Picking New Tires, Trying To Get More Front Grip

ScottOmatic

Hey,

I have been laboring looking through hundreds of posts trying to gain the necessary information needed for when I buy new tires a little later this summer (Still on the stock sport package RE050's at 22,500 miles).

There has been a lot of great information given out and I thank you all for that, it is really helping me hone in on my choices.

As the title states though, I am thinking about taking some of the grip away from the rears and bringing it up towards the front. Not that the Z understeers all that much but I think I would like to free it up a little more by getting more contact with the road with the front tires.

Maybe this is not the smartest way of going about it, maybe it is a dumb idea, maybe it isn't even possible to make much of a difference with out the VDC light coming on all the time (which I don't really want to see) but I figure that if it's possible to loosen the car up by changing the tire size at the front, this is going to be cheaper than upgrading the suspension (currently I am stock everything besides exhaust) and I got to get new tires anyways.

Below I have attached an image from a tire size calculator, comparing the stock tires to common options I found on tirerack.com (I think I was primarily looking at sizes in the Bridgestone S-04 Pole Position simply because there are a lot of choices, for the sake of punching in numbers into the calculator).

If I am doing and processing everything correctly, the only way to get more surface area and thus more grip to the front tires would be going with something like 245/45R 19 or 275/40R 19, everything else that is wider (that is available) is in 35 or 30 sidewall percentage and that actually comes up short compared to the stock size and thus, less surface area and less grip (in theory).

If I were to think that the 245/45's seem like a nice bump up.. if we then look at the rears, the stock 275/35 is 675.10mm OD, 3.5mm smaller than the stock fronts (245/40).. they are now 18mm smaller than the fronts if the updated 245/45s. I am guessing thats a pretty big difference and will cause the VDC light to go on constantly.

The other issue is I don't think I want a lot more front sidewall than rear sidewall, if aesthetics mean anything to me, I would much prefer the rear tires having a fatter sidewall.

I could bump the rears up to 285/35 19's for a 1.04% increase but that still might trigger the VDC and the sidewall will be noticeably smaller than with 245/45s at the front, or even 270/40s on the front (if those even fit).

I could leave the fronts at the stock 245/40 and try to thin out the rears a little with a 305/30 (665.60mm OD) or a 295/30 (659.60mm OD) but I am not sure that is the right way to go.

I may just end up going with the default sizes if this idea doesn't pan out.

If anyone has any insight on what I am trying to do here, please feel free to share your thoughts. Thanks!

Attached Images

tire_sizes.jpg (215.2 KB, 31 views)

PharmDZ

275/35r19 square setup = quick understeer fix. Don't have to complicate it all too much - they fit more than fine on the stock Rays. It's the setup a lot of street autocross guys go with. I daily drive on Hankook RS3 275/35r19 tires front/rear. You don't want to create a bigger gap in size difference between the front/rear or that'll make the understeer worse.

gomer_110

275/35-19 Bridgestone RE-71R's all around if you want grip. Also, based on the results of the very wet Toledo Pro Solo this last weekend they do well even in the wet.

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MacCool

You are making the incorrect assumption that increased contact patch surface area will increase traction or grip. Friction is not dependent on surface area. A wider tire won't get you more grip.

kenchan

like i stated on the other thread, we need to all run bicycle tires..

JARblue

All things being equal, an increased contact patch surface area will absolutely increase grip. But it is not the only factor, nor is it necessarily the most important. There are a number of factors that affect grip, many of which directly influence the contact patch surface area. Things like tire pressure, tire temperature, camber, and wheel width can all affect the size of the contact patch.

OP, I agree with the first two responses. Try a 275 square setup and see what that does for you

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ScottOmatic

Thanks for your input guys,

I heed all of the info you have given, I understand the science of it may not be so cut and dry to understand but I will certainly listen to anyone that has gotten good results on their rides.

I did see the RE-71R's mentioned in another thread ( think it was the tail end of the RE-11 thread) but with the tire being one of the newest with less info on them, would like more info on road handling in the wet and tread life.

I drive the Z maybe 5,000 miles a year so tread life isn't the biggest concern, and if does fairly well in damp conditions, I might as well pick something in the Extreme Performance Summer category over Max Performance Summer Category.

My main thought with putting a wider tire on the front, such as the square setup was that even if you have a certain side ratio and wider tire width, with the rim only being 9 inches wide compared to 10 in the back, the tire might crown considerably more and the contact patch may be considerably different.

If people say 275/35r 19's all around are good, I certainly won't argue with that.

Or I can take Kenchan's advice and put bicycle tires on.... the back!

MacCool

Uh...no, it absolutely will not. The OP is on a fool's errand.


.

Brendan

So then what would you recommend?

Rusty

Care to explain please.

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Red__Zed

People always say things like this because the Physics 101 equations (F.friction = mu * F.normal) say friction isn't dependent on surface area, but the Coulomb model has a couple of holes in practice, especially in regards to car tires.

Increasing contact patch does help with a tire for a couple of reasons, especially because we are concerned with traction, rather than just friction.

One element is maintaining stability over rough surfaces. A wider tire gives you more opportunity to have rubber in contact with the road, as the tire deforms over imperfections. If you've ever cornered on a road bicycle and hit something mid corner, you'll understand why this is important.

Adhesion plays a role in traction as well. If you slap a piece of tape on your desk and try to slide it, you can see this. It will be very difficult to slide, despite a very minimal normal force acting on it. Adhesion comes into play on car tires as well - there are dozens of SAE papers out there on it, and the Wikipedia page on friction has some links for you as well.

If you really want to get into the weeds on cornering performance, a wider tire also tends to help with slip angle. And of course heat management comes into play.

Other reading:
https://en.wikipedia.org/wiki/Tire_load_sensitivity

Red__Zed

To OP: I'd go square. Best modification I made for my Z's handling.

ScottOmatic

Thanks,

I was just searching most of the points you have made here a half hour ago, lot's of things going on here.

Another interesting factor that I saw brought up was viscoelasticity. Tires are not simple creatures.

MacCool

Slip angle, rough surface traction, heat management, and therefore cornering performance, assuming you're pushing it hard enough to generate that much heat that it matters, are absolutely valid points in the discussion of traction vs friction. The OP is contemplating differing tires sizes to manage understeer/oversteer. Those factors don't come into play. He want's to "loosen it up" and "free it up a little more by getting more contact with the road with the front tires". We're back to high school physics.

Red__Zed

You're neglecting adhesion in your response. And oversteer/under steer is just f/r management of traction...

That basic equation assumes minimally elastic solids. Surface area matters more as the material becomes more elastic.

There are a lot of good resources to school up on traction out there. I'd recommend taking a look.