what causes steering to 'load up'?(unassisted rack)
Discussion
Fume Troll said:
Please note that, as the article says, when people talk about adding caster, they're really talking about adding mechanical trail. The more the trail, the longer the moment against which you must rotate the contact patch - the leverage is working against you. If all you do is to add caster, you will necessarily add trail, but it is possible to reduce caster whilst maintaining trail, in which case you will maintain, not reduce, the steering weight and self-aligning torque.Also the article is mistaken in saying that a high caster angle causes jacking. The higher the caster angle, the more negative the jacking.
flemke said:
Fume Troll said:
Please note that, as the article says, when people talk about adding caster, they're really talking about adding mechanical trail. The more the trail, the longer the moment against which you must rotate the contact patch - the leverage is working against you. If all you do is to add caster, you will necessarily add trail, but it is possible to reduce caster whilst maintaining trail, in which case you will maintain, not reduce, the steering weight and self-aligning torque.Also the article is mistaken in saying that a high caster angle causes jacking. The higher the caster angle, the more negative the jacking.
In fact you could set up a wheel so it had lots of caster angle, but no trail, or vice versa, if you really wanted to.
Cheers,
FT.
Fume Troll said:
flemke said:
Fume Troll said:
Please note that, as the article says, when people talk about adding caster, they're really talking about adding mechanical trail. The more the trail, the longer the moment against which you must rotate the contact patch - the leverage is working against you. If all you do is to add caster, you will necessarily add trail, but it is possible to reduce caster whilst maintaining trail, in which case you will maintain, not reduce, the steering weight and self-aligning torque.Also the article is mistaken in saying that a high caster angle causes jacking. The higher the caster angle, the more negative the jacking.
In fact you could set up a wheel so it had lots of caster angle, but no trail, or vice versa, if you really wanted to.
Cheers,
FT.
Please don't shoot me down on this guys i am genuinely interested.
wheels-inmotion said:
Just out of interest why would you want to manipulate the castor or trail?...
Because it can have a big effect on steering feel and feedback, and also on grip (because it alters the load on the tyre due to jacking and because it effects the camber angle of the tyre in relation to the road as you turn the steering).wheels-inmotion said:
...and the term "Jacking" what does this mean?
You'll come across it in two contexts, when discussing suspension design.The more common is the tendency for the sideways thrust of the tyre trying to tuck the wheel underneath the car on an independent suspension system, which effectively 'jacks' that side of the car up. Some suspension designs are worse than others (basically, independent suspension with a high geometric roll centre will usually start ringing alarm bells!); the Triumph Herald/Spitfire Swing Axle arrangement was particulalry comical.
...but in relation to castor, it's simply that the act of rotating the steering around an axis that is not perpendicular to the ground plane will physically lift one side of the car, slightly.
Edited by Sam_68 on Friday 25th July 17:13
Interesting stuff this!!
I play around with added castor on my drift car, the jacking effect or lifting of the body as you go from lock to lock when stationary is the most noticeable effect. Used to great effect for self centering when sideways so I don't have to do much with the steering wheel, it does most of it by itself.
Would be keen to learn a little more about trail effects though rememebr a lot about from my mountainbiking days, but how it applies to cars & handling would be interesting.
Also been playing with castor & camber to get a flatter contact patch up front whilst sideways. The set up I have at the moment is very effective & wears the tyres completely flat.
Here's a pic so you can see what I'm on about
I play around with added castor on my drift car, the jacking effect or lifting of the body as you go from lock to lock when stationary is the most noticeable effect. Used to great effect for self centering when sideways so I don't have to do much with the steering wheel, it does most of it by itself.
Would be keen to learn a little more about trail effects though rememebr a lot about from my mountainbiking days, but how it applies to cars & handling would be interesting.
Also been playing with castor & camber to get a flatter contact patch up front whilst sideways. The set up I have at the moment is very effective & wears the tyres completely flat.
Here's a pic so you can see what I'm on about
Edited by cptsideways on Friday 25th July 23:34
The bit that stands out for me in that pic is that the left front wheel has turned through more angle than the right front wheel. I guess as you spend more time sideways then ackerman becomes less of an issue and having both wheels pointing in the direction of travel is more desirable, but is the greater turn on the left hand wheel something you've designed into the system on purpose?
trackcar said:
The bit that stands out for me in that pic is that the left front wheel has turned through more angle than the right front wheel. I guess as you spend more time sideways then ackerman becomes less of an issue and having both wheels pointing in the direction of travel is more desirable, but is the greater turn on the left hand wheel something you've designed into the system on purpose?
