garudatwo

Hi folks,

Does anyone have laptimes/v-min data on GT4 Clubsports at Lime Rock Park, between race slicks and street tires (100tw+) please? Mainly interested in v-min for the left hander, up hill, west bend, and downhill, and overall laptime differences.

Thanks!

Frank 993 C4S

There is really no auch generic data because it depends on driver, setup, specific tire conditions, track conditions and weather conditions. You can look on YouTube to get Min speeds at corners across various cars and tire types. That's what I do when I sample data on a track I've never been to in advance of a race weekend.

ProCoach

I have data for the 981 GT4 CS and 718 GT4 CS (slicks and 200TW tires, endurance class racing requirement), on the same track with the same drivers, but not at LRP. Given that the vMin for the whole track is the Left Hander, I would figure 2-3 mph.

Biggest difference is in braking commitment and in throttle acceptance (not so good for ClubSports set up for slicks on street tires) between those two tires, so not sure vMin study alone will help you.

The other issue is that it's hard to find street tire data using the same level driver as you would see on slicks in top level professional competition (IMSA or SRO), so the variance can be magnified between a representative top slick time and a club level driver on street tires. At least that is my experience.

I would get Jonathan Goring or equivalent to do a back-to-back comparison, if you have the car and the tires.

ProCoach

Did a little research and can give you an approximate split on lap times, albeit between GT4 cars.

In AER competition in 2020, a pro team with a pro-am driver who is mid pack in very competitive IMSA and SRO races, did a 57.6 with 200 TW tires.

In IMSA this year, the leading 4 liter (718 GT4 CS RS) on slicks did almost exactly four seconds faster than that, 53.6. In 2019, a 718 GT4 CS (3.9) did a 54.3 on slicks.

garudatwo

Thank you so much Peter! I was thinking having vMin data would help me paper napkin baseline mechanical grip improvements, and thus minimum laptime improvements from moving to slicks. Basing off your estimates of 2-3 MPH for the Left Hander, with a PB of 93.3 average velocity, slicks would take my PB of 57.9 on street tires down to a ~56.1 at least, but I neglected to consider your point on reduction of time spent off full throttle. My goal is to setup a street based Toyota Supra to hit similar laptimes as the factory GT4 effort, with purely suspension+aero+tire changes. The AER datapoint is extremely helpful, and suggests I'm within striking distance!

38D

the AER car was I believe a 981. A 981 CS on slicks is about .75 secs slower at Line Rock given equal drivers.

i have data from my 981 CS on 200 TW tires doing a 57.9 at a test day. We were not exactly going all out that day, so I’m sure this is more there, likely in the high 56s. vMin in the left hander that lap was 63.5mph.

ProCoach

AER data from a 2019 M4GT4, Al Carter.

I agree that the 981 GT4 CS is .75 slower than the 718 GT4 CS is .75 slower than the 718 GT4 CS RS.

All on slicks with MacAleer driving.

63.5 sounds a little low to me. Must be a better tune than IMSA to make it up elsewhere. Good speed on street tires, though.

38D

Ah the Random Vandals car. That car was much faster in the straights than our 981 Clubsport at AER competitions. i'm guessing it had something in the 40-50hp more range. AER has since adopted a max power to weight which didn't exist back then.

Nope, stock tune on the car.

ProCoach

Interesting.

WRL has done the same thing, but cut the tune on both the Porsche, BMW and Aston GT4 cars.

Usually looking at 67.1-68.9 vMin in the Left Hander on slicks. Don’t have data for 200 TW tires.

paradocs98

I know the OP and his Supra, and he's fast. I mainly see the back of his car...

garudatwo

Thanks guys, found the Random Vandals vid to ref!

And thanks all also for the vMin data; I'm in the 62's there, there may be more that I can squeeze out but seems acceptable for a 3400 lb wet weight platform.

Matt Romanowski

Now use www.comparemylaps.com to compare you video and theirs to see where the time difference is. The delta functions in compare my laps is really powerful and will help you figure it out pretty quick.

garudatwo

This estimate turned out to be spot on! Was able to squeeze out a ~64mph on the left-hander on street tires.

LuigiVampa

The left hander is one of those corners where people debate what line is quickest. There is the line you took, which is sort of a double apex, a rim shot where you hug it tight, and then a line where you drive towards the bathrooms and then treat the left hander as a decreasing radius turn, getting tighter and tighter until you end up on the rumbles.

I like a rim shot if you are looking to defend the corner, but if you are looking to set up for the best entry into no name (ahem - Newman Straight), I prefer the decreasing radius. The decreasing radius turn allows you to end up perpendicular to the left side of the track for the short amount of straight before you make the right turn for no name. You do a great job of hustling over to the left side but by making your wheel tighter you can get all the way on the rumble, and be flat a tenth longer, as your car will be straight sooner.

No name is the second longest "straight" so the entry into the right hander is all important and getting the car set up properly is the key. Walking the track gives confidence as you will see that there is a nice amount of banking in the right hander into no name, as well as plenty of room to track out using the rumbles on exit.

garudatwo

Thanks LV, hopefully next Monday becomes a dry day so I can log the decreasing radius/school line! Any chance you're noticing other low hanging fruits for me to pluck some time from please?