Took a Novice on m first runs so they could see the course in "Real Time" … you can see the 235/45/17's fill the wheel well and that I have had to raise the Mini up on the spring perches for clearance purposes.
I am ready to go back to the fast 225/45/17s and lower the Mini which will be about 1" lower with tire change and spring perch adjustments. Still fun on any tire tho...

 

My street tires are the 195 - 16” Continental RFTs that came on the car. Hey, why spend money on tires when a set came with the car? ...

“...a complete new rear (caster)” - caster in the rear? That is a new one on me...

 

So some interesting numbers. The 235/45/17's mounted on 7.5" rims stacked measured 37.15". yesterday I dismounted them and stacked they measure 37.75". I know that is just .6 inches divided by four tires BUT it shows some effects of smaller rims. Now the 225/45/17's mounted stack at 35.25" compared to the 245/45/17s at 37.15" . The Section width is 1.9" between the four (mounted) or .475" per tire on 7.5" rims. Not a huge amount of tread width loss either...

I know from previous AutoX Runs that the 225/45/17s run faster than the 235/45/17's...whether it is from the Diameter decrease (quicker acceleration) or from the sidewall response on proper rim size...or a combo of that and the raised Mini Height to compensate for tire diameter.

The Tires will drop the Mini .5" and I can lower the spring perches about .25" and still have clearance...so the COG will be much better at .75" lower suspension settings/tire diameter difference

 

Your experience is similar to my own on the track. I have run 205/50x15 (RE71R), 215/45x17 (ZIII) and 225/45x17 (R888) on the same track, same day, with results that were very similar. The 205s were the slowest, but I also had 3 additional shift points with those that I did not have with the 17” tires. They are also 2” smaller in diameter, which lowers the car by an inch. The 225s are clearly pinched on the 7” wide wheels and, even being R-comps, they were nearly the same as the ZIIs (200 wear tire). This is a long track (3.4 mi) with a 2:25-ish lap time. The 205s were only about a second slower. On a short track (1.5 mi) the 205s are clearly fastest. The 8% improvement in gearing is clearly noticeable as is the 3 - 4 lbs per wheel decrease in weight. I expect the lower cg is in there too.

Looking forward to your next run. You have also confirmed my next wheel and tire purchase for the JCW...

 

I got lucky and got to test two sizes and without testing the 3rd size … anecdotally figured that the 225/45/17's on 17x7.5 rims were the right ones. I sold the first set of 225/45/17's after 6 AutoXs...I sold the 235/45/17s after 3 AutoXs and got a full refund on the 245/40/17s which covered the new 225/45/17s...so all in all it wasn't terribly costly to figure out. The Mini felt much more stable and precise on the 225/45/17s and lower COG...

I can't wait till October 5th and 12th for the next 2 AutoXs on the new tires/adjusted suspension.

 

Not to complicate things, but did you consider the 215/40x17? They are only 0.1” smaller in section and tread widths compared to the 225/45s and they are 1.1” less in diameter...

 

As it stands, most AutoXs are done in 2nd gear...if I went any shorter I would be caught between shifting from 2nd to third for just a moment and then right back to second...or, just hitting top revs and not gaining speed. As for some other Bridgestone sizes...they would be 205/45/17s (24.3" OD ... 7" Tread Width) … 215/45/17s (24.7" OD … 7.2" Tread Width) … 225/45/17s (25" OD … 7.6" Tread Width)
The 225/45/17s have proven themselves to be right on the mark...and are perfect fit on the 7.5" rims
The only other real option would be the 235/45/17s at 25.4" OD … 7.7" Tread Width where the tread width is basically identical and the height a bit taller... I wish they came in 235/40/17s so I could spend days/weeks/months trying to figure it out LOL

The 225/45/17s fit 7-8.5" rims
The 235/45/17s fit 7.5-9" rims
I would rather be in the middle of 7-8.5" rims with better clearance for lowering the Mini

Just a Note: The wheels/weight/tires/mounted weight 40.2 pounds each (225/45/17s) on the NM RSe05 Wheels...The JCW Stock Wheels 18x7 and Run-Flats weight in at 40.1

 

Thanks for the tire info. And a note about the few brands with 235/40x17 tires on TR - they are freaking expensive, with some 200 wear rated tires being more expensive than the R-Comp versions.

 

I look up tires on TireRack.com because they have a better layout but I buy them off Discounttires.com because they have better pricing...

 

For Ref. I measured "sidewalls from floor not mounted" (4) 205/45/17 BF Goodrich G-force Comp-2 A/S total approx 34-1/8", single tire 8-5/8". My current P7 run flat is just a tad over 8" wide. I'm hoping when mounted the BF's clear the strut, only have 5mm clearance with narrow P7's.