woody6244

New to autocross with a 04 zo6. Guys in my club are telling me that the car would be more competitive with tires like A6s over Rivals. How much time should a driver improve with A6s tires vs Rivals a 50 second course?

ltborg

I always was told going to race tires gave you 2 seconds on a sixty second course. That said, unless you're running national level events, stay on the street tires.

woody6244

That doesn't pencil out well. On 60 second run the difference between AS and SSR pax is 2.34 seconds.

talon95

This even depends on the surface. The 2 tires are generally closer together on asphalt than concrete for example. We re-ran the 2013 Nats courses last weekend at the Lincoln Div. I was 2-3 seconds off my Nats times from last year (A6's vs. RS3V2's). Lincoln tends to heavily favor race rubber though, so that's probably the bigger delta you might see.

Also, those courses are longer than 50 seconds. (West was mid-50's, East was low-mid 70's)

brenb

more competitve in what way?

Are you running SCCA classing? Do you concern yourself with PAX? Or, are you just looking to get around the course as quickly as possible?

Bill Dearborn

A couple of comments.
I ran a lot of autocrosses on Go Kart tracks. The advantage of doing so meant the only variance from one event to another was the weather and maybe how much dirt had blown onto the track. That being said it was easy to compare times from one event to another over years of events. I knew what the tire pressure in each tire had to be, I knew exactly where each bump in the course was located and where the car had to be positioned on track to get the best speed based on those bumps/irregularities. If I ran street tires my times were in the 1:28 range and if I ran R compounds they were in the ralways in the 1:24 range. Usually the 1:24 range would pretty much guarantee that I would get FTD unless one other Vette competitor (he had the record for the lowest ever recorded time on the track) or single seat formula cars were at the event.

Doesn't PAX also depend on course setup? I have been on many parking lot SCCA courses that had many tight turns with short straights connecting them and were extremely easy for light nimble small cars and not so easy for a Vette that had no way to use its power. Then I have been on Go Kart tracks where the opposite is true. Turns that aren't as tight and where a Vette can use its power coming off the apex with at least 200 ft of straight before the next turn. When I ran began autocrossing with my 86 a friend of mine had a well setup VW GTI that would blow me away by a quarter second in the tight courses the local SCCA setup in parking lots but once we started running at a local Go Kart track I was blowing him away by over a second. After experiencing that difference I became a firm believer that PAX doesn't really work unless there is some sort of balance in course setup.

Bill

brenb

PAX is a performance multiplier applied to each class - it has no dependency on cours design, surface, weather, or what have you.

woody6244

I race with a local club that uses scca pax. So I am looking to win not fastest raw time. I also am 2 hrs from Packwood and plan there next year.

talon95

So, are you saying you will be running in a class that is based on PAX?? Or will you just be running in either A-street (street tires) or SSR (R-comps)??

The car will be about equally competitive in either AS or SSR with the respective tire.

Your competitiveness on PAX will be about equal on either tire also (with the respective AS or SSR PAX), but this will be surface/course/condition/etc... dependent (no I disagree BrenB). PAX is a fun bench racing tool, but is pretty useless for determining class position IMO.

woody6244

Not trying to have a quickest raw time. We get 60 to 80 drivers and have classes grouped together, I run with SS AS BS and CS.

brenb

Yeah I misread, I was thinking he meant the PAX multiplier would change for course dependency, not the impact on relative finishing position.

If you want to win on pax I'd recommend a focus ST in GS.

Racing on PAX is terrible, and even worse this year is the street tire PAX which is based on little to no actual data.

Anyway, I agree with your local guys that Hoosiers will generally get you higher in PAX, and besides, they are a hell of a lot more fun.