Likes to race old junk.
Join Date: Aug 2009
Location: Innisfail, Alberta and Baffin Island, Nunavut Territory, Canada
Motorcycle: Singles, Twins, a Triple, Four's, a Six and an Eight!
Re: Swing arm upgrade on my 87' GSXR 750
Anything is possible, but is this realistic?
A 180 or wider rear tire will require a minimum 6" rim.
Measure your existing set up and see if this is really feasible...your rear sprocket still needs to be in line with the counter sprocket, regardless of the swing arm or late model rim.
A drag bike would get around this with an offset counter sprocket and an outboard bearing to support it.
You can squeeze a marginally wider tire than a 140 on your existing rim, but it will change the tire's profile and upset the handling.
Back in the day, racers would have had their rims widened by companies like Kosman.
Your '87 has 18" rims and tire choices are limited today.
Several members here have updated their Slabby's to 2nd gen 17" wheels, which would let you run a wider tire and a greater selection of rubber, but nothing near current liter bike sizes. I think that's likely your best bet.
Anything more, just sounds like penis envy...