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Location:
Terrigal
Registered:
May 2002
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Negative effects of shortening control arms.
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Thu, 28 April 2005 00:58
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Hello, just wanted to get peoples opinions on any negative effects of shortening control arms on a mac strut setup as in the RA28.
Lets assume the control arm pivot points were moved out bound 30mm, and then you took 30mm off the control arm.
So there will be no camber changes. Track width would stay the same.
Bump steer isn't a concern here either (i realise there would be changes but I understand those).
But yeah, any downsides to this?
Cheers
Joel
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Location:
South Australia
Registered:
July 2002
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Re: Negative effects of shortening control arms.
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Thu, 28 April 2005 02:08
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Roll centre?
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Location:
Brisbane
Registered:
May 2002
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Re: Negative effects of shortening control arms.
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Thu, 28 April 2005 02:44
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Camber curve also?
Cheers
Wilbo
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Negative effects of shortening control arms.
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Thu, 28 April 2005 02:56
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yup, greater change in camber due to control arm movement, and could also affect bumpsteer (as you will know by now  )
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Location:
Adelaide
Registered:
May 2002
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Re: Negative effects of shortening control arms.
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Thu, 28 April 2005 02:57
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In general this will increas the rate at which your camber changes. ie it for a given suspension deflection the camber will change more for the shorter arms.
It will also change the way that your Roll centre will migrate throught suspension trave. With shorter arms the roll centre will move more possibly creating less predictable handling.
Of course you really need figures to back this all up, you may find these effects to be negligable.
Also if you moved the control arm pivot points out you would need to adjust the inner steering tie rod point to avoid bump steer.
my 2c 
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Negative effects of shortening control arms.
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Thu, 28 April 2005 03:05
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bah, just solid mount the struts to the body and piss off the springs.. then you'll never have to worry about camber change/bump steer again 
did i just say that! 
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Location:
Adelaide
Registered:
May 2003
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Re: Negative effects of shortening control arms.
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Thu, 28 April 2005 04:01
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Haha, you are sounding like a drifter now Stewart.
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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: Negative effects of shortening control arms.
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Thu, 28 April 2005 04:04
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tut tut, thats DORIFTA to you 
so anyhoo Joel,
is this to match the rack width or some other reason?
oh and using some circle gemoetry, you can kinda work out what the difference will be, based on expected suspension movement... if you can be bothered
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Location:
Adelaide
Registered:
May 2003
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Re: Negative effects of shortening control arms.
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Thu, 28 April 2005 04:19
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Hm, i think ill have to do those calculations sometime for my offset RCAs. Currently they are the best option available to me, but it would be interesting to see what sort of difference they really make.
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Location:
Terrigal
Registered:
May 2002
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Re: Negative effects of shortening control arms.
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Thu, 28 April 2005 04:28
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Thanks all for the info so far.. camber curve is a good point i wasn't thinking of.
Basically in my ra28 frontcut/3sgte project.. I have been toying with the idea instead of modifying the ta23 xmember and mounting a rack to it and moving control arm pivot points around to eliminate bump steer etc (which is all what i've done in the ra28 currently)..
I found a RA60 (rack n pinion) xmember *almost* bolts in - a lot less modifications than a ta23 xmember with rack mounted to it requires.
Only problem is, it would bring the track width out 40mm each side. This is too much really.. I'm happy to increase it by say 20mm or so which is what I have already.
So still 20mm too wide each side.. Thinking only way would be to find some control arms 20mm shorter or cut n shut some 20mm shorter..
So yeah just playing around with this idea to get an idea of the negatives and problems I might run into.
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Location:
brisvegas
Registered:
August 2004
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Re: Negative effects of shortening control arms.
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Thu, 28 April 2005 05:06
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why not use some AE86 control arms (if you can find some)
there is a post if you havn't seen it on lower control arms..the ra40/ra60 arms i have found are the same..about 5mm longer than AE86 ones..this might bring it back in..you will still have a fair bit of camber, which isn't really a bad thing..
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Location:
Madrid - Spain
Registered:
August 2002
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Re: Negative effects of shortening control arms.
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Fri, 29 April 2005 00:27
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You could use the same setup you already have and change to MA61 struts. This will bring camber back to a normal angle and retain the longer arms. The supra struts have a bigger angle between the strut and hub and sit the hub closer to the strut. This will help the track problem but may give you greif with wheel offset.
Feel free to come and look at my front end if your interested. You could even try your wheels on it. If I had time, I would measure up your geometry and plot some camber curves and roll centre positions but you may have to wait until after the move for that one.
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