Billet Spindles with Bolt On Hub Assemblies

[cfordyce05]

I'm just starting to get into the intricacies of A Body suspension geometry, so I have been doing a lot of research on what the ideal geometry should be for handling performance. Is there a billet spindle available that corrects any geometry issues such as roll center, bump steering, camber curves, etc.? I'm going to show my greenness here, but are there any significant geometry issues that could be solved with a blank slate spindle design? As far as I know, the only type of aftermarket spindle available is a 2in drop spindle, which I hear can raise the roll center.

I was talking to Bob Reed and he suggested that I cut 1" off the top of my spindle and add 1" to the bottom to improve the geometry and lower the roll center. Because I own a machine shop, I was thinking I might just design and machine some spindles from billet, but I didn't want to deal with the integrated shaft and having to whittle all that material away from a block to get down to the rest of the spindle. That got me thinking about the Corvette style hubs that bolt onto the spindle. They are the wrong wheel bolt pattern at 5x4.75, but there are other makes that have 5x4.5 (5x114.3) bolt on hubs as well.

Creating a new spindle design would also allow me to adapt whatever brakes I wanted or incorporate dust shields with air ducts, like the Corvette. With that in mind, does anyone have ideas for brake systems that you always wished could bolt onto our cars?

If there are improvements that could be made with a new spindle, would anyone actually be interested in a set?

 

[HemiDenny]

Just spitballing......

Sounds like Bullet Bob is suggesting something along the line of a 1" drop spindle ( bacically raising the pin 1")......which has me stumped for addressing your handing needs.

There are several on here that really know how to make the factory suspension handle and none of it that I have read involves reinventing the spindle.....

(JMHO)

 

[cfordyce05]

Just spitballing......

Sounds like Bullet Bob is suggesting something along the line of a 1" drop spindle ( bacically raising the pin 1")......which has me stumped for addressing your handing needs.

There are several on here that really know how to make the factory suspension handle and none of it that I have read involves reinventing the spindle.....

(JMHO)

I think the Bob Reed I have talked to is not the "Bullet Bob". He is a retired dentist in California that races a 67 Barracuda with a gen 3 hemi. I've been slowly gathering dimensions to model the suspension geometry and see what the 1" change actually does.

If there are no improvements to be had, I'll redirect my energies.

 

[72bluNblu]

Have you looked at the geometry of the factory suspension? Because it really isn't bad. This article from Mopar Muscle, while being about a brake swap comparison, has the camber curves and bump steer geometry plotted out for the 73+ A-body and FMJ spindles. The FMJ spindles were already slightly improved in some areas with a slightly better SAI. Of course, everything in suspension design is a trade off, so, there are cons to using the FMJ spindles too Swapping Disc-Brake Spindles - Mopar Muscle Magazine Keep in mind too that the article used factory UCA's, aftermarket UCA's typically add caster and improve on the geometry further. The factory bump steer numbers aren't bad at all either, in fact if it's actually to factory spec it's pretty good, a point made when they did all the suspension articles on the Green Brick.

Truly though, the factory spindle design isn't bad. Certainly not bad enough to bother designing a new spindle to work with the original suspension mounting points, which would seriously limit what you could do anyway. There are a ton of brake options for the original spindles as well. DoctorDiff has some very nice 13" rotor set ups that bolt right up with the factory spindles, and of course Wilwood and Baer have set ups as well.

And, about the 1" "off the top" and added to the bottom- that's just a drop spindle. The 2" drop spindles on the market now do exactly that. In fact, they're basically a factory 73+ spindle, just with the axis point moved 2" higher. That's it. What you're suggesting would be the same, just a 1" drop instead. To consider what happens with the roll center, you have to think about how the roll center is calculated. It comes from the angle of the control arms. If you lower the car with the torsion bar adjusters, you change the angle of the control arms, and you end up with a lower roll center than you do with drop spindles. This would be true for a 1" drop spindle or a 2" drop spindle. I had the calculations done for a 2" drop spindle because I ran them briefly on my Challenger. They resulting suspension geometry is worse than just lowering the car with the torsion bar adjusters and increasing the size of the torsion bars to compensate for the lost suspension travel (you need bigger torsion bars for a better handling car anyway).

These are for an E-body, so, not all of this would directly correlate to A-body geometry. But, the FMJ spindles are pretty much the same as the E-body spindles, and I use FMJ spindles on both my A and E body.

Stock E-body, lowered with the torsion bar adjusters

2" drop spindle E-body. These cars sat at the same ride height. Look at the roll center height, significantly higher. Also, look at the angle of the control arms. The camber curves for this set up with the drop spindles would be worse, although I don't have those numbers. Bump steer was slightly worse as well. For an A-body the numbers would be slightly different, I know Peter Bergman had said at one point that his roll center was actually calculating out as negative (below ground!) on his Dart and he installed a set of drop spindles as well as a way to correct that issue. He ended up going back to stock spindles though.

