Hg

I was wondering what the best wheel size is for handling and/or auto-X? I have 16x8 wheels with P245/50-ZR16 Eagle GS-C tires right now. I seem to recall hearing that 16 was actually better, because they are good enough to grip, but the sidewalls are big enough that they can flex enough to squeal or give you a good sign that you're pushing the limit and about to lose traction. BUT, my friends with 17s and what not, their cars seem to be alot more crisp... I dunno... I'm contemplating moving up to 17x9.5 wheels with P275/40-ZR17 tires...


Any handling/auto-X gurus out there that could enlighten me? Thanks.

CrazyHawaiian

the 275's will provide you with a bigger contact patch and therefore more grip. Going to a smaller sidewall is a good thing because the sidewall flexes less. The goal when you want grip is to get the least ammount of flex possible and the biggest contact patch possible. The 'crisp' feeling you describe is probably because their 40 sidewall tires flex less than your 50 sidewall tires giving them quicker response. I recommend going with the 17's and 275 tires. That mod alone will probably make a bigger handling difference than the rest of your suspension mods.

Axoid

I agree that a 17x9.5 with 275/40 tire is a better choice (especially for street tires), but I'll through out a counter argument for Autocross/R compound tires.

A 245/45 tire has about the same height side wall as a 275/40 tire. It does have a smaller contact patch, but the smaller tire wheel combo also decreases the unsprung weight. Unspung weight is the worst kind of weight to have. It is said that on a drag strip that losing 100 lbs is worth a 0.1 of a second. The same is true on a road or autocross course and if it's unspung weight it's worth even more.

Also keep in mind the kind of roads in you area. If you have a lot of bumpy and rutted roads a slightly taller side wall my be better, because it will lower the effective spring rate and swallow more for the road imperfections.

It is all a balancing act, finding the right compromise for you situation.

(BR)G-Machine

I dont know about this contact patch is more grip thing. I am an engineering student and all of the physics I work with friction does not depend on the ammount of contact, rather the normal force (gravity in this case) and the coefficitent of friction (the stickness of the tires.) The coefficient does not go up as the patch grows.

Having said this there are alot of racers and engineers that say that patch is everything. Like the Mule guy... forgot his name... builds a custon 4 link for what? Bigger tires. And the Trans Am cars have like 2 foot wide tires, and there is a first gen camaro subframe that lets you put 300+s on the front.

But the guy from Baer brakes is a big supporter that the friction base forces (braking, turning, accelerating) that the Gs a tire can possibly make is NOT dependant on the contact patch, and he would have alot of research data.

The only thing that I can think of that lines up with the physics for bigger tires is that there is more leverage action to compensate for rear end torqueing and sway in the front.

I dunno

Dewey316

i have often wondered this too. from a purley physics stand point, there should be no diffrence in the friction given the same rubber compound, and same air pressure in the tire. but we have seen over and over in real life that the wider tires help :shrugs: it might have to do with the shape of the contact patch you get at a given psi, with a given width tire.

Zepher

iTrader: (1)

Well, weight has something to do with it. Heavy car with skinny tires will pull less g's than the same car with wider tires of the same compound.

When you look at drag racing, they run wider tires in the back, if the contact patch had nothing to do with traction then they would run skinier tires, right?

CheezX

I also thought about that once. I did some reading and found out why. The coefficient of friction of a tire isn't linear. It changes with load. The graph of coefficent of friction vs load would be a curve. I can't remember all the details but the answer is wider is always better (unless you don't have enough power to move the extra rotational weight, like an LO3 ). The guys who win the SCCA auto-x nationals use 315's on all 4 corners.

(BR)G-Machine

Ya... that would make sense. I assume that the curve of the coeffiecient would favor the less psi the ground is pushing on it, so same load more area, less psi. That would mean that there is also alot more to lightening the car then just the more easily it is acccelerated. the pressure would be less and the coefficient would get eve more sticky. Hmmmmmm...

slowTA

iTrader: (1)

I read an autocrossing and road racing book, please don't ask the name of it now. I remember that it was a rather large book with a picture of an older model race car on it.

My point is that the coefficient of friction versus weight on the tire is deffinately not what you would normally think. From what I read the more weight on a tire, the lower the coefficient of friction became. However, the change was rather small and more weight on a tire equals more traction.

