What effect would complete elimination of body roll give to handling?
On a three wheeler with two front wheels and one rear wheel, what if I could reduce body roll to zero. Would it be a good thing?
I mean if I made the front anti-roll totally rigid but still had full vertical suspension all round, would there be there any handling disadvantage?
Anything bad at all? Risk of tipping over without warning perhaps?
I think a lot of (tadpole) three wheelers are really stiff in roll at the front - I seem to remember the indycycle had an arrangement with a mono
shock that allowed virtually no roll!
quote:Originally posted by Wadders
Just curious, but how would you totally eliminate roll while still maintaining useful suspension movement?
Al.
How about a rigid frame that mounted both front wheels that allowed no twist. The whole thing could pivot allowing free vertical movement. I know
what Dave is thinking and am interested to see what people think without giving the game away.
quote:Originally posted by Dave Ashurst
On a three wheeler with two front wheels and one rear wheel, what if I could reduce body roll to zero. Would it be a good thing?
I mean if I made the front anti-roll totally rigid but still had full vertical suspension all round, would there be there any handling disadvantage?
Anything bad at all? Risk of tipping over without warning perhaps?
Depends how bumpy the road is! For a thought exercise consider how the handling of a beam front axle (read truck) compares to independent suspension
(read modern car)
Tipping over is hardly an issue with even the best of sticky three.
Cheers!
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
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Building: enthusiasm for getting my car back on the road!
posted on 30/6/14 at 08:49 PM
Hi Dave,
It's done today on some main stream cars - such as LandRover and Range Rover. It's called Active Roll Control.
It stops the body rolling during cornering and as such it's considered a comfort feature.
It can stop geometry change in the suspension when the body rolls and handling effects caused by that but it can't stop the weight transfer.
Handling doesn't change directly because of this system.
Active Roll Control is done with an Anti-Roll bar and a Hydraulic actuator controlled by an ECU with a hydraulic pump and some valves.
It also reduces the drivers opportunities for sensing slip during limit handling manouvres. That means you can't tell what's happening
when the car slides and it feels like the slide happens more abruptly with less warning.
It doesn't but most drivers rely upon the body roll to warn them or at least allow them to sense when the car is cornering hard and
on-the-limit.
You need to tune the Slip-Control-System and the tyre grip-slip behaviour to make it manageable.
quote:Originally posted by Wadders
Just curious, but how would you totally eliminate roll while still maintaining useful suspension movement?
Al.
Very easy just design the roll axis to pass through the cg.
The roll axis is a virtual line drawn between the front and rear roll centres.
In fact if the roll axis is above the cg height they body will lean into the corner like a motorcycle.
Both have been tried and found to result in very odd handling.
[Edited on 30/6/14 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
I don't think you'd tip over unless your CofG was high compared to your track width, but you may end up lifting a wheel off the ground if
they cannot move independently. If they can move independently then you will get body roll unless, as BritishTrident says, you can get the CofG level
to or beneath the roll axis (or use a active roll control). To be fair even without independent movement you will still get a small amount of body
roll due to the flex in the tyres. Also if the wheels are rigidly linked you've basically got a live axle, and there's plenty of info on
that subject!
If you wanted to use an active roll control system, there may be some mileage in that. I vaguely remember one of the F1 teams had something similar
and it was disliked. If it allows you to keep your tyres vertical to the road then it helps maintain a large, and square contact patch. There is a
fair amount of electrickery involve from what I know
In summary I don't think there'd be any benefit to a mechanical system - probably quite the opposite. However if you think you have a
winning idea don't let me discourage you from trying it
If disfunction is a function, then I must be some kind of genius.
quote:Originally posted by britishtrident
Very easy just design the roll axis to pass through the cg.
Plenty of vintage specials (cars like John Bolster's Bloody Mary) are very close to this condition.
With independent suspension the main problem is jacking as a result of the high roll centre (though this can be limited by limiting the available
droop movement, albeit with side effects of its own).
With beam axles (as Bloody Mary and other low-slung vintage jobs with big wheels), there is no jacking effect, but the remaining problem is that the
driver finds it more difficult to sense the build-up of lateral forces, hence the approaching limit of grip. Many single seaters have run so stiff in
front roll that they effectively corner flat, though... you just need a top-notch driver who can judge and respond to other cues.
With a tadpole trike, bear in mind that if you run the front so stiff that it allows negligible roll (and assuming your roll axis isn't
coincident with your CoG), some of the lateral weight transfer will be translated into compression of the rear spring, so it will tend to make the car
squat rather than roll.
quote:Originally posted by britishtrident
Very easy just design the roll axis to pass through the cg.
Plenty of vintage specials (cars like John Bolster's Bloody Mary) are very close to this condition.
