Tom@TPC Racing

^ Correct, the toe curve is same as the bump steer curve, just a different name. Also correct, adjusting the toe setting is changing the static value within the curve but not changing the shape of the curve.

I'd consider the TPC links to be a bump steer correction product rather than a bump steer adjustment product since this product provides an improvement to the end user but not an adjustment for the shape of the curve.

Have a look at the graph in the bottom of post #1 in this thread-
https://rennlist.com/forums/gt4/9731...toe-links.html

jmartpr

Tom...correct me if I'm wrong...but you get less toe change with the TPC links across the whole suspension travel which improves rear-end behavior considerably on the strut type suspension of the 981.

Tom@TPC Racing

Its more than 50% reduction on the amount of toe deviation when the suspension travels exceeds 0.25" in either direction.

jmartpr

Update on the 275/675-19 Pirelli Slick DH....it fits nicely and basically same dimensions as a RE71R 245/35-20 (OEM Size)...as suspected they came in narrower than the advertised specs.
Checked dimensions and did a short drive around the shop going over bumps and irregularities...no rubbing or anything. Not even with the front brake ducts, which I was expecting to happen.
Of course we have to see with more suspension travel/movement like going over curbs.
You do need camber plates to tuck that tire in.....January 20th first track test.

TRAKCAR

jmartpr

I start mine at 26 psi so the Circuit mode doesn't go crazy and then bleed accordingly so by the end of the session I have a max of 32 psi.
I could start at 24 psi cold but then it takes too long to warm up to the optimum psi and our track days sessions are short between 10-12 laps, max 15 laps.
Be careful when doing the first 2 laps and bring the pressure up before going full and hitting curbs.
I find that at 30 psi the car behaves perfectly...if I see anything above 33 psi I slow down.
I'm also buying scrubs from GT Racing Tires but before using them I apply Keyser Hot Lap Tire Treatment.....it does help with temps and tires last longer while making them sticky, not new sticky but good enough for track day/ED.

911therapy

awesome, thx for the R&D!

TRAKCAR

Thank you. Appreciate the info confirming I'm on the right track.
For a 2 day. 8 cycle lifetime, probable don't need to treat them?

jmartpr

No Problem...I would treat them anyway........try to use the Hot Lap Victory Lane formula.....it last a long time (+200 laps) but it's detectable, for track days is not an issue.
Tires do wear much better with this stuff. Any little thing that help with tires is good!

GT3 Jockey

Peter the slicks are far better than Hoosiers. Their "therapeutic" window is very narrow. And they take longer to come up to temperature. So you have to be patient when you first go out. I usually start 21 in the front 24 in the back and shoot for 27/29 hot pressures. You should easily get 8-10 heat cycles out of them. The other good thing about the slicks is that the grip doesn't fall off the cliff like it does with Hoosiers. You'll notice in your lap time that the grip is not what it used to be but the loss of grip is not as sudden and dramatic as it is with Hoosiers.

TRAKCAR

^^ Thanks.
I did the same start pressures 20 all around, my rears come up a lot more then the fronts but that's an RS thing.
I will shoot for 30 hot to be on the safe side. On Hoosiers I even had to start a bit higher in front because with ST rotors its harder to get heat into the fronts!

After all the broken Hoosiers, even with careful heating up for two laps to get them to 28 before going, I think I will start higher and then bleed, it didn't help with Hoosiers (Going out 26, bleed after 3/4 laps) but I hope it will prevent issues with slicks.
Not looking for laptime, I just want the tires not go bad on me for two days!

jmartpr

My GT4 does the same thing...but it could be the track also.

jmartpr

I had a chance today to compare and measure Bridgestone RE71R in stock 20" size with the Pirelli DH in 275 off the car.
The Bridgestone came in at 9.8" (exactly as advertised) section wide.
The Pirelli DH in 275 is 0.5" wider than the RE71R, so not much of a difference to cause problems. It came 0.5" under the advertised spec.
That means that my previous Pirellis DH in 255 were narrower than stock (also a bit more than 1" lower). The 275 is 0.2" lower than a stock tire.
I will try them at the track in a week and report how the car handles vs the narrower 255.

jmartpr

TRACK UPDATE

We just did our first 2019 track day.......275s DH worked perfectly...no rubbing, no cutting of the front brake duct, nothing....The car has much better turn-in than the 255s (of course they are wider!!!) and the height is almost OEM, just a tiny bit lower up front.
You do need to mount these on 9" rims. I also liked the idea of more sidewall so I can feel better about going over the curbs in turns. Very happy how the car felt and times were very consistent. Was able to beat my personal best (1.05:80 vs 1.05:92).
Have already two track days on these DH scrubs and they still have good life left....times have been very consistent. Maybe new one could shave a few tenths but for track days this are more than OK.
I also attribute part of this to the Hot Lap treatment. This stuff works and I highly recommend it if buying scrubs...you can even do it on new tire so they last longer.
Pressure wise we ended up at 30 psi all around....even with Nitrogen you will need to start very low (22-24 psi) to end up at 30-31 psi....our you can go out with 26 psi and then bleed. Outside temps were in the 80s F
As far as Alignment we ran -3 camber up front, -2.5 rear. Front toe out - 2 mm total and Rear toe in 3 mm Total....I do have Tarrett front camber plates, TPC rear toe links and DSC for this alignment to work.
So there you go guys...R&D is done and hope this info helps those going for PIrelli DHs......Just hope my track/wheel setup also works on the new 718 GT4!!!!

TRAKCAR

^^^ Thanks!

my 0.02c:

I ran Pirelli HD the last 4 days at Sebring.
Had to go out on 19PSI to keep them under 30 where they are the fastest.

Chasing PSI down with the rising temps all day, I pretty much ran them at 35 hot, going down to 32/33 when I had traffic.
I wanted to be safe while trying them out so I didn't mind, they offered about the same grip as new Hoosier R7 (2:13's/2:14's).

I did 8 sessions on the first set, the last 2 sessions the rears were done, losing 4 seconds a lap, I estimate 2 secs due to typical Sebring temp and track and 2 secs because the rears where done.
Mounted the next set, I did 7 sessions on those, they performed the same, losing a bit of an edge in the last session.

All in all a success. I will try to run the next set a little lower, keeping the rears under 32 and the fronts under 30.
You guys were right, thank you !!

I have 3 more sets for the next 6 days at Sebring, next week Tuesday and Wednesday David Murry (open track all day) followed by 48 hours at Sebring Thursday through Sunday.

The car looks a bit goofy with the skinny 275 in front and the 315 in the rear but it all works fine so far.
Another luxury over Hoosier garbage is that not one rotated on the rim!