Wheel tire question for SCCA Solo CAM-T car

[one mile]

Back working on my Daughters '65 Barracuda and need some recommendations on wheels and tires to compete SCCA CAM-T Solo Autocross car. We already have tubular upper control arms, PST bushings throughout, quick ratio power steering box, tubular sway bar. Most parts are from Firm Feel. We have the 340 torsion bars and K member & lower control arm gussets installed. This list is just to let everyone know that we are trying to be serious and really have hit an area that I have NO knowledge from personal experience. I am thinking to keep the car as low as we can without bottoming out the A frames in every dip. I also looking to run about a 17" rim and a pretty wide tire on the front. (back tires will be on the same 17" rims but wider combo) Any and all positive input is welcome. Have had wonderful help from FABO so far ! Thanks, Tim

 

[72bluNblu]

I can give you a little info on the 17's, 'fraid I'm not as much help with the early A's as I am with the '67 up cars though. What are you running for spindle and brakes? If you're doing the 73+ mopar disks with 17's you'll be limited to about ~5.6" of backspace on a lot of rims because of outer tie rod interference. Some rims can get away with more than that (I've heard of almost 6" of backspace working on the Mustang Cobra R rims), but 5.6" would be the "safe" number where most rims would still clear the tie rod without any issues. That would also probably make a 17x8 your best bet, I don't think you'll be able to pull of a 17x9 with the fender clearance on an early A, but like I said that's not my area of expertise. I have heard of 245's being run on the front of early A's.

You might try member @vntned, he has a lowered early Dart he runs 15x8's on with 225's. With 17's you can definitely run more backspace and I would bet based on vntned's backspace numbers a 245 would work if it was the right height, a 245/40/17 would be 24.7" tall and that should work on the early cars, I usually shoot for closer to 26" tall on the 67+ cars but I know lowered early A's can't run that tall of a tire if there's a lot of width to it. There are some good, soft compound (200 A AA) tires available in a 245/40/17.

If you haven't seen this thread there's a few folks on here that do road race stuff with the early A's, a little different than CAM-T but I bet there's still useful info there Trans-Am info for the 1966 Barracuda

Not sure how light the car is, but I know even on the early A's a lot of the road race cars were running larger torsion bars, in the 1.12" range. And the vintage road race guys don't have anywhere near the tire options you have for CAM-T, with the soft compounds available for use in that class I think the 340 torsion bars will be undersized.

 

[one mile]

I can give you a little info on the 17's, 'fraid I'm not as much help with the early A's as I am with the '67 up cars though. What are you running for spindle and brakes? If you're doing the 73+ mopar disks with 17's you'll be limited to about ~5.6" of backspace on a lot of rims because of outer tie rod interference. Some rims can get away with more than that (I've heard of almost 6" of backspace working on the Mustang Cobra R rims), but 5.6" would be the "safe" number where most rims would still clear the tie rod without any issues. That would also probably make a 17x8 your best bet, I don't think you'll be able to pull of a 17x9 with the fender clearance on an early A, but like I said that's not my area of expertise. I have heard of 245's being run on the front of early A's.

You might try member @vntned, he has a lowered early Dart he runs 15x8's on with 225's. With 17's you can definitely run more backspace and I would bet based on vntned's backspace numbers a 245 would work if it was the right height, a 245/40/17 would be 24.7" tall and that should work on the early cars, I usually shoot for closer to 26" tall on the 67+ cars but I know lowered early A's can't run that tall of a tire if there's a lot of width to it. There are some good, soft compound (200 A AA) tires available in a 245/40/17.

If you haven't seen this thread there's a few folks on here that do road race stuff with the early A's, a little different than CAM-T but I bet there's still useful info there Trans-Am info for the 1966 Barracuda

Not sure how light the car is, but I know even on the early A's a lot of the road race cars were running larger torsion bars, in the 1.12" range. And the vintage road race guys don't have anywhere near the tire options you have for CAM-T, with the soft compounds available for use in that class I think the 340 torsion bars will be undersized.

Thanks for the info 72bluNblu! I do have the Kelsey-Hayes disc setup on the front. (Pretty good stuff with 4 piston calipers) The 340 bars will have to stay for now they are a B**** to put in with the Doug headers using up most of the room under the car. I will check out your links.

 

[one mile]

Thanks for the info 72bluNblu! I do have the Kelsey-Hayes disc setup on the front. (Pretty good stuff with 4 piston calipers) The 340 bars will have to stay for now they are a B**** to put in with the Doug headers using up most of the room under the car. I will check out your links.

I am running 225/45/17 on 17x8 rims now but I need to know if I can & go bigger.(front only)

 

[72bluNblu]

What backspace? How much clearance do you have to the fender?

