Spyder_Venom

This is a debate that I have been listening to for years (literally).

Do you think that you will increase handling and traction by going to a wider tire - for example going from a 17X9 to a 17X11?

Please debate.

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The local track whore

FastShark85

Wider tires are NOT better in the snow (not that you asked).

You'd be better off getting a better quality 17x9 tire than a poor quality wide tire.

Tire quality issues aside, traction will be better with wider tires since there's more rubber hitting the pavement. Not sure about handling, but I suspect the same is true.

I've got 17x7.5 in the front (Toyo Proxes) and 17x9 in the back (Kumho Supra Ecstas). I very rarely lose traction, and I've got 320+ hp. Both the Toyos and the Kumhos are budget-priced (about $115 per tire) and have experienced very little wear in the 10,000+ miles I have on them.

Booty Man

werd. BTW what width tires are you runnin' on the 17X9's??

FastShark85

My 17x9s are 255/40/17.

Spyder_Venom

I want to mention I am speaking from a 100% performance, dry pavent point of view.

Also I am not suggesting any one tire size over another. The 17X9 vs. a 17X11 was just a point to start from since it is a common upgrade for drag racers and road racers alike.

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The local track whore

FastShark85

Well, I use 16x7.5 all around during the winter months, and I can tell you from experience that both handling and traction are worse on the narrower tires. However, I have to admit the 16" tires are probably lower quality than my 17" tires and are being replaced with Blizzaks for the snow. Swapping wheels and tires twice a year probably isn't too common, though, but it works for me.

FastShark85

By the way....what kind of car are you driving, Spyder?

Spyder_Venom

I have a 1995 Firebird Formula... Its not a street car, this is a debate that has been beat into the ground through out the SCCA community and it usually is very intresting to listen to. Its not a simple awnser by any means but its always intresting to listen to what people have to say.

Later on I will post some info reguarding my findings

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tinfoil

As everyone said, wider tires suck in the winter....

And on dry pavement I would assume that rotational mass would eventually cancel out anything you gain in traction. Get insanely large and the extra rolling resistance and wieght etc....

*shrug* and then again I may just be talking out of my ass.... again.

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FastShark85

I've got a buddy who races his 928 at auto-x events. Instead of getting wider tires, he went with race slicks, but he really tears through those things fast.

Ramega

Rotational mass is not the important physical property here. You are concerned about two things: coefficient of static friction and, more importantly, coefficient of dynamic friction.

The wider the tire the less downforce per square inch of the tire you have on the road. The coefficient of static friction plots on a linear graph for materials with a very low coefficient of dynamic friction. Therefore if your tires were made of marble then it wouldn't matter how wide they were. 1" wide tires would provide lots of PSI to the pavement but would have a small contact patch. 10" wide marble tires would have a much larger contact patch but less PSI to the pavement. The result would be the same.

Car tires, however, are sticky. That changes everything. Car tires rub off on the road (which is why you get black shit in your beer at a NASCAR race) and therefore wider is better. You eventually run in to problems steering and fitting the tires under your fenders, but basically you should go as wide as you can afford and your car will allow.

Just my $.02

FastShark85

Again, make sure those are wider, high quality tires, or you'll not be any better off.

Spyder_Venom

"wider tire will not put any more rubber on the ground because as long as the car's weight remains the same the same amount of tire will be in contact with the road. For example (totally made up numbers, here), if a 7-inch wide tire puts a 7x2" patch on the ground, then an 8-inch tire will put an 8x1.75" patch on the ground... no more rubber than before.

I know my examples are super-basic. But I'm sure I've said enough to clarify my question. "

A pratical example of what Ramega was getting at. This is where things get fun. Wider tires will have a differnt sidewall profile that a narrower tire. Now the dynamics of the slip angle on a wider tire will be differnt then the dynamics of a narrower one.

Remember that tires are done as a ratio of width to height so sidewall then would become a factor in this debate. Just as some ammount of body roll helps our car on the skid pad, so does the flex of the tire's sidewall. The smaller the sidewall the less area there is to flex, that is a given. But the thing that is over looked is the fact that the fast way through a corner is by using the correct slip angle. This is discribed as a felling of a very small mount of push in the car. It actually is a veriance between the tires direction and the acutal direction of the car. This differnce is in one part by skid and another part by the flex within the tire. With a thinner side wall you have a smaller performance envolope for the tire to operate in. This will make it signicatly harder to control the slip angle while also making the car more subseptibale to "coming around on you".

So after all this is said and done I would assume you are thinking, there is a performance envolope to tires. There is a point of deminishing returns..... Wider = more unsprung weight an a smaller AND lighter contact patch. Also since you have more tire mass with less friction it requires more time to heat up the tire and longer to cool off. Remember, tires need to be warm to get traction. Then again, we can't run a 13X5 on cars.... that just wouldn't work.

