Suspension options 67 Dart convertible

[jjack]

New member, not sure if I'm bringing my questions to the correct forum.

I have posted in the tire/wheel forum. I did not get the answers I need. I'm wondering if my questions are more suspension than tire/wheel.

I'm planning a 1967 Dart convertible to 1970 340 swinger looking convertible. I would like to find the largest tire/wheel that fits both front and rear. I want to carry one spare.

The suggestion is that a 15X7 rally wheel and a 235 60 R15 tire is the largest tire/wheel that won't rub. Is that with the 67/72 disc suspension or the 73+ suspension?

It appears that the 73+ disc front suspension and a 67/70 B Body 8 3/4 axle have nearly the same track width. Would that combo allow the 15X7 wheel to fill out the wheel wells equally all around?

Does anyone know why Chrysler built these cars with a wider front track? Will equalizing the track width negatively affect handling?

 

[el5dart]

ultimately you will need a wheel size fitment tool. you can also use a straight edge and a tape measure if you dont want to buy the tool. your car should be near some sort of completion to get correct measurements.

onthe back of my car stock chassis 245 is as wide as i could go. 255 was rubbing a little on the outer of quarter panel. 71 swinger 15x7 cop car wheels dr diff 8 3/4 housing with 2.5” drum brakes.

 

[remytherat]

67/70 B Body 8 3/4 axle

Unlikely to fit your dart. Works in some other a bodies though.

Is that with the 67/72 disc suspension or the 73+ suspension?

This applies for both, because the likely place for rubbing is at the front of the wheel opening, dependent on wheel diameter more than width

 

[junkyardhero]

a 67/70 B Body 8 3/4 axle have nearly the same track width. Would that combo allow the 15X7 wheel to fill out the wheel wells equally all around?

unlikely you fit rims with stock back spacing with the b-body rear end.

 

[Professor Fate]

Does anyone know why Chrysler built these cars with a wider front track? Will equalizing the track width negatively affect handling?

The rear end width/track (and basically the whole rear subframe) remained unchanged from 1963 until the end of production in 1976 (with minor width variations between 7.25, 8.25, and 8.75).
However, with the 1967 redesign the engine bay and front track were widened to ease assembly line V8 installations- and allow the big block to fit more easily- and a byproduct of that was improved handling. But they never significantly changed the rear end or subframe. Thus the difference in track width between the front and rear in '67 and up A bodies.

 

[jjack]

The rear end width/track (and basically the whole rear subframe) remained unchanged from 1963 until the end of production in 1976 (with minor width variations between 7.25, 8.25, and 8.75).
However, with the 1967 redesign the engine bay and front track were widened to ease assembly line V8 installations- and allow the big block to fit more easily- and a byproduct of that was improved handling. But they never significantly changed the rear end or subframe. Thus the difference in track width between the front and rear in '67 and up A bodies.

That makes sense. I didn't think to check the early A specs. Chrysler does like to utilize existing parts.

 

[el5dart]

btw i love the 70 convertible conversions i’ve seen. be sure and post pics of your journey so i can be jealous

 

[jjack]

I'm planning to install a 6.4 Hemi. The SRT cars with that engine usually come with 20 X 9 wheels, with about an 8" tread width depending on tire selection. My 300 had Goodyear 245 45 R20 8" tread width. I replaced them with Pirelli 275 40 R20 9" tread width.

Which suspension combination allows for similar wheel spacing to the wheel lips front and back, the same size tire/wheel all around, and an 8"-9" tread width?

 

[junkyardhero]

Which suspension combination allows for similar wheel spacing to the wheel lips front and back, the same size tire/wheel all around, and an 8"-9" tread width?

at least 17" but probably a 18 or 19" rim will be needed for that. and at that point, you're fully clearing the front suspension so it becomes a moot point. out back is a little more questionable because of the confined nature of the slab sided wheel wells.

@72bluNblu would know more specifics because he's running wheel and tire packages in that size.

 

[72bluNblu]

For a 15x7 you don’t want a B-body rear axle out back because you can’t get enough backspacing.

An 8” rim up front will need a 17” wheel, which will take a 245/45/17 up front with a 5.25-5.6” backspace. A 245/45/17 will also work out back on a 17x8, but that backspace needs to be about 5”. Some cars could probably run 5.25”, which would overlap with the front, some might need a small spacer. Some cars could get away with 255/45/17 all the way around but others would need some trimming to make that work.

