How to maximize lateral grip?

[zipdoa]

So, as per this:

http://www.caranddriver.com/features/effects-of-upsized-wheels-and-tires-tested

It appears that depending on the car, lateral grip will be maximized at a certain wheel size, and will actually decrease beyond that point.

I had plans of running these 20x9 A8 W12 wheels with 275/35/20's on my Allroad, but am now wondering if 18x8.5 RS6 or 17x8 A6 S-line wheels would provide better lateral grip. I understand that unsprung weight will affect handling, but I'm more so interested in what will achieve maximum lateral grip, given the same brand and model of tire.

For reference sake, Audi ran 255/40/17 and 255/40/18 correspondingly on the 17x8 and 18x8.5 wheels from the factory.

For arguments sake, lets say I'm choosing the Michelin Pilot SS.

Does anyone feel like weighing in with some nasty physics to help educate me on this subject? I always thought that a wider tire would equal more grip, but that doesn't seem to be the case.

Aesthetics don't matter too much to me, as both sizes of this wheel look fairly good:

20x9 D3 W12 S-line Wheels

http://www.fourtitude.com/gallery/albums//Features/Feature%20Cars/allroad%20Plus/032.jpg

18x8.5 C5 RS6 Wheels

http://www.audizine.com/gallery/data/504/medium/IMG00041-20100907-0947.jpg

17x8

http://cimg7.ibsrv.net/gimg/www.audiworld.com-vbulletin/640x480/picture_php_pictureid_95602_2ab7ef5a9f7f492514530fd6d8b6010f913f94d9.jpg

[rage2]

It's a very complex set of factors that determine absolute lateral acceleration of a vehicle. But to answer your question as dumbed down as possible, assuming the same tire width and rolling diameter, the larger the wheel size, the smaller and stiffer the sidewall, and the smoother the road surface is needed to maintain maximum lateral acceleration. Bigger wheels also weigh more, and more unsprung weight means more sensitive to bumps, as well as the mass that the tires are trying to withstand before breaking loose. That's why there's a point of diminishing returns in the real world, even though the wider tire has a longer contact patch resulting in lower slip angles at the same lateral G's.

Anyways, there's easier ways to find cornering speed before looking at wheel sizing.

1. Lower center of gravity.
2. Less weight.

Those are the easier ways. After that then you can figure out what wheel is losing grip first (typically front on a street car) and work on increasing grip to that wheel through alignment, suspension work, without trading off drivability.

[Chrisw]

So this guy didn't nail it? He was going for less slip angle...
https://files.nyu.edu/rq265/public/images/rim3.jpg

Lets be real for a second. You don't care about the slip angle. It's a street car. You should be far more concerned about what you think looks good and what RIDES well. You are not going to be pushing that wagon to it's limits so don't worry so much about extending that limit the slightest bit. It's not a race car... It's just a cool looking audi :thumbsup:

[rage2]

Slip angle of the tire, not the car lol.

http://en.wikipedia.org/wiki/Slip_angle

[mr2mike]

My guess is you don't need 19's to get better lateral. Tire type and brand is more important. Look for a set of P Zero Corsa System tires.

Then look for suspension upgrades.

IMO, on the street, you can have 275 tires but your body roll will be out of control. Also, roads around here aren't too smooth and this will kill you and your performance.

Go 20's and don't care about lateral performance.
Go 18's and spend the rest on good track tires.

[zipdoa]

I love the way the 20x9's look in that first pic, but it seems more logical to follow what Audi spec'd on the RS6 and go 18x8.5 w/ 255/40/17 Michelin PSS.

Keep in mind the allroad has air suspension, and I'm not really interested in going to coils. I can go as low as I need to using the 402-mod. I'm also adding hotchkiss swaybars, and I think that will be about the limit of practical handling modifications.

The allroad is a pig and won't ever be competitive in the corners, but this is all good information to have when I source an R33 GTR.

[T-Dubbs]

if you are worried about lateral grip, you bought the wrong car.

[zipdoa]

Originally posted by T-Dubbs
if you are worried about lateral grip, you bought the wrong car.

Your intellectual contribution to this thread is invaluable.

