formula ford zetec versus duratec

[Alonso]

Hey guys how you doing? I have been working with zetec formula ford over in my country for the last while at a very sucessful level we have now moved to the duratec series. I was just woundering if anybody would be so kind as to assist me in the following questions i have. The zetec ford total weight driver and car is 540kg in our country the duratec cars are now going to be 490kg the motor is 35kg lighter than the zetec. I have found theat the spring rate on the zetec would be best at 450pounds front and about 800 to 750 pounds to the rear. Would it be a good starting mark to run the current spring rates and work from there or would there be a huge change in the spring rates. Maybe this is a stupid question but just thought maybe it could help me out.
Thanks
alonso

[machin]

Well that's a 10% decrease in weight... so if you had the spring rates right before that'll mean yo're effectively 10% stiffer than the optimum... I guess the answer is to run it and see how it feels... but springs are pretty cheap...

[Belatti]

1) post in the right forum... this belongs to "another racing series", now you have given some extra job to the mods...

2) when you talk about suspension you have to talk about frequency, not rates. If you already had a good setup with the 540kg car, measure each corner weight, then the motion ratio of the suspension in each axle and then with the spring rate you have got, calculate the suspension frequency:



If the motion ratio is a variable one, try to use a value that its arround the center of wheel movement to the first inch of bump.

In "M" just put the corner weight.

In "K" put the wheel rate (Kef), not the spring rate (Ks):

where MR is motion ratio.

Check your units, they must be in Hz.

To get the same frequency with a lighter car you will have to use softer springs.

[Belatti]

Oh I forgot...

This works if the tyres are the same. If you use tyres with a different rate, then in K use Kwheel that is:

[Alonso]

Afternoon guys i was just woundering if anybody could help me. Here in south Africa we have just started duratec formula ford and i have run zetec at a very sucessful level here just a few things i need to find out about.
1) the weight of the zetec with driver 540kg/the weight of the duratec with driver 490kg
2)the spring rates of the zetec front 550 an the rear 750 okay this is were i would need some input. The zetec shocks have been placed on the duratec and i am trying to get a ball park figure of spring rates for the duratec.
3) i am going to try the following front 550 rear 550 to try see were i am. What would the the car be like in terms of character with equal spring rates front to back. Please keep in mnd that the driver i am running likes the car to understeer.
Thanks alot
Alonso.

[Fil]

I guess u didn't like the answers you got to your questions here.. first time around?

[Alonso]

No No please dont get me wrong. Just moved it to the rite forum. tried to do the formulas but very difficult to figure. all the info i can gather will help me more an more.
Thanks
alonso

[Ciro Pabón]

Thanks, fil. Alonso, welcome. Next time you could PM me or Tomba or simply, click the report button and explain to us what you need (move the topic or anything).

I suggest to Alonso to try to figure the formulas and post whatever you get. People like Belatti, that volunteers himself to help you to figure something are few. On the other hand, critics are legion.

It's the same at the office: ask people to help you to write something and they will run. Write something instead and show it to them: they will start to nag you about your errors. It never fails...

[Belatti]

No No please dont get me wrong. Just moved it to the rite forum. tried to do the formulas but very difficult to figure. all the info i can gather will help me more an more.
Thanks
alonso

OK, lets start from the beginning: to se how stiff a suspension is, you have to watch mass and springs altogether. Imagine a 550 pound/inch spring (if you put a 550 pound force to it, it will deform 1 inch) mounted in a bus: that suspension would be way too soft. Now imagine the same spring mounted in a bike: that suspension would be way too stiff. So its all about combining spring and mass.
So, the formula that relates them is the one of frequency:



K is your wheel rate (not the spring rate) and M is the mass of the given wheel corner you are looking at.

Proceed like this: measure corner weights.

Lets supose your 490Kg duratec weights 135Kg at each rear wheel and 110Kg at each front wheel. So to determine rear frequency you will have to use 135Kg in the formula.

Now lets supose your 750 pounds/inch rear springs are mounted in a way that the spring moves 1 cm for every cm that the wheel moves. That is indicating us that the motion ratio is 1. Motion ratio = wheel movement / component movement.
You can measure component movement between shock mounting points if the spring is coilover the shock.

For a motion ratio = 1 you have that the K at the wheel is 750 pound/inch that equals 131.345 N/m. One Newton is 9,8 Kgm/s2 so:
K = 1,287,181 Kg/s2 (Kg mass, not force)

Now, the frequency at the wheel is:
f = 1/2pi * sqrt(1,287,181 Kg/s2 / 135Kg) = 15,54 1/s = 15,54 Hertz.

Its evidently that the motion ratio is not 1 because 15Hz is a very high natural frequency for a racing car. Street cars are arround 1Hz and small racing formulas can be arround 3 Hz.

So, remember K at the spring = K at the wheel *
Once you measure MR you can calculate wich is the K at the wheel you will have to insert in the frequency formula.

Good luck!

[Belatti]

Oh, its pretty obvious but I will mention that what you should do is to first calculate frequencies for the zetec and then calculate wich spring rates would give you the same frequencies in the lighter duratec.

Remember there is always the chance to calculate nothing and go testing different spring rates till you get the one you need. That costs too much time and money anyway.

[autogyro]

You could always ask a few chassis manufacturers.
That should give you a couple of choices, which would be difficult to quantify with the Math anyway.

[Alonso]

Evening guys.
We went testing today with the duratec and it was pretty good, started of by running 550 front rates and 550 rear rates. we had understeer but my driver likes an understeering car. Just a little worried had to dial out alot of preload on the front to get it better under turn in and found that it squated a little more than it should under power. Was thinking maybe i should go to the 650 rear spring and leave the 550 front that will give me better front end and less squate on power. Any ideas???
thanks
Alonso

[Belatti]

So you are gonna let the maths for this kind of people?

[Belatti]

And BTW, does somebody knows where to buy a 2.0 standard duratec in USA?

[Carlos]

Here you are Bellati http://www.usedpartscentral.com/search_california.htm
Access to all the auto salvage recyclers (btw - junkyards is what they are with a shiny name)in California. I choose Californiia because they can easily ship by sea.