Back spacing question

[273]

I got a 68 Valiant Signet. I want to autox and drag race it a few times a year. Not worried about being competitive, just for fun. Bought Viking fully adjustable shocks to help with making work on strip/autox/street.

Tires and rims trying to make a decent compromise. I like the big little look and also pro tour too.

Looking to run 15 x 7 up front and 18 x 8 out back, looking at the American Racing torq thrust ll. Comes in both 15 and 18 kind of old school look at decent price.

And tires i want to run BFgoodrich Rival S 1.5 225 45 r15 and 245 40 r18 seems like a decent all around performing tire that I can get a couple of years out of them.

Now I'll being installing 11.75 rotor on a 2" dropped spindle with tubular upper control arm. And out back swapping axles (8 3/4) to have 5 x 4.5 all around.

My question what back spacing front and back do I need ?

I imagine the car will sit pretty low.

 

[72bluNblu]

I'll get the backspacing first, then address some things.

In the front with a 15x7" wide rim you'll want a 4.25" to 4.5" backspace (you cant run more than ~4.5" with a 15" rim). In the back, with an 8" rim and 245's you'll want between 5" and 5.25" of backspace. More is always better, you can correct with spacers or have room to convert to disk brakes (which widen the track).

I really don't think you'll be happy with 15's up front and 18's out back. That's a big diameter difference, and it's gonna look strange. The other thing is, a 225/45/15 is only 23" tall. That's really short. With drop spindles and those tires your headers will sit on the ground. Literally, sit on the ground. If you're going 18's in the back, I would suggest at least 17's in the front. You could get a 17x7, run 4.5" to 5" of backspace, and use the same BFG Rivals but in a 225/45/17, which would be 25" tall. Still a little on the short side, but not extreme.

I'll throw out another option for you, which might make your life a lot easier. Run a set of 17x8's all the way around, 5.25" of backspace, with 245/45/17's. That takes you out of the Rivals, which only come in a 245/40/17, which would be pretty short (24.7"). Or you could run those. But a set of Falken Azeni's would be a good option too, and they come in a 245/45/17 https://www.tirerack.com/tires/tire...T615KPXL&vehicleSearch=false&fromCompare1=yes. The rims are available from Summit, basically AR knock-offs. Same rims I run on my Challenger but in a 17x9. Vision American Muscle 141 Legend 5 Series Gunmetal Wheels 141H7865GM19 Now you can rotate tires, and your handling performance will be much more balanced. No, it won't have that "big and little" look, but the performance will be much improved and you can get more life out of whatever tires you choose. Which will be handy if you plan on running 200 treadwear tires.

Finally, you've probably heard this from me before, but you don't need drop spindles. Not if you're planning a car that will handle well. You can run a set of PST 1.03" torsion bars, run a button style poly bump stop on the LCA, and drop the car almost 2". Probably not quite the full 2" with 1.03" bars, but you can get pretty low. And the Viking shocks will tame those 1.03's just fine. Heck the Vikings should do just fine with 1.06" bars too, which would mean you could lower more. Your drag strip times may suffer a little, but your autoX performance will improve greatly. And so will the handling on the street, which sounds like your primary concern. Just my .02.

 

[273]

Thank i was hoping youd answer.
Guess im gonna have to think it over some more.

Problem is I already own the drop spindles.
Not like Have to use them. But I can go 5.25 back space with 17" rims and dropped spindles ?

I have 1.03 and sway bars for her.

The reason I was thinking 15 and 18
Is i like the 14/15 205/275 most run for big and little. Im running now 14/15 215/245.
At 1st the plan was 225 45 r15 all around until i seen they had 17 and 18 and figure to try to make a big and small look.

But I dont like the look of 17 on the back as much it dont seem to fill it out as much as the front wheel well.



But the 245 45 r17 all around is probably the best idea.

 

[72bluNblu]

Thank i was hoping youd answer.
Guess im gonna have to think it over some more.

Problem is I already own the drop spindles.
Not like Have to use them. But I can go 5.25 back space with 17" rims and dropped spindles ?

I have 1.03 and sway bars for her.

The reason I was thinking 15 and 18
Is i like the 14/15 205/275 most run for big and little. Im running now 14/15 215/245.
At 1st the plan was 225 45 r15 all around until i seen they had 17 and 18 and figure to try to make a big and small look.

But I dont like the look of 17 on the back as much it dont seem to fill it out as much as the front wheel well.



But the 245 45 r17 all around is probably the best idea.

You can probably sell the drop spindles and still have money left over after you buy standard 73+ spindles. I had a set, that's what I did. Even losing money on the drop spindles they still go for double what the regular spindles sell for.

I honestly don't know if the 17x8's with 5.25" backspace will clear with the drop spindles. On my challenger I have 17x9's with 5" of backspace, and those did clear with the drop spindles when I had them, but only by about 3/16". But the outer tie rod end geometry isn't the same for the E's and A's, so, I'm not sure. They would probably work with a small spacer, and with 245's you'd still have a little room to the fender so you could use a spacer there if it was too close. Less than a 1/4" on the spacer though, that's all the extra you'd have to the fender.

With the 17's I think you'd be surprised about how they fill out the fender. I know your Valiant has a higher wheel arch (like my Duster), but the 245/45/17's are 25.6" tall. That's tall enough that they should fill things out pretty well. I know when I was running my Challenger around all the time I had a quite a few folks surprised that I was running 17" rims, they were frequently mistaken for 15's. I don't really see that, but the 275/40/17's on my Challenger are 25.7" tall, so they'd look similar to the 245/45/17's. And the Challenger has similar height wheel arches as well. With the 15's it almost looks like the rear rim is smaller, because of the illusion you get from the taller sidewall. But with the same tire height front and rear they look the same.

The lighting is totally different, but this is my Challenger with 215/60/15's and 235/60/15's in the first picture, compared to the 275/40/17's in the second. With the same style 17" Vision wheels as I linked above

 

[273]

Probably gonna just use normal spindles.

Ive been looking at Valiants with 17 wheels actually suits the car. I think its mainly on the darts I don't like them.

Im pretty sure the plan is now 245 45 r17 all around.

Appreciate the help