The other day I was just cruising along behind an early 90's Mazda MPV minivan, the RWD version. Well, I was looking at the rear axle as its fairly visible from the rear and I happened to notice that the rear end housing looks identical to the RX-7's unit, just probably wider. One thing that really caught my eye though was the swap bar they used on it. It was very obviously larger than the RX-7 one, and seemed to have the same general shape. Has anyone looked into putting an MPV rear sway bar on a 1st gen? It looked to be pretty beefy, probably 3/4", mabey a little less. Perfect to help control that snap oversteer the 1st gen exibits. Anyone have the dimentions or a pic of one off the vehicle? Hopefully I just stumbled across a cheap alternative to an aftermarket sway bar.

 

Stiffening up the rear end and reducing it's ability to lean can increase the snap oversteer tendency. If you want to reduce this 'fun' tendency, spend some time in the race tech section and see what mods work best.

 

Try running the car with the rear bar disconnected, removing the rear anti-sway bar is the first upgrade I do, but I enjoy driving a car with less understeer and controllable, progressive oversteer.

My 0.02c

 

you take the bar off? isnt that "counter-productive", so-to-speak?

 

Absolutely, try it, despite how it initially appears the rear bar affects the ability of the front end to turn in sharply and creates understeer.

 

+1

I removed mine. The car is alot more predictable in the hard corners now. And it dropped a good 15lbs (don't recall exactly) off the rear.

 

my car came from the factory without one.

 

not for nothing guys..but i've read about doing this on several ocassions, but i've been a lttle wary as i've got MUCH wider tires on my 81 due to the widebody kit and all...anybody still think this would be beneficial?..i have noticed a bit of understeer in the car...i'd love to dial that out and be able to feel the rear a bit better...what do we think guys?

 

I read in many places about having a stiffer rear bar keeps the rear from rolling as much and doesn't allow the suspension to bind up which is the cause of snap oversteer. A stiffer rear bar may make oversteer worse, but snap oversteer is decreased.

In any case, it could be a good addition to go with a 3 link and panhard setup.

 

If one is going to stiffen the rear sway bar, the front one needs upgraded also. I have the ST bars on the front and rear, and the rear is adjustable for under/neutral and oversteer. So far, so good, but I haven't really pushed the widebody with the big tires. When I still had the stock tires, it was fun and very predictable. Keep in mind that my entire suspension and brake systems have been upgraded. Simply changing sway bars on a tired suspension will not produce the same results.

 

I agree with you trochoid that upgrading sway bars on a tired suspension is not going to do much. But I have RB springs in front and 150lb/in springs in the rear (front springs from a late 70's to early 80's Fiat). I plan on upgrading the front sway bar to a RB unit, but I figured if the rear bar from an MPV was a close fit, I could adapt one of them for less than half the cost of a RB rear bar. Anyway, the point of this thread was not to discuss the advantages and disadvantages of a stiffer rear bar, just to try to figure out if the MPV rear bar would fit an RX-7.

 

The RB front bar will make a huge difference! Once you have that on, then you can consider either using the stock rear bar, or even a stiffer one. I was running autox with my rear bar off, but couldn't really tell any difference after I removed it except for less of a tendency to spin the inside rear tire on hard turns. Since I added the RB front bar, rear wheel spin is negligible. So now I will either put the stock bar back on, or look for an upgrade.

I agree with 85rotarypower though. The snap oversteer is caused by binding in the rear, which can be reduced by reducing the overall suspension movement. Stiffer springs, shocks, and swaybar may increase oversteer a bit but should reduce the dangerous "snap oversteer" which I've had the pleasure of encountering once or twice.

With my current setup (see sig) my biggest issue is understeer in hard cornering. A stiffer rear bar may help with that, but I think my next step will be some camber plates. Good luck with your setup, and if you try that bar out (from the MPV) let me know how it works out for you...

 

A stiffer rear bar in any car with a solid rear end will increase understeer.....

I have camber plates, coilovers, eibach springs, Koni shocks my car turns in like you wouldn't believe, the bind up issue has nothing to do with the rear sway bar, it is the unequal length rear control arms and poorly designed watts linkage that causes this.

 

True, a rear sway bar has nothing to do with snap oversteer, but the point is that reducing the amount the rear axle articulates in relation to the body reduces or even eliminates snap oversteer. Snap oversteer occurs because of binding in the watts linkage and control arms when the body rolls on the rear axle, when this binding gets bad enough, the rear end locks up and just slids out uncontrollably in an instant. Thats the way I understand it anyway.

 

I say again, try it......the rear end does not lock up, it stops traveling on the suspension path due to the binding of the rotating linkages which no longer can rotate any further, causing the suspension to stop and the body to take the energy tranfer causing the body to break traction suddenly, this occurs due to poor design, old bushings, rust and other variables, the correct way to fix snap understeer is to redesign the rear locating arms to a superior design, anything else is a jerry-rig fix. The rear anti-sway bar has zero effect upon this...

As I keep advising people try it, undo one endlink, and then go do an autocross, doing runs back to back with one end attached and then not attached.

 

Kool I am gonna try it.

 

Aussie, did you mean to say that a stiffer rear bar will increase oversteer?

Also, I'm not arguing with your logic. The rear end binds when it reaches a certain point in travel. But if you reduce the amount of travel in the rear using springs, sway bars, etc. then you might not reach the point of travel where the binding occurs. Makes sense?

 

You my friend are correct. no rear bar will make the car under steer, but snap oversteer will happen faster due to allowing the watts and upperlinks bind up.

 

I removed my rear sway bar and installed rb rear springs and it made a huge difference witht he snap oversteer issue. Later, I broke on of the rear lower control arms on a heavy launch racing and then realized one of the bolts was seized in the bushing. I suggest you undo one end of each of your control arm bolts and check for this and then lube up each bolt as you put them back on. My snap oversteer issues have since disappeared.

 

No a stiffer rear anti sway bar will increase understeer on a RWD vehicle with a solid rear axle.

You are correct about stiffening the rates of the rear shocks and springs reducing the amount of required travel but this doesn't solve the issue, it merely causes it to happen less. This doesn't solve the problem, but avoids it from occuring so often.

 

That is dead wrong.

Stiffer rear swaybar = less understeer. Same goes for stiffer springs or higher tire pressure. This is one of the basics of suspension tuning.

The stiffer one end of the car is the more slip angle it will have due to weight transfer. Imagine having a solid suspension. The entire weight transfer would be handled by the outside tire.

 

I keep saying, try it.

Rear anti sway bar transfers its forces to the opposite end of the vehicle, front bar affects oversteer, rear bar affects understeer.....think about it, the rear bar ties the rear to a flatter body roll, this transfers these forces to the opposite end not held by that bar. The front bar does the exact opposite, transfering forces to the rear.

The original 79 models had no rear anti sway bar, but due to the average driver's limited driving skills, a rear anti sway bar was added thereafter.

All manufacturers tend to dial in thier cars to have understeer as it is easier for bad drivers to control and causes less legal problems for them in the case of an accident.

Sorry Revhead but you are dead wrong on a RWD car with a solid rear end.

 

What does a car with stiiff suspension tend to do? It wants to pick up the inside tire during hard cornering. Doesn't that tell you a bit about whats happening in regards to weight transfer?

What you're saying defies all suspension tuning literature I've read as well as the laws of physics themselves.

 

well does anyone have an old mpv laying around, or some extra cash, and a junk yard near by??

 

Then dont try it....