Bronson M

iTrader: (1)

Everyone is hitting the bump stops.....I mean everyone. I'm running 800/450 rates and I'll tag em on big dips and pot holes. The guys running north of 1000 lb/in. springs are hitting them too but not as often and not as hard. The factory suspension was designed to use them as springs in fact, the Bilstein shock curves are an example of that as they are valved for much stiffer springs than what are installed stock.

crispyBYM

How did you clear the unibody in the rear? When I cycled my suspension it looked like I would contact my upper control arm with the body of the car.

Bronson M

iTrader: (1)

This is exactly the point, there are a dozen different shock lengths, build tolerances ECT. That prevent a hard and fast rule of 36mm to work...... With that said I own an angle grinder and I'm not afraid to use it, check out my build thread.

pizzle

Bronson, thanks for the explanation. I really, really appreciate it. Maybe I'm just retarded, or I too often do this research while drunk, but the good stuff is kind of scattered or in a way implied based on a previous comment. Years ago I also got a 510 in the writing/comprehension portion of the SAT, which wasn't taken while drunk, so yeah, I suck at this.

Anyways, other than the wheel hitting the chassis, is there another lower-limit to bump stop length? Or do you simply assume it does an infinite amount of damping in an infinitely short distance? Or does this not really matter because the wheel clearance pretty much takes care of you? Or does it not matter because the wheel will hit the chassis before the bumps get fully compressed?

Bronson M

iTrader: (1)

No worries bud, you're on the cusp of having they light come on.

The is a point where the bump stop gets too short, when I was running NB hard S on an na the rear bump stop ended up being in the 15mm range. It was just too short, car would spin when I would tag it. I really needed extended top hats to allow for a longer bump stop that wasn't so abrupt. I fixed the issue by buying a whole NB Miata and now it's closer to 25mm and much more progressive when I get into them. 36mm would be a smoother engagement but I would have almost no travel.

sixshooter

iTrader: (12)

It also a possibility if it isn't into the bumpstops he is getting coil bind. I run the tallest springs I can that still let me get down to the ride height I want. In this case 7in get the car plenty low and minimize the chance of bind. My adjusters are most of the way to the bottom.

But I bet he's on the bumpstops and needs to consider ISC Racing extended top hats and/or elevating the ride height to allow the shocks and springs to work.

huesmann

iTrader: (1)

What spring rates are you running on those 7" springs, sixshooter?

sixshooter

iTrader: (12)

550/350 currently, using a 1in adjustable front sway bar set to fully stiff and a larger than stock adjustable rear bar set to full soft. The bars were used of unknown origin and painted light gray. Both sets of springs are 7in. The car isn't as tail happy as I was told to expect with the larger rear bar but I've got it adjusted to minimize the f/r bias.

huesmann

iTrader: (1)

That sounds rock hard. Would springs around FM rates (318/233) work in 7" length to lower maybe 3/4-1 inch, or is 7" too short for those kinds of rates?

crispyBYM

FWIW I've planned on upgrading to those rates from 450/300 that I have now. It's not very harsh to me but it's definitely subjective.

sixshooter

iTrader: (12)

7in springs can get you much lower than stock, if that's what you are asking.

The spring rates need to match your tire choice and usage of the car. I had 400/275 with the same sways and shocks and it was comfortable and controlled on the street and was ok for being matched with 205 street tires. But when using secondhand r-compound tires on the track it wasn't enough spring and sway bar to keep it off the bumpstops in the sweepers so I had to go up to 550/350. For ride quality on the street the 400/275 would be my choice with these shocks, but the ratio between front and rear needs to take your choice of sways into account because sways are essentially springs too. They "borrow" some of the spring rates from the opposite side of the car to help the side under compression. Your combination may be better with 400/300 or 450/300 depending upon your sways.

huesmann

iTrader: (1)

Has either of you tried (or driven in) something around the FM rates?

Edit: LOL looks like we posted near simultaneously. Yes, this would be for a street car. Bars are currently stock, but open to upgrade, probability is FM.

sixshooter

iTrader: (12)

I have not. If you run lower rates you will need a bit more travel (ride height) or some other tactic to avoid contact with the bumpstops if you drive it hard. Or be just fine with it contacting the stops like it does what's the stock springs. I couldn't tolerate the sudden rate change from hitting bump stops on the track because it unsettled the car. Your needs may vary.

sixshooter

iTrader: (12)

And remember that bigger sways give you the benefit of essentially having a heavier spring when cornering without the detriment of having a heavier spring in other aspects of driving. They don't hurt ride quality and offer benefits in the control and stability of the car.

TalkingPie

While I don't contradict you on the benefits of upgrading sways, I want to point out that it's not a completely free ride. Bigger sways do reduce the "independence" of the suspension when only one side hits a bump, so the impact on ride quality isn't zero. They also do nothing for reducing dive and squat. There's a reason why nearly everyone upgrades at least the front bar, though, of course.

