Not sure if this has been covered, but what about a mumford link in the rear?
I'm sure you would need to fabricate a good deal to make it work but shouldn't it lower the rear roll center?
http://www.not2fast.com/chassis/mumford.gif

You are correct, you do lose a little turning radius, (not a lot), but it is not because of the rack, it is because the inside of the tire strikes the sway bar, which in the respeed setup is thicker than stock. I am running 205-50-15s, not sure of the exact offset,(its close to stock). If you have more narrow tires / different offset you would have a sharper turning radius.

I lost a SHIT TON of steering radius when I installed the respeed rack and pinion. :(
Its the ackerman that really kills it.

If it wasnt so tight and awesome at speeds I would really dislike the conversion. I find it much harder to get out of a tight driveway now :(

Come spring I plan to explore some modifications to restore proper ackerman geometry... Does'nt seem like an easy task with the stock tie rod ends though.
Maybe some turn in spacers put on the opposite sides from a stock setup?
Longer control arms?
Anyone else try to remedy that issue with the respeed setup??

I would absolutely love it if I could restore the turning radius.




Edit: Sorry to derail the rear suspension thread.. someone start a front end thread!!! haha

I'll start by saying that I have a huge amount of respect for Billy since he's the only guy out there developing new products for our cars. He also happens to be one of the nicest guys I've dealt with! :bigthumb:
However I'm surprised no one else has posted about the issues with the turning radius on the respeed setup. I have the rack and pinion kit on both my FB's and while I absolutly love the feel of the steering while driving, any kind of parking lot/driveway etc is very annoying, to say the least.
I have spoken to Billy about this a few times and basically the fix is to make a new knuckle arm that angles outward (away from the car) this of course requires a bigger wheel as it would hit the stock sized wheels... Apparently taking the stock arms and simply switching them around though will angle it out too much so some modifications would be needed. I've been toying with the idea of experimenting with this, however I haven't gotton around to it.
Anyone else do anything with it?
Also sorry to have gotton off topic ;)

My understanding is that the fix is possible (correcting ackerman with the R&P kit),
but would cost some money.

I think that if enough people were interested in a correction, and were willing
to pay the costs, then Billy would provide a solution.

I dont care how much it costs! Im in for a solution!! Thats the only bothersome thing about the respeed kit.

No disrespects to Billy!!! Great guy, awesome products! Just a minor issue...




IIRC the tie rod clearance issue is with the brake rotor, and not necessarily the wheel.
I was thinking about looking into a combination of roll center blocks and custom outward angled steering knuckles?
Just not sure about clearances until I get under the car again.

I run 17" wheels so Im sure I can get away with the wheel clearance, just not exactly sure what kinda fabwork its gonna take.. Either way Im determined to remedy this issue!

If someone doesnt beat me to a front suspension thread, Ill make one when Im ready to experiment with the R+P kit.

Cheers!

As far as the rear end geometry, I was think why not just add longer/adjustable upper control arms, then change where the watts link rods mount to the body. I guess to compensate for lowering the car. Just an idea

I checked some references to see if I was messed up. I was correct in my assumption that those spacers cannot add steering angle unless it changes the
angle of the steering arm in relation to the spindle. It does alter the roll center giving the effect that it turns in better. Take a read on this page as it does explain it well.

http://www.smithees-racetech.com.au/ackerman.html

For quicker turn in, you cound move the outer tie rod closer to the spindle. But it would most likely be along he same vector and still not adding or changing the Ackerman angle.

Good discussion!

GD

I think a slight modification to the design of the steering knuckle the comes with the kit to angle the steering knuckles outward would increase ackerman and shorten the turning radius. All it would take would be for the two holes for the bolts to moved slightly.
It would move the tip of the knuckle out. Wouldnt that help? I have considered asking Billy to sell me two knuckles without the mounting holes so that I can drill them myself.

Ok, bear with me here and use your imagination. The Ackerman as it stands has the steering arms angled inward. Correct? So if you want to tighten the Ackerman, heat and bend the steering arms inward and then weld a gusset to maintain the dimension. Now you have more Ackerman. It should turn in faster. Check the bump steer as it will accentuate this. The rack, or relay rod will either have to be moved up or down to remove any bumpsteer,. Or the outer tierod.

Angle the arm outward only will decrease the Ackerman angle.

GD .

