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# RH, spring rate and damper travel

### Tech Articles

Discussion and questions related to the course Suspension Tuning & Optimization

Hi everybody,

first of all I have to apologize for my terrible english. Please forgive me.

I'm having an issue trying to properly adjust a beautiful brand new set of KW V4 Clubsport suspensions for a GR Yaris...

The package comes with front coilover (for Mc Pherson struts), with springs already installed and here it comes the problem:

spring rate is 60 N/mm for the main springs and 10 N/mm for the helper ones. Spring lenghts are 200 mm and 80 mm respectively, with 4 mm spacer between them, for 284 mm of total spring lenght. Fully compressed springs and spacer are 175 mm (wrong... it's 97 mm). While I have 420 kg (some gas and 85 kg driver) on each wheel of the front axis, I calculated a "steady state" spring lenght of about 154 mm, so I have only 57 mm of "compression" left before having both springs fully packed.

Dampers have about 127 mm of travel, so having only 57 mm of compression leads me really far from the 1/3 - 2/3 extension - compression ratio, that would be a good starting point.

I can't figure out where I'm wrong, assuming that KW provides coilovers with the right spring rate...

Any idea?

Thanks a lot!!!

Paolo

What is the installed length of the springs with no load (ie, full droop)?

I don't understand - if the spring are fully bound at 175mm, how you can have a steady-state height of 154 -- it seems like you would need to be greater than 175 (but less than then installed length).

Perhaps you're telling us the springs installed length is 175 (full droop), and they compress to 154 (steady state - static ride height), so 175-154= 21mm droop travel. If you have 57mm to full bind (154 - 57 = 97mm at full bind). Total range is 21mm (droop) + 57mm (compression) or 78mm. Droop is 21/78 =about 27%, compression is 57/78 or 73% That's probably close enough to the right range.

Hi David,

first of all, thanks for your quick aid! Sorry, but I pasted something wrong.... Minimum spring (main+spacer+helper) lenght is 97 mm.

Here are numbers (I really don't understand how to attach a spreadsheet...)

Spring lenght: 200 mm

Spring rate: 60 N/mm

Spring min lenght: 74 mm

Spacer: 4 mm

Helper spring lenght: 80 mm

Helper spring rate: 10 N/mm

Helper spring min lenght: 19 mm

Damper max travel: 127 mm

Total springs max lenght: 284 mm

Total springs min lenght: 97 mm

Weight: 420 kg/wheel

Total springs lenght: 154 mm

Residual lenght: 57 mm

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