I have an 84 Camaro that I looking to do some auto crossing with. I not looking to be extremely competitive, just looking to see what I should do as far as tires. I have 255/70s R15s T/A Radials in the rear. I would like to know what I should do for front tires. I have 15 in rims there too. Budget wise I could maybe get 2 new tires.

 

Thats a pretty tall sidewall for something that's going to be ripping some twists. I would suggest some larger wheels before you throw a chunk of money at a set of new tires. A 255/70 will have a ton of sidewall flex contributing to roll and loss of traction.

I would probably go with the cooper cobra radial gt or the Bridgestone radial TA in that size but I still wouldnt want to run on a course with them.

Your better off with something along the lines of a 17"x8.5 or 9 all around. Give you less sidewall give and you have much better options as far as tires go.

 

You should actually use the tires you already have unless they are too worn out to be driven on. I just started racing in autocross events and the most important aspect in the beginning is to get some races under your belt. The tire compounds that come in your tire size are too hard to get good times.
Another reasonable option to 17" or 18" rims are some 16"x8" factory camaro wheels. Get them really cheap at a junkyard and several tire sizes will fit them. Tire rack.com has a really large selection of tires (including competition tires) for the 16"x8" wheels that came with my camaro. Talk to the racers at the events and they can help you out a lot.

 

Ok so getting a set of 16r is best for me budget wise. Thanks.

 

16's are hard to get a good tire compound in too now. Not many choices in the 16x8 category.

There are R compound tires like the Nitto NT01's, but those are Auto-X special tires and are crap for normal street driving in anything but the best weather, as well as wearing out very quickly.

 

There are a few choices to fit 16" wheels, but there are many more 275-40-17 sized tires to ponder. And the advantage of a 275-40-17 tires over a 245-50-16 one is quite large...

 

Oh yes, I know this. 17x9 ZR1s wrapped in NT05 rubber. New, grippy, wider shoes = epic handling mod. On-ramps are way more fun now. Ignore the skyjacked effect. Too much weight loss up front, and I need to lower it anyways.

 

Funny you mentioned that...

Just picked up a really nice 89 GTA the other day. On stock 16" wheels and all season Coopers, the handling felt blah. I stuck on a set of CTW Motorsports wheels with 275-40-17 Continental DWs on it and it went from blah to OMG is this the same car? Even with a 59k dead stock (i.e. worn out) suspension, you could feel the tires gripping and not letting to let go. I have another set of wheels with Falken 615Ks (much more aggressive), that I will try out this week. Can't wait to redo the suspension to take full advantage of the big tires!

 

You gotta check out Tirerack.com. There are more tire selections for my stock 16'' wheels than my C5 Corvette rims. Auto-X tires and Race tires are truly meant to be mounted on a spare set of rims, specifically for racing only.

 

Tirerack has 11 choices for 245/50/16s. Discount Tire has 12.

Tirerack has 37 choices for 275/40/17s. Discount Tire has 28.

And the choices in the performance categories are better for the 245/40/17s. The problem is that 245/50/16's aren't a popular choice anymore and MFGs go where the money is. Its not that you can't make a great performing tire in the 245/50/16 range.

As for seeing Auto-X tires on daily driven vehicles? Read my quote again, I wasn't recommending putting a set of R compound tires. Notice my comments were negative on that respect. My NT05's are street tires, summer only tires, but street tires none the less.

 

Tirerack has 64 choices for 225/50/16. I have this size on my rims.

He can also fit 245/45/16s which is why Tirerack and DiscountTire.com are so great. Even if there are a few more tires with the 17" rims, there are plenty of selections with the 16" factory rims as a BUDGET alternative to what the other guys suggested (not to mention they are cheaper).

I actually forgot to mention him keeping the wheels and tires he has for daily driving and having the factory set of 16x8 wheels with competition tires like your Nitto NT-05(not as good for the street) or even full R-comps like Hoosier A6s. This way, he can have it all, even if he wants to just test the waters with grippy summer tires like Hankook Ventus R-S3 and others. The massive choices are mind boggling.

 

As said, 245-50-16 isn't a popular replacement size these days. But a 225-55 tire is the same diameter as a 245-50 and there are many choices - as many as the 275-40-17 ones in fact.

There is a price difference between the 16" and 17" tires, definitely - but the difference in grip is too much to ignore.

The only real questions are budget and class rules - as an example I have had a lot of CMC racers contact me lately as they are allowed a 17" x 9.5" wheel in that class, and my company offers that size without spacers.

 

How much different in grip is there? Have you tested it out? I have 2 sets of rims and If I can swing a G-Tech pro and/or other data acquisition equipment by next racing season, I may possibly get 2 sets of different size extreme performance summer tires to test them out. A good auto magazine tested out wider tires and it made a positive difference, just not a really big one

 

Doubling the width should give a 15% improvement based on some old test data I saw.