 

[one mile]

What backspace? How much clearance do you have to the fender?

4 3/4 backspace , fender clearance is 1/8

 

[one mile]

4 3/4 backspace , fender clearance is 1/8

Complete front end is new so Camber has not been set, that could help a little bit but not much. I am going to try to run "Best of both worlds" on the front end alignment and settings. I hate a car that "plows through a curve" (under steer) so that is why this is so critical to me. Any more wheel & Tire thoughts from you all ? Thanks, Tim

 

[72bluNblu]

4 3/4 backspace , fender clearance is 1/8

Wow! That doesn't rub on the fender?

Well, this is the info you need here, post #6
Measuring for Backspace Front Wheels

Keith Mopar has 17x8's with 225/45/17's on his '65 cuda with 5.5" of backspace. Only catch is he says he has wilwood disks, at least in the rear. Not sure in the front. If his track width is the same, it would mean you could run 17x8's with a 5.25" backspace and 245/40/17's up front. Same clearance to the fender as your current set up, same clearance to the suspension as his. Problem is I think his track width is probably wider with the wilwoods than yours is with the KH's, I'd have to know what kit he's using.

Thing is you should be able to run similar backspaces as the later cars, after all the control arms are the same length. The KH disks have a narrower track width, so that would reduce the backspace some compared to the later cars with BBP disks. The sway bar set up in the front might limit it too if you have a stock bar. Not sure if they have sway bars for the early A's that are shaped for big tires.

Like I said before, Early A's are not my area of expertise, I'm just comparing other set ups and looking at the math. Obviously there's more to it than that, so hopefully someone else will chime in.

 

[one mile]

Wow! That doesn't rub on the fender?

Well, this is the info you need here, post #6
Measuring for Backspace Front Wheels

Keith Mopar has 17x8's with 225/45/17's on his '65 cuda with 5.5" of backspace. Only catch is he says he has wilwood disks, at least in the rear. Not sure in the front. If his track width is the same, it would mean you could run 17x8's with a 5.25" backspace and 245/40/17's up front. Same clearance to the fender as your current set up, same clearance to the suspension as his. Problem is I think his track width is probably wider with the wilwoods than yours is with the KH's, I'd have to know what kit he's using.

Thing is you should be able to run similar backspaces as the later cars, after all the control arms are the same length. The KH disks have a narrower track width, so that would reduce the backspace some compared to the later cars with BBP disks. The sway bar set up in the front might limit it too if you have a stock bar. Not sure if they have sway bars for the early A's that are shaped for big tires.

Like I said before, Early A's are not my area of expertise, I'm just comparing other set ups and looking at the math. Obviously there's more to it than that, so hopefully someone else will chime in.

Thank you very much for the info. I will post a pic. or 2 if I can get my daughter to help me. LOL ! Like I said all of this stuff is new and has not "settled" or had proper alignment. Car is not a finished car so it has not been driven to see in fact how it will react going into and out of driveways on an incline or hitting a dip while in a deep turn. I am just trying my best to do it as close to "Right" as i can the 1st time. Thanks, Tim

 

[pishta]

In the rear, I have some 4.5 backspace rims that are close to the stock leaf, you could go a little deeper with offset springs but your interference now becomes the inner wheelwell edge.

 

[one mile]

In the rear, I have some 4.5 backspace rims that are close to the stock leaf, you could go a little deeper with offset springs but your interference now becomes the inner wheelwell edge.

All of this is good info !

 

[one mile]

All of this is good info !

A few friends and I were "Bench Racing" last night and everyone seems to think I need to change my torsion bars like you spoke of before 72bluNblu. I have a new set of KYB "Gas-A-Just" shocks on the car now and I will get the number off the bars that are on the car now. I was told they were 340 bars. so what Torsion bars would you suggest that are reasonably priced ? Keep in mind this car will be on the street from time to time but mainly SOLO X . Pishta has also been a good source of info for us in the past, what have you got to say ? Thanks, Tim

 

[pishta]

I only know the dimensions of the early A's as I got one 20 feet from me in the garage and have been wheel swapping for years looking for the most meat under a stock 8 3/4 track width. Chevy 2 15" Centerlines dual drilled for the SBP is about as close as I can get to the spring without hitting it and I could probably use a 1/2 spacer to get it more centered. The autocross 65 I saw had very well done rear fender lips cut out to match the wheel profile like a Mustang. You could not tell it was custom if you were not familiar with this body style so its possible, but maybe not in your class? That would open the doors to wheel width selection.

