What effect would complete elimination of body roll give to handling?Dave Ashurst - 30/6/14 at 08:17 PM
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?
JC - 30/6/14 at 08:24 PM
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!
Wadders - 30/6/14 at 08:30 PM
Just curious, but how would you totally eliminate roll while still maintaining useful suspension movement?
Al.
v8kid - 30/6/14 at 08:39 PM
quote:Originally posted by Wadders
Just curious, but how would you totally eliminate roll while still maintaining useful suspension movement?
Al.
Both front wheels go up and down at the same time?
smart51 - 30/6/14 at 08:43 PM
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.
v8kid - 30/6/14 at 08:44 PM
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!
JAG - 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.
Wasn't the Citroen Xantia Activa the quickest car through the elk test?
That had virtually no roll.
britishtrident - 30/6/14 at 09:25 PM
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]
Badger_McLetcher - 30/6/14 at 09:49 PM
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
Dave Ashurst - 30/6/14 at 10:02 PM
Thanks all for your excellent feedback. Very helpful food for thought and much appreciated.
I might need to buy myself some meccano.... unless you can suggest an alternative for modelling with!
best
D
nick205 - 30/6/14 at 10:35 PM
quote:Originally posted by Dave Ashurst
Thanks all for your excellent feedback. Very helpful food for thought and much appreