superloaf

Oh, ok, got it. Sorry, I appreciate your help and would love any and all equations. I just thought that since I'm not tracking the car, I'm not looking for an uber alles suspension but one that works and rides decently and which also feels great to me. I know that's a tall order loaded with subjective clouding but I also think there are plenty of absolutes which others could post here from their experiences but that knowledge is quite hard to get out of people. Maybe there aren't as many Escort users as I thought and maybe many don't know or have forgotten the details of their set ups but these shocks seem fairly popular and yet not many if any trial and error testing posts/threads exist.

Anyways, I didn't mean to offend or sound ungrateful so please rejoin this thread and post whatever knowledge or equations you think appropriate.


Thanks so much for that link; love that guy and the way he explains things which other tuners don't even give a thought. I will be watching all his videos while visiting family and away from my beloved fleet but will be back testing with new rear springs once the holidays are over.

Thanks to all for contributing and hopefully by the time this thread runs its course, I will be able to post some helpful things for others and I will have a go kart which rides like a modern car. Ok, probably not but it's fun trying.

superloaf

I'm trying to figure the rates for the rear with the stock torsion bar but I've seen conflicting data about exactly what size TB is stock for '86 951's. Sometimes I see 23.5 and other times it is 25.5mm. So what is the correct size?

Also, I've found a chart which says the effective rate for 126# for 23.5 and 175# for 25.5 bars. Just want to make sure I have the right info???

And finally, what is the proper spring rate ratio for front to rear on a street driven 951? I think I'm going to go with around 425 for the front and was thinking around 300-375 for the rear depending on the torsion bar size, so basically a ratio of 370 effective front to about 340 effective rear--any suggestions? How does this ratio sound? (car has 26.8mm front bar, stock rear; 17" Michelin PS2's, 225/45 F and 245/40 R; going to keep ride height close to stock.)

Many thanks.

Dave W.

From what I've seen a stock 951 has 23.5mm torsion bars. The M030 option has 25.5mm torsion bars.
For a street car your effective rates of 370F/340R is a good choice. It'll give the car a little bit of understeer which is safe on the street. The 26.8/18mm swaybars are also biased a little for understeer.

superloaf

Ok, thanks, sounds like I'm in the ballpark.

Today I went for a drive on some fun roads and I was really impressed with this suspension. The shocks are truly impressive. They absorb so much! Don't get me wrong, this set up is very stiff. And sometimes it shakes you quite a bit. And things rattle. And it's tough to see things in the rearview mirror but somehow it doesn't beat you up. And it never bottoms like the stock suspension used to do. I can hit those flat long speed bumps at 40 mph and it just absorbs them. I can literally pass SUV's on speed bumps! You feel them quite strongly but nothing crashes or feels like it's about to break. And also I can hit city streets which dip and I used to have to slow down, you know the kind where the pavement is all gouged from normal cars scraping and everyone around you has to slow to 15mph, and there I am going through them at 30-40 with no problems. These shocks just do what they're supposed to do.

As a result, the whole car feels more together. I can go through curves at a whole new speed, so much different that I have to rethink it all. And since I can carry so much more speed through the turn, I can come out so much faster without flooring the throttle and introducing boost induced oversteer. Therefore, driving fast is just much smoother and complete without full throttle jerkiness.

Right now since the set up is far from perfected, it's more about planting the front end (which once set just digs in and sticks) and then adding throttle smoothly to exit the turn. The rear definitely needs more spring to allow it to dig in and stick like the front as now it's a bit squishy and sloppy. Can't wait to get the coil over springs on the rear to get this car balanced however, it's actually not as bad as you would think considering how much more spring rate I have in the front. It will understeer if on a smooth turn and pushing it but since the front end is so much better behaved, the front just sticks while the rear tries to keep up. It's actually kind of a fun street set up which keeps the speeds down but still rewards smooth driving.

Oh, and the brakes feel much better too since there is so little dive. I love this car now and hope to get it dialed in even better. Ok, the ride may be **** now but small price to pay. And it's not as bad as it sounds. It just depends on the road; some imperfections it can handle amazingly well while sometimes it just crashes and forces you to slow down just to maintain a grip on the steering wheel. I also have manual steering which doesn't help things but that's another issue.

