Hi All,
With thanks to all who offered help / advice (on and off list) re going to coilovers and I'd like to run some numbers by you to see if I I'm going in the right direction please (and this is just for the basic static calcs so I'll worry about the Roll Center Height etc later on). ;-)
It's a Rickman Ranger kit car based on a 1978 MK2 Escort 1300 saloon. It's a 'jeep' style and I'd like soft / compliant rather than race rigid suspension and can't seem to get that via sock off_the_ shelf springs and bespoke are as expensive as coilovers so ..
Let's assume the thing weighs 1 tonne that's 2200 (good ole English) lbs.
Assume the weight is split 50:50 (front / back). I will put it on a weighbridge and weigh the front and back separately asap.
So that's 1100lb on the front, 550lb on each front corner.
So, if I start with a 110lb/in spring then to support that weight it will compress 5". So if the suspension has (say) 4" of travel and I wanted it to sit half way (wet kerbside weight etc) that would mean a preload on the spring of 3"? (do you get spring compressors to suit the 2-1/4" coilovers or is it just a matter of getting in there with the C spanner and winding it up please)?
Other considerations:
The spring sits inside the road wheel so I guess I'd get an increased load on the spring compared with the road wheel (lever effect).
I would subtract the un sprung weight (wheel, lower strut inc brake caliper assy, half the weight of the tca and anti roll bar etc)?
Could those two cancel each other out (roughly) so (in this case) I could end up with the straight 110lb spring?
I would also have to have a spring long enough to accept a full (4") suspension compression without the coils binding.
Looking at places like RallyDesign etc they show a 110lb 2-1/4" spring in only the 10.5" free length but the 100lb spring in lengths from 8" to 14".
FWIW (and according to the HBOL) the std Ford spring has a free length of ~13" but it's suggested was quite light at around 90 lb / in. As it's only got ~6 turns they are quite well spaced. I'm not sure what the details are with coilover types but will ring RD in while and see if they have any extra data etc (I just rang them and they didn't) ;-(
So, are my principles correct do you think, have I missed anything (before I waste any money on unsuitable bits, although I guess this isn't an exact science at this level).
All the best .. and thanks for your time
T i m