Daze, the board owner should be able to help a lot with that question.
Mail him.

http://irsforum.boardhost.com/profile.php?id=2

Ralphy

Last edited by Ralphy (1/26/2012 1:27 pm)

I'm still messing with spring rates on my '65 Mustang convertible.  I've decided on 4 coilovers but until I get the car up to curb weight I can't calculate what spring rate to use.  For now I am installing some stock XKE coil overs. I was looking through my old pictures and found this torsion bar idea I considered.   My Mustang project kind of got side lined while I finished assembling my '57 Nomad.  Time to clean off the dust and get back to it. 

Just watching on the sidelines here and wondering what a pair of heavy duty Motorcycle shocks would give you? 
Some pretty nice ones out there and prices much less than the QA1s etc -- might work a dual mount easy?
I'm back on the bench on this one now...  (Football talk over for the season now)
Cheers - Jim

The torsen bar is a cool idea but I dont think the stock LCA would be up to the task.  As far as motorcycle shocks. Many large bikes use a single rear shock  with a compounding linkage.   The best example I know of is the CBR 900rr I own has a spring rate of 275 lb/in and it is a super light bike for its displacement. Big road cruisers can weigh in at over 12oo lbs and some are equipped with a single rear coil over.  The shocks would be superior to nearly any thing available for the Jag configuration.  The only real drawbacks would have to be price and they have half the travel the stock Jag ones do.
    Back to the Torsion spring idea.   I think that Torsion bars  would make big tube exhaust more  feasible..   From the beginning I have been struggling with my exhaust routing.  I have a tubing bender and want to use 3" exhaust all the way back but I have found that to be a pipe dream.   I would have to bend a tighter radius than 3" can be bent.  I have also been working with some rectangle tube I purchased on e-bay.  I am still making the rectangle mandrels for my bender.   The big  question is if I can bend it with as tight as I need with out kinking.   I have seen a Mustang  with the 3" exhaust routed through the floor , into the trunk then back through the floor to exit in the normal position.   Not the route I want to use.

Hi Daze.  Good to be back.  Finished working on my Nomad and now I can finally get back to the '65 Mustang project.   I just completed some mini-tubs and am considering a safer fuel tank.  You and I had quite a discussion going on in the old forum about spring pre-load, spring rates and motion ratio.  Like you, I arrived at something between 300 and 400 pounds as a place to start.  I'm hoping the early jaguar springs will work with my heavier convertible.
Cecil,  do you have any corner weight data for your coupe? 

Last edited by irstang (3/11/2012 9:25 pm)

Knowing the corner weights on the rear is the first step in calculating the spring rate you need for your Mustang.  I'm going to assume you want to stick with two springs per side unless you tell me different.  Jaguar put two springs on each side to keep from twisting the LCA's.  Jaguars ride like a dream as they tuned the frequency of the suspension pretty well.   Jaguar E-types weigh between 2770 and 3018 lbs depending on the model.  They have a much better weight distribution than a Mustang;  close to 49% at the rear as I recall.  So a Jaguar average weight of  2894 would have a rear end weight of  1418 pounds.  Close enough that I recommend you try some stock Jaguar XKE coil-overs.
   
If you do not want to try the stock springs, you will have to  calculate spring rate.  There are a bunch of questions before you can proceed to the second step; determining the motion ratio of your springs. What donor suspension do you have?  Are you using the stock cage or are you mounting the suspension out of the cage?  What hub to hub dimension are you planning to use?  Once you have your suspension mounted and set the ride height you want, it is easy to measure the motion ratio.  Motion ratio is simply spring travel divided by wheel travel.  As you know, the coil-overs are canted on an angle and they don't provide a downward force directly at the tire patch, but rather act part way up a lever arm.  For these reasons, a 400 lb/in spring, for example, is not going to provide 400 lbs for every inch the wheel deflects.

In order to complete the calculation you will need to know the compression  of the spring in the coil-over at pre-load and how much the spring compresses from pre-load to ride-height.  Remember there is only about three inches of travel in a Jag coil-over to work with.  I know I have not answered your question exactly, but until I have all the data, all I can do is give you my best estimate.  You might want to contact Mustsed, see posts transferred from the old forum, to see what coil-overs he used in his '67.

This is a picture of my '65 when I first tacked the tubular cage in place.  The straps  are about maximum length for a coil-over at full extension.   I was ready at this point to determine motion ratio and determine the coil-over compressed length.   After running some numbers, I have decided to try some stock XKE coil-overs.

Last edited by irstang (3/17/2012 11:48 pm)