Bullwings

How much faster do you think a 17x10.5 on 275 RC1 is compared to a 17x10 255?

Also, to all the rest of you clowns, did you immediately go to Phil's Tire Service and order up all of the 17x9.5 +47s in black? They contacted me saying they got wiped at super faster and were really surprised. I tried ordering up 6 black wheels... guess i'm getting silver now...

anorexicpoodle

Pretty confident a 275 will be universally slower than a 255 everywhere but streets of willow (or similar tracks where mechanical grip is rewarded over speed).

The drag penalty paid is real, Dustin did back to back tests and even with 400hp, the penalty was 8mph on the front straight of big willow.

imstimpy

I bought my two sets from speadfreaksusa and had great service. They also show an affordable Spoon 17x9.5+63.

DavidNJ

Maxxis specs show the two sizes have the same OD and the 275 only .3" (7.6mm) wider when measured on a wheel 1/2" wider (9.5" vs 9.0"). What causes it to have a higher drag?

https://www.maxxis.com/catalog/tire-450-107-victra-rc-1

anorexicpoodle

Thats a question for newton. My best guess is it squares off more rather than being a slight stretch on a 10" wheel, combined with a heavier carcass (ive lifted both, its tangible).

Regardless, the results of a back to back test was 8mph at the end of the straight with similar exit speeds from T9.

We only compared 10" wheels, we have lots of them (949 6UL's). The results were enough to discourage me from running the 275 on an NA car which is already fighting for top speed.

Also worth noting, no tangible improvement in lateral grip over the 255 through T2 which is a high speed sustained right. A 255 RE71R posted noticeably better grip than the 275 RC1, proving compound over girth.

Perhaps they would perform better with a slight strech (10.5 or 11" wheel?). As it sits, they were disapointing.

DavidNJ

I find the whole think dubious. This is a picture of a 225/40 Hoosier R7 to a 255/40-17 RC-1. Hoosier says its tire is 9.6, Maxxis says theirs is 10.5, yet the Hoosiers are wider. I'm guessing one of them isn't being accurate in their specs. Maybe its the Hoosier. Otherwise, why is Sickdayracing using 225 R7s when the 245 would fit the TT5 rules (rules: 266mm, spec: 262mm)?

I found this review of the RC-1 on a Miata (Maxxis RC-1 - Race & Track Driving (formerly Win HPDE) ) that implies that it may like a lot of negative camber.



This is the Hoosier 245/40-17 on a 9.5" rim:

Have drivers done back-to-back tests on rim width? It would be interesting to see a driver doing consistent lap times due back-to-back runs. The change should have a small effect on sidewall stiffness and a slight change in OD. Tread width, molded into the tire, shouldn't change. More sidewall stiffness could be a detriment, depending on shocks tuning and the rest of the setup. 1/2 inch of rim width, especially within manufacturer's specs, seems unlikely to make a huge difference.

Sickdayracing

What do you guys mean by "main tire"? If you are taking about the fastest, it is the Hoosier R7. The RC1 is a great tire to go out and do practice laps on but depending on the track the 225 R7 is 2-4 seconds faster then a 255 RC1. People run RC1s but they aren't going to win if there is a competently driven Hoosier car there.

I started TT late last Summer and my total Hoosier expense has been $150 for a set of scrubs. From then, I won multiple Hoosiers and have placed 1st and 2nd in every TT I entered in as a TTC, TT4, and TT5 car. I typically go out and do 2 warm up sessions on RC1s and 2 fast sessions on Hoosiers.

225 R7s are wide as 255 RC1s and 245 R7s are way wider then a 255 RC1. The 245 R7 measures about 265mm and will not fit the 266mm tire template on a 9.5" or wider wheel. I will be testing it on a set of 17x9 TC105N's that I bought and research shows that it will probably work.

RC1's are an excellent tire regardless. Last year, I did 3000 miles total including driving to events at Watkins Glen all the way down to VIR. I had 38 heat cycles on them and they were still fast and had plenty of life when I took them off.

roel03

Just an FYI: the 17" TC105N don't fit in the rear if you have adjustable upper ball joints. I learned the hard way this weekend.

DavidNJ

Why not run an 18" wheel? Hoosier has a 245/35-18 that is 24.4" tall with a 9.4" tread. Hoosier recommends an 8"-9.5" rim and it tests at 9.9 in section width on an 8.5" DOT test rim. It should be just at the ST5 266mm max on a 9.5" rim and definitely pass on a 9" rim. There is probably a better selection of 18" rims available and it should clear any suspension links and brakes with a bit greater margin.

BTW, what do you folks run in the rain? The Hoosier H2O? A non-race street tire? Just park it as the crash risk is too high?

Bullwings

Thanks. I just went with Phil's since I already had the order on hand. Silver might be nice. I've been running black wheels for so long, it'll be a nice change. As for the spoons, that's really good price, but +63 is too high of an offset, especially for a 9.5. I'll definitely have problems rubbing the inner upper wheel well.