Underwhelming Turn-in

BmacIL · Jul 10, 2017

Norm Peterson said:
What does the front suspension lateral link use for its chassis side pivot bushing? Compliance there for the more important outside front will directly reduce the amount of negative camber and indirectly cause the toe to drift toward 'out'. On the inside front, toe would migrate inward and camber further negative None of which is good for response.

Norm

A big-ass bushing. The reasonably-priced spherical bearing replacements are just hitting the aftermarket.

Donaldman · Jul 13, 2017

I have the same suspension/set up, even ran 285's all around, tested the tangible differences of going to a 285 front tire and noticed lower lateral G's and a slightly slower time, and harder to control. i lied to myself and kept my car like that for a while, finally switched back to 265 in the front and holy crap, first day back at the track G' were significantly higher, turn in was way faster and overall was much easier to control be nimble with. IMO you can upgrade the car to handle 285's better than it does but the sweet spot for me has been a 265 tire in the front.

my 2 cents.

jasonstang · Jul 13, 2017

Donaldman said:
I have the same suspension/set up, even ran 285's all around, tested the tangible differences of going to a 285 front tire and noticed lower lateral G's and a slightly slower time, and harder to control. i lied to myself and kept my car like that for a while, finally switched back to 265 in the front and holy crap, first day back at the track G' were significantly higher, turn in was way faster and overall was much easier to control be nimble with. IMO you can upgrade the car to handle 285's better than it does but the sweet spot for me has been a 265 tire in the front.

my 2 cents.

How wide are the front wheels?
Maybe they are just too narrow for the 285?

lugz · Jul 13, 2017

jasonstang said:
How wide are the front wheels?
Maybe they are just too narrow for the 285?

That was my thought too. I'm running 19x9.5, which is on the narrow side, but *should* be OK for the RE-71.

NightmareMoon · Jul 13, 2017

9.5" wheels are fine for the 285 RE71R.

A little toe out will probably make the biggest difference, at the expense of being a bit more darty on the highway.

In general, as previously mentioned, softening the front suspension (swaybar) will increase front grip, and getting yourself some decent camber is also a good idea. FRPP specs are suitable for a street car, not for track/autox.

If you have adjustable shocks you can play with those too.

wmfateam · Jul 13, 2017

IMO from my personal testing, I would say a 285 is too wide, performance wise, for a 9.5 wheel. I ran a 255 and 275 back to back same day on a 9 inch wheel, same tire (Maxxis RC1) and was over .5ths faster with better turn in, steering feel and mid corner feel. In a left/right application, you want as close to a stretch, if not a small stretch as possible.

BmacIL · Jul 13, 2017

wmfateam said:
IMO from my personal testing, I would say a 285 is too wide, performance wise, for a 9.5 wheel. I ran a 255 and 275 back to back same day on a 9 inch wheel, same tire (Maxxis RC1) and was over .5ths faster with better turn in, steering feel and mid corner feel. In a left/right application, you want as close to a stretch, if not a small stretch as possible.

That would be true for feel in most cases. That said, for autocross, you want as much grip as you can, and can usually afford to sacrifice some precision/feel to get it.

wmfateam · Jul 13, 2017

BmacIL said:
That would be true for feel in most cases. That said, for autocross, you want as much grip as you can, and can usually afford to sacrifice some precision/feel to get it.

Ah, yeah I have no useful info on parking lot things.

Norm Peterson · Jul 13, 2017

NightmareMoon said:
9.5" wheels are fine for the 285 RE71R.

When competition class rules don't let you run wider wheels, that's when it's fine because any direct competitors driving the same model car as you can't run wider wheels either. No need to restrict yourself to SCCA's F-Street rules unless you're specifically competing there.

Even a 285/xx RE71R is going to be better supported on an 11" wide rim than on a 9.5 . . . and a bit better-behaved up around the limit.

Norm

Norm Peterson · Jul 13, 2017

BmacIL said:
That would be true for feel in most cases. That said, for autocross, you want as much grip as you can, and can usually afford to sacrifice some precision/feel to get it.

As much grip as you can get on limited-width wheels. Important distinction.

FWIW,
I have a MPSS track set, 285/35-18 on 11's, and a MPSS street set, 265/40-18 on 9.5's. Tread widths on the ground are the same at 10.2", but the track set is noticeably more linear and better-behaved at 0.91g than the street set is at 0.84g when driven on the same test loop. g's per datalog, no other changes in car setup.

Norm

qtrracer · Jul 22, 2017

I have MPSS 285/19 on the rear; 265/19 on the front. Run 1/8" toe out on the front; 1/4" toe in on the rear. Turn in is crisp. Cold pressure needs to be at 30 or under (I had two readings - sensors and gauge; two pound difference). I ran 31/30 cold based on sensors. 20 minute track at Summit Point Shenandoah. Lots of turns on that course. Also have KW v3s set at their spec. Car handled very well.

BmacIL · Jul 22, 2017

Norm Peterson said:
As much grip as you can get on limited-width wheels. Important distinction.

FWIW,
I have a MPSS track set, 285/35-18 on 11's, and a MPSS street set, 265/40-18 on 9.5's. Tread widths on the ground are the same at 10.2", but the track set is noticeably more linear and better-behaved at 0.91g than the street set is at 0.84g when driven on the same test loop. g's per datalog, no other changes in car setup.

Norm

Agreed on all counts, Norm.

Stuntman · Aug 7, 2017

Where's your turn-in issue? On the street, autocross, road course?

Is it turn-in response and or corner entry front grip?

Youre losing a lot of response by putting a wide tire on a narrow wheel the 285 RE71R has a 10.1" tread width. A 265 would be a better fit with it's 9.6" tread width.

lugz · Aug 7, 2017

Stuntman said:
Where's your turn-in issue? On the street, autocross, road course?

Is it turn-in response and or corner entry front grip?

Youre losing a lot of response by putting a wide tire on a narrow wheel the 285 RE71R has a 10.1" tread width. A 265 would be a better fit with it's 9.6" tread width.

I noticed it on the road course and ax, particularly with sharp, relatively low speed turns, but it's really gotten on my neves driving on the street. Corner entry front grip might be a better way to describe it. The car just "feels" a lot heavier than it is. Think when I wear out these RE-71s I'm most likely going back to a 275 40. Just not a good selection of 200TW tires in that size.

Stuntman · Aug 7, 2017

It's probably your camber. Where does FRPP recommend -1.6*/-1.98* camber? The GT350R specs are -1.75*/-1.25*

A probe type pyrometer is the best way to dial in your alignment but I think your issue is too much rear camber. Stand the rear up to -1.25* or the stock 1.5* and see how it responds. Softening the front bar will hurt turn-in sharpness and response but will help with front grip mid corner, especially hairpins, if you aren't rolling over on the outside of the front tire.

Underwhelming Turn-in

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