Suspension and ride height query

[Graham King]

Folks, appreciate a little bit of advice here please. I am trying to help out my neighbour who is in the process of rebuilding a Tiger Cub (7 esque), he has replaced the suspension as the old dampers were siezed. He replaced these with quality new adjustable units of the same length and new springs (supposedly of the same rating, 300lbs). It has been on axle stands for months but he took it down yesterday and it is ridiculously low (we're talking front is approx 40mm off the floor ☹️).

 

I have little experience of suspension but a couple of points worth noting.

 

1) The lower wishbones are below parallel to the ground

2) Trying to raise the ride height by adjusting the suspension just results in the springs compressing, it doesn't raise the car

3) Jacking the car up to what would look like a decent ride height (70mm under the sump) has the lower wishbones above parallel with the floor

 

I have done some searching on here and some threads mention mounting the dampers upside down to raise the ride height, why would this have any effect?. I guess he needs stronger springs to stop the effect in point 2?. Would elongating the dampers have any effect?

 

Does anyone have any suggestions or is able to offer any insight into this for me. He has spent so much time getting it back into a decent state, and has made a lovely job of it, I'd like to be able to help him out.

 

Graham.

[Pendennis]

Sounds like the dampers are too short.

Suppose the front springs are progressive but even so would still expect some change. Measure the dampers when spring compressed, then jack her up and measure again see if the dampers become longer. That should give you the answer

[oldbutnotslow]

I agree it sounds as if there is insufficient length available in the damper pistons.

I am happy to help if you want to pass my e-mail to him.

[Graham King]

Thanks both for the responses, there seems to be a common theme to them. I'll have a chat with him and see if we can work out what is going on by taking some measurements.

 

Grant I'll pass on your kind offer as well.

 

Graham

[Phil B]

Hi,

 

You don't mention what size wheels/tyres he is running. Most of the 7 esque cars around use 15" wheels and low profile tyres, so the ground clearance is not much. This will influence the inclination of wishbones at what would be a typical sump clearance of a 7 running the more typical 185/70 or 185/60 x 13" tyres.

Also from what I have observed the angle of the front dampers tends to be pretty shallow so the effective spring rate is much reduced hence adjusting the platforms doesn't change the ride height much.

When I went widetrack on my early chassis car I took account of the reduced angle of my dampers and increased the spring rate to 300ibs (was 260). Although this may sound high, due to the shallow geometry the actual effective wheel rate gives me a compliant ride with no crashing on bumps, even with a Zetec in the front.

 

Has your friend tried posting a request for help on the Southern Kit Car forum? They're a friendly bunch and plenty of members in the Surrey/Sussex area.

 

Phil

[Graham King]

Phil, I do think the tyres are some of the issue, he is running 195/50 R15. The angle of the dampers is almost identical to the 7, so you're right that adjusting has limited impact on ride height. I reckon he needs approx another 4" of ride height which is a lot of extra length on the dampers if that is the answer. Unfortunately the car wasn't a runner when he got it and the old dampers were seized so we've never seen it on the road to compare to now.

 

Graham.

[6speedmanual]

Widetrack style damper extension piece?

 

As stated above, it does all depand on how much lift you need and the geom of the damper length to wheel travel ratio. Could still be that teh overall lenth of the sring/damper assembly is wrong.

 

Peter

[Stationary M25 Traveller]

Another 4" of ride height .... over the 40mm already under the sump ? 😳

[charlie_pank]

Graham, the first part of the adjustment will just add preload. What happens if you keep adjusting? If you end up with a travel that is too small then he might need some beefier springs - it's the dampers that are expensive, not the springs so this shouldn't be a problem...

[Graham King]

Ian, I say 4" (it's only a guesstimate) as that is what I think he needs at the front, the bottom of the nosecone support (it's not like a Caterham) rests on a frame, the frame is approx 2" off the floor at the moment. I haven't measured mine as it's on stands at the moment but I guessed about 6" of clearance from the nosecone to the ground.

 

CP, he and I are going to do some measurements this weekend and see if we can work something out, this thread (and the email responses I have had) have helped with my understanding of how things work, so it's been an interesting exercise.

 

Graham.