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Old 04-16-2012, 03:47 PM   #1 (permalink)
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Default Suspension geometry

Hey guys!

I had my suspension alignment done today, and tried to make it a bit more like a fast road setup. The settings were as follows:

Front (L/R)
Camber: -206' / -200'
Caster: 435' / 435'
Toe: 006' / 006'

Rear (L/R)
Camber: -159' / -159'
Toe: 012' / 012'

I then realized from reading several topics about it, that there should have been more camber on the rear than on the front. However the car seems to handle much more nicely than before, when the settings were all over the place.

What would this difference in camber between the rear and the front cause, in practice? I've read somewhere that there should be a -050' difference in camber in the rear, compared to the front, whereas mine was setup with ~ +041' difference.


Cheers!
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Old 04-16-2012, 03:53 PM   #2 (permalink)
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Default Re: Suspension geometry

All the fast setups are biased towards more front negative camber. You'll likely hear differently over on m.net where 10-15 year old techniques are treated as gospel.

More rear negative camber vs front = safer more understeer prone setup (good for unexperienced/street driver)
More front negative camber vs rear= should turn in, rotate and have a general more oversteer tendency.
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Old 04-17-2012, 01:11 AM   #3 (permalink)
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Default Re: Suspension geometry

The big question is what is the camber GAIN at each end.

If you have greater negative camber at the front, it should help the turn in more quickly.

But if as the car rolls, the rear suspension gains more camber, or rather, combined with body roll loses less camber, then that will reduce any tendency to oversteer or decrease any understeer.

To put it in more concrete terms, I used this site:

http://www.virkki.com/jyri/miata/camber/

I adjusted the curves to your cambers and set the ride height by guessing at 12.5"f and 13.0"r.

When I do that, body roll that pushes the two tires upward 3" (relative to the body) increases the negative camber at the front to -5.04 and to -5.2 at the rear. Now those figures are relative to a "vertical" that rolls with the car, but the important point is that the difference in camber between front and rear changes by 09.6'. That takes the rears from leaning inward less than the fronts to leaning outward less.

So good turn in, followed by stabilizing camber change.

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Old 04-17-2012, 05:01 AM   #4 (permalink)
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Default Re: Suspension geometry

Wow, that was a great write up! I guess I had thought that far, but never actually put it into numbers and exact measurements. Thanks a lot for the input!

After all I guess my settings do make some sense... My suspension is a lot stiffer in the front too, so that will account for less body roll/compression in the front when compared to the rear. I will use those models (assuming they are correct) and make an estimation of what my dynamic values are
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Old 04-17-2012, 05:58 AM   #5 (permalink)
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Default Re: Suspension geometry

I measured the ride height on my car, from the center of the wheels to the arches, and came up with figures of 12.2" front and 12.6" rear.

I added something close to those values on the website and this is what I got:



Now assuming the front does not compress by more than 2 inches, and that the rear compresses just a bit more, I'd say that on full compression they're at a difference of roughly 04'... That should be a good mark!
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