Noahs944

Whoops! Sorry.

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Justin, thanks for getting those 250 lb/springs for me.

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Question about DELRIN.
Since I'm seriously considering delrin sway bar and front & rear control arm bushings... for the street mostly with some track use. Is delrin to noisey/squeaky? or should I go rubber?

morghen

Never tried them, a friend did..they made noises and wore out.
Years ago I measured and made a drawing for a delrin shifter bushing..the one next to the gearbox.
Its worn faster than the 30+ years old part even though I designed minimal play between the metal and the bushing.

If you want stiffness go for polyurethane.
You can buy the powerflex bushings from ideola's garage or there are other options.

mel_t_vin

Not completely correct.

Motion ratio on front springs...M(f) = ~0.9
Motion ratio on rear springs...M(r) = ~0.65^2 [~0.42]
M(r) does not apply to torsion bars.

Ergo...Morghen's 924 GTS is running equivalent spring rates of ~252 lb/in [280 * 0.9] up front and ~211 lb/in [~137 + (200 * 0.42)] out back. This is in line with the real world result he reports...relatively neutral handling, with probably a slight tendency to understeer when pushed.

924srr27l

Excellent,

What 's the Wheel rate ? is this different or the same thing
If the front (.9 rate) is on the shorter 924 wishbone, what's the longer later 944 / 968 type?

Does an incorrect wishbone angle from excessive lowering change the motion ratio or not? and this only affects the camber change?

The rear Hollow 27mm T bars I have currently fitted Elephant Racing rate at 220Lbs, so this computes to 132 Lbs actual ? and my 190Lbs fronts 171Lbs
which would also explain why have a hit if understeer also if the rear is 30% softer Correct?


R

mel_t_vin

My mistake.

Where I said motion ratio, I should have said wheel rate. Have always seen rear wheel rate from a coilover spring calculated as: W(r) = M(r)^2 * spring rate, where M(r) = ~0.65

And have always seen front wheel rate calculated as: W(f) = M(f) * spring rate, where M(f) = ~0.9

But, as previously mentioned, motion ratio does not apply to torsion bars. Your 220 lb/in-rated 27 mm bars convey to the torsion/coilover summation equation directly [220 lb/in], as they are axially coincident with the spring plate pivot point.

Re: early offset/late offset control arms...good question. Have not seen anyone reference different numbers for front motion ratio to compensate for the ~25mm difference.

Re: your slight understeer...suspect that can be attributed more to your oversized 26.8 mm sway [with respect to your lightweight chassis] than to the difference in front-to-rear spring rate. Suggest you either step down the front bar or step up the rear bar.

924srr27l

Ok so this means my front 190 Lb's Springs give a wheels rate of 171Lbs, but the rear 220 lbs is the actual , which is almost a 30% Stiffer rear springs but I have some very (slight) understeer which was worst on the 8x16 ;s rims compared to 7x16 's . Sure the front bar may be a tad stiff , I could come down to 25mm or go up from 18mm to 20mm rear.

For Sprints & a Production competition I was thinking of sorting the Non parrallel Wishbones, and tie rods then Increasing the front springs to 250Lbs and fitting coil over Springs as well as the T bars, so looking a the above calulations the rear springs would need to be about 150Lbs? if the 220lb T bars simply add the coil spring rate on top (total 370Lbs) but the .65 rear coil wheel rate is 97.5 (Wheel rate Total 317.50Lbs)

R

Noahs944

Just read up on Delrin. I think I'll skip since my car isn't a competition car. Rubber is the plan but I'd like to see if powerflex is a good choice for long term daily use.

morghen

Take care with poly as well..
As far as I understand the material, Delrin is not high resilience and will take a set...make noises and affect alignment.

mel_t_vin

Front W(r) = ~171 lb/in...correct [190 * 0.9]
Rear W(r) = ~220 lb/in...correct [for 27 mm torsions]

Not quite.

Rear W(r) = M(r)^2 * spring rate
Rear W(r) = 0.65^2 * 150 = ~63.4 lb/in

Total rear W(r) = springs + torsions = ~63.4 + ~220 = ~283.4 lb/in

924srr27l

Ok, how does a .65 ratio work out to be 63.4Lbs from a 150 Lb spring?

.65 of 150 is 97.5 ?


R

porscheaddicted

I would go with a Bilstein P8 suspension kit IIWY

924srr27l

Not heard of that one, is it New?

R

J1NX3D

He probably means B8's. not a kit, just another bilstein shock.

924srr27l

BUMP.....

mikey_audiogeek

0.65 squared (that's what ^2 means) is 0.4225. Multiply that by the spring rate gives you the answer as given.

Cheers,
Mike