When it comes to the rear bar, the consensus here seems to be that you don't want to go crazy with it. I got the whole FM package when my stock shocks were worn out five years ago, thinking that it would be good to get parts that were designed to work together from someone who knows what they're doing. Overall, I still think that I got a good product for the money - the transition onto the bump stops is pretty smooth for what's a relatively low spring rate. However, I join others in believing that the FM rear bar is too much. Even with FM's conservative alignment (more negative camber in the rear), the front bar on stiff, and the rear on soft, I find my NB (with FM butterfly brace) to be on the verge of too loose. When I had it set to FM's recommendations of soft front, medium rear, I couldn't even think about trail braking on the track without the rear wanting to come around. It was by no means dangerous on the street where you're not pushing that hard - it was kind of fun - but I wouldn't call it balanced. Had I known about Emilio's recommendations at the time I probably would've left the rear bar stock and chosen an alignment with more front camber. I'll probably try that the next time I go for an alignment.

sixshooter

iTrader: (12)

The spring rates work in conjunction with the sway bar rates to give you an overall roll balance. If you have a bigger rear bar then you need less rear spring to achieve that balance. If you run no rear bar then you have to run to higher spring rate in the rear to achieve a balance.

edmcguirk

There are so many compromises to deal with when you start talking about springs and sway bars. Sometimes it gets difficult to keep them all in your head at the same time.

First off, take my opinion with a grain of salt but also look carefully at expert's opinions too. When an expert mentions that sway bars reduce traction, re-read the opinion again very carefully. A front sway bar does reduce front traction but that's not a bad thing because a front sway bar is giving most of that traction to the rear of the car (same idea with a rear sway bar trading traction to the front). And stiff springs reduce mechanical traction just as much as a stiff sway bar, so pick your poison. Also when an expert claims that a sway bar reduces the "independence" of the wheels, slow down and think again because all springs are tied through the chassis. A bump on one wheel is automatically transferred to all the other wheels even on a fully independent suspension. It's just the relation between all the springs and sway bars that will govern how much load shows up at the other wheels. The load that gets to another wheel through a sway bar is indistinguishable from a load that gets there through springs. There's no such thing as completely 100% independent.

Second, you need to make an honest decision on how much you want a race car and how much you want a street car. A race car can go all-in with stiff springs and just use sway bars for fine tuning traction. A street car will need spring rates that supply a pleasant ride. You can choose street spring rates that will not "bob" or "porpoise" on the highway (Flat Ride from FatCat Motorsports) but that will probably need a good front sway bar to balance out a set of front springs that will probably be a bit too soft. Or you can go a little softer front and back and balance the soft springs with front and rear sway bars. Or if you are going more race car, you can try the current trendy solution of stiff springs with no sway bars. The car may corner beautifully but tend to bob around on the highway a little. Then add a small front or rear sway bar to get it right where you want it.

Anyway, that's why you almost always get an answer of "try it and see" when you ask about "what size sway bars should I get?" or "what relation should the front and rear spring rates be?"

I know it's a bunch of math but the calculators at FatCat Motorsports can go a long way towards answering those questions. Just keep changing numbers and see what happens. My opinion is that a ballpark 55%-65% Front Roll Couple and a .95-1.0 Bounce Frequency Ratio is a good starting point. Raise or lower the Roll Stiffness until you find your compromise for how far the car leans and how quick the car can transition side to side vs how bone jarring you can live with.

Tutorial
http://www.fatcatmotorsports.com/FRC...S_TUTORIAL.htm
NA
FCM_MSDS_1_6NA.xls
NB
FCM_MSDS_1_8NB.xls

sixshooter

iTrader: (12)

Read "Chassis Engineering" by Herb Adams if you get a chance.

Heitzke

I think i've finally rolled through this thread enough times to talk in a semi-intelligent manner:

'90 NA - Current setup (the car as received):
- RB springs
- Koni str.t
- unverified bumpstop situation
- Solid RB f/r sways (rear is full-stiff still, I think, and was on factory end links)

I like to try to set the end in mind before parts hunting aimlessly. I also feel in a slight time-crunch because the current setup makes it painful to drive this car. It's pretty bad, man.

Desired height: 12-12.25 front - 12.5-12.75" rear
Car use: auto-x, drive to track. Too tough to use as DD anymore (optioned no a/c, p/s, abs)

Scenario A) - happen across a reasonably-priced and lower-mileage MSM setup
- Advanced auto sleeves https://www.advanced-autosports.com/...sleeve-and-nut
- Teggy bumpstops https://www.summitracing.com/parts/i...9-50/overview/
- 7" summit springs 600f/350r (will that be enough to help compensate when the bigger rear sway is on the softer setting?)
- ISC 1.5" mount rear, NB front - https://iscracing.net/suspension/
- Iso's - https://www.summitracing.com/parts/ens-9-6103r
- Spring washers - https://www.summitracing.com/parts/art-70010828

Scenario B) - MSM setup too hard to find and i want to beat this car to death. Similar setup to A but:
- NA Billie HD's
- Same sleeves but 500f/300r 7" springs (again, i'm unsure of working with a larger rear sway)
- NA mount front, ISC 1.5" rear (I assume at my proposed height i'll continue to need the travel)

My understanding is the ots NA HD's can't handle the same rates as the MSM/Hard S setups, but can deal with 500's alright.

There was some 6" front spring talk in the 20's of the thread pages, but seems to me that the 7" spring would help maintain physical contact when the suspension is completely unloaded.

JoeTheZoe

iTrader: (1)

Look at the FCM calculator for your chassis (FCM_MSDS_1_6NA.xls). Enter your proposed setup data, including the rear bar. I think you may need to do some conversions to determine the equivalent sway diameter at the stock arm length (as yours may be different...it's adjustable).

Take this calculator with a grain of salt --> Have we verified that previous concerns in the FRC% calculation have been addressed by Shaikh with an update?