Coil rear shock - spring weights....?

I thought somewhere a few years ago I'd seen a rough guide to what spring weight you needed according to rider weight, but now when I 'google' it there are all sorts of other factors you have take into consideration.

Is there still a basic rough guide, or can anyone help...rider weight roughly 145lbs, 4" travel rear, 80mm travel front....

It depends on the bike -- different frames have different leverage ratios, and would need different springs even if the travel and rider were the same. It's easy enough to figure out empirically if you've already got a spring. You need to know what the shock stroke is, if you don't know you can measure it. Assume that it's 50mm. You're aiming for a quarter to a third of the travel as sag when you sit on the bike, so the shock should be 12-16mm shorter with your weight on the bike. Twiddle the preload ring until it is -- wind it towards the spring to reduce sag, away to increase it. If you can't get enough sag even with the preload ring just touching the spring at rest, you need a softer spring. If you need more than a few turns of preload to get it to sit high enough you need a harder spring. Preload is fine tuning really, you want to have as little as possible so it's best to get the right spring.

Different manufatcurers have different spring weights to shock rate so just a rough guide won't alxays work. The spring should never be compressed more than 1-5mm by the compression ring, ideally it should just be holding it to stop it rattling.



There you go




http://www.tftunedshox.com/info/spring_calculator.aspx

Thanks guys, I'll have a play around with it when the bike turns up, it's just from past experience the springs were always far too 'heavy' for my weight and I couldn't get much movement out of them.....