Autocross/Road Course driving on 15" wheels. What's your experience?

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MRGTX

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Has anyone attempted this recently?

What did you run for tires? How did they perform? Did you find an optimal tire pressure?

Would you do it again?

These questions are a perpetual plague on people who prefer stock wheel sizes...I'm not sure if the question has been asked recently or in this way. Any insights are welcome.
 
He's a good resource on a lot of these topics but for his own modded Duster/Demon, he's running 18"s.
correct, but I'd guess he's ran 15s before
 
I'm also interested in this topic as this is something I'm contemplating (I like the look of the old/older school 15" wheels/tires combo), but if autocross is something I'm into I think the answer is large rims and lower profile tires with stiff sidewalls (there is also more sticker tire options with 17/18" wheels). I think the answer may be keep the 15's for the look and swap for larger rims with stickier tires at the track for performance, but I'll await the more experienced member to chime in.
 
IMO it would come down to the tires available in 15 inch sizes. Without an A/B
lap time comparison of 15 vs 17 or larger tires who really knows. I do know smaller
lighter is faster than bigger heavier (wheel tire combo)
 
Has anyone attempted this recently?

What did you run for tires? How did they perform? Did you find an optimal tire pressure?

Would you do it again?

These questions are a perpetual plague on people who prefer stock wheel sizes...I'm not sure if the question has been asked recently or in this way. Any insights are welcome.

Remind me what size tires you're running again?

It really depends on two things- 1- what size rims you have and the tire sizes you're running, and 2- how serious/competitive you're planning on being

With 15" rims it's not so much the sidewall flex that hurts you, it's the lack of available tire sizes and compounds. Sure the taller sidewalls flex more, but that's a pretty minor deal compared to not being able to run a decent compound. There really aren't a lot of options, especially if you're running wider tires. And if you're planning on a single set of tires- as in, you're running the same tires on the street and on the track, well good luck. More than likely you'll either have to run 400 tread wear tires on the track, or track only tires on the street.

If the goal is just to go have some fun autoX'ing, then just run your BFG T/A's or Cooper Cobra's and have a good time. It'll be fun, you'll just slide all over the place and guys with better tires will be faster. On a road track you'll have to be more careful, as the speeds increase the lack of grip can cause bigger issues. But again, if you're just looking to have some fun then carefully figure out what your street tires can handle and have a good time.

Tire pressures depend a lot on the track, the weather, how your car is set up for suspension, how your tire size relates to your rim size, what alignment you've set, etc. What works for one person's car may not be ideal for yours. It's something you have to mess around with. When I was doing trackdays with my motorcycle a lot of days the track provider's staff would give some suggestions on tire pressures, but they were just general guidelines. Some of it is just driver preference too.

I have run 15's autoX'ing, but that was on my '56 Healey 100 and you could get decent tires back then. That car also used a much shorter tire, which is a big deal. If you go down to ~24" tall tires you can still get R888's, Proxes RA1's, Pirelli's, etc for a 15" rim. Can probably thank all the spec Miata guys for that. But go over 25" tall on the tire height and there's basically nothing now.

If you're looking to get serious/competitive, I would suggest getting a set of 17" or 18" Bullits or something similar so you can have a track set up. Nice thing about the Bullits is you can get them as take off's locally for cheap usually.

I'm also interested in this topic as this is something I'm contemplating (I like the look of the old/older school 15" wheels/tires combo), but if autocross is something I'm into I think the answer is large rims and lower profile tires with stiff sidewalls (there is also more sticker tire options with 17/18" wheels). I think the answer may be keep the 15's for the look and swap for larger rims with stickier tires at the track for performance, but I'll await the more experienced member to chime in.

Exactly. Try it out, have some fun, if you decide autoX is something you want to do frequently then I would wager you'll be looking for a set of 17/18" rims in short order. The tire selection at 15" just keeps getting worse. If you run sizes that are generally right for these cars, you're pretty much running BFG T/A's or Cooper Cobra's. Maybe a Nitto if you're running the right size.

IMO it would come down to the tires available in 15 inch sizes. Without an A/B
lap time comparison of 15 vs 17 or larger tires who really knows. I do know smaller
lighter is faster than bigger heavier (wheel tire combo)

Yes, but smaller is not always lighter and bigger is not always heavier. The 275/35/18's on 18x9's that I run are lighter than the 225/60/15's on 15x7's that I took off. For that matter, the 295's in the back were lighter too.

tireweights_zpsf3d39dce-jpg.jpg


img_5256_zps9f4a2a43-jpg.jpg
 
As 72bluNblu 17 " is the way to go.
Avon tyres as 225 / 255/275 in 15" if you really want 15" but $$$$ compare to a set of 17"

The return road on my local dragstrip is part of the road course ... for sure if I do a track days it will be on 17". My t/a are too soapy for fast driving.