9” wide rims need an 18” wheel. On a Dart with the stock spring locations the back will limit the size to a 255 regardless. With a 1/2” spring offset and 18x9’s you could probably run 275/35/18’s all the way around, it will still be really tight in the back. The front would need an 18x9” with about a 6” backspace for that, if you offset the rear springs the back would need about 5.5” to 5.75”. A 65-67 B rear might help at that point to even things up on the backspace. But a 68-70 would be a little too wide to even up the front and rear perfectly.

 

[jjack]

For a 15x7 you don’t want a B-body rear axle out back because you can’t get enough backspacing.

An 8” rim up front will need a 17” wheel, which will take a 245/45/17 up front with a 5.25-5.6” backspace. A 245/45/17 will also work out back on a 17x8, but that backspace needs to be about 5”. Some cars could probably run 5.25”, which would overlap with the front, some might need a small spacer. Some cars could get away with 255/45/17 all the way around but others would need some trimming to make that work.

9” wide rims need an 18” wheel. On a Dart with the stock spring locations the back will limit the size to a 255 regardless. With a 1/2” spring offset and 18x9’s you could probably run 275/35/18’s all the way around, it will still be really tight in the back. The front would need an 18x9” with about a 6” backspace for that, if you offset the rear springs the back would need about 5.5” to 5.75”. A 65-67 B rear might help at that point to even things up on the backspace. But a 68-70 would be a little too wide to even up the front and rear perfectly.

Is there a suspension combination that fits the same 8" or 9" wide wheel front and back? The dart is rather slab sided, so I was thinking the track width needs to be equal front to back in order to use one wheel profile? I think that would be a 73+ front suspension and B-body axle, or possibly 67-72 disc front suspension and an a-body axle with disc brakes and B-body axles.

In the front, how wide can the tire/wheel be before it starts to rub something while turning? The 67-72 sway bar should be the first part to rub, but will the 73+ suspension rub the strut rod before the tire will rub the frame on the back side? Will a coil-over suspension allow for a wider tire/wheel?

I'm reading your thread about the Demon build. Great job!

 

[72bluNblu]

Is there a suspension combination that fits the same 8" or 9" wide wheel front and back? The dart is rather slab sided, so I was thinking the track width needs to be equal front to back in order to use one wheel profile?

I mean sure, a custom width rear end isn’t all that hard to accomplish. With factory parts it’s not exact but close enough.

With 8” wide wheels in 17” or 18” you could run a 245 wide tire all the way around with about 5.25” of backspace with the 73+ brakes/suspension up from and an A-body 8 3/4 and BBP axles and brakes with the stock spring locations in the back. Depending on the exact tires you might need a small spacer in the back, but we’re talking ~1/8”, nothing crazy. Disks in the rear would take care of that, no spacer needed.

With 9” wide wheels you need a 1/2” spring offset in the back, there’s not enough room in the back to run wide enough tires to need the 9” wide wheel with stock spring locations on a Dart. 9’s in the front need about 6” of backspace, that eliminates the 17’s because they hit the outer tie rods end at about 5.7” of backspace. So 18x9’s up front with ~6” backspace. In the back with the 1/2” offset and an A-body 8 3/4 with BBP axles an 18x9 with a 6” backspace is a bit much, but again it’s close. The spacer you’d need would probably be a 1/4” or less. And real close to not needing a spacer with disks instead of drums. 255/40/18’s would fit, 275/35/18’s would be close but might need some quarter lip rolling or trimming on some cars because of body tolerances.

In the front, how wide can the tire/wheel be before it starts to rub something while turning?

You can run 275/35/18’s up front without any significant body modifications as long as the ride height isn’t too low.

The 67-72 sway bar should be the first part to rub

Usually at about a 235 or 245 wide tire with the factory sway bar tab locations. There are aftermarket sway bars that get around that.

but will the 73+ suspension rub the strut rod before the tire will rub the frame on the back side? Will a coil-over suspension allow for a wider tire/wheel?

The strut rod won’t rub on anything. With the 73+ suspension and an 18x9” at around 6” of backspace the 275’s are right on the frame at full steering lock in the back and right on the fenders without rolling the lips or pushing the arch out. Unless you start into fender mods 275’s will fill up pretty much the entire front wheel well.

