Pick a few brains

[StewartG]

Having aquired a wide-track suspension kit and some adjustable spring platforms I,ve got loads more set up things to think about. 1) Should I use the shock lenghtheners or not. If you fit them the shocks have next to no compression travel but the ride height is about right if you leave them out the shocks have roughly equal comp and rebound travel but the ride heiht is so low I cant get over speed bumps. 2) What should the ride height be? 3) Some people fit the shocks upside down,presumably lees unsprung weight, can you really notice any difference?

[Chelspeed]

1 Dont fit the spacers you loose too much bump.

2 Move the circlip further up the shocker body so that the ride height is OK with the adjuster in mid adjust or get longer springs.

3 Caterham say something like 140mm front and 150mm rear, I'd run more like 120mm and 135mm, measurements are under the chassis rails behind the front wishbone and at the rear of the cockpit.

[Tim Seipel]

But ride height really does depend on the tyre size you use. Is the car for obsolute best performance on the track or does sump height matter to you. They conflict with sleeping policemen.

[Mike Bees]

As Tim says, the ride height is dependent on the wheel/tyre diameter you're using. If you're on 15in wheels and you set the rear ride height to 135mm then it'll understeer like a pig. What is important is setting the ride height such that the suspension geometry works properly - this is much much much more important than how low you can get the chassis to the ground.

 

Mike

[Peter Carmichael]

Just to balance up the opinions, I use the spacers with 13in wheels.

 

I get about 10mm of damper travel before the bumpstops come into play. That is equivalent to about 25mm of wheel travel. I also reckon I can compress the bumpstops by 5mm by hand (12mm), with forces that are irrelevant to the cars handling.

 

It is important to remember that a properly engineered bumpstop (ahem) does a very important job, providing a rising spring rate and some damping. Even from a handling point of view, it is preferable to have the bumpstops coming into play rather than clanking your sump on the ground.

 

My setup has an inch and a half of wheel travel before the bumpstop starts to take over and it has 2 inches of ground clearance under the sump. This seems to be a good balance.

 

However, the sump is only going to come into contact with the ground when both wheels deflect. In cornering, one side is going to be in compression the other in extension. In this situation an inch and a half of wheel travel might not be enough and the bumpstops may be coming into play without the sump being at risk. This has never been an issue for me because the car is quite stiff in roll.

[StewartG]

Having now experimented with and without the spacers in the front shocks and having adjusted the platforms to give the same ride height and having left the rear suspension alone my preference is to leave the spacers out. This conclusion was reached for road driving. It seems that more bump travel allows the wheels to follow the road better causing it to skip sideways less on mid corner bumps. With the spacers in the suspension feels as if it starts to work but then locks solid. My current front ride height is set with the wishbones parallel to the ground (about 130mm) and I'm moving on to the mysteries of rear suspension set up.

[Peter Carmichael]

What antiroll bar(s) do you have?

[deanteam]

By adjusting the ride height via the platforms the track rod angle changes and therefore toe-in. I understood that the optimum to reduce bump steer was to have the track rod horizontal. Is this correct? What height adjustment can be made without having toe-in reset?

[Peter Carmichael]

Bumpsteer is frequently misunderstood.

 

You cannot get rid of it and it can be useful. However the most important thing is to have the same amount side to side, so set up everything symmetrically.

 

[StewartG]

As far as I can measure setting the ride height with the lower wishbones parallel to the floor also sets the trackrods parallel to the floor and this minimises the toe in change over bumps (I'm using zero toe-in by the way) The front and rear anti-roll bars are 9/16 red bushes I think.

 

Edited by - stewartg on 1 Sep 2000 13:16:46