Ok, I have a sierra track car, and i need to calculate the correct spring rates for the car, i know its partially trial and error, but i wouldnt mind
a guestimate as to what i need, and to fine tune once ive had it on the track 
Im not overly concerned about lowering the car, however i think a drop will help the handling as the Centre of gravity
What i want to know, is has anyone got any experience with spring rates for a completely stripped out sierra with a pinto in the front? Or any
calculations to work out roughly what is needed?
The fuel tank will be fitted over the rear axle for better location and weight distribution.
Thanks
Nate
Hmmm, tough one, mate. First, you have to know what each end of the car weighs, all in. Don't know of any programs that can calculate for you,
but if you assume that the suspension should only settle 1" with the car's weight on it, you can figure it out. Eg, if the front end weighs
1000 lbs., each front spring supports 500 lbs, and for it to compress the 1", you need 500 lb. springs. That assumes no angle of lean on the
springs, but there are simple calculations to account for lean angle. That's what we did anyway, and it sure seems to work!
The easy answer is the softest you can get away with so the suspension doesnt bottom too much in critical parts of the track or the car doesnt ground
in the critical parts of the track.
I do not have specific experience of the Sierra but my starting guess would be 350lb/" front, 250lb/" rear. Hopefully you will get a more
definite answer but remember all other things being equal softer will give more grip.
John
quote:
Originally posted by zetec7
Hmmm, tough one, mate. First, you have to know what each end of the car weighs, all in. Don't know of any programs that can calculate for you, but if you assume that the suspension should only settle 1" with the car's weight on it, you can figure it out. Eg, if the front end weighs 1000 lbs., each front spring supports 500 lbs, and for it to compress the 1", you need 500 lb. springs. That assumes no angle of lean on the springs, but there are simple calculations to account for lean angle. That's what we did anyway, and it sure seems to work!
just a thought off the cuff.
Okay bathroom scales will weigh up to say 20 stone, so if you got a 6 foot plank of wood one end on the scales, the car half way along and the other
on a block of wood to the same height you can now weigh 40 stone. On this basis move the car about on the plank until you read off 20 stone, if its a
third of the way then that corner must be 60 stone.
Corner weights are tricky things, so you need to pivot the front of the car upon its central axis (trolley back in the middle of the cross member)
then weigh each rear in turn, swap around jack in middle of diff and weigh the fronts.
Not 100% accurate but a free starting point.
To set up corner weights requires a completely flat surface, but as you do not have the option of changing spring platforms you will have to live with
uncle ford.
Regards Mark
NB/ why not try knocking a hoop off the standard springs, that should drop the car by around an inch and the length of the coil is reduced so ups the
poundage (8 coils to 7 coils = 1/8 harder spring).
quote:
Originally posted by mark chandler
just a thought off the cuff.
Okay bathroom scales will weigh up to say 20 stone, so if you got a 6 foot plank of wood one end on the scales, the car half way along and the other on a block of wood to the same height you can now weigh 40 stone. On this basis move the car about on the plank until you read off 20 stone, if its a third of the way then that corner must be 60 stone.
Corner weights are tricky things, so you need to pivot the front of the car upon its central axis (trolley back in the middle of the cross member) then weigh each rear in turn, swap around jack in middle of diff and weigh the fronts.
Not 100% accurate but a free starting point.
<SNIP>
Regards Mark
NB/ why not try knocking a hoop off the standard springs, that should drop the car by around an inch and the length of the coil is reduced so ups the poundage (8 coils to 7 coils = 1/8 harder spring).
You can set corner weights accuratll without scales by using a balance. You are not really concerned on the weight just that they are the same.
So you make a beam that pivots in the middle. Put a wheel on each end and when it is level you have equal corner weights.
This shows cheap versus expensive for doing the corner wieghts.
I made a balance beam. This has 2 pads for the wheels to sit on
and a central pivot. The rear wheels sit on level pads and the front
adjusted until the beam is level.
I then had the chance to borrow digital corner wieght scales. My method was
as accurate as the digital scales within the limits of rpeatability.
However I then read that the way to set corner wieghts is to make each side of the car
have the same front rear distribution. So in my case the left side has a front / back
ratio of 47.5 / 52.5 and also the right side has the same ratio. This does mean that
each wheel carries different wieght and my balance beam will not work.
John
I've been waiting for the words “Suspension Frequency” to turn up in this thread.
As all defenders of the hard way to do things (extensive use of maths) seem to be on vacation I just drop a few links. They are not extremely good but
at least a start.
http://www.athon-motorsport.co.uk/suspensioncalc1.html
http://www.smithees-racetech.com.au/performancefactors.html
Cheers!
[Edited on 06-7-3 by leto]
No, no no...not again.
Cheers,
Syd.
more discussion here
Syd - So how do you go about deciding what spring rates to start with?. We are all here to learn.
Cheers
Fred W B