Motorcycle coilovers for live axle?

I know there have been some discussions on the board in the past about the use of motorcycle shocks on smaller sports cars. I have this old RA29 celica that I'm working on now and am considering different options for the rear suspension. (For now I just want to consider the rear suspension)

For the time being I'm sticking with a live axle, and I was originally going to set up the car to run AE86 shocks/springs. However, it's going to require some fabrication work to change out the spring perches (different diameter) and maybe some additional work to fit AE86 shocks. Rather than do this, I'm considering just setting up a pushrod assembly. If I do this, I'm thinking I might be able to find some suitable motorcycle shocks/coilovers that would work in this application, and I wanted to hear what thoughts everyone had about this.

Essentially, I'd like to know if there's any chance this will work, any problems I might encounter, and what calculations I should be looking at to determine what's going to work well.

Some specs for the car:

• 2,000 - 2,300 lbs loaded (54% front)

• Narrowed Ford 8.8 rear axle (~180 lbs)

If I do a pushrod setup, I can make pretty much any motion ratio I want, through the rocker arms, right? So I'm hoping that I can get a good spring rate out of a set of MC coilovers and still have a fair amount of suspension travel available. Also, packaging isn't much of a concern since the shocks will be in the trunk, so the attached reservoir setups should fit just fine.

The car will be used for time trial, hill climb and auto-x along with the occasional around-town driving (not DD).

If you guys could point me towards some good options to consider and things to look at/watch out for, I'd really appreciate it.

Late model sport bike shocks are very good quality,the problem is they have a really short stroke.Only way imo to possibly use them is with a rocker set-up to increase wheel travel without bottoming the shock.Also not sure about how the damping will respond to a heavy ass live axle,the mass they are designed to control is WAYYY lighter.

He mentioned using rocker arms. Has anyone here explored using dual mc shocks per side for the added mass?

I think you should make a challenge car and try it

In reply to cheechthechi:

Well, this car might turn out that way.

Should be very doable. I'd recommend picking up a copy of "Tune to Win," It'll have lots of information on rocker design. If you can get your hands on a copy of something like WinGeo or any other kinematic analysis program, it'll be a huge help. A pushrod suspension is nothing but a 4-bar linkage, so there's plenty of sources on the equations of motion if you need them.

As far as determining motion ration, I'd figure out what wheel rate you want (going off of stock parts, or something like that) and adjust your motion ratio accordingly. Be sure and keep the motion ratio linear, you're going to want to minimize handling interactions as much as possible to make the car tuneable. On the ones I designed for an FSAE car, I had the shock motion ratios to within 0.005 of linear through the full range of wheel travel, but anything around 0.01 should be more than enough for a street car.

why not just use any brands SB model shocks? Cheap, easy to get, rates availible from 80-425 LBS?

Heck I saw 4 good used one this AM for $175 with coil over kits.

Nocones is doing this on his MG with RX-7 drivetrain and a homebuilt spaceframe. Slightly different since his is independent rear suspension...

In reply to 44Dwarf:

The biggest thing is price. I've seen the MC coilovers go as low as $20 each in good condition. They also have a ton of adjustments (bump and rebound damping, ride height).

In reply to RossD:

Yeah, I was hoping to hear from NoCones about what might work with a car and axle that are this heavy.

If anyone knows of a good database with info on MC coilover spring rates and stroke length, that would be super helpful. The links I found in previous threads are all dead now.

Here's a new link to the page that DitchDigger posted a year or so ago. It has OEM spring rates:

http://racetech.com/VehicleSearch

If anyone has a database with stroke info that would be great,

You rang?

I am using them however my car hasn't moved yet so everything I have is theory they may not work.

On a live axle I think the only way will be some kind of rockers arms. Most of these have a 2" ish stroke. To get anything like 4 total " of travel out of the suspension will require a very stiff spring as your Motion Ratio will be 2+ so Spring rate will be 4+ times wheel rate. Hyabusa shocks are probably the best I've seen as they have longer strokes than most and can be adjusted to minimal preload. My MG has very little droop travel because of the amount of preload the shocks have. I may end up having to build custom stops to eliminate preload.

For the belcrank design I would try to design something with a rising rate at least at the end of the stroke. Due to the short stroke that will require short belcrank arms which is good for packaging. Have the angle between the pushrod axis and the belcrank pivot radius be equal to or slightly less than 90 degrees and you should avoid falling rate fairly easily.
As to the weight issue I'm not sure how much it matters. The load on the shock is pretty much dictated by the springrate. Compressing it 2" with 300lbs of bike and rider isn't different to the shock than compressing it 2" with 600lbs of car. Due to the relationship between MR Wheel Rate and Spring rate I'm not sure you can set it up on a vehicle that can require it to control/damp more mass than it is designed for assuming you retain the stock or lighter spring. I would imagine you may see slightly higher shock temps but I don't think it will be too bad. A live axle may tax it more due to unsprung mass but I'm unsure it wasn't an issue I had to consider.

What kind of car is this going on?

cheechthechi wrote: I think you should make a challenge car and try it

Someone has. Ask Osterkraut. He was part of a build where I saw them on a Miata at the challenge years ago. It was the same year that Andy first brought his SBC powered VW.

In reply to nocones:

It's being considered for a 1977 Celica GT. The suspension setup is very similar to the AE86 (corolla GTS) chassis, and I noticed that Chris Dorsey is running a pushrod setup on his live axle AE86 (EP Solo National Champion last year). It looks like a great way to get an awesome spring/shock setup in the car for very little money. Also, having that kind of adjustability and access to the shocks/springs is very attractive.