As far as air pressure goes it is just used to keep the tire in its correct shape. Not enough PSI and the tire deforms, too much PSI and the tire becomes too hard to take the form of the road underneath it.

Once again we bring up the 'perfect balance' topic.

prockbp

Mark Madarash, 2000&2001 ESP National champion runs 17x10s in front with 275/40 17 hoosiers
and 16x10s in the back with 275/45 16 hoosiers


Sam Strano won ESP in 2002... i think he ran 16x10s with 275/45 16's hoosiers all around
(both of those cars are probably around 3200lbs though, that's light)


tire squeal has nothing to do with tire size... it has everything to do with compound......
street tires make a lot of noise in the upper limits of their traction range... race tires do not, once you hear your race tires squealing you have pretty much lost traction



as a reply to this contact patch talk...
-all tires being equal-and equal air pressures- the area(size) of the contact patch does not change... only the shape of the contact patch changes
changing the shape of the contact patch changes your slip angles.. a wider contact patch gives you smaller slip angles


trans am race cars have 14" wide tires out back... lol.. that 2foot wide thing made me laugh

Hg

Ok, thanks guys. Do you think 1g is possible on the 16x8 wheels with 245/50-16 tires and suspension mods? Or should I get the 17x9.5's with 275/40-17s if I want to do any kinda damage to the pavement?

AGood2.8

1g is possible on a stock Camaro with 15" rims if it is running decent shocks and "A" compound autocross tires. Its not hard to do with a good set of rubber, street tires is a whole different ballfield.

Hey CheeseX, my little L03 shamed several F-body V8's on racing rubber about a month ago- I was in full street dress- Have a good day. The fastest F-body that day got me by only just under 7 seconds (not a large margin at all for a 400+ HP car completely stripped with racing rubber)

Hg

Is it incredibly hard on street tires or something? I'd be running street tires...

AGood2.8

Your tires will overheat about 20 seconds into it and will entirely loose lateral grip because of their hardness. Street tire will not become sticky- they glaze over and become an ice skating rink.

CrazyHawaiian

Or you can forget about all the scientific aspects and try a real world test. Find 4 factory spare tires and slap them on all 4 corners. Big difference yeah?? Have fun!! LOL (yes I have done this before, crazy drift experiemnt gone bad LOL)

AGood2.8

You crazy SOB, those spare tires do say 50mph max.

prockbp

wrong.

street tires work fine... but they need to be new(don't go out there on 2 year old tires)
street tires do not glaze over during autocross

street tires don't overheat in autocross... but overheating is very real on the road course, 20 minutes at a time is pretty much the standard(and even then you can end up losing some chunks)


street tires will outlast race tires for autocross use.. but don't expect more than 10k miles out of a set of tires that you also use for autocross

Kuhmo 712's and Sumitomo htrz's are great street tires for autocross because they work and have the best pricing on the market(as far as brand name tires go)


i've raced plenty on street tires and race tires.... race tires are for people that want to compete, because you will have FUN regardless of which tires you run


yes, autocross is very very hard on tires

AGood2.8

Sorry, right, You the expert! By the way- Kumho 712's suck. If your tires don't go away then you obviously are not pushing your car hard and can not drive- Thanks for the idiotic imput though- I happen to have bought and owned well over 50 set of tires (racing and street tires) in my life time, and have tried numerous street tires on race tracks also- I promise I have alot more experience than you- but then again you say I'm wrong -Go figure Lets see some time slips or proof of your experience to be contesting me.

Oh yes, here's a pic of some street tires I just ran about a month back. They happen to be the best street tire money can buy in a 16" tire for our cars- Take a look at how they overheated and crumbled smart guy- you want more proof?- just ask

slowTA

iTrader: (1)

So what kind of tires are those? They look like the Dunlops I had for a while, but I'm not sure.

I haven't had the opportunity to buy any dedicated autocross tires yet, so it has been all street tire use so far. I can say that the Dunlops I tried on the front were better than the BFG Comp TAs I had on there. Stock size for 16" rims. With the BFGs the front would tend to chatter in some turns and shake the whole car. The Dunlops were smoother at the edge and more predictable due to that. Just my .02.

AGood2.8

They are the new Goodyear Eagle F1 GS-D3's 245/50-16's
Rear pic-when they were new (only 1 month ago)

slowTA

iTrader: (1)

I guess you get what you pay for... but they aren't really all that pricey either.

