Large rear tires in the twisties

[ModsAway]

Running a setup like 275 front 315 back, what does this do to the handling characteristics of the car?... Ideally a fatter tire is good for launching but what about the twisties? Sprited street driving I'm sure is fine but ideal for auto x or open track applications?

Thanks.

 

[goodquest]

bump

 

[KOOY]

same quesiton.

 

[sir-blah]

I have 315's out back. Mine almost seems to float around, wouldn't probably do well on an auto-x. You're right though, launches are awesome, but I think I need some suspension upgrades and an alignment to get back some handling.

 

[DaleM]

Last OCT I did HWY 129 aka "the tail of the dragon", has it's own WebSite. My 315s scraped about 1/8 inch inside the inner fender well lip. Just enough to remove the paint but not cut the tire. i also have 1/2 spacer to clear everything.

 

[ygohome]

the 315/35/17 nitto on the rear of my car with 17x10.5 wheels seem to float around a bit too. They are slightly taller and softer sidewalls than the 275/40/17 used to be. don't know if michelins or bfgs in the same 315 size would have similar "float" issues.

 

[briantt]

I would think it would cause over steer. But for the straight line it's great. If the stock cobra rims where a bit wider it would'nt be as bad.:burnout:

 

[toofast4u]

Those that are complaining of float have you changed your IRS assembly bushings yet? The stock bushings cause a floating sensation especially when you use a sticky rear tire. I run a very stiff suspension set-up with 555R 315s in the rear and I don't float.

 

[ygohome]

I havnt change my rear bushings. I heard they are a pain in the butt to change though... but maybe I will anyways, its scary sometimes the way it is now. Thanks - Ben

 

[toofast4u]

Originally posted by ygohome
I havnt change my rear bushings. I heard they are a pain in the butt to change though... but maybe I will anyways, its scary sometimes the way it is now. Thanks - Ben

I have changed mine and they are definitely a memorable experience, but they do significantly change the handling especially in turns.

 

[ShelbyGuy]

larger tire on the back increases understeer.

 

[predator]

Originally posted by ShelbyGuy
larger tire on the back increases understeer.

.........Which is already a problem in our cars. Like toofast4u implied... if you are going to any type of serious "twisties" then you need to think about the bigger picture..i.e. tuning your suspension.

 

[SVTCobra2001]

Not talking about any rubbing. If you put more grip in the rear you are going to increase PUSH.. So when you make the turn your car tires will slide and you will not turn. For street use it will not hurt anything. For AX you are hurting your times. This is speaking on the line of stock or minor susp. mods.

Eric

 

[KOOY]

what is the float? Could someone explain a bit more? thanks..

 

[predator]

Originally posted by KOOY
what is the float? Could someone explain a bit more? thanks..

The lack of that sharp, responsive feeling in the IRS because of the rubber bushings used in the UCA/LCA/diff/SF...(Upper control arms/lower control arms/front and rear differential/IRS-to-subfram). These flex under load and greatly dampen the responsive capabilities of the IRS giving you that "floating" feel and thereby inhibiting the ability to have a truly exhiliarating driving experience! :thumbsup:

 

[cito]

I have 305/30/18's in the back. The understeer seems no worse than with 275's and traction out of the corners is much improved.

 

[toofast4u]

Understeer is caused basically by the rear tires having more traction then the front tires. What happens is the front tires travel in a larger arc then the rear tires through the turn. Understeer is after referred to as plowing, push, or being tight. Oversteer is the opposite condition where the front tires have more traction then the rear. In oversteer the rear tires travel in a larger arc then the front tires. This is often referred to as being loose, tail-out, or drifting. Of the two oversteer can be a very dangerous configuration for new drivers which is why most car manufactures design there cars to have understeer from the factory. Several things cause these conditions to occur some are behavioral and some are structural. The stock Mustang chassis is notorious for understeer and a large reason for it is due to the uncontrolled movement of weight from the front to the back while corning. This can be minimized by increasing the rear spring wheel rate. Adding larger or stickier tires is going to increase the traction potential of those tires, but in a properly configured suspension set-up this will already be factored into the configuration.

 

[Jimmysidecarr]

Originally posted by toofast4u
Understeer is caused basically by the rear tires having more traction then the front tires. What happens is the front tires travel in a larger arc then the rear tires through the turn. Understeer is after referred to as plowing, push, or being tight. Oversteer is the opposite condition where the front tires have more traction then the rear. In oversteer the rear tires travel in a larger arc then the front tires. This is often referred to as being loose, tail-out, or drifting. Of the two oversteer can be a very dangerous configuration for new drivers which is why most car manufactures design there cars to have understeer from the factory. Several things cause these conditions to occur some are behavioral and some are structural. The stock Mustang chassis is notorious for understeer and a large reason for it is due to the uncontrolled movement of weight from the front to the back while corning. This can be minimized by increasing the rear spring wheel rate. Adding larger or stickier tires is going to increase the traction potential of those tires, but in a properly configured suspension set-up this will already be factored into the configuration.

That is exactly why ........ I LOVE THIS FORUM!!!!!
What an excellent write up....
No confusing "polar moments of inertia" crap.... Just meat and potatoes... here it is!:rockon:
Jimmy:thumbsup:

 

[larryc7777]

Many maximum performance vehicles utilize wider rear tires: Porsche, Ferrari, Vipers, Corvette ZO6, ect.

A lot depends on the TYPE of tire that we are talking about. The guys running drag radials have to expect to have a little bit of a "vague" feeling from the rear. These tires are designed for straight line traction. Their sidewalls are not as stiff as ultra performance street radials. Consequently, they flex more which in turn affects transition response.

 

[konakimo]

Originally posted by cito
I have 305/30/18's in the back. The understeer seems no worse than with 275's and traction out of the corners is much improved.

What brand of tires are you running, I think the only type of 305/30/18 that I could find was a auto-x road race style.