Balanced Tire Sizes for road racing [Archive]

MrQuick

01-02-2006, 09:52 AM

You know, your really fighting for balance. The last thing you want to do is use you tires as a tuning device. Pick your sizes and build around it. You want to tune for an almost neutral feel.

If your building a road racer 1:1 is best ~IMHO~ we tend to go too wide for sake of looks.

275's are a perfect set up cause they will fit most chassis with no problems. Remember ask 10 different people you will get 10 different answers.

sinned

01-02-2006, 10:12 AM

Dennis

Educate me if i'm wrong don't you want the ass end of the car to kick out rather then the front, and isn't that oversteer?
No, you do not "want" over steer (ask me how I know :drive2: ). Almost every vehicle built has under steer or push designed into and for a reason. In an over steer condition, depending on what caused it, it is almost impossible to have full control of what is going to happen next. In an understeer condition, almost every time, simply lifting out of the throttle or tapping the brakes will allow the driver to fully regain control of the vehicle. This assumes no ice, loose gravel, tec... as the cause of the condition, in which case it doesn't matter, your ****ed anyway.

Ralph LoGrasso

01-02-2006, 10:13 AM

If you can fit a wide enough tire up front (275+) then there's no reason you can't run the 335 out back. A very well respected suspension company in the PT world is building their newest project car around a 315/335 combo, and the products they're developing on the car, once for sale, will give the PT crowd the ability to run some really wide tires up front (275-295-315); to balance out the wide rear tires that some people choose to run. Vince is right though, some people tend to go too wide in the rear for the sake of looks. 335s out back are useless with 235s up front, IMO.

CarlC

01-02-2006, 11:50 AM

If costs are included, using a 1:1 tire ratio allows for tire rotation which will lead to a longer usable tire life. On most of our cars were going to wear the front tires faster than the rears, so being able to rotate tires will help longevity and reduce costs.

Also, just picking a size and going for it may not work in your best interest. Tire brand, size, tread type, speed ratings, and compounds may be limited in certain sizes which will reduce your options. The 275/40/17 size is about as popular as it gets, for now.

Blown353

01-02-2006, 12:29 PM

If costs are included, using a 1:1 tire ratio allows for tire rotation which will lead to a longer usable tire life.

Very true and definately something to consider. While having matching sized wheels and tires all the way around may not "look as cool" as having steamrollers out back, being able to rotate the tires is a big benefit to life-- either from burnout wear out back or cornering wear up front.

I run even sizes all the way around and even though I could use a lot more tire out back for my severe forward-traction issues being able to rotate the tires has really extended the overall service life of my tires-- heck, I got almost 8,000 miles out of this set, which is a new record for me. When the fronts start showing a bit of cornering wear I toss 'em on the back and after some right foot abuse they're pretty even again. LOL. My fronts are starting to edge-wear again and could use to be rotated to the back but unfortunately my back tires have started to chunk in spots-- and I'm not taking chances putting chunked tires on the front of the car.

Keep in mind the front tires are responsible for the majority of the braking (not to mention direction changing) so there's no reason not to go as wide as you possibly can up front. If you go with 315's on the back I would try to fit at least 275's up front; a 315/35 & 275/40 combo would probably work out well and they will have the same OD or be very close in OD (depending on what wheel width you mount them on.)

Troy

rohrt

01-03-2006, 02:11 PM

Carl I refer to your web site quit often and I see you you run 275 all the way around without the mini tubb. How has your car performed and what events have you been in?

Just curious what the thrasher and red witch have front and back for tire sizes? I couldn't find the info.

Also MrQuick I understand what your saying about

"You know, your really fighting for balance. The last thing you want to do is use your tires as a tuning device. Pick your sizes and build around it. You want to tune for an almost neutral feel."

I want function B-4 looks and to learn from you guys that are out there being competitive to find out what trick parts to use use and what is a wast of money.

Thanks for the replys

CarlC

01-03-2006, 09:27 PM

The car is mostly a street car but makes it to track days 2-3 times per year. It's a rolling laboratory for me, and is getting progressively better.

sinned

01-03-2006, 09:43 PM

Also MrQuick I understand what your saying about
"You know, your really fighting for balance. The last thing you want to do is use your tires as a tuning device. Pick your sizes and build around it. You want to tune for an almost neutral feel."
That being said I wonder why....

I want function B-4 looks and to learn from you guys that are out there being competitive to find out what trick parts to use use and what is a wast of money.
So we realize that you need to have some kind of balance and NOT buy tires based on what looks good but rather what works; and then we go here...