Yeah, that would make sense for the stock front end, however the respeed kit is front steer.
To get proper ackerman they would have to angle outwards and in that case the brake rotor appears to be in the way :(

I already said it changes the angle that the steering arm mounts to the strut tube & LCA therefore the spindle...
You can kinda tell on the pic on his site
These are the new ones
http://www.gforceengineering.net/ima..._Optimized.jpg
It's much more clear on his older ones.
https://www.rx7club.com/attachment.p...0&d=1252720637

Agreed, its really the only downside to the kit. As for clearance you're right the rotor is what keeps it from going out too far, but I also believe there could be issues with the bottom of the tie rod rubbing on the wheel as thats already an issue if you are using certain brands of tie rods and the 13" wheels. OEM Mazda tie rods are nice and compact and fit fine, but aftermarket ones tend to rub. I think moving the tie rod further out would increase the possibility. Not really an issue if you are running bigger wheels like I usually do, but I like the option of going back to the stockers sometimes.
Maybe Billy can chime in as I'm sure he can explain it a whole lot better than I can :)

A well designed Watts link would be very nice, but the issue of the upper links being ridiculously shorter that the lowers still needs to be remedied.

Attachment 710922


I do like the idea of a mumford setup, increased bump scrub, and the ability to set the roll center below ground. packaging may be a little harder.

Attachment 710923

Attachment 710924


Isaac

Mumford isn't worth the effort, especially on a street car. Too much fab, weight, noise, ground clearance issues.

The upper links can be made longer but then they protrude thru the floor and into the storage bin area.

Thanks Drivefast, that was what I was thinking... weight and fabrication would outweigh the pros.

Can you guys explain what the benefits of having equal length control arms are? I'm still in the dark on rear end setups...thanks!

Also, is a lotus link a triangulated 4-link? I was having trouble making out those pictures.

Thanks! That clears thing up quite a bit.

Sincerely,

GD

Attachment 412592

I just ordered a set of turn in spacers from Jim to see if they will work.

The question is, will they change the angle of the knuckles so much that they interfere with the brake rotor, we'll see.

Equal length controls arm help with pinion angle changes as the rearend moves up and down. It is an ideal situation that isn't always feesible or necessary. There are some pretty effective suspension in use that have radically different control arm lengths such as the 2005-Present Mustang.

These cars have a 3 link suspension with a pan hard bar. The upper link is much shorter than the lower arms. Despite their size and weight, these cars are very good autocrossers/road racers.

When I designed the 3 link for my STU RX7 I built it to use 3 equal length arms. Which is has. But after considering how the suspension will move in racing conditions I think I could have run a shorter upper arm and been fine. That is because with a stiff racing suspension on a relatively smooth race track the rear suspension have very little vertical travel. Almost all of the movement/angle change occurs out on the ends of the axle as the car moves through corner roll. Pictuers below of the 3 link I fab'd

The Lotus link suspension is a three link because the axle is located at three points. The lower lpoint is a ink ormed by a triangle that also serves to locate the axle laterally.

Chassis mount for the third link. Has 6 adjustment holes. The control arm is extruded aluminum with 5/8" Auora heims at both ends.

http://inlinethumb49.webshots.com/44...600x600Q85.jpg

Third with cover in place. The mount is triangulated into the chassis on multiple planes for strength.

http://inlinethumb30.webshots.com/42...600x600Q85.jpg

http://inlinethumb55.webshots.com/20...600x600Q85.jpg

Hey Guys. Thanks to Kentetsu for pointing me here. I have not had as much time to hang out on the forums lately and thus had not seen this thread since the first few pages.

I hate to muck up such a good rear geometry thread with front end geometry stuff mostly relating to our rack kit. Shell we move the discussion to a new thread?

Someone mind posting a new thread and point me to it. I can then see if a mod will move the related post.

-billy

Mustanghammer: Very nice tri link setup! I'm planning to do something similar although I was going to mount it slightly lower and wasn't planning to make the cover around it so wide. Was there a reason you made the box around it so big? I wouldn't imagine the upper link would see that much side to side motion, just more of a twisting as one wheel goes up on a bump etc..

There is tons of good information in this thread. I bookmarked it for when I get myself another FB.

Thanks. The box did come out rather large but that was done to make service and adjustment easy. Remember that the cover has to be big enough to allow for the removal of hardware and the use of tools. I welded the cover in place for fire safety. Also, since it is serviced from below I off set the link so that the drive shaft wouldn't be in the way. There is notthing worse than a racecar that is hard to work on.

The mounting bracket is high to accomodate the location of the mount on the rear axle as well an adjustable ride height that will let the car get pretty low. Also to allow for a very wide range of adjustment at the chassis. I put this same suspension on a Mustang and was very suprised at some of the arm angles I had to use to make the car work in certain situations.

thanks the ft end needed its own thread!

My current 3-link isn't radically different upper vs. lower, but I did try equal length/parallel arms before and hated it. Kept shortening the link and lowering the front pivot until I ran out of room, basically.

My upper link is a 14.5" Afco 3/4" thread threaded sleeve, with Summit 5/8" hole rod ends. I went for Teflon lined and they still squeak and clatter and make all sorts of racket. I'd hate to have them in every link.

