 914 Suspension motion ratios, Comparing notes |
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| groot |
 Dec 2 2004, 10:03 AM
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#41
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Dis member  Group: Members Posts: 897 Joined: 17-December 03 From: Michigan Member No.: 1,444  |
QUOTE(slivel @ Dec 2 2004, 07:26 AM) Additionally this may change the roll center but doesn't this now cause the arc of the wheel to be other than vertical under suspension travel? Steve The wheel travel is never strictly vertical because the lower control arm pivots about a point. The shorter the control arm, the more track change you get during the suspension travel. |
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| slivel |
Dec 2 2004, 04:03 PM
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#42
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Old car....... older driver Group: Members Posts: 532 Joined: 10-July 04 From: San Diego Member No.: 2,332 Region Association: Southern California |
QUOTE(groot @ Dec 2 2004, 08:03 AM) QUOTE(slivel @ Dec 2 2004, 07:26 AM) Additionally this may change the roll center but doesn't this now cause the arc of the wheel to be other than vertical under suspension travel? Steve The wheel travel is never strictly vertical because the lower control arm pivots about a point. The shorter the control arm, the more track change you get during the suspension travel. Yea, that makes sense. In my case using stock arms I am probably better off not mucking with trying to change the roll center without changing the pickup points. From the pics in the earlier thread - you certainly did make some "minor modifications". I don't think that I can go that radical with the rules in the clubs that I run. I am a fairly experienced club racer (10 years) but only recently have started to seriously think about chassis and suspension tweaks. Thank you for your informative posts. Steve |
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| ottox914 |
Dec 1 2005, 06:42 PM
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#43
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The glory that once was. Group: Members Posts: 1,302 Joined: 15-December 03 From: Mahtomedi, MN Member No.: 1,438 Region Association: Upper MidWest  |
I've been using MR SEARCH to try to find out what the stock motion ratios are. I found a post by "slivel" stating the stock rear was 1.68. I haven't been able to find a stock front motion ratio. Would like this to help figure out spring rates for a DP autocross car. Anyone know what that stock front motion ratio would be, or could give me a rough guestimate?
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| groot |
Dec 4 2005, 09:00 AM
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#44
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Dis member Group: Members Posts: 897 Joined: 17-December 03 From: Michigan Member No.: 1,444 |
Typically a strut front suspension has a motion ratio of ~.92-.95 : 1... meaning the strut moves .9x and the wheel moves 1.
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| ottox914 |
Dec 5 2005, 07:53 PM
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#45
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The glory that once was. Group: Members Posts: 1,302 Joined: 15-December 03 From: Mahtomedi, MN Member No.: 1,438 Region Association: Upper MidWest |
Great, exactally what we were looking for. thanks!
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| maf914 |
Dec 6 2005, 10:28 AM
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#46
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Not a Guru! Group: Members Posts: 3,049 Joined: 30-April 03 From: Central Florida Member No.: 632 Region Association: None 
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You guys are way ahead of me when it comes to the technical theory of suspension design, but this is an interesting thread. For an example of short versus long a-arms, look at any modern open wheel or sports racing car. A-arms are as long as possible. In F-1 the lower a-arms pivot at the centerline of the chassis. |
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| groot |
Dec 6 2005, 11:09 AM
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#47
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Dis member Group: Members Posts: 897 Joined: 17-December 03 From: Michigan Member No.: 1,444 |
Longer arms reduce the camber, toe and roll center changes. Better in every way (if you get the geometry right).... except package.
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| Brett W |
Dec 6 2005, 01:48 PM
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#48
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Advanced Member Group: Members Posts: 2,859 Joined: 17-September 03 From: huntsville, al Member No.: 1,169 Region Association: None
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Kevin's right packaging is a big problem with long a-arms. I am having to run pretty short upper and lower arms in the rear to get around the tranny. Up front I could run as long as necessary but found that the 21in length will work fine for my application. With as little wheel travel as I am planning for the camber change is minimal.
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