Fiat Uno - springs rate

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Lui
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Fiat Uno - springs rate

Post by Lui »

I'm preparing my uno for track racing. I have custom made coilover suspension (on adjustable koni shocks) and 35kg/cm front springs. I used wheel frequency calculator from racingaspirations.com. I calculated that those springs give me 115cpm w.f. It is ok? [unsprung weight - 35kg, corner weight -270kg(I assume it, but I'm going to measure it)

What spring rate rear springs schould have (unsprung weight 30kg, corner weight 150kg)? They should give the same cpm, or lower/higher, or maybe I should focus on other factors?

What is the suspension leverage?
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hcd
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Re: Fiat Uno - springs rate

Post by hcd »

Hi Lui,

Thanks for using the calculator. 115cpm sounds a good starting point for the front and rear. RWD racers are usually set-up a bit softer at the rear to give slight understeer (more grip at the back = more understeer), it's better for four wheel drifts... Not drifting - that'll be the reverse.

You'll probably find your unsprung weight is a lot higher than you think, my 750 racer isn't much less than 30 kgs with lightweight wheels, alloy hubs and uprights, alloy calipers, alloy shocks etc...

If the pivot is on the left then... 25 / 15 = 1.6 = 1.6:1

Huw
Guy Croft
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Re: Fiat Uno - springs rate

Post by Guy Croft »

MODEL POST!

what a nice interesting little post - a constructive and useful discussion, with - I hope - a functional solution. How nice to see a bit of maths and 'mechanics' (in the true sense) being employed here!

Huw - your on-line calculators at your racecar site are 1st class and it's good of you to share them. I do like your detailed and analytical approach to things.

Well done both!

GC
3zeR
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Re: Fiat Uno - springs rate

Post by 3zeR »

Hi,
I have similar problem like Lui. I was using two calculators - one was from racingaspirations.com and second one was from program called VHPA and used for tech simulations for LFS game. Both of them showed me that I need such a springs: 500 lbs/in in front and 125 lbs/in in the rear to get cpm around 115-120.
I did calculations for corner weight 275 kg front (car + my body) and 200 kg per rear.
Unsprung weight is around 35 kg front and 40 kg rear.
In front I have double wishbones, in the rear is an drive axle.

My question is - why there is so much difference between front and rear? I have to order springs and I need to know if this calculations are ok. Can anyone help me with this?
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Guy Croft
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Re: Fiat Uno - springs rate

Post by Guy Croft »

You may know all of this - but in case you don't - and to get a 'handle' on the subject of weight distribution - its effects and how alterations are achieved here is a useful link:


http://www.turnfast.com/tech_handling/h ... _weightxfr


GC
3zeR
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Re: Fiat Uno - springs rate

Post by 3zeR »

this one is nice, but it doesn't give me an answer about this huge difference in stifness. thank you
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Guy Croft
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Re: Fiat Uno - springs rate

Post by Guy Croft »

Wait a second!

Before you disregard that article - what type of car is it?

You'll never get 50-50 weight distribution on an ordinary vehicle - that is rarely achieveable on anything except a single seat race car. If you jack up the spring rates to try and achieve it you can develop terminal over or understeer.

With a saloon car it is far more important to develop a decent compromise on weight distribution and try and build in a neutral response or a degree of oversteer. Understeer is extremely dangerous whereas a good driver can control oversteer (within limits of course). If you jack up the front springs to very high poundage in the mistaken belief that it will help handling by equalising F-R weight distribution - chronic understeer is exactly what you will get.

GC
3zeR
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Re: Fiat Uno - springs rate

Post by 3zeR »

I do not disregard this article, it is very good one and a very good page that I didn't know.

The car is 4 door sedan type, old style car, with rwd on a solid axle. The weight distribution is about 60/40 I guess. That's why I wrote that I'm taking corner weight about 275 kg for front suspension and 200 kg for rear, but still don't know why I get 4 times stiffer springs on the front, it's way to much I think.

Best regards and thanks for discussion

BTW. I was wondering if you know any schools in europe where you can study competition engines building or something like this. Next time i'm finishing my university and I'm thinking about something like this. Can you recommend something?
regards
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Guy Croft
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Re: Fiat Uno - springs rate

Post by Guy Croft »

If it's rear wheel drive it could be nearer 56/44.

I don't know why you got such high spring rates either. I don't know what programme you were reading but if was you I would forget calculations. I would buy a corner weight gauge and measure the standard corner weights. Then I would look at uprating front and rear springs by the same percentage, eg 20%. The dampers will need alteration as well.

GC
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