Coilovers don’t make any more room for wheels in the front. With the a-body suspension the fenders, frame and inner fenders are the limiting factors.

The same is actually true in the back if you do a 1/2” spring offset, the wheel tub and quarters are the limiting factors at that point.

I'm reading your thread about the Demon build. Great job!

thanks!

 

[jjack]

I mean sure, a custom width rear end isn’t all that hard to accomplish. With factory parts it’s not exact but close enough.

With 8” wide wheels in 17” or 18” you could run a 245 wide tire all the way around with about 5.25” of backspace with the 73+ brakes/suspension up from and an A-body 8 3/4 and BBP axles and brakes with the stock spring locations in the back. Depending on the exact tires you might need a small spacer in the back, but we’re talking ~1/8”, nothing crazy. Disks in the rear would take care of that, no spacer needed.

With 9” wide wheels you need a 1/2” spring offset in the back, there’s not enough room in the back to run wide enough tires to need the 9” wide wheel with stock spring locations on a Dart. 9’s in the front need about 6” of backspace, that eliminates the 17’s because they hit the outer tie rods end at about 5.7” of backspace. So 18x9’s up front with ~6” backspace. In the back with the 1/2” offset and an A-body 8 3/4 with BBP axles an 18x9 with a 6” backspace is a bit much, but again it’s close. The spacer you’d need would probably be a 1/4” or less. And real close to not needing a spacer with disks instead of drums. 255/40/18’s would fit, 275/35/18’s would be close but might need some quarter lip rolling or trimming on some cars because of body tolerances.


You can run 275/35/18’s up front without any significant body modifications as long as the ride height isn’t too low.



Usually at about a 235 or 245 wide tire with the factory sway bar tab locations. There are aftermarket sway bars that get around that.



The strut rod won’t rub on anything. With the 73+ suspension and an 18x9” at around 6” of backspace the 275’s are right on the frame at full steering lock in the back and right on the fenders without rolling the lips or pushing the arch out. Unless you start into fender mods 275’s will fill up pretty much the entire front wheel well.

Coilovers don’t make any more room for wheels in the front. With the a-body suspension the fenders, frame and inner fenders are the limiting factors.

The same is actually true in the back if you do a 1/2” spring offset, the wheel tub and quarters are the limiting factors at that point.



thanks!

72 bluNblu,
Thanks for such a thorough response. I thought the hard part would be figuring out what fits. I spent time this weekend searching wheels and tires. Not easy finding wheels. When I found something interesting, the wheel was not made in my size. I found a few I liked, but they are only available in 18X9.5.

I read that Chrysler widened the front wheel opening for the 1972 dart. I don't know where it was enlarged, but would that provide more clearance?

I believe traction and handling improves with a larger tire contact patch. My 300 SRT came with 245 45 R20 Goodyears that had an 8" tread width. With traction control on, I would get some wheel spin on a hard launch. I installed Pirelli P Zero 275 40 R20. Same diameter, one inch wider tread. Now the car won't spin the tires on hard launch with TC on. The car simply digs in and goes. In this case, I'm not sure if it's because of the old Goodyears, the new better Pirelli's, or the larger contact patch.

That being said, in case of my A body, does it matter how I get to an 8"-9" wide tread?

Would a 17" tire have a smaller contact patch than an 18" tire?

If there is a 255 tire with an 8.5" tread, and a 275 tire with an 8.5" tread, would the traction be the same?

 

[72bluNblu]

72 bluNblu,
Thanks for such a thorough response. I thought the hard part would be figuring out what fits. I spent time this weekend searching wheels and tires. Not easy finding wheels. When I found something interesting, the wheel was not made in my size. I found a few I liked, but they are only available in 18X9.5.

18x9.5” is possible on the front, as well as the rear if you do the 1/2” spring offset.

I read that Chrysler widened the front wheel opening for the 1972 dart. I don't know where it was enlarged, but would that provide more clearance?

