Ride height setting confusion

[Dana67Dart]

. As a side note, are you the original owner of your Dart

Technically. I was there when my dad bought it in 67.

 

[1973dust]

Your setting is pretty close to factory, and yes, they looked like 4x4's. Even in the promotional pictures you can see a lot of the cars were almost nose high. So, you didn't do anything wrong at all. The 1/2" to the factory bump stop is also close to correct, these cars in stock trim used the lower bumpstop quite frequently. It's a progressive bump stop that helped to make up for the ridiculously soft factory torsion bars. Most people with stock set ups don't even realize that they're constantly all over the lower bump stops. A dab of grease on the top of the bump stop and a trip around town will pretty much always show contact with factory settings and bars.

View attachment 1716063433

I run my Duster at about 24 7/8" from ground to fender. It's lowered about 2" from factory. Following the factory method for measuring A-B to determine the ride height I'm pretty much at 0. I run an upper bumpstop that's about 2.75" tall, and a lower bump stop that's about 3/8" tall. But I also run the earlier style QA1 LCA's, which aren't as thick and therefore add more clearance. I end up with a little less than 1" of clearance at the bump stop. Which yeah, is probably a bit more than factory. But because I run a short, non-progressive polyurethane bumpstop, I don't want to be using it all the time. I want my suspension to stay off the bump stops, where the factory basically counted on using the bump stops.



The camber curves are available for a lowered car, they were published for a car lowered 1" from factory buy Bill Reilly. The curves were published in data form in this article, for both the factory 73+ A-body disk spindle and the FMJ spindles. Swapping Disc-Brake Spindles - Mopar Muscle Magazine

The best suspension geometry for the A-body suspension with radial tires comes very close to being when the LCA is parallel to the ground, or A-B = 0. You can actually see this in the tables published in that article. Because the length of the control arms doesn't change, the data points are not going to change substantially. Lowering the car doesn't change the data points, it just means that you're moving along the curve (through the data points) from a different starting spot. Which is important, because if you start from the LCA level to the ground all the upward travel of the suspension adds negative camber, which is exactly what you want for best handling with radial tires. Now, making static camber and caster adjustments does change those curves a little, but really, for the most part you can look at those curves and have a decent idea of what you'll get. If you're setting up for competition the devil is in the details and you'll want to measure your own car, but for most street cars, even ones set up for handling, the general idea of what the curve is doing is just fine.

Now, why is the factory ride heigh the way it is? Well, the factory ride height puts the control arms at an angle. From where the suspension starts at the factory ride height, you get positive camber gain initially, which is better for bias ply's. Which is why it was designed the way it is. But it's not good for radials, which do better for handling with negative camber gain. Fortunately, because torsion bar suspension is very ride height adjustable, we can literally correct for the factory setting the car up for bias ply's just by lowering the car and adjusting the bump stops around the new center point. The best handling for a radial tire equipped A-body ends up being lowered quite a bit from factory.

I believe I've read that as you lower the front without lowering the rear, you lose caster? I don't intend on doing anything with the rear but I just think a little rake looks best. I assume that up to 1" lowered in the front would still give more handling benefit than that lost from the lost caster. I do have the problem-solver uppers installed for more caster. If I'm understanding and doing the math right, a 1" drop on a 108" wheelbase loses about 1/2 degree of caster so I probably will still end up with much more than factory.

 

[Ironracer]

Yes, I love the stance of both of your cars. Do I remember right that you have 15's on the rear and 14's on the front of the blue car? My front tires are taller than I would prefer at about 26" but they will have to do for now.

I ran Staggered on my 66 Sat. Loved it, looked raked, but still had good ground clearance

 

[72bluNblu]

I believe I've read that as you lower the front without lowering the rear, you lose caster? I don't intend on doing anything with the rear but I just think a little rake looks best. I assume that up to 1" lowered in the front would still give more handling benefit than that lost from the lost caster. I do have the problem-solver uppers installed for more caster. If I'm understanding and doing the math right, a 1" drop on a 108" wheelbase loses about 1/2 degree of caster so I probably will still end up with much more than factory.