So a 275 is 12% wider than a 245. So I would expect a lateral grip increase of about 2%. Not bad for such a simple change.

You will get a much better improvement by picking a quality performance tire, over upping the size.

 

Well the main thing I see missing here is what class your going for, that will dictate what size wheels your going to be able to run. Head over to grassrootsmotorsports.com and check out their tire tests. Here's a link http://grassrootsmotorsports.com/articles/top-tires/ to test of the latest crop of tires. Also as it was pointed out earlier, just stick with the tires you have till you get some runs under your belt and decide what class you want to end up in with the car.

 

What about the difference in sidewall height? Wouldnt a 17 inch wheel with its shorter sidewalls be more responsive?

 

Sure, technically a shorter sidewall will have less flex all else being equal.

I'm talking steady state grip though. Not the transient, but once the car settles into a turn.

 

They probably are but it doesn't matter with racing slicks because with Formula 1, Nascar, and Trans-Am racing, the slicks don't have short sidewalls.

 

Actually, at first, the original poster may not need to know what class because the workers at the race will know what class to place him in. The article is good, but each car will feel and perform different with these same tires. How many competitors autocross with a 4th generation Civic?

 

The point of that comment was to ensure the OP didn't put himself into an unexpected class solely based on tire choice. If you want to be competitve, the car needs to be built around a specific class.

 

You are correct, that's exactly what I was going for.

When I went to my first autocross I was in a 240SX that was pretty much stock except for swapping in Q45 brakes, this bumped me up into a class that was pretty anything goes with the mods you could do. I had brought a knife to a bazooka fight and while I still had fun I was near the bottom of the barrel.
Move on a couple years later and I was racing my daily driver SAAB 9000 Turbo, not exactly a corner carver, but I usually ended up in 2nd place with that car, usually losing to a Focus SVT. The difference was I had kept my mods to only what was allowed for the stock class. So choose your path first, then choose the right shoes for it.

I don't know if your doing SCCA autocross, but here's a link to the rule book so you can figure out where your car will end up. Rule Book

 

Yes actually it does matter. Formula 1, Nascar ect are not doing autoX number one. Number two the tires on those cars are specifically tailored to their sole purpose. Three There is a happy medium as with anything, you need some side wall give, but not a lot. This helps the full surface of the tire to contact the ground at all times.

These are the standard look for a sidewall on a road race tire. Note: they dont look like a truck tire sidewall.

 

They are all limited to a wheel size to limit brake size and other aspects of performance and therefore limit cornering speeds along with other cost and safety reasons. It's a safety thing.

We are not limited in wheel diameter. So if there is a performance advantage there why not go after it? And its always been my impression that there's a huge performance advantage there.

 

[quote=Homer23;5382373]How much different in grip is there? Have you tested it out? I have 2 sets of rims and If I can swing a G-Tech pro and/or other data acquisition equipment by next racing season, I may possibly get 2 sets of different size extreme performance summer tires to test them out. A good auto magazine tested out wider tires and it made a positive difference, just not a really big one[/]

The feel of increase in grip to be is tremendous, obviously it is a combination of a decrease in sidewall, increase in tread width, and a different tire (pattern and compound).

Each car responds differently to an increase in tire width - maybe a Lambo with a super sophisticated suspension may pick up 15% from an increase. I've been doing a lot of research on the subject and have found that the increase in grip from a Z28 with 215-65-15 tires to an IROC with 245-50-16 tires goes from .81-.82g to .88g-.89g. I tried to back out the effect of slightly larger swaybars and the effect of being about 1/2" lower with a slightly higher spring rate - I came up with 0.03g for the suspension and 0.04g for the tires. Then I took the 4.87% increase in grip and put that up against the 12.24% increase in section width and it comes out to a 39.8% correlation. This is street car applications, not a car on slicks with a zero compliant suspension. I have also seen a few tests where a car on 245-50-16 tires jumped .04 to .05g by swapping to 275-40-17 tires of the same exact pattern and compound.

 

From what I have seen in published tests on street f-bodies, there is a 3.5 to 4.5% increase in lateral g grip by switching a 245-50-16 tire to a 275-40-17 one, typically 0.04 to 0.05g increase for the 12.2% increase in tire section.

 

The reason for that is the ultra stiff spring rates needed to keep the car balanced with all the downforce they make. Short sidewalls would have less "give" and would make the car undriveable for long periods, plus you would have a lot more tire and wheel failure when they run over curbs.

 

Could be. I don't pretend to know, just some test data I am seen in the past. Either way, we both agree a 100% increase in width does not equal a 100% increase in grip, not even close. That seems to be a common misconception.