Working out spring rates

[qwerty]

So the coilovers on the Liana are just the cheapest I could find (maxpeedingrods),and they're a bit bouncy, tend to make the car pogo.
I'm assuming that this means they're underdampened/over sprung.

Is there a way to work out what would be a better spring rate? Or is it a bit of trial and error? The car weighs 1145kg.

Cheers

Tom

[stealthstylz]

I take mine to a local company and test them. They do stock car stuff so might be somewhere similar up your way.

[nickwheeler]

I use a hydraulic press, bathroom scales and a ruler.

[qwerty]

stealthstylz nickwheeler I was wondering if there was a general rule of thumb to work out what spring rate is needed. Or am I vastly over simplifying it?

Tom

[xbl]

Have a look HERE

[nickwheeler]

Mar 23, 2023 10:27:55 GMT qwerty said:

stealthstylz nickwheeler I was wondering if there was a general rule of thumb to work out what spring rate is needed. Or am I vastly over simplifying it?

Tom

Do you mean calculating what rate a spring you have is, or what the spring needs to be?

The first is easier to measure as mentioned, and the second requires a number of calculations to give a good starting rate for development - not everybody wants the same result.

[stealthstylz]

Mar 23, 2023 10:27:55 GMT qwerty said:

stealthstylz nickwheeler I was wondering if there was a general rule of thumb to work out what spring rate is needed. Or am I vastly over simplifying it?

Tom

I guess lol. Tend to stick with the active coil rule (more coils, same thickness wire = usually softer) to start with to get in the ballpark then test what rate works, and then buy some at a rate I think will work from there.

[crogthomas]

All the inexpensive coilover kits I've seen have had very poorly chosen spring rates. I'm not sure if this is primarily because they are intended for extreme lowering and/or drifting, which means they don't work properly, or if the manufacturer has simply guessed on the spring rates with no real knowledge of the vehicle in question.

The usual approach to choose spring rate is to do it based on spring/ride frequency. You look at the surface the vehicle will be driven on, the suspension travel required and then choose a frequency based on the eventual aim, in a range from comfort through to sporty handling.
Spring frequencies allow you to compare the behavior of different vehicles irrespective of their total mass or distribution of mass. You can compare a Caterham with a 911 (or a double decker bus) despite them being at totally opposite ends of the scale. This is what you want, it 'simplifies' the whole process.

There are many other factors that have an impact on the way a car handles, but getting the spring rate right is a key one. It will involve taking lots of measurements and doing calculations (or finding someone, or software to do the calculations for you). For a good overview I can recommend the book 'Race and Rally car sourcebook' by Allan Staniforth. But there are many others, plus resources online. This is one of the best I have seen:
downloads.optimumg.com/Technical_Papers/Springs%26Dampers_Tech_Tip_1.pdf

Choosing dampers is a whole other level of complexity and mathematical complication, but one of the benefits of taking all the measurements to choose your springs means that you can give all that to a proper damper company to provide you with a set of dampers to match your springs, which you would have to do anyway, unless you can rebuild your own dampers.

[qwerty]

Mar 23, 2023 13:59:30 GMT stealthstylz said:

Mar 23, 2023 10:27:55 GMT qwerty said:

stealthstylz nickwheeler I was wondering if there was a general rule of thumb to work out what spring rate is needed. Or am I vastly over simplifying it?

Tom

I guess lol. Tend to stick with the active coil rule (more coils, same thickness wire = usually softer) to start with to get in the ballpark then test what rate works, and then buy some at a rate I think will work from there.

I'm going to go for an "educated" guess and go for 240lbs up front and 180lbs out back!

[slater]

Sounds like a good starting point to me! Had those rates on my mk1 fiesta and it worked on that.