[TomDK]

Hi

I have a specific question regarding 80mm Tough Dog springs for The Jimny.

Can anyone tell me the difference between 80mm medium load lift springs and 80mm HD heavy load lift springs from Tough Dog. The European importer is not sure.

Are both springs equal length with one being of higher rate, or is the HD version just a longer spring?

Cheers

Tom

[30ONA]

usually the Hd springs are for carrying constant load. Around 300kg, towing for example

[Gwagensteve]

That hasn't really answered the question though 30ONA. I can't answer it, sorry, TomDK, but I do know a bit about spring design. I'm not surprised that the local agent for Tough Dog doesn't have this information - it's generally considered proprietary.

There's two ways of getting a spring to support more load at the same height -

1) Make the spring longer

let's say the spring rate of the light spring is 100lb/" and it compresses 3" from free length to ride height. that means it has 300lb on load on it.

If we made the spring 1" longer but with the same rate, the spring could support 100lb more load and end up the same ride height.

2)Make the spring with a higher rate

So, we make the "HD" spring in the example above with a rate of 133lb/" so even though it's the same length as the light spring when unladen, it will now compress 3" under 400lb of load

However, there are some engineering issues with just making the spring longer. Making the spring longer will generally increase the number of wraps in the coil. This increases the bound length of the spring. That's a problem in the front of a Jimny, where even regular 2" lift springs go close to bind.

Additionally, making the spring longer will potentially make the spring tight when the shocks are fully open. This is bad practice which places excessive load on the shocks and mounts.

The more common solution to add load carrying capacity is to just increase wire diameter, leaving other parameters unchanged. If the local agent has the springs in stock, comparing the wire diameter and free length is all you need to really know to answer the question.

[fordem]

You can also try asking ToughDog - I've found that most lift spring manufacturers will answer questions about their products -

[Gwagensteve]

Sometimes.

Depends on how happy the vendor is for people to mix and match their parts and how confident they are in their dealer network. For example, bilstien publish damping specs for their generic multi-fit shocks, Rancho don’t.