Comparing and Choosing Spring Rates

We find people often focus heavily on spring rates when deciding on a new suspension kit or changing their suspensions characteristics. We totally get this as there are very few details on a typical suspension spec list that actually give any indication of how that set will perform or ride. 

The unfortunate reality is that comparing spring rates to other products on the market (suspension brands and variations of dampers) or other products they’ve owned/experienced gives virtually no meaningful indication of how the end product will work for your particular setup. This is because spring rates are only one part of a huge puzzle that makes up a vehicles suspension setup, Below we will try and give you a basic understanding of this. 

Comparing Spring Rates Between Products

Aspects like shock absorber travel, bumpstops, adjustment range, spring travel and wheel travel range all play a huge role in the final outcome, with valving being the biggest factor in our opinion.

Internal Valving:

Valving is the most variable factor with there being practically infinite ways it can be designed and tuned. Without having a good understanding of the valving in a particular setup, along with the other factors mentioned above, it’s impossible to have an idea of what to expect from a setup.

For example a 5kg spring paired with a damper that has a more restrictive internal valving can feel stiffer than a 10kg spring paired with a damper with a less restrictive internal valving setup on the same car. This is one reason It’s hard to compare spring rates between different products as different products will have different valving like trying to compare a 5kg spring on our Pro Sport Kit to our Voston Comfort kit or other brands. Another aspect that can have the same effect on the spring rate and also the damper is the motion ratios. 

Spring & Damper Motion Ratios:

One thing that many people don’t know about and have possibly never heard of is “motion ratios”. A motion ratio is a way of showing how much leverage the wheel has over the spring and damper. This can vary depending on the vehicle and can also vary front to rear.

The motion ratio changes depending on how and where the suspension is mounted in relationship to the wheel. Generally speaking, for vehicles with independent suspension (not solid axles or beam axles), if the spring and/or damper is mounted close to the wheel, then there will be less leverage than if it’s mounted further away from the wheel. For example, a 0.7:1 motion ratio means that for every 100mm the wheel moves, the spring and/or damper moves 70mm. 

When working out spring rates, valving and how much damper travel is required, this motion ratio plays a huge role. A simple example would be working out the true “wheel rate” of a spring.

If a spring rate is 10kg/mm and is mounted on a 0.7:1 motion ratio then you times the spring rate by the motion ratio once for the “kg” component of the spring rate and once again for the “mm” component. In doing this it shows that a 10kg/mm spring mounted on a 0.7:1 motion ratio has an effective spring rate at the wheel of 4.9kg/mm.

Let’s say you wanted to have a 0.9:1 motion ratio rather than the 0.7:1 as previously used, then this would give spring rate closer to 10kg/mm (8.1kgmm compared to 4.9kg/mm). So you can see that motion ratios make a very big difference to the kind of spring rates you would use, and the same goes for calculating the valving.


This is why a Mazda MX5 for example even though much lighter than an Evo has a higher spring rate than the Evo because the motion ratio has more leverage of the spring on the MX5. 


We Can Help Make Sure You Have The Right Spring Rate.

One massive benefit of purchasing MCA Suspension is that all our products are designed, tested and assembled by us to order here in Australia. This means if you want to try different spring rates for your suspension and it’s one of our products, we can make calculated recommendations based off our valving and designs for your needs, no guess work needed.