I wish someone wrote a book on suspension. What spring rate should I run?

[Ansharky]

So my car is essentially going to be a weekend car that I can daily drive, is better at cornering than stock, and can launch from a dig for some light street racing. I was looking at feal for coilovers.

The guy at maximum motorsports said to not run feals true rear coilovers due to axle travel issues for a daily driver. He also said their default spring rates of 8k front/ 5k rear were too stiff for what I was building, especially in the front. I called feal and they said they just have a different philosophy, and what they offer for their “balance comfort and performance” package would work fine for what I’m building.

So what rate coilovers is everyone running? What spring rates would be optimal for a street car with 300-350 hp? Im desperately trying to piece together information based on what I can find, but theres not exactly a book on this shite

IN DEPTH RESPONSES WELCOME!

 

[Mustang5L5]

8k front/ 5k rear

Feal's spring rates are just measured differently. When they say 8K then are referring to 8 kg/mm of linear rate. A lot of other vendors use lb/in.

So 8 kg/mm converts to 450 lb/in
5 kg/mm is 280 lb/in


Every manufacturer has different recommended rates as they just all have different ways of doing things. Typically lower rates are more for drag and street driving and then you get higher rates for competition. With stiffer springs, you need higher quality dampers or you will get bounce. If you ever observe a lowered car bouncing as they hit a bump on the road, they don't have enough damper.

Maxmotorsports has a good chart as a general rule of thumb.


That isn't to say it's the only way to think, but I know them best so that's why i'm using their reference material as an example. As you can see the feal front rates would put you near the stiff end of their chart with a rate of 450 lb/ft. Feal certainly doesn't make junk at all, but I do agree that their philosophy is a little bit different than some of the other Mustang suspension companies like MM, Steeda, KennyBrown, QA1, etc.



I run 250lb/ft front springs on Bilstiens with conventional rear springs (would have to look up the rates). I make about 325HP, and it's a good compromise with good street manners and performance driving. If i was more serious about road racing, i'd probably be in the 325-375 lb/ft range and might consider a rear MM coil-over setup and 125# in the rear. I considered this but most likely am going to leave things like they are.

 

[duh09]

Feal is not a bad brand, but just to reiterate what's already been said, their bread and butter is not Mustangs. They seem to be a little more prevalent on drift cars than anywhere else in the SN95 world.

I lean towards the tried and true Maximum Motorsports, Griggs, Kenny Brown, etc because they are all-in on these cars. You're not going to find 240SX or 911 parts coming from any of them.

There are a million options to do exactly what you want - it really comes down to what you want and what you're willing to spend. Some folks are going to think that 400lb is going to be a smooth ride, some folks are going to think 250lb is too harsh, so there's no one answer fits all solution. Read through some of the build threads on here. Read through the suspension stickies. I'm sure you could find a Foxbody/SN95 suspension book if you looked hard enough too.

 

[Ansharky]

Feal is not a bad brand, but just to reiterate what's already been said, their bread and butter is not Mustangs. They seem to be a little more prevalent on drift cars than anywhere else in the SN95 world.

I lean towards the tried and true Maximum Motorsports, Griggs, Kenny Brown, etc because they are all-in on these cars. You're not going to find 240SX or 911 parts coming from any of them.

There are a million options to do exactly what you want - it really comes down to what you want and what you're willing to spend. Some folks are going to think that 400lb is going to be a smooth ride, some folks are going to think 250lb is too harsh, so there's no one answer fits all solution. Read through some of the build threads on here. Read through the suspension stickies. I'm sure you could find a Foxbody/SN95 suspension book if you looked hard enough too.

That’s a good point, thank you! I’ll do that

 

[MachSVT]

In speaking with MM, I did coil over front / rear with 300lb front / 200lb rear with the Koni yellows already on the car and still new. My end result was exactly what I was after...very pleased. That said, it did take some planning / work / trial & error.

Note: If memory serves me correctly, MM recommends a 150lb split front / rear. I wanted a little more spring in the rear for my future plans of a (possibly) trunk mount heat exchanger tank and MM torque arm with the trimmings. I already have a remote mount battery which I also considered. That said, plan out your future upgrades to accommodate!

I experienced these issues:

1. Interference of the front drivers side coil spring to the unibody. MM calls this out in their instructions, but due to my miss with #2, I did not have any initial interference, until I corrected #2...

2. With MM camber plates, they provide shaft spacers to locate the top coil spring mount down from the protruding bolts on the underside of the camber plates. I did not space the top coil spring mount far enough down / catch the initial interference and ground up that top mount on both sides...GRRR!

3. For whatever reason, after I fixed my embarrassing miss in #2, I then experienced #1.

Had I taken my time and checked / re-checked, I would have not had any issue. Middle of summer, hot azz garage w/a/c on high, no lift, 53 years old, blah, blah, blah...I just wasn't as methodical as I usually am and it bit me.

What wasn't recommended / discussed was:

A. I ended up needing helper springs from Hyperco and helper spring mounts (forgot the correct part verbiage) where the helper spring meets the coil spring. It's pretty hilly here in Va, so I had instances where rear articulation would unseat the coil spring and give the loud "POP!" when it reseated. YMMV if where you live is mostly flat. Also, I just didn't like the coil springs being loose when jacking up the car, then setting the car back down again..."POP!

B. I replaced the recommended 10" rear spring with 8". I simply could not get the desired ride height w/10" spring.

Overall, do your research (check!), take your time to look over your work to be certain everything is setup correctly (FAIL!); If using adjustable dampers, some fine tuning on your rebound / compression settings to dial in the ride you desire and enjoy!

 

[Terrorist 5.0]

Realistically, if this is not a purpose built track car, I would ditch the idea of coil overs and just go with a good set of lowering springs and shocks. 1/100 people actually set up their coil overs properly and mostly just want the adjustable ride height aspect of it. A non coil over setup is cheaper, and you don’t have to mess with anything. You just pick springs with a rate you want, match up the shocks and go from there.

 

[r3dn3ck]

350# front is pretty stout without being jarring. I have IRS and run #600 rears. IIRC when I had a solid axle & TA/PHB I ran #250 rear springs which was pretty darned firm.

 

[MachSVT]

There is a lot of different takes, here. One thing I wanted to point out to anyone reading this that might be confused is spring rate. How do you translate stock divorced spring rate / ride to a coil over spring setup?

For example, a 600lb divorced spring in the rear is roughly 50% effective due to it's placement midway on the lower control arm vs. a 200lb coil over, which is actually mounted behind the rear axle vertical centerline, will have (don't quote me, do your research) around 115% effective wheel rate.

In that example, the 600lb divorced spring has a 300lb wheel effective rate, while the coil over spring will have a 230lb effective wheel rate.

If coil overs are for you (and you like your current ride quality), simply take your current stock spring rate and do the math to find your coil over spring rate.

You can afford to go up in effective wheel rate while still keeping a better than stock ride because any loss in effective wheel rate (due to a divorced spring setup) means the % loss is putting pressure on your control arm pivot point = suspension bind. Inversely, the closer the wheel effective rate is to the coil spring rate, the less suspension bind you will have.