P1050908b

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Comment by Andy Smith on February 7, 2013 at 22:24

I also think that you need to give your measurement technique some thought as to what is happening with the weight transfer as you jack the car up. 

Comment by Andy Smith on February 7, 2013 at 22:09

You only need to add half the wishbones, spring, shocker weight to the weight of the true unsprung component of the wheel hub stub brake - what I do is ignore the wishbones as this allows for the contribution of the metalastics - if using friction free bushes like Rose joints then you can add the 0.5 bone back in. 

Whats your measured leverage on the lower wishbone?

Comment by James Doulton on February 7, 2013 at 21:46

I take your point about the lowering block and the dynamic behaviour. I was only intending to see if it resolved the issue at the front. I am sure that you are right and the only sensible long term solution is new rear springs. I'll probably need two in order to be sure that they match. So if anyone has a spare pair then I am in the market...

Comment by James Doulton on February 7, 2013 at 21:40

Unsprung weight is a very good question! I was thinking about that whilst in a meeting this afternoon and so I plotted the force vs displacement and bingo, my original calculations of spring rate were wrong. When I had disassembled by car to replace the discs and calipers I had weighed the wheel, brakes and hubs at 28.3Kg, so I needed to add in the axle and wishbones etc. Looking at my chart from Excel, my unsprung weight is almost exactly 40Kg and the effective spring rate is about 120lb/in. I bet that Big Vern is right and it will bottom over every bump.

Comment by Andy Smith on February 7, 2013 at 20:04

And the weighing method would be better with an investment in another 6 scales to especially with the weight diagonal issue you have - using a lowering block may solve the issue with the cars static balance but dynamically it will not be great if one of those rear springs is a different rate.

Comment by Andy Smith on February 7, 2013 at 19:51

What figure did you have for the unsprung components

Comment by Pete Clayton on February 7, 2013 at 15:28

Another thought as to why its low at the front, they could be modified Capri struts instead of Escort ones lowering the front by an extra inch.

Comment by James Doulton on February 7, 2013 at 13:03

My engine sits very high in the car, as shown by the cutouts in the bonnet for the camshaft and the oil filler. That is probably how it survived. I don't think it was driven much after the rear spring was replaced either. At the moment the car is all over the place.

The other variable is, of course, the spring length. If the spring length is longer than normal then it could generate sufficient thrust at the normal ride height. The spring rate also affects how well the wheels follow the dips in the road, and around here they are considerable, so I might be better off with a longer spring of a lower rate. We'll see.

Comment by Big Vern on February 7, 2013 at 12:49

Pinto engined? Have you driven it extensively over a wide range of roads? still got a sump left?

James car sits low on 240lb/in so I would expect 200lb/in to sitting on the bumpstops!

Comment by Dave Adams on February 7, 2013 at 11:59

As it happens vern i now own a S4 phaeton........the springs on it come in at something like 200lb they look like motorcycle shocks.

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