Yes and yes. The wheel opening got longer in ‘72, so there is more clearance to the tire at the lower front corner of the wheel opening. Which is definitely helpful in avoiding fender modifications with wider or taller tires. It won’t necessarily allow a larger tire, 275/35/18 is still probably as big as you’re gonna get away with unless you do other fender modifications. But it might keep you from doing mods to get the 275 comfortably in there

I believe traction and handling improves with a larger tire contact patch. My 300 SRT came with 245 45 R20 Goodyears that had an 8" tread width. With traction control on, I would get some wheel spin on a hard launch. I installed Pirelli P Zero 275 40 R20. Same diameter, one inch wider tread. Now the car won't spin the tires on hard launch with TC on. The car simply digs in and goes. In this case, I'm not sure if it's because of the old Goodyears, the new better Pirelli's, or the larger contact patch.

Yep, more tread on the ground means more traction on dry pavement

That being said, in case of my A body, does it matter how I get to an 8"-9" wide tread?

It does, because just having a tire with that tread width doesn’t necessarily mean you’re getting all of it on the ground. That’s where the tire manufacturers recommended wheel sizes come in, as in, it’s generally better to run a 275 on the widest wheel it fits on rather than the narrowest if handling is the goal. But some of that can be altered with tire pressures too.

Would a 17" tire have a smaller contact patch than an 18" tire?

Not if the diameter of the tire is the same. Again the width of the wheel would make a bigger difference.

If there is a 255 tire with an 8.5" tread, and a 275 tire with an 8.5" tread, would the traction be the same?

All other things being equal, yes. It’s certainly worth paying attention to the actual measured specs of the tires, because not all 275’s have the same tread width. But when you start comparing tires from different manufacturers that’s not necessarily a clear cut answer because of differences in compounds, tread design, tire construction etc.

 

[junkyardhero]

All other things being equal, yes. It’s certainly worth paying attention to the actual measured specs of the tires, because not all 275’s have the same tread width. But when you start comparing tires from different manufacturers that’s not necessarily a clear cut answer because of differences in compounds, tread design, tire construction etc.

this is an absolutely critical point.

just because it says 275 doesn't mean it's the same size as another 275 even from the same company. pore over the published specs and look online for information just to be sure.

a lot of tires for spec series racing are like this. for instance the more racy 205/50-15's offered by bridgestone and falken are definitely not your pappy's 205!

 

[jjack]

18x9.5” is possible on the front, as well as the rear if you do the 1/2” spring offset.

Yes and yes. The wheel opening got longer in ‘72, so there is more clearance to the tire at the lower front corner of the wheel opening. Which is definitely helpful in avoiding fender modifications with wider or taller tires. It won’t necessarily allow a larger tire, 275/35/18 is still probably as big as you’re gonna get away with unless you do other fender modifications. But it might keep you from doing mods to get the 275 comfortably in there


Yep, more tread on the ground means more traction on dry pavement


It does, because just having a tire with that tread width doesn’t necessarily mean you’re getting all of it on the ground. That’s where the tire manufacturers recommended wheel sizes come in, as in, it’s generally better to run a 275 on the widest wheel it fits on rather than the narrowest if handling is the goal. But some of that can be altered with tire pressures too.


Not if the diameter of the tire is the same. Again the width of the wheel would make a bigger difference.


All other things being equal, yes. It’s certainly worth paying attention to the actual measured specs of the tires, because not all 275’s have the same tread width. But when you start comparing tires from different manufacturers that’s not necessarily a clear cut answer because of differences in compounds, tread design, tire construction etc.

I messed up the whole quote thing. I'll figure it out.

I'm not opposed to anything to make it work right. I think the 275 tire meets my needs for handling and traction. I don't see any benefits going larger. I wouldn't do a mini tube to add larger tires mostly because I want all the wheels to be the same profile. However, will the suspension work better with spring relocation VS off set hangers? Will the suspension work better if the pivot points are directly above the springs?

Nice to know I can use 9.5" wheels if I find one I like. Would a 9.5" wheel need a 6.5" backspace? The specs I found for the 275 tires all base their measurements on a 9.5" wheel. It appears that some C6 Corvettes us a 275 35 R18 tire, so availability should be good.

I will try to get measurements for the 1972 fender. I have seen some posts where tire clearance is added by cutting a thin wedge from the fender, then the wheel lip is pushed forward and rewelded. I want wheel opening trim. Not sure if the trim will fit if that much modification is needed. I have seen 1972 darts with wheel opening trim.

I have read several posts about making a taller spindle, using the taller F M J spindles, taller UBJ, etc. I have not found a post that explains the problem they are trying to fix?

