THSCC Forums

So which one would you rather have?

245 tire with a 56mph 2nd gear and a *tad* better acceleration or
275 tire with a 60mph 2nd gear??

The 275 has almost 0.75" more tread then the 245

I can't decide which one to get!

-Tom

Ask me next year. We will be going from 245's to 275's on the Talon. More width, more grip, and more $$$$ for tires.

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Vincent Keene
'06 Ford Mustang GT (track rat)
'15 Dodge Charger R/T (yeah, it's got a HEMI!)
'07 Ford Fusion SE (205,000 miles and counting)
'98 Chevy Z-24 (retired)
'93 Acura Integra (Team SWB 24HOL Car)

You need to try both, which can be expensive. I think I would give up a little overall acceleration for more overall cornering grip, but that's in a FWD car. In an AWD car, it's a whole different ballgame. - AB

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'14 Toyota Sequoia Platinum 4WD
Super Westerfield Bros - '93 Integra - LeChump Du Jour
STX 93 - Scion FR-S

Tom - I have always considered 60 MPH in 2nd to be a sweet-spot for a car with torque for the typical event in this area. Keeps from shifting to 3rd too often. When I was running with little wheels on the BMW and a 54 MPH limit I hated it.

What can you hit in your WRX now in 2nd?

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Mike Whitney
whit32@gmail.com, 919-454-5445
V10, V8, V8t, I6, I6, V6, F4t, I4, I4, I4, I4, I2, 1, 1

I think he's talking about tires for the STi. But I could be wrong... I'd probably lean towards the 275's for the extra width and the extra (taller) gearing. Seems like the best of both worlds in terms of cornering and not having to shift as much where the acceleration difference can't come close to counteracting.

I'm having a similar but opposite dilemma deciding between running 225-45/15's or 235-45/13's next year. I ran the 15's this year but I think (changes daily pretty much) I'm going to switch to the 13's next year. The 13's happen to be wider but might give me more power-induced traction issues (which I can luckily turn down) due to the shorter gearing. They will also drop my speed in 2nd gear to around 59mph but I think I can live with it for the extra cornering grip. I think...

Jim

I was also leaning towards the extra cornering grip, its not like the STi is lacking anything in acceleration and sapping a tad of that might just *help* by keeping the rear of the car in line Convert the car into a little more of a momentum maintenance car.

Whitney - great point! I didn't think about what the WRX is now

WRX is 62 mph now and I could use a *tad* less.

I guess the way I'm trying to think about it, is that with high grip of the STi and the 300+ HP, I *will* be hitting 60mph on courses that I normally wouldn't hit that fast in the WRX now. For example, even at the last night ESA course I was on the rev limiter through the finish. On race tires I woudl have been on the rev limiter WAY before that. Also, the 1st slalom at sanford last event there. I carried rev limiter *through it*.

-Tom

Tom,

A couple of potential factors in addition to the ones noted already:

1) What class (Stock/Street Touring/Street Prepared)? For some cars the extra width in an R tire might not let it heat up enough to take advantage of the wider tread. I suspect that with your car and driving style that won't be an issue.
2) What wheel width(s)/diameter(s) for the two options? With a relatively heavy car, a wide tire on a relatively narrow rim may cost responsiveness unless the rim diameter is increased also.
3) Gearing is an issue but so is weight (both the rotational aspects and the unsprung aspects).

All that said, I believe Peter Raymond did rather well in his stock Miata with relatively large tires compared to other competitors.

Since I'm typically traction limited out of common corners with my FF, I found that going from a 60mph gear to a 66mph second gear was a good move.

Being able to stay out of third can be a big advantage BUT only if it doesn't hurt the corner exit accel and/or the balance/ability to turn in and then accelerate. Are you traction limited now out of corners or are the tires hooked up? If you are traction limited out of most relatively slow corners then the higher traction and taller gearing could be a double plus since you may get through the corner quicker (which will help the gearing anyway) and may be able to get the power down sooner.

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Dick Rasmussen

FS 50 2018 Mustang GT

My 2nd is 57mph and it's a few mph short of ideal. I am on the limiter or up-shifting a lot more than I'd like on our courses. Sounds like power is not going to be an issue for you, so I would consider the 275's and enjoy the top speed and the cornering advantage.

1) Its in AS on the STi, on 7.5" rims. There were a couple of competitors in BS that ran 275s on 7.5" rims on the same weight car (350z). Not heating up the tires as much was an advantage as with the front heavier car they don't overheat so they wear *better*

2) 7.5" wide wheel. I wouldn't have believed either that they fit, but carter made me into a believer

3) Didn't think about that. The 275s would probably be a bit heavier. With me running heavy wheels already..hmm......I will check into weights...

Here is an excerpt from an email from carter on 275s on a 7.5" wheel
"We are running Kumho victor racers and Hoosier 275's
on 7.5's. They fit pretty good, I would not say
perfect. both tires bulge a little but I do not think
it hurts performance much. We could tell a big big
difference between the 245's and the 275's though. The
275's are much better and I would recommend trying
them. You have to remember that my car is very heavy
(3150) and with no camber adjustments up front. This
puts allot of stress on the front tires so the 275's
can handle it much better.
"

-Tom

Tom,

That is certainly credible info from Carter!!!

If I ever buy autocross tires for my Mustang I'll have to seriously consider the 275's. I certainly have tons of low end torque and the car has 8 inch rims. It only weighs a little more than the 350Z and no more than your car and even has slightly less front weight than yours (according to road test specs). We won't mention the unsprung rear end weight of a solid axle Mustang or the height of the engine

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Dick Rasmussen

FS 50 2018 Mustang GT

Tom,

What brand of tires are you going to use? Reason for asking is that the Hoosiers may not be as happy with a 7.5 inch rim as Carter's Kumhos were. Note that it appears that the Kumho 275's are 40 series vs 45 series for the 245's. The specs show the essenially same dia for both. If I read the specs right, the Hoosiers do have different diameters.

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Dick Rasmussen

FS 50 2018 Mustang GT

Tom,
245 vs 275. What aspect ratio and diameter. I got the 7.5" width part. I'm trying to figure out what tires in 275 would fit a 7.5" rim safely. My car has 275/40-17 all the way around. The rims are 17x9.5. Recommended is 9-11" rims.
Graham

I was going to use the Kumho V710s. Carter tried hoosiers and kumhos. He ran hoosier nationally and kumhos locally.

Now that I think about it, I just assumed the kumhos came in 245/40/17....It looks like they don't

So options look like this now
1) 275/40/17 kumhos <- best option
2) 245/40/17 hoosiers <- might work just as well
3) 235/40/17 V700s <- seems to thin and too short
4) 245/45/17 victoracers <- I would prefer the below size to this one..
5) 255/40/17 victoracers <- would be perfect if it wasn't a victoracer



I am talking about 275/40/17. Mounting race tires and street tires is a little different. Tires this wide can be mounted on wheels that thin if they have a stiff enough sidewall of a race tire. I wouldn't do this with regular street tires though. I will be using falken 245/45/17 as our street/rain tire.

-Tom