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Location:
Auckland, New Zealand
Registered:
July 2002
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Live axle upgrades...
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Mon, 28 October 2002 20:48
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When you upgrade you're diffs (live axles) do you need to get an increased spring rate to compensate for it at all?
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Location:
Finland
Registered:
June 2002
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Re: Live axle upgrades...
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Mon, 28 October 2002 22:04
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I may be alone with this view of mine.
Nope. Same springs still are okay.
After thinking about this about a year ago, I came to a conclusion that we'd be better off by slightly increasing body weight at back!
Okay, increasing is misleading word - redistributing is what I mean here.
Let's exaggerate quite a bit to make things clearer. What would happen if we'd bolt on rear axle that weighs 150kilos? To my mind we'd be more or less okay on a perfectly smooth asphalt. Problematic area would definately be rough terrain at moderately high speed. Stock axle was able to follow undulations of road surface. Heavy axle would not follow road surface even remotely as well.
I think we'd need two things to make heavier axle work better: higher rating springs and more weight at back of chassis.
With higher rate springs alone, I think back end of car would just lift clean off the road for a fraction of a second when run into a bump. Higher rate spring would not find a solid backing against which get compressed. It would push that solid backing (ie chassis) ahead of it when encountering a bump on a road.
Under normal circumstances springs would be loaded now, and they would return axle down to road when expanding. With higher rate springs we have back end just lingering in the air with unloaded spings. Right?
Tossing 200 kilos of load in the trunk would make rear work much better. That would be a no-no when it comes to cornering characteristics.
I reckon it would be worth a shot to retain present spring/shock combo and transfer battery (and some other accessories) to trunk for more rear end biased weight distribution.
I know for a fact that in smaller rwd Toyota's overshot rear spring rates are terrible in gravel rallying. Same characteristics do arise under spirited street driving. For example arriving to a speed bump with such rear suspension will make rear shoot straight upwards. Talk about handling problems if that happens to be in mid corner! (This will show very clearly with stock shocks and uprated springs - don't do it.)
We need moderate rear spring rates to allow rear axle to neatly give in when running into such speed bump. This setup is too soft on a perfectly even asphalt circuit work, unnerving body roll most likely is evident.
Experiment what settings suite your particular use.
-A.
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Registered:
June 2002
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Re: Live axle upgrades...
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Tue, 29 October 2002 11:37
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i'd have to agree with that...even in a crown, which most think is a heavy car...it's not really. 1300kg!! or thereabouts and i'm talking 1968/69 model. The rear spring rates are terrible. once you've got a full tank of fuel and a bit of weight in the back it corners and handles a whole lot better...just a bit underpowered to make it work better though.
i found softer springs with koni adjustables fixed it up...also added a second top control arm to my crown and dumped the panhard rod in favour of a watts link.
cheers struan.
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Location:
South Australia
Registered:
July 2002
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Re: Live axle upgrades...
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Thu, 31 October 2002 13:27
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I would say personally that depending on the extra weight you added (which is likely not much) then you should think about upgrading your shocks. The extra weight that you might add with a different live rear axle is unsprung, and hence, has very little bearing on the action of the springs (except in some small cases). It does add some weight to the rear of the car, which may effect the loading of the tyres a little, but unlikely to be enough to require the spring rate to be adjusted.
However, the extra momentum created by more vibrating mass may require more damping and hence different shocks.
Whenever you add more unsprung mass to a car, it *will* generally lessen the cars handling, no matter how many compromises you make.
As said though - the standard springs should be alright, but the dampers may need attention.
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