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Old 01-16-2013, 10:31 AM   #1
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Default Drop spindle discussion

A fellow on a local forum has peaked my interest on drop spindles and suspension geometry. I don't understand all of it, obviously, but he has worked with the concepts quite a bit with his custom built ariel atom type car, bigger than a formula style car. I don't know for sure if he's applied his concepts to going fast that much, though. He seems fairly knowledgeable.

So my main question is why aren't drop spindles more common amongst miatas or any other regularly tracked car.

The guy states lowering the car 1inch past stock is harming the car more than helping and adding spring, camber, and a good damper isn't the correct way or doing it. Since I don't fully understand this, why wouldn't all the fast track miatas have a ''correct'' setup. Too much cost, too unreliable, reinventing the wheel, or too cumbersome?

Did a search on here, only found things about rusted stock spindles, spindles for sale, and some guy asking Emilio if he's made some yet.

My view is, I'm less concerned about all the geometry and more concerned about what setup is more reliable and faster. It's also easier and cheaper to just copy the fast guys
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Old 01-16-2013, 10:46 AM   #2
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Quote:
Originally Posted by flier129 View Post
A fellow on a local forum has peaked my interest on drop spindles and suspension geometry. I don't understand all of it, obviously, but he has worked with the concepts quite a bit with his custom built ariel atom type car, bigger than a formula style car. I don't know for sure if he's applied his concepts to going fast that much, though. He seems fairly knowledgeable.

So my main question is why aren't drop spindles more common amongst miatas or any other regularly tracked car.

The guy states lowering the car 1inch past stock is harming the car more than helping and adding spring, camber, and a good damper isn't the correct way or doing it.
Since I don't fully understand this, why wouldn't all the fast track miatas have a ''correct'' setup. Too much cost, too unreliable, reinventing the wheel, or too cumbersome?

Did a search on here, only found things about rusted stock spindles, spindles for sale, and some guy asking Emilio if he's made some yet.

My view is, I'm less concerned about all the geometry and more concerned about what setup is more reliable and faster. It's also easier and cheaper to just copy the fast guys
This part os true for a lot of cars however the miata's suspension geometry is less than perfect at stock ride height and gets better as you lower it. This is why you do not see this type of thing on miatas.

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Old 01-16-2013, 10:50 AM   #3
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Originally Posted by flier129 View Post
..Too much cost, too unreliable
Very, very few racing classes allow non-OEM spindles, so the market is a bit limited. That might be changing a bit with the growing number of points-based classing systems (NASA, CASC).

That said, if/when V8 Roadsters brings a set to the market, I'll be very interested. A spindle is a part that has to be manufactured exactly right, and one that you don't ever want to fail.

I've seen one-offs made for auto-cross only cars.

Last edited by wildo; 01-16-2013 at 11:03 AM.
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Old 01-16-2013, 12:12 PM   #4
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I thought I stuck in ''non oem spindles aren't legal for 95 percent of classes'' in the thread lol.

I figure with an billet aluminum spindle would be nice for loss of un-sprung weight, but may not be too strong.
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Old 01-16-2013, 12:18 PM   #5
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It'll be as strong as you make it. I'm sure we could get a race only version down to around 3 pounds. You have to get all the way up to street mod before you use non-factory spindles in solo. Of course in that class you have free reign over the entire suspension besides the pickup points on the chassis.
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Old 01-17-2013, 01:50 PM   #6
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Something like what Driftworks does for the S-Chassis cars would probably be more affordable to the masses. Theirs are a fabricated steel weldments, so it would open up the number of facilities that could do it (once the jig is made). Might not be as light as a stock (should be similar), but it would be more durable than aluminum.

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Old 01-17-2013, 02:48 PM   #7
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I remember these being hugely popular in the aircooled VW world many years ago. In that context, they were attractive principally because they offered a bolt-on alternative to removing and dismantling the front torsion beam, cutting it into three pieces, and re-welding it together with adjusters in the middle. The principle problem being solved there was not a matter of geometry, but rather a complete lack of adjustability in the stock design.

I'm not intimately familiar with the 240sx, however I do know that it used MacPhearson strut suspension in the front and an odd multi-link setup in the rear. It's entirely possible that these designs are less adaptable (insofar as static ride-height adjustment and / or interference-limited travel) than the double A-Arm system found in the Miata.


What's the real problem that we are trying to solve?