You’re correct, if you lower the front without lowering the rear you lose some positive caster. I haven’t checked your math or anything but it’s a fairly minor effect as long as you don’t run a massive rake on the car.

How wide are your front tires? With just the offset bushings that’s the only thing I could see being an issue. The wider the front tires are the more positive caster is helpful to counter the effects you get from really wide front tires. And with just offset bushings your ability to dial in more caster will be limited. My set up is a bit extreme, but with 275/35/18’s on the front of my car I like to have +6° to +6.5° of caster. Which is more than you can get with the offset UCA bushings regardless of any rake.

 

[Ironracer]

I probably need to loosen up the LCAs and raise mine, I read somewhere that the head of your adjusting bolt should be flushed with the bottom of the LCA, mine's up in there quite a bit just to get clearance that's about within factory specs but I'm running a 215 60 15 on the front, I really kind of wanted to find that in a 70... it's definitely kind of a weird area for me, I don't care about looking cool but I want the damn car to handle good however mine looks raked as heck.

 

[1973dust]

You’re correct, if you lower the front without lowering the rear you lose some positive caster. I haven’t checked your math or anything but it’s a fairly minor effect as long as you don’t run a massive rake on the car.

How wide are your front tires? With just the offset bushings that’s the only thing I could see being an issue. The wider the front tires are the more positive caster is helpful to counter the effects you get from really wide front tires. And with just offset bushings your ability to dial in more caster will be limited. My set up is a bit extreme, but with 275/35/18’s on the front of my car I like to have +6° to +6.5° of caster. Which is more than you can get with the offset UCA bushings regardless of any rake.

I've only got 215/55r17's on the front right now so I assume that would not be a problem. In a few years, when I need new tires, I was planning to go either 235/45 or 245/45 on the front and 255's on the rear as that's the widest recommended on an 8" rim. Even 225/50's on the front would also be a decent height. Any of the above obviously still have far more tread contact than the 205/70R14's I had. At what width of tire would you consider the limited caster to really start to be a problem?. I do have factory power steering, by the way.

 

[Ironracer]

I've only got 215/55r17's on the front right now so I assume that would not be a problem. In a few years, when I need new tires, I was planning to go either 235/45 or 245/45 on the front and 255's on the rear as that's the widest recommended on an 8" rim. Even 225/50's on the front would also be a decent height. Any of the above obviously still have far more tread contact than the 205/70R14's I had. At what width of tire would you consider the limited caster to really start to be a problem?. I do have factory power steering, by the way.

Sounds like you got her set up nice, Man

 

[Dave999]

i'd come back and mesaure again after a month of use
if its all new it will settle a little to give you a baseline to work from
everything is nice and tight at the mo. so it will ride just a little higher than it will eventually settle to. the new bars have to learn to live in the place they are now in and all the bushes will need a little bit of exercise.

dave

 

[72bluNblu]

I've only got 215/55r17's on the front right now so I assume that would not be a problem. In a few years, when I need new tires, I was planning to go either 235/45 or 245/45 on the front and 255's on the rear as that's the widest recommended on an 8" rim. Even 225/50's on the front would also be a decent height. Any of the above obviously still have far more tread contact than the 205/70R14's I had. At what width of tire would you consider the limited caster to really start to be a problem?. I do have factory power steering, by the way.

It's not like there's a size where additional caster becomes mandatory, it's just an effect of increasing the tire width. The wider the front tires get, the more they tend to track the imperfections in the road surface. I've run 275's with as little as about +3.5° caster and as much as +8° caster, for my car and my driving preferences I've found that +6.5° works best for me and my set up. But it's not like the car was dangerous to drive at +3.5° caster, it's just more pleasurable at +6.5° - feels more stable, fewer steering corrections needed etc. Above that the trade off between stability and steering effort isn't worth the additional steering effort, at least IMO, but I also run a 16:1 manual steering box. And it depends on your roads too, apparently a lot of the roads I drive have "ruts" from semi-truck traffic and at lower positive caster values the 275's like to seek them out and follow them. If all your roads are nice and smooth it wouldn't be as significant an occurrence.

I'd say that since the offset bushings should get you into the +3.5° to +4° caster range you shouldn't have any really noticeable effects if you stay with a front tire less than 245 wide. At 245 or above I'd personally want more than +4° of caster, which the offset UCA bushings and stock UCA's probably won't get you, especially with some rake on the car. Some folks have been able to get more than that but it will depend on your car and settings. Typically though if you want much more than +4° you'd need to start looking into tubular or adjustable UCA's.

 

[Ahoey]

It's not like there's a size where additional caster becomes mandatory, it's just an effect of increasing the tire width. The wider the front tires get, the more they tend to track the imperfections in the road surface. I've run 275's with as little as about +3.5° caster and as much as +8° caster, for my car and my driving preferences I've found that +6.5° works best for me and my set up. But it's not like the car was dangerous to drive at +3.5° caster, it's just more pleasurable at +6.5° - feels more stable, fewer steering corrections needed etc. Above that the trade off between stability and steering effort isn't worth the additional steering effort, at least IMO, but I also run a 16:1 manual steering box. And it depends on your roads too, apparently a lot of the roads I drive have "ruts" from semi-truck traffic and at lower positive caster values the 275's like to seek them out and follow them. If all your roads are nice and smooth it wouldn't be as significant an occurrence.

I'd say that since the offset bushings should get you into the +3.5° to +4° caster range you shouldn't have any really noticeable effects if you stay with a front tire less than 245 wide. At 245 or above I'd personally want more than +4° of caster, which the offset UCA bushings and stock UCA's probably won't get you, especially with some rake on the car. Some folks have been able to get more than that but it will depend on your car and settings. Typically though if you want much more than +4° you'd need to start looking into tubular or adjustable UCA's.

When my dart was new, that’s on of the things I noticed about it, was the fact that when you crossed the centre line the car would want to dart over to the other lane. Took it back to dealer they said front end was right on spec. Drove well didn’t wear tires so I thought it was a quirk in the car. You just new it would want to do this.

 

[Ahoey]

When my dart was new, that’s on of the things I noticed about it, was the fact that when you crossed the centre line the car would want to dart over to the other lane. Took it back to dealer they said front end was right on spec. Drove well didn’t wear tires so I thought it was a quirk in the car. You just new it would want to do this.

Had to know it would want to do this

 

[Ceedawg]

My service manual gives the spec between the bump stops and the frame where they make contact. But adjust to your liking. A small bit at the time until it sits level but where you want it.

Had to know it would want to do this

View attachment 1716062869

View attachment 1716062863

View attachment 1716062865
I'm trying to get the ride height and alignment properly set after doing a full front-end rebuild over the winter. I do have a factory service manual and, assuming I am really measuring at the correct locations, I'm currently at 1 3/4" which is 1/8" lower than stock. I am measuring to the extreme lower point of the ball joint and the "rib" directly underneath the torsion bar socket on the adjuster. I think the front-end looks 4x4 height currently. I'm at 26 3/4" from the floor to the fender opening and the k-frame is 7 1/2" off the floor. What is really confusing me is that I only have about 1/2" clearance to the LCA bump-stop which, I would think, should be much greater at my current ride height. If I lower the car to the height that looks right to me, it's practically sitting on the bump-stop. I'm hoping someone can give me an idea what I am doing wrong. FYI, I do intend to shorten the sway-bar links and bolts once I get the ride height ironed out.

I’m almost sure My fsm says to measure under the TB socket and under the ball joint. Not sure how these quotes got on here.

 

[72bluNblu]

When my dart was new, that’s on of the things I noticed about it, was the fact that when you crossed the centre line the car would want to dart over to the other lane. Took it back to dealer they said front end was right on spec. Drove well didn’t wear tires so I thought it was a quirk in the car. You just new it would want to do this.

If you're talking about "was new" as in the 1970's, the factory alignment specs call for 0° to -1° caster for a manual steering car and no more than +1.25° for a power steering car. That's because of the bias ply tires. But even with bias ply's that gives you very little "return to center" effect for your steering, so something like crossing over the crown of the road would do exactly as you describe. You can see the factory specs in the picture from the FSM below.