I was planning on setting the car to factory ride height, I see many people are lowering the front end. Is this for looks or is there an advantage to lower the front ride height?

 

[jjack]

this is an absolutely critical point.

just because it says 275 doesn't mean it's the same size as another 275 even from the same company. pore over the published specs and look online for information just to be sure.

a lot of tires for spec series racing are like this. for instance the more racy 205/50-15's offered by bridgestone and falken are definitely not your pappy's 205!

I'm seeing that as I search for tires. So far, the tires I'm considering are all about the same. They are 10.9" overall width, 9.6" tread width, on a 9.5" wide wheel. These tires can go on 9"-11" wide wheels.

Thanks

 

[DionR]

I have read several posts about making a taller spindle, using the taller F M J spindles, taller UBJ, etc. I have not found a post that explains the problem they are trying to fix?

Generally an F-Body spindle or longer UBJ's are used to improve suspension geometry by raising the outer pivot point of the UCA. The goal is to get a better roll center and better camber gains when the suspension compresses.

I was planning on setting the car to factory ride height, I see many people are lowering the front end. Is this for looks or is there an advantage to lower the front ride height?

One of the best ways to improve the suspension geometry and handling on an A-Body is to lower it. But you need stiffer torsion bars to avoid bottoming out and you need better shocks to control those torsion bars.

And (just my opinion), I think they look better lowered.

 

[DionR]

Oh, and if you want to make use of those wider tires and lower the car, don't follow it up with the factory alignment specs either. Look for the "skosh chart".

 

[jjack]

Generally an F-Body spindle or longer UBJ's are used to improve suspension geometry by raising the outer pivot point of the UCA. The goal is to get a better roll center and better camber gains when the suspension compresses.



One of the best ways to improve the suspension geometry and handling on an A-Body is to lower it. But you need stiffer torsion bars to avoid bottoming out and you need better shocks to control those torsion bars.

And (just my opinion), I think they look better lowered.

Are these streetcar issues or racetrack issues?

I looked under my Dart this morning. Both control arms angle down toward the spindle. Is the goal to get the upper control arm level so that as the suspension compresses, the arc of the upper control arm will pull the upper part of the spindle in? Does the factory suspension maintain zero camber change through the full suspension travel?

If it would benefit my car to use a F-spindle and a longer UBJ, will that clear an 18" wheel?

Does a lowered spindle lower roll center? Would that be better than lowering the suspension?

I still don't fully understand roll center. I understand what it is and why it matters, but I'm not sure about the cause and affect of changes. I read that lowering the roll center increases the moment of the center of gravity. Does that negate some of the benefit of lowering the roll center? Is the roll center on A-bodies bad or do the changes simply make the car better?

Reading about roll center, it appears the formula to determine it is based on the center of the tires contact patch. How will wider tires and more backspace affect roll center? They will move the centerline of the contact patch relative to the ball joint.

How much can I lower the front suspension before I create a fender rubbing problem with an 18" wheel and a 275 tire?

 

[DionR]

Are these streetcar issues or racetrack issues?

Depends. I think a car that handles well is more fun than one that doesn't. I am working on my stuff not for a track but so I can enjoy it on the street, but if I ever do make it to the track I am sure it will be far more enjoyable than a stock setup.

But the car would probably drive fine with a stock suspension and ride height. I just wouldn't tangle with any 4 cylinder Foxbodies in the twisties as they will probably take your lunch money.

I looked under my Dart this morning. Both control arms angle down toward the spindle. Is the goal to get the upper control arm level so that as the suspension compresses, the arc of the upper control arm will pull the upper part of the spindle in? Does the factory suspension maintain zero camber change through the full suspension travel?

The potential camber gain of having the UCA slope down towards the car is one potential benefit, the other is moving the roll center.

Here is a visual of how the slope of the upper arm can change the roll center:

If the LCA slopes down as well, it doesn't necessarily mean the instant center is outside the car like the top image. You would have to map that out.

Not really sure if the stock suspension maintains zero camber, but if it did it would be a drawback. You want some camber gain as the suspension compresses, if only to offset the roll of the body as that also de-cambers the outside tire.

If it would benefit my car to use a F-spindle and a longer UBJ, will that clear an 18" wheel?

Yes. @BergmanAutoCraft runs an 18" wheel with 1" long UBJ's and an F-Body spindle.

