patsmx5

iTrader: (16)

Love your avatar.

I've searched so much on fixing wheel hop with an IRS suspension. What I said is what I found. Don't let the front of the diff move and put long arms to support the A-arms. A few V8 guys did the long arms on the A-arms and reported success. Another Just triangulated them from the A-arms back to the subframe. Not as optimal, but it didn't affect ground clearance doing it that way.

y8s

iTrader: (8)

I doubt the diff pivots much at all. it's rigidly attached to the motor.

oh and for the record, YAW, PITCH, and ROLL are the words you want.

yaw is left to right like you steer

pitch is up and down like pat's signature pic

roll is side to side like when you have wimpy sway bars.

sixshooter

iTrader: (12)

The only downside to the long arm is the front mounting point. As I discovered when installing Stein's framerail kit, the stock framerail is thin and soft. Maybe at the very back where it is reinforced.

Since my last post I have searched and only found the diff movement idea (which is not a problem for ours because of the torque arm between the diff and the trans/engine) and the need for less compliant A-arm bushings to disallow wind up. As you know, once there is wind up there is often a dramatic release.

The long arm helps to compensate (take the brunt of the force) for the softer stock bushings and I assume that is why it helps. Thoughts?

Edit: We have people who have noticed at least an inch of movement front to rear (I guess that is FORE and AFT ) at the wheels.

AbeFM

iTrader: (3)

fore and art, I love it. My car pulled hard to starboard till I evened out the tire pressure. But you're right, the terms are better than an arbitrary XYZ.

Anyway, how about a small shock absorber? Tie it to the front with a shock - so it pulls forward, fine, but then it won't HOP back.

I'd love to see a pic (pat or anyone) of this tieing the a-arm thing. I would guess something like solid bushings would help, at least getting the travel low enough...

BTW - FM's frame rail kit certainly helps a bit. :-) I took my butterfly off (left the rails) recently and the car feels noodley.

BenR

iTrader: (2)

I suspect the PPF does alot of twisting and bending.

Interesting idea for a video shot.

DammitBeavis

While it wasn't IRS, my old '86 T-Bird Turbo Coupe had these small shock absorbers attached to brackets that stuck up from the ends of the rear axle. The dampers were mounted horizontally and the other end attached to the frame either in front of or behind the wheel (don't remember which way). I was told it was to avoid wheel hop caused by the large rubber bushings in the rear trailing arms.

Edit: found a link here -->http://www.foxthundercats.com/tctechhighlights.htm

BradC

iTrader: (6)

Anyone try something like this out?

Mazda Performance Parts: Miata PPF Power Kit

patsmx5

iTrader: (16)

Yeah, I can "see" exactly what would need to be fabbed to build a set of long arms. I have no cad skills though. I could draw them out on paper, but I have no dimensions to go by. I would basically build a bracket that I would weld to the frame rail. From it would hinge the long arm things that go to the bottom of the A-arms, directly under the hub. The piece that went on the A-arm would weld to the arm and then then you'd put the arm in and slide a bolt/bushing in. Both ends would be hinged basically.

Of course the problem is that now the A-arms want to move in an arc. However, I don't 'think' this is gonna be too significant. IE- how much suspension travel does a stock miata have from say normal ride height to the bump stops?

Or as someone suggested, a badass shock instead of an arm might would work. It would not limit the movement, just damp it to prevent an oscillation (wheel hop).

AbeFM

iTrader: (3)

Yeah - the shock (awesome find) on the t-bird isn't really doing what we're talking about, though I suspect it helps anyway - it's keeping the whole axel/diff from rotating. Certainly that's what I was thinking with a shock - I don't care where the wheel is, I just don't want it to hop, and it's plenty compliant.

Why would you tie to the a-arm, and not the spindle/brake/etc? Something on the end of the travel, and even with the axel as much as possible? That is where the force is applied, restricting only one A-arm would help,but would potentially introduce a torque twisting the entire hub.

Pat, why don't you sketch up this picture?

DammitBeavis

Even though the hubs are not twisting at the ends of the control arms, it would dampen any fore-aft movement as well. I'm looking to see if they ever sold replacements for those things.

y8s

iTrader: (8)

ideas.

I should point out that these below with the trailing link work because there are two bottom arms and they allow some amount of rotation as the wheel moves up and down. that means you replace the miata component with two arms with heim joints, not standard cylindrical bushings or you will bind.

patsmx5

iTrader: (16)

Yeah, I wasn't thinking about it twisting if I don't hold it from the hub. But I'm not sure that's doable either. IE-there's a lot of stuff there like a CV joint and shock. So not sure you could really mount a braket in there. And even then, I'm not sure you could get it to go down to clear everything and put your arm for support. Guess that's why I was shinking of just holding the bottom one.

I need a decent picture that shows the rear suspension and the frame rails to draw to. Searched and I don't have any pics like this, and haven't found any posted yet.

DammitBeavis

That 2nd pic that y8s posted looks like the rear suspension of an STI. I own a 2006 and I can tell you that it still wheelhops pretty bad sometimes.

DammitBeavis

Found some part numbers for those little dampers.
Monroe 32242
Koni Red 25-1215 $209.95/pair
KYB KG 4521 $ 79.95/pair

It was also stated in the Ford Mustang forums that the KYB's were much stiffer, and that cheap replacements were available for $25 from some discount parts places.

AbeFM

iTrader: (3)

It still seems that the cause of the hop would be good to get down - is the wheel moving back and forth, are we just feeling the tire grip and relax, etc? Some high speed video of the rear wheels on a launch would be awesome. I never should have quit my job working for the high speed video camera guys. :-)

Still, I think I have something here at work which might be able to get at least a few hundred FPS, it probably doens't have to be the highest resolution. I'd have to think about it...

AbeFM

iTrader: (3)

"The" two arms? You mean, these trailing arms we'd put in or?

patsmx5

iTrader: (16)

A few hundred FPS would be PLENTY. Get to it Abe!

AbeFM

iTrader: (3)

I wonder if you couldn't mount a camera to the car itself. I imagine a webcam would be too slow (though it's the lowest investment, and would follow the wheel). I should look around. And see if we still have the pco.1200

y8s

iTrader: (8)

replace lower arm with two heim jointed links

M-Tuned

iTrader: (6)

We will be making Miata Traction bars very soon. I just need to find some time when the Hoist is not busy with a Honda getting Traction bars fabbed up for our new models.

Traction Bars is what we do... Checkout Http://www.etdracing.com (Parent company of M-Tuned.com).

Just need the hoist free and pull my miata out of storage.