I am debating between tire sizes for my 98 Kawasaki ZX6R.
I am not even sure I am calculating this correctly.
The stock size should be 120/60-17 (23.07") and 170/60-17 (25.59").
The previous owner installed a 180/55-17 (25.35") on the rear.
I am considering going to a 120/70-17 (24.09") front and a 190/55-17 (25.83") rear.
The only downside I see is a slight loss in acceleration that I could correct, or even do much better than stock with a gearng change. And about a +1/4" rise in ride height from stock when corrected, and about a +1/2 of where it is now if it had been corrected.
The tire I am going to go with is the Michelin Pilot Road 3. Optimal is a 6" rim for the rear, but compatibal with a 5.5" rim as well.
So here is the decision I need to make, and you can stop reading after this if you not interested on how I got to this point:
Changing to the 120/70 front from the 120/60 front.
And on the rear:
180/55 with a 9.5mm drop in the trees to keep geometry stock.
-OR-
190/55 with a 4.5mm drop in the trees to keep the geometry stock.
I was looking at the calculations in this manner.
-For the Rear, 1/2 the diameter of the installed tire diameter difference, between the 170/60 stock size and 190/55 size on the rear.
-For the front, calculating if I needed to lower the front. 1/2 the diameter of the front tire difference. Then taking the difference of the front and rear tires than dividing that by 2. I have read somewhere that 1mm drop at the tripple tree is a 2mm drop (or close to) for geometry calculations.
Here are my calculations: (all measurements taken from Michelin fitment chart)
Rear: 25.83"-25.50"=.33", .33/2=.155" rise in the rear of the bike.
Front: 24.09"-23.07"=1.02", 1.02/2=.51" rise in the front of the bike.
so the differnce between the the front and the rear tire axle rise is .355" or 9.017mm in the front. So for a compensation I would need to drop the forks in the tripple tree half that amount. 9.017/2=4.5mm to remain at the stock geometry.
Currently for the front to have stock geometry with just the 185/55(r) I should drop the front 3mm in the trippletrees and it currently is not.
I was going to drop the front 6mm in the tripple trees (1.5mm from stock) to get a slight increase in turn in. The Profile of the front and rear tire combination should help even further than that with turn in. I would loose a little trackion in the rear compared to the 180/55 because of the contact patch (maybe) but be able to lean the bike further over, +.25” increase in ride height, and wider tread patterns on both the front and rear tires.
This all started because I will be running the 120/70 front tire and not raising the rear of the bike with aftermarket adjustable dogbones, Or have to excessively drop the front of the bike in the tripple trees like I would have to with the 120/70, 180/55 combination. (to remain stock that would be a 9.525mm drop in the tripple tree)
So here is where we are at with my 2 options: (I will be putting the 120/70 on the front)
180/55 with a 9.5mm drop in the trees to keep geometry stock.
-OR-
190/55 with a 4.5mm drop in the trees to keep the geometry stock.
Am I completely off base here, or is there not enough difference to even care?