Just curious what the thrasher and red witch have front and back for tire sizes? I couldn't find the info.
What possible difference could that make as to what tires YOU need?
Not looking to start an argument or erk you but it doesn't sound like you are nearly as interested in running the best tires as you are the best looking tires.

Ralph LoGrasso

01-03-2006, 10:43 PM

What possible difference could that make as to what tires YOU need?

Perhaps he's looking for past examples of what similar, well sorted out cars have run?

MrQuick

01-03-2006, 11:50 PM

yeah Dennis, will you quit questioning his questions with questions and answer his questions with an actual answer...CC made you abrasive man! ok now im confused.

Looks aren't bad right? You ran 315's that rub and really didn't help keep you on the track...if I remember correctly?? Hey hows the rain out there? Pretty nasty hu?

I think Ralph is right with his hypothosis. Seems Rohrt has a mini tubbed 69 and doesn't want to waste the space,but in the same breath wants a nice handling car...my advice, go with 315's in the rear and MAKE 275's fit up front. Then make the car work with that tire arrangement.

sinned

01-04-2006, 06:15 AM

Looks aren't bad right? You ran 315's that rub and really didn't help keep you on the track...if I remember correctly?? Hey hows the rain out there? Pretty nasty hu?
Nope, 315's were on for a month or so before the 285's went back on. Rain sucks, especially working outside.

Agreed looks are not bad, just don't claim you are a function over fashion type person while trying squeeze maximum rubber. :poke:

rohrt

01-04-2006, 06:53 AM

No offense taken Dennis. I have two 68s F bodys. One vert one hard top. I'm still finishing the vert right now(non PT car). The Hard top is a Southern Cal car that I would like to drive to and put in some races. I have most of it planed out with exception to the entire suspension system and wheel tire combo.

It is not yet mini tubbed or any work as of yet, but I had planned to do that mainly for the fact of what Ralph had stated "Perhaps he's looking for past examples of what similar, well sorted out cars have run"

So yeah I will forgo the mini tub idea if its not beneficial. Also I apologize that I only know of a few of you guys that race their cars on this forum. Being a PHR reader I have read the article of Stielows lap of america (wish I still had that), I have read Mike Pozzi web site, looked at what Detroit speed is doing, seen hundreds of web sites of others that have built cars and have seen the never ending supply of aftermarket parts that have come out. Its enough to make my head spin.

I would like to see maybe 4 cars that are competitive and what they did to achieve that?

I do admit I'm at a loss when it comes to the what types of races there are out there I would like to compete in. The Silver state classic is one that I read the rules on but I don't consider it a true competition in the sense that your racing against a clock and not another driver.
This Forum is my education and thank you to thoses that teach.

MrQuick

01-04-2006, 07:57 AM

Agreed looks are not bad, just don't claim you are a function over fashion type person while trying squeeze maximum rubber. I go both ways...depends on the car, plus you know me...I like BIG looking rears. LOL
OUTSIDE?!?! My you went up didn't you!
Rohrt, mini tubbing is not necassary. You can achive very good traction with a 10inch wide tire. 285/275 combo works real well. I don't know your background but if your new to the race scene try a few autoX events,maybe hit the drags or maybe an open track day and see what your into. You can't really know till you try.

Silver state is a big race to jump into.

rohrt

01-04-2006, 11:34 AM

I have been to the 1/4 mile drags plenty of times. I just googled the autoX events and they look pretty cool.

http://www.fbody-event.org/bin/autox.cgi

I'm finding lots of stuff out there. I will keep looking to see what is close to me.

Thank you

Damn True

01-04-2006, 11:41 AM

I do admit I'm at a loss when it comes to the what types of races there are out there I would like to compete in. The Silver state classic is one that I read the rules on but I don't consider it a true competition in the sense that your racing against a clock and not another driver.
This Forum is my education and thank you to thoses that teach.

If you are looking to go wheel-to-wheel racing you may find the opportunities very limited.

In order to race against other cars of your vintage there are only two venues:

a) Historic T/A. The problem there is that they only allow genuine log-booked cars from the original T/A series to compete. You cannot build a car and race with them.

b) SCCA vintage. The problem there is that you have to build to period spec with the exception of modern safety items. So no big changes to suspension, 15" wheels, 4 speed, old school rubber.

