Springs (No not that question)

[Mark (smokey mow)]

That time has come to find some new springs for the single seater rebuild. I've got use to the fact that nothing is standard or indeed ever easy and the springs are proving to be no exception.

With an all up minimum weight (including driver) of 500lbs (220kg) the spring rates adopted in period were 85lbs/ins front and 105lbs/ins for the rear.

Faulkner have a range that comes close to this offering 80,100 and 125lbs/ins in a 1.9" diameter but i'm struggling to find anyone doing 85 or 105 unless I pay the extra for custom made specials.

So the big question... Does anyone make 85lbs/ins and 105lbs/ins springs in a 1.9" diameter with an 8" free length?

[DamperMan]

Off the shelf it may be a struggle... Some other stockists are.... Suplex, Eibach UK, maybe call DT as they deal with them all. As regards to an 8" 85lbs / inch spring it won't be very popular.. Off the top of my head I'd say it would have about 5" of travel giving it max theoretical load of 425 lbs so a practical working load of less than half of that. I'm quite sure I have no paper clip spring stock of the size you want but I'll check. if you want me to double check some numbers to see if the spring rates are correct I can do that. I would need corner weights with driver. Motion ratio of the wheel relative to the spring.. The easiest way is to put the wheel at ride height and measure the length of the damper. Then move the wheel 1" either side of the ride hight position and measure the damper lengths. Then email the info to me tony_shakeshaft@spaxperformance.com and with a few more possible questions I can calculate some ball park figures of spring rate.

[DamperMan]

To add to that based on such a light car your abig % of the overall weight. So depending on your weight the spring rates may want to be different to achieve the original designed settings. May be an extra bacon butty each day would help

[Mark (smokey mow)]

Thanks for your offer Tony,

I am confident of the spring rates being correct. I'm working from a technical article from the the 750 motorclub journal from way back in 1967 which quotes amongst other things the spring rates in a track test review. i've also had one of my orignal (and very rusty) front springs tested which confirms these as correct.

As a point of interest the orignal dampers were Armstrong AT7's

[DamperMan]

COMPLETELY OFF TOPIC!!!!    Good old Armstrong....  Bought by tenecco walker, re branded as monroe.   All the competition stuff disappeared over time.  Companies like Woodheads manufactured under licence and has since gone.  There are a number of companies world wide which stared by manufacturing dampers under licence or bought technology from Armstrong.       Although these things are not openly published I believe Sachs is one.     Bilstien started making something like door hinges then at some point bought the technology of GAS over oil from De-Carbon.  I know Spax bought components from Armstrong and Woodheads back in the mists of time so there was some commonality.     Basically an incestuous business.   

[Captain Colonial]

Smokey-Wan, maybe a trip to the Autosport Show at the NEC would be a good way to network quickly to find what you need, both springs and other bits?

 

http://www.autosportinternational.com/public/page.cfm/action=ExhibList/ListID=1/t=m

 

Lee Spring will be there:

 

http://www.leespring.co.uk/uk_index.asp

 

http://www.leespring.co.uk/uk_int_about_custom.asp

[BLiNK Motorsport]

To add to that based on such a light car your abig % of the overall weight. So depending on your weight the spring rates may want to be different to achieve the original designed settings. May be an extra bacon butty each day would help

 

 

Yo obviously haven't met Mark - he weighs approximately 0st 0lbs - he is a true racing snake :-)

 

(Wish I was as slim!)  

[Mark (smokey mow)]

Yo obviously haven't met Mark - he weighs approximately 0st 0lbs - he is a true racing snake :-)

 

(Wish I was as slim!)  

Evening Fraser  I'm not quite as lightweight as I was but I'm still a relatively featherweight 67kg  it's just as well, else I probably wouldn't fit in the car

[Mark (smokey mow)]

Just to add some numbers to this:

Front suspension

Distance from wishbone pivot to damper mount (D1) = 115mm
Distance from wishbone pivot to upright pivot (D2) = 153mm
Motion Ratio (MR) = D1/D2 = 0.75

Damper angle from vertical (A) = 18deg
Angle correction factor (ACF) = Cos A = 0.95

Spring Rate (K) = 85 lbs/ins
Wheel Rate (WR) = MR² x K x ACF = 0.75² x 85 x 0.95 = 45.4

Assuming a vehicle weight of 485lbs (220kg) including driver and a 40/60 Weight distribution front to rear
Corner Weight (CW) = 97lbs
Suspension Frequency (SF) = 187.8 x SQRT(WR/CW) = 187.8 x SQRT (97/145) = 154

Suspension Frequency in Hz = SF/ 60 = 154/60 = 2.5Hz

Rear suspension

Distance from wishbone pivot to damper mount (D1) = 400mm
Distance from wishbone pivot to upright pivot (D2) = 400mm
Motion Ratio (MR) = D1/D2 = 1.0

Damper angle from vertical (A) = 33deg
Angle correction factor (ACF) = Cos A = 0.84

Spring Rate (K) = 105 lbs/ins
Wheel Rate (WR) = MR² x K x ACF = 1.0² x 105 x 0.84 = 88.2

Assuming a vehicle weight of 485lbs (220kg) including driver and a 40/60 Weight distribution front to rear
Corner Weight (CW) = 145lbs
Suspension Frequency (SF) = 187.8 x SQRT(WR/CW) = 187.8 x SQRT (88.2/145) = 146.5

Suspension Frequency in Hz = SF/60 = 146.5/60 = 2.4Hz



So....  how does that look to the educated?

[pete g]

_{can you work mine out}  

[Mark (smokey mow)]

_{can you work mine out}  

The calculations came from here

http://eibach.com/m-america/en/motorsport/products/suspension-worksheet

Proving you know a few basic geometric dimensions from the car and the suspension frequency then it's not too tricky.

Typically suspension frequencies for various types of car seem to be (very roughly) in the region of:

Road car upto 1Hz

Sports car 1 - 2Hz

Occasional track car 2 - 2.5Hz

Full track / Race car 2.5-3.5 Hz

Race car with downforce 4Hz

[DamperMan]

I'd generally look at use 1.5 to 1.75 on this sort of car as a start. As far as using ratios of lower arm and angles of dampers it's ok if thats all you have to work on. The best model is the car as all the geometry is included. People will spend more time measuring all the details and sending them to me than it would have taken to measure the Mr direct off the car with fewer errors. With the body on stands and no springs fitted, jack the wheel 1" either side of the normal ride position. If the damper moved 1" for the 2" of wheel movement the Mr is 0.5.

If for an example you want a spring rate at the wheel of 100 lbs per inch. This is called wheel rate.. To achieve this with a 0.5 Mr you need a spring to produce 200lbs force when compressed 1/2 inch making it a 400 spring. Mr can make a massive difference to the fitted spring rate to achieve a particular wheel rate. Also from a damper point of view dampers are velocity sensitive. If the damper only moves 1/2 the distance the wheel moves it will be moving half the speed. And if it's low speed movement and a low friction damper it may produce 1/4 of the force which at the wheel is 1/8 of the force... knowing the Mr allows me to chose the relivent test speeds and target force figure to produce the correct damping at the wheel.

[Mark (smokey mow)]

Thanks everyone for your help. To close this thread, I spoke to Faulkner Springs This morning and they'll be custom making me a set of specials at the correct spring rate and length