The front pivot is basically on the floor immediately behind the crossmember, the rear pivot is 4-4.5" above the top of the diff. I forget exactly how high it is, but it will come a couple inches through the floor, which is why I had to cut the floor out clear back to the spare tire well. I never did make a box to cover it, there's just a piece of truck mudflap held down by bungees. I braced the snot out of everything but I think I crushed/ovalled the rearend housing, as there's a gap in the middle of the banjo right now, but only on the driver's side. Looks like I get to find another rearend housing if I can't straighten it out.

Between that, and the Panhard rod (1" below axle centerline), I have enough rear bite that I had to go to 200lb springs in the rear for the front end to do anything useful. The funny/scary thing is, even with springs that stiff in the back, it still has tremendous bite.

Disclaimer: I run 25.5" diameter tires on rough dirt/grass/gravel. Your mileage may vary...

Found a progress pic.
http://c4.ac-images.myspacecdn.com/i...08e4cbc147.jpg

the box is fine! if it was mine, i might have made it full width, and put the fuel system next to it. fuel above the floor AND in a fire proof box = win...

parallel 4 link? or still 3 link?

the factory car has parallel 4 links, they used what looks to the untrained eye as the SA bin reinforcement as a mount for the upper control arms.

doing the parallel equal length 4 link is common in the hatchi world too

Nice idea except that isn't supported by the rules I am building the car to. Also, there isn't that much room there - my 12 gal ATL cell would not fit there. So the cell has to stay behind the rear axle.

I have seen that done in an SCCA GTL Miata - the cell sits next to the driver. Kinda scary if you ask me but it sure would help with weight distribution.

From my perspective if you are running suspension elements in the interior of the car in a wheel to wheel racing class care needs to be taken to create a fire barrier. I was unfortunately at an SCCA club race in which a driver died in part to fire. He was not able to get out his car and fire crews could not get to him fast enough. I have seen allot of fires at club races and no matter how well a club race is covered by safety workers it takes time to get proper fire fighting equipment to a car. A fire barrier buys you time.

so no ones really answered my question about adding longer/adjustable upper control arms. and changing where the watts link mounts to the chasis to compensate for the car being lowered....in my head it seems like it would at least be an improvement.

j9fd3s - I only ever played with 3 links. The first one I did was kind of an emergency measure after the wheelwells fell apart. This chassis has solid wheelwells but the 3-link works so well! It also takes a lot less fab work relative to making the boxes for a 4-link.

ayo513 - the only issue with relocating the Watts is that any 4-link that does not have parallel arms will have its own defined roll center. (Did you know that you can, in fact, drive a 1st-gen around just fine with no Watts at all, provided that the upper links are in good shape?) Any additional lateral location must coincide with the 4-link's roll center or you will get roll bind. The main problem with the Mazda 4-link is that the upper links just plain suck!

3-links also have a self-defined roll center but it's a lot more "fluid". It doesn't cause a bind if you move the lateral location around height-wise, but it does change roll steer effects. A 3-link with the stock Watts will make that very noticable :)

4-links are, simply put, harder to make work perfectly. That's why you see people running 3-links, or torque arms, or "Lotus links" (AKA A-frame), or even truck arms.

I still can't quite figure out some of the circle track suspensions out there. Decoupled torque arms, reversed upper links, brake reaction links... and everything has springs or elastomerics to fine-tune everything further!

- Pete (Speedway Catalogs are my pr0n)

It's been answered you've just not read it.
In short, longer upper links in the stock location would fix nothing. It's cheaper and lighter and you get a lower roll center to go with a panhard then redesign a watts link.

on a side note: got my panhard mount welded in. Look's like crap, but it works, really well.
https://www.rx7club.com/attachment.p...1&d=1291603212
https://www.rx7club.com/attachment.p...1&d=1291603212

Eh, it looks a lot nicer than mine. :)

Mine is a piece of slapper bar (think leaf-spring traction aid) welded to the right chassis rail (reinforced with plate) with a couple tabs welded to it. The axle side is a piece of Watts link welded near the shock. To make it double shear, I added a doubler plate that had to be removable, and I later realized that the doubler's second stud was interfering with the shock, and... well it's not pretty.

Anyway, I drilled a large hole in the left side chassis rail (facing down) for clearance for a nut I encaptivated (zap zap zap) to a beefy washer. That nut was for the bolt for the Panhard brace, which is just a piece of 1x1 square stock that I mashed flat at the ends. The other end bolts to the outside of the Panhard bracket, using the same bolt as the bar.

For extra paranoia factor, I braced *that* to the front of the spare tire well using another piece of mashed 1x1.

