Anti-Ackerman
11-30-2016, 01:55 PM
#1
Instructor
Thread Starter
Anti-Ackerman
I read a post in the C7 Z06 section that referenced a video which explained Akerman steering. The video also talked about anti-Ackerman which, I had never heard of. So, I did some exploring and as I did, I stumbled across three short videos produced by Honda and Rahal Letterman racing on the subject of chassis design and tuning. The expertise and explanation come from the team’s Technical Director. They are very instructive and touch on many subjects that are regularly debated on these forums (including anti-Ackerman). Since I hadn’t seen these referenced before, I thought I would share this “find”.
The first one is about Camber, Caster, Toe and Ackerman and when it finishes it leads to the other two videos. The Indy Car graphic aide they use also does nice job of showing how a full-on race car design moves weight to the center and onto the car’s springs.
The first thing I found was this video which more closely parallels how I learned about Ackerman (a long time ago) but it has the addition of an ideal and “imaginary” center wheel which I found helpful to the explanation. Don’t be put off by the simple trigonometry. It’s just a vehicle for showing how engineers quantify the angles their designs must satisfy and how they look at the problem when they design.
Hope this adds to the collective knowledge base.
The first one is about Camber, Caster, Toe and Ackerman and when it finishes it leads to the other two videos. The Indy Car graphic aide they use also does nice job of showing how a full-on race car design moves weight to the center and onto the car’s springs.
The first thing I found was this video which more closely parallels how I learned about Ackerman (a long time ago) but it has the addition of an ideal and “imaginary” center wheel which I found helpful to the explanation. Don’t be put off by the simple trigonometry. It’s just a vehicle for showing how engineers quantify the angles their designs must satisfy and how they look at the problem when they design.
Hope this adds to the collective knowledge base.
12-05-2016, 11:36 PM
#2
Will watch. Anti Ackerman isn't something's easy to change and generally you want more Ackerman not less. Anti Ackerman might be good with huge radius turns and low scrub, but generally the c5's need much more Ackerman for most fairly tight turns.
12-06-2016, 06:03 PM
#3
Melting Slicks
What happens with a racing car is that the inside front tire, because it doesn't have much weight on it, will just slide that tire if you have too much ackerman. If you look at a tires slip angle curves you'll see that at low weights you can't support much slip angle before the tire gives up. While the outside tire is generating a lot of slip angle that is causing more steering input than is normal for lower g situations. This higher steering input puts too much steering angle into the inside front tire and as it unloads it can just get dragged along.
The first skid pad test I ever did was with a Datsun 510 on the stock tires (circa 1971). It had so much ackerman that the inside front tire would actually momentarily stop because it was turned to far into the corner and it was just scrubbing along.
Colin Chapman was one of the first guys to figure out that you didn't want too much ackerman effect and in certain situations you actually wanted anti-ackerman to get the most out of the inside front tire.
The first skid pad test I ever did was with a Datsun 510 on the stock tires (circa 1971). It had so much ackerman that the inside front tire would actually momentarily stop because it was turned to far into the corner and it was just scrubbing along.
Colin Chapman was one of the first guys to figure out that you didn't want too much ackerman effect and in certain situations you actually wanted anti-ackerman to get the most out of the inside front tire.
12-07-2016, 12:41 PM
#4
Instructor
Thread Starter
Yes, thanks to both of you. It made sense as soon as I saw the video clip. I had just never before thought through the subject that far (happens more often than I'd like). There are many interesting problems to be solved when trying to make a car go fast. Whether road racing, oval or straight line, it's all interesting.
12-07-2016, 12:56 PM
#5
What happens with a racing car is that the inside front tire, because it doesn't have much weight on it, will just slide that tire if you have too much ackerman. If you look at a tires slip angle curves you'll see that at low weights you can't support much slip angle before the tire gives up.
12-08-2016, 08:20 AM
#6
Melting Slicks
That depends on the tire. Some tires will want positive Ackerman. Others will want anti-ackerman. You have to look at the slip angle vs. lateral mu curves at different normal loads for the tire you're running in order to be able to determine which one your tire wants.
When anti-ackerman was discovered, that was in the days of bias ply tires and slip angles were higher than they are now (in general) with more modern tires.
12-08-2016, 12:21 PM
#7
Yes, exactly, but you also have to consider the outside tire slip angle and what that does to overall steering angle. With a highly loaded outside tire and a relatively soft (high slip angle tire) like a racing tire, you tend to see a lot of steering lock and that magnifies the ackerman effect.
When anti-ackerman was discovered, that was in the days of bias ply tires and slip angles were higher than they are now (in general) with more modern tires.
When anti-ackerman was discovered, that was in the days of bias ply tires and slip angles were higher than they are now (in general) with more modern tires.
