Wingnut
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| posted on 12/11/07 at 12:26 PM |
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Light steering, any advice on geo changes?
My mid engined spaceframe car has steering that is rather on the light side, it's not a problem as such, but I feel a bit more weight would add
to the 'feel' of the car.
I'll dial in a few more degrees of castor, but was wondering about also shortening the steering arms.
The steering arms bolt onto the upright (to make life easier!). & the distance from balljoint to kingpin is about 150mm
Also I feel the ackerman is very wrong & whilst in doesn't seem to be a problem it would be nice to improve it.
Does anyone have any advice or opinions?
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nitram38
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| posted on 12/11/07 at 01:05 PM |
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How much castor do you have?
Normally increasing this will make your steering centre easier and will improve feedback through the steering wheel.
I run my rear engined car with 7 degrees of castor and the feedback/feel is really good.
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andrews_45
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| posted on 12/11/07 at 01:30 PM |
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...Be carefull asking questions about caster 
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nitram38
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| posted on 12/11/07 at 01:34 PM |
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quote:
Originally posted by andrews_45
...Be carefull asking questions about caster
He's not building a 7 so he should be ok! 
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hampshe
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| posted on 12/11/07 at 01:38 PM |
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Light front end
From my experience it sounds like you need a better weight distribution, on our old formula Fords, they were designed with radiators and batteries in
the front to help with this
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nitram38
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| posted on 12/11/07 at 01:57 PM |
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I did take a look at your steering arms on your hub and they do look a bit long.
My homebuilt jobies are only about 120mm from the upright centres.
You may have to move your rack as well.
Your picture:
.jpg)
My front end:
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Wingnut
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| posted on 12/11/07 at 03:14 PM |
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Gents,
thx for the replies,
Hampshe, weight distribution is 43% frnt 57% rear. Unfortunately it's too late in the build to be moving stiff around in the chassis, but thx
for making me aware of the problem.
Nitram38, thx for taking the time to post the pictures. i hope I can shorten the steering arms without moving the rack!
Presumably as long as the arms don't foul the rack at any point it won't be necessary to move it??
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designer
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| posted on 12/11/07 at 03:31 PM |
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Can't see anything wrong with weight distribution of 43f/57r.
I also think that you could get rid of the Akermann.
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britishtrident
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| posted on 12/11/07 at 08:19 PM |
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No easy answer
One of the difficulties is caster & king pin inclination are related and king pin inclination can't be adjusted independently of camber (an
exception Sierra based front ends with offset mushrooms).
Generally if you use more caster you want also to increase the KPI, but normally the only way to increase KPI without changing the upright design is
to increase the negative camber.
Uprights designed for cars that are light at the front tend to use lots of KPI to go with the increased caster.
Heavier cars tend to use low KPI and small ammouts of caster most of the self centering coming from the self-aligning torque of the heavier loaded
tyre; ie greater the distortion of the sidewall of a radial tyre (within limits) the greater the self-aligning torque.
If building a Midi I would probably use MGTF (ie modified Metro) front end parts or failing that good old ancient Triumph bits.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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britishtrident
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| posted on 12/11/07 at 08:32 PM |
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Steering arms & ackerman
The steering arms look long but if you shorten the steering arms you will end up in an anti-ackerman situation even if you move the hole for the outer
track rod ends as far out as possible.
As it dosen't look possible to move the steering rack back to gain a quasi ackerman effect the only way open would be to move both top and
bottom ball joints forward (eg effectively increase the wheelbase) in addition to the ammount require to add more caster.
How much ackerman you need depends on what you use the car for but even if you intend to use the car exclusively for track days a percentage of
ackerman helps the turn in to slow speed corners.
[Edited on 12/11/07 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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