highroller101

I’ve read lots of reviews including Emilio’s recent write up, but posing a slightly different question…

Preface: I like the consistency and grip of the Toyo RR tires, however they only offer up to 245s (I wrote a petition email asking to add 275s and they responded they will evaluate demand). My current setup is 15x8 kosei k4r and 225 Toyo RR.

I’m planning to upgrade wheels and tires. So looking for input:

15x9 dekagrams wrapped in Toyo RR 245
15x10 dekagrams wrapped in Toyo RR 245
15x10 dekagrams wrapped in Nankang AR-1 275
other options?

more info…
dedicated track car
supermiata sway bars 1-1/8 front
afco coilovers 650/450
-4.0/-3.2 camber
9lives airdamn
9lives big **** (being installed)

Arca_ex

iTrader: (2)

You don't make enough power to warrant 275's quite yet. Going to a 245 on a 15x10 is already borderline overkill, you also don't have enough spring to take advantage of that level of grip either and will find yourself wanting new suspension soon and as you get faster you'll need bigger brakes.

highroller101

Thanks for the reply, my car has a c30-74 Rotrex making 177 at the wheels, I’m gathering parts to upgrade to c30-84 with a 75mm pulley hoping to get in the 210-220 hp range. I have my eyes open waiting for a set of gen2 xidas to come up for sale, but with the afcos they will accept up to 900lb springs.

as far as the brakes go, I have a proportioning valve that I need to install and I run dtc60s with srf fluid, no ducts yet. I have zero brake fade, but the brake’s definitely leave something to be desired. I easily lock up the fronts and know I need to dial in more rear brakes.

if the 275 is that much overkill, how much of a difference are 10’s over 9’s?

emilio700

iTrader: (3)

He's right. Your car will be faster on 245's. We have built a bunch of NA/Nb track cars from 100-450whp over the years. Depending on the track, you need north of 350whp to be faster on 275's. Autocross benefits from being over tired, but full size road courses don't.

Outside of Hoosier R7's, the Nankang CRS V2 is the fastest 245 for the NA/NB right now. Probably 1-2s faster a lap than the RR

highroller101

Emilio,

a 200TW tire is faster than a semi-slick 40TW? I was about 1 sec slower on the RRs than R7s, but truth be told I don’t know the true age of the R7s as they were stickers but in a garage for who knows how long.

emilio700

iTrader: (3)

First step is to ignore UTQG treadwear ratings, they mean nothing and have no bearing on wear rate or grip. They are stated relation to other tires within the same brand and have no relation to tires from other brands. And even within the same brand they are all over the map.
Nankang's 200tw CRS V2 is way faster than their own 100tw AR1 for example.

GRM publishes the only real controlled data on tire performance, worth a digital subscription just for that.

highroller101

so read all the articles from them but I didn’t see them compare the crs v2 against the RR, just the R1R and R888R. They did a shootout ar-1 vs RR vs RC-1 and said the Toyo RR was the best of the bunch but not by much.

so if your recommendation is 245 crs v2, would you run 15x9 or 15x10?

out of curiosity why do you not subscribe to more width = lower lap times? I get frictional drag, but the wider the tire and larger in diameter, the larger the contact patch leading to better braking and on the gas longer… do you disagree?

emilio700

iTrader: (3)

Wheels should be same width as tread measurement, for best grip. 7" tread = 7" wheel, 11" tread = 11" wheel. 245's best on 10's.
Yes, frictional losses. Not a matter of whether I agree with or subscribe to, just decades of data from many sources show the crossover point to be well above your power level.

Avg road course min speeds in corners is between 70-90mph. Radials generate max lateral grip at a slight slip angle, 1-2%. That means dragging all 4 (very sticky) tires across rubbered in pavement at say, 80mph. You need to not only be able to maintain that slip angle, but actually accelerate past the apex.
But if you're determined to run 275's, go for it. If you want to know the actual data rather than just relying on intuition, then you'll need to conduct controlled testing. That means same car/driver/day/track/weather and two fresh sets of tires.

Diameters about the same for al the sizes you mentioned BTW

Funny that GRM test. We did the exact same three tires about 5 years ago when the AR1 was first released. Rented Streets of Willow for just us. 3 drivers, 2 cars I think. Came to the same conclusion. Were considering making the AR1 or RR the spec tire for the Supermiata Race Series we ran in California. It's now Super Spec Cup. I switched them to Hankook RS4's right before I handed the series over to its new owner.

highroller101

Ok,

so just to be clear you are saying the fastest combo after R7s is a 245 CRS on a 10 rim?

how many heat cycles do the crs last? Or run then until theirs no tread left?

highroller101

Picked up a set of 15x10 dekagrams from Goodwin. CRS v2 will be on order closer to season start!