New Project Update 14th April 2004

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Update 14th April 2004

If you wish to view previous work then links to updates are above. Work before this date was organised in sections (chassis, engine, bodywork etc.) you can see this work by going to "New Project Title Page" above.

This update is all about the suspension specifications and set up. Unfortunately there are no pictures.

I have set the corner wieghts on the car. First I did this with home made equipment (basically the rear wheels were placed on level pads and the front wheels on a beam that pivoted in the centre) and a spirit level. Then I borrowed a set of digital corner scales. My home made method was as accurate as the digital scales!

The weights on each wheel are as follows (me in the car):

Left Front 244 kg / 538 lbs..... Right Front 244 kg / 538 lbs
Left Rear 259 kg / 569 lbs....... Right Rear 277 kg / 613 lbs

It was difficult to get a repeatability better than 3kg. I always repeat all my measurements and often get varying results even though I have changed nothing.

This gives a total vehicle weight with me in it of 1024 kg / 2258 lbs. The vehicle wieght is approx 950 kg. This is heavier than I expected but in race trim I expect to reduce this. The passenger seat and harness is approx 10kg and the hood and frame I estimate to be about 20kg. I will also initiate a wieght saving exercise. The 6mm and 8mm alloy floors can have sections reduced in thickness and there are a few other areas where I can save a little.

While I had the scales I was able to determine that each front corner has an unsprung wieght of approx 28kg / 62 lbs and each rear corner has an unsprung wieght of approx 33 kg / 72 lbs. Each wheel and tyre (Ford Sierra Cosworth 3 door 7"x15", 195/45/15) wieghs16kg.

From these wieghts I could determine that the sprung wieght on each corner is as follows:
LF 476 lbs RF 476 lbs
LR 497 lbs RR 541 lbs
This information would help with spring selection. Each damper has 130mm stroke, my ride hieght is approx with the damper compressed 50mm / 2". This leaves 80mm of compression left. So to obtain this I require a spring rate of approx 250 lbs (approx 500 lbs on each corner will compress the 250 lb / inch spring 2")

Many text books talk about wheel frequency (though Carroll Smith never bothered).
Wheel frequency = 187.8 x square root of(wheel rate divided by sprung wieght) For my car this is approx 133 cycles per minute. According to Allan Staniforth this is in the ball park for circuit racing cars.

 

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