SCCA Autocrossing- Time to take it up a notch

[TDC]

So after a season of autocrossing I've decided to get a little more serious.

I run a GT350 in AS class and am planning on buying a set of factory spec rims with the exception that SCCA allows for a change in offset of up to 7mm.

Question is should I max the rim offset front and rear or should I just use spacers instead so I could change offset at will?

For tires Im planning RE-71R tires, 19", 305 square.

Sponsored

 

[Zerobar78]

Just my .02 would I would feel a lot better having a proper sized wheel vs. a spacer, though I can't argue the convenience of a spacer.

 

[tedj101]

Just my .02 would I would feel a lot better having a proper sized wheel vs. a spacer, though I can't argue the convenience of a spacer.

I agree. I avoid spacers for track use.

<TED>

 

[Zerobar78]

I agree. I avoid spacers for track use.

<TED>

My buddy uses them for his track wheels on his GT500, but he has the upgraded studs and such so it's built to handle it.

 

[SteveW]

It is very common in autocross for competitors to use up to 1/4" spacers in stock classes. I use a set on my front wheels but use them for tire clearance on the struts.

How do the specs on 305 RE71Rs compare to the OEM tires? Do you think you would have clearance issues with the new setup? If so, a small spacer probably would help that. Or you could use the spacer to test if a wider track at one end or the other fixes a handling problem.

 

[TDC]

Re71 tread wear is 200 vs 300 for the factory pilot super sports.

Section width/ tread width/ overall diameter
11.9" 11.1" 27.1". Super sports front
12.3" 10.7". 27.4" Super sports rear

12.3" 11.1" 26.2". RE71 front and back

Since the overall diameter is smaller I don't believe I will have any clearance issues.

I noticed that Ford keeps the track widths consistent front and back from the standard GT350 and the R model. Maybe this is an indication that I shouldn't mess with the offsets. Then again they didn't figure it for an autocross setup.

I will use the factory rims for track days.

 

[NightmareMoon]

7mm isn't a whole lot. I don't see that being much of a competitive advantage unless you end up needing it for clearance (which you shouldn't). If it were me, I might go +5mm all round just for show.

+5mm is 5mm closer to the cones though

Glad to see someone using the GT350 for sport and putting some propper tires on it. I've seen a couple of Shelbys at autox events, but not yet driven by anyone who could push the limits very far. I keep offering to trade someone for my clearly faster GT w/ PP but none of the GT350 owners will take me up on it. :headbonk:

 

[qtrracer]

7mm is a bit more than .25". I've been running .5" spacers on my Fox for years. The issue is not shear-loading if the lugs are on per spec. Racers have been using spacer tuning for years.

To allow the most adjustability within the rules, I'd recommend spacers. The trick is finding wheel off-sets that allow you to go both +/-7mm on all wheels. Not an easy proposition. So short tracks with tight corners may need wider front track, whereas tracks with large radius sweepers my need a wider rear track.

At least the GT350 is closer to even F/R track-width in stock trim than the GT. Based upon my research, the new Mustang is set-up for a long front-travel/low roll geometry, so you will also need to consider that when modding the car within the rules.

 

[wildcatgoal]

I feel like your tire selection and driving skill to take advantage of their grip characteristics is going to affect a lot more than 7mm of offset/spacer. But if you want the adjust-ability and they let you use them - spacers all day.

Sponsored