Spring Rates VS Ride Height VS Bump Travel (Calculations...)

MWP

New member
Hi all,

So im currently building up some new front coilover struts using koni dampers, steel sleeve kit and T3 strut tops.

I just cant see how its possible to get a decently low ride height, and still maintain a decent amount of bump travel.

Conventional suspension setup wisdom says you should have 1/3rd droop, to 2/3rds bump travel.

If i use 8kg/mm (450lb/in) front springs, and assume a front corner weight of 440kg (970lb) it works out like:
440kg/8kg = 55mm of droop travel
55mm * 2 = 110mm of ideal bump travel
55mm + 110mm = 165mm req travel

Its just not possible to get 165mm of travel without making the ride height ridiculously high, or by moving the top of the strut tower upwards.

What have you guys done?
 

Mafix

New member
you should start at 10k. 8k is not enough, imho.
eliminate any droop. that's just wasted space. recalculate.
 

bajallama

New member
MWP":34ws5sn7 said:
What have you guys done?

I have cheapy coilovers for now until I build a proper kit. They are similar to the Teins, 8k front 4k rear. I think the rear needs to more but I haven't cared to swap out because I think my dampers aren't properly sized.

Do you know what sprung natural frequency you're looking for? I can go through the calcs for determining what spring rate you need. I know you want some droop but I think 1/3 might be too much (maybe for a regular passenger car, that's fine).
 

MWP

New member
Mafix":2x0b4sdq said:
you should start at 10k. 8k is not enough, imho.
eliminate any droop. that's just wasted space. recalculate.

No way. 10k is far too stiff, and droop is very much required.
Any time a tyre is not on the ground, its not giving grip.

I know for a fact that the TTE WRC cars ran a 8kg/mm front spring in some tarmac rounds, and that was considered to be quite stiff.
 

MWP

New member
This helps a little...
I've extended the bottom of the tube down about 15mm, then cut 15mm out of the middle.
This effectively gives me another ~15mm of bump travel.

DSC_0270.jpg
 

Mafix

New member
if you think that's enough spring. perhaps then you need huge sway bars to compensate. I've done the calculations, your spring rates are only good (and yes all the aftermarket junk too) for 2500 lbs with a 22mm rear bar and no front bar. last I checked the alltracs and even the fwd cars were quite a bit heavier.
 

Mafix

New member
i'll have to look it all up again. been about a year. just weight calculations for initial setup
 

MWP

New member
Mafix":gk1dvzfo said:
i'll have to look it all up again. been about a year. just weight calculations for initial setup

Spring rate vs ride height is easy... i would like to know how you came up with antiroll bar sizes.
 

MWP

New member
Almost there.
Will install them tomorrow to check ride height and spring sleeve position then weld em up.
Springs are 475lb/in.

DSC_0282.jpg
 

bajallama

New member
Mafix":1j7667oo said:
nice. I don't see any droop. perhaps we define that differently.

Droop would be the wheel travel below the static ride height. So he would have to mount them then jack up a corner to see if his calcs or corner weight estimate was right.
 

MWP

New member
^^ yup that :)

All finished and back in the car today.
Haven't taken it on a decent test drive yet though.
 

EvanP246

New member
Have you all considered the orientation of the axles?

Doesn't It negatively affect the handling if they are angled upward? I have heard that they have to be angled downward or level for the optimum handling.

This is how my car currently sits on TEIN SS. I would like to go about a quarter inch lower but the axles are parallel with the ground as it sits.



I have an AW11 steering flip kit to install, so bump steer shouldn't be an issue.

What are your thoughts on this?
 

MWP

New member
All done and working brilliantly.
100x better than the old progressive lowering springs and KYB ExcelG inserts.

The soft'ish springs and adjustable digressive compression damping means the car handles like the springs are stiff, but i can hit big bumps, potholes, etc and they soak em up as if the springs are soft.

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CMS-GT4

Active member
So I had been talking to someone else who builds housings for these about using them in the alltrac. Did not know much about them until my research began this week when looking into my future setup. I am considering a custom set of coilovers using these struts. So far your response is one of the few that answers what I want to know (but could not find), which is how they handle rough pavement.

Now here are my other questions now that I found someone with a similar application.
* Why king springs over swift or hyperco?
* How much shorter is the new assembly than the factory struts?
* How much lower is your car at your new settings?
* At full compression do your tires rub anywhere?
* What tire size?

Thanks.
 

MWP

New member
Why king springs over swift or hyperco?

Because Australia (King Springs are made here).

I made a slight mistake with the springs, i should have got 250mm long springs, not 200mm.

How much shorter is the new assembly than the factory struts?

Longer, not shorter... by about 5mm.
I took about 10mm off the mid section of the tube, and added about 15mm on the bottom.

One of the 8611 koni inserts that is slight shorter may have been a better option.
These 8611-1259 will do the job for me though.

How much lower is your car at your new settings?

Its higher. The car was too low on the old springs.
Front wheel eyebrow height is now set at 345mm (lowest legally allowed here).

At full compression do your tires rub anywhere?

Nope.

What tire size?

Currently 225/45/17 on a 17x7 +41 wheel.
Soon to be 17x8 +35 (OZ Chronos).
 
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