I'm making some modifications to a motorbike I have, which requires much firmer springs for the forks, I have read extensively that cutting a spring down increases its spring rate - so I will be getting some alu spacers made to take the few cm I am removing, thereby keeping the ride height, but increasing the spring rate. (I understand this isn;t the best option, but its a free option vs. bespoke springs which will definitely not be free!)

However I have drawn a blank at the best way to do it - I was thinking, vice/ angle grinder - but the top of the spring is flat, and if I chop it, it won't be.

Anyone done this before, and can offer some advise?

If not I'll just give it a go - the bike was a cheapy project, and I can buy replacement parts if needs be (just not bespoke springs when a free option is available) the worst that can happen is that I'm not to impressed with the results.

I will need a heavier rear spring and potential revalve for the rear shock - which I can't DIY - so that will need to be paid for.

If you are packing out with a spacer then simple grind a bed in the spacer to locate the curly end

Yes cutting down does increase the rate, think of a coil spring straightened as a straight rod, you can twist a long bar easily not a short one this is all a spring is a tightly packaged rod.

No problem doing this, in the past I have cut a hoop off to increase the rate and moved the platform up on mcpheason struts to maintain ride height.

Regards Mark

As Mark suggested, cut a seat into the ally spacer for the cut end of the spring to locate in. If you look at a typical McPherson strut, the lower seat has something similar to help locate the end of the spring.

thanks guys

i didnt think you could use an angle grinder on spring steel as the heat softens the metal

Geeeez! Wrap a soaking wet rag around the spring where the cut is going to be done.
Then use your Angle grinder .
Wet rag will keep temps under control happily on a wee Moto spring.
Car springs require sitting in a bucket of water
Grind a nice flat coil on the messed cut end Then cut a PVC (plastic :-) Pipe as a spacer.. It's what Pro susp tuners like Racetech use. Clearly this works "fine".

[Edited on 10/5/12 by Bare]

Just remember that cut springs could go coil-bound at much lower applied force.
Useful info here

[Edited on 10/5/12 by minitici]

Cut it off to a point and weld a washer to it if you want the base flat, I don't worry about the heat it will only be local. I've had to grind new ones to fit in spring seats before and they have had no problems

[Edited on 10/5/12 by Peteff]