Track widths and wheel base

[Jimbob]

I'm building some front and rear uprights from BMW hubs. Mostly because I had them lying around but that's another matter.

This means I've got to work out the best position for wishbone fittings on the mods to the hubs.

Does anyone know the exact front and rear track and wheel base for the roadster?

Ta

[GraemeWebb]

Originally Posted by Jimbob

I'm building some front and rear uprights from BMW hubs. Mostly because I had them lying around but that's another matter.

This means I've got to work out the best position for wishbone fittings on the mods to the hubs.

Does anyone know the exact front and rear track and wheel base for the roadster?

Ta

Hi,

I am using front and rear beemer hubs from an E36. Rears are pretty much sorted but am still busy with the fronts. What top joint location on the hub are you planning for the fronts? I plan to fabricate something that will attach to the strut locations.
I hope to do a layout drawing of the Sierra/roadster front suspension this weekend. Then overlay the BMW hub in such a position to keep the track the same. I will then modify wishbone thengths to suit, keeping geometry and roll centres within an acceptable range.
Where are you based?

[Jimbob]

The E30 struts I'm intending to modify for the front are welded onto the strut tube, so I'll be incorporating the bottom of that tube into the upright. The position of the ball joint will be made to match as closely to the original as possible. However the E30 seems to have a much smaller caster offset than the Haynes Roadster, or an E36. I'm not sure if this can be entirely designed out with this strut, but may not really matter...

One thing that's been bugging me about both the intended Sierra uprights is that they seem to be set up for a few degrees of NEGATIVE caster (ie the swivel axis meets ground behind centre of wheel) which is the opposite to the Roadster!

Is this correct or have I made it up? It's just that this opposite setup naturally results in some horrible ball joint angles, because the casting is the opposite way round.

The Roadster caster is 6.7 degree, and the Sierra looks like it's naturally (ie with nicely lined up ball joint and horizontal steering arm) about -4.3 degrees. So that's 11 degrees on the ball joint from go. Crazy..?


Can anyone put this one to rest or have any ideas? I think I'm going mad

Thanks

Graeme,
Is there really any need to adjust wishbone lengths? If you can determine the mounting points on the uprights, then surely you can vary them to achieve correct wheel position/track/camber with the existing wishbones.

Then you wont have to re-estalish a roll centre.

James

[GraemeWebb]

James, I'm not sure if I have to change the length of the wishbones as I havnt done the drawing yet. But the position of the lower pick up point of the beemer hub is different to the ford in relation to cars stub axle line. To keep the track the same it could result in a differnt length of wishbone and therefore a different static roll centre. As I will fabricate the upper half of the upright I maybe will be able postision the upper pivot point to suit. Hope this makes sense.

[LeonN]

jimbob. wots the plan for attaching the front uprights to the top wishbone?
haw far have you got with the rear hubs? are you willing the existing baring carrier similar to graham?

do you have a build thread?

[Jimbob]

To connect the top ball joint I'm cutting a circle in 15mm thick plate and welding it into the top of the strut tube. Probably having a narrow cut out in the side of the tube for access to the nut on the bottom of the taper pin.

I might incline this circle plate so the ball joint sits closer to vertical.

I have worked out the SAI from the book to be 11 degrees. And the ball joint centre distance to be something like 200mm. So I'll use those dimensions with a caster line intersecting the stub axle.