bselltiz

Last year I ran Toy888's on my stock C6 rims for HPDE. Sizes were 305/30-19 and 265/35-18. The Toyo's are said to run wide. That being said there was quite a bit of crowning, where the tire bowed out from the point it mounted on the rim.
I don't have anything to compare them to, and I need to buy a new set. Will the crowning negatively affect the performance? Should I go a size skinnier?
Thanks,
Brian

meldog21

If you are experiencing crowning you should seek medical aid immediately.

http://medical-dictionary.thefreedic...y.com/crowning

Chances are you will be very "tired" soon.



Oh, going a size skinnier is always a good choice.



Dog












Sorry, I couldn't resist.

bselltiz

introitus - entrance or opening to a hollow organ or tube

Hey, we learned something :->

JoeDubya

People autocross successfully with tires like that. The main effect you should
worry about is uneven tread wear. An oversized tire can still work fine, but it
will be more sensitive to your getting the pressure right. If the side wall is
stiff, it will try to roll the outside edges up, as if you have too much pressure.
So, take your tire temps across the surface and get them as even as you can
for your purposes, and you should be OK.

bselltiz

Not too worried about uneven treadware since these tires seems to heat cycle out before they are close to getting worn down.

Would a size smaller give me better performance?

JoeDubya

As long as you are getting heat into the outside portions of the tire, you are
most likely getting more traction than if you went narrower. Wider is almost
always better.

bselltiz

hmmmm, opposite of what meldog21 said

JoeDubya

Winning Tip:
"Wider is almost always better. It is usually worth doing whatever you have to do to get a wider tire under the car, even if it means a larger tire diameter. Every single time we put a wider tire under the car (even if it was taller) we went faster."

http://farnorthracing.com/autocross_secrets4.html

geerookie

I think he was talking about choices in women, not tires

Narrower tires can be a better choice depending on many variables.
Some of them are sidewall stiffness and is the tire rolling over when cornering.

Weight, which effects un-sprung weight, rotating mass and has significant gyroscopic effects which contribute to "feel" and turn in.

bselltiz

Idk, fat chicks usually try harder...but I digress

Do you think the tire is more likely or less likely to roll over if it is wider than the rim it is mounted on?

Bill Dearborn

Last year I tried running some R888s on my Z. The front tires were 305/35/18 mounted on stock C6Z front wheels. The tires were crowning since the wheels were an inch and a half narrower than the recommended width for the tires. I ran a low air pressure in them to get the tread to make contact but under hard turns the tires rolled over and the edges wore much faster than I anticipated. The steering also had a vague feel although that didn't bother me that much.

Bill

geerookie

More likely.
If the rim is wider than the tire the forces have to push much harder against the side wall to get it to roll. Most racing tires are designed for the sidewall to be perpendicular to the track.

froggy47

Yep.

John Shiels

It will simply come down to which one has more rubber on the ground. Larger tire might not heat up a fast or it could if you are sliding around. Popping a tire size over recommended (10-15MM) on a rim is not the end of the world but I would not go much more.

meldog21

Ding ding ding ! Yes, I was talking about women.

Sorry if my poor jokes and sarcasm don't always translate well in a post on the forum. Just trying to add a little (very little) light hearted humor.

You can tell a joke isn't very good when you have to explain it.

Dog

Shaka

Mmmm. Nice name. This is serious stuff. Do you want tire failure? The tire must fit on the rim it is designed for. If you cant find the right tire size, you must change the rim or wheel. Manufacturers may differ on the tread width even if it is the same size as it's competitor..
NASCAR has varying width treads on their tires. The construction of the tire is quite different for each. Each NASCAR team may have as many as 25 different structural designs during one race depending on which corner of the car the tire is mounted, the type of surface of the track and the changing conditions during the race.
A wider tire than what is specified for the rim can give you less grip than the narrower tire if it is the wrong size. You don't increase the contact patch with a wider tire, just the aspect ratio of the patch. A wider tire changes the %tage of the contact patch that is slipping relative to the fraction that is gripping if the sidewalls are at the design angle .
Buy placing a wider tire on a narrow rim will give you crowning or correctly, reverse curvature. An absolute no no.
The 30/35 series tire has critical apex construction and should not be forced to run at a sidewall angle that it is not designed for. The construction and materials will determine how long it will take to fail, but fail it will.
A high aspect ratio tire has high enough forces in the sidewall and carcass anyway which is further aggravated by camber thrust and track irregularities without compounding them with the side wall operating at adverse angles.
The sidewalls may experience spike loads of 2000lbs and more across one and a half inches shared by both sides relatively evenly in normal conditions.
Low profile tires already have high camber stiffness which generates huge amounts of camber or twisting torque. You have just prevented the tire from working properly. You won't understand what the car is doing on the track.
A wider tire on a narrow rim will increases the stresses in the belt and carcass cords and bead wires, plus the stress distributions will be uneven across the tire. The tread will flutter which will lead to pressure points and concentrated wear on the tread surface.
That wear underscores much more serious internal deterioration including belt separation especially if there are steel plies.
The tires work really hard for their living. A tire failure can cost you big time. Always stay within design limitations.

PDF: Race Car Tire Modeling

http://www.google.com/url?sa=t&rct=j...UV_HGTaRu4e36A