Coil overs, three link, and a-arms

Discussion about Datsun 1500, 1600, and 2000 race cars.

Moderator: Chris Coker

NomadTrash
Posts: 187
Joined: Fri Mar 07, 2003 9:11 am
Location: Krum , TX

Coil overs, three link, and a-arms

Postby NomadTrash » Tue Apr 06, 2004 10:53 pm

I would like to upgrade some of the front and rear suspension components. The OEM parts are pretty expensive and not the best for racing. I want to have some upper and lower a-arms made with adjustability and cheaper than the $175 ball joints that roadsters use. I would also like to fit coil over shocks in the rear and eliminate the leaf springs.

Has anyone used tubular a-arms? What ball jonts work with the roadster spindles? Do you have some specs or drawings to help me make/buy the right parts?

Refresh my memory. Does a three link consist of a a panhard bar and a trailing arm at each end of the axle which controls both the fore/aft movement and the twist of the axle? Where do you mount the trailing arms? Can they be mounted to the front spring perch?

Can the coil overs on the rear mount to the stock shock absorber locations?

Does anyone have photos of a three link on a car?

I'm thinking about running with a weight around 1600 pounds if possible. What would be a good spring rate in the front and rear?

Thanks,
Andy Cost

1968 Datsun Roadster "Bucephalus"
E-Mod 68

Bolt on modification? I used some bolts.

Image

Chris Coker
Site Admin
Posts: 427
Joined: Sat Jan 11, 2003 6:42 am
Location: Washington Twp, MI
Contact:

Re: Coil overs, three link, and a-arms

Postby Chris Coker » Wed Apr 07, 2004 6:42 am

NomadTrash wrote:I would like to upgrade some of the front and rear suspension components. The OEM parts are pretty expensive and not the best for racing. I want to have some upper and lower a-arms made with adjustability and cheaper than the $175 ball joints that roadsters use. I would also like to fit coil over shocks in the rear and eliminate the leaf springs.


The front suspension has some poor qualities for a race car...Bad bump steer, not enough camber gain, etc. If you're going to go to the trouble of upgrading components, try to eliminate some of the poor kinematics while you're at it.

NomadTrash wrote:What ball jonts work with the roadster spindles?


You can be flexible with the ball joint taper, as they'll almost have to be reamed out with a tapered reamer to match up the tapers.

NomadTrash wrote:Refresh my memory. Does a three link consist of a a panhard bar and a trailing arm at each end of the axle which controls both the fore/aft movement and the twist of the axle? Where do you mount the trailing arms? Can they be mounted to the front spring perch?


A three link has three fore-aft links, and a panhard bar (or watt's link). Two lower links should mount approximately at the front spring eyes, and should be flat when the car is at ride height. The upper link should be about 40-50 mm offset to the right from car centerline. It's length and location control the anti-squat characteristics.

Note that the chassis attachment points need to be carefully designed. If you use the front spring eye points for the lower links, they should be reinforced. You're changing a lot of load paths when you switch from leaf spring setup. The panhard/watt's link will also be the only link to carry lateral load, where the leaf springs serve to carry some of the load with the old setup. That link will see at least 800 lbs at 1g. At the very least, it should probably be designed to handle 2 g.

Car manufacturers use a "3-2-1" load case for passenger cars and light trucks. Simultaneously apply 3g vertical, 2g lateral, and 1g longitudinal, at the wheels. Calculate loads and stresses in all suspension components. If you stay below the yield stress of the material, you're generally good. There's a bunch of other load cases to look at, but that's a good general one. Racing loads are probably higher for the roadster.


NomadTrash wrote:Can the coil overs on the rear mount to the stock shock absorber locations?


Probably. You'll have a hard time finding a coilover with a bayonette style lower attachment though. The shock location doesn't have the best motion ratios, though.

NomadTrash wrote:I'm thinking about running with a weight around 1600 pounds if possible. What would be a good spring rate in the front and rear?


That depends on what motion ratios you have with your new suspension. Wheel rates should be consistent, though. Calculate natural frequencies using wheel rates (k) and corner weights (m), using {square root (k/m)}. Natural frequencies should fall in the 1.5-2.1 Hz range (open for debate/discussion). 2 Hz will be pretty stiff. The rear/front frequency ratio should be about 1.2 (rear nat. freq. slightly higher than the front). Once you know what wheel rate you want, use the motion ratio of the suspension to back out what spring rate you need.

This is a good project, and one I plan on undertaking for my race car at some point. I've come up with a few designs, and have been playing around with ideas, but haven't had time to get anything on the car yet. There are a few 3-links already out there, though!
Chris C.


Return to “General Discussion”

Who is online

Users browsing this forum: No registered users and 1 guest