Staggered vs. all the same width...

[Al N.]

Folks, this is touched in other threads, but I wanted to explore it some more...

 

If I do get a new set of dedicated auto-x rims and tires...should they be all the same size or wider in the back. My car is the standard Caterham USA "Supersport" 200 hp Zetec set up.

 

Would 8" all around work? Caterham sells the 6" and 8" 13-inch wheels...and I think they fit the narrower 6" ones upfront as semi-standard issue (like Scott L's) when 13" wheels are fitted to Superlights. I figure if I'm going to do this, I might as well buy wide as semi-reasonable to start.

[slngsht]

My autox instructor's opinion on that subject was to run the same size all around, then use suspension to tune.

 

You see that I listened so well.... running 305's in the back

[R1 Seven]

My car has a 60% weight bias to the REAR when I am in it. If the tires are the same all the way around, guess which end is going to have more heat/grip? Porsches and many other mid to rear engined cars generally have wider tires on the rear for the same reason. It is a necessity in my case.

 

I don't think that they car based seven is going to be quite as rear-biased as mine is but it probably is somewhat.

 

My $.02 YMMV

[Boxologist]

r400 and 500 got the staggered rim iirc. 6" wide, 205width up front and 8" 235+ in the back to get traction. seriously, hold off till ur sure u want to get competitive in motorsports. when u finally drive ORange in anger, then make the determination.

[Boxologist]

and u should be saving the windscreen and mirror if u really get going because i'd be swapping those at every event.

[slngsht]

r400 and 500 got the staggered rim iirc. 6" wide, 205width up front and 8" 235+ in the back to get traction. seriously, hold off till ur sure u want to get competitive in motorsports. when u finally drive ORange in anger, then make the determination.

 

That's good advice.

 

Also, less traction won't get you really fast times, but it sure as hell is fun. I found that out when I got wider wheels and R compounds for my vette. At first, it was alot of fun to just punch it where it used to slide, and have it stick... but after a while, I missed the slide-on-demand feature

[pierats]

but after a while, I missed the slide-on-demand feature

 

You just need more power then!

[slngsht]

 

You just need more power then!

 

Hence 440hp Seven :yesnod:

[Al N.]

when u finally drive ORange in anger....

 

Did you go on any of the AM drives or try to keep up with Mazda and Scott at Skyline last year? :jester:

 

You guys are right, of course. In truth, the whole spending hours in a hot parking lot is not entirely appealing to me....but I think my car is set up very well for Auto-X (with the motor and tranny I have) and it will be fun to see how it compares to other Se7ens and how I can improve my times. I'll probably be like that Corvette that ran at the ETR/SCCA & Se7ens combined Auto-X...driving well below my car's ability.

 

August 19th, although I did have a family obligation which I am bailing out of, is still looking okay. I will probably trailer in case I break anything.

[yellowss7]

I will probably trailer in case I break anything.

 

Al, it's an autox not a demolition derby. Your car should be well sorted after all the miles you've done. Runs at Warminster for a fast 7 average around 50-60 seconds. We usually get in at least 4 runs. I'm sure your car can "hold together" for 4 minutes.

 

Remember you're the one driving! Most course designs will keep us in 2nd gear. I'm chief of Grid so you can work Grid if you want, no shagging cones. And there are some really good instructors to help out if you want help.

 

Now let's try to get a bunch of 7's there!!! :party: Tom

[slngsht]

 

Did you go on any of the AM drives or try to keep up with Mazda and Scott at Skyline last year? :jester:

 

You guys are right, of course. In truth, the whole spending hours in a hot parking lot is not entirely appealing to me....but I think my car is set up very well for Auto-X (with the motor and tranny I have) and it will be fun to see how it compares to other Se7ens and how I can improve my times. I'll probably be like that Corvette that ran at the ETR/SCCA & Se7ens combined Auto-X...driving well below my car's ability.

 

August 19th, although I did have a family obligation which I am bailing out of, is still looking okay. I will probably trailer in case I break anything.

 

Al, after you roast in a few autocrosses, you'll come to the conclusion that autox schools are the way to go... You'll still have to man the cones, but at least you get 30 runs in one day.

[Davemk1]

I'm not the end all be all of info on this subject but I do have a reasonable amount of experience in autocross.

 

Tire width can be a funny thing. Keeping in mind that the runs are short (about 1 minute in most cases) you'll realize that getting heat into the tires can be a real issue. You are in effect running on cold tires most all of the time. Here in Montana we run plenty of events where the morning temps are in the 50's. I feel tire width choices need to be made considering your temperatures and your horsepower.

 

I'm running a Birkin with about 140hp and 13x7 wheels in front and 13x8 wheels in back. I'm also using Hoosiers (25A compound) in a 7" width in front and a 8" width in the rear. This is a bit narrow compared to national class cars which run 10" in many cases. The narrow tire allows for a much quicker heat build up and in the end better grip than I'd have with a wider tire. If I lived in Texas the choice would be different. So a narrow but warm tire will outgrip and wide cold one every time.

