Mumford link?
 

All righty... now we're at the point of insanity. Basicially, since we're building a new ITA chassis anyway, I'm tossing around the idea of replacing the G-Force panhard bar with a home fabricated mumford link. Nothing *wrong* with the panhard, except I know that it's less than ideal whereas the mumford is AFAICT as close to optimal for a live axle rear. At least Mallock thought so.

Anyone know offhand how you calculate roll center for the mumford? I *can* figure it out myself, but it would be nice to have some reference. The other thing is, well, has anyone actually heard of anything like this being done in any 7?

This is probably going to be one of those threads where noone has any idea what I'm talking about.

That bit was crossposted to the 1st gen section. http://not2fast.wryday.com/chassis/mumford.gif is a scan of an article explaining it. And come to think of it, duh, I do know how to calculate roll center of it.

Link down.

Which sucks, as I kinda want to know what the heck a mumford is. Off to google!

edit:

..."What I liked about the Mumford Bars was the ability to adjust the roll centre. Here's a photo of a sports racer (Mallock) with the Mumford. you can see the two outer 6061T6 bars coming together in a "V" shape. The point at which they would intersect is the roll centre. "

posted by Aussie Cobra guy 750hp at http://www.clubcobra.com/t41392.html

Looks complicated. Have fun!

I have yet to see a Mumford link setup in person on a car. Thanks for posting the web sites.

I would think it would be ITA legal; I don't recall restrictions on how you can control lateral location of the rear axle. However, check the GCR to be sure.

I am curious as to how much real gain you would get out of it. You are adding a decent amount of sprung weight to build a frame strong enough to mount the chassis pivots, and I am wondering about binding of the chassis pivots at full compression and full droop.

One thing: you still would need a Tri-link to control the vertical axle location.

This would be a good analysis to run by Susko; Jim are you out there lurking?

sorry about the massive gravedig but it's still very relevant. i'm looking at a number of different configurations for my gen 1 and this is one of the main ones. kenku, have you done this since 04?

i am joining up on oz-cobra as we speak to try and get in touch with the fella who did it in brisbane and i have emailed another guy in the states who has done this to his autocross car.

any and all help is appreciated :D

A mumford link retrofitted to a chassis is a lot of work for not a lot of return. Building a chassis from scratch and using one might be worth it but trying to fit one under an FB wouldn't be. If it was worth the effort and weight Jim at GForce would do it and sell one. Jim and I were partners in a couple FB race cars when he first started working on the parts he sells. IIRC he had modeled the roll center at different ride heights and when matching it with what you end up with in the front there wasn't much difference having it in the range of about 6"-8" above ground. Lower wasn't better and higher wasn't better. If the Mumford controls roll center movement better that would be the only advantage you might get.

Holy back-from-the-dead! No, never got to playing around with it because... well, while being able to move the roll center farther down is theoreticially all well and good (especially for sports racers and other things with no roofs) it hasn't seemed of great value for an EProd car. High (ish, compared to Mallocks and Cobras) CG combined with low roll center... well, then we'd have to stiffen the rear suspension, and that doesn't seem helpful.

hmm... time to start thinking about other methods then.. any other ideas for reduction of roll and especially the reduction of the snap oversteer that is so bad in gen 1 RX7s? getting an MX5/miata subframe has been mentioned although this seems like much too much work for not enough gain (as people have mentioned witht eh mumford) and some have said that the MX5 rear suspension design it too "high"

anyone got any other ideas? i'm open to suggestion

Body roll is a matter for spring rates, IMO, and some front bar. Snap oversteer we fixed by going to a tri-link; eliminated the binding in the rear links.