It'something I've been working on, sort of a reverse ackerman system. It was more of an experiment that I found works! not quite sure why but it does. Total steering lock is rather critical too & the car has almost 50 degs available now as opposed to 34deg as standard. It would appear using a regular steering system that in the same scenario, the inside wheel turns less & so drags it's way round the corner as can almost been seen in the car behind. It's quite easy to spot with the rubber marks left on the track.
cptsideways said:
trackcar said:
The bit that stands out for me in that pic is that the left front wheel has turned through more angle than the right front wheel. I guess as you spend more time sideways then ackerman becomes less of an issue and having both wheels pointing in the direction of travel is more desirable, but is the greater turn on the left hand wheel something you've designed into the system on purpose?
It'something I've been working on, sort of a reverse ackerman system. It was more of an experiment that I found works! not quite sure why but it does. Total steering lock is rather critical too & the car has almost 50 degs available now as opposed to 34deg as standard. It would appear using a regular steering system that in the same scenario, the inside wheel turns less & so drags it's way round the corner as can almost been seen in the car behind. It's quite easy to spot with the rubber marks left on the track.
cptsideways said:
trackcar said:
The bit that stands out for me in that pic is that the left front wheel has turned through more angle than the right front wheel. I guess as you spend more time sideways then ackerman becomes less of an issue and having both wheels pointing in the direction of travel is more desirable, but is the greater turn on the left hand wheel something you've designed into the system on purpose?
It'something I've been working on, sort of a reverse ackerman system. It was more of an experiment that I found works! not quite sure why but it does. Total steering lock is rather critical too & the car has almost 50 degs available now as opposed to 34deg as standard. It would appear using a regular steering system that in the same scenario, the inside wheel turns less & so drags it's way round the corner as can almost been seen in the car behind. It's quite easy to spot with the rubber marks left on the track.
Reading some of the above replies and articles, it appears some of you are really knowledgable about suspension set up, so going on from "steering loading up". I have a similar trait with my TVR S1. I have assumed it is set up like this on purpose with a lot of castor, for stability for road use, but as the author questions, the stering loads up too much, and it makes the car difficult to manouvere at high cornering speeds (trackdays etc), which is not desirable! Unfortunately the castor is not adjustable, not at least without modiying the wishbone mounts to allow horizontal adjstment.
The other question I have concerns roll. The suspension uses double wishbones at the front, and trailing arms at the rear. The rear spring/shock mounting is forward of the wheel centre, so given my limited way of thinking, does not work well in resisting roll. I have changed spring rates progressively, and gianed considerable improvement, and infact for road use, is now excellent. However, I want to reduce roll even further, so I have had a brainwave of fitting a rear anti roll bar. At present, the car enters a corner, steering and lateral forces build up, followed by a small amount of body roll. If you push it further, you have the distinct feeling the back end will snap. In practice, soemtimes it does, and sometimes it progressive. So in otherwords, its a challenge (some people like this who apparently have lots of hair on their chest, I for one really want a car that drives like a go cart).
The logic behind the rear antiroll bar, is that as the lateral forces build up, the loads will be transfered sooner to the outside tyre, making it break sooner and more progressively, and also reducing further body roll. I am not looking for ultimate cornering speed, just controllable fun.
Am I barking up the wrong tree?
Thanks
Mark
The other question I have concerns roll. The suspension uses double wishbones at the front, and trailing arms at the rear. The rear spring/shock mounting is forward of the wheel centre, so given my limited way of thinking, does not work well in resisting roll. I have changed spring rates progressively, and gianed considerable improvement, and infact for road use, is now excellent. However, I want to reduce roll even further, so I have had a brainwave of fitting a rear anti roll bar. At present, the car enters a corner, steering and lateral forces build up, followed by a small amount of body roll. If you push it further, you have the distinct feeling the back end will snap. In practice, soemtimes it does, and sometimes it progressive. So in otherwords, its a challenge (some people like this who apparently have lots of hair on their chest, I for one really want a car that drives like a go cart).
The logic behind the rear antiroll bar, is that as the lateral forces build up, the loads will be transfered sooner to the outside tyre, making it break sooner and more progressively, and also reducing further body roll. I am not looking for ultimate cornering speed, just controllable fun.
Am I barking up the wrong tree?
Thanks
Mark
CTE said:
Reading some of the above replies and articles, it appears some of you are really knowledgable about suspension set up, so going on from "steering loading up". I have a similar trait with my TVR S1. I have assumed it is set up like this on purpose with a lot of castor, for stability for road use, but as the author questions, the stering loads up too much, and it makes the car difficult to manouvere at high cornering speeds (trackdays etc), which is not desirable! Unfortunately the castor is not adjustable, not at least without modiying the wishbone mounts to allow horizontal adjstment.
The other question I have concerns roll. The suspension uses double wishbones at the front, and trailing arms at the rear. The rear spring/shock mounting is forward of the wheel centre, so given my limited way of thinking, does not work well in resisting roll. I have changed spring rates progressively, and gianed considerable improvement, and infact for road use, is now excellent. However, I want to reduce roll even further, so I have had a brainwave of fitting a rear anti roll bar. At present, the car enters a corner, steering and lateral forces build up, followed by a small amount of body roll. If you push it further, you have the distinct feeling the back end will snap. In practice, soemtimes it does, and sometimes it progressive. So in otherwords, its a challenge (some people like this who apparently have lots of hair on their chest, I for one really want a car that drives like a go cart).
The logic behind the rear antiroll bar, is that as the lateral forces build up, the loads will be transfered sooner to the outside tyre, making it break sooner and more progressively, and also reducing further body roll. I am not looking for ultimate cornering speed, just controllable fun.
Am I barking up the wrong tree?
Thanks
Mark
I think you'll find an anti roll bar has a greater effect on the opposing end of the car, transferring weight diagonally across the car in yaw motion. So a rear a/r bar would increase front end dive at the outside side, loading your steering up even more. The other question I have concerns roll. The suspension uses double wishbones at the front, and trailing arms at the rear. The rear spring/shock mounting is forward of the wheel centre, so given my limited way of thinking, does not work well in resisting roll. I have changed spring rates progressively, and gianed considerable improvement, and infact for road use, is now excellent. However, I want to reduce roll even further, so I have had a brainwave of fitting a rear anti roll bar. At present, the car enters a corner, steering and lateral forces build up, followed by a small amount of body roll. If you push it further, you have the distinct feeling the back end will snap. In practice, soemtimes it does, and sometimes it progressive. So in otherwords, its a challenge (some people like this who apparently have lots of hair on their chest, I for one really want a car that drives like a go cart).
The logic behind the rear antiroll bar, is that as the lateral forces build up, the loads will be transfered sooner to the outside tyre, making it break sooner and more progressively, and also reducing further body roll. I am not looking for ultimate cornering speed, just controllable fun.
Am I barking up the wrong tree?
Thanks
Mark
A front a/r bar will do the opposite & apply weight to the rear of the car.
I may be wrong but that is what I have learnt so far but happy to be corrected or to learn some about it all.
Declan,
Thanks for your thoughts.
I did disconnect the front anti roll bar once to see what happened. I only took the car on the road so could not be silly, but it seemed to destabilise the car, but did reduce understeer. I did not feel the need to spend more time adjusting dampers etc to overcome the loss of stability, thinking the anti roll bar was there for a good reason. Given your experience I have to respect what you say, although I would add that different suspension set ups probably react differently. I do not know how the rear suspension works on your drift car, but my TVR has rear trailing arms, and indeed so has virtually every car I have owned. The only one of which that truly handles neutrally is my MK5 Golf which has a rear anti roll bar. I also used to own a MK4 Golf and one suspension mod to that was to fit a rear anti roll bar which makes the handling more neutral, flatter.
I will try and comprehend how the weight transfers diagonally, I suspect you are right, but I do not yet understand.
Thanks for your thoughts.
I did disconnect the front anti roll bar once to see what happened. I only took the car on the road so could not be silly, but it seemed to destabilise the car, but did reduce understeer. I did not feel the need to spend more time adjusting dampers etc to overcome the loss of stability, thinking the anti roll bar was there for a good reason. Given your experience I have to respect what you say, although I would add that different suspension set ups probably react differently. I do not know how the rear suspension works on your drift car, but my TVR has rear trailing arms, and indeed so has virtually every car I have owned. The only one of which that truly handles neutrally is my MK5 Golf which has a rear anti roll bar. I also used to own a MK4 Golf and one suspension mod to that was to fit a rear anti roll bar which makes the handling more neutral, flatter.
I will try and comprehend how the weight transfers diagonally, I suspect you are right, but I do not yet understand.
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