For radial tires much more positive caster can be tolerated and is needed to a certain extent because of their construction. If you run radials with the factory alignment specs it feels like driving a shopping cart, and the factory specs should NEVER be used for radial tires, that's where the SKOSH chart comes in. But even accounting for radial tires, most modern cars run A LOT more positive caster, as it adds the "return to center" effect and makes the car much more stable. It also makes the car more difficult to turn to a certain extent, but given modern steering systems that's a lot less noticeable than it used to be.

But like I said, I run manual 16:1 steering and +6.5° of caster with 275/35/18's, the car still turns just fine. Some of that is clearly driver's preference though.

I’m almost sure My fsm says to measure under the TB socket and under the ball joint. Not sure how these quotes got on here.

It does. All of the FSM's for the 67+ A-bodies do. RRR may be referring to an early A FSM.

This is the FSM for the later A's (this is a couple of pages combined to show the entire ride height process and height/alignment specs)

Here's a blown up version of the picture, you can clearly see the "A" and "B" locations are the bottom of the lower ball joint and the torsion bar adjusting blade

 

[1973dust]

It's not like there's a size where additional caster becomes mandatory, it's just an effect of increasing the tire width. The wider the front tires get, the more they tend to track the imperfections in the road surface. I've run 275's with as little as about +3.5° caster and as much as +8° caster, for my car and my driving preferences I've found that +6.5° works best for me and my set up. But it's not like the car was dangerous to drive at +3.5° caster, it's just more pleasurable at +6.5° - feels more stable, fewer steering corrections needed etc. Above that the trade off between stability and steering effort isn't worth the additional steering effort, at least IMO, but I also run a 16:1 manual steering box. And it depends on your roads too, apparently a lot of the roads I drive have "ruts" from semi-truck traffic and at lower positive caster values the 275's like to seek them out and follow them. If all your roads are nice and smooth it wouldn't be as significant an occurrence.

I'd say that since the offset bushings should get you into the +3.5° to +4° caster range you shouldn't have any really noticeable effects if you stay with a front tire less than 245 wide. At 245 or above I'd personally want more than +4° of caster, which the offset UCA bushings and stock UCA's probably won't get you, especially with some rake on the car. Some folks have been able to get more than that but it will depend on your car and settings. Typically though if you want much more than +4° you'd need to start looking into tubular or adjustable UCA's.

Thanks for explaining this. I'll keep the tire width in mind when the time comes for new as I currently have no plans to make any other major suspension changes. It's already surprising to me how much more contact patch the 215/55's have versus 205/70's for only 10mm more section width. 225's or 235's will be plenty for anything I'll probably ever do. And no, Illinois roads are pathetic like many other places.

 

[1973dust]

If you're talking about "was new" as in the 1970's, the factory alignment specs call for 0° to -1° caster for a manual steering car and no more than +1.25° for a power steering car. That's because of the bias ply tires. But even with bias ply's that gives you very little "return to center" effect for your steering, so something like crossing over the crown of the road would do exactly as you describe. You can see the factory specs in the picture from the FSM below.

For radial tires much more positive caster can be tolerated and is needed to a certain extent because of their construction. If you run radials with the factory alignment specs it feels like driving a shopping cart, and the factory specs should NEVER be used for radial tires, that's where the SKOSH chart comes in. But even accounting for radial tires, most modern cars run A LOT more positive caster, as it adds the "return to center" effect and makes the car much more stable. It also makes the car more difficult to turn to a certain extent, but given modern steering systems that's a lot less noticeable than it used to be.

But like I said, I run manual 16:1 steering and +6.5° of caster with 275/35/18's, the car still turns just fine. Some of that is clearly driver's preference though.

It does. All of the FSM's for the 67+ A-bodies do. RRR may be referring to an early A FSM.

This is the FSM for the later A's (this is a couple of pages combined to show the entire ride height process and height/alignment specs)
View attachment 1716064237

Here's a blown up version of the picture, you can clearly see the "A" and "B" locations are the bottom of the lower ball joint and the torsion bar adjusting blade
View attachment 1716064239

Wow, your blow up was much more successful than when I tried to do that. It's obvious as can be now. When I originally put my car back together with the original suspension from the donor car, I measured to the torsion bar socket rather than the blade so I thought I was at factory height and that my rear springs were really strong since I had a little rake. In hindsight, I was definitely giving the bump stops a workout. The car did seem to drive pretty well, all considering.