After adding stiffer springs to 2 of my cars and being awestruck with the results, I just can't imagine why sports car makers don't do this from the start. It makes a car feel like it should. My 951 feels like a race car, not like a go kart as my scirocco does, but this is a heavier and much different car.

All in all, I'm quite happy so far. We'll see how the stiffness settles and what happens when I add the rear coilover springs. But for now, I'm looking forward to the fully sorted car.

superloaf

Ok, still working on what rear springs to go with and right when I think I have it figured out, I see new information which says that the info which is on Paragon's site is wrong and the correct factor for the rear effective spring rate is actually .42 which is a big difference. So instead of being in the 200-300# range, I'm looking at 450-600 to match the front spring choice of 350-400. This is with the stock TB of 23.5mm which has a rate of 126#.

So what is correct? I'm so confused. And even for the front, there is conflicting info. Is the correct front factor .92 or .94 or .96????

The car is over 35 years old; why isn't this info more easily known?

Please help.

Also, this is interesting info:

http://members.rennlist.com/dan10101/944SpringRates.htm

mikey_audiogeek

Motion ratio for the rear is about 0.65 so spring rate ratio = (0.65)^2 which is 0.42. This is where everyone gets confused...
Don't sweat too much about the front spring rate ratio, it's close to 0.9.

As you've seen, the car is surprisingly driveable even with compromised spring rates. I also drove mine with 400lb front springs and stock torsions for a while. Fun.

Don't get too hung up on the math. The car is too dumb to understand the math, it just knows what feels right!

Cheers,
Mike

superloaf

yeah, it's funny because spring rates are all over the place and even "experts" like at paragon etc are suggesting incorrect spring rates if the .42 ratio is correct. But as you've expressed, even with horribly out of balance rates, the stiffly sprung 944 still handles quite well, as seen from the completely diverse rates chosen by various people.

however, i still think a front to rear ratio of 1:1 is the starting point. And i'm surprised there's not a more definite spring choice out there but I suppose suspension engineering is still a black art.

So mikey, what are your spring rates?

Droops83

You are basically answering your own question over and over again: there are many, many variables for the "correct" spring rates. Weight distribution (it is 50/50 stock, but generally becomes more forward biased if the interior is stripped), wheel/tire size, alignment settings, aero, intended use, and the most important variable, driver preference! Some drivers like a more "pointy" car that rotates easily, so they would likely choose a setup that is stiffer in the rear. Other drivers want a more stable, predictable car and as such would tend toward softer rear rates and/or stiffer in front. Adjustable sway bars are a plus for fine tuning.

I just read that you are attempting to run helper coilover springs in conjunction with the stock T-bars. My best advice is to ditch the T-bars altogether and get stiffer rear springs. When you try to go much stiffer than, say, 200# with the helper springs, it is very difficult and time-consuming to get the two different springs to work with each other. Porsche did it with the 951 Cup cars, but likely after much R&D. With 400# front springs, I briefly tried 300 and then 350# helpers with stock '86 T-bars and even after re-indexing the T-bars and playing with ride height (eccentrics and coilover perches), the two springs would fight each other mid-corner and the handling was not confidence-inspiring on street or track.

I ditched the T-bars and never looked back, and the handling is much better. It is strongly recommended to install stiffer spring plate bushings while you are at it, as without the T-bars the torsion tube covers do not have as much support and the handling will be "squirmy" in the rear.

If you ditch the T-bars, the best plan is to start with the stiffest front spring rate that you are willing to put up with on the street and adjust the rear rate accordingly. The 50/50 balanced setup that you mention is a great starting point in theory, but in practice, 400# front springs would need to be paired with 875# rear springs, which would create scary oversteer. If you search through the plethora of spring rate threads, you will find that a rear wheel rate that is about 70% of the front rate seems to be the median preference and is a good starting point.

Ergo, 400# fronts and 600# rears would be great (I run 450F/650R in my often tracked but street driven 951). The 2.5" rear springs that most 944 rear coilover setups use are inexpensive, readily available, and easy to change. Buy a couple sets and try em out until you achieve the balance that you like. Ensure that you shocks are in good shape and are valved accordingly, however.

