though it will mean tire envy for me with the newer bikes. Help please.
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post #5 of 8 (permalink) Old 05-15-2001, 11:08 AM
 
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You can not use radial tires because your rim is too skinny to hold the tire in its intended shape.

I believe you have a 3.5 or 4.00 rim on the back. The modern radials are designed to have 5.5 or 6 inch rims. To mount one of these tires on your rim would triangulate the tire and destroy all handling.

All tires are designed for a specific rim width. Unfortunately, I am unaware of any radials meant for a 3.5 or 4 inch rim, except for front tires.

A new CBR929 would have a 3.5 inch front and uses a 120 section tire. That is the tire you would have to use if you went to a radial. But using a front tire on the back introduces a whole new set of problems.

Bottom line: don't be silly. Check the dimensions of your rims and order tires that are made for those sizes. To order anything meant for a wider rim will hurt handling and could possibly be dangerous.
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post #6 of 8 (permalink) Old 05-15-2001, 11:58 PM
 
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Go with the 140!

I have an '86 GSXR750 Ltd., and I'm running Dunlop 591's. Those are still available in a 140/70-VB18, and that's plenty of tire for that bike!

As the others stated, your choice of tires will be limited, but I raced in the AMA National Supersport series in '88-'90, using those same 591's. While obviously not up to today's tire standards, they are still a pretty decent tire.

The hot set up for the older GSXR's is to use the rims off the '88 GSXR1100. That bike was the original first-generation body and frame style, but for that one year, they went to a 3-spoke wheel, with a 4.5" x 18 rear rim. And best of all, those rims bolted right on the other GSXR's with no modifications.

Unfortunately, those particular rims are very hard to come by, as ever since, Suzuki has used only 17" rims, and most of those 18's have been grabbed up by now.

Of course, you can always go with aftermarket rims, up to 5.5" x 17.

But for the stock 3.5-18, use the 140 tire...
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post #7 of 8 (permalink) Old 06-18-2001, 08:21 PM
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my one teammate had a 86 750le and he put 17" rims from a newer gsxr on it (i think they were 5.5 and 3.5 x 17's from a 94ish 750). i don't know if he had to change the swingarm. i remember a friend's 89 750 couldn't fit a 180 rear tire, but it was also a 17x 4.5" rim too.

Tony

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post #8 of 8 (permalink) Old 11-05-2001, 02:54 PM
 
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Radials can be used on a 4" rim

See my info below the ****

[QUOTE]Originally posted by NitrousFJ6
[B]You can not use radial tires because your rim is too skinny to hold the tire in its intended shape.

I believe you have a 3.5 or 4.00 rim on the back. The modern radials are designed to have 5.5 or 6 inch rims. To mount one of these tires on your rim would triangulate the tire and destroy all handling.

All tires are designed for a specific rim width. Unfortunately, I am unaware of any radials meant for a 3.5 or 4 inch rim, except for front tires.
***********************************************

I have been running radials for years on my FZR 400, an so havent all the other 400 racers around the country. The 400 has a 4" X 18 " rear rim. A 150 fits up nicely. Metzeler/Pirelli and Bridgestone currently make radials that fit the 4" X 18" rear rim on these and other bikes. I have even seen some FZR 600 at the reack with their 3.5"X18" rims with radials mounted.

Best thing to do is check with the manufacturer, try their web site, and I bet you will find all the major manufacturers have radial tires that will fit. (they might not be the latest design, but they will stick better than any bias ply tire that was designed in 1985)

Steve

Last edited by GRRR; 11-05-2001 at 02:56 PM.
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