Tire question, stock 235/50 so between these others, what say you?

Mr_Q · Mar 24, 2008

I am using the stock rim so I can't go too crazy but I would be mounting the tires for race day only. So I am not too concerned with "looks". They'll come off after the race.

My size choices for a usable range are: (tire is the Potenza RE01)

255/35
245/45
245/40

Which would be best, this is for all you auto-x and road course guys/gals. I am leaning towards more rubber on the ground so the 255/35.

Redfire 05 · Mar 24, 2008

Do you have a tuner? Because you will need to adjust your speedo for any of those tire sizes. They are all shorter than stock. And be sure you consider ride height as well. The 255/35 17 would lower your car a little over 1.5 inches. If you are using lowering springs as well you could be pretty close to the ground. I think that is why most people are going with 18's or bigger. You can have low profile tires without loosing a lot of ride height. So ideally you should go with 18's.

Having said that the 245/45's will drop you only 3/4 inch lower and I was looking at 255/45 17's which would drop you a little over a half an inch and they are a little wider. They might be better choices if your ride height is already low.

Mr_Q · Mar 25, 2008

Yeah I considered that. A lower center of gravity at the track is a good thing. The Shelby GT already has the complete Ford Racing suspension kit on it and is thus lowered as is. Also the car has 18s on it right now too, again stock.

Since these tires would be mounted *only* for track day I am not too worried about it. it will actually help. And as for the speedo I am not concerned with "watching" my speed at the track, heh.

Mr_Q · Mar 25, 2008

I know everyone is waiting in anticipation so I will post my final choice.

Bridgestone RE-01s in 245-45-18 (140tw)

This will give me .4" more overall width, only .3" lower profile and only a .6" overall drop in the car. Perfect.

And the speedo offset is: 65mph is really 63.4mph. So cop safe for me.

$952 shipped from Tirerack unless I can find better.

CBus 06 GT · Mar 25, 2008

Mr_Q said:
I know everyone is waiting in anticipation so I will post my final choice.

Bridgestone RE-01s in 245-45-18 (140tw)

This will give me .4" more overall width, only .3" lower profile and only a .6" overall drop in the car. Perfect.

And the speedo offset is: 65mph is really 63.4mph. So cop safe for me.

$952 shipped from Tirerack unless I can find better.

Umm, wouldn't a .3" lower profile result in a .3" drop

Mr_Q · Mar 25, 2008

CBus 06 GT said:
Umm, wouldn't a .3" lower profile result in a .3" drop

http://www.discounttire.com/dtcs/infoTireMath.dos

SpartaPerformance · Mar 25, 2008

Getting a lower profile tire isn't going to lower the center of gravity, it's going to lower the car. The center of gravity gets lower by control arm pitch and SAI angles.

CBus 06 GT · Mar 25, 2008

Mr_Q said:
http://www.discounttire.com/dtcs/infoTireMath.dos

Well, your ride height is affected by the radius of the tire, not the diameter. The center line of the axle to the ground only crosses the sidewall once, thereby dropping your ride height by .3, not .6.

Mr_Q · Mar 25, 2008

So their tire calc is wrong you are saying? That's where I got the numbers.

CBus 06 GT · Mar 25, 2008

tommyroc said:
Getting a lower profile tire isn't going to lower the center of gravity, it's going to lower the car. The center of gravity gets lower by control arm pitch and SAI angles.

The center of gravity would drop with a lower profile tire (.3" in this case). I think what you are talking about is roll center. Don't really know what it is except that suspension components affect it (thinking back to the days of following sprint cars and how different length radius rods and mounting points of those rods changed the roll center which changed how the car handled).

CBus 06 GT · Mar 25, 2008

Mr_Q said:
So their tire calc is wrong you are saying? That's where I got the numbers.

Not saying their numbers are wrong, I'm saying your application of the numbers is wrong. If the sidewall height is dropped .3", that's how much the ride height will drop. The diameter will drop .6", but half of that (the top sidewall) only shows up as a .3" larger gap to the fender.

Snooze · Mar 26, 2008

tracking your car. i would keep your 255/35 all around. or 255 rear, 245(or235)/35 front.

1) lower profile, and tighter fitting tire WILL improve handling and feel of the car around a corner. less slopp in the side-wall's. big bonus.

2) wider foot-print in the rear will give you better turn-out potential, and more grip after a hairpin.

3) skinny tire's will carve a corner much better. tire scrub is less of an issue, which gives you potential for more lateral G's.

if you go to the track with custom alignment (i'm not sure what mustangs run for toe to eliminate scrub) but my subaru runs +0.23degree's total on the front toe, and it definatly feel's tighter when taking a corner..

Redfire 05 · Mar 26, 2008

But mustangs come from the factory with understeer. Wouldn't narrower tires in the front and wider tires in the rear make the understeer worse? Unless you have corrected the understeer issue.

I mean yes, the narrower fronts would turn better at low speeds, but they would loose grip more quickly than the rears right? Unless you have a big horsepower car you really shouldn't need the bigger rear tires. With non-supercharged horsepower levels you should be able to easily control the power on oversteer by slowly applying throttle.

Mr_Q · Mar 26, 2008

With the front heaviness of our cars I am wanting to keep the tire widths the same all around. Skinnier up front is only going to promote understeer. And as long as I behave, power oversteer I can wrangle far better.

Snooze · Mar 26, 2008

with the traction that the re-01 will supply, i honestly doubt you'll have understeer issues more prominant than running a wider tire.

personal choice i suppose. I'm spoiled with my subaru when i'm on the track, the stang just feels like a dead-weight, while the subi is running 225/35 tires.

Mr_Q · Mar 26, 2008

From my time in the Subi I found it boring honestly. I mean once you mastered it's limits, the damn car practically drives itself!

I love tossing the big V8s around the track, too much fun! Like bull riding!

s1roush · Mar 27, 2008

Let us know how you like those tires.

This is my next set: Nitto Invo 275/40ZR-18

Snooze · Mar 27, 2008

Mr_Q said:
From my time in the Subi I found it boring honestly. I mean once you mastered it's limits, the damn car practically drives itself!

I love tossing the big V8s around the track, too much fun! Like bull riding!

Definatly true. some friends of mine that own other construction business i work with, when we go to the track its always hard competition for fast driving.

i've taken my mustang to have fun before, but when i try to pit it against a friends 05 porsche gt3. or another's fox body with 550hp and a xxx/65 tire. almost pointless!
it can't keep up to a gt3 in a corner (and its very hard pressed to meet it on a straight away without him making an error) and the fox when it hits a straight, makes up for any loss!

the gt3 owner also has a Cascar (cdn nascar) and holy ****.. 400hp, and maybe 1850lbs give or take 500. some of his employee's drive that car when its not broken down. and even for novice/amateur drivers, that car insanly fast.

Tire question, stock 235/50 so between these others, what say you?

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