harley rider
Well-known member
just wondering how many guys know what Ackerman steering meens ? And if anyone ever checks this.how important is it?
Ackerman steering?
- Thread starter harley rider
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dmw56
Busted and Rusted on Route 66
Ackermann steering geometry is a geometric arrangement of linkages in the steering of a car or other vehicle designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of different radii. It was invented by the German Carriage Builder "Lankensperger" in 1817, then patented by his agent in England Rudolph Ackermann (1764–1834) in 1818 for horse drawn carriages. Erasmus Darwin may have a prior claim as the inventor dating from 1758.
The intention of Ackermann geometry is to avoid the need for tyres to slip sideways when following the path around a curve. The geometrical solution to this is for all wheels to have their axles arranged as radii of a circle with a common centre point. As the rear wheels are fixed, this centre point must be on a line extended from the rear axle. Intersecting the axes of the front wheels on this line as well requires that the inside front wheel is turned, when steering, through a greater angle than the outside wheel.
Rather than the preceding "turntable" steering, where both front wheels turned around a common pivot, each wheel gained its own pivot, close to its own hub. A linkage between these hubs moved the two wheels together, and by careful arrangement of the linkage dimensions the Ackermann geometry could be approximated. This was achieved by making the linkage not a simple parallelogram, but by making the length of the track rod (the moving link between the hubs) shorter than that of the axle, so that the steering arms of the hubs appeared to "toe out". As the steering moved, the wheels turned according to Ackermann, with the inner wheel turning further. If the track rod is placed ahead of the axle, it should instead be longer in comparison, thus preserving this same "toe out".
Simple approximation for designing Ackermann geometryA simple approximation to perfect Ackermann steering geometry may be generated by moving the steering pivot points inward so as to lie on a line drawn between the steering kingpins and the centre of the rear axle. The steering pivot points are joined by a rigid bar called the tie rod which can also be part of the steering mechanism, in the form of a rack and pinion for instance. With perfect Ackermann, at any angle of steering, the centre point of all of the circles traced by all wheels will lie at a common point. Note that this may be difficult to arrange in practice with simple linkages, and designers are advised to draw or analyze their steering systems over the full range of steering angles.
Modern cars do not use pure Ackermann steering, partly because it ignores important dynamic and compliant effects, but the principle is sound for low speed manoeuvres. Some race cars use reverse Ackermann geometry to compensate for the large difference in slip angle between the inner and outer front tyres while cornering at high speed. The use of such geometry helps reduce tyre temperatures during high-speed cornering but compromises performance in low speed maneuvers.
I checked mine when I built my rod. Very little tire scrub during turns.
The intention of Ackermann geometry is to avoid the need for tyres to slip sideways when following the path around a curve. The geometrical solution to this is for all wheels to have their axles arranged as radii of a circle with a common centre point. As the rear wheels are fixed, this centre point must be on a line extended from the rear axle. Intersecting the axes of the front wheels on this line as well requires that the inside front wheel is turned, when steering, through a greater angle than the outside wheel.
Rather than the preceding "turntable" steering, where both front wheels turned around a common pivot, each wheel gained its own pivot, close to its own hub. A linkage between these hubs moved the two wheels together, and by careful arrangement of the linkage dimensions the Ackermann geometry could be approximated. This was achieved by making the linkage not a simple parallelogram, but by making the length of the track rod (the moving link between the hubs) shorter than that of the axle, so that the steering arms of the hubs appeared to "toe out". As the steering moved, the wheels turned according to Ackermann, with the inner wheel turning further. If the track rod is placed ahead of the axle, it should instead be longer in comparison, thus preserving this same "toe out".
Simple approximation for designing Ackermann geometryA simple approximation to perfect Ackermann steering geometry may be generated by moving the steering pivot points inward so as to lie on a line drawn between the steering kingpins and the centre of the rear axle. The steering pivot points are joined by a rigid bar called the tie rod which can also be part of the steering mechanism, in the form of a rack and pinion for instance. With perfect Ackermann, at any angle of steering, the centre point of all of the circles traced by all wheels will lie at a common point. Note that this may be difficult to arrange in practice with simple linkages, and designers are advised to draw or analyze their steering systems over the full range of steering angles.
Modern cars do not use pure Ackermann steering, partly because it ignores important dynamic and compliant effects, but the principle is sound for low speed manoeuvres. Some race cars use reverse Ackermann geometry to compensate for the large difference in slip angle between the inner and outer front tyres while cornering at high speed. The use of such geometry helps reduce tyre temperatures during high-speed cornering but compromises performance in low speed maneuvers.
I checked mine when I built my rod. Very little tire scrub during turns.
cornfield customs
Well-known member
it depends on what you are wanting to build? it is important to prevent tire wear and tire scrub. if not set up right it can also make it hard to turn the car. a couple of my friends car the ackerman is off and it drives good, tires just squeal an wear when turning. i always get it as close as possible, mainly because i am picky about my work
old lady's mad
Well-known member
well i read about it, but went ahead and did what i wanted to anway.
darkk
Well-known member
I see some front ends low enough that the tie rod is in front of the axle. Is that still safe or doesn't it matter?
cornfield customs
Well-known member
with steering arms out front you can not get your ackerman 100% correct. there is no issue running it this way, besides faster wear on your tires when you turn, and scrubbing on your tires. i am, running like that on two cars i am building now, i am going to heat up the steering arms and move them outward (towards the wheels) as much as possible to help with the ackerman.
donsrods
Well-known member
Of all the sins you can commit when building a rod, bad Ackermann is the least serious. Yes, it is nice to engineer perfect geometry and all into a front end, but sometimes, especially on a super low car, you simply have no room behind to put the tie rod...........it wants to occupy the same space as the frame or wishbones.
My 23 was one such case, I had to put the tie rod out front. The only time I noticed it was anything but perfect was when turning sharp into a parking spot, then the tires would scrub a little. But going down the road and normal driving you never noticed anything. As for tire wear, after 3 years and lots of miles there was no cupping or edge wear whatsoever, the tires were wearing evenly.
Again, this is one of those subjects where you have people lined up on both sides and neither will concede that the other one is right. As I always have said, there is the perfect world and the real world. In the perfect one you would have proper Ackermann in all cases, but in our rear, hot rod building world we have to do what we have to do sometimes to make things work.
Don
My 23 was one such case, I had to put the tie rod out front. The only time I noticed it was anything but perfect was when turning sharp into a parking spot, then the tires would scrub a little. But going down the road and normal driving you never noticed anything. As for tire wear, after 3 years and lots of miles there was no cupping or edge wear whatsoever, the tires were wearing evenly.
Again, this is one of those subjects where you have people lined up on both sides and neither will concede that the other one is right. As I always have said, there is the perfect world and the real world. In the perfect one you would have proper Ackermann in all cases, but in our rear, hot rod building world we have to do what we have to do sometimes to make things work.
Don