By all means, if you want to get into designing a new spindle and you have the means to produce such an item, don't let me stop you. But consider that the aftermarket drop spindles out there now use exactly the factory design with a relocated axle. Also consider that of all the aftermarket companies out there, pretty much every piece of suspension hardware is reproduced in some kind of tubular or adjustable form -tubular UCA's, fully adjustable UCA's, tubular LCA's, adjustable strut rods, solid tie rod adjusters, full on tubular K frames, giant torsion bars, sway bars, etc. The only piece that everyone uses the factory geometry for is the spindle.

 

[HemiDenny]

makes sense, I really was feeling bad (even at 6 in the morning) for questioning the wisdom of Bullet Bob Reed, even though to me, he is a straight line guy. However, If he told me the sun rose in the west, I would tend to look for it there.

I admire your effort and wish you good luck.

 

[cfordyce05]

Have you looked at the geometry of the factory suspension? Because it really isn't bad. This article from Mopar Muscle, while being about a brake swap comparison, has the camber curves and bump steer geometry plotted out for the 73+ A-body and FMJ spindles. The FMJ spindles were already slightly improved in some areas with a slightly better SAI. Of course, everything in suspension design is a trade off, so, there are cons to using the FMJ spindles too Swapping Disc-Brake Spindles - Mopar Muscle Magazine Keep in mind too that the article used factory UCA's, aftermarket UCA's typically add caster and improve on the geometry further. The factory bump steer numbers aren't bad at all either, in fact if it's actually to factory spec it's pretty good, a point made when they did all the suspension articles on the Green Brick.

Truly though, the factory spindle design isn't bad. Certainly not bad enough to bother designing a new spindle to work with the original suspension mounting points, which would seriously limit what you could do anyway. There are a ton of brake options for the original spindles as well. DoctorDiff has some very nice 13" rotor set ups that bolt right up with the factory spindles, and of course Wilwood and Baer have set ups as well.

And, about the 1" "off the top" and added to the bottom- that's just a drop spindle. The 2" drop spindles on the market now do exactly that. In fact, they're basically a factory 73+ spindle, just with the axis point moved 2" higher. That's it. What you're suggesting would be the same, just a 1" drop instead. To consider what happens with the roll center, you have to think about how the roll center is calculated. It comes from the angle of the control arms. If you lower the car with the torsion bar adjusters, you change the angle of the control arms, and you end up with a lower roll center than you do with drop spindles. This would be true for a 1" drop spindle or a 2" drop spindle. I had the calculations done for a 2" drop spindle because I ran them briefly on my Challenger. They resulting suspension geometry is worse than just lowering the car with the torsion bar adjusters and increasing the size of the torsion bars to compensate for the lost suspension travel (you need bigger torsion bars for a better handling car anyway).

These are for an E-body, so, not all of this would directly correlate to A-body geometry. But, the FMJ spindles are pretty much the same as the E-body spindles, and I use FMJ spindles on both my A and E body.

Stock E-body, lowered with the torsion bar adjusters
View attachment 1715055486

2" drop spindle E-body. These cars sat at the same ride height. Look at the roll center height, significantly higher. Also, look at the angle of the control arms. The camber curves for this set up with the drop spindles would be worse, although I don't have those numbers. Bump steer was slightly worse as well. For an A-body the numbers would be slightly different, I know Peter Bergman had said at one point that his roll center was actually calculating out as negative (below ground!) on his Dart and he installed a set of drop spindles as well as a way to correct that issue. He ended up going back to stock spindles though.
View attachment 1715055487

By all means, if you want to get into designing a new spindle and you have the means to produce such an item, don't let me stop you. But consider that the aftermarket drop spindles out there now use exactly the factory design with a relocated axle. Also consider that of all the aftermarket companies out there, pretty much every piece of suspension hardware is reproduced in some kind of tubular or adjustable form -tubular UCA's, fully adjustable UCA's, tubular LCA's, adjustable strut rods, solid tie rod adjusters, full on tubular K frames, giant torsion bars, sway bars, etc. The only piece that everyone uses the factory geometry for is the spindle.

Thanks for chiming in. I was hoping you would, as I've followed many of your suspension based posts closely. I don't have my heart set on making them if there is no benefit. I see a lot of posts stating "if you do this, then the roll center will be at this height", but no posts that actually list all the dimensions required to calculate the roll center. I'm currently gathering those dimensions so I can plug them into CAD or into the website vsusp.com and be able to see what the changes are going to do for myself.

I thought all the cutting and welding was going to do was create a drop spindle, but Bob Reed said that it was going to lower the roll center. It seems the consensus is that a drop spindle is going to raise the roll center. He just wanted me to get my roll center into the 2-3" range.