I still don't fully understand roll center. I understand what it is and why it matters, but I'm not sure about the cause and affect of changes. I read that lowering the roll center increases the moment of the center of gravity. Does that negate some of the benefit of lowering the roll center? Is the roll center on A-bodies bad or do the changes simply make the car better?

I think there are two camps on the roll center. One says get the roll center as low as possible (but above ground) while the other says to get it as close to the CG as possible and reduce the roll couple. There are also the two camps of no swaybars and heavy springs vs. lighter springs and bigger swaybars.

So there is the possibility that lowering the roll center makes the roll couple longer and is a drawback. But I suspect that the benefits outweigh that.

Not sure on the stock A-Body roll center. But I know lowering it makes it better for sure. Wouldn't be surprised to learn that a stock A-Body has a roll center underground. I will know at some point as I plan to layout it out and see.

Reading about roll center, it appears the formula to determine it is based on the center of the tires contact patch. How will wider tires and more backspace affect roll center? They will move the centerline of the contact patch relative to the ball joint.

True. My bet is it doesn't affect it a whole lot. The pivot points are the key, the center of the tire probably just tweaks it.

How much can I lower the front suspension before I create a fender rubbing problem with an 18" wheel and a 275 tire?

All depends on the wheel and setup. I know @72bluNblu has his pretty low with a 275/35R18 on an 18x9 +35mm wheel and had to push the front lower corner of his fender out to clear, but that is all he had to do. Pretty sure he is lower now than this pictures shows (it's from 2016, first one I found).

 

[72bluNblu]

The ‘72 Dart fender measurements are here in this thread

Front Fender Dimensions

Are these streetcar issues or racetrack issues?

Depends on how you use your streetcar. If cars and coffee is the most use it gets, probably doesn’t matter. If you want to carve up some mountain roads, you’ll want better than factory geometry

I looked under my Dart this morning. Both control arms angle down toward the spindle. Is the goal to get the upper control arm level so that as the suspension compresses, the arc of the upper control arm will pull the upper part of the spindle in? Does the factory suspension maintain zero camber change through the full suspension travel?

Yes. At factory ride height the camber gain isn’t great (it was designed for bias plys, which want very different geometry). If you lower the car so that the UCA is parallel to the ground the camber gain is significantly improved, which keeps your outside wheel flatter on the ground as the suspension compresses with cornering load.

No camber change throughout a suspensions travel isn’t a thing. Certainly not with anything that uses control arms. If you’re on a fixed length control arm the suspension can’t travel purely vertical, the spindle rotates around the suspension points as it travels. Unequal length A arms can minimize that some, but not eliminate it. Even if you could, you wouldn’t want to because adding negative camber to the outside wheel as the suspension loads helps keep the outside wheel flat to maximize traction. Ideally, you’d match your negative camber gain to the roll angle of the car at maximum tire load

If it would benefit my car to use a F-spindle and a longer UBJ, will that clear an 18" wheel?

The FMJ spindles clear fine, and they improve camber gain slightly over the A body spindles. They clear 18’s fine. I’m not sure what the tallest UBJ that will clear the 18 but it’s at least a 1/2”, I can’t remember if @BergmanAutoCraft is running a 1” taller UBJ or 1/2”.

Does a lowered spindle lower roll center? Would that be better than lowering the suspension?

No. A drop spindle lowers the car, while maintaining the control arm angles. When @HPP ran a car (my Challenger) with 2” drop spindles vs a car at the same ride height lowered with stock spindles the geometry of the stock spindles was better. The 2” drop spindles added bump steer and did not improve the other geometry.

How much can I lower the front suspension before I create a fender rubbing problem with an 18" wheel and a 275 tire?

About 2”. You could probably go more with some fender mods, but other issues come up too.

My Duster is lowered about 2” from stock. That puts the LCA parallel to the ground, which is close to ideal for the geometry. 275/35/18’s work at that height with a ‘71 fender opening, I pushed the lower corner of the fender out by lengthening the fender to bumper brace about 2”.

You also have to run shorter bump stops to maintain suspension travel, and I run QA1 tubular LCA’s that also allow for about 1” extra compression travel. With those mods, at full compression the 275’s just touch the inner fender when the suspension bottoms.

