Incurable harsh ride

[Tremelune]

I have me an '84 M491 coupe with a 3.6. It was a race car when I bought it. The roads I drive on can be awful. Sometimes I find myself avoiding driving the car unless the roads will be smooth. That's no good. I'd like to adapt the car to the drive, but I'm not sure where else I can go. I have an '87 coupe that is bone stock. The ride is far superior in the comfort department, and it's serving as my baseline. If I could get my '84 to behave like my '87 (possibly even smoother), I would be happy.

The car is ~2500 pounds and rides on 17" wheels with tire pressure around 28-32psi. I don't want to go to 16" wheels, because tire selection is slim for wheels this wide (9/11), though I might could go smaller in width for the sake of tires...meh. I've gone from 17" to 16" on another car and the change was not dramatic in changing the ride quality compared to a change in springs/shocks. If my E46 M3 could ride smooth on 19s, I suspect this car can with 17s.

I got the car with (I think) 23mm torsion bars in the front and 33mm torsion bars in the rear, with a set of shocks to match. It currently wears a set of stock 930 shocks and bars (18.4/26) that I bought from a Pelicaner. This change was significant, but it didn't go far enough. Thing is...I don't think there are softer springs for these cars, so I don't know if I could go softer here even if I wanted to. I plan to add maybe 100 pounds to the car (front bumper, sound deadening), but I don't expect that to have a tremendous effect on the suspension.

It wears Smart Racing sway bars front and rear, and they are quite thick. I would suspect that these are the culprit, but train tracks and ruts that affect both wheels equally are just as jarring as single-wheel impacts, so I believe the situation would still exist if I had no sway bars.

The car is lower than stock, but I don't believe ride height effects ride quality until something hits a bump stop. Here is how it currently sits:



I plan to replace my rear spring plate bushings this winter, and while I didn't plan on changing anything else while I was in there...well, now I'm wondering if maybe I should...So...This thread. Would softer bushings up front have a profound effect or is it marginal? My guess is that the ones that are there are as hard as they come.

Is there a more scientific way I can go about determining what is the primary contributor to my harsh ride?

[twistoffat]

What sort of seats do you have. A new drivers seat might be an easy solution than messing with the suspension. A softer tire compound will also help slightly but its only a slight benefit. If you are having back problems with the ride then IŽd definitely look at your seat, especially after going back to stock turbo shocks.

[Tremelune]

Nah. I'm afraid parts are gonna start falling off this car with the amount of jarring going on.

[twistoffat]

Hate to say it but if thats the worry then its maybe not suited to what you want. Either you spend a lot taking it back to stock or you start applying locktite to every possible screw. IŽd just enjoy it and not worry too much. You still have the 87 for those relaxed leafy drives and the race car when you feel like giving the roads a good spanking.

[tirwin]

Do you have monoballs on the front and/or rear. I would expect that with a dedicated race car. They can make a big difference because they can transfer a lot of energy, whereas rubber will dampen more.

I drove my 911 for 3-4 years before I started working on the suspension. It was a very harsh ride -- jarring like you said. I did a refresh of a lot of components including stiffer torsion bars. My suspension feels so much better now. There is a railroad crossing I drive over near my house. I used to hit it and WHAM, I would feel it. Now I barely notice it. So reducing the spring rate of the torsion bars isn't the only factor.

You need to look at the front and rear setups as systems. You can throw a lot of money at changing parts in an attempt to make it better. See if you can identify all the components so you can figure out what is stock and what isn't. Once you know what you've got on the front and rear it is easier to formulate a plan.

[T77911S]

shocks can do a LOT as far as how harsh the ride is. check to see if they are adjustable.
also make sure the suspension is not stuck. usually happens in the front,.
if the car is lowered it could be down on or near the stops and it is hitting the stops when you hit a bump.

my 77 was lowered and was very harsh. the front along can make the entire car feel harsh because there is so much input from the front.
my 930 is like your other car, the ride is incredible. stiff and firm but comfortable.

