con40

So I may get an earful about this and I'm sure many of you consider this topic to be settled. Chatted with a TireRack guy online and still not sure which way to go. What I'd really like (and I know this doesn't make sense on stock rims, nor is available) is the resulting grip to be close Mich. Pilot Super Sports in 225 Front and 265 Rear.

I'm ready to change out my Bridgestone RE050's at 215 Front and 245 Rear and would like to increase the overall grip without adding any over-steer. I'm targeting Max Performance Summer tires as I still want to keep my wet grip. If anything a tad less ('04 AP2 without traction or stability) over-steer would be preferred. My best guess on how to do this is increase the width of the contact patch (what TireRack calls Tread Width) on both tires and try to keep the same ratio of Rear to Front width as stock or higher. I have yet to see any clear argument that Section width is a better indicator of contact patch width, especially when looking at the same manufacturer. Based on this process it looks like my favorite Michelin Pilot Super Sports, they are just too skinny at 245/40R17.

Keeping things within the Bridgestone family (mainly for comparison and discussion accuracy)

OEM Fitment
Bridgestone Potenza RE050
Front: 215/45R17
Tread Width: 6.7"
Rear: 245/40R17
Tread Width: 9"
Rear to Front Ratio: 1.34(lower = more over-steer, higher = less)

Max Summer Tires with OEM Sizes
Bridgestone Potenza S-04 Pole Position
Front: 215/45R17
Tread Width: 7.7"
Rear: 245/40R17
Tread Width: 9"
Rear to Front Ratio: 1.17 Would likely have more over-steer at the limit

Max Summer Tires recommended fitment
Bridgestone Potenza S-04 Pole Position
Front: 215/45R17
Tread Width: 7.7"
Rear: 255/40R17
Tread Width: 9.2"
Rear to Front Ratio: 1.19 Would likely have more over-steer at the limit, limit should be harder to reach.

Max Summer Tires using target ratio for sizing
Bridgestone Potenza S-04 Pole Position
Front: 205/45R17
Tread Width: 7.4"
Rear: 255/40R17
Tread Width: 9.2"
Rear to Front Ratio: 1.24 Would likely have slightly more over-steer at the limit, limit should be harder to reach. Closest to OEM Ratio.

Extreme Summer Tires recommended fitment
Bridgestone Potenza RE-11
Front: 215/45R17
Tread Width: 8"
Rear: 255/40R17
Tread Width: 9.4"
Rear to Front Ratio: 1.18 Would likely have more over-steer at the limit, limit should be harder to reach due to tire class.

Extreme Summer Tires using target ratio for sizing
Bridgestone Potenza RE-11
Front: 205/45R17
Tread Width: 7.5"
Rear: 255/40R17
Tread Width: 9.4"
Rear to Front Ratio: 1.25 Would likely have slightly more over-steer at the limit, limit should be harder to reach. Closest to OEM Ratio.


So is my math junk, if so why?

Given my priorities, and ignoring price, what should I select?

Should I target maximum grip and ignore this ratio since I can't really get where I think is right? If so, which setup would you select?

Is going 255 in the rear worth missing out on the terrific Michelin Pilot Super Sports?

Jim@tirerack

Your math is correct. The OE Bridgestones are narrow for the size front and wide for the size rear. That is why the 215/45R17 front and 255/40R17 rear is a good match. Nobody really makes any 265/40R17 in the same level of performance. The section width is not a good way to look at contact patch. You are correct on the Super Sport though and I don't think you can go wrong with that tire.
If you are looking for more performance I would go with the RE-11. They are a non nonsense stree/track tire that gives a lot of grip.
If I can help let me know.

ZDan

Grip doesn't vary linearly with tread width. Particularly for street tires/street usage, and even at the track to some degree.
I've driven a pretty wide combination of front/rear sizes on the street and at the track in my AP1, and the handling balance was not dramatically affected by pretty wide swings in tread width stagger.

As Jim alludes to, tread width isn't the same as "contact patch width" anyway. Highly unlikely that any tire, properly inflated, in any driving condition will have a contact patch that fully spans the tread, and the difference from tire to tire will likely be pretty significant.

Even given your specific concerns, I wouldn't worry about running 215/245 despite what "rear to front ratio" that gives you for any particular tire.

Many Extreme Performance tires do give great "wet grip", but what they will generally lack in vs. Max Performance tires is *hydroplaning resistance*, particularly when worn beyond halfway. It is simply a brute mechanical fact that a lower void ratio tire will hydroplane at a lower speed in standing water vs. a higher void-ratio tire.

Given your concerns, I would go with Michelin Pilot Super Sport in 215/45-17, 245/40-17 and not worry about the different "tread width stagger" vs. OEM, or lack of 255 size.

FWIW, I just put PSSs on my RX-7 last year, probably put about 5500 miles on them since, plenty in wet/inundated condtions. Very pleased with their performance (including 184.8mph Texas Mile run!) vs. the StarSpecs they replaced

con40

Thanks guys, very helpful answers. I'm leaning toward the RE-11 at F215/R255 at the moment. Is it just plain wrong to think about putting any 205 tire on the front regardless of the tread width?

ZDan

No reason to go 205 fronts. Also, no reason to exclude PSS based on 245 rears. IMO you're barking up the wrong tree fixating on tread width stagger.

That said, if 215/255 is a requirement, if tracking I'd go with Dunlop ZII or BFG Rival (I'd also go with 225 fronts), if not tracking I'd go B'stone S-04, or if softish/flexy sidewalls aren't a concern, Conti DW.

Another possibility is Toyo R1R. Fantastic in the wet. Reportedly not up to hard track days, but should be great for autoX.

RE-11 should be a great tire, but IMO there are better choices, esp. if $$$ is a consideration.