In the Miata, it's entirely practical to adjust the static ride height of the vehicle at both ends through the use of adjustable coilover perches, which are quite inexpensive and require no custom fabrication. Springs are also commonly available in a variety of length and stiffness, allowing for a large degree of customization even without the use of adjustable perches.

One potential limiting factor is the "free" compression travel at low static heights; the distance between the top of the shock body and the bottom of the upper shock mount. This is particularly troublesome in the NAs, but it is easily ameliorated in any car by a combination of shorter bumpstops and either converting from NA to NB upper mounts, or in more extreme cases, the use of "raised" upper shock mounts, such as those from ISC Racing.

Additionally, many aftermarket dampers are available whose body length (from the lower eyelet to the top of the tube) is shorter than stock, which also contributes to an improvement in compression travel.

Obviously at some point you will run into interference problems other than with the shock-to-mount interface, such as from the control arms coming into contact with tie rods or other components. I don't have any hard data in front of me to demonstrate at what point exactly this become problematic, however we have a large amount of anecdotal evidence to demonstrate that even with relatively small tires, the stock suspension is capable of being adjusted downwards to the point where tire-to-fender clearance becomes the limiting factor, rather than interference at the control arms.
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Old 01-17-2013, 03:40 PM   #8
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I believe these are designed to correct roll center problems created when the lower control arm drops below parallel on many suspension. I've yet to take accurate measurements of our suspension so I have not done the kinematic analysis on it and cannot say for certain if this is the case with ours, but it HIGHLY likely it is.
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Old 01-17-2013, 03:52 PM   #9
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It's not very scientific, but my thoughts are:

If none of the guys who race and put a LOT of money into their cars aren't worried about it, then neither am I. If they were a big deal, someone would already be selling them now. Or maybe Emilio does have some and isn't telling anyone, and that's his secret to going fast.

If they are a problem for d0r1ft0rs, well then maybe don't slam your car and you won't need to worry about the changes to the suspension geometry.
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Old 01-17-2013, 04:05 PM   #10
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Quote:
Originally Posted by thenuge26 View Post
It's not very scientific, but my thoughts are:

If none of the guys who race and put a LOT of money into their cars aren't worried about it, then neither am I. If they were a big deal, someone would already be selling them now. Or maybe Emilio does have some and isn't telling anyone, and that's his secret to going fast.

If they are a problem for d0r1ft0rs, well then maybe don't slam your car and you won't need to worry about the changes to the suspension geometry.
I'll be running modified stock spindles on my car. Just purchased a full tubular setup from a SCCA EP driver. Front spindles aren't modified just the rears.
Picture of the modified spindle:
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Old 01-17-2013, 08:19 PM   #11
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Originally Posted by Leafy View Post
I believe these are designed to correct roll center problems created when the lower control arm drops below parallel on many suspension. I've yet to take accurate measurements of our suspension so I have not done the kinematic analysis on it and cannot say for certain if this is the case with ours, but it HIGHLY likely it is.
Yes, that is/was my take. I measured and modeled up the Miata suspension sears ago. Without changing the location of the suspension pickup points, lowering the chassis on the springs moves the roll center and instant centers to an unfavorable position (down below ground level and in, iirc). Dropping the height of the spindles by the same amount of your overall ride height drop negates that change.

Back when I measured and modeled the suspension, I paid for the software and it was kind of a PITA. I've been through several computers and computer crashes since then, and likely don't have the data anymore. That said, there is a free online tool that simplifies the process a bit. I bet if we pool our knowledge it wouldn't take much to recreate the Miata suspension here: Vehicle Suspension: Front View Online Suspension Simulator . Might be a cool tool for the community.

Going back a few years, I believe drop spindles were available from Mazda Comp(etition, now known as MazdaSpeed Motorsports) for Production / GT Miatas. They weren't cheap.

If drop spindles were allowed in Spec Miata, everyone would have them and the price (should/would) be reasonable.

The ones V8 Roadsters were working on sounded great, made with mounts for radial-mount Wilwoods, if I remember that right. Its been a couple of years since I read anything about them.
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Old 01-17-2013, 09:38 PM   #12
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Running smaller diameter tires has the same effect as drop spindles - lowering the car without changing the geometry. However you get a smaller tire footprint - but maybe it can be made up for with a wider tire.

