So my 235/45/17s are mounted on my NM Eng. RSe05 17x7.5 wheels...sitting next to my unmounted 245/40/17s. The stacks measure 37.15" for the 235/45/17's and 40" for the 245/40/17s..
That means the extra width of.7125"/2=.357" on each side when it comes to clearance. I hope that when the 245/40/17's are mounted that it shrinks down just a tad...but I think I can fit them
with the proper spacers and camber settings. Ride height will drop about .5" without adjusting the spring perches...so if they a bit too wide I can leave the perches where they are at and see if
any rubbing occurs during the AutoX this weekend (If I get around to swapping the tires. I will decide today and swap tomorrow if I want to do it. Thinking to run the 245/45/17's this weekend
for their 3rd AutoX and then decide.

 

Interesting side by side view right there! The listed specs on TR show only a 0.2" section width difference and that is with the 40-series on a 1/2" wider rim. It will be interesting to see how much both tires change in stack height when you swap the rims over. I run 245/45/17's on 17x8" rims on my Mustang, but never measured the stack height to compare them to yours on 7.5" rims.

 

Not going to be able to do them before this weekend...

After this weekends AutoX I am going to fit a 245/40/17 to one rim and test fit on the front...I will measure that tire against one that is not mounted to verify the difference

I am hoping that the 2.75" difference for the stack goes down about 1" and then I am just getting a .435" diff from the 235/45/17's

 

I'm looking (still) into wheels, was thinking 17x7.5, 215/45 tires (no AutoX or track). I'm surprised that your tire varies so much from the listing measurement, interested to see once mounted. Thanks for keeping us posted.

 

I will tell you that 225's fit like a glove for street use...you might need a 5mm spacer for clearance but get the NM Wheels for brake caliper clearance. Be careful about the wheel spacers that fit Stock Wheels
from some sellers. They don't fit in the NM Wheels like they should. Just a flat 5mm spacer will still leave enuff of the protrusion from the mini to fit perfectly.

 

225/45's? There's a good selection of tires in both 215/45 & 225/45. The wheels I'm looking at are (Advan RZ2) 17x7.5 48 offset so the 225 will most likely interfere inboard. I wanted a fit that didn't require spacers.
Waiting to hear from retailer if they clear the calipers. Your set up is pretty sweet. Why does everyone diss these run-flats, they're expensive tires?

 

The Run Flats sidewalls are very stiff (so they can run flat)...that also makes them very ruff riding and a bit squirely IMO.

 

I would have assume a stiffer tire would have provide better handling on the track.

 

Problem is (for AutoX or Track Use) you can't do much adjusting of handling by air pressure changes...it doesn't affect sidewalls as much...

 

So finished 2nd today on the 235/45/17's. 5 runs...on 4th and 5th runs I finally decided that because of the sidewall height I should add 5psi in all four tires. Went from 55.613 to 55.102 on 4th run and didn't change a thing and got down to 54.747 on 5th run. Almost a full second quicker. The sidewalls felt stiffer and less mushy. Between the sidewall flex and the added OD of 1 full inch...the 235/45/17's are just too tall for the JCW. A friend wanted them for his Audi so I sold them on the spot for 1/2 of what I paid after three full AutoXs.

So Far the RE71Rs in 225/45/17s fit the easiest and worked the best overall. They allowed me to lower the car more than the taller wider tires and seemed to work better. I would like to try the 245/40/17's I have in the garage...but...they are still unused and could be returned for the 225/45/17s...gotta think a bit...especially about mounting on a 7.5" rim...but the 245/40/17s are shorter than the 225/45/17's and might Be the Ticket...if they fit...

 

If you get a chance throw the tires on a scale. curious what the weight difference is per size/brand. You have a ton of chassis improvements, have you considered or tried the iSweep body brace?

 

The iSweep goes in two directions fore to aft and laterally...not legal in the Street Touring Class...otherwise it would be ON

As for tire weights you can go to www.TireRack.com and look at specs... All the tires I have tried are within 1 to 2 pounds of each other

225/45/17 @ 23# (first ones tried) 25"
235/45/17 @ 24# (second ones tried) 25.7"

245/40/17 @23# (next ones to try) 24.7"

235/40/17...wish Bridgestone made this size...probably would be perfect on 7.5-8" rims!! Falken has some 200AA in 235/40/17s that are 22# 24.4" by 9.4 by 8.5 … come on Bridgestone, add 1 size

 

More tire fun!

 

I think 225 size fits right, for bigger 235/245 you need reinforced drive shafts for continous fun. The only thing whats counts is tire temperature, if you under 80 degree, you wrong. What shows you that
the performance tires of 80% fitted are for show only. Michelin recommands for fast round 2.5 bar max 90 Degree optimum temperature.

If you finished your lap and you can touch your tires without burn you........

 

I think 225 size fits right, for bigger 235/245 you need reinforced drive shafts for continous fun. The only thing whats counts is tire temperature, if you under 80 degree, you wrong. What shows you that
the performance tires of 80% fitted are for show only. Michelin recommands for fast round 2.5 bar max 90 Degree optimum temperature.

If you finished your lap and you can touch your tires without burn you........


For those which are really serious, a temperature coding is recommanded, which shows for each wheel temperature besides pressure. I wonder who of you have done that .