And it puts a set Doug’s headers a smidge under 4” to the ground, which is about as low as you can comfortably go and still navigate speed bumps without leaving your exhaust behind.

 

[jjack]

Depends. I think a car that handles well is more fun than one that doesn't. I am working on my stuff not for a track but so I can enjoy it on the street, but if I ever do make it to the track I am sure it will be far more enjoyable than a stock setup.

But the car would probably drive fine with a stock suspension and ride height. I just wouldn't tangle with any 4 cylinder Foxbodies in the twisties as they will probably take your lunch money.



The potential camber gain of having the UCA slope down towards the car is one potential benefit, the other is moving the roll center.

Here is a visual of how the slope of the upper arm can change the roll center:

If the LCA slopes down as well, it doesn't necessarily mean the instant center is outside the car like the top image. You would have to map that out.

Not really sure if the stock suspension maintains zero camber, but if it did it would be a drawback. You want some camber gain as the suspension compresses, if only to offset the roll of the body as that also de-cambers the outside tire.



Yes. @BergmanAutoCraft runs an 18" wheel with 1" long UBJ's and an F-Body spindle.



I think there are two camps on the roll center. One says get the roll center as low as possible (but above ground) while the other says to get it as close to the CG as possible and reduce the roll couple. There are also the two camps of no swaybars and heavy springs vs. lighter springs and bigger swaybars.

So there is the possibility that lowering the roll center makes the roll couple longer and is a drawback. But I suspect that the benefits outweigh that.

Not sure on the stock A-Body roll center. But I know lowering it makes it better for sure. Wouldn't be surprised to learn that a stock A-Body has a roll center underground. I will know at some point as I plan to layout it out and see.



True. My bet is it doesn't affect it a whole lot. The pivot points are the key, the center of the tire probably just tweaks it.



All depends on the wheel and setup. I know @72bluNblu has his pretty low with a 275/35R18 on an 18x9 +35mm wheel and had to push the front lower corner of his fender out to clear, but that is all he had to do. Pretty sure he is lower now than this pictures shows (it's from 2016, first one I found).

I do want my car to handle well and be sure footed. It is interesting to see how suspension changes affect the steering geometry. I learn a lot from your response. Thanks.

 

[jjack]

The ‘72 Dart fender measurements are here in this thread

Front Fender Dimensions



Depends on how you use your streetcar. If cars and coffee is the most use it gets, probably doesn’t matter. If you want to carve up some mountain roads, you’ll want better than factory geometry



Yes. At factory ride height the camber gain isn’t great (it was designed for bias plys, which want very different geometry). If you lower the car so that the UCA is parallel to the ground the camber gain is significantly improved, which keeps your outside wheel flatter on the ground as the suspension compresses with cornering load.

No camber change throughout a suspensions travel isn’t a thing. Certainly not with anything that uses control arms. If you’re on a fixed length control arm the suspension can’t travel purely vertical, the spindle rotates around the suspension points as it travels. Unequal length A arms can minimize that some, but not eliminate it. Even if you could, you wouldn’t want to because adding negative camber to the outside wheel as the suspension loads helps keep the outside wheel flat to maximize traction. Ideally, you’d match your negative camber gain to the roll angle of the car at maximum tire load



The FMJ spindles clear fine, and they improve camber gain slightly over the A body spindles. They clear 18’s fine. I’m not sure what the tallest UBJ that will clear the 18 but it’s at least a 1/2”, I can’t remember if @BergmanAutoCraft is running a 1” taller UBJ or 1/2”.



No. A drop spindle lowers the car, while maintaining the control arm angles. When @HPP ran a car (my Challenger) with 2” drop spindles vs a car at the same ride height lowered with stock spindles the geometry of the stock spindles was better. The 2” drop spindles added bump steer and did not improve the other geometry.


About 2”. You could probably go more with some fender mods, but other issues come up too.

My Duster is lowered about 2” from stock. That puts the LCA parallel to the ground, which is close to ideal for the geometry. 275/35/18’s work at that height with a ‘71 fender opening, I pushed the lower corner of the fender out by lengthening the fender to bumper brace about 2”.

You also have to run shorter bump stops to maintain suspension travel, and I run QA1 tubular LCA’s that also allow for about 1” extra compression travel. With those mods, at full compression the 275’s just touch the inner fender when the suspension bottoms.

