Ride Height Adjustment

Jimmy M · 10-16-07, 08:17 PM

Hi all,

I am in the process of getting suspension for my DRB Kit. They use AVO coil-overs as standard equipment.
I am curious about the way ride height is adjusted by actually adjusting spring preload.

From my days of motorcycle road racing, ride height was to adjust the upper rod end, which screwed into the shock body.

Preload on the spring (sag) was set to rider weight and is a fairly critical adjustment.
Is this not so with setting up cars?

I cant seem to find any manufacturers which offer a shock with independant ride height adjustment.

Any input would be greatly appreciated.

JM

Russ Noble · 10-17-07, 01:01 AM

Jimmy,

I am not familiar with bikes but in the absence of anyone else replying here's my two cents.

With car coilovers the weight on the spring stays constant thus if you raise the spring platform an inch, you will raise the top of the spring one inch also. This will of course raise the car. Spring rates stay the same until you get to full droop.

With coilovers the preload on the spring only affects full droop, and at that point any springing is a bit irrelevant because you will more than likely be airborne or at least have that one wheel off the deck. So the spring rate in those conditions (i.e. with no weight on the wheel) will have no effect on the way the car handles.

Although, if you've got all of the wheels airborne, you'll just have to hope everything is heading in the right direction. The niceties of suspension characteristics and any input from the driver in that situation is unlikely to stave off impending doom!

Cheers,

Jimmy M · 10-17-07, 03:52 PM

Thanks Russ,

Youve just made me think as to how a bike is different.

Under heavy braking the rear of the bike will rise. You nee to have a predetermined amount of sag (10 to 15mm) to stop the suspension 'topping out' with too much force (or in car terms hitting 'full droop').

I guess this is different as with a bike the weight transfere (proportionally) is probably alot higher than you will get in a car, therefore more actual travel of the damper going from hard acceleration to hard braking.

What units will you be using if you dont mind me asking?

Cheers

JM

Russ Noble · 10-27-07, 01:57 AM

Sorry, somehow I missed this post last week Jimmy M.

I think the difference with bikes is the short wheelbase. Given enough rubber it doesn't seem to be too hard to rotate them around either the front or rear axles.

I will be using Koni 8212 series, aluminium double adjustables.

Just noticed you are from Christchurch, it's becoming a hotbed of GT40 enthusiasts! We should all catch up over an ale sometime. Give me a ring on 960 7442 H or 384 9023 W if you want to meet up.

Cheers,

Kalun D · 10-27-07, 03:00 AM

You probably won't find a car coilover with a separate ride height adjustment. I think bikes need this due to ride height being more affected by rider weight. On a car rider weight is less of a percentage of total so as to not be a factor.

Richard B. · 10-27-07, 10:24 AM

You have to be carefull adjusting ride hieght with the spring preload adjusters because you can quickly take a shock out of its operational range. We used to run into this all the time on drag cars. People thought you could just adjust the spring up and down to raise and lower the car, and we would get cars that either had the shocks completely topped out or bottomed out. You can probably go about 1/2" on the shock from suggested installed height, but once you go past that you will have problems. If you need more adjustment than that, you need either a longer or shorter shock, or an adjustable mounting position.

Jimmy M · 10-27-07, 04:51 PM

Russ, Yes I will call next week,

Richard, Yes adjusting the preload will move the operating zone on the damper. The only way to correct that is to change the spring for a heaver or lighter weight.
So if you're setting up a new car and only have a ball park idea of what spring weight you need is, you can end up owning a lot of springs while trying to get it right.

I see one shock manufacturer (koni I think) does have different lenght end fittings for their shocks. I believe they change in increments of 0.200". This seems the best idea to me as that way you can get your corner weights right with preload and then cahnge the fittings as required to get the desired ride height.