Tire question

[Kyle M.]

78 GS750, stock rims. What is the widest rear tire I can run? Stock is a 120/90 18 right? I want a lower profile tire and wide, like a sport bike tire.

[Kyle M.]

would a 130/80/18 be good?

[bwringer]

Unlike more primitive four-wheeled forms of transport, wider is NOT better with motorcycle tires.

On a motorcycle, the curvature of the tread makes a big difference in handling. Stuff a wider tire on there, and it goofs up the tire profile and makes your bike handle like a turd.

4.00-18 translates to 110/90-18 in more modern tire sizes, although 120/90-18 might be OK too.

There are some who have invested great sums of money and time grafting later model sportybike swingarms, forks, and wheels onto their elderly bikes in search of that phat tire look.

Basically, if you want to go wider, your options are to either buy a sportbike or find a buddy with a machine shop and graft on sportbike suspension and wheels.

Or, and I know this is CRAZY talk, how about this... mount up the correct size tires and ride the snot out of your timeless classic motorcycle. You can get very modern, very sticky rubber (Avon AM26 RoadRider or Pirelli Sport Demon) in the correct sizes.

Stir in a bit of suspension work, learn to ride, and believe me, these old Suzukis will handle. Pay attention to your riding skills and you'll have no trouble staying ahead of or keeping up with the squids in the twisties.

[Steve]

The 130 will probably fit.
The 80 profile will keep it about the same diameter as the 120.
Do you care at all how the bike handles, or do you just want "the look"?
A wider tire on a narrow rim will not have the stability that it really needs for proper handling.
If you really have to have that really wide tire, you are going to have to do something to get a wider wheel in there, too.

.

[earlfor]

I ran a 130 rear on my 79 750E for the 40k miles I had the bike and had no problems with it. Use a sticky tire though, not a touring type. Anything bigger will not fit between the swingarm anyhow.

Earl

[80GS1000]

....or find a buddy with a machine shop and graft on sportbike suspension and wheels.

I have no idea what you're talking about.

Seriously though, performance bias Pirelli Sport Demons or Avon Roadriders in a max 130 rear can make your GS handle quite well.

Michelin Pilot Power, Bridgestone BT002 RS or Pirelli Diablo Corsa 3 radials with the right suspension components and steering geometry can make your GS handle even better, but that's a whole different story.

[bwringer]

I ran a 130 rear on my 79 750E for the 40k miles I had the bike and had no problems with it. Use a sticky tire though, not a touring type. Anything bigger will not fit between the swingarm anyhow.

Earl

There you have it folks.

Earl, was that a 130/90-18 or a 130/80-18?

[Kyle M.]

I guess I will just get the 120/90/18 for the rear and a 100/90/19 for the front...sound good?

[Steve]

Sounds good to me.

There have been MAJOR advances in tire compounds since these bikes were made, and the current batch of tires might even be better than the racing rubber that was available at that time. Get the right size tires, then "ride the snot" out of them as suggested.

.

[psyguy]

comparing 120/90 and 130/80, the 130 tyre will not be any wider than 120!
if you want the widest look possible you want a 130/90 tyre

[Nessism]

What size rear rim is on the 750? The 850/1000/1100 bikes have a 2.5" rear wheel which accepts a 130 quite nicely - in fact, it's the GSR defacto standard tires size for those bikes. 120 is fine but I'd go 130 if the rim is wide enough.

[snark]

And I'll post it again...

http://www.steelthundercc.com/tiresizes.html

Here is a tire conversion chart that will give you the measurements for each tire.
I went from a 120/90-16 to a 130/90-16. There is very little difference in the handling with that small of a change...but these guys are right. The wider the tire, the slower the handling. Start with a quality tire and a small size increase.

Measure the clearance from every angle. Not only do you have to worry about the swingarm rubbing, you've got the chain also.

[Joe Nardy]

comparing 120/90 and 130/80, the 130 tyre will not be any wider than 120!
if you want the widest look possible you want a 130/90 tyre

Actually, a 130 tire of any aspect ratio (the 90/80/70 part of the size) should be the same width, 130mm. The 90 aspect ratio tire will have taller sidewalls, roughly 90% of the width. The 80 aspect ratio will be roughly 80% as tall as it is wide, and so on. In actuality, the lower aspect ratio tires tend to be wider than the same width tire with a higher aspect ratio but that's what the numbers were meant to designate.

Thanks,
Joe

[snark]

120/90 is 4.50 to 4.75 inches wide.

130/90 is 5.00 to 5.10 inches wide.

[Joe Nardy]

120/90 is 4.50 to 4.75 inches wide.

.....or 120 mm.................

130/90 is 5.00 to 5.10 inches wide.

.......or 130 mm..............