 

[Ahoey]

If you're talking about "was new" as in the 1970's, the factory alignment specs call for 0° to -1° caster for a manual steering car and no more than +1.25° for a power steering car. That's because of the bias ply tires. But even with bias ply's that gives you very little "return to center" effect for your steering, so something like crossing over the crown of the road would do exactly as you describe. You can see the factory specs in the picture from the FSM below.

For radial tires much more positive caster can be tolerated and is needed to a certain extent because of their construction. If you run radials with the factory alignment specs it feels like driving a shopping cart, and the factory specs should NEVER be used for radial tires, that's where the SKOSH chart comes in. But even accounting for radial tires, most modern cars run A LOT more positive caster, as it adds the "return to center" effect and makes the car much more stable. It also makes the car more difficult to turn to a certain extent, but given modern steering systems that's a lot less noticeable than it used to be.

But like I said, I run manual 16:1 steering and +6.5° of caster with 275/35/18's, the car still turns just fine. Some of that is clearly driver's preference though.

It does. All of the FSM's for the 67+ A-bodies do. RRR may be referring to an early A FSM.

This is the FSM for the later A's (this is a couple of pages combined to show the entire ride height process and height/alignment specs)
View attachment 1716064237

Here's a blown up version of the picture, you can clearly see the "A" and "B" locations are the bottom of the lower ball joint and the torsion bar adjusting blade
View attachment 1716064239

No I’m talking NEW in 74. Really appreciate your info on radial tires, should get an alignment, know a grey whiskered front end man will pass the info on thanks

 

[72bluNblu]

Wow, your blow up was much more successful than when I tried to do that. It's obvious as can be now. When I originally put my car back together with the original suspension from the donor car, I measured to the torsion bar socket rather than the blade so I thought I was at factory height and that my rear springs were really strong since I had a little rake. In hindsight, I was definitely giving the bump stops a workout. The car did seem to drive pretty well, all considering.

As long as you have the progressive style factory rubber LCA bump stops you can use them quite a bit without really noticing. Again, the factory definitely intended them to be used as part of the suspension. Obviously you don't want to use them too much, but I've literally had a conversation with another member that was running around with his car sitting on the bump stops at ride height that didn't notice. Obviously not ideal!

With your 1.03" bars you can reduce the gap between the bumpstop and the frame compared to factory, you probably have twice as much wheel rate as would have been original so even half the distance wouldn't likely result in much more bump stop use than from the factory. Personally I'd want more of a gap than that, but that's just me. The poly bump stops I run are not progressive in nature, so on my car the height needs to be set so the bump stops are not frequently contacted. But I also run 1.12" torsion bars, so between those and the shorter bump stops I run I have no issues with the car being lowered by about 2" compared to factory.

No I’m talking NEW in 74. Really appreciate your info on radial tires, should get an alignment, know a grey whiskered front end man will pass the info on thanks

Yup, that would have been an effect of not having enough caster.

With radial tires a good place to start is the SKOSH chart

It’s pretty spot on in its description, I think if anything it’s still too conservative on caster though. I’d say you can add +1.5° of caster to its recommendations across the board. But the SKOSH has been around for awhile and was probably made with only factory UCA's with offset bushings and nothing larger than 15" or 16" rims in mind. So +4° caster was pretty close to the maximum you could realistically expect for most cars and with the backspace limitations of those rims you can't run super wide front tires. Now with the prevalence of aftermarket UCA's with additional caster built in it's not difficult to get a lot more than what's suggested in the SKOSH. But it depends on what tires you're running and your preferences, with 15" rims the SKOSH recommendations are pretty close because you really can't run much more than a 225 up front anyway. With 18" rims you can easily run 245's up to about 275's up front, and that takes more + caster to tame some of the side effects of those wider tires.

 

[Ahoey]

With the roads I drive around here, I’m going to stick with the original mags, and they are mags and 205/70/R14, 225/70/R14 on back. Bought those slot mags with tires 3 weeks after I bought the car. Originals up in deep storage