And it puts a set Doug’s headers a smidge under 4” to the ground, which is about as low as you can comfortably go and still navigate speed bumps without leaving your exhaust behind.

Thanks for the fender link. That saved me from a lot of research. I have been searching for pics of both fenders to determine the difference. I was thinking I would need to get one of each to find the difference. I need to acquire the whole front clip, so it does not matter which parts I get, I have none at this time. I think I could get a full 1972 clip and swap out the grill.

I doubt that I would ever drive this car on a track. The only mountains we have in Michigan are garbage dumps! I Have owned several ex-police cars. I like the firmer ride, flat cornering, and good brakes.

I was opposed to lowering the front end for several reasons, but I now understand why it's necessary. I'm planning for a stock 6.4 engine, and I will use factory exhaust manifolds, so header clearance won't be an issue. Perhaps as this project evolves, I will change my mind about same size wheels and tires. So many newer high-performance cars have larger wheels in back. I could buy run flat tires and forget about a spare. I do like the way your car looks.

So far, my wheel search has been slow. Many wheels are advertised without all the specs. Should I look at 9.5" or 10" wheels? Any Pros or cons? The tire should fit the wheel better, but wider wheels add weight. If I found a wheel that I like, do you know what back space and offset I need for a 9.5" or a 10:" wheel?

If I use the same size wheel all around, do I need to make the track widths the same? If the track width and the wheels are the same, will the wheel lip clearance be the same front and back on a dart?

With everyone's help I think most of the suspension elements have been figured out.
73+ K frame
F-Body spindles and brakes (or aftermarket brakes)
Aftermarket upper and lower control arms + taller UBJ
After market adjustable strut rods.
Bigger sway bar and torsion bars
275 35 R18 tires and min 9" wide wheels
Lower front ride height about 2"
6 leaf HD rear springs
1/2 off set hangers or mini tubs and spring relocate
Rear sway bar

I did find one wheel I like. Not sure how it would look on a dart. It came on some 2010-2014 Mustang GT500's. An aftermarket company is making these so no mustang logo in the center caps. Based on the published specs will they fit?

 

[bjkadron]

Thanks for the fender link. That saved me from a lot of research. I have been searching for pics of both fenders to determine the difference. I was thinking I would need to get one of each to find the difference. I need to acquire the whole front clip, so it does not matter which parts I get, I have none at this time. I think I could get a full 1972 clip and swap out the grill.

I doubt that I would ever drive this car on a track. The only mountains we have in Michigan are garbage dumps! I Have owned several ex-police cars. I like the firmer ride, flat cornering, and good brakes.

I was opposed to lowering the front end for several reasons, but I now understand why it's necessary. I'm planning for a stock 6.4 engine, and I will use factory exhaust manifolds, so header clearance won't be an issue. Perhaps as this project evolves, I will change my mind about same size wheels and tires. So many newer high-performance cars have larger wheels in back. I could buy run flat tires and forget about a spare. I do like the way your car looks.

So far, my wheel search has been slow. Many wheels are advertised without all the specs. Should I look at 9.5" or 10" wheels? Any Pros or cons? The tire should fit the wheel better, but wider wheels add weight. If I found a wheel that I like, do you know what back space and offset I need for a 9.5" or a 10:" wheel?

If I use the same size wheel all around, do I need to make the track widths the same? If the track width and the wheels are the same, will the wheel lip clearance be the same front and back on a dart?

With everyone's help I think most of the suspension elements have been figured out.
73+ K frame
F-Body spindles and brakes (or aftermarket brakes)
Aftermarket upper and lower control arms + taller UBJ
After market adjustable strut rods.
Bigger sway bar and torsion bars
275 35 R18 tires and min 9" wide wheels
Lower front ride height about 2"
6 leaf HD rear springs
1/2 off set hangers or mini tubs and spring relocate
Rear sway bar

I did find one wheel I like. Not sure how it would look on a dart. It came on some 2010-2014 Mustang GT500's. An aftermarket company is making these so no mustang logo in the center caps. Based on the published specs will they fit?

View attachment 1716395906

View attachment 1716395907

View attachment 1716395908

View attachment 1716395911

I believe Wade used the older version of the GT500 wheels. Not sure how they compare: Build thread- 73 duster, forged 5.7 w/ PS and AC, 5 spd, big brakes and floater rear