The debate goes on.......

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The local track whore

Vogad

Wider tires WILL put more rubber in contact with the road (given that tire circumferance remains a constant).
Problem is that there's a lot of variables to consider (ie; air pressure, sidewall height, tire ratings, ets,etc).

Ashton

Spyder_Venom

A wider tire will not put more rubber on the road (althought it is commonly thought it would), there is less PSI on the tire (not air pressure) so the lateral contact patch will shrink. The footprint of the tire then becomes wider but shorter with a wide tire. Its a ratio if you shrink it one way, it grows the other way.

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Scorps

My van has wider tires on the rear and they never slie but the front are skinnier and they will slide in the rain, and make loud noise when they get warm.

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Spyder_Venom

You are dealing with many factors there that you have not taken into account - 1 rain isn't apt for performnace, 2 differnt weight distrobution, 3 differnt forces being applied to the tire, 4 lack of proper suspesnion setup.

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The local track whore

Ramega

Wider tires can allow you a greater contact patch, for sure. You may have to fiddle with your air pressure, but you can certainly do it. A lot of drag racers run wider tires with less pressure, thereby giving them a bigger sticky patch.

And yes, the ideal solution would be a tire that extends the entire width of the car like a rolling pin.

Scorps

Well has run great for the past 10 years, so im going to leave, the body is going so im going to take the engine rebuild and into the S10 it goes. the rims will be redipped and I will have suspention set to handle them kick ass Crager SS's

350Z

lowering the tire pressure increases traction by increasing surface area, but not by as much as youd think, because more surface area just means less weight per square inch, which technically means identical amount of traction regaurdless of contact patch, like if 3000lbs is on a single square inch, itd be the same as 2 square inches with 1500lbs on each. but the world isnt perfect, and its much more complicated than that.

but lowering the pressure and wider tires creates massive amounts of drag. so make sure you have the power needing these tires or they can actually slow you down in the long run. good traction compound and a properly tuned suspension can do wonders without hurting drag.

*owner of 9.5"rims 275/40/18* and they are a bit wide for the car I have them on, I need about another 100hp no joke, before that much tread is really worthwhile. but Id rather have the traction before I add the hp rather than add it and suffer for 5 months.
my 2 cents

phatman

Spyder's post about the correct slip angles is essentially 100% correct. There is an envelope where going wider will give you better performance but depending on the wheel it will drop off eventually.

And if your sitll interested about all the real theory behind how all of this works I highly recomend "Race Car Vehicle Dynamics" by the Milliken brothers. Everything you want to know is in there.

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The.Lunatic

Bassically what he said.

Wider will increase wear on your powerstearing and axle ballberrings if your not carful.

Spyder_Venom

Okay, I see now that you guys posted about air pressures and remember at the top I posted "with the same air pressure".

See the issue with lowering tire pressures it it GREATLY effects handling. So now your running into the issue of you are going to give up handling for traction... well who gives a damn about traction down the streight if you can't turn worth a darn.... That is why I suggested keeping tire pressures at a constand. Once you talk about adjusting pressures then you need to take into account the differnce in performances between the two tires which is a verible that has a infinate ammount of awnsers.

Now in the 380 HP motor we run in American Sedan, I can get a 9" slick spinning (all throttle, no clutch work) at 50 MPH on a streight line, exiting a turn its even easier because of the lateral load the tire has applied to it. Now the funny part is it is harder to sping that 17X11 in a streight line but the ass end is much more "active" exiting a turn with the 17X11. The main reason is the profile of the tire has less give to it and it will not eat up the inperfections in the road. On top of it, the 17X9 will keep a larger contact patch (both on the X and Y axis) while under threshold weight transfers. By this I mean going from the max skid pad (lateral load) transfering to max horazontal load (acceleration). Both of these were done on a 35 series tire with what was considered optimal air pressures (not the same)..

Opinions?

BTW: Carol Smith's Race Car Setup books are another great series

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The local track whore

acpower

there is more contact patch in wider tires which means more chance of hydroplaning

WarWagon

BTW, with drag racing and reducing air pressure, there's more to it than just the contact patch. Air pressure is typically reduced to slightly lower than desired for optimal straight line traction, due the increase in pressure after the burnout. Also, a reduction in air pressure allows the tire/rear of the car to squat and the tire to wrinkle, allowing for optimal weight transfer.

The relationship of traction in regards to pressure and contact area is not linear, so one can't say that a narrow tire exerting x pounds of pressure will have the same amount of traction as a wider tire exerting lesser pressure.