 

Clutch - I believe your temperatures are in “deg C”. In “deg F” that would be 176 to 194 deg... if I did my conversion correctly.
Also, remember that the OP is doing autocross. These about 60 second runs with a cool down time in between runs. It is really tough to get tires up to temperature and keep them there. Just part of the fun of trying to be fastest around a bunch of cones in a parking lot...

 

What about the Donlup ZIII?
235/40x17 @ 23# and 24.5” dia, 8.9” by 8.4
https://www.tirerack.com/tires/tires...omCompare1=yes

They are a bit narrower in cross-section which may help them to fit more easily.

How is the wheel width (7.5”) working out with the larger tire size? The min width for the 245/45 is 8”. They are not overly pinched?

 

After a bunch more research AND the experience on the fit and times on the RE-71R's 225/45/17's on 17x7.5" I have decided to go back to the 225/45/17's. Wider tires 235 or 245 do put more tread on the ground BUT the sidewall pinch which results in sidewall flex makes the tires less responsive IMO (on my 235/45/17's that I am running...the 245/40/17's might be a little better with the lower profile but the increased pinch/fitment will not work as well IMO)

Going to send the 245/40/17 back and get the 225/45/17s and just work them and drive better...

 

I am in South Texas and in the summer our temps are near 100F all the time. Yes, I am just doing AutoX right now...cones in a parking lot!!! But, I used to race Karts and then SCCA Showroom Stock in a Mazda Miata for two years (SW Divisional Champ both years)...then in Escort Racing,,,then back to SCCA ITA in a RX-7...on to 12 and 24 hour with Mazda...raced the first Mazda Spec Car built at The 24 Hours of Moroso which started on New Years Eve 1999 and ended on New Years Day 2000. 6 driver team (3 were people who paid to run) and I ran 10 hours straight thru the Night in the Down pouring Rain. 4 of the other 5 ran the other 14 hours.

From an article about the first Spec Miata: In October 1998, Shannon McMasters, Tim Evans, Danny Benzer and Wally Darbyshire starting building a prototype Spec Miata for the 24 Hours in Moroso. We got Mazda, Kumho, Miata.Net and Texas Body Works to sponsor our team. Shannon found a used miata and we hauled the car to Todd Oppermann who had built cages for some of John Phillips Grand Am Cup Miatas. Once that was completed, Shannon replaced all bushings and rubber in the suspension and then we all got together one weekend to hang the new suspension and drop in a new crate motor.

We raced the SM prototype in November 1998 in ITA and finished first in class. From there, we went to Moroso and finished 10th overall and 2nd in ITA in the 24 hour event. David Del Genio also brought 3 of his older Grand Am Cup cars that were prototype 1994-97 1.8 SM's. Our 1.6l prototype SM finished in front of the 1.8l's.

 

On the discussion of heat...
I'm running the Rivals 1.5s, which in my opinion handle heat much better than the stones, and I'm having to spray them down often to keep from overheating.
Between the massive brakes, front tires doing all the work with all the weight, and the compact engine compartment that doesn't vent off heat very well... its incredible how hot the front wheels and tires get with just one autocross run.

 

In the NE, where I live, the autoX courses tend to short, in the 40 second or less range. With these short runs the tires didn’t get a chance to get heated up. At least mine didn’t. Or, maybe, I just don’t drive fast enough...

 

The issue I have with the Rivals is the price...about $25 more per tire over the same size Stones...

 

I run into a different issue. The stones are less expensive and are sticky, but they wear fast especially on the track. For a track tire, the wear seems to off set the savings. And they tend to get overheated. The 200 wear tires seem to be driven by the autocross market which values sticky when cold and not so much on wear when hot. My next tires are likely to be the Hankooks as I have read that they do well in endurance racing. I may actually try a set of Toyo R888Rs. They might wear like the Stones, but be even more stick... But that’s for next year. We have winter coming and my “autocross” car of choice for that season is my Wrangler ...

 

Had a local try Z3's on his second car (less serious build than his S2k STR car), said they weren't close to the Bridgestones or BFG's (and now Yokos), his times reflected that. There's a GRM test that shows them more favorably but nobody in the competitive autox scene has adopted them as far as I can tell.
Tire compound is more important than width when it comes to searching for the fastest times.

The difference between the Stones and BFG's is small, worth the price if the surface/setup/driver favors the BFG's and if you don't want to lose an important event by 0.1-0.2s but otherwise I'd agree on testing and tuning and getting better with the cheaper 'stones.

imho not much point to spraying unless the tires are too hot to touch, they don't start working until 140°F and probing after a run we rarely push that number even on the >60s courses in 105°F heat, by the time the next run comes around they're below where they need to be. I have no doubt some can overheat their tires to the point where spraying is helpful, just more anecdotes on the internet.

 

To be honest for my daily 90% slowmo drive, i give a **** on tires and look for price. For competion thats different Michelin 17 offers for 120 Euros a compound developed for Porsche where its cost 400 per tire.

Next year the car will get a new setup, the choosen wheels will have low offset and wider track and 3,5 camber and a complete new rear (caster), you can drive certin sections only as manschurian candiate, with the present setup. I allways choose the tires first and its availabilty but 245 will it be. the record runs of VW/ Renault where are all with 245/30-18.