jon b
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 posted on 2/7/09 at 08:36 PM |
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spring weights
The front corners of my car are 300lbs, if i give the wheel 50mm of travel i get 28mm shock travel, as this is nearly 2-1 does this mean i nead
300lbs springs.
jon
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charliemouse
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| posted on 2/7/09 at 09:46 PM |
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Spring weights
Oh what a can of worms!
Simply - 300lb/in springs would mean you would get 1" of spring compression static. Weight transfer charasterisitics would then govern how much
farther the springs compress dynamically (as you drive along).Weight tranfer can come form cornering forces or braking (or both), Also, when you hit a
bump, the force of the bump will compress the spring. If you hit a bump, whilst cornering hard, and braking - there will be a lot more than the 300lb
static weight of the car acting on the spring.
As you correctly worked out already the actual weight the spring sees is affected by the angle it sits at. It will also be affected by the stiffness
(or sticktion - sic A Staniforth RIP) in the suspension joints. It will also be affected by an bump damping in the shock absorber - but only
dynamically - not statically!
Weight transfer from front to rear will be affected by ride height (front and rear), rear bump and rebound stiffness and relative corner weights.
Weight tranfer side-to-side will be affected by an anti-rollbar if fitted...
Ok - From here it gets complicated and you need to calculate roll centres and assemble all the actual stats for your car for it to be meaningful.
Instead - for road use fit 250-300lb front and 150-180lb rear (depending what you weigh and if you normally fly solo or with passenger - and you
compromise between comfort and ultimate road-holding (and local roads condition). For race use start with 400lb front and 150lb rear with a 5/8"
anti-roll bar acting with approx 10" levers. And then go testing...
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Steve Hignett
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| posted on 3/7/09 at 12:47 AM |
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I read the first three paragraphs and they kinda made sense, but then when you said from here it gets complicated I kinda lost the plot a small
amount.
I thought that I had weight transfer pretty well sorted too, but then pannicked when you stated that I would have to fit 250-300Lb springs for road
use at the front, what with the angle that I'm running my springs and dampers at seems so heavy compared to what a normal Locost angle seems to
be... So it doesn't matter if the angle of the Dampers is roughly 10 degrees, or if it's 40degrees?
Steve
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mark chandler
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| posted on 3/7/09 at 05:31 AM |
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Hello Steve
The angle does matter, as does the bracket position on the wishbone.
I need to view things more simply so imagine the damper upright, and directly bolted to the centre of the wheel, 1" of wheel movement = 1"
of damper travel.
Now imagine the damper horizontal, 1" of wheel movement = 0" of damper travel, so simplistically a damper at 45" will travel
1/2". In reality its not quite this simple but the principle is fine as you lift the wheel the angle changes so do the loadings.
Next imagine the damper bolted to the wishbone half way between the chassis bush and the centre of the wheel, the wishbone now becomes a lever,
1" of wheel movement now becomes 1/2" of damper travel.
On a locost you have both factors operating, you need to experiment.
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