Avenger Tiger - Hillclimb and Sprint Car

To add to the things you are thinking about - What happens to the leverage ratio being applied to the mass supporting coilover when the other end of the axle is in the air?

ETA

Until the 300lb spring goes coil bound, which will be quite a way as it's so close to the 350 rate, your wheel rate is currently about 75lb/inch ! (84lb - 56lb) - which I imagine is probably less than a stock Avenger Delux super wafty wheel rate.

It will be good to get the actual measurements so that the figures can be corrected but I think your issues are.

The compound springs giving a low 160lb rate
Falling rate suspension due to the inclined angle of the coilover
The high roll centre

Any one of the above is bad enough.

Get the springs vertical and correct the poundage to match with the front wheel rate.
Fit a Panhard/Watts/Mumford to get the rear roll centre lower. (Will require parallel top arms)

Ok,

The dampers are at exactly 30 degrees from the vertical. The bottom mount is inboard of the Hub face BUT the wheel centre line is also inboard of the hub face (to clear the arches with an 8" wheel/ 200 tyre) the difference between the 2 is approximately 100mm. So therefore i see why the ratio is not exactly 1:1.

Ok, not sure i follow the explanation but i shall have a sketch and see what happens to my understanding.

Ok, the first spring is i thought 2" and is near coil bound at normal ride height. But that doesn't seem correct with the spring rates i have in my notes as were supplied with the dampers. I need to measure their length and read the rate directly as its printed on them.

Ah reading the rate of the photo it says 300

IMG_2237 by Nevtiger, on Flickr

And at normal ride height minus my weight





Falling rate spring - ok i understand but i just need to see the math to comprehend fully.

High RCH - yep got that. I modelled the rear and front to see the relationships as i used to get a weird thing happening but i had a very steep slope to the front between the two RCH's since sorted with my new front set up and better controlled lateral at the front as well.

Low rate - done to get traction and grip from a live axle.


Ok, then we hit the snag. I am very disinclined to 'turret' the rear although not completely as the car is a genuine Tiger and that might detract from its value. Also i need to take account of the issue with suspension mods and staying in Road Production Modified and not straying into Sports Libre because of changes to the monique in between the wheelbase/relocated suspension pick up points etc.

Watts and Mumford i have both investigated at a lowish level via both Staniforths book and Milican & Milican. I also modelled it but at the time saw no benefit in the extensive mods i would need to do. I certainly don't want to 4 link the rear end as that will take me out of class but maybe a 3 link set up could be added without major surgery to allow Mumford or Watts?

If i were to try anything it would be vertical dampers first but that will require major surgery as the damper will go up throughout the chassis rail.

Yes, i have worked it back out now.....

Do you think having the coilovers behind the axle will affect how it moves as well ? The weight of the car is trying to twist the axle up at the front. With the springs back in their original position the weight of the car twists the axle down at the front, this compensates for the forces you get when accelerating.

I struggle with trying to work stuff out and resort to building lego models of things, sounds a bit daft but it's easy to see the effect of vertical and inclines springs.
With the coilovers inclined you need to have rising rate springs to end up with linear rate.

As everything is still there I would try springs in the standard position again. Keep the shocks but just take the springs etc off and see if it makes a difference.

Makes no difference front or rear, the axle moves vertically restrained in its movement by the upper and lower trailing links. The triangulation of the upper links providing the lateral location and also establishing the high roll centre.




That would be a step in the right direction, as it will remove the falling rate and the compound springing in one go.
What is the leverage ratio on the lower trailing arm / spring and what was the rate previously used - Looks like the original had an element of rising rate built into the geometry.

Until the conversation about my rear end got into full flow i had not fully realised the angles involved (or ignored them) and that as the car squats the angle increases and then that is compounded by the lean taken on by the body which worsens the angle even more.

Last first!

That is - i think - Alans recent car. A very tail happy rally car. The Panhard rod - in my view- is not really doing anything as its fighting the top links. The top links allow no lateral movement but the Panhard will introduce a small amount when travelling through its arc.

Remember a rally car will carry at least two spare wheels and much more fuel, they also bounce around more. This causes an issue With an Avenger, the rear chassis over the axle splits due to the high loads carried behind the axle line and thus needs double skinning but i have never seen the damper mounts become stressed.

Ok i understand the thinking with the rear spring and rising rate now. My 2.25" mount had the spring vertical and that was to allow the mounting to be held in place rather than any desire to have the springs vertical. I could make new mounts the that put the spring at the same angle as OEM.

You have asked a very interesting question about what the Works team did with the rear suspension.

Its a long story but they ended up leaving it as standard even on the World Rally Championship winning Sunbeam Lotus of '81. The team went through a development project with the Avenger using different arrangements when they fitted the 4HA from an Aston Martin (O'Dell was ex AM) including the same set up as used on the back of the Escort but with a Watts Linkage (Escort was Panhard Rod at the time). The archives don't talk about link length but they gave up on it as a suitable rally car suspension....... I have a feeling Tony Pond tried a car with a 4 linked rear end and did not like compared to standard but for what reason i do not know.

It is also of note that the Avenger Estate uses parallel top links which are quite short and a panhard rod, standard bottom arms are used.

When the car ran on the 048's i used 250 rate at the front and used to work well with those tyres once they were up to temp. The 250's seemed way to soft for the 'slicks' though, albeit without the heavy ARB set up i have now.

300F/400R would be similar to a couple of race Avengers that used to be around. Not sure of the current Sunbeam race cars though?

It must be remembered that the front suspension can give a low RCH to but is much less controlled and the lower it gets the less controlled it is laterally although this can be mitigated by less wheel travel i suppose. It isn't a rally car after all :-)

I think engineering a Mumford or WOBlink would require a fair bit of work BUT could go in without to much butchery which is a bonus.

And the strut tops seem to have survived!