cwbaader wrote:
[quote]Ok, below is Toyo’s recommendation for the wreck pinata:
Spec Miata Setup Guidelines
The information provided in this guideline are general recommendations, your final setup may deviate
from what is stated here.
Full Tread 4/32nds Full Tread 4/32nds
IP (kPa) 220 220 220 220
Load (kg) 370 370 370 370
Kz (N/mm) 245 233 272 251
Ky (N/mm) 158 178 188 194
Kx (N/mm) 454 473 495 495
IP (PSI) 32.0 32.0 32.0 32.0
Load (lbs) 816 816 816 816
Kz (lbs/in) 1,397 1,328 1,550 1,431
Ky (lbs/in) 901 1,015 1,072 1,106
Kx (lbs/in) 2,588 2,696 2,822 2,822
CP (kN/deg) 1.03 1.35 1.25 1.46
(kN) 2.98 3.69 3.72 4.02
CP (lbs/deg) 231.6 303.5 281.0 328.2
CF w/4deg Slip Angle (lbs) 669.9 829.5 836.3 903.7
RA1 R888
CF w/4deg Slip Angle
Stiffness
Cornering Power (CP) / Cornering Force (CF)
As shown in the chart above the Proxes R888 is stiffer (higher spring rate) and creates more cornering
power and force than the RA1. These changes in tire design might require chassis setup changes and
driving behavior to maximize performance and wear.
Shaving
The R888 was designed to be raced on at full tread depths (6/32nds). In back-to-back testing, a full tread
depth R888 is faster than an RA1 that has been shaved to 4/32nds. Racers looking to maximize wear life
should strongly consider using the R888 at full tread depths. The R888 can also be shaved for an
increase in performance, but less remaining tread means less usable life.
Air Pressure
The R888 can be used at lower hot pressures as compared to the RA1 because of its design.
Decreasing the air pressure will improve contact pressure and footprint shape. A recommended hot
pressure range is 32 – 38 psi. For a light weight vehicle such as the Spec Miata, 32 psi hot is a good
starting point.
Tread Temperatures
The optimum tread temperature for the R888 is 160°F to 220°F. Below 140°F and above 250°F the tire
may not provide sufficient grip. Generally there will be a 25°F temperature gradient from inside to outside
shoulder, with the inside shoulder being the hottest. Most distance and time on a race track is in a
straight line therefore, the inside shoulder is hottest because of negative camber. The same
temperatures across the tread face should not be expected.
Understand the track layout before pit entry. If for example there is a long right hand turn before entry, the
left tires will be hotter. Take tire temperatures and pressures after a few laps to get the temperatures and
pressures stabilized and come in after a hot lap.
Camber
To maximize the potential of the RA1 a lot of negative camber might have been required. The R888 on
the other hand produces more camber thrust at the same camber angles as the RA1, therefore less
negative camber might be beneficial. Reducing negative camber will improve contact pressure
distribution across the tread face improving wear. Start at -2.5° in the front and -3.0° in the rear.
Analyzing the tire temperatures, wear, and chassis behavior will help you dial-in the optimum camber for
your setup.
Front Toe
One of the benefits of the increased stiffness of the R888 is the improved steering response over the
RA1. Setting the front with a little to zero toe out will likely improve wear life, straight line speed, and
stability with minimal sacrifice to steering response. The exact setting will vary depending on driver and
situation.
Driving
Due to the higher cornering performance compared to the RA1 a driving style with less slip (steering)
angle is possible. As shown in the chart above the R888 is generating more cornering force at a typical 4
degrees of slip angle. The RA1 would require more slip angle to generate comparable forces. The R888
will be quickest when it is not sliding too much or being over-driven.
Graining
The following are reasons why race tires grain:
The tire was not properly brought up to working temperature. This will cause the tires to slide and
not adhere to the track surface.
Low track temperatures will not allow tire to come up to proper working temperatures.
A vehicle that is setup poorly in suspension or alignment.
If graining is seen on the front tires the car may be understeering. The front tires are not generating
enough grip (or rear tires may be generating too much) therefore the front tires are sliding creating this
wear pattern.
Graining will contribute to poor grip and sliding which can cause more graining in an endless cycle.[/quote]
So pretty much what I said. I believe the optimum temperature gradient should be less than what is stated above but who knows?