CheezX

That happened to my brand new crappy street tires too. The edges were completely gone. I wouldn't say they were overheated though. More like they got ripped up by the road surface. Really rough ones chew up the tires a lot quicker. But it is true that there would be more heat build up on a new tire with deep tread from all the extra rubber flexing back and forth. So maybe a combination of both.

BTW AGood 2.8, I thought you had a V6? LO3 is the 305 TBI. And as for a V8 getting you by 7 seconds, was that for auto-x? Seems normal to me. Little formula cars were getting me by about 10s and my car was pretty much stock except for springs.

prockbp

what "slips" do you want to see? lol... autocross courses are different every time

you're such a jackass.

712's do not suck.. that's idiotic to say... they're not the best tire to win nationnals in street tire classes, but that has absolutely nothing to do with serving a purpose


talking big doesn't mean that you know jack ****

how many evolution driving schools or evolution test and tunes have you been to? i've been to one test and tune and 2 schools.. i know plenty about tires...

if you want to challenge me.. i race in SCCA, Equipe Rapide and the BMW club all in the dallas/fort worth area.. there's an event practically every weekend of the season... come on out


lol.. the wear you're showing in those pics is perfectly normal for a street tire...



lol... and another thing.. correct driving techniques will make your tires last a whole lot longer... so a better driver will do more with less rubber(and where did you get the idea that i don't wear out my tires?)


everytime you say something.. you sound even more ignorant

prockbp

first of all... g forces are measured during static handling condtions.. the SHOCKs have little to no effect on how many g's can be pulled in that situation...
it depends on tires and springs rates(including sway bars)... spring rates help to neutralize the static handling of the car(static means making a constant turn in one direction)

the main purpose of shocks is for transitional control and going over bumps(transitions are the moments when you make changes to the various inputs such as brakes, acceleration and turning)




and then.... it doesn't matter how many v8 cars your lil lo3 shamed in a local autocross event.... why don't you see how many v8's you can shame at a regional or national event.. then come talk some smack

AGood2.8

Sorry but true 712's do suck. One test and tune and two schools make you a qualified expert? You considered that adequate experience- I think not.
Street tires have harder rubber compounds- when that harder compound is heated excessively like with autoX runs (unlike regular street driving where you go a full block, turn a corner, go another full block turn again...) the street tire tread will glaze and crumble becoming very slick- racing tires remain sticky and do not prduce this problem when tread becomes hot

CheeseX, sorry you are correct, I don't have an L03- I have even worse- an LB8 Sorry I'm not up on the rpo code mumbojumbo. The top f-body had me by exactly 6.60secs. Race tires are good for 3-4 second and HP can very on different based on whether its a HP track or not (HP track has more tight corners and longer straights) This was a HP track and a faster motor would show gains of 3-5 secs also-

I have many years experience messing around in BSP class and dominating with my Vette by 6-8 seconds over the next closest car in BSP- and would generally 2 out of 3 times be the overall fastest Vette of the day and always in the top 5 times of the day.

I boast much experience with timesheets to prove

Hg

AGood2.8: What street tires have you had/what street tires do you think are good then? I think I might try and get the R15s this summer.... just gotta pick a tire now...

prockbp

it's no secret that street tires are harder.. duh.. why even mention it

nobody is asking you to say that race tires are better.. that's another huge duh


you're acting like street tires are unacceptable... when you couldn't be farther from the truth....

it's as simple as that

where is your proof that 712's are no good? i'd like to see that.


and about your autocross experience.. get real.. it's not how many people that you are faster than... it's who you can beat...
since you've been doing this soooo long.. i'm sure you know at least a few national champs.. why don't you have one of them call me up on the phone and give me your credentials


just in case you forgot your buddy's names.... look'em up on this list.. i'm sure they'll be there
http://www.scca.org/amateur/solo2/na...lts/index.html

AGood2.8

Tires on Camaro- 3 sets of the old Comp T/A tires, 1 set of Firestone Firehawk SZ50's, 2 sets of SZ50EP's , current Goodyears GS-D3's

Tires I've owned in general-
Pirellis-various sets and types
At least 40 sets of various BFG's including radial t/a's, hr4's comp t/a's, and a set of KDW's. also many sets of Comp R1's in both R & A compounds
Hooisers R race coumpound-1 set
Dunlops- 3 different sets
Kumho's-1 set
A few cheap sets of michelin & bridgestones
Yokohama- 1 set
4 or 5 sets of Goodyears- gatorbacks, etc..

