Autocross tire pressures

[eejay56]

At the ABFM I picked up some Yoko autocross tires. I got 2 A048s and 2 A021Rs 205/60 13. I plan to run the 48s in the rear and the 21s in front. Does anybody have recommendations for what tire pressure to use? The car is a 78 Spitfire.

 

[dougie]

Eric,

I suggest you make a couple practice runs with 27 psi, then check how much each tire increases in psi after each run. Make you adjustments so you're able to obtain your ideal tire pressure by the time you cross the finish line. My bias-ply Hoosier's grow 5 psi, but that's over a 20 minute race.

Dougie

 

[GeeBee1]

I put chalk on the outside edge of the tires to see how much rollover I am getting and adjust them accordingly.

Pat

 

[aeronca65t]

I have a set of 185-60/13 A048s for my Spridget.

I also use chaulk to get a basic idea of how they are rolling over.

For racing, I start with about 34 to 36 psi <span style="text-decoration: underline">cold</span>, but with a goal of 38 to 40 psi <span style="text-decoration: underline">hot</span>.
In cooler weather (like our Watkins Glen event in 5 weeks), I'll shoot for 36 to 38 hot.

I also have Toyo 888 DOT radials and I treat them the same way.

FYI-my car weighs 1700# without me.

I'm not sure how this tranlates to autocross (I haven't run one in 15 years), but do think you should check pressures at the end of the run (when they're as hot as possible). In that car, I'd say make sure they're all about even.

 

[BoyRacer]

Why are you shooting for 36 - 38 - 40 degrees hot? With those kind of pressures you are reducing your contact patch significantly. If I only weighed !700# I would be starting cold at about 20 psi. Try it, you'll like it. I like Watkins Glen too!

 

[aeronca65t]

Richard:

As I said, I've found that 36 to 40 psi hot works well on my slightly pudgy Spridget.
Toyo recommends 32 to 38 psi hot depending on application, so I'm in their ballpark.

Here's a link to that recommendation:

https://toyotires.com/tire/pattern/proxes-r888

My friend and fellow racer, Phil, at philstireservice.com recommends "around 40 hot" (his words). He sells hundreds of Toyo DOT radials each year.

Most SpecMiata racers tend to run high 30s to low 40s in the various DOT radials used in that series.

20 psi would be fine for a lighter car with bias Hoosier TDs. But I'd slide off the track on the first turn if I ran that kind of pressure in DOT radials.

 

[BoyRacer]

OK, fine. Just my two cents. Sometimes it's good to think outside the box. The tire sellers always recommend very high tire pressures (I'm an attorney - think liability). What makes you think you would slide off the track if you started at 20 or 22 psi? Did someone tell you this? Was this person a real racer? Have you ever tried it? I'm just trying to help you out here. I have raced on radials and bias ply tires over the last 28 years of racing my Healey 3000. My Healey is over 2200# before I even get into my office. I am not an auto-crosser but even in balls out road racing, I start out with pressures in the low 20's. When I finish a 20-25 minute race I do not want my tires at more than 28 psi. This is my last post on this topic. Cheers.