linear rate conventional coil spring question

[zombiekiller]

Hey guys. I'm in the midst of fine tuning my ride height and I've been attempting to calculate estimated ride height based on corner weight - unsprung rate then taking that number and dividing it by the spring rate to get the amount of compression on the free length of a coil spring at static height ( standing still).

My problem is that I've been unable to find anything that will give me some sort of equation to estimate the effect of the two other additional factors:

Coil diameter and wire diameter.

Does anyone have any equations or knowledge that they can lend?

My estimation skills are further effected by going from a variable rate coil to a linear rate, but I don't really have any other choice.

Thanks!

[exwestracer]

http://www.miracerros.com/mustang/springs_calcs.htm

This has the actual rate formula, which includes spring mean diameter and wire diameter. Hope it answers your question.

[MIKE67]

Dave, don't forget the installation ratio. That is the leverage that the wheel has over the spring and accounts for spring/shock inclination also. And remember that because both the force and displacement of the spring are reduced by this amount, it must be squared to relate it to the wheel rate.
Wheel Rate (lb/in) = spring rate(lb/in) x (installation ratio(in/in))squared

Also, the number of active coils can be hard to estimate if the spring is wound closed.

Ray, I use a shear modulus of 11,250,000lbs/in instead of 12,000,000 lbs/in that is referenced in your link.(probably doesn't mater much in this example).

[zombiekiller]

thanks guys!

I'm in a bit of a spot because the spring houses that I've talked to refuse to sell me coils for more of a drop than 3" below the factory height. it doesn't matter to them that my engine, trans and exhaust are tucked, My shocks are fully adjustable, I've adapted non- standard swaybars ( from other vehicles) to work, The trans tunnel has been raised 3" and wheel wells have been re-flared with new wheelhouses for additional tire clearance.

Galaxies were sold with a ride height closer to a monster truck than a car.

That being said, a spring company that shall remain nameless sold me springs that they advertised as 2" drop. I came to find out that these are actually stock height springs.

SO, I will be using nascar coils with adjustable shims. My adjusted corner weight ( with unsprung weight subtracted is just a WEEEEEEEEE bit more than your average stock car. ( oh say + 250 lbs per spring rear and we won't speak of the front :) )

I'm also going from progressive rate to linear rate. The wire diameter is much smaller, but the coil diameter is also smaller.

am I short changing myself if I shoot for a 3" - 3.5" travel with a spring block height of 1" below the height of the progressive rate bumpstops that are going in? ( i.e. the progressive bump will cushion hard bottoms and effectively increase the spring rate ( not like the spring doesnt do this naturally). I'm borrowing the same type of bumpstops that I used as a jeepspeeder. I'll have roughly 2" of adjustment in ride height on the adjustable shims. ( which will be neat as I should also be able to engineer a poor man's coilover for alot less than coilovers and be able to swap out springs much faster.)

I'm shooting for a spring rate that is a 30-35% increase from the factory. My car is a heavy mother compared to many of your pony cars ( floating at +/- 4,000 lbs ).