[Twin_Cam_Turbo]

Don't worry so much about the weight of the wheels as the type of tire and alignment/suspension choices in my opinion.

[94boosted]

Just curious as to why you want to achieve maximum lateral grip? Are you planning on tracking or autocrossing the car?

If it were me, out of those wheel choices I'd choose the 18x8.5, stick a good sticky 255 tire on it and then focus on sway bars, shocks, springs and alignment.

[My_name_is_Rob]

Originally posted by zipdoa
I love the way the 20x9's look in that first pic, but it seems more logical to follow what Audi spec'd on the RS6 and go 18x8.5 w/ 255/40/18 Michelin PSS.

^ Fixed for you. :thumbsup:

[Shlade]

Originally posted by 94boosted
Just curious as to why you want to achieve maximum lateral grip? Are you planning on tracking or autocrossing the car?

If it were me, out of those wheel choices I'd choose the 18x8.5, stick a good sticky 255 tire on it and then focus on sway bars, shocks, springs and alignment.

This. I'd get an 18x9 though to run a 255 personally. Really think 275's would be a little overkill. Would plant the car evenly I'm sure but 255's all around should do the trick on a 18x9 wheel. Could do 18x8.5 but might stretch a little which I don't think you want

[94boosted]

Originally posted by Shlade


This. I'd get an 18x9 though to run a 255 personally. Really think 275's would be a little overkill. Would plant the car evenly I'm sure but 255's all around should do the trick on a 18x9 wheel. Could do 18x8.5 but might stretch a little which I don't think you want

I was only suggesting the 8.5" because that was one of the OP's 3 options and supposedly the factory runs a 255 on both the 8" and 8.5"

[Shlade]

I guess it depends on the tire. I wouldn't really go more than a 255 set up on that car

[zipdoa]

Yeah, keep in mind I used my allroad as an example because it's the vehicle I'm going to buy wheels and tires for this summer. I was curious to find out why wider tires don't always equal more grip, as per the article I linked in the OP.

I'll be grabbing the hotchkis swaybars and going with either the 17x8 or 18x8.5's, depending which are easier to find. Definitely going to run 255/40 regardless.

[mr2mike]

Yeah don't run too aggressive rims if you're going to have to camber them out and lose part of the tires placement on the road.

[Tik-Tok]

Originally posted by zipdoa

I'll be grabbing the hotchkis swaybars and going with either the 17x8 or 18x8.5's, depending which are easier to find. Definitely going to run 255/40 regardless.

Are they making them again? I tried ordering them for 2 years but their die was broken or some shit, so I gave up.

Oh, and *cough*shamelessplug (http://www.eurodrivers.ca/forums/showthread.php?27103-FS-Vertini-Riviera-19-quot-x-8-5-quot-5x112) *cough* (I'm sure you've seen them already though)

[Shlade]

I see absolutely no need to have his wheels cambered at all for what he's hoping to achieve

[tsi_neal]

Originally posted by zipdoa
Yeah, keep in mind I used my allroad as an example because it's the vehicle I'm going to buy wheels and tires for this summer. I was curious to find out why wider tires don't always equal more grip, as per the article I linked in the OP.

I'll be grabbing the hotchkis swaybars and going with either the 17x8 or 18x8.5's, depending which are easier to find. Definitely going to run 255/40 regardless.


Assuming correctly sized tires wider wheels will make more traction, the article didn't do this, they plus sized the diameter and the width. more diameter doesn't always work out, as described by rage. Other thing to consider is traction is dictated by maximizing the contact patch (size and shape) on the ground. If I use a 225 tire perfectly its going to have a far better contact patch than a 255 used poorly, and make more traction. This is where alignment, dampers, springs/swaybars, and bushings all come into play (in that order). A well designed suspension is a full system just not one component.

I will also agree with everyone in here that says for the street whats the point. Its very easy to do to much to a car in the handling department and while it might be a delight on the track it will be plain miserable on the street. Also the limit could get so high that pushing it on the street is stupid and dangerous. IMO for a street car run what wheel/tire you think looks good and get an alignment that suits your driving to maximize tire wear.

[SkiBum5.0]

Careful of the 17" option as it will limit tire choice. PSS has way more options in 18."