1. I've always wondered if going wider adds friction...
My physics class would so NO...but I am all ears to those who know the real world and what they know from experience (as opposed to myth and folk law)....
As an engineer, I know that friction does not depend upon surface area. As a car nut, I know that wider tires have better traction. How do you explain this contradiction?

note: 255/40's is as wide as we can go on our SLK32's 17" rims, where as you SRT guys are pushing 285's on 19's...= much more contact area.

2. Another thought as well was a discussion around how much wider on a rim can you go..
My thoughts are - if your tire is much wider than your rim, the tire wall will bulge and not provide the cornering stability you may want from time to time. The SLK32 has 217mm rims (8.5") - so with 245/45/17 tires as spec you get [14mm overhang] on each side.
With my 255/40's I've increased that to 19mm and you can definitely tell (visually).

3. But....does this added bulge help you with hookup?
Much like the top fuelers - as you hook - you have some absorption in the tire wall which stores energy and helps you even out hookup. Is this a real consideration?
Low profile tires would obviously work in the opposite direction = harder to hook. Is this your experience?
Would I get better hookup if I went to a 16" rim with a 245/45? There are factory SLK32's that came out with such a tire configuration.

 

What type of engineer? If you go to TireRack there is a ton of info there. Under tire info for each brand is a min and max wheel width for each tire width. and the recommended width. You are correct in assuming that too wide a tire will result in some sidewall bead instability. It will also decrease your footprint unless it is run under inflated. I wouldn't do it despite what a lot of guys have said on this forum. Your biggest footprint will come from the largest tire you can fit both width and diameter. Smaller wheels with bigger ratio tires will have equal contact area as bigger wheel with lower ratio tires, width being equal but the softer sidewall of the smaller wheel higher ratio tire combo may help you hookup a bit better. But will not be as stable in high speed cornering.

 

I just had my new tires mounted on my 2002 SLK32 AMG last week. Prior to this I had heard stories of guys smoking their tires and such. Well I tested that and left a black streak 30-40ft. long in the street and I also left smoke that was as high as the street poles and it followed that black streak that we'll call 35ft. down the street. I have never seen such smoke from spinning tire as I did that day and it was from my car! Usually it is some other car that does such a thing.
Sitting in my living room were a pair of 255/40-17 TOYO PROXES R888 road race tires that are D.O.T. legal. At my sisters were the fronts, a pair of 225/45-17's. I called the Tire Kingdom and made an appointment to have these tires mounted.
Well I'm no baby when it comes to pushing my car but my fear to push the tires has yet to overcome the adhesion these tires have on the roads where I do most of my driving! These tires stick! You even listed the extra size I went with on the rears also. This gave me the first opportunity I had to get under the car and check things out. The rear set-up even had what seemed like enough to install a wheel with the width an extra 1/4" extra both inside and out. I love the look of wide tires on my cars but they must fit in the allotted space given by the engineers of the car. My all time favorite is the Porshe 911 turbo that has the rear wheel wells designed to hold whatever size tire that fits them, great look! Thanks for the thread, Mark
PS: I can no longer smoke the tires!

A taller tire with a patch that is long rather than wide will create better traction, another study for the physics class.

 

perform this thought experiment: you have a very tall tire and a very squat wide tire. You test both tires on perfect, slightly wet ice. No traction. Now, use the same tires on a dry asphalt surface. The surface is comparatively rough and provides millions of hookup points for tire treads.

At the molecular, nano and micron scale there are no irregularities in the surface of the ice into which the molecular, nano and microscopic irregularities on a tire's outside surface can interlock and push against. It is the interlocking of these irregularities that we call friction and provides the transient instantaneous pushing that converts the rotational tire forces into the linear force that creates forward motion. This is why the wider contact patch works - it provides a larger statistical opportunity for millions of micro hookups that a taller tire cannot (practically) provide with its smaller contact patch.

I have often wondered why drag racers don't experiment with sticking (super strong) sandpaper to the track (grit facing up) for the first 30-60ft of a run. Has anyone ever heard of someone trying this just for fun?

 

[QUOTE=Billy22Bob;829275]1. I've always wondered if going wider adds friction...
My physics class would so NO...but I am all ears to those who know the real world and what they know from experience (as opposed to myth and folk law)....
As an engineer, I know that friction does not depend upon surface area. As a car nut, I know that wider tires have better traction. How do you explain this contradiction?



Cars driven for maximum fuel efficiency such as those used down your way in the electric car competitions will typically use skinny tall tires wanting to have as little friction as possible.

Real world that.

Unless you are concerned with same, I suggest as wide as you can go to add as much friction as possible when accelerating, cornering and braking.

Friction can provide for positive results.

 

Tire Tech Information - Contact Patch - Tire Rack

www.tirerack.com › Tires › Tech

 

Tire Tech Information - Contact Patch - Tire Rack

www.tirerack.com › Tires › Tech

For those who do not read every post made in a thread

 

Wider tire on narrow rim has excess tire roll and loose slight tread contact and tire will roll more in cornering,
Wider rim with narrower tire will make a stiffer sidewall.

They are pushing 285 on stock rims just a hair over reccomended (9.5 - 11 for a 285) yes it fits but will roll tire more in cornering , 305/30 is max size that will fit but 10.5" + rim is needed (305/30 - 10.5 - 11.5).
I thinking about getting tsw bathurst 19x10.5 and can be perfect for 275 I running now (275/35 - 9-11 width rim) and can run wider for my summer tires if I want.

 

a) traction is fractal, only partly to do with friction
b) ever hear of "unladen understeer" ?