Shock Absorbers - Determine Correct Size? - Winkelmann WDF-2

[CTR28]

On my Wink WDF-2 that was recently refurbished and raced it was noted that the rear shocks are likely too short. Is there a formula or calculator for determining correct size (length, compression, etc) as well as other aspects for choosing a shock absorber?

And/or ... does any on have information on the correct shock sizes for the front and rear of a WDF-2?

TYIA

[Steve Demeter]

I know of no magic formula. Put the car up on stands. remove the shocks. Measure the length required at full droop. Subtract length to get whatever droop you want to limit it to. Raise the suspension by using a jack under the upright til you get to what you thing the maximum bump displacement will be and measure again. Then use your best judgement to determine a final length. Obviously on most cars you will not need to go til the suspension binds in bump. YMMV but this has never failed me

[S Lathrop]

There are several things you have to know before you decide on a shock length.

What ride height are you aiming for. This is a number that should be chosen by looking at the suspension geometry and determine where the geometry is optimized. Pulling a number out of the race car either is not going to work very well. For any suspension geometry, there is an optimum number. When the designer of you car intended the ride height to be some particular number.


Once you get the ride height, you can easily choose a shock length. Say your shocks have 3" stroke. I would choose 2" for bump and one for rebound. Given that most cars of the vintage of you car had motion ratios close to 1/2 inch of shock movement for 2 inches of wheel travel. You should know what that motion ratio is, accurate to 3 decimals places. You will use this number a lot as you develop your setups.

You also need to know the loaded weight of each corner of your car. .Now you can determine what springs will be needed to support you car. As a starting point, I would suggest that you start with a spring that will give you a wheel rate that is the same number as the weight on that corner. This sis probably teh high end of the spring range you will want but it will be close and a good place to start. One thing you want to avoid is a big difference in the weight to spring rate for the front compared to the rear. I tend to choose a front rate that is a bit stiffer than the rear but not by much. I tune the car by changine this ratio of the springs to the load at the wheels. I don't change any other variable until I get this number optimized. After that you can play with sway bars.

Given teh low motion ratios of cars like yours, spending money on expensive adjustable shocks is a total waste. I do make use of bump stops on the shocks and I use packers to tune handling.

This whole subject you have asked can take many volumes of thick books to explain.

[Hawke]

I supply and fit shocks to many older formula cars, and can only reinforce what Steve Lathrop has said. It’s a great starting point, and it really is that simple. I struggle to understand why so many stuff it up.

One point I will make is that you never just replace the shocks with the same length that came with the car. These things are like Grandpa’s Axe. You may be on the 3rd or 4th replacement shock since it was made. And, even when made, it’s possible (even probable) that the wrong length was fitted when built. Keep in mind that when these cars were built, many components were chosen on price before specification.

Most shock suppliers will have a range of eyes of different lengths, often in increments of 6mm to allow you to exactly determine the right length.

In my experience, if you have to compromise on length, go shorter on the front, longer on the back.

Most shock suppliers supply valving that is usually OK for springs up 500 lbs. However, its not hard to alter that valving - usually just the rebound shims.

You asked for some other advice regrading shocks. If you are an amateur or newbie, just get some steel bodied single knob adjustable shocks. They will serve you well. You could spend up big and get some aluminium double or triple adjustable shocks, but you would not be quicker. Spend that money on track time or driver training. That will make you faster.

When you are fast, get some different shocks.

[CTR28]

Thank you Steve,

That is good information as provides me a good base to solve this issue.

~ Michael

I know of no magic formula. Put the car up on stands. remove the shocks. Measure the length required at full droop. Subtract length to get whatever droop you want to limit it to. Raise the suspension by using a jack under the upright til you get to what you thing the maximum bump displacement will be and measure again. Then use your best judgement to determine a final length. Obviously on most cars you will not need to go til the suspension binds in bump. YMMV but this has never failed me

[CTR28]

Steve, thank you for the comprehensive information. In researching Apex Speed for any information I found a reply you had sent on another shock absorber question and I was hoping you would respond to my question.

~ Michael

[CTR28]

Thank you for this information. As a returning newb, after a 40+ year absence from this form of racing, your suggestions will really help as I go through this process.

~ Be well