Tires I've driven on- Other cars(not mine) BFG kd G-force Wow!
Several different runflats- Any runflats are terrible.
Too many to list- I have driven alot of diffferent performance cars and setups
Heck I have driven a full blown Nascar at speed even with racing Goodyear skins.
Its really a tossup between the Firehawk SZ50Ep's and the current Goodyears(GS-D3's) I am running. The SZ50Ep's had a better turn in response (more predictable) but once set into a hard corner, the Goodyears have better edge grip and better braking. Goodyears just lack in transition, They have a slight sloppiness that give a tad bit of an uneasy feel for a moment (slight loss of reponse feel until transition is done.

If I had 17" rims I would DEFINATELY be running BFG KD G-Forces in the 245/45-17 size.

AGood2.8

Got to add to my list- Drove a $90,000 Jaguar XJ"R" today with Continentals on it at the Jaguar exhibit test track at HSR West - scared the crap out of the sales person- oh what fun- Brother was in the backseat with a video camera- great footage And didn't knock down one cone to boot.

ronterry

Hey 'AGood2.8' what's your opinion on Hoosier R's?
I'm narrowing my personal search to Hoosiers 275/50-15's to go on a set of Aero 10" wheels. The Goodyear G-19 I really wanted are becoming a logistical nightmare. Down right hard to find any good distributors in Denver for the G-19's, but the Hoosiers Radials seem to be a little easier to find & cheaper...(I think?)


Thanks,
Ron

CrazyHawaiian

Hey prockbp, its great that you can give us different opinions of stuff, but you dont really need to act like that. Chill out. Go read the sticky at the top of the forums. Its cool to talk tech, but no need to insult people.

I've never raced on a race compound tire so I cant really compare. And I've never been to any driving schools or anything, so maybe you wont take me seriously ... everything I know I've learned on my own or by watching other people drive. In the sport of drifting its very common to experience what AGood2.8 explained (tires glazing over). Because there is so much friction over and over the tires heat up alot faster than they do in grip roadracing. Since the rears spin so much, the front tires are really what we pay attention to. I've tried about 5 different tires in the front and they all vary in how slippery they get when hot. The trick of course is to find the ones that grip good even when hot and run those only in the front (rears need to spin). The latest set I've been running is the Kumho Supra 712 255/45/17, and they do a little better than the BF Comp T/A's (I'm working with cheap tires here!! lol). But after about 15 minutes of hard drifting even the 712's start to slide (I can notice the difference). When I'm done the rubber looks alot worse than the pics posted.

AGood2.8

Hoosier "A"s are the best thing out right now in my opinion for autoX. We have always run R coumpound tires on the race Vette (especially when I used to autox it) because the rears will eat the A compound in a hurry with the power we put down (540RWHP) combined with all that low-speed high-torque excellerations . The R's last longer. We also run this car at many nostalgic events at places like Willowsprings, California Speedway, Etc.. Better for us to have a road race coumpound.

I would go through a set of the older BFG comp t/a R1's A-compound in 3 events- most guys would last a year or two on one set.

AGood2.8

CrazyH, The 712's are fine for what you are doing- you drive more of a road course rather than a tight autoX course- Also you need to slide . I still say 712's suck for autoX though.

To all without direct knowledge on this subject- Street tirs will perform much better at higher speed longer courses than compared to that same tire in a tight slow speed AutoX course- why?- the higher speed stuff more allows the tire to cool between corners (they still overheat, but they cool back down some on the straights and give you half a chance going into the next corner. AutoX is designed that no straight be longer than 100ft, thus you are always turning even in a "straight" because it is so short you are setting up the car to the side of the lane for better apex. You are always turning and tires are given no relief until you stop- This is why in 20 seconds the grip is gone.

prockbp

umm.. why don't you send your repremands to all guilty parties...

i'm very chilled out. i would never start a fight on a forum. so re-read this post and figure things out ... that other guy started in with the insults

jdaniel

Whats the biggest tire you can put on the 16x8 wheel. I'm lowering mine 1 1/2 and want to fill up the wheelwell.

Axoid

A 255/50/16 is pretty much the bigest street tire your going to find to fit a 16x8 wheel. I've squeezed a 265/45/16 Kumho autocross tire on 16x8's, but Kumho recommends a 16x9 for them.