 

[72bluNblu]

A few friends and I were "Bench Racing" last night and everyone seems to think I need to change my torsion bars like you spoke of before 72bluNblu. I have a new set of KYB "Gas-A-Just" shocks on the car now and I will get the number off the bars that are on the car now. I was told they were 340 bars. so what Torsion bars would you suggest that are reasonably priced ? Keep in mind this car will be on the street from time to time but mainly SOLO X . Pishta has also been a good source of info for us in the past, what have you got to say ? Thanks, Tim

Well, if reasonably priced is part of the selection I think PST 1.03's would be the way to go. At $239 list, plus the FABO discount, they're almost $150 cheaper than the 1.06" or 1.12" Firm Feel bars. For a car that's mainly autoX the 1.03's might be a little on the small side. But considering that the early A's are lighter to begin with and you'll be running narrower tires than the later A-bodies they might actually work pretty well with a good sized sway bar. I mean, I like the 1.12's on my '74 Duster but it has 275's up front and probably weighs close to 500 lbs more.

I would also plan on getting rid of those KYB's, those things are just harsh. AutoX courses are usually pretty smooth, so they KYB's shouldn't slaughter your times, but a set of Bilsteins or Hotchkis Fox shocks would make driving the car a lot more enjoyable. I was amazed how much better my Challenger felt with the 1.12" torsion bars when I finally tossed the KYB's that were on it for set of Bilsteins. Huge difference in ride quality.

 

[one mile]

Well, if reasonably priced is part of the selection I think PST 1.03's would be the way to go. At $239 list, plus the FABO discount, they're almost $150 cheaper than the 1.06" or 1.12" Firm Feel bars. For a car that's mainly autoX the 1.03's might be a little on the small side. But considering that the early A's are lighter to begin with and you'll be running narrower tires than the later A-bodies they might actually work pretty well with a good sized sway bar. I mean, I like the 1.12's on my '74 Duster but it has 275's up front and probably weighs close to 500 lbs more.

I would also plan on getting rid of those KYB's, those things are just harsh. AutoX courses are usually pretty smooth, so they KYB's shouldn't slaughter your times, but a set of Bilsteins or Hotchkis Fox shocks would make driving the car a lot more enjoyable. I was amazed how much better my Challenger felt with the 1.12" torsion bars when I finally tossed the KYB's that were on it for set of Bilsteins. Huge difference in ride quality.

Great info guys ! Still smoking over bar size. Shocks are new so I have to use them for now. In view of that ,should they be OK with a lighter bar ?

 

[one mile]

Just got out from under the car and the bars are #892 R & #893 L . Don't have any more info.....does any listing tell me what these are out of ? Also has 482 on each bar. Anybody ?

 

[72bluNblu]

Great info guys ! Still smoking over bar size. Shocks are new so I have to use them for now. In view of that ,should they be OK with a lighter bar ?

Just got out from under the car and the bars are #892 R & #893 L . Don't have any more info.....does any listing tell me what these are out of ? Also has 482 on each bar. Anybody ?

892/893 is a set of 340 bars. They should be .87" in diameter, which will give them a wheel rate of 120 lb/in. By comparison, the 1.12" bars I run on my Duster are 300 lb/in. The PST 1.03's are about twice as stiff as the ones you've got now.

As for the KYB's, the fact that they're really harsh will be masked by the softer torsion bars, sure. They will still make the smaller torsion bars feel like they're bigger than they are when it comes to ride quality, but probably won't do anything for your handling. You can upgrade that stuff at any point. The green brick started out with 383 bars, so, .89" and 130 lb/in. The later version used .92's (150 lb/in). That car was also pretty light, but it still used 15" rims and only ran 225's. The more grip you add the more load you put into the suspension, and the more wheel rate you'll need to control those loads. The green brick used the smallest bars out of any of the cars I know to compete, pretty much everyone else starts at 1.03 and goes up from there. The "red brick" runs 1.20" torsion bars, that has to be a rate north of 350 lb/in. autoxcuda runs 1.14's that are 320 lb/in, tomswheels ran 1.06's from Firm Feel (252 lb/in), I think Peter Bergman is still running MP 1.04's (250 lb/in).

It's not like you can't run it as is and upgrade later, just something to consider. Might be worth putting the torsion bars and shocks on the old "wish list" and saving up. Or upgrade to the 1.03's and wait on the shocks, as a primary autoX car the ride quality of the KYB's probably won't be as bothersome as someone that runs on the street all the time.

 

[one mile]

I'm back to reasearching wheels and tires to run on front and just running what I have gotten together for suspension for now. Just like you said, building from there with a "wish list". I am grateful for the info and will use it as I move forward. As always money is a big issue Lol ! I will just keep my eyes open for that "super deal" on some bigger bars. Thanks, Tim