Coilover Ride Height Adjustment – The Correct Way
HP Academy & Suspension Secrets have highlighted coilover manunfacturers giving wrong information on coilover ride height adjustment to their customers. In this article I want to boil down the key points to make the concept as easy to understand as possible.
NOTE: This article will be looking at coilovers which have an adjustable bottom bracket and an adjustable spring seat eg like coilovers from K-Sport & BC etc
The Principle
The goal of correct coilover ride height adjustment is to get the car to the desired ride height and with the correct bump to rebound ratio.
I’ll repeat that last sentence because it is key. To do coilover ride height adjustment correctly, we need to maintain the correct bump to rebound ratio at the ride height we want.
Bump/Bump Travel – The amount a suspension can compress from its static position when the car is stationary.
Rebound/Droop Travel – The amount a suspension can move (expand) from its static position when the car is stationary.
The Ratio
In a podcast with HP Academy, KW have said the bump to rebound ratio should be biased towards rebound ie to have more rebound travel than bump travel, as a broad guide they say 45% bump travel to 55% rebound/droop travel. Suspension Secrets on the other hand give a number of 2:1 in favour of bump travel ie to have twice as much bump travel as droop travel.
Let’s assume 50:50 is ideal for this article.
The Process – Ride Height Adjustment
I’ll give a very brief guide to how to achieve our goal of 50:50 bump to rebound travel.
Step 1
Remove the spring from the damper unit.
Step 2
Choose your desired ride height. eg how far from the fender lip do you want the centre of the wheel?
Record this number (the distance between the fender lip and the wheel centre)
Step 3
Without the spring, mount the damper on the car with the wheel. Support the suspension on a height adjustable platform. Compress the suspension to the maximum the damper will allow. Record the new distance between the centre of the wheel and lip of the fender.
Check for contact between vehicle body and tyre with different amounts of steering lock. Check for any suspension to suspension/body contact.
If you have contact, adjust the bottom bracket until no contact is made.
Record the maximum compression travel.
Step 4
Extend the suspension as far as the damper will allow. Measure and record the distance between the fender lip and the wheel centre. Check for any suspension to suspension/body contact.
Step 5
Some math. Calculate the difference between the numbers recorded in Step 2 and Step 3, this is the compression travel. And calculate the difference between the numbers recorded in Step 2 and Step 4, this is the rebound travel.
If we are going for a 50:50 split between bump and rebound travel, our bump/compression travel and our rebound travel should be identical. If the numbers are not identical adjust the bottom bracket on the damper until they are identical. (Keep in mind body contact if that was an issue in Step 3 and/or Step 4).
NOTE: Spring Bind – With the bottom bracket adjusted, it is worthwhile/essential (especially if we are dealing with a custom suspension) to measure the actual compression distance/travel between our desired ride height & full compression *at the damper*. Will our springs bind before full compression is reached? If so, we need to select shorter springs or adjust our desired ride height.
Step 6
When you get the bump travel and rebound travel numbers the same, we can refit the spring to the damper and install the unit on the car. Repeat these steps for all four corners of the car.
Step 7
With the complete coilover kit installed on the car with our correctly adjusted bottom brackets, measure the distance between the wheel centre and the lip of the fender.
Adjust the spring seat of each damper until you get the ride height (the distance between wheel centre and fender lip you chose in Step 2).
With all four corners at the ride height you want, the coilover ride height adjustment process is complete.
Possible Problems
There are a few problems that might affect the setup process.
Damper Problems
The ride height you want may not be achievable because of tyre contact with the bodywork. For example, in Step 3 it’s possible the tyre will contact the bodywork (try different steering angles to be sure). If this happens there are four main options
Option 1
Modify the bodywork to make room for the wheel & tyre
Option 2
Use a different length damper
Option 3
Compromise on the bump rebound ratio. You will have to judge how big a compromise you want to make. Going from Suspension Secrets vs KW’s numbers there is no hard and fast correct ratio. Suspension Secrets say 66% of travel for compression, KW say 45% of travel for compression. That is quite a big window. Straying too far outside these numbers is probably not correct.
Option 4
Choose a different tyre width and/or wheel offset
Other Problems – Springs
1.Your springs are binding before full compression. Solution, use shorter springs. Ideally we will have checked our spring compressed lengths in Step 5 before fitting the springs and the suspension to the car.
2.Your springs are dislocating from the spring seats at full droop. Solution, use helper springs. Drop the spring seats by the compressed height of your helper springs and the thickness of their main spring joining collar.
Summary – Coilover Ride Height Adjustment
This process is probably going to take longer and require more brain & muscle power than simply setting the spring seat so the spring is not loose and then doing all the height adjustment with the bottom bracket.
Is It Worth It?
It depends.
Going back to HP Academy’s comments about some coilover manufacturers giving the customers wrong information.
In theory, if they (some coilover manufacturers) are saying all height adjustment should be done by the spring seat, then yes, technically it’s wrong.
On the other hand, I’d like to think that coilover manufacturers have done their homework on spring lengths and damper lengths for each specific application so I’d imagine the bump/rebound travel ratio is going to be in the ball park.
However, I have yet to see a coilover manufacturer specify the ride height they used when they selected the components for a specific kit. Without this information, to be sure the ride height is set properly, we have to do the adjustment the long (correct) way.
Consequences of not using this process for setting ride height
Running into the bump stops unnecessarily leading to an unnecessarily uncomfortable ride and less grip/performance.
Running out of/insufficient droop giving the car the feeling of dropping coming off bumps/undulations. It could also lead to the tyres leave the surface resulting in no/less grip.
Benefits of using the longer, correst process
Getting the most comfortable ride possible
Getting the most grip possible
Wrapping Up
The pluses of having a properly set ride height I think vastly outweight the negatives.
If you only want to set your ride height once and forget about it, I think the one-time effort is well worth it.
If you will be adjusting ride height regularly eg chasing lap times, I think the effort involved in getting the maximum performance from your suspension is well worth it.
In other words, the process is well worth it.
It might be a pain in the short-term but the long-term benefits will probably pay back many times over.