The bar itself is a Watts link that I'd lengthened using my favorite suspension material: galvanized water pipe. Hold your breath when welding :)

Looks absolutely disgusting. On the other hand, it withstands side hits heavy enough to yank the inside wheels a foot off the ground, so it's strong enough.

what i was saying was to modify the upper control arms to correct pinion angle. and "re" mount the watts link rods to correct the geometry. im saying change the location the stock bars mount to the body.

Maybe strange, but I never had pinion angle issues that weren't related to floor issues.

You won't be able to relocate the Watts to correct anything. That's the problem. The 4-link's design HAS the roll center that high. Lowering the car makes the roll center even higher. The only thing you'd be able to do to "correct" anything would involve massive relocation of all mounting points, easiest way to do this is to relocate them on the axle housing.

Or you could just not lower the car, and use tires that are in the 23" diameter range.

ok now im getting it, im not very knowledgeable with suspension geometry, so im trying my best to figure things out. What if you centered the watts link and mounted it low on the axle housing?

PJ is right, actually. the factory competition suspension package included a different axle with different upper mounts so they had longer upper arms. (and then later they also relocated the mount in the body)

they also moved the watts link pivot so its on the bottom of the axle

LOL! So true. You should see what 190whp does to the driveshaft tunnel with a slammed FB. It has self clearanced the body. The panhard itself changed the car in unimaginable ways. I never thought it could make such a difference.

You mean like this?

http://inlinethumb11.webshots.com/45...600x600Q85.jpg

http://inlinethumb30.webshots.com/75...600x600Q85.jpg

This is a four link on an E Production FB. The upper links are approx as long as the lowers. They connect to rear axle using the factory mount. This car has a panhard bar instead of a watts. If an alternate watts is used it would be better to mount it to the rear of the axle housing. By the way, this suspension works very well. Note that the lower contiol arm mount is lowered 2.5" below the stock point on the axle to compensate for the lowered ride height

About 15 years ago I helped buld an FB racecar that used the stock 4 link and the stock watts link. Every bushing was replaced with a spherical bearing. The result was not very good. We broke the factory lower control arms and the watts link pin on the axle housing. The lower arms broke due to bind and the watts pin broke because it is too week. The factory Watts setup is a street part.....a non-starter for racing.

I'm going to post this in both thread because I thinks it has some good info.

http://www.gtcars.ca/online/car-care...need-know.html

I know its not FB related but still.

thanks for the input. planing on useing a setup like this. was planing to build something more complicated, but seems like this is just the best setup one can build in he garage for themselves and make a big difference in the way the car handles.

Thank you that is an awesome resource.

Here is the rearend housing I built for my STU car.

Lower control arm mounts are 1.5", 3" and 4.5" lower than the stock mount. The shock mounts are 2" lower than stock. The factory watts mount has been cut off as well as the right side upper control arm mount. The left side upperr control arm mount has been trimed down and used to help support the panhard mount. The panhard mount is braced to the back of the rearend housing. A third link mount is attached to the top the rearend. The factory spring pads were cut off and replaced with adjustable mounts for 2.5" coil over springs.

Rear end housing from the right side

http://inlinethumb49.webshots.com/36...600x600Q85.jpg

Panhard mount detail

http://inlinethumb09.webshots.com/15...600x600Q85.jpg

Panhard mount detail

http://inlinethumb52.webshots.com/26...600x600Q85.jpg

Lower control arm mount

http://inlinethumb25.webshots.com/67...600x600Q85.jpg

Third Link mount

http://inlinethumb59.webshots.com/27...600x600Q85.jpg

Very nice work mustanghammer! I know you're running a fuel cell, but do you think your panhard bar would hit the stock gas tank? It looks like the bar itself is quite a bit farther back off the housing than the G-force bar is.

Thanks. I don't know about a stock tank but my fuel will have to move back about a 1/2 inch. Because the pan hard mount is to the outside of the shock it needs to be away from the axle housing for shock clearance. This makes the panhard bar longer.

Nothing wrong with the G Force part - it works very well. I just wanted the longest possible panhard bar.

I am pretty certain that the G-Force bar clears the stock tank.

Yeah the G force panhard clears the stock tank with no issues. I had one on my T2 FB for a while but the noise for the heim joints was too much for a daily driver (for me at least). I've been thinking about making my own but with poly bushings. This thread has given me a lot of good ideas!

A good compromise would be a heim on the rearend and a poly bushing on the chassis. Allot of the mustang street panhard kits are made this way.

Nice work there Scott! Adjustable lower link mounts is a great idea.

Thanks. The brackets are from All Star products - they are predrilled 5/8" holes on an arc that is pretty close to what you need for an rx7. I got them from a local circle track shop - online they are sold by Pitstop USA. I used the stock mounting holes (drilled out) and a couple 5/8 bolts to line everything up.