Ride height

[Peter Mears]

Before I started changing the rear spring today I took a measure of height just in front of rear wing. 

I cant remember where to measure the front and what sort of difference there should be? I think it should be 15mm lower at the front!

As it happened one of the shocks was less than in good condition so they have gone off to be serviced, but It would be good to set the rear height once they are back.

[SM25T]

Under chassis rails level with the rear edge of the front cycle wing ..... and under the chassis at the front of the rear wing. Make sure you put the equivalent of your weight on the driver's seat when you do it.

[Peter Mears]

Is that the weight I tell the Dr I am or the real one, and as Ive got flares I will guess at the front :)

Cheers

[SM25T]

It is your real weight. It is very scary when you pile it in !!

[elie boone]

There is no extra weight needed when you set the rake, on a Imperial chassis it's 15mm with linear springs and 35mm with progressive springs.

[Paul Deslandes]

meaure ride height at the front edge of the pedal box and at the back edge of the (standard not lowered) floor/front of rear wing.

I used 42 house bricks in the drivers seat although I may be able to remove a few next time as I've lost a bit of weight since ..........

[Peter Mears]

Are there any tips or tricks when setting rear ride height.

Is the only way to measure, jack up, whip the wheels off, adjust, put wheels back on and repeat?

[martyn]

An inspection pit or ramp similar to this is perfect because you can wind the spring perch from underneath without having to remove the wheels.

Most people dont have an inspection pit, so try to figure some way to raise the car a little so you can lie under the back of it.  Something like two planks of wood running lengthways might do the trick.

Once you've figured out how to get under the car, it is likely that you'll still need to jack it up a little to take the weight off the spring before you can adjust it. But give it a try fully weighted first and see how you get on.

[TomB]

Doesn't each ful rotation of the collar give 1mm travel - so you can measure roughly how much you need, and turn accordingly. I don't know, but if jack up the rear and put it on axle stands, can you lie under and adjust each side, then drop down? On mine the adjusters are at the bottom of the damper, so fairly easy to reach. 

[TomB]

Just to pick up the latest post on ride height, which coincidently I was the last person to post to!

I need to adjust mine, as a long story cut short - I have 60 profile ride height setting, but wearing 70 profile tyres, so the dampers are too short and the fronts are almost at the end stops with the car resting on its weight.  I need to fit my 60 tyres and reset the ride heights and then refit the 70s temporarily until I replace them.

For purposes of adjustment, particularly on the rears which are vertical, does 1mm of collar movement equal 1mm of ride height? Or does the presence of a spring mean this isnt a linear relationship? I probably need to up the height on the 60 profile tyres by ~15mm, so does this equal 15 full turns? 

PS they are Ohlins, not Billies, I perhaps naively hope / assume they are a standard thread pitch for adjusters. 

[Mankee]

According to Simon's guide: "10mm of thread on the spring platform will be approx 5mm of ride height change."

[Simon.Rogers]

The front has a Motion Ratio of approx 0.6 so yeas as above but the rear its closer to 0.8.

However the spring won't react in a linear way but to get the majority of the way there you can use the motion ratio's.

 

[Simon.Rogers]

I should add you can not count on the damper threads being 1mm.  They all differ.

[revilla]

I know this was a long time ago now but I didn't see Elie's post first time around. Is that really correct, 35mm rake with progressive springs? I had only ever heard of around 15mm rake before so that's what I've been running, but I do have progressive springs and by that reckoning I am miles away from optimum.

[TomB]

It's 15mm rake with passengers, before I started messing unloaded mine wasn't far off 3cm. That was with progressive rears. There isn't much room in the turrets for adjustment - after playing night night I'm thinking it might be quicker to to the coarse adjustment after removing the rears. 

[Mankee]

Tom, can you fit the Ohlins un-inverted (double negative?) so that you can get to the platforms, fiddle with the ride height and then flip them back to the normal inverted fitment to check them once you are happy?

[TomB]

Possibly, thats occured to me. But whats interesting it your use of 'inverted' - Ive fitted them with the height adjuster rings up the damper turret, are you suggesting the normal fitment is for the adjusters to be above the de-dion?   

[Simon.Rogers]

You can run a gas pressurized damper any way up.

But you have to look at the clearances and many dampers particularly on the rear will only fit one way due to the lower de dion tube mount.

[Mankee]

And I've probably had a brain fart moment and got myself confused, which is easily done!

[Mankee]

I've just thought about my ropey use of terminology. Standard Bilsteins are traditionally fitted with the bodies and adjusting platforms at the bottom. Aftermarket have the bodies fitted at the top, hence my use of the word "inverted", with respect to standard Bilsteins. And double negative of "un-inverted", fitting them temporarily with the adjusting platforms and bodies at the bottom near the de Dion tube so that you can get to them more easily. If that's at all possible of course.

[TomB]

So to pick up my last comments on this topic, Ive now fitted 55 profile tyres from 70s.  I decided that having 70 profile tyres with high end dampers was probably not allowing the dampers to work to their optimum giving the unpredictable side wall movement.  So Ive restored a set of SLR split rims and fitted a set of CR500.  

Now the sump clearance is 60mm which is a touch low - Im aiming to 80mm.  So can I run through my thought process before I mess it up? 

1) Put 3x25kg bags of sand from B&Q to simulate my weight.

2) Increase ride height adjusting the front to get 80mm under the sump.

3) Measure front clearance under the chassis rail at rear of front cycle wings

4) Adjust rear to be front clearance plus 15mm.  

5) Check height across the axles, try to get the same height on each side, front and rear.  

Is this correct?  If Im low on one corner, for example front left, do I need to adjust the opposite ie lower rear right to raise the front left?  

When I last played with the height when I fitted the Ohlins, it was much easier than with the old Bilsteins as they responded and settled to height more quickly and with better repeatability.

If the ride height are equalized with weight in the car, will this be close to what Id be able to achieve with a corner weigh session?  

Thanks 

PS - should I remove / disconnect front and rear ARB to do this?  

[SM25T]

All sounds OK.

[Richard Price]

Tom,

Yes - disconnect the rear ARB.

Your method may result in reasonable ride height, but your corner weights may be way out!

Without gear to check corner weights, I'd jack the car up at the front and check that the spring lengths are similar when at full droop.

[TomB]

Thanks for your thoughts. 

Ive got my sump height adjusted to 80mm unladen and 75kg of sand bags in the garage. Just a couple of things to check with you - am I right in assuming I need to aim for all the ride height laden with weight in the car i.e. 

15mm of rake - laden. Sump height of 80mm - laden. Equal on each corner as close as I can get it - laden. 

Why does the rear ARB need disconnecting but not the front? If I'm running the ARB on the road, don't I need it to be connected? 

[SM25T]

Yes to setting up with your weight equivalent in the seat.