Ride height

[gav]

Hi all

A quick question or two on ride heights if I may;

1. What is the concensus on optimal ride height for racing and hillclimbing?

2. Has anyone established the lowest ride height possible whilst maintaining the correct geometry (including wishbone angles) using a rose joint set up?

The reason is that I want to run a low ride height but this is creating sharp angles with the wishbones which presumably impacts on camber correction within the suspension travel. I shall check this but am interested to learn how far I can go without altering pick up points.

Many thanks
Gavin

[rgh0]

Hi Gav

I run about 100mm ride height. About 30mm of the drop is smaller diameter tyres and about 20 mm is lowered suspension. This small drop in suspension height sets up a nice 1/2 to 1 degree negative camber at both ends at normal ride height.

Works OK for me. Much lower ride height and I would have exhaust clearance problems with the 50mm tail pipe as clearance undr the exhaust is around 50mm. I would also have problems getting it on and off the trailer with nose and tail clearance.

To low and you bottom out on the kerbs on a track if you go over them which can be interesting to say the least in what that does to the handling in an already stressed situation so you need to know what the kerbs are like where you plan to race.

cheers
Rohan

[gav]

Rohan

Thanks for your reply - very helpful.

Do you know how much suspension travel you use in bump and droop?

Regards
Gavin

[rgh0]

Suspension travel is still close to standard but adjusted by the approx 15 to 20 mm lower suspension height.


i.e. measured at the spring (wheel travel greater than spring at front)
bump travel front std 52mm mine approx 37 to 32 mm
bump travel rear std 77mm mine approx 62 to 57mm

droop travel front std 44mm mine 59 to 64mm
droop travel rear std 81mm mine 96 to 101mm.

I use a relatively soft suspension as I like the forgiving handling this gives and I use all of the bump travel in corners. The front never goes into full droop due to the relatively stiff roll bar. The rear in restrained by a droop strap that limits the last 10mm or so of droop with Cv's to about the standard droop achieved with donuts.

My understanding of racing suspension is you want around a minimum 2 inches / 50mm of wheel travel in bump to have a car that is drivable unless your the STIG or have a formula 1 licence

regards
Rohan

[toomspj]

I run between 80-100mm measured at centre of front chassis member. But the right height depends on tyre size, how stiff you run your car, what you want to use it for etc. First season I ran it too low and I'm no Stig - car was a pig at the limit as it would land on the bump stops.

I think in general lower is better but there are some things to watch for.

You need to keep enough travel not to hit the bump stops - it's quite common to cut the bump rubber in half and depending on who's front shock units you're using you might be able to eliminate some of the wasted space where it mounts at the top.

If you have moved the wishbones to get more castor then check that the upper 'bones don't foul the chassis upright.

For racing, getting rid of bump steer is one of the most important things, but it's pretty hard to get it zero throughout the range - you need to be sure that your new ride height is still in a good range which might require reshimming the rack.

Most people run the rear a little higher than the front. I've got similar front bump travel to those that Rohan quotes, less at the rear. I use TTR shocks which give less droop by a long way.

What spring rates do you use or plan on using?

Paul

[gav]

Paul and Rohan

Thanks for your replies.

I am building a modsports car which was converted to run in Donnington GTs. It has an air dam and splitter at the front and a large wing at the back.

I am planning to run 75mm ride at the front and 85mm at the rear. The rear uprights are double wishbones and carrying out a quick check on camber travel, the effect of lowering the car without changing the wishbone pick ups is some rather extreme wishbone angles and unwanted camber change from bump to droop.

Talking to other drivers with similar set ups, they tend to run 500lb springs at the front and 300lb springs at the rear with around 3" suspension travel. I am no Stig either but I gather that if they are run too soft, the aerodynamics tend to compress the springs making it worse to drive than using stiff springs.

My suspension travel at the rear is limited because I cant fit any longer dampers.

I am not able to raise the suspension pick up points easily so am toying with altering the height of the uprights in effect changing the axle height.
However unless the camber change through the suspension travel is neutralised, this could worsen the position.

Its a bit like 3d chess.

My other alternative is to raise the ride height which i will do as a last resort but I wanted to see whether I could solve the problem by adjustment first - hence the earlier questions.

What are your thoughts ?

Thanks
Gavin

[toomspj]

I think your rear suspension will have such a dramatic effect on the way the car behaves that my experience of a historic roadsports set up will be largely irrelevant.

However it sounds like you are keeping standard type front suspension so your ride height doesn't sound too far different to mine. So far as I know at the front, the lower you go, the more neg camber you get which is largely a good thing for the more modern rubber. But making sure you don't hit the bump stops at the wrong time is still something to take care of.
Ensuring you have the bump steer dialled out seems to be one of the most important things to do on a competition Elan - it's can be a long and tedious job but worth every minute.

The 26R's used cranked wishbones at the front to allow them to ride lower without getting weird angles. Can you do that for your rear wishbones?

Your planned spring rates are quite a bit higher than mine but then I don't have any aero effects to worry about.

Pat Thomas at Kelvedon Motors has a modsports elan for sale on his site so he might be able to give you some better ideas or leads:
http://www.kelsport.net/sales/details.asp?VehicleID=50

Paul

[paddy]

The 26R's used cranked wishbones at the front to allow them to ride lower without getting weird angles. Can you do that for your rear wishbones?

Hmm... isn't the geometry determined by the location of the pickup points and the (straight) distance between the joint centres in the wishbone?. I wouldn't expect the actual shape of the wishbone to affect anything, except possibly what it might foul at extreme angles. (And I suppose if the body of the ball joint is rotated relative to the wishbone, it would allow for more movement of the joint in one direction before binding.)

I don't know why the 26R wishbones were cranked like that. Were they the same length as a normal wishbone?

Paddy

[rgh0]

Hi Gavin

What your doing with a modsports Elan is well removed from any of my experience . For what its worth general guidance says

1. Try to have as much wheel travel in bump as possible - 50mm is good if you can get it. With real downforce this means stiff springs matched to the amount of downforce you get on each track you compete on

2. Modern radial slicks like some negative camber and with a stiff suspension and lots of downforce you will not have much roll in the corners just increasing negative camber with downforce suspesnion deflection. Be careful on long fast straights as to much downforce and to much neg camber can lead to overheating of the inner edges of the tyres

Bst to track down other new or old modsports cars to see what they are doing.

cheers
Rohan

[gav]

Rohan, Paul and Paddy

Many thanks for your thoughts and comments.

They are much appreciated.

Regards
Gavin

[jkolb]

Rohan - what tires are you running?

Jerry

[rgh0]

I currently using my last set of Yokohama A032R's in 175/60. I will change to Dunlop DZ03G in the same size for my next set as these appear the best available now that is on our permitted list for the class I race in ( it does not allow slicks or non road legal tyres or special extremely soft compound tyres eg wets) and in the size allowed - 175/60 which is maximum width allowed for an Elan.

cheers
Rohan