Board logo

Rear suspension wishbones
macintosh - 20/7/05 at 08:14 AM

Hi all,

as most people in this forum I'm also building locost (based on McSorley 7+442 drawings).
I will use Sierra IRS so I have find back part design somwhere - thats was a bit problem, but I did solve it.

One question troubles me: if we look front wishbonbes,
then they are parallel but if we look back wishbones they are not exacly parallel.

Does anyone know why are back wishbones not parallel?

Russ-Turner - 20/7/05 at 08:17 AM

Sorry to jump in but where did you find the plans for an i.r.s. set up please? I'm not having much luck finding 'em.

ADD - 20/7/05 at 08:29 AM

Try thr tiger build book for IRS drawings, make sure you get the second edition, not so many mistakes!. I am sure a lot of people on here will have drawing as well.

britishtrident - 20/7/05 at 11:26 AM

Cue anybody who has attempted to build a car from the Tiger Avon book --- ;-)

andylancaster3000 - 20/7/05 at 11:27 AM

Top and bottom wishbones shouldn't really be parallel. The top wishbone should angle down slightly from the wheel to chassis, with the lower one roughly horizontal. But this is a very simplistic way of looking at some quite complicated suspension geometry so I wouldn't worry about it too much.

HTH (I have a feeling that i am reading your question wrong though!)

Andy

[Edited on 20/7/05 by andylancaster3000]

[Edited on 20/7/05 by andylancaster3000]

britishtrident - 20/7/05 at 11:34 AM

quote:
Originally posted by macintosh
Hi all,

as most people in this forum I'm also building locost (based on McSorley 7+442 drawings).
I will use Sierra IRS so I have find back part design somwhere - thats was a bit problem, but I did solve it.

One question troubles me: if we look front wishbonbes,
then they are parallel but if we look back wishbones they are not exacly parallel.

Does anyone know why are back wishbones not parallel?



All to do with roll centres BUT the front wishbones shouldn't be parallel when viewed in front elevation, as this would give a ground level roll centre which will give too much roll and won't keep the tyre treads in full contact with the road surface.
see this image on the Luego site
http://www.luegosportscars.com/images/viento1.jpg

[Edited on 20/7/05 by britishtrident]

ned - 20/7/05 at 11:38 AM

quote:
Originally posted by britishtrident
Cue anybody who has attempted to build a car from the Tiger Avon book --- ;-)

Kingr built his car as a locost front end with avon IRS from the tiger book grafted on.

Ned.

macintosh - 20/7/05 at 11:46 AM

quote:
Originally posted by Russ-Turner
Sorry to jump in but where did you find the plans for an i.r.s. set up please? I'm not having much luck finding 'em.


http://finance.groups.yahoo.com/group/locost/files/Construction/
http://locost7.info/mirror/chassis.php

macintosh - 20/7/05 at 11:48 AM

quote:

HTH (I have a feeling that i am reading your question wrong though!)
Andy

Not really. My question is actually, why?
Or to be precise: what happens if I make them parallel?

[Edited on 20/7/05 by macintosh]

britishtrident - 20/7/05 at 01:46 PM

It will give you a ground level static roll centre --- roll centres don't really exist they are just a concept that lets us calculate the weight transfer on each wheel in a corner and give some prediction how a car will behave in corner
Sports cars should always have low roll centres but the really import thing is the roll axis which is an imaginary line connecting the front and rear static roll centres. Together with other factors this determines the initial understeer-oversteer charateristic of the car.


With with Seven the general consensus you want the roll centres a few inches above ground level with the rear an inch or so higher than the front.