Mac front suspension spring rates.

I'm having a hard time finding a link I read a few times that I now need to reference. It detailed why you need to run high spring rates on a macpherson front suspension and why a 4link solid axle needs softer rates. Anyone got some good suspension tech in their brain? Or a link to a wizard? Lol

On the TR8 200# to 250# front and rear is a nice street combo for spring rates. It has struts front and solid axle rear. I've gone as high as 450# front on the race car, but always try to keep the rear somewhat soft. Anything stiff on the rear and the rear of the car just bounces, and won't lean to give mechanical grip. The stiffer the front and the better the car is at turn in, but ultimately the smoothness of the track dictates how stiff you can go.

I think you may find a strut car, all else being equal, will need a softer spring than a double control arm, because the strut is pushing down farther out on the lower control arm, so the effective rate of the spring is higher. Rear spring depends on the same thing. Is the spring in front of the axle, on top of it, or behind the axle? A stiff spring in a 244 Volvo (behind the axle) would be soft in a Monte Carlo (spring in front of the axle) if both vehicles weigh the same.

Struts tend to need stiffer springs to reduce suspension travel to the optimum working range to minimize camber, caster and toe changes (all of which tend to happen with strut equipped suspensions as it moves through its travel).

Solid axles tend to have a very small amount of camber change, so allowing them to move will not hurt traction, but will in fact help to a certain extent. Too stiff and you can have forward bite issues on solid axle RWD cars.

It is all based on wheel rate. A strut mounted spring will have a lower rate than one mounted half way up the control arm.

Same thing applies to a solid axle. How far away from the wheel is the spring mounted.

Spring/wheel rate also depends on the use of the vehicle.

Body roll is generally controlled by anti sway (roll) bars.

I've always just taken the car weight in pounds, divided by ten, and made that the front spring rate...

I run 550/450 on a Mazda2. May go up to 750-900 front and 600ish rear when it becomes an auto-x only car(also higher rate for R-comps)

My motion ratios are .97 and .96 roughly for reference. 700-750 each front corner and 450-400 each rear corner or so.

I'm running no front sway bar but I need to add tabs to my homemade strut housings so I can run one next year.

Some other 2 autocrossers experimenting with 700/500 springs no front bar and the results are good from what I hear.

Read this:

http://farnorthracing.com/autocross_secrets.html

Stefan (Not Bruce) wrote: Struts tend to need stiffer springs to reduce suspension travel to the optimum working range to minimize camber, caster and toe changes (all of which tend to happen with strut equipped suspensions as it moves through its travel). Solid axles tend to have a very small amount of camber change, so allowing them to move will not hurt traction, but will in fact help to a certain extent. Too stiff and you can have forward bite issues on solid axle RWD cars.

This is what I remember reading. (Still can't find that website...) this guy had an early 90's camaro and ran 1000lb front springs and like 200lb rears. Thanks guys. Also, can any one point me in the easy direction for calculating motion ratio? The rear is an 8.8 but the shocks are not straight up and down. The front is obviously Mac strut. An online calculator (can't trust these, consistently) asked for droop % and the Internet apparently does not have info on how to find droop %. I can measure my arms and blah blah blah, but droop...

Camaros don't put the spring on the strut, there is a hefty motion ratio.

flatlander937 wrote: I run 550/450 on a Mazda2. May go up to 750-900 front and 600ish rear when it becomes an auto-x only car(also higher rate for R-comps) My motion ratios are .97 and .96 roughly for reference. 700-750 each front corner and 450-400 each rear corner or so. I'm running no front sway bar but I need to add tabs to my homemade strut housings so I can run one next year. Some other 2 autocrossers experimenting with 700/500 springs no front bar and the results are good from what I hear. Read this: http://farnorthracing.com/autocross_secrets.html

On your 2 you should run the stiffer spring in the rear

Check the B Spec spring rate.

From farnorth 2.0hz front, 2.5 hz rear.

I have a "Steve Smith Autosports" book "Advanced Race Car Suspension Development" It explains it all.

So buy a book... If it comes to that I will.

iceracer wrote:

flatlander937 wrote: I run 550/450 on a Mazda2. May go up to 750-900 front and 600ish rear when it becomes an auto-x only car(also higher rate for R-comps) My motion ratios are .97 and .96 roughly for reference. 700-750 each front corner and 450-400 each rear corner or so. I'm running no front sway bar but I need to add tabs to my homemade strut housings so I can run one next year. Some other 2 autocrossers experimenting with 700/500 springs no front bar and the results are good from what I hear. Read this: http://farnorthracing.com/autocross_secrets.html

On your 2 you should run the stiffer spring in the rear Check the B Spec spring rate.

With no front bar it helps a lot with corner exit but requires higher rates.

I do still have a higher rear frequency.. Mine are 2.4/2.9. It either needs a bar added to the front, or heavier springs.

Despite heavier than ideal rates, it results in more grip due to less camber loss. Higher rear rates would likely help, but its about as much as I'll tolerate while I'm commuting 100 miles daily. I've got about 8-9k miles on this setup.

Lesson learned is test test test if you have the means. Look up the spring rates of the Acura RSX that won nationals this year, IIRC they were stupid high.

In reply to iceracer: far north.... Now bookmarked for life. Thank you.

I used far north HZ guide,was way to soft.Before that I spent 9 yrs with an AE86,they like lostsa camber up front,do most of the roll control up front as well.Make sure the 4 link doesn't bind in roll and don't use too short a rear shock to limit droop travel.

I prefer no sways,tested tons of combo's and everytime I unhooked sways it got better.If its a street car than that's not likely going to work out for you however.

Do all your work on the rear of the car first until it has more grip then the front,then go to work on the front and work to balance the car....repeat for 9 yrs

Unless you really get carried away with changes to the rear(geometry of the arms,panhard bar heights etc) the front will always be making less than optimal grip for neutral handling.

Well the car in topic is my Celica (ra64, really similar to your ae86) as far as geometry changes to the rear I was only going to even out the panhard for neutral handling in left and right corners (you know, because I don't do nascar) if I ever win the lottery I'll do a watts link.

Cool,yep damn near identical to the AE86 underneath.To level out the panhard are you just lowering it until the bar is level or are you planning to move one end or the other?.It being out of level doesn't really affect corning power each direction,having it level will minimize the rear ends lateral movement with compression/extension though.

Don't use poly bushings in the rear control arms,new rubber bushings in 3 arms and leave one upper with old or drilled out bushings.

Whats the use for the car?,how hardcore is it going to be?.

FWIW, I have tried a decent range of setups on various AE86's over the years. I have only used seat-of-the-pants tuning, (books and math???) but settled on 335lbs/in front and 240lbs/in rear for a dual-duty street/HPDE AE86 using street tires. I run stock sways with aftermarket bushings and at least 3 degrees negative camber up front. Much stiffer than that doesn't work as well on real roads with potentially rough surfaces.

For a track-only Corolla with race rubber and a cage the popular rates seem to be 500-650lbs/in F and 325-450lbs/in R. For those not into Toyotas, the rear spring perch is directly on top of the rear axle.

The fbody guys really like to drop the entire panhard bar, and level it, to reduce roll center. Once I had a working suspension the panhard bar never bothered me, but i never had grippy ass tires like you guys run.

I always wanted a watts link though, and the kits for the fbodies run around 1K, but I always tossed around the idea of using a mini truck kit, which are considerably cheaper, and building my own.

You can google mini truck watts links and find kits ranging from 250 to 500

In reply to Opti:

Exactly,picture of my not so pretty but effective AE86 set-up.

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