R100 Sports Sedan

Hi Everyone,
I race a 1969 Mazda R100 Sports Sedan in Australia, it’s been a race car since the late 70’s. The car is set up for bias ply slicks but due to Dunlop not making the correct size tyres anymore, I bought a set of Hoosier bias ply slicks (GT2 Tread Pattern) NOT a DOT Tyre.
In Australia no one seems to use Hoosier slicks that I can find, so I would like to know if anyone can help with what tyres pressure to run. Currently I run the Dunlop’s at 22-24 cold and 28 hot. From the Hoosier web site and other forums I’ve read, it looks like I need to run around 38 hot for the Hoosiers?
This seems like a high pressure to me, the car only weighs around 800kg. Any help would be appreciated.
Here is a photo of tha R100 in action

jgrewe

iTrader: (1)

I don't know the exact tire you chose but the 9.5x23x15 ones we use like 26 to 28 hot. These are the cantilever slicks for the narrow rims in EP up here. You should be safe for a session if you start at the same cold temps as the Dunlops and see what the pyrometer tells you.

Don49

iTrader: (3)

+1. I run 19-20#'s cold on my RX7 and see 26+#'s hot. The Hoosier guys tell me this is where I want to be with tire temps around 180 degrees.

R100 Sports Sedan

Thank you for the replies was a bit worried going out at such high pressure for the initial run in to cure them & stuffing the tyres.

Seems strange Hoosier would advertise this chart on their web site and possibly be incorrect.

Tire Pressure recommendations
Hoosier Tire typically require higher pressures than other brands.
Reference the following chart for suggested pressures:

Vehicle size recommended hot pressure cold pressure
1800-2200 lbs 39-42+ 31-36
2200-2600 lbs 40-43+ 32-37
2600-3000 lbs 42-46+ 32-37
over 3000 lbs 43-48+ 32-38


This is the tyre I have bought for the R100 of the Hoosier web site in the R35 Compound.
Part #43470 22.0 x 10.0-16 GT2 Tread Pattern (Full Racing slick)

If anyone has any further advise or feedback on this tyre would be much appreciated, i belive some cars that race in the SCCA use this type of tyre.

jgrewe

iTrader: (1)

That chart is for the radial DOT legal tires, not the bias ply slicks. The tire we use is right above the ones you bought on the spec list.

Start at 20 psi cold and you'll be right in the range you want.

Gene

iTrader: (1)

You can also contact Hoosier directly, their support is pretty good.

jd to rescue

iTrader: (3)

You can contact Mid-Atlantic Motor Sports. (248) 844-7148. Speak to Tom. He will tell you exactly what pressure you need to be running. He is an old race dog who sells racing tires for Hoosier. He'll probably tell you a couple of war stories in the process. Also try their website Mid-AtlanticMotorSport.com. Let us know what you find out.