With independent suspension the main problem is jacking as a result of the high roll centre (though this can be limited by limiting the available
droop movement, albeit with side effects of its own).
With beam axles (as Bloody Mary and other low-slung vintage jobs with big wheels), there is no jacking effect, but the remaining problem is that the
driver finds it more difficult to sense the build-up of lateral forces, hence the approaching limit of grip. Many single seaters have run so stiff in
front roll that they effectively corner flat, though... you just need a top-notch driver who can judge and respond to other cues.
With a tadpole trike, bear in mind that if you run the front so stiff that it allows negligible roll (and assuming your roll axis isn't
coincident with your CoG), some of the lateral weight transfer will be translated into compression of the rear spring, so it will tend to make the car
squat rather than roll.
I can't quite get my head round this could you expand? Do you mean if the front and rear slip angles are different the lateral force is not at
right angles to the centerline and there will be a longitudinal component acting through the c of g. Surely this will be proportional to the slip
angles at small angles and negligible?
Cheers!
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
Photo Archive
Building: Fisher Fury 4.3 V8 with Speeduino
posted on 3/7/14 at 06:34 AM
quote:Originally posted by Badger_McLetcher
If you wanted to use an active roll control system, there may be some mileage in that. I vaguely remember one of the F1 teams had something similar
and it was disliked. If it allows you to keep your tyres vertical to the road then it helps maintain a large, and square contact patch. There is a
fair amount of electrickery involve from what I know
quote:Originally posted by britishtrident
Very easy just design the roll axis to pass through the cg.
Plenty of vintage specials (cars like John Bolster's Bloody Mary) are very close to this condition.
With independent suspension the main problem is jacking as a result of the high roll centre (though this can be limited by limiting the available
droop movement, albeit with side effects of its own).
With beam axles (as Bloody Mary and other low-slung vintage jobs with big wheels), there is no jacking effect, but the remaining problem is that the
driver finds it more difficult to sense the build-up of lateral forces, hence the approaching limit of grip. Many single seaters have run so stiff in
front roll that they effectively corner flat, though... you just need a top-notch driver who can judge and respond to other cues.
With a tadpole trike, bear in mind that if you run the front so stiff that it allows negligible roll (and assuming your roll axis isn't
coincident with your CoG), some of the lateral weight transfer will be translated into compression of the rear spring, so it will tend to make the car
squat rather than roll.
I can't quite get my head round this could you expand? Do you mean if the front and rear slip angles are different the lateral force is not at
right angles to the centerline and there will be a longitudinal component acting through the c of g. Surely this will be proportional to the slip
angles at small angles and negligible?
Cheers!
More to do with the lateral disposition of the wheels relative to the vehicle centre line.
Easier to get your head around if you think about it reversed ie. a normal trike, a kids pedal trike or Reliant style 3 wheeler.
Corner one of those on the limit and as the inside rear starts to lift the weight transferred not only to the rear outside but also to to front
wheel increases...... which is why convention 3 wheelers have nasty reputation for flipping over.
The reverse trike configuration is of course more stable
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
quote:Originally posted by britishtrident
Very easy just design the roll axis to pass through the cg.
Plenty of vintage specials (cars like John Bolster's Bloody Mary) are very close to this condition.
With independent suspension the main problem is jacking as a result of the high roll centre (though this can be limited by limiting the available
droop movement, albeit with side effects of its own).
With beam axles (as Bloody Mary and other low-slung vintage jobs with big wheels), there is no jacking effect, but the remaining problem is that the
driver finds it more difficult to sense the build-up of lateral forces, hence the approaching limit of grip. Many single seaters have run so stiff in
front roll that they effectively corner flat, though... you just need a top-notch driver who can judge and respond to other cues.
With a tadpole trike, bear in mind that if you run the front so stiff that it allows negligible roll (and assuming your roll axis isn't
coincident with your CoG), some of the lateral weight transfer will be translated into compression of the rear spring, so it will tend to make the car
squat rather than roll.
I can't quite get my head round this could you expand? Do you mean if the front and rear slip angles are different the lateral force is not at
right angles to the centerline and there will be a longitudinal component acting through the c of g. Surely this will be proportional to the slip
angles at small angles and negligible?
Cheers!
More to do with the lateral disposition of the wheels relative to the vehicle centre line.
Easier to get your head around if you think about it reversed ie. a normal trike, a kids pedal trike or Reliant style 3 wheeler.
Corner one of those on the limit and as the inside rear starts to lift the weight transferred not only to the rear outside but also to to front
wheel increases...... which is why convention 3 wheelers have nasty reputation for flipping over.
