120/80-18 on a GS1000?

[atvpyrofreak]

So, I really need new tires and I've decided on Avon Roadriders. I'm just having some issues with what size to go with. I've searched around and found lots of info, but I'm still unsure.

I have 19" and 18" rims front and rear (stock spokes). Im planning on using a 100/90-19 up front, as thats what most seam to recommend (and thats also currently whats on my bike). The rear is a different story. Currently I have a 5.2/18 on the rear which I know is on the large side. I see recommendations for 110/90's, 120/90's, and 130/80's, but I haven't seen anyone with 120/80-18's. Does anyone see any problems with this size? It should be about the same width as the 90, but about an inch shorter, right?

My problem is that im only about 5'6"-5'7". After sliding the forks up a bit and cutting my seat down a bit, I can ALMOST flat foot this bike, and I really think with a little shorter tire I will be able to. I know my RPM's will run a tad higher, but I'm not really all that concerned about that. I just want to know if there will be any mounting or performance issues.

[Nessism]

A smig less cornering clearance, and higher rpm for any given speed. If you are okay with that, go for it!

[tkent02]

So, I really need new tires and I've decided on Avon Roadriders. I'm just having some issues with what size to go with. I've searched around and found lots of info, but I'm still unsure.

I have 19" and 18" rims front and rear (stock spokes). Im planning on using a 100/90-19 up front, as thats what most seam to recommend (and thats also currently whats on my bike). The rear is a different story. Currently I have a 5.2/18 on the rear which I know is on the large side. I see recommendations for 110/90's, 120/90's, and 130/80's, but I haven't seen anyone with 120/80-18's. Does anyone see any problems with this size? It should be about the same width as the 90, but about an inch shorter, right?

My problem is that im only about 5'6"-5'7". After sliding the forks up a bit and cutting my seat down a bit, I can ALMOST flat foot this bike, and I really think with a little shorter tire I will be able to. I know my RPM's will run a tad higher, but I'm not really all that concerned about that. I just want to know if there will be any mounting or performance issues.

Lowering the tires is a bad way to lower a bike, stay with 120/90 or 130/90, the profile is important. How wide is your rear rim?

One of my 1000s has 2/12" wheels, the older one has spoke wheels and the rear is 1/4" or so narrower, I run 130/90 and 120/90 respectively.

Road riders are great tires.

Any bike I can flat foot is too small, that's what tiptoes are for. :-)

[atvpyrofreak]

Lowering the tires is a bad way to lower a bike, stay with 120/90 or 130/90, the profile is important. How wide is your rear rim?

Its a 78 GS1000C, and I'm pretty sure its the standard 2.15 width. I measured the outside width and its just a tad over 2.5.

Thats kinda what I was wondering, if by shortening the sidewall, if it would flatten out to tread or something like that. Its not a huge deal that I can flat foot it, but i just thought it would be nice if it didn't affect performance. I think it might also help once I get my rearsets built so my legs can go strait down from the seat, instead of having to pull them back behind the pegs.

[SqDancerLynn1]

I can not flat foot my 850. It's never been a problem

[psyguy]

Thats kinda what I was wondering, if by shortening the sidewall, if it would flatten out to tread or something like that.

by installing a lower profile tyre (120/80 vs 120/90) you re likely to have the threaded surface curve more not less as the sidewall is shorter
120/80 ideally calls for bit wider rim than the 120/90

the overall difference in height between the two would be just under an inch, hence you d be lowering the rear end by 1/2 inch

[atvpyrofreak]

Thanks guys, as always, the GSR's have pulled through with its wealth of knowledge. I think I'll just stick with with the 120/90.

[8trackmind]

Thanks guys, as always, the GSR's have pulled with its wealth of knowledge. I think I'll just stick with with the 120/90.

That's what I'm running. When I got my 78 GS1000, it had 130/80 on the rear. The tire was pinched and it didn't help the handling one bit. When I installed a 120/90, it was a huge improvement.