As for running auto x for fun the bf will" do it". Have fun and learn!!
I run auto x and road course for almost 20 plus year mainly on my honda crx .
 
upload_2019-9-24_23-26-7.png

R888R 235/50r15 Slightly less camber hungry than the RA1 and better on dry surfaces than the RA1.
Upped the t-bar sizes after switching to a fresh set these.

upload_2019-9-24_23-29-43.png

RA1 225/50r15 decent in the wet as well as the dry. Go have fun.

upload_2019-9-24_23-44-7.png

Hoosier 'Street TDs' 245/45 -15 Lots of fun. Hardest to drive well. Lightweight. Too lightly built for any street use.

Now go put some shoes on and get out there. ;)
 
As of Spring '19, 1.12"
Started using the R888R for events in '17
Otherwise I think the summary here is up to date.
67 Barracuda Autocross Tech.

Your Barracuda is amazing! There's a ton of good info in your link too. Thanks for putting that together. I'm psyched to see that you're running a Torqueflight in that monster. :cool:

I still can't figure out why Barracudas look just fine with smaller outer diameter tires. Anthing smaller than 26" on the rear of a Duster/Demon/Dart Sport and it looks like you stole the wheels off of a Falcon.
 
IMO the first consideration when changing sizes is to check the load rating.
Using shorter tires for competition drops the CG and roll centers while also improving the gearing when the car is not a dedicated competition vehicle.

Very hard to judge visuals based on track photos, especially autocross. Bodies move around alot. Heck, everything moves around a lot. LOL. Look at the tires - especially the Hoosiers. Even rims flex a little, especially spun and stamped ones. When Scott Harvey recommended doubling up on the wheel spiders, he knew what he was talking about - and that was for rally's with tire technology 50 years ago!

Same wheels and tires as top photo, hitting the brakes after the finish - and this was a run in the damp. See how much room appears over rear tires. LOL
upload_2019-10-8_10-24-51.png


I was looking for a pic of modern 'vette in the 180 but 'stang entering the same turnaround will do as an example.
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I've done two time attack events in my Duster with 15" Rallyes and fat tires (215/65-15 front and 275/60-15 rear) and it sucks lol. On one lap I tried airing down my fronts from 40 to 35 psi hoping for a bit more grip but all that happened was the sidewalls started rolling under the wheels and my grip got worse.

Over the winter I plan to go to 18" wheels and some legit performance 40 or 45 aspect ratio all- seasons. I'll see how those do at the next track event I can get to and if I need more grip I'll get another set of wheels with track- only tires.
 
On most cars, higher pressure on fronts and less on the rear.
Even for rallycross its recommended to air up rather than down - that's partly to make sure the tire stay on the rim.
I think running unequal size tires makes it more difficult to get the 'balance'.

If you have or can borrow an extra set of rims, end of seasons used to be a good time of year to pick up used race tires. I assume it still is.
Even better if you have a friend close enough swap or borrow a set already mounted.
@CPDave brought an old set to a T&T and we ran them back to back against what I brought.
That's how I ended switching from the Street TDs to the RA1s.
The difference in precision and feedback outweighed (pun intended) the fun of being able to hang in well past the best grip point.

One thing to be aware of with race tires and near race tires is the optimal cambers they want. Whatever you look at when you got to spend the big bucks on new, check the manufacturer's recommendation. Another thing is operating tempoeratures. A lot of the 200 TW near race tires (labeled street but really sold for competition in the 200 TW classes) are not recommended for use when temperatures are below 50*F. Based on your location - that could be an issue. There are r-comps that can be used down to 32 (although not ideal of course) which means they are more versitle than those particular ultra-high performance summer tires.
 
I still can't figure out why Barracudas look just fine with smaller outer diameter tires. Anthing smaller than 26" on the rear of a Duster/Demon/Dart Sport and it looks like you stole the wheels off of a Falcon.

Parked side by side, the A-body Barracuda is mush smaller so it allows the look of a smaller tire
 
Hi guys, I am looking for a little help. I recently installed a QA1 suspension on all four corners of my 1970 Duster 340. I am looking to take her to both track and autocross events. I also upgraded to the 5X4.5 bolt pattern all around. I am looking at 18x10 inch rims currently. Does anyone have any guidance on backspacing and offset? I saw two articles about Dusters doing the same thing running 18x10 and one was using a 25mm "backspacing", I believe they meant offset. one was running 315/30R18 all around and the other was running 275/35/18. Any guidance would be greatly appreciated.
 
Going to have a hard time getting 15" tires on those rims. :poke:

Serious. If there's no threads about 18" rims then start a new thread. Its totally legit. Others will be interested in the topic.
 
Hi guys, I am looking for a little help. I recently installed a QA1 suspension on all four corners of my 1970 Duster 340. I am looking to take her to both track and autocross events. I also upgraded to the 5X4.5 bolt pattern all around. I am looking at 18x10 inch rims currently. Does anyone have any guidance on backspacing and offset? I saw two articles about Dusters doing the same thing running 18x10 and one was using a 25mm "backspacing", I believe they meant offset. one was running 315/30R18 all around and the other was running 275/35/18. Any guidance would be greatly appreciated.
Start your own thread and I’ll answer your question. I just went thru this
 
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