Picking New Tires, Trying To Get More Front Grip
 

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!

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.

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.

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.

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

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 :driving:

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! :D

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


.

So then what would you recommend?

Care to explain please.

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

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

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.

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.

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.

Thank you for the enlightening response :tiphat:

:icon08: Let me get this straight. You acknowledge those factors are all part of cornering performance, then proceed to state that since the OP wants to manage under/oversteer those factors don't come into play.

:facepalm: Want to try that again?

Or maybe you can explain how to induce understeer or oversteer without turning the steering wheel :ugh2:

bicycle tires.

:iagree:

Wouldn't motorcycle tires be better optios?:stirthepot:

no need to add the extra width. it won't make any difference anyway. :stirthepot:

Oh damn you're right and i thought those were gonna be better for grip and cornering. Never mind!

Typical troll responses. Plenty of "you're wrong because I said so" with zero usable information pertaining to the OPs original question. Please stop wasting everyone's time. The rest of us are here for answers.

If you have a solution, state it. Otherwise, kindly feel free to fu[k right off.

Hey it's cool guys...

Due to the wealth of info provided in this thread, I was able to pick out the optimal tires for my needs...

http://webpages.charter.net/scottoma..._new_tires.jpg

The cards in the spokes are kick asss. :tup:

I can see this trend catching on with EVs so that the blind can hear them coming. =)

The basic equation accounts for adhesion as part of the coefficient of friction. Surface area doesn't matter.

The solution, obvious solution, to oversteering or understeering is suspension, not tires. I can't help it if your grasp of rudimentary physics is so lacking that these concepts are beyond your ability to understand. Public education apparently isn't what it used to be.

Hmm. I was going to suggest a square set up as well, but really in order to keep tire size and compound a constant more than to play with relative grip -- a lot of that will depend on alignment settings and weight distribution/suspension more than anything.

I guess you could buy ultra sticky fronts relative to the rears, but that sounds like it will just make the car unpredictable...

So, assuming equal sized tires of same make, you want to stiffen up the rear relative to the front. That means a beefier rear anti-sway bar and firmer damper settings in the rear and softer in the front, if you can adjust them. Any other bracing you can add to the rear (without adding significant weight) will tend to nudge you more towards oversteer.

I think, maybe a little more camber in the front relative to the rear will help tuck the nose in too... not 100% certain on that one off the top of my head.

Scan over this site for lots and lots of advice on setting up cars for road racing

Autocross to Win (DGs Autocross Secrets) - ATW Home Page

This thread is helpful too :tup:

http://www.the370z.com/brakes-suspen...-handling.html

I was in the same boat and after enjoying much understeer on my first autocross event, I also started reading threads for solutions. I went from the base 18's Bridgestone 225 & 245 to Rays Sport 19's on Bridgestone S-04 Pole Position 265/40zr19 and 285/35zr19. They fit perfect and I can turn much harder without issue.

Finally a replacement for spinners

GT Porsche 911 track cars often run harder rear compounds due to all the weight being over the rear axle but of course, those are engineered to work correctly from the tire supplier and the rest of the setup is dialed in in every other aspect along with track time.

I think running 2 different street tires with different compounds and different tread patterns that are meant and have only been tested running on all 4 corners is hairy at best.

Even if the effect is generally positive in the dry it could be a nightmare in the wet.

As you touched on, the other idea I have had was upgrading the rear sway-bar and leaving the front alone. This would be a pretty cheap upgrade and I could always add the front later when getting new springs/struts or Coil-Overs, which I am sure would take out most of the understeer with default tire sizes.

The reason I don't want to just spend the money on a full suspension setup right now is that I am trying to pay off my 2014 FJ Cruiser early (that currently takes precedence when funneling money into cars) and to be honest, I am slightly worried I will get the bug for a different sports car in a few years and know it will be hard to get my money back in upgrades (Currently under 23,000 miles on my Z so everything but the tires are still pretty fresh).

Maybe I will get some new suspension components in awhile, maybe I will eventually get a tune, but until I make that decision I am going with the bang for the buck approach.

I should say I already bit the bullet on a cat-back exhaust a year ago, I'm sorry but the default exhaust setup just had to go!

You should read the track section. Everyone is running the stiffest front bars, and the biggest tires they can. Some are running no rear bar at all.

Your best savings will be reading and searching. I do quite a bit of that on here. Only spend the money once, will save you a fortune in the future.

I think that's great idea! The OEM tires are actually pretty good (the Nismo RE-11's are better, but the ones you have now are still excellent).

Also, it's probably best to play with only one (or two) variable(s) at a time. I think go with the stiffer rear sway and hold off on the front for now, as you said, and see how that feels.

The only other change you might play with at the same time would be alignment, but otherwise, manipulating one thing at a time (in this case rear sway) is the best way to gauge its individual effect.

So, in summary (I'm rambling, sorry :icon17: ), a good way to go might be to try the rear sway first, see how it feels, and then either do front sway or tweak alignment next.

Dang, beat me to the Far North Racing link. :( :icon17:

Too wide and heavy and rolling resistance would increase torsional loads.

:stirthepot:

almost sounds like someone didnt read my post about S04's being unreasonably narrow in the 275/35/19 size for some reason, bought it and now trying to convince one's self it's the way it should be? :confused:

the 285/35/19 S04's i run on my G's 10.5" are :yum:

Simply not true. What you are describing is the Coulomb model of Physics, not Physics. If you had any background in physics you would know that adhesion and deformation are two of the most standard cases to break you out of the Coulomb model. Your 7th grade Physics equation assumes "hard" solids - it's a terrible approximation of a tire, especially on a performance car, where you are using "sticky" tires and air pressures that allow for a good bit of deformation.


That's for sure - now they explain the limitations of basic models to junior high students. Go do some research on the adhesion and deformative components - you can find a start on Wikipedia, but any modern Physics textbook will get you up to speed here.

Here's a relevant quote to get you started:

Points are true in general, but the Z tends to have more issues with stiffness up front (depending on tire selection), and not need a whole lot of help in the rear. The additional camber up front is very important. The Z runs best with 3+* of camber and a bigass bar up front from what I've seen - all the really fast guys have a Hotchkis bar and as much tire as they can get up front, preferably with a stiff sidewall. There's already a ton of stiffness out back on the Z, and a stiffer rear bar doesn't do as much for you.

Here I am of thinking on going with 305's in the front to go with my 345's in the rear in search for more grip. :shakes head: Now I'm going to have to rethink everything. Maybe I'll start a new trend by going with 145's in the front and 155's in the rear. :tup:

As for the roll-bars, its interesting what Red and Rusty are pointing out and what people are saying on the track forum, more front bar and stock or taking out the rear giving more oversteer.

Which goes against the generalized principals but I guess when something is at an extreme value, especially relative to the other end of the car, many theories can go out the window.

I may actually just try to take out the rear ARB and see how that changes the handling dynamics before I get the new tires, I still probably have a couple months before I have to really.