 

I also feel that the choice to run staggered sizes or not depends on your driving style and the cars power and balance. As basic as it sounds, if the car is loose or tail happy then wider rubber in the rear would help..........if it pushes then having the same size all round would benefit. If you have plenty of power then wider rears might make sense. At over 200hp I'd put you in this camp. I drive pretty aggressively and tend to steer a good bit with my right foot and the slightly wider rear tire keeps me from spinning and wiping out cones with the back end of the car.

 

FWIW I've used a few different tire brands over the years and have come to realize why about 90% of the winners at Nationals are all running Hoosier 25A's. They are simply the best for autocross. They stick hard and have a very progressive breakaway which you can use to your advantage. I love them and will never run without them again.

 

So......if I owned your car I'd lean toward running wider rears. I hope that helps and doesn't confuse the matter more. I've attached a photo of my car cornering hard on the Hoosiers. This event was last weekend and I took second fastest time of the day about .3 seconds behind a 125cc shifter cart. Hoosiers rock.

 

Dave

 

http://www.usa7s.com/aspnetforum/upload/161956215_DSC_6475.jpg

[WestTexasS2K]

I run the same rim size 17x8 but stager tire size 225/45/17 on front 255/40/17 on rear. I am fixing to try 275/40/17 on the rear. It is pushing it with an 8" rim but 9" are hard to find unless you custom order them.

[JohnK]

A related area - once you've decided on tire size(s) what latitude do you have re rim width? I recall someone noting that a particular tire size he was running could be used with several different rim widths. Is there a standard rule for this or do you trust what the vendor you buy the tire from tells you. And, of course are there difference in behaviour when you run a particular tire size on different rim widths.

 

Cheers,

 

John K

Cincinnati

 

PS - Does anyone else find all the the clutter of the "Add Smiley" box annoying when you're trying to compose a msg?

[slngsht]

 

PS - Does anyone else find all the the clutter of the "Add Smiley" box annoying when you're trying to compose a msg?

 

Most of the time, you can just use the "Quick Reply" at the bottom of the page, so you don't have to go to the page that has the smilies.

[Al N.]

A related area - once you've decided on tire size(s) what latitude do you have re rim width? I recall someone noting that a particular tire size he was running could be used with several different rim widths. Is there a standard rule for this or do you trust what the vendor you buy the tire from tells you. And, of course are there difference in behaviour when you run a particular tire size on different rim widths.

 

John-So far, the tire mfgs I've encountered all post a range of rim widths per tire size and then highlight what they consider the "optimum" width to be. Based on what every one has said so far, I think I'm going to try 7" up front and 8" in the rear...this covers a tires by several mfgs in the 13" category.

[Davemk1]

The tire should not be any wider than the wheel. If it is you get the tread rounding out and lots of sidewall flex. It's slower by all accounts. It's tempting to stuff big wide 9" tires on your 7" rims but it will suck. I learned the hard way and the tech guys from Hoosier set me straight and he was dead right.

 

I use 7" tires on 7" rims in front and 8" tires on 8" rims in back. This makes for a very stable sidewall and allows for the use of lower pressures and a bigger footprint without the tire rolling over.

 

Have fun,

 

Dave

 

 

[James A]

I run Hoosier A6s now 205-15s on the front and 225-15s on the rear. When I first tired the Hoosiers 3 years ago, the A3S04s, I had 205s all the way around and the car definitely needed more rear "grip". In sweepers it was hard to keep it contained. The little extra in the rear makes a very nice difference.

Sure wish Hoosier made an A6 205 in 13 inch, they have the A6 in 225-13.

[Kitcat]

I replaced my 195 Pilots on my 15" Prisoner wheels ago w/Toyo RA1 205's a few months ago. I use the car mostly for track days and quite a bit of commuting to work. With full tread they have decent grip and are fine in the rain. They are a mammoth improvement over the Pilots.

 

Hoosiers have more grip but have a very short life span, I expect to get 5-10K miles out of the Toyos. I doubt I'd get 500 miles from Hoosiers, which aren't really appropriate for general street use anyhow. Perfect for auto-x tho and I ran them on my CSP Miata for years in auto-x.

 

Anyhow, I am planning on bumping the rears to 225s as I have had an imbalance between front and rear grip, with the rears breaking lose much more easily. Also, the car can get real squirrely if braking occurs at the same time as turning. My son did a lovely 360 degree spin in it at a track day where we shared the car. (Fortunately it was all spectacle/no damage). Heat isnt an issue as high speed laps on a race course are different than the few short, relatively slow blasts around an auto-x course.

 

I will file a update once the switch is made and I get some more track days under my belt, probably next spring (sadly the season is over for now in my chilly, soon to be snowy, area of the country).

[DeanG]

Do any of you folks with wide tires find that you are bogging the engine?