CIH Posted October 17, 2009 Report Share Posted October 17, 2009 *I'm currently reading abook by Allan Staniforth about competition car design so expect questions lol Quick recap about Roll Centres. I noticed fixed axle and DeDion type rear suspension has a roll centre roughly parallel with the wheel centre (on the vertical plain). Am i correct in assuming a large disparity front-to-rear ie; a low RC with twin-wishbone front but fairly high rear, could give an inherent over/understeer balance ? If so, it seems odd that they are still common in the caterham-type track-day specific cars ? Or any high performance application for that matter ? Or does that simply show how dated the basic design is compaired to a multilink affair ? Now that I think about it, I'm wondering how RC is calculated when the rear is a forrest of arms and bushes etc ? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 17, 2009 Report Share Posted October 17, 2009 You know what mate over the years i've gone right of this roll centre bollox.... Roll couple this and transfer roll transition that!!! What are we really talking about? Beyond the design stage all we are interested in is the handling, if this needs advancing to formulate a particular modification then as calibrators we need to take attention ( to the modification ) not the design elements. Suspension dynamics is twined to chassis dynamics but both have very different laws and opinions depending on the side of the fence. Let the designers conclude the roll centres and leave us alone to "tune" the modifications Quote Link to comment Share on other sites More sharing options...
CIH Posted October 17, 2009 Author Report Share Posted October 17, 2009 haha I expected you to say something like that Seriously though, if you were presented with either a custom chassis or a radically altered OEM design isn't it helpful to know these things ? I find it quite interesting too, though I imagine I'd be bored of such speculation if I had been at it aslong as you dude. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 18, 2009 Report Share Posted October 18, 2009 No not really.... As a "heads up" the DI and roll data is supportive but at the end of the day it's the actual matter of fact data that really matters. The "Midget/BMW" hybrid we had in recently was totally mystical as to what settings would be applied, the chassis/ suspension and acquired data offered a unique suggestion to the calibration, this combined with internal knowledge ended with a good handling car. Quote Link to comment Share on other sites More sharing options...
CIH Posted October 18, 2009 Author Report Share Posted October 18, 2009 Do rollcentres give any clues toward effective camber positioning ie; what would/not work for a car ? Can't say why exactly but they seem to me to be linked. Possibily weight transfer principles ? I suppose this goes back to my question in the training thread regarding loosely similar cars ie; s14 200SX & E46 330CI but differing OEM geo positions. Quote Link to comment Share on other sites More sharing options...
Tristan Posted November 5, 2009 Report Share Posted November 5, 2009 Sorry to wander , but whats De dion suspension? Quote Link to comment Share on other sites More sharing options...
Tony Posted November 6, 2009 Report Share Posted November 6, 2009 Although independent suspensions were invented decades ago, non-independent suspensions still dominated the market until the late 70s. The first reason was: cheap. The second reason: it offers quite good handling despite of poor ride. Since the wheels are rigidly linked by an axle, they remain perpendicular to the road surface regardless of body roll. Therefore the car corners quite stable. In contrast, in many types of independent suspensions, camber angle may be changed due to body roll. However, a live axle has too much unsprung weight, and leads to poor ride quality. Therefore many budget sports cars or coupes chose DeDion Axle (rear) suspensions over live axle. DeDion axle suspension has much less unsprung weight because the final drive / differential and driving shafts are not rigidly attached to the wheels. Like independent suspensions, they are part of the car body and flexibly linked to the wheels by universal joints. In other words, they are sprung. The wheels are interconnected by a DeDion Tube, which has a sliding joint to permit wheel track variation during suspension movement, this helps in refining ride quality too. The DeDion tube keeps both wheels parallel to each other under all conditions, so they are always perpendicular to the road surface regardless of body roll. Quote Link to comment Share on other sites More sharing options...
Tristan Posted November 6, 2009 Report Share Posted November 6, 2009 thats a great pic . So De Dion is like a halfway between Independant and live axle ? With lower unsprung weight . The only possible problem is the occasion where one wheel rides up on something , it causes a camber change on the other side , to a positive value? Quote Link to comment Share on other sites More sharing options...
Tony Posted November 6, 2009 Report Share Posted November 6, 2009 It was a transition that changed a whole way of thinking. Quote Link to comment Share on other sites More sharing options...
CIH Posted November 6, 2009 Author Report Share Posted November 6, 2009 Sometimes refered to as "semi-indipendent" The single wheel bump leads to changes in track (or so I read) and rear-steer, probably a similar sensation to bump steer I think ? Wasn't the sliding DeDion tube a Rover design, and the exeception to the normal sliding driveshafts ? Quote Link to comment Share on other sites More sharing options...
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