Yep lowering a car will lower the roll center faster than the CoG. This increases the roll couple - the amount of roll force absorbed by the springs instead of the suspension arms, and increases roll angle, all else being equal. That is where cornering forces result in an upward force at the CoG. I haven't seen numbers though. Wildo, what sort of amount of lowering started to look bad?
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Old 01-17-2013, 09:38 PM   #13
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I was going to do it like I did the formula car. As a sketch in solid works. Works really well. Having the roll center below the ground isnt bad. IMO I like it down there because as the suspension is compressed you gain mechanical grip rather than loose it. BUT you never ever ever everever want the roll center to switch from above to below ground in any normal suspension movement. Dis is bad, it creates a discontinuity in the suspension output. Basically you loose all grip for a split second, this is why if you lower an AP1 s2k the wrong way they become spin machines.
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Old 01-17-2013, 09:58 PM   #14
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In.
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Old 01-18-2013, 10:15 AM   #15
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Quote:
Originally Posted by Leafy View Post
I believe these are designed to correct roll center problems created when the lower control arm drops below parallel on many suspension. [...]
Strut suspensions develop serious camber problems when lowered by simply shortening the springs, thus explaining the popularity of drop spindles with that crowd. That's less of a problem with double wishbones.

I've had freeCAD installed for a while, thinking that I could model an entire Miata chassis, but haven't come anywhere near actually using it.
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Old 01-18-2013, 11:19 AM   #16
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Quote:
Originally Posted by Leafy View Post
I believe these are designed to correct roll center problems created when the lower control arm drops below parallel on many suspension. I've yet to take accurate measurements of our suspension so I have not done the kinematic analysis on it and cannot say for certain if this is the case with ours, but it HIGHLY likely it is.
I think the issue you are referring to is mostly with MacPherson struts. I think its the angle of the LCA with the strut. Once its greater than 90* it develops a positive camber curve. I have heard some of those BMW guys run 5+* of camber to over come it, but I couldn't tell ya for sure.

We did some of this stuff with the Formula Hybrid car, but I wasn't particularly involved.
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Old 01-18-2013, 11:54 AM   #17
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Lots of great info in this thread thus far, thanks for the responses .

wildo mentioned that if they were common in SM, than we would see them a lot more. I don't think they keep the "spirit of the rules" as I've heard a few times about SCCA rules. That being said I think for Solo or Club Racing only Mod or Prepared classes even allow these, limiting the market.

I ganked this from a m.net thread, note this is quoting someone that quoted him(maybe he'll open this thread )

Emilio said-

"The camber curve of a Miata with the LCA's angled the wrong way is in the non linear part of the curve. Changing the inner or outer pickup points can fix that.

The lateral force acting on an LCA angled upward compresses the suspension instead of being fairly neutral as it is a stock ride height.

The CG is lowered by an amount proportionate to the change in ride height. The roll centers are lowered non-proportionately to ride height. The (sic) lowers roll resistance.

The two latter issues both require additional spring rate to combat the change in suspension geomtery compressing the suspension more for a given lateral acceleration than at stock ride height. Address the roll center issue and we could all run lower spring rates with the same roll stiffness and lower (optimize) bounce frequency. Both of which would increase mechanical grip.

That Miatas are freakishly fast without the geometry fix is a testament to the soundness of the basic car's design and big tires. Watch a nationally competitive DP roadracing Miata on a fast track though, and you will see what more is available with better suspension geometry."




So I started looking through NASA TT rules and someone correct me on this if I'm wrong but I couldn't find it specifically listed under points nor no-point mods.

"16) Relocation of front suspension mounting points +6
17) Relocation of rear suspension mounting points +6"


I don't think these too rules apply to the spindle mounting to the control arm, but the CAs to the f/r sub-frame? If it does apply, 12 points is A LOT and that's why you don't see them in NASA much, either.
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Old 01-18-2013, 03:19 PM   #18
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...Wildo, what sort of amount of lowering started to look bad?
Sorry, I don't remember the specifics, and I don't want to spread wrong information.

What I do remember is that at track/race car ride heights (I was running SCCA ITA at the time, more similar to SM than EP or GT), that 1-2" drop spindles would have been beneficial (on paper).

I'm not a suspension engineer (or engineer of any sort), and went through that process and read as much as I could for a few months during that time, in an effort to broaden my understanding of suspension dynamics. Some of it stuck, but like high school, I have forgotten more than I remember.
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Old 01-18-2013, 05:07 PM   #19
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Cliff notes:

If you're not 4+ seconds under the Spec Miata track record you don't even need to begin to worry about this.

DUH
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Old 01-18-2013, 06:08 PM   #20
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These would be beneficial for track cars and street cars.
You would be lower and your suspension will continue to function properly. Many race cars have drop spindles on them. It make simple sense.
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