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Mixing straight rate fork springs with progressive rate rear shock springs?

Chuck78

Chuck78

Forum Sage
Past Site Supporter
Is it a terrible idea to mix straight rate front springs such as a Sonic .90kg/mm(50#/in) or 1.0kg/mm(55#/in) (or my chopped OEM's at .85kg/mm or 47 lbs/in) with progressive rate rear springs? The Fox manual calls the short blue rear spring a medium and the long red progressive spring a medium-soft. I roughly calculated the rates to be around 100 lbs/in initial (1.8kg/mm) and 138lbs@3.2" travel (2.46kg/mm). I was originally shooting for around 120 lb/in straight rate, but I got these really good vintage Fox Piggybacks to rebuild.

The main parts guy for these may have other springs, and I was going to bump up the lighter short blue spring a slight bit, but I could keep that and try and get a straight rate long red spring if it would be far better while running a straight rate up front.

What's the consensus? Any major ill handling effects?

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Also, cartridge Emulators on the front to help get up to speed with the really good dampening setup on the Fox Factory Shox.
 
Chuck78 said:
Is it a terrible idea to mix straight rate front springs such as a Sonic .90kg/mm(50#/in) or 1.0kg/mm(55#/in) (or my chopped OEM's at .85kg/mm or 47 lbs/in) with progressive rate rear springs? The Fox manual calls the short blue rear spring a medium and the long red progressive spring a medium-soft. I roughly calculated the rates to be around 100 lbs/in initial (1.8kg/mm) and 138lbs@3.2" travel (2.46kg/mm). I was originally shooting for around 120 lb/in straight rate, but I got these really good vintage Fox Piggybacks to rebuild.

The main parts guy for these may have other springs, and I was going to bump up the lighter short blue spring a slight bit, but I could keep that and try and get a straight rate long red spring if it would be far better while running a straight rate up front.

What's the consensus? Any major ill handling effects?
Click to expand...

It's not perfect, but it's a huge improvement over stock. Try them like that, you can always get straight rate springs later if you think you need them.
 
Stock calculated in around 102# initial, but with soooo many coils as the oem suzuki progressive shock springs have, they will not reach any where near the rate that the Fox will at travel. Stock is not anywherr near stiff enough even for a -50lb lightened 500lb gs750 with my skinny butt on it.
 
Straights and Progressives can sleep together, cats and dogs, not so much.

Suspect that both of those suppositions are correct but can't prove either.
 
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