Board logo

Sierra track? - Long wish bones?
danro - 7/2/06 at 10:01 AM

Hi Guys n Gals.
After a long period of zero motivation I have got off my butt and restarted the locost.
I'm using a sierra as a donor, and a chassis with +4 in the cockpit but to take a 'normal' nosecone.
As I have non standard chassis and non standard donor I was expecting to have to recalculate most of the lengths etc.

In order to establish how long the wishbones should be I measured the steering rack from the sierra, added 2x 86.5mm (from the uploads area sierra_upright.jpg)
This gives me the distance between the outermost faces of the brake disks.
Then I work back, subtract (2x 104.16mm) then subtract the distance between the bottom n/s and o/s brackets.
This remaining result is then divided by 2 as there are two wishbones.

The result is approx 4inches (100mm) extra length PER wishbone!!
Total wishbone length will be approx 455mm

So my questions are...
1. Are my calculation right or have I missed something daft?
2. Should I be trying to keep the same track as the sierra or should I reduce it?
3. If my calcs are correct will 'the book' 19mm 16swg CDS tube be up to the extra length or will they need reinforcing?

I'm half inclined to build bookish length bottom wishbones and then calculate what the tops should be, but fear the car would look odd and handle poorly.

Can anyone shed any light?

Many thanks


James - 7/2/06 at 11:48 AM

Hi Danro,

The Sierra track is 4" wider.
Your chassis is 4" wider.

Therefore people doing a normal chassis but Sierra track add 2" to their bottom wishbones.

The simple answer for you is book bottom wishbones. The top wishbones need to be a little longer as the BJ off-set is different between Sierra and Cortina uprights.

The handling will I guess change a little- whether this will be to the benefit or detrement I'm not qualified to say!

Hope that helps,

EDIT: Out of interest, how will you fit a standard nose cone on a 4" wider chassis? I know how I've done it but my chassis is only a little wider at the nose!

[Edited on 7/2/06 by James]

danro - 7/2/06 at 12:49 PM

Thanks James.
That adds up.
I was assuming the steering rack was straight on the sierra which it probably wasn't.
Am I glad of this board or what?

I added 4" to the back of the car and cockpit and kept the front 'normal' this was discussed a fair bit on this and 'the other' board a fair bit when I was planning and initially starting (Sept 2001!!!!).
The result is the parallel tubes N1/2, A1/2 are wider and the converging tubes J1/2, D1/2 and F1/2 converge at a slightly steeper angle than a book chassis.
I believe McSorleys 7+442 does the same but I did not go for the 2" extra height.

Many thanks for your quick response