Confirming what is legal for SCCA F-Street Setup

[Simmons-Racing]

Yes you can +/- the wheel size by 1" as long as the widths are maintained and and offset of 7mm is allowed.

In all honesty, I would try a few events with the stock setup and get a feel for how your car behaves before modding it for FS.

I took my GT PP out to its first autocross last Sunday. For reference, my previous FS car was a 2011 GT/CS with dual adjustable Konis, 18x8.5 Enkei RPF-01, Strano rear swaybar, on Hankook RS3v2. Out of the box, the GT PP is superior in every respect at the end of the day I was still looking for the limits on the 2016. I am still relearning all my braking points, you can go much deeper into corners carrying a lot more speed. The balance is much better. It doesn't push in corners where the old one would and it is much more responsive to trail braking. You can confidently get on the throttle sooner on exit as well. Steady state turns are great and the rear end steps out progressively and predictably. Transitions are a lot smoother.

If I have one complaint, it is with the tires. They aren't nearly as bad as a lot of people make them out to be. They are not however, very communicative particularly in rapid transitions. This problem is probably exacerbated by the heavy factory wheels.
Dumping some unsprung weight and stickier tires is about all I have planned at this point.

I totally agree, my 15 GT PP was way better then my 14 GT. All I did was tires and strut/camber mod, and was really competitive.

Simmons

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[z3papa]

Honestly, you'd have to spend some serious hours converting this car back to be F Street legal, you might as well look at STP or CAM-C but you need to develop the patience to read the rules, not gloss over them. If you had read the rules closely, many of your questions would not have been brought up or re-raised (springs). What I don't suggest you do is fudge the rules for local competition. Starts bad habits.

 

[Static_LV]

For what its worth, I have not experienced the wheel hop issues on mine at all.
I would take it out to a couple of events before doing anything to the car particularly if you are planning on staying in F-Street.

Also, keep an eye on the suspension thread about the PP vs FR shocks/struts. Hopefully someone is going to have a dyno of the FR's here pretty soon and I am very curious to see what the differences are if any between these and the PP.

 

[Syracuse315]

For what its worth, I have not experienced the wheel hop issues on mine at all.
I would take it out to a couple of events before doing anything to the car particularly if you are planning on staying in F-Street.

That's the plan at the moment, especially messing around with tire PSI.

Also, keep an eye on the suspension thread about the PP vs FR shocks/struts. Hopefully someone is going to have a dyno of the FR's here pretty soon and I am very curious to see what the differences are if any between these and the PP.

That will be interesting. I've seen a few posts claiming a massively improved feel, but haven't seen any back up except "the ford engineer I talked to said the were different" or "the part numbers are different."

 

[Static_LV]

Hot temps of 37 on the fronts and 35 on the rear worked very well for me with the stock Pirellis. Ambient temp was 65*-75* over the course of the day.
Surface was a mix of concrete and asphalt.

 

[Syracuse315]

Hot temps of 37 on the fronts and 35 on the rear worked very well for me with the stock Pirellis. Ambient temp was 65*-75* over the course of the day.
Surface was a mix of concrete and asphalt.

Thanks! I'm driving around town at 37 all around, and get a bit of hop on quicker take offs. I'll test out 35 in the rear tires and see if it helps.

 

[jdub.csu]

I ran 37 in the fronts and 34 in the rear on the stock pirellis and never had too much hop.

 

[kz]

Thanks! I'm driving around town at 37 all around, and get a bit of hop on quicker take offs. I'll test out 35 in the rear tires and see if it helps.

Of course you do as you are way overinflated. I ran 32 psi all around for autox and could go lower looking at wear. No wheel hop either. If you look at the FS thread, SteveW (much more experienced driver) was running 28 psi on Pirellis

 

[Static_LV]

Of course you do as you are way overinflated. I ran 32 psi all around for autox and could go lower looking at wear. No wheel hop either. If you look at the FS thread, SteveW (much more experienced driver) was running 28 psi on Pirellis

To clarify, those are hot or cold temps?

 

[SteveW]

To clarify, those are hot or cold temps?

Both. Start off at that pressure and maintain it between runs by bleeding off air pressure. The 28-30 was in the rear and if I remember right I was somewhere around 34 up front.

Higher pressures made the tires feel "edgy" to me or too narrow of a max grip window to drive through the elements at the limit with.

Pretty sure most everyone who was winning FS trophies was in the upper 20s to low 30s with PSI, even on RE71Rs.

 

[Static_LV]

That is interesting, the same tires on my last car (S197) really didn't seem to like lower pressures. They felt very erratic especially in rapid transitions. I will play with this a bit next time out.

 

[qtrracer]

Recently I've been playing with air pressure. The wheels are stock GTPP with MPSS at 265/285/40s plus a 7mm front spacer, stock bars and KW v3s (not FS legal). I run a K&N drop in, MM CC plates (camber is modest at -2* F; 1.9* rear), and replaced the resonator with an x-pipe; stock cat-back. Stock tune and other suspension pieces.

Three weeks ago I tried cold at 33/29 F/R. Course was about 53 sec for the fast cars, with ambient 92. PSI increased to 37/33 after the hour drive to the venue. Pre run paddock heat was 140/138 F/R using an IR sighted on the middle. In paddock the sun was on the DS.

After each run I measured front heat only which increased to 145 - but the heat was not the same for both sides (cooler on the PS). Course was about even for L/R turns with the one long sweeper a left hander. PSI stayed pretty much where it was after the drive in - 37/33 with the F never getting above 38.

impressions - The front stuck pretty well but the rear moved out twice which caused throttle lift and steering correction. As a result I did not have confidence the rear would stay where I wanted.

Yesterday, I started with cold pressures at 35/31 F/R. After the drive to the venue pressures increased to 39/35. I didn't measure heat this time. Ambient was 97. In paddock, sun was on the PS. After each run pressure increased to 40/36. Course was a big car horsepower design. Fast cars were in the 46s.

Impressions: The rear was much more settled and the front spoke much louder but stayed put. Much more confidence.

Take away: For these tires on this car at ambient in the mid 90s, running front cold at 35ish with a 4 psi spread seems to work well. Next week I'll try a little more cold pressure since the weather is projected to be in the low 80s.

 

[BmacIL]

I've usually liked a ~2-3 psi stagger and 31-32 F, 28-29 R hot with RE71Rs. MPSS/PS4S will need higher overall.

 

[NightmareMoon]

40 front sounds high, but your experience with the rear pressures sounds about right tho. Try keeping the fronts at 37 hot next time and see how you like it.

 

[Grintch]

I did and read every page, but multiple items above weren't mentioned specifically. Thanks for the clarifications.

Sure seems like a mustang running in FS has to just live with the wheel hop issues :shrug:

If it doesn't say you can, you can't is the rules philosophy in Street. The other FS thread didn't spend any time talking about those mods because they were clearly illegal in FS.

Several of your planned mods are also illegal in the higher Street Touring and Street Prepared categories. But you were smart enough to ask first, so good job.

Now you have to decide if you REALY want to do them anyway, and how you feel about that bumping you to CAM-C with some very highly modified cars.

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