Spacenut Posted October 20, 2009 Report Share Posted October 20, 2009 Hi everyone. I am trying to understand the relationship between the KPI/SAI of a stub axle and the selected caster angle. The relationship appears to be something to do with steering in a corner reducing the camber as the wheel is turned, so more caster is dialled in to compensate. The thinking seems to be that the greater the caster angle, the larger the camber gain introduced into the outside wheel when turned, which makes sense. I am trying to figure out how my Ford derived KPI of 4.9° will affect the optimum caster angle. I guess my suspension geometry will come into this somewhere too, the primary goal is to keep the outside tyre flat on the road. Can anyone enlighten me? Thanks, Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted October 20, 2009 Report Share Posted October 20, 2009 The later pages of CIH's traning thread explored this, you have to include Ackermann into the migration as well. Quote Link to comment Share on other sites More sharing options...
CIH Posted October 20, 2009 Report Share Posted October 20, 2009 I don't think we've gone through any direct relationships between kpi, ackermann and castor though ? Is it true that part of the reason for camber migration/steered gains is kpi itself ? Quote Link to comment Share on other sites More sharing options...
Tony Posted October 20, 2009 Report Share Posted October 20, 2009 I don't think we've gone through any direct relationships between kpi, ackermann and castor though ? Is it true that part of the reason for camber migration/steered gains is kpi itself ? We covered this in the area of SR.... The Achermann acts to migrate the camber and allow the castor to sweep forward on the inner wheel, the KPI also increases (decreases figuitivally) and attempts to lift the car, the cars weight pushing back down on the KPI forces the steering to return. Quote Link to comment Share on other sites More sharing options...
CIH Posted October 20, 2009 Report Share Posted October 20, 2009 uh, we did ? soz thread hijacking. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 20, 2009 Report Share Posted October 20, 2009 uh, we did ? soz thread hijacking. The entire sequence of SR migration encompasses this topic. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 20, 2009 Report Share Posted October 20, 2009 How this for a tuned Ackermann/ camber/ castor/ toe/ KPI migration and maintain the contact patch...... Quote Link to comment Share on other sites More sharing options...
CIH Posted October 20, 2009 Report Share Posted October 20, 2009 Sorry Tony you're correct. You actually mentioned Ackermann & castor in the first page. Me = teh fool. More detail pg7-8. I think we should maybe have another look over the subject in that thread as, re-reading the posts, I think I've missed a few points. Quote Link to comment Share on other sites More sharing options...
Spacenut Posted October 20, 2009 Author Report Share Posted October 20, 2009 That's a lot of lock there - you sure the steering isn't broken? I see your point though - large contact patch still in contact with the tarmac even at extreme wheel angle. I hadn't considered the Ackermann as directly affecting the equation, but clearly the ultimate steering angle is determined by this factor. From what I can gather Ford Cortina uprights have pretty poor Ackermann geometry as well - not helped by being front-steer of course. My Nova wheelbase is 2400mm and the Cortina is 2578mm. I projected a line back from the steering arms with the wheels straight ahead and the lines didn't intersect at either of these points I think this might explain the heavy steering on a car with only 46% of its weight over the front wheels. So Cam's training thread is the one to read then? Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted October 20, 2009 Report Share Posted October 20, 2009 Sorry Tony you're correct. You actually mentioned Ackermann & castor in the first page. Me = teh fool. There's a lot to consume mate.... I wouldn't call you a fool by any means. Quote Link to comment Share on other sites More sharing options...
Tony Posted October 20, 2009 Report Share Posted October 20, 2009 That's a lot of lock there - you sure the steering isn't broken? I see your point though - large contact patch still in contact with the tarmac even at extreme wheel angle. I hadn't considered the Ackermann as directly affecting the equation, but clearly the ultimate steering angle is determined by this factor. From what I can gather Ford Cortina uprights have pretty poor Ackermann geometry as well - not helped by being front-steer of course. My Nova wheelbase is 2400mm and the Cortina is 2578mm. I projected a line back from the steering arms with the wheels straight ahead and the lines didn't intersect at either of these points I think this might explain the heavy steering on a car with only 46% of its weight over the front wheels. So Cam's training thread is the one to read then? Lauren That car is from Pro-Drift and as you may know these cars don't actually turn so Ackermann is no use to them. Nevertheless for the camber/ KPI/ SR to migrate there needs to be a disparity between the front wheels that allows these angles to migrate fluidly, this is the Ackermann. CIH training thread progressivally transports information on a need to know basis, i think you will agree it's a difficult topic but an interesting read. Quote Link to comment Share on other sites More sharing options...
CIH Posted October 20, 2009 Report Share Posted October 20, 2009 I read one 1980s F1 philosophy was to forget ackermann as the outer wheel bore most of the losf making the innerwheel almost irrelevant. Since then F1 has moved to negative ackermann, ofcourse. Presume for similar reasons, would you think ? Tony, do I recall correctly that, for drift, nill camber gains on lock is the aim ? Quote Link to comment Share on other sites More sharing options...
Spacenut Posted October 21, 2009 Author Report Share Posted October 21, 2009 CIH training thread progressivally transports information on a need to know basis, i think you will agree it's a difficult topic but an interesting read. Oh yes! Its giving the old grey matter a good workout, and I'm only on page 2... Excellent thread! Lauren Quote Link to comment Share on other sites More sharing options...
Tony Posted October 21, 2009 Report Share Posted October 21, 2009 I read one 1980s F1 philosophy was to forget ackermann as the outer wheel bore most of the losf making the innerwheel almost irrelevant. Since then F1 has moved to negative ackermann, ofcourse. Presume for similar reasons, would you think ? Tony, do I recall correctly that, for drift, nill camber gains on lock is the aim ? Zero camber at full lock, so there is a migration. Quote Link to comment Share on other sites More sharing options...
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