AutoX wheel rate recommendations wanted for streetable FWD

This is relevant to my interests.

Hope you get it worked out. Kinda want to do the same thing to my Malibu at some point in time but mine is a good 600 lbs lighter.

CadVetteStang wrote: But I do know that the FE3 sport spring will still ride softer than say.....a Taurus.

I'd bet it would feel like air ride compared to my Taurus.....damn Koni inserts/2.5" coilover springs.

Oh, and look into Koni strut inserts that will work with the setup you're looking at, they might not be the best for your application/desire, but they'll be leaps and bounds ahead of Monroes.

As an idiot that has autox'd a taurus, I approve of other oddballs doing it.

Fr3AkAzOiD wrote: This is relevant to my interests. Hope you get it worked out. Kinda want to do the same thing to my Malibu at some point in time but mine is a good 600 lbs lighter.

Rethinking ; Mustang performance springs come two ways... To hook up on launch and to corner well. The drag setup has much softer rear springs.... So maybe I don't have to keep the rate of increase close.

Can you post the rates of lowering springs for the Malibu?

Sorry, only have the stocks. Not much of anything available for the Malibu, going to either have to make something from a saab 9-3 work or make it up as I go along.

It's a project for next winter though.

series8217 wrote: Here's a chart of front and rear ride frequencies, corner weights, unsprung weights, sprung rates, and ride rates for factory suspension setups on various cars: Note that ride rate is not the same as wheel rate. Ride Rate (Kr) = Kw * Kt / (Kw + Kw), where Kw is the wheel rate and Kt is the tire spring rate. (From this Powerpoint presentation on suspension design from FSAE Lead Design Judge, Steve Lyman from DaimlerChrysler

Thank you for this. I spent a day looking for this info and came up with nothing.

CadVetteStang wrote: @ series8217, Thank you; I have only been able to glance at the info in a quick summery due to my work schedule, but if I am interpreting correctly, I should keep the percentage of increase in spring rate front to rear as equal as possible to maintain “flat ride”. 3X increase in Rear spring rate = 1,050 3X increase in Front spring rate = 408 2X increase in rear = 700 2X increase in front = 272 That should maintain flat ride. However, a 2X increase in rear = 700 And a 3X increase in front = 408 Could cause pitch problems with pitch over bumps.... Am I on the right track here?

Assuming the difference in front to rear frequencies gives you level ride with your typical weight distribution, yes... sort of. The stiffer your springs are the smaller the oscillation amplitude will be, and the less you need to have a ride frequency difference front to rear... and the less you can ultimately achieve level ride because the car will simply follow the bumps or jump over them (no suspension travel at all). At any reasonable frequency what you are suggesting will work :-)

If the difference in frequency is 10 to 20% you should be OK. Dennis Grant (farnorthracing.com) says to have an 0.2 Hz higher frequency in the rear than the front, rather than a percentage. That may be to account for the diminishing frequency difference needed to achieve level ride at higher frequencies.

<img src="" /> <img src="" /> Here are a couple of pics of the fully extended rear suspension.

Edited to include :

A-arm length from mounting points is 14.2"

Inboard mounting point to center of spring is 7.4"

Inboard mounting point to shock bolt is 10.6"

yamaha wrote:

CadVetteStang wrote: But I do know that the FE3 sport spring will still ride softer than say.....a Taurus.

I'd bet it would feel like air ride compared to my Taurus.....damn Koni inserts/2.5" coilover springs. Oh, and look into Koni strut inserts that will work with the setup you're looking at, they might not be the best for your application/desire, but they'll be leaps and bounds ahead of Monroes. As an idiot that has autox'd a taurus, I approve of other oddballs doing it.

I used to drive a Taurus, but never autocrossed it; however, there is this VERY curvy 4 lane road in a remote area during my daily commute that a lot of the sports car drivers have fun “getting in a big hurry” to drive through. I had fun passing them in the Taurus. However, there is this local autocrosser who leaves racing numbers on the door of his 2nd gen. Impreza WRX who would regularly pass me on the tighter corners and leave me behind…. That is until I got my current Eldorado that we are discussing. After coming from behind, passing and putting the WRX ten car lengths behind me on two separate occasions (dry and not so dry conditions) he no longer challenges me and just lets me go by…. This morning, I was about 15 car lengths behind a big winged Honda that had a very tight suspension. When it crossed the railroad tracks that begin this fun road, his car followed the contour of the dip like a fighter jet doing a quick dive and climb. My car stayed pretty much level through the dip, except that I bottomed out the rear and drug the exhaust system… He did not like getting passed in turn two… the “race” was on and I enjoyed watching how his stiff little car looked…. In the rear view mirror, LOL! …. I don’t think My car needs a whole lot of work, but I hate the floaty soft ride and the bottoming out.

In reply to CadVetteStang:

Well, I'm into the "Exotic Taurus" that came with the "row your own" gearbox and a silly japanese engine.

<img src="" /> TOP: 489 lb./in. spring. Bottom: 279 lb/In. stock rear spring in my Eldorado.

If I did the math right, cutting 3 coils would rate it at 672 lbs./in. And cutting 4 coils would make it a 733 lb./in. spring. I don’t know which would be better right now. I think that with the leverage the A-Arm has on the spring, the 733# would be better, but I don’t want it to sit too low. Can anyone do the math to get a spring and shock motion ratio from the measurements in the previous picture post (the one that shows the rear suspension)?

By comparison, the SVT Cobra IRS Motion Ratios are: Spring – 1.78 and Shock – 1.42

Don't have a chance right now because my lunch break is nearing its end, but I just wanted to remind you to square the motion ratio to get the spring-rate to wheel-rate conversion factor, since many people forget that step! (It's squared because of the combination of mechanical leverage on the spring and reduction of spring motion)

http://www.racingaspirations.com/apps/wheel-frequency-calculator

Just been playing with this. Looks like unsprung weights have much less effect than spring rate or corner weight. Making educated guesses on that part will get you pretty close. Within a handful of CPS at least.

@ Yamaha, Thank you for the info about Koni strut inserts. That is now a planned future upgrade. I may start off with a spring that won't over power the stock strut and then take it a step further in the future. The rear springs I found are the stiffest OEM units that will fit and after cutting will be 2 times stiffer than the factory spring. I may not go go over the 350 lb. Rate for the front... Until I do the Koni upgrade. I found after market springs that will fit the rear and after cutting should be in the 950 lb. Range. I could then match the fronts with 450 to 500 pound springs.

The car handles so good, I would hate to go stiffer than needed to get the job done.

Update; I discovered that my rear spring motion ratio is .2413

I then pulled the front springs from a Dodge Dakota Sport truck and will cut them to be 900 lb. / in. That will give my car a rear wheel rate of 217.17 lbs. Note that a SVT Cobra uses 600 lb. / in. rear springs and has a rear wheel rate of 200 lbs.

Hope I'm on the right track here; I divided my soon to be rear wheel rate with the approximate unsprung rear corner weigh of 606 lbs. I then multiplied that by the approximate unsprung weight of the front corner (1101 lbs. ) to find a front wheel rate in proportion to the rear and came up with something like 398 lbs. Depending on what the front strut motion ratio is, I might be close to target by using the variable rate W-body springs advertised as 450 lbs. / in.

They are cheap and the ads say that they can be used with the stock struts (I'm guessing because of the variable rate )

Input???