I've been contemplating a tall sidewall 130 on a GSXR front end for a chopper project I've got going on. It might be a bit before I get it mounted up and checked, but I am pretty sure a 140 is far too wide unless you run a taller sidewall tire. My brothers CBR250R had a low profile IRC brand 140 out back and it was pretty wide.
140/80-17 is the size I would look for on the used to test fit the thing, but, buying one brand new could result in a useless (and expensive) tire laying around.
A 140 will be distorted on the stock slingy rim which means it will wear quickly & not seat correctly irrespective of wether you can get it in there or not
If you want a bigger tyre you need a wider rim its as simple as that really, i have no problems sticking wider wheels in the front even though it does affect handling & have done it a few times but mounting a bigger tyre than the rim is meant for can be dangerous
I think the 140 would fit, but it would change the tire profile. To get the same profile, you would need a smaller profile ratio (140/60/17), but less sidewall means less ability to make up for the larger tire. Stocks are 120/70/17
The only tire I found in 140/60/17 is the Shinko 006 Podium Rear Tire for $110
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