Alcino's MII suspension uncovered

[alcino]

Ever since the article in PHR about my car, I get a lot a questions on my suspension and how I pulled .99g and 5.95sec slalom. It’s amazing handling in the tests shocked many people, including me. I've read a few books on suspension and knew I was a long shot at doing well in handling. For one its a Mustang II suspension, known for its bad geometry caused by its short and misplaced control arms and two I had lowered the car so far down(mostly for looks) that I had broken the cardinal rule of having the lower control arm not angling down from the chassis to the spindle. So I decided look into it more and write about the details.

Facts about the suspension.
1. Completely factory stock suspension parts except poly bushings.
2. Alignment. -2* camber, 3*caster, 0.25" toe out.
3. Front inner lower control arm pivot height from ground = ~6 3/8"
4. Lower balljoint from ground height = ~7"
5. Track width from center of tread to center of chassis = ~29 3/4"
6. Tires in front are 205/50/15 and rear 225/50/15 Toyo RA-1

Using Suspension analyzer and its included 78 mustang ii file set to height, tire and alignment parameters of my car to test the Roll Center(RC) height at rest and migration with 2* roll, .5* steering input(left turn) and .25 dive/bump(lets call all this "dynamic").



At rest RC is 0.11" above ground. I think this is really low. Care to comment?

Now the interesting part. Dynamic. As I start adding the steer the RC moves 4.17" Passenger side from center(call this "P"), then as I add the roll it moves the other way and ends up 6.94" Drivers side from center(lets call "D"), then as crazy as it seems as I add the bump some where around .13" it goes as far as ~144" D then ~104" P and as I get to .25 bump RC ends up at 2.71 P. Note height of CR doesn't seem to change much other that following the chassis. So it ended up -.14".

Seeing this happen in animation is wild to say the least. But explains Why my car feels hairy when I let off or touch my brakes in a fast turn. A condition that is not tested and means a great deal in the real world race situations.

So knowing the problem. What are some solutions? I tested a few ideas that are mentioned all the time.

Such as using common 2" drop spindles and restoring ride height. This corrected the Lower control arm angle and put static RC ht at 2.93". Adding the steer caused no movement of RC, adding roll slowly moved RC 4.37" D, lastly adding the dive only pulled the RC slightly leaving it at 4.97" D and 2.47" off ground.

Another trick is longer control arms and shallow dish wheels. I made my arm 3" longer. Static RC ht. 2.6". Adding steer = nothing, adding roll = 3.78" to D, adding the bump pulls it to 4.37" D from center with 2.20" from ground.

For comparison Suspension Analyzer has a 2001 corvette. Static RC ht. = 2.92". Dynamically the RC barely moves and ends up at 0.73" D from center and 2.62" from the ground. must feel very predictable.

Playing with the MII suspension even more found me some places that help it act more like a c5. Such as a taller spindle which is available from chassis works (and maybe ATS in future). Also moving the upper control arm inner pivots down. Just to see I used the last MII scenario moved the upper ball joints 1.5" to simulate the tall chassis works spindle and moved the upper inner a-arm points down an inch. Static RC ht. = 5.59". Dynamic RC = 1.57" D and 5.23" from ground. Is that a High RC? Closer to c5 RC migration, right. But could you still call it an MII suspension?

Conclusion. My tires are great and… I need some freaking drop spindles stat!

Hope someone enjoys my work here.

[bret]

Congrats, first, on taking a less than optimum suspension [on paper]and wringing out impressive performance, and second, for documenting why. Thanks for taking the time to explore this issue. One [many?] would think that being a proponent of the MII front suspension that I would have have this info at my fingertips...but I don't. My real world experience with this suspension has been subjectively similar, although not documented and likely not quite as successful as yours. Even though there are dynos, races continue to be run...even though therory says this suspension should not work this well, it apparantly does in this case.
Congrats as well on continuing to try to improve your hotrod...it is why the free world still goes to work every morning!

[BRIAN]

Probably the BEST suspension post on this site. You took a less than optimal suspension, didn't buy the "Must Have" parts and made them perform very well.