[3literpwr]

I've been building and tuning racing shocks for 15 years. Shocks play a larger role in harshness then spring rates in many cases. I currently have 23/31 on my G50 car with adjustable Hotbits dampers and the ride is great...but it can be made far too stiff when you crank up the rebound and compression.

[Elombard]

Did you install a set of used 930 dampers? I wonder if some have issues, or need fresh?

I wonder if you have some binding in the suspension some where because of bushings? If you can disassemble and make sure the arms move freely? its a lot of work to do that.

I 2nd the above comment I wonder if its too low and its hitting bump stops (or worse).

Are you running R comp tires? Incredibly stiff sidewalls

[Elombard]

Also - remember on the E46 that car was designed to run 19s, the engineers know they would have no sidewall stiff tires and they tuned the shocks and springs for that. The first inch of compression on a stock E46 with factory 19s is probably VERY soft to allow for an acceptable ride. No one had even thought of that tech when our 911s were designed.

If we mess with this car enough it will get there but it may take some money, and effort.

[Tremelune]

This is all valuable. It seems like bushings might be a real contributor, such that I should take the front apart and at least see what I'm working with. I don't believe anything is frozen/seized—there is definite give, it just seems slight, particularly at high speeds.

I would be happy if a set of shocks could significantly improve things. I still have the set of race-valved Bilsteins lying around, and I was thinking of having them (digressively?) revalved by Bilstein with the softer springs in mind...I was waiting until I got the major weight changes complete (fiberglass bumpers to heavier stock bumpers...putting in an interior).

The shocks currently on the car (stock 930 green Bilsteins, no adjustment) were installed by a shop, and one was replaced when they found it to be worn, so I assume they at least did a cursory test to them all before putting them on. I would assume that a set of shocks gets softer as they wear, so these would either be stock-hard or softer-than-stock-hard, no?

The tires are Continental ExtremeContact DW in 245/45-17 and 275/40-17.

Tirwin, what do you expect the culprit was in your case, since your ride got smoother with stiffer bars? Shock change? Fresh/soft bushings?

Originally Posted by T77911S

if lowered the adjustment up front puts a lot of twist or preloading in the front Tbar.

This I don't understand. Isn't the ride height mostly determined by the tension of the torsion bars and the weight over the front/rear? With the same weight and torsion bars, the car would "settle" downwards the same distance whether it was raised or lowered, since it's just a case of where the bars are indexed, right?

I'm encouraged because it seems like I can still get better-than-stock drivability with some time/money, but discouraged because I don't want to take everything apart. More than anything, I don't want to do it over and over, chasing the dragon...

Oh well. It'll start snowing soon. I guess I'll start by investigating.

[Elombard]

you know what would be pretty easy to check now that I think about it? raise the ride ht 1/2 inch and try it? I guess the rear is not easy.

When I installed a head liner after more than a year with out it - also a layer of closed cell foam above headliner. It drastically changed the way the car felt. Maybe installing the interior would help a lot? Not hearing the sharp noises so clearly seemed to give me the perception of a better ride.

[will hung]

Definitely consider changing bushings. My car had stock bushings and rode like a turd, and this is coming from a guy that drove around in an old Impreza with 450lb/in springs for years. I was certain that it had upgraded torsion bars.

When I rebuilt the suspension, I was surprised to find that the torsion bars were stock. I replaced all the bushings with Elephant Racing's rubber bushings and I immediately regretted not upgrading the torsion bars. It road like a Cadillac.

That winter, I lowered the car a little further because I can't leave anything alone and it handled and road like a turd again. So I raised the spindles up front and added Elephant Racing's Strut Shortening Wiper Seals. Both were added to increase shock travel at a lower ride height. It transformed the car. It rides like a stock car, but handles significantly better. And more importantly, it sits the way I want it to look. As a result, it rides soft enough that my wife will go for rides, but it handles and looks the way I want.

