max width tire on a 19in stock wheel?
 

Just wondering if a 305/30-19 is too wide for my stock 19 in. 2010 XKR rear wheels? I've read somewhere that they are only 9.5 in wide vs the optional 20 in wheels are 10 in. Thinking the 305 might give a little better traction than the stock 275s.

OK, I'll answer my own question with a response from Tire Rack in case there is any interest.


"Tire size 305/30 19 has a rim width range of 10.5" to 11.5", they will not fit on 9.5" wide wheels.


The widest rear size you will be able to use with the factory wheels is 285/35 19."


A little disappointing as I was hoping to get some more rubber to the road, without purchasing new wheels.

Max tire size on stock wheels
 

Here's the rear stock 19" wheel of my 2011 XKR with a Michelin Pilot Super Sport 295-35 ZR19 I had America's tire install. Fits fine, salesman said I could have gone to the 305 with no problem.

logoguy thanks for the real-world example. I might go for a taller, wider tire with the same stock aspect ratio (35) but my question to tire rack was about fitment of a wider aspect tire (30 series), and I imagine that they are accurate in their assessment that a 30 series is too wide for the stock 19 in 9.5in wide wheel. I don't have the tire dimensions calculator handy, but I'm wondering if 305 is getting a little tall and if it would mess up the ABS or speedometer etc. with 305s in the rear it might be necessary to go higher on the fronts to better match the ratio of diameters of the staggered setup.

Using a tyre-size calculator (Visual Tyre Size Calculator | Kouki Tech), and based on 275/35/19 as standard:

285/35/19: actual speed would be 1% higher than indicated
295/35/19: 2.1% higher
305/35/19: 3.1% higher

295/30/19: 2.3% lower
305/30/19: 1.4% lower

Ngarara,
thanks for the metrics. I've used that calculator and somewhere around 325/30/19 or so the "actual speed" aka tire circumference would equal the stock 275/35/19. Unfortunately, one would need at least a 10.5 in wheel to mount this size on, so says the experts at tire rack.

And you're likely to have issues with clearance within the wheel arch with a 325, I suspect.

logoguy, did you keep the fronts stock? I'm just wondering when the difference in stock to aftermarket size ratio would cause problems. Seems to be a 2.1% circumference difference in the 295s that you used. If you had chosen 305s and left the fronts stock, you'd be up to a 3.1% difference from stock and thus difference from the factory "staggered ratio". One solution would be to up the front size when doing the rears, but I'm less interested in wider tires in the front, and troubleshooting fitment there too.