I did a little research on this myself this morning.
I am planning on having two sets of wheels for my 40, one for street use and one for track. Here is what I have come up with for the "street" sizing.
My car will be a GT40NZ there fore I am going from the recommended tires from their site.
They recommend a 225-15 front and 305-15 rear which add up to be a approximately 25inch tall front and 27 inch tall rear tire.
These are also the recommended tire heights from ERA being 25.6 max height front and 27 rear.
As we all know, 15 inch tires in a decent "speed" rating are impossible to find anymore without going to a comp type tire.
I did some calculating and came up with these 16 inch sizes as possible alternatives.
225/50/16 Front= approx 24.8 inches tall
255/50/16 Rear=approx 26.03 inches tall
as you can see, these are about one inch shorter than the recommended 15 inch tires.
This should lower your ride height by about 1/2 an inch.
Now here is the GOOD NEWS!
A quick check on the tire rack website found 13 different speed rated tires (VR or better) that are available in both F&R sizes!!!!
Of these 13 possibilities, 2 are comp DOT type tires, which leaves 11 possible dot legal high speed rated tire brands available.
here are the models:
Michelin Pilot Sport YR-rated
Pilot SX MXX3 ZR-rated
Dunlop SP sport 8000 ZR-rated
Firestone firehawk ZR
Goodyear Eagle HP ultra-plus ZR
Kumho Ecsta Supra 712 WR
Sumitomo HTRZ WR
BFG comp T/A VR
Dunlop Sport 5000 WR
Michelin Pilot XGT V4 VR
Yokohoma Avid H4/V4 VR
the cometition tires available are the
Hoosier and the Yokohoma A032R
also the hoosier is available in a little wider at 275/45/16,,,,which adds up to 25.7 inches tall.
I believe that for a street car needing a good overall quality tire, the 16 inch is the best compromise.
The drawback is that they are around one inch overall shorter than recommended, but the available tires are of much better quality than a the 15 inch units.
This not only means a beeter grip while accelerating and cornering,,,but also a much better tire under braking is available in the 16 inch sizing.
(trust me, when I tell you, the single best way to improve the braking performance of a street driven car, is to use the highest quality tire available.)
(big brakes, for track use, are needed to resist fade under high heat/use,,,,,not shorten stopping distances.)
Although there are 17 inch tires available, the overall height becomes shorter still, and you lose precious sidewall height, which takes away from the "period look" of the car.
My #1 choice for an excellent street tire.
The Michelin Pilot Sports. They are probably the most expensive of the bunch, but I have them on my 500e "rocket sled", and am very impressed with their abilities.
For a "more reasonably priced" street tire, you may want to consider the Sumitomo.
The are about half the cost of the Michelins, and although I have no personal experience with them,,, I've heard good feedback from others who use them.
For a no-compromise autocross, track time tire, my choice is the Hoosier.
I will get the larger 275/45s for the rear of my car, in order to have the largest footprint possible.
Simply put, the Hoosier is the fastest DOT sticky comp tire that money can buy. They also have the shortest lifespan.
Hopefully the above info is helpful.
here is a link to the tire rack site:
http://www.tirerack.com/index.jsp