[Chuck.H]

I have an 89 M491 that used to ride harsh with poly bronze bushings and adjustable sway bars, but I'm slowly returning it to stock as I track it less and less. Still have my 17" wheels (9 and 11") though.

With near stock ride height, neatrix rubber bushings, and disconnected sway bars, I find it a blast to drive on the street, and I can take corners twice as fast with the compliant suspension.

My town likes to continuously paint the white crosswalk strips, to the point they are all about 2" above the pavement, which used to send the car bouncing sideways in corners. I still feel them, but not as disruptive.

Unless you have adjusted spindles, raising the front end will make a world of difference in how the car feels and handles... It's that SAI angle as I understand it.

My last change will be to swap out the front Koni shocks - I think even at their softest setting they are still to harsh.

Best,
Chuck.H
'89 TurboLookTarga, 421k miles

[T77911S]

Originally Posted by Tremelune

This is all valuable. It seems like bushings might be a real contributor, such that I should take the front apart and at least see what I'm working with. I don't believe anything is frozen/seized—there is definite give, it just seems slight, particularly at high speeds.

I would be happy if a set of shocks could significantly improve things. I still have the set of race-valved Bilsteins lying around, and I was thinking of having them (digressively?) revalved by Bilstein with the softer springs in mind...I was waiting until I got the major weight changes complete (fiberglass bumpers to heavier stock bumpers...putting in an interior).

The shocks currently on the car (stock 930 green Bilsteins, no adjustment) were installed by a shop, and one was replaced when they found it to be worn, so I assume they at least did a cursory test to them all before putting them on. I would assume that a set of shocks gets softer as they wear, so these would either be stock-hard or softer-than-stock-hard, no?

The tires are Continental ExtremeContact DW in 245/45-17 and 275/40-17.

Tirwin, what do you expect the culprit was in your case, since your ride got smoother with stiffer bars? Shock change? Fresh/soft bushings?



This I don't understand. Isn't the ride height mostly determined by the tension of the torsion bars and the weight over the front/rear? With the same weight and torsion bars, the car would "settle" downwards the same distance whether it was raised or lowered, since it's just a case of where the bars are indexed, right?

I'm encouraged because it seems like I can still get better-than-stock drivability with some time/money, but discouraged because I don't want to take everything apart. More than anything, I don't want to do it over and over, chasing the dragon...

Oh well. It'll start snowing soon. I guess I'll start by investigating.

my mistake, I was thinking of something else

[javadog]

Change all the suspension bushings back to stock. Have the shocks rebuilt to suit the bars in the car. Put stock Porsche sway bars back in it. Put a set of 16" Fuchs on it, with new tires. Raise it up to a more normal height and carefully align and balance the suspension.

Each of these will help incrementally (especially the wheels/tires) and together they will make a noticeable difference. There's no one little thing that will get you there, you need to do all of it.

JR

[Joe Bob]

Harsh ride is a result of either bad shocks, crappy shocks like cheapo POS KYBs, too low a suspension and/or rock hard tires or aspect height. 40s MAY look cool but can kill your back. 45s is the least you should be using. Stock is 55 or 60. Porsche called tall tires the comfort package.

Post what you have and we can give suggestions.

[tobluforu]

Its pretty easy to disconnect the bars without removing them to see if it helps.

[911 Rod]

I have mono-balls and polybronze bushing and my car is quite comfortable. I'd be checking the front end to see if the t bars are indexed to the end. Next would be shocks.

[Steve@Rennsport]

JMHO,.....

23mm & 33mm torsion bars will beat you to death; those spring rates are for track cars, only.

Install 21mm & 28mm torsion bars and have the shocks custom valved to suit if they are Bilsteins.

Voila'

[brianlay]

I would disconnect a droplink on the front and rear sway bars and see what stiffness the bars are contributing. I know my large SmartRacing bars really affect the ride quality...I actually disconnect them for street use.
The ARBs are stamped with the size on the end. You might be able to install smaller bars.