I'd stumbled onto a few engineering explained videos and quickly noticed how certain fundamental points were being overlooked there. The video similar to this one explaining all wheel steering sorta illustrates it. Good videos ! Keep Kyle Explains videos coming
I'm slowly rebuilding a dodge stealth. It has active rear steering to crab at high speeds. The line where all rotted so it has now bean bypassed (I'll be removing the rear rack in a couple weeks when I have the time to pull the sub-frame). The best way I can describe it as slightly unpredictable, overly complicated, and not overly effective. I've considered re-connecting it with a popper electronic control, but they hydraulics end up overly complicated.
The rear wheels in mentioned scenarios I presume would also have some form of Ackerman steering as well as the front, since the inner rear tire would be under less load and following a tighter turning radius similar to multi-link rear suspension with dynamic toe.
+hmushmann2 Potentially, however on the rear the steer angle is comparitively small with respect to the front, therefore I would think that the effect of ackerman would be minimal and you could get away with parallel steering and not have to deal with yaw moment differences with steering changes. Ackerman would also be difficult to define as it typically taken about the point from the rear axle line, and in 4 wheel steer cases that will shift depending on the rear wheel orientation. This would be very difficult to calculate as you would have to get ackerman calculated from all 4 wheels and this will vary significanlty depending on speed, direction of steer and slip angles. I'm sure that the car companies have played around with it a fair bit though, and you could definitely have it working simliar to dynamic toe, the only problem is that this would mean your dynamic toe would now be more slip/steer angle dominated than lateral load dominated, which may cause handling issues? Although it would mean you could have dynamic toe without bump steer... Not sure, if someone could lend me a new 911 to take a peak at the geometry that would be splendid though!
+KYLE.DRIVES honestly I think rear wheel steer is a marketing ploy, as it really only changes the yaw attitude of the chassis. I understand that it can help with faster rear end response, but once the yaw moment is stabilized after the load transition on the tires the only benefit I can see is optimizing the slip angle on the inside rear tire compared to a "static" toe rear end.
Rear steering sounds like the way an aircraft empennage works, which makes me realize they are exactly backwards compared to a car. Elevators and rudders always kick around the rear of the plane to change the angle of attack on the main wing. Therefore, airplanes are rear-steering, front wheel drive cars.
So, four-wheel steering can help car to fight moment of inertia on corner entry. Does it have enough advantages over esp-based torque vecoring to justify extra mass and overcomplication?
+Алексей Любимов Well, straight away I would think yes, as if we assume that the tyres have equal grip in all directions, the moment arm of torque vectoring would only be equivalent to the track of the car, while the moment arm from 4 wheel steering would be the wheelbase of the car. As the wheelbase is somewhere between 1.5-2 times the track, you can then see that in the most basic theoretical sense that 4 wheel steer should be 1.5-2 times as effective as torque vectoring. Torque vectoring also can't provide the stability perception enhancement that I mentioned here was well, as it is not changing the steady state cornering behavior (suspension kinematics) significantly. As 4 wheel steering systems aren't really that heavy or complicated with respect to the entire vehicle (especially if the rear end already has the twist of the upright supported by the tie rods), I would say that the systems are justified, and will only be more justified as actuator technology improves. Lets not forget, torque vectoring doesn't adjust the orientation of your tyres with respect to the curve, nor does it manage slip angles. Also, a 4 wheel system can easily be set up to assist with parking as well!
Over complication? Theoretical explanation - Torque vectoring is easier to explain than 4 wheel steering hence the misunderstandings and confusion of 4 wheel steering (also referred to as rear wheel steering). Physical application - Torque vectoring is far more complicated than 4 wheel steering as the only way Torque vectoring can be applied is electronically while 4 wheel steering can be mechanical which literally lasts forever with ZERO maintenance. Weight - The difference between the two is possibly negligible as the only weight added by the 4ws is electronic servos on each wheel which is comparable to the mechanisms required for the Torque vectoring system (wiring and computers being of equal weight on each system).
Active rear wheel steering is awesome! But I love the passive rear wheel sterring of my car... Every corner a surprise! Sometimes even in straight line, while braking, it can scare the sh* t out of me because it works with wheight distribution of the car! The cars aways feels alive... Late 90's and early 2000's
Your engineering knowledge is always appreciated! I've got a video idea if you're ever interested in suggestions; whats the deal with Kawasaki motorbikes and their 'rosette' style brake rotors? Instinctively one would have thought that decreasing surface area would be a bad thing.. So perhaps initial bite or over fancy gas expulsion at play.. hmmm, interested to hear your thoughts. Cheers, please keep up the awesome vids for us all :)
I think old school rear steer is different? The 86-91 RX-7 had rear steer as well; it was load based suspension magic iirc; some didn't like it from what I recall in the forums.
I'd stumbled onto a few engineering explained videos and quickly noticed how certain fundamental points were being overlooked there. The video similar to this one explaining all wheel steering sorta illustrates it. Good videos ! Keep Kyle Explains videos coming
U say four wheeler steering I think about the halo warthog
I'm slowly rebuilding a dodge stealth. It has active rear steering to crab at high speeds.
The line where all rotted so it has now bean bypassed (I'll be removing the rear rack in a couple weeks when I have the time to pull the sub-frame).
The best way I can describe it as slightly unpredictable, overly complicated, and not overly effective.
I've considered re-connecting it with a popper electronic control, but they hydraulics end up overly complicated.
last time i saw a 4 wheel steer chevy truck and it tripped me the fuck out i have never seen one before!!