You can build into a series like the NASA American Iron or American Iron Extreme, and the AV8SS series. A few older cars have run there. But, you will be running against Camaros and Mustangs 35 years newer than your car.

sinned

01-04-2006, 12:26 PM

Serious track whores almost always an "R" compound tire or at least a dual purpose. You'll find that most company’s build 275's and some will do 285's with one doing a 295. The bigger, blingier sizes are not typically built for competition use with the exception of the 315 (Corvette OE size). Keep that in mind when selecting tire size.

I think the biggest rear tire anybody on a race track is running on the back of an early "F" body is 275.

Ralph LoGrasso

01-04-2006, 12:35 PM

Agreed looks are not bad, just don't claim you are a function over fashion type person while trying squeeze maximum rubber. :poke:

This is something I disagree with. If you've got the room, capability, and a properly designed and tuned suspension to go along with them, why wouldn't a 315/335 combo outhandle a 245/275 combo? If the suspension's been designed around the wide rubber, why wouldn't it perform better? Wider tires should transpond into increased lateral grip, and better handling. I'm sure the car will follow damn near every crack in the road (my 275/295 SS does), but on the race track, it should really shine.

sinned

01-04-2006, 03:46 PM

Sure, but at what point do you reach diminishing returns? Fitting a 315/335 combo on an early "F" body will not outperform the same car with 275's enough to justify the work.

alcino

01-04-2006, 04:49 PM

I like my wheels and tires on the small and light side( I have 205/50/15 front and 225/50/15 rear). Helps braking and accelerating from the reduced rotational mass. I actually noticed the difference going from 45 pound wheels and tires to 35 lbs when i would launch. Felt like it had a more power and lost a half second on my 1/4 time.

Granted my car is a lot smaller than the f body, so 205 may not be enough ( but 245 to 275 should do it).

IMHO its way more about tire compound than size. If you want to be competitive its easier to get R compound tires than to dump thousands in suspension, wheels, and engine mods. Trust me on this one. The drawback is faster tire wear. My Toyo RA1s are getting me about 10,000 miles. I feel this is a good compromise for the competitive edge.

Alcino

what I have
15x8 bassett spun steel wheels 16.0lbs
toyo RA1 205 and 225/50/15 ~20lbs full tread

Ralph LoGrasso

01-04-2006, 09:50 PM

Sure, but at what point do you reach diminishing returns? Fitting a 315/335 combo on an early "F" body will not outperform the same car with 275's enough to justify the work.

I agree with you there--there has to be some point where the marginal gain just isn't enough to justify the work, or cost. That point probably comes when you start going in excess of 275s all the way around. But, if you've got the coin and time to make it work, and you want the look / slightly better performance, there's no reason not to go with it. Fitting 315 (or if not 315s, then likely 295s) on the front of an early F-body will not be so hard in the near future. There's an aftermarket sub in the works that will allow that size tire. The rear will require a mini-tub. It takes a decent amount of work, but the larger tires can still be fitted.

Alcino makes a good point about compound and tires as well. You can't pull 1G if your tires will only hold till .9. When I swapped from 17s to 18s on my SS, the car actually handled better with the 18s. Mostly because the 17s were a cheaper brand, HPZ or something like that. I went from 275/40/17 all the way around to 275/35/18 l 295/35/18 Kumho Ecsta MX. I was expecting a slight decrease in handling, and a definite decrease in traction because of the smaller sidewall in the rear -- but it was the exact opposite. Good tires go a long ways. I've seen people that build high performance cars, put lots of money into the susp, etc. and then go with cheapie tires. It just doesn't make sense to me.

sinned

01-04-2006, 10:11 PM

Just a point since Ralph brought up tire sizes....Trans-Am cars pull in excess of 1.8g of lateral traction with 16" tires. Just something to think about.

They also pull 0-60 in the sub 3 second world and 1/4 times ~10seconds. So running 335/18's really isn't required to handle very well.

rohrt

01-06-2006, 09:28 AM

One thing that just came to mind on why to go with a biger tire in the back and correct me if i'm wrong. If you wind though a 90 degree turn into a strait away and punch it wouldn't you want the extra meat in the back to get the best grip you can to keep from spinning. Maybe I'm just splitting hairs at this point but I was just wondering if that a valid concern.

sinned

01-06-2006, 04:41 PM

Well, you don't ever "punch it" on a road course. O/T, HPDE, road racing are all finesse driving skills events. Go punch it on the drag strip. On a road course there is such a thing as having too much HP and most PT cars being built have way too much for a road course car. If you can easily overpower a 10" dedicated track tire you need to turn it down a pinch. Tires should always be balanced, if you have an over steer issue than there is something wrong with the driver or the set-up that needs to be corrected.