Good luck.

superloaf

Yes, I am answering my own question because I couldn't find anyone else to answer it accurately and therefore I am just trying to confirm what I've learned and make sure I am correct before purchasing and installing springs. Because if the ratio is .42 and the front to rear starting point is 1:1 then that would mean the correct rear spring for a 400# front would be 875 without torsion bars or 575 with 23.5 TB's which is way stiffer than ever recommended. So your appended ratio of .7 front to rear makes a lot of sense although your's is actually .63.

And while I know it's more than the math and I shouldn't get hung up on the numbers, I still need a starting point as I can't afford to try multiple spring rates right now. They do add up. Furthermore, I know keeping the torsion bars isn't the way to go but for right now I'm going to give it a try until I can get in there and redo all the rear bushings.

And I'm not trying to cause conflict, it's just that with all my other cars, there are definite rates to use and they aren't too tough to find out from others so I am just surprised that it's been so difficult getting the proper rates for the 944 since so many folks modify and race them and they also tend to be more into the technical numbers.

Anyways, thank you for the newfound .70 ratio as that would tend to explain a lot as the math of 1:1 never really agrees with what most people actually run and I do think going too firm on the rear could cause nasty handling especially on the street.

Let me ask you one other question: Do you notice a difference between the 400 and 450 fronts? Also, what length springs are you using, both front and rear?

Thanks.

Oddjob

Droops - what adverse handling characteristics did you have with running the combined rear spring setup? What was the car doing to give the feeling/indication that the springs were fighting each other?

What index angles did you try with the t-bars, or how much preload was on the coilover vs the t-bar?

mikey_audiogeek

I'm running 400 front and 850 rear, which are the springs H&R selected for their RSS coilover kit.

Oddjob

What's your use for the car? Street, Auto-x, Full Road Course, other?

What sway bars? No rear bar?

Is H&R suspension the relabled Bilstein Cup, or something other?

Droops83

Hi Jim,

I only briefly tried helper coil over springs with the stock '86 T-bars. Admittedly I was not using the best setup, they were actually used 968M030 rear shocks, so the spring perches were not adjustable.

Nonetheless, I re-indexed the rear torsion bars so the spring plates were horizontal at rest and installed the Elephant spring plate bushings at the same time.

The resulting ride height was exactly where I wanted it, and normal street driving and mildly sprited driving felt OK. However, during hard cornering, I could feel the sudden ramp-up in spring rate as the outside rear coil compressed, and that combined with the inadequate damping resulted in a feeling of the 2 springs fighting each other.

Lacking a coil over adjustment, I played around with rear eccentric height and sway bar settings and never got it to feel right. I went with proper Ground Control inverted rear coil overs and pulled out the T-bars, and the handling is great.

I do realize that half of my problem may have been inadequate rear damping, but even with a properly valved rear coilover shock, it does seem like a lot of work to get the 2 systems to work with each other. It only seems worth it if you are forced to because of PCA class rules.

Thanks,
Chris

Droops83

I don't feel a huge difference between 400 and 450. I just wanted to try it out. I think my final setup will be something like 500F/750R, but I'll beed to for few track days on my new setup to know.

As for front spring length, that depends on your front ride height. For a street car, I don't recommend lowering the front more than an inch or so; any lower and the suspension geometry will be compromised and front body roll will actually increase.

Therefore, you should run 9 or 10" front springs if your car is at stock ride height or slightly lowered.. I run 8" springs, but my car is very low (more than 1.5" lower than stock in front), but I have shorter struts from Ground Control and geometry correcting ball joint pins welded to the spindles. Check out this thread for more info:
https://rennlist.com/forums/944-turb...-solution.html

As for the rear, I am not sure what length springs your Bilsteins should use but I think 7-8" is correct. If you find that either the front or rear springs are a bit too short and they come off the perch when the suspension droops from driving over dips, you can install zero rate helper springs with spacers to keep them on the perches.

mikey_audiogeek

Street, m030 bars, rear set on soft. H&R RSS Clubsport appears to be Bilstein Firehawk front 380/150 valving; Bilstein Escort rear 565/218.
Cheers,
Mike