Forgot to copy the group...brian
>Date: Fri, 28 Jan 2000 09:20:34 -0500
>To: Simon Favre <simon@mondes.com>
>From: Brian Evans <brian@uunet.ca>
>Subject: Re: wheel rates on formula/sports racer cars
>
>Double checked with Carroll Smith this morning. Tune to Win says "motion
>ratio = wheel travel / spring travel. Wheel rate = spring rate / motion
>ratio squared. My motion ratio is about ( I have yet to check with really
>accurate tools in the precise range that my car runs in at it's race ride
>height) 2" wheel travel to 1" spring travel, so MR = 2. so for a 900 Lb
>spring, WR will be 900 / 2^2, or 900 / 4 = 225 Lbs.
>
>Which indeed seem absurdly stiff to me, hence my question to the massed
>experts of Vintage-Race! I strongly suspect that if I were to put these
>springs on, the chassis would sneer at me, and proceed to dis-assemble
>into it's component parts! The modern FFords have motion ratio's close to
>1:1 apparently, so they can put a 300# spring in and get a 225# wheel
>rate. The old cars like we have, with the laydown springs attached midway
>out the lower control arm, have a far higher MR.
>
>So it gets back to what do people run? Anyone done some testing that they
>care to share? The guys at
>http://server5.ezboard.com/bformulafordunderground that are discussing
>this are constructors of modern FFords, and guys who go to the runoff's
>and sometimes win! I don't think that what works on modern cars is
>directly applicable to ours, but guys running 20 year old club fords are
>talking about their 1000# springs! Boggles the mind, but they think this
>works.
>
>Thanks, Brian
>
>
>At 09:03 PM 01/27/2000 -0500, Simon Favre wrote:
>>Are you sure that formula calls for the square of the motion
>>ratio? 900# springs seem absurdly stiff for a 1000# car. I think
>>what you're calculating is the amount of spring travel per unit
>>of wheel travel, which would be linear, not squared. That would
>>mean your car should have 450# springs, not the 200# it has now.
>>Those FFord guys are running the latest space-age materials in
>>their suspensions, right? Is yours as strong? I think you're on
>>the right track to stiffen the front, but double check that
>>formula!
>>
>>I can't recall the spring rates in my Formula Junior. I know they
>>are low by comparison. I could go stiffer, but I'm concerned for
>>the fragility of the beast. I've got a bit of understeer, which
>>used to be a lot worse before I changed the spring rates.
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