Springs and things

[malcolm]

I've been reading some very interesting stuff on spring rates and lengths, some of which has been posted here.  I need to find out what exactly what I've got and am finding it a bit hard.

 

If you look at this picture of my V8 FHC you can see it looks lower at the back than the front.

 

It is fitted with TR7/8 Spax adjustable shocks front and back.  There are also receipts for 1/2" lowered 200lbs front springs.  The rear springs may be standard??  There are no receipts for replacements and the history is very detailed.

 

The question is how can I check?  To me one spring looks much as another.  If I have to measure them is it compressed or uncompressed length?  There are check straps which prevent the axle from dropping too far when I jack the rear up and this is usually only done with short springs I think?

 

So many questions.....

 

Malcolm.

[Guest ajttriumph]

the best setup i have found (thanks to some input from larry JC and a few others) is to have the front sitting a little higher than the rear about 25mm seems to be enough, its all to do witrh the weight transfer under braking, if someone has spent the money on adjustable shocks and uprated front springs its unlikely that they didnt change the rear springs.

 

I have found that a softer  (and lower) rear works well,

 

I use 400lb front and 250lb rear on the hillclimb setup and 600 front and 350rear on a track setup.

 

If you push the rear with a firm shove the difference between standard and uprated should be obvious (as long as you have a standard to reference to).

 

You could also check the colours (most aftermarket springs that i have come across are bright red or yellow).

 

If you want to get technical check the diameters of the wire that the spring is made from and the number of turns against a standard item, whilst it is theoretically possible to heat treat from one rating to another it is probably not going to be economical.

 

Or you can take the spring out and take it to a spring making works to get checked.

 

Finally there is no need with the standard setup for check straps/retainers that alone indicates that the springs are almost certainly non standard.

good luck

[andrewt]

I agree with aj that 1" or so lower at the back is best. Malcolm your car looks about ideal in that respect. Also if the rear springs are standard, they must be knackered to sit that low. To this effect i raised the front ride height of mine by 5/8" at the weekend. The rates I use are 250lb/in front & 200lb/in rear for the road, this gives excellent turn in. The rear springs are standard length but the spring platform is lowered instead. This has the benefit of keeping a longer spring. I had to have my bilsteins shortened to prevent the spring falling out as they were forest length dampers, with tarmac length springs. (I didn't want straps & the shocker also bottomed out too early)

If you want to get an approximation of your spring rates, then see if you can borrow a corner weight gauge with a spring adapter. This will allow an indicative measurement to be made directly on the spring. Though it wont be accurate to  better than 5 or 10 lbs, it will show the difference between 88lb/in & 200lb/in. You could also find a set of scales that will measure 300/400 lbs. Place them on a jack with the spring on top & jack up against something fixed to take a small preload. Measure the spring length & zero the scales or note the reading at least. Jack the spring up exactly 1" (or as close as you can) and re-read the scales to see the rate. Now this is obviously a potentially dangerous thing to do so you would need to do it in a closed box such that the spring couldn't escape as it would knock your block off it it popped out! Doing this in a lathe with a shaft up the middle might be a way forward, then it would also be easy to displace it 1". Please take extreme care before even considering these suggestions as an escaping spring could be lethal, i have seen people break both wrists because a compressor tool slipped!

I do have a spare pair of 200lb/in rear springs for standard rear arms if you are interested as this may be a safer way to get what you need.

 

Enjoy

Andy

[martynharrison]

As a slightly frivolous question, can you not just put 400 pounds of weight on the back and expect it to descend by one inch if you have 200 pound springs on each rear corner?

[andrewt]

Well yes, but no, because the spring has a lever advantage due to being part of the way up the bottom arm. You could work out the proportions & get an approximation to see calculate the rates but probably easiest to see if the rates are substantially different between cars. Of course Malcolm will have the advantage of being able to compare his wifes standard 4 speed car, so it is probably a good starting point.

 

Andy