rohrt

01-08-2006, 02:52 PM

Thanks Dennis

This thread has helped me figure out a few things. One of wich is that there just are not many road race type events out there to compete in in the Mid West. I did find this one

http://www.roadamerica.com/2006/index.htm

There just isn't the Buttonwillow type tracks around hear.
So instead of thinking how to make the best corner carving car I can, I might as well lean more on just making it comfortable, fun and safe. I figure once I get the car built I will be lucky if I can get to two road race events in a year. I go to the 1/4 track more often since they are close. My original goal was to run in the Silver State and I still plan on doing that.
http://www.silverstateclassic.com
So I'm going to look into what other events are out there and try to decide what looks fun.

Steve Chryssos

01-08-2006, 04:44 PM

Now turn this whole thing around. The real question here is if most of us are NOT performing the mods necessary to add 275 tires up front, what is max rear tire size that is appropriate for a 255 front? That 245 or 255 front tire is the true limiting factor. Way too damn many 255/335 cars out there now and coming together. Folks see the Mule's 335's and overlook the 275's up front. And they forget or just don't know how much work went into fitting those 275's AND maintaining proper turning radius (the frame rails were cut)

As rear wheel power output increases, a wider rear tire will be beneficial (up to a point-700RWP will still fry a 335/30), so greater tire size differential can be justified. The numbers change with other variables as well such as overall weight, weight bias, etc. AA small light car needs less tire than a big heavy car. A mid-engined F40 really does need big ass rear tires. More differential is appropriate. So a hard and fast 1.0:1 rule is a bit oversimplified. Maybe 1.2:1 is better as a guideline.

The only hard and fast rule I can think of is as follows:
The big doggies (the cars that can make a thudding sound when they whip it out and lay it on the table) are NOT sporting a significant front to rear tire size differential. And they're NOT running steamrollers that don't want to turn. If you're stuck with a 255 or smaller tire up front, the only reason to run 335's is to overcompensate for something. :eek: Hopefully it's just too much horsepower.

335's look cool. Mini-tubs are cool. If you have a typical 3300lb car with 500RWP and a 255 up front, draw the line! Buy those mini-tubs and then fill em with 295's or 305's. 600HP? Go 315mm. It's not like the mini-tubs will shrink over time. You'll always have room for 335's if you decide at a later time that you absolutely, positively just gotta have 'em.

And if you come across someone with 235/335's and a bone stock ZZ4?

Snicker. :hah:

redss86

01-10-2006, 05:45 AM

335's look cool. Mini-tubs are cool. If you have a typical 3300lb car with 500RWP and a 255 up front, draw the line! Buy those mini-tubs and then fill em with 295's or 305's. 600HP? Go 315mm. It's not like the mini-tubs will shrink over time. You'll always have room for 335's if you decide at a later time that you absolutely, positively just gotta have 'em.

So, if I were to have a 550-600hp engine, and can only fit a 255 front, then I should be ok w/ a 295 rear? These will be on an 86 Monte Carlo so it will be little be heavier than your f bodies. Also, could I get away w/ the 255 on an 8" rim, or do I need a wider rim? TIA

Joe

Ralph LoGrasso

01-10-2006, 05:54 AM

Joe, you would probably be better with the 255 on an 8.5" rim, but an 8" rim should work.

As for the 295s with 550hp, and the entire tire debate really. It's all subjective. I can spin my 295/35/18s with 360hp in my 4th gen SS. Mat the gas from a stop or a 5-10 roll, and they'll spin plenty nice. I'm sure you'd be able to spin them through 2 or 3 gears with 550hp. Once you start talking about excess of 500hp, and "low profile" street tires (not drag radials) traction is always going to be hard to come by, no matter the size. A wider tire will likely grab more than a thinner one (especially coming out of turns), but don't expect a 335/30/18 to dead hook a 500rwhp car. You'd have a much more balanced car with the 295 rear, so that would be your best choice, IMO.

Damn True

06-23-2006, 04:57 PM

Serious track whores almost always an "R" compound tire or at least a dual purpose. You'll find that most company’s build 275's and some will do 285's with one doing a 295. The bigger, blingier sizes are not typically built for competition use with the exception of the 315 (Corvette OE size). Keep that in mind when selecting tire size.

Not many offerings in that size (315-35-17) is there?

Plenty up through 275/40, but after that.....not a lot.....other than "R" compound.