Running different spring rates in each fork leg

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Freddy
Posts: 695
Joined: 06 Sep 2017, 11:06
Location: Sydney Australia

Running different spring rates in each fork leg

Post by Freddy »

Just as the title says, as soon as I get the sump back on the bike I plan to try different front fork springs in each leg ...... The story:

For quite some time I've run 0.90 kg/mm front springs. Nice and supportive, very stable at speed, BUT can be a little firm on slow undulations (maybe excessive slow speed compression damping). Anyhow to try and address this firmness though I'd stick in a set of 0.85 kg/mm front springs to see if was spring weight or excessive slow speed compression damping that was the problem. Much easier to experiment with the springs first.

The 0.85 springs are WAY better through the corners, the bike turns in MUCH better. Reason I reckon.... my rear aftermarket shocks (Wilbers 632 TS piggybacks) are running dual rate springs. So the rear compresses down a little easily as you enter the turn, but the firmer 0.90 kg/mm front springs don't compress as much. This creates a nose up attitude and the bike wants to run wide. Running the 0.85 kg/mm springs and a lower viscosity of fork oil allows the front to compresses more, maintaining a more level attitude and a quicker turn in.

HOWEVER, at speed the 0.85 kg/mm springs are no where near as 'solid' as the 0.90 kg/mm in terms of straight line or fast sweepers stability. So here was me considering what to do, run the 0.85's for the faster turn in, or the 0.90 for greater stability.

THEN I discover that it is not uncommon for people to really fine tune the front spring rates by running different spring weights in each leg. Run a 0.90 in one, and a 0.85 in the other to give an overall 0.875 kg/mm spring rate (hopefully a better compromise between both worlds). As the whole front suspension is locked together by the front axle it works as a single unit. Some makes of bikes don't even have a spring in one leg. I've also increased the front slow speed compression damping just a tiny fraction. With Race Tech cartridge emulators that's as simple as increasing the size or number of the slow speed bleed holes.

I'll report back on the results, once I get my sump back.
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