That is exactly what should be done. It would allow a lot of younger people with low funds enjoy their PT cars rather than buy the big buck piece of the week. You are the Rat Rod of Pro Touring and I do not mean that as an insult.


One question; Did you ever perform the test with a different tire just to see how much they effect the G's??

[alcino]

Probably the BEST suspension post on this site. You took a less than optimal suspension, didn't buy the "Must Have" parts and made them perform very well.

That is exactly what should be done. It would allow a lot of younger people with low funds enjoy their PT cars rather than buy the big buck piece of the week. You are the Rat Rod of Pro Touring and I do not mean that as an insult.

Thanks.

One question; Did you ever perform the test with a different tire just to see how much they effect the G's??

No, and probably never will. I was lucky that I was able to have this data collected. Lots of people wonder what their car could do, but don't have the resources to do it. That's me no resources. No extra wheels/tires, no fancy timing lights. I might be wrong, but didn't PHR do a write up on tires a few months ago? I think it was all Nitto brand, but might have had some numbers comparing the different compounds.

[Stu Seitz]

That’s awesome, but if your springs are stock and you’re pulling .99 g’s how are you not hitting the suspension stops? I would assume that, in it of it self would some what hinder performance at the limit. And if your shocks are stock and you’re already at .99 g’s I think that a good set of Koni’s or Penske’s would go a long way and wouldn’t break the bank. Once again man awesome post; I really like what you’re doing with your car.

[alcino]

And if you shocks are stock

Ooops, forgot to mention that I have KYB Gas Adjusts in the front and KYB GR2 in the rear. And they don't seem to be binding. Maybe next time at AutoX or something I will put a zip tie on the shock shaft and see how close it gets to bottoming.

[red65FB]

alcino-

Great post! I used to have a C5 - and your assumption is correct - very stable and predictable.

I have some old software I can use to solid model some arms, and I might be able to get some fabbed. I wonder if the Chassisworks spindles are a direct bolt in - brake mounts, axle snout, ball joint taper, etc., are the same as stock?

[JJSmitches]

There is a 1976 Mustang Cobra in the SF Craigslist for 1k. GO GO GO!

[alcino]

Here is the Chassis Works spindle next to the stock. Axle snout is the same. Not sure if the Balljoint taper is stock or Chrysler. But the most irratating thing is that they limit you to a 11.75" rotor with their cast in caliper bracket. ATS, please rescue us!

[CAMAROBOY69]

The fact that you were also running 15" wheels and tires amazes me. Do you think you would do even better with 16" or 17" wheels. I know my car cornered a lot better with 18" than it did with 14" or 15".

[Norm Peterson]

Hope someone enjoys my work here.

Very much. Do you happen to have the coordinates of the upper pivots and balljoint handy?

Wild lateral migration of the geometric RC occur as the upper and lower arms pass through being parallel to one another. I see the same effect in a 2-D spreadsheet with an animated plot. The shorter uppers rotate as seen in front view faster than do the longer lowers in roughly inverse proportion to the relative arm lengths.

Norm

[kmcanally]

The fact that you were also running 15" wheels and tires amazes me. Do you think you would do even better with 16" or 17" wheels. I know my car cornered a lot better with 18" than it did with 14" or 15".

Jay Bittle's Trans Am Mustang pulled 1.01g with a modified stock suspension on period correct vintage 15" bias ply race rubber.

[David Pozzi]

Al,
Try the LCA frame pivot 1" higher than the lower balljoint at starting ride height.
Use the taller drop spindle, how much taller is it?
Then play with UCA inner pivot heights to get some neg camber gain.

The Mustang II has some advantages especially in a slalom.
Shorter wheelbase requires less wheel turn to get around the cones, less work for the front tires.
The inside rear wheel is what will hit a cone on a turn, a shorter wheelbase has less difference in path betweeen the front and rear wheels.
Car width is less, the car takes a straighter line through the cones, less degrees of turn per cone.

[red65FB]

ok - I quickly threw together a model based on a Heidts style tubular control arm using 1" tubing. This is very quick - only for visualization. Please note this is only with quick measuring crawling under the car. But, it does give you a good idea of what an extended length (added 3") LCA might look like using the stock MII crossmember. This assumes staying with the stock spring perch type and upper pocket set up - no coil overs. One thing that immediately pops out is the increased leverage on the spring.

For the experienced among us - can I assume that the spring would need an increase in rate? If so, how much?

[David Pozzi]

"can I assume that the spring would need an increase in rate? If so, how much?"

No it will get stiffer, the spring will now be closer to the balljoint percentage wise if the arm is lengthened inboard of the shock.
Hope the spring and shock angles won't cause problems. I assume the shock is inside the spring?

[alcino]

Do you happen to have the coordinates of the upper pivots and balljoint handy?

Wild lateral migration of the geometric RC occur as the upper and lower arms pass through being parallel to one another.

Yes! That's what what must be happening. The arms are near parallel at rest. forgot about that in my suspension books.

Do you think you would do even better with 16" or 17" wheels.

Not sure? I feel it doesn't matter much on wheel. Just profile and compound of rubber.

David, I will play some more with the analyzer to see what happens. When is the RC considered too high?

For the experienced among us - can I assume that the spring would need an increase in rate? If so, how much?

I think if the wheel doesn't move outboard with the arms that the spring rate could stay the same. Correct me if I'm wrong.

[Norm Peterson]

ok - I quickly threw together a model based on a Heidts style tubular control arm using 1" tubing. This is very quick - only for visualization. Please note this is only with quick measuring crawling under the car. But, it does give you a good idea of what an extended length (added 3") LCA might look like using the stock MII crossmember. This assumes staying with the stock spring perch type and upper pocket set up - no coil overs. One thing that immediately pops out is the increased leverage on the spring.

For the experienced among us - can I assume that the spring would need an increase in rate? If so, how much?

If all of the length increase is added between the spring seat and the balljoint, then yes, you will want more spring rate (in the ratio of [motion ratio]^2).

If it's all added between the spring seat and the chassis pivot, less spring. How much less would also depend on how much the spring angle changed.

Norm

[hssss]

FWIW. Could you use the spindles off either a Granada or Torino? I believe both were front steer and should be taller. I believe the granada and MII both grew out of the same parent, the Falcon. The box style Towncar came factory with tubular UCAs and the spindles look like Torino. I have found that engineers don't reinvent anything they don't have to so possibly a set of spindles off a larger car with the CAs adjusted to accomodate them might be the answer. Being Frugal/cheap whenever possible I like to use production parts which are generaly also stronger. Just ran accross this they will make the spindle effectivly a bit taller http://www.scandc.com/balljoints.htm

[alcino]

hsss, thanks for letting me know about the balljoints.

I called Chassisworks about their spindle. The first thing they said was that it would not work on my car. Only on their suspension kit. Ya right! I asked some more questions, but the guy didn't really know what he was talking about.

I ordered them to see what they were and make comparisons. I will make a better write up, but on the quick glance over.

1. The snouts are the same as the stock II using the same bearings with only the nut being a different thread pitch.
2. The upper Ball joint is moved 1 1/16" higher than stock.
3. These babies are heavy duty and you can feel it in the weight. stock is just over 8 lbs. while these come in at 12.5 lbs. I'm thinking I could grind some material away since my car is light.
4. the snout is moved up 2" giving it that amount of chassis drop.
5. Seems to accept the same style balljoints and tierods.

I tried a factory 9" rotor and it would hit the bracket for the caliper. Maybe I could get some time this week and see how my wilwood rotors fit.

[hssss]

alcino What if you used something like the 95 Cobra R wheel 17x9x5.95(offset) this would allow lengthening the lca and still maintaining the track width? I just got 17x10.5x6.9 for the LC7. If you have any thoughts toward a 3 link these would allow the use of a 05+ Mustang 8.8 while mantaining about the same tred width. I saw a MII a while back that he had raised the rear wheel opening to the beltline and the front a bit less which opens your choice of tires and wheels a bunch and realy looked nice. It removed a bit of the coke bottle look.