Alternate tire sizes

[F14CRAZY]

From what I know, my K75C is wearing factory sized rubber, at 100/90-18 on the front and 120/90-18 on the rear.

To expand the selection of replacement tires, how much can the sizes change?

[K75RT Keith]

Rim width limits your choices but, on the front a 110 should fit without mods or rubbing on the fender.  Rear, 130 or 140 clear with no trouble and fit the 2.75 (Y spoke) or 3.00" ( 3 spoke) rear rim.  If you find a K1100RS 4.5" rear rim, you ought to be able to fit a 150 on the back just watch the clearance on the centerstand.   

Check a tire size chart for diameter,and look for a tire size close to stock. Smaller diameter means more RPM's and a bigger variance in the accuracy of the speedometer.   Larger, (if it will fit in the allotted space) lower RPM"s.

[TimTyler]

When tires get hot from riding fast do the width and height clearances diminish?

[K75RT Keith]

Some.  But you'd be down to needing a feeler gauge to determine clearance, If that's the case, it might be to large to start with.

I've run 110's and 140's on my RT and even on short rides of 750 miles at 80 mph average speed not had a clearance problem.

[Gio]

Good info Keith ... I was curious to do the math on the stock 130/90 vs alternate 140/80 for the rear of the K75s 3 spoke and see how many mm difference it made ... so if my math is correct the stock 130/90 is 117 mm diam vs 112mm for the 140/80 or 5mm less - I guess this would increase the rpms for a given road-speed (but my math is not good enough to calculate by how much?)

Reason I was curious is that I would say the last thing the K needed was more rpms ... in fact a sixth gear would be nice for those longer stretches at higher speed.