I don't think the car is too heavy for the tires. It just takes a big setup change to keep the tires happy.

 

Could you elaborate?

 

My co-driver is pretty tire sensitive and absolutely hated the 255 R1R's on my AP1. We put those tires on his '06 MX5 (very light STR prepped) and they were like razors on turn in. If we prepped his car for STR, we would be using the R1R's.

 

Sure, the Toyo is a pretty sensitive tire to setup. Even though the tire can take the high slip angles the idea is to try not to. The high slip angles are what kills the tire as the tread begins to "grind away". The front tires are more prone to wear than the rears since it will experience more deflection and squirm. More camber is needed and softer roll stiffness. I am currently testing out 235/40R17 Toyo's. The theory is that with the tire properly supported by its sidewalls (235 on a 9") the tire will deflect less and create less heat and squirm. Now the reason why I think the car isn't too heavy for the tires is because my car definitely puts power down way better on 235 Toyos than the 255 Dunlops i've been running. Conventional thought would say that 235 width tires are too skinny, which may be true but for this tire I believe that they need to be on the appropriate size rim.(235=9", 245=9.5", 255=10"). A 235/40 would probably work even better on an MX5, but with the new crop of tires coming out it is probably a moot point.

 

Sure, the Toyo is a pretty sensitive tire to setup. Even though the tire can take the high slip angles the idea is to try not to. The high slip angles are what kills the tire as the tread begins to "grind away". The front tires are more prone to wear than the rears since it will experience more deflection and squirm. More camber is needed and softer roll stiffness. I am currently testing out 235/40R17 Toyo's. The theory is that with the tire properly supported by its sidewalls (235 on a 9") the tire will deflect less and create less heat and squirm. Now the reason why I think the car isn't too heavy for the tires is because my car definitely puts power down way better on 235 Toyos than the 255 Dunlops i've been running. Conventional thought would say that 235 width tires are too skinny, which may be true but for this tire I believe that they need to be on the appropriate size rim.(235=9", 245=9.5", 255=10"). A 235/40 would probably work even better on an MX5, but with the new crop of tires coming out it is probably a moot point.
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Good points, thanks. I think most 235 tires are measured based on a 8" rim, (assuming 235/45, based on what the Tirerack website uses) and from what I understand the section width increases by ~5mm for every additional 0.5" of wheel width over the "measured rim width." Your 235s would then have a nearly 245mm section width on a 9" rim, but probably allow a better sidewall orientation relative to the wheel, and might deflect less under load as you indicate. Next year's new tires will be interesting to see tested, for sure--I am especially intrigued by the Michelin PSS vs the Dunlop ZII.

 

Sorry to just jump in here but I have been researching STR and am planning on running it next year. I just picked up some Volk Ce28 17x9 (rear) 17x7.5 (front) I was planning on running the RS3s 255/40-17 (rear) 225/45-17 (front). The miata tire calculator had that as perfect match. These will also be my street wheels and tires. Then I plan on getting a second set of wheels and tires for the track. Not sure of the type of wheels but they will be non-staggered. The tires will be either the NT01s or the R888s. So my question is, does this sound like a reasonable idea or will I be shooting my self in the foot not running 255s up front in STR? My order of precedence in racing is 1st track 2nd autocross, but I would like to be competitive in autocross.

Thanks for any good information. Nicholas

 

I think you will be ok but you will want to plan on getting a 9" front rim if you become serious about STR.

 

Is there a benefit with having multiple sets of wheels/tires? I am debating selling a set of wheels and run one set of wheels next season. Changing tires when needed of course.

 

Some typical reasons to have multiple sets are for...

- dry and rain.
- street and autocross.
- hot and cold.
- all of the above.

For local autocross I have street tires on OEM wheels and RS3s on 9" wheels that get trailered/swapped at the event.

For national tour events and nationals I drive there on 9" wheels with Dunlop Star Specs, better for cold/wet IMO. On the trailer are the RS3s which I like for when it's hot (75F or above). Some drivers use Dunlop as the primary tire and have Toyos as there cold/wet tires. It just depends on your setup and what you like.

I like to trailer my main tires to preserve them for wear, heat cycling, or risk of damage (especially when driving 100, 500, or more miles to an event).

On the flip side there are nationally competitive drivers that daily drive their autocross tires and drive them thousands of miles to events. You can certainly manage to live with one set of wheels/tires. It just depends on your personal situation for the logistics and financial aspects. Some people trailer their whole car and only use it for competition.

 

So is there nobody running a staggered set-up that is regionally/nationally competitive? Not that I'm in that pack I just want to have realistic expectations for my current set of wheels and tires.