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

Suspension and other discussion

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

Postby MWP » Mon Oct 13, 2014 12:54 pm

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?
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby Mafix » Mon Oct 13, 2014 3:55 pm

you should start at 10k. 8k is not enough, imho.
eliminate any droop. that's just wasted space. recalculate.
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby bajallama » Mon Oct 13, 2014 8:00 pm

MWP wrote: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).
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby MWP » Tue Oct 14, 2014 1:49 am

Mafix wrote: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.
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby MWP » Wed Oct 15, 2014 10:57 am

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.

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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby Mafix » Fri Oct 24, 2014 2:21 pm

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.
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby MWP » Fri Oct 24, 2014 2:38 pm

What calculations are those?
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby Mafix » Fri Oct 24, 2014 3:39 pm

i'll have to look it all up again. been about a year. just weight calculations for initial setup
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby klue » Fri Oct 24, 2014 9:36 pm

what springs are you using?
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby MWP » Sat Oct 25, 2014 1:39 am

Mafix wrote: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.
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby MWP » Sat Oct 25, 2014 5:54 am

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

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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby Mafix » Sat Oct 25, 2014 4:44 pm

koni shock?
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby MWP » Sun Oct 26, 2014 12:34 am

Yeah.
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby Mafix » Wed Oct 29, 2014 7:34 pm

nice. I don't see any droop. perhaps we define that differently.
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Re: Spring Rates VS Ride Height VS Bump Travel (Calculations

Postby bajallama » Thu Oct 30, 2014 1:16 am

Mafix wrote: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.
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