What do you think about geometric 4 wheel steering?
In other words, relocating rear axle tie rod heights to cause bump steer under body roll?
Can you make a video about tire pressure?
Talking about changing wheel/tires sizes, weight, wear, grip and those things...?
The rear wheels in mentioned scenarios I presume would also have some form of Ackerman steering as well as the front, since the inner rear tire would be under less load and following a tighter turning radius similar to multi-link rear suspension with dynamic toe.
+hmushmann2 Potentially, however on the rear the steer angle is comparitively small with respect to the front, therefore I would think that the effect of ackerman would be minimal and you could get away with parallel steering and not have to deal with yaw moment differences with steering changes. Ackerman would also be difficult to define as it typically taken about the point from the rear axle line, and in 4 wheel steer cases that will shift depending on the rear wheel orientation. This would be very difficult to calculate as you would have to get ackerman calculated from all 4 wheels and this will vary significanlty depending on speed, direction of steer and slip angles. I'm sure that the car companies have played around with it a fair bit though, and you could definitely have it working simliar to dynamic toe, the only problem is that this would mean your dynamic toe would now be more slip/steer angle dominated than lateral load dominated, which may cause handling issues? Although it would mean you could have dynamic toe without bump steer... Not sure, if someone could lend me a new 911 to take a peak at the geometry that would be splendid though!
+KYLE.DRIVES honestly I think rear wheel steer is a marketing ploy, as it really only changes the yaw attitude of the chassis. I understand that it can help with faster rear end response, but once the yaw moment is stabilized after the load transition on the tires the only benefit I can see is optimizing the slip angle on the inside rear tire compared to a "static" toe rear end.
Is there any reason why cars don't use symmetric active four wheel steering? (Back wheels turning almost as much as the front wheels turn)
Rear steering sounds like the way an aircraft empennage works, which makes me realize they are exactly backwards compared to a car. Elevators and rudders always kick around the rear of the plane to change the angle of attack on the main wing.
Therefore, airplanes are rear-steering, front wheel drive cars.
Can u please make a video on how steering setup should be made for drifting..
So, four-wheel steering can help car to fight moment of inertia on corner entry. Does it have enough advantages over esp-based torque vecoring to justify extra mass and overcomplication?
+Алексей Любимов Well, straight away I would think yes, as if we assume that the tyres have equal grip in all directions, the moment arm of torque vectoring would only be equivalent to the track of the car, while the moment arm from 4 wheel steering would be the wheelbase of the car. As the wheelbase is somewhere between 1.5-2 times the track, you can then see that in the most basic theoretical sense that 4 wheel steer should be 1.5-2 times as effective as torque vectoring. Torque vectoring also can't provide the stability perception enhancement that I mentioned here was well, as it is not changing the steady state cornering behavior (suspension kinematics) significantly.
As 4 wheel steering systems aren't really that heavy or complicated with respect to the entire vehicle (especially if the rear end already has the twist of the upright supported by the tie rods), I would say that the systems are justified, and will only be more justified as actuator technology improves. Lets not forget, torque vectoring doesn't adjust the orientation of your tyres with respect to the curve, nor does it manage slip angles. Also, a 4 wheel system can easily be set up to assist with parking as well!
Over complication?
Theoretical explanation - Torque vectoring is easier to explain than 4 wheel steering hence the misunderstandings and confusion of 4 wheel steering (also referred to as rear wheel steering).
Physical application - Torque vectoring is far more complicated than 4 wheel steering as the only way Torque vectoring can be applied is electronically while 4 wheel steering can be mechanical which literally lasts forever with ZERO maintenance.
Weight - The difference between the two is possibly negligible as the only weight added by the 4ws is electronic servos on each wheel which is comparable to the mechanisms required for the Torque vectoring system (wiring and computers being of equal weight on each system).
Nope. Torque vectoring add zero extra weight and mecanical complexity, because it use sensors and servos that is already here to do mandatory ESP job.
Please can you do a video on suspension geometry design for FSAE!?
+David MS I get a lot of video requests from you SAE guys, don't you think you should be doing your own research? ;)
Active rear wheel steering is awesome! But I love the passive rear wheel sterring of my car... Every corner a surprise!
Sometimes even in straight line, while braking, it can scare the sh* t out of me because it works with wheight distribution of the car!
The cars aways feels alive... Late 90's and early 2000's
Is it a Mazda? They had that twin trapezoidal link that have the mechanical 4WS
Great informative video! 🦅🦅🇺🇸
Your engineering knowledge is always appreciated!
I've got a video idea if you're ever interested in suggestions; whats the deal with Kawasaki motorbikes and their 'rosette' style brake rotors? Instinctively one would have thought that decreasing surface area would be a bad thing..
So perhaps initial bite or over fancy gas expulsion at play.. hmmm, interested to hear your thoughts.
Cheers, please keep up the awesome vids for us all :)
Lower rotating mass
For a simpler factor just say take and handle turns faster
How can a guy convert his Volvo 240 to 4-wheel steering?
Anyone?
this is the same mechanism that made the Nissan r32 famous??
I think old school rear steer is different?
The 86-91 RX-7 had rear steer as well; it was load based suspension magic iirc; some didn't like it from what I recall in the forums.
N JUST THINK THE HONDA PRELUDE ALSO HAD 4WS.....HONDA
It’s been out for years, I had a 91 skyline gtr that had 4ws
@@madmac4535 I had a 88 RX-7 that had it