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Guide to calculating Shock Absorber lengths

Guide to calculating Shock Absorber lengths

Guide to calculating Shock Absorber lengths

Guide to calculating Shock Absorber lengths

Guide to calculating Shock Absorber lengths

My vehicle is standard height, do I need to take measurements?

If you are sure that your vehicle has never been lowered, then you don't need to take measurements. You can choose a shock absorber from our standard size Spax range, which are listed by model and year, rather than by style and size. These shocks have exactly the same features as the custom size items, the only difference is that you don't need to measure anything. If you are unsure as to whether the vehicle has been lowered, following our measuring procedures will ensure that you get the correct shock absorber for the vehicle.

Can I simply measure my existing shock absorbers?

We wouldn't recommend this route, as the previous owner may not have used the correct size shock absorber. If you are sure that the existing shock absorbers are not 'Bottoming out' or 'Topping out' then you will be OK to go this route (we would still recommend measuring as per our procedures, to be 100% sure though).

Can I take measurements without removing my shock absorbers?

We wouldn't recommend this, as the previous owner may not have used the correct size shock absorber. We have encountered standard size shock absorbers being fitted to many lowered vehicles, the shock absorbers would be 'Bottomed out' and effectively holding the car up higher than it should have been. Hence taking measurements with the shocks still on, would give a totally false measurement and result in the wrong shock absorbers being fitted.
The only way to know for sure, is to remove the existing shock absorbers and ensure the vehicle is resting at it's natural height, then taking proper measurements.

Where do I take my measurements from (Style 1 Shock Absorbers)?

For Style 1 shock absorbers, you should take your top measurement from the hole at the top of the axle beam strut, as shown in Figure 1 (but obviously with the shock absorber removed). This effectively means that you are measuring from the 'centre' of the top bush on the shock absorber, as shown at the top of Figure 2. The bottom measurement should be taken from the 'centre' of the bottom mounting stud.

Fig 1

Fig 2

Where do I take my measurements from (Style 2 and 3 Shock Absorbers)?

For Style 2 and Style 3 shock absorbers, you should take your measurement from the 'centre' of the mounting bolts or studs that hold the shock absorber in place, both top and bottom, as indicated by Figure 1 and Figure 2 (but obviously with the shock absorber removed).

Fig 1

Fig 2

I just have a rolling chassis at the moment, how does this affect things?

We wouldn't recommend taking measurements until the body is refitted and built up again, and hence the vehicle has it's full road weight. This will make a big difference in the ride height of the vehicle, hence measuring up prior to this stage would result in shock absorbers that are too long.

I am fitting dropped spindles to my vehicle, does this make a difference?

If you are using dropped spindles alone, without any other lowering device, then you can choose standard length shock absorbers from our Spax range.

I am fitting dropped spindles to my vehicle, but I am also using Axle adjusters, does this make a difference?

If you are combining dropped spindles with axle adjusters or another lowering device, then you will need to take measurements from the vehicle, as per our procedures. You will most likely end up using an intermediate length shock absorber, even if the vehicle is very low, due to the dropped spindles.

What does 'Compression' mean?

Alongside each custom length Spax shock absorber, we show the size of the shock absorber when totally compressed, to it's shortest length.
Once the shock absorber is fitted to the vehicle, if the vehicle moves downwards, hence the shock absorber closes / gets shorter, this is called 'Compression'. You should aim to fit a shock absorber that once fitted, has 70% of the stroke of the shock absorber available for compression, to allow for downward movement of the vehicle. At an absolute minimum, 50% compression is acceptable, as long as this is not less than 50mm.

What does 'Extension' mean?

Alongside each custom length Spax shock absorber, we show the size of the shock absorber when totally extended to it's longest length.
Once the shock absorber is fitted to the vehicle, if the vehicle moves upwards, hence the shock absorber opens up / gets longer, this is called 'Extension'. In normal road use, extension happens less than compression, hence the reason that you need to allow for less.

What does 'Stroke' mean?

Stroke is a just a technical word for the amount of movement that a shock absorber is capable of, it is the difference between the extended figure, and the compressed figure. For example, a shock absorber that is 230mm compressed, and 330mm extended, has a stroke of 100mm.

I'm stuck, I have got my measurements, but I can't decide on the correct size to go for. What do I do?

Simply send us an email via the 'Contact Us' page on the website, and let us know the following information -

• Vehicle type
• Model year
• Any suspension modifications that have been performed
• 'Bolt to Bolt' measurement from your vehicle, as explained in the 'How to'

Unfortunately we cannot help without having the 'Bolt to Bolt' measurement.
We should be able to quickly assist you in selecting the correct shock absorber for your vehicle.