The reverse trike configuration is of course more stable
Nope that can't be the explanation if that were the case the weight would be transferred towards the two wheel end!
Cheers!
You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a
chainsaw
I can't quite get my head round this could you expand? Do you mean if the front and rear slip angles are different the lateral force is not at
right angles to the centerline and there will be a longitudinal component acting through the c of g. Surely this will be proportional to the slip
angles at small angles and negligible?
Cheers!
Is it the lateral weight transfer/squat bit you're struggling with?
Easy way to visualise it is to:
* Imagine a trike with a bit of string tied to its centre of gravity (the point at which lateral forces will be acting on the sprung mass when
you're cornering). The piece of string represents the lateral cornering force. Imagine that the steering is locked and the outside front wheel
is glued to the ground so it can never slide.
* Pull directly sideways on the bit of string until the opposite ('inside' ) front wheel just lifts of the ground (and lets assume it
doesn't slide first). This represents the point at which you've got 100% load transfer.
* All the weight that was on the inside wheel has now gone somewhere else... it's now being carried by the other wheels, yes?
* You will hopefully be able to visualise that if the CoG was actually on the front axle centreline, that weight would have simply transferred,
100%, straight over to the other front wheel. But the CoG will never be that far forward.
* If the CoG was in front of the front axle line (even less likely, but bear with me), you will hopefully be able to visualise that pulling on
a piece of string attached to it would not only transfer all the weight from the 'inside' front wheel onto the outer front wheel, but it
will have pulled some of the weight from the rear wheel forward onto the outside front, too. Assuming it didn't slide first, if you kept on
pulling the car would eventually tip across and forward so that both the rear and inside front wheels are off the ground, and it's balanced
entirely on the outside front.
* Now think about what happens if the CoG is behind the front axle line (which is what we have in reality). Pulling on that piece of string
attached to it will pull weight from the inside front wheel, partly onto the outside front, but also partly backward onto the rear wheel.
* That extra weight being pulled onto the rear wheel will compress the spring and cause the car to squat a bit.
Photo Archive
Building: Scimitar Sabre turbo and SS1 Turbo hillclimbers
posted on 3/7/14 at 07:50 PM
A lot of single seater race cars use near zero roll front setups, often coupled with a monoshock. Both pushrods connect to the monoshock, with
Belleville washers to allowaa a tad of sideways movement. Does make for a car that needs a near perfect prepared ssurface though! Anything used on the
road is unlikely to be suitable in imho
"Racing is life, everything else, before or after, is just waiting"---Steve McQueen
Yes, monoshocks are interesting and a bit of a black art. I'm not going to say too much about what I think I know about how they work,
other than to say that they're not quite as compromised on bumpy surfaces as you might expect... which explains why, contrary to all
expectations, they've become very successful on relatively bumpy and steeply cambered UK hillclimb tracks in recent years.
Monoshock or not, there has been a trend in recent years for for single seaters to run very stiff in roll at the front and very soft in
roll at the back, making them almost analogous to tadpole trikes, in fact, in terms of weight transfer characteristics.
One of the features that made the original Range Rover work was the roll-centres were located high enough to allow relatively soft wheel rates
without using anti-roll bars, endowing with it both saloon car like road manners and good off road traction.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
Photo Archive
Building: Scimitar Sabre turbo and SS1 Turbo hillclimbers
posted on 4/7/14 at 01:39 PM
quote:Originally posted by Sam_68
Yes, monoshocks are interesting and a bit of a black art. I'm not going to say too much about what I think I know about how they work,
other than to say that they're not quite as compromised on bumpy surfaces as you might expect... which explains why, contrary to all
expectations, they've become very successful on relatively bumpy and steeply cambered UK hillclimb tracks in recent years.
Monoshock or not, there has been a trend in recent years for for single seaters to run very stiff in roll at the front and very soft in
roll at the back, making them almost analogous to tadpole trikes, in fact, in terms of weight transfer characteristics.
Youre right, often what circuit racers can see as negatives with zero droop, uber stiff in roll single seater monoshock front ends, hillclimbers see
as an advantage. Often see the run off guys waving a wheel in the air, doing most of their cornering on one front wheel which along with more
Ackermann can help to put temp into the tyres on short runs such as hillclimbs. Most hills SS use mega soft rear ends with a 3rd spring setup to stop
it dragging its bum like a dog with worms, as the aero loads add to the springing demands of the soft corner coilovers. as theres no minimium weight
limit, most of the fast SS are monoshock as its one less damper to 'carry' and often the 3rd spring at the rear is made up of bump rubbers
rather than a steel spring for same reason. GWJs Raptor is a lovely design both F&R
"Racing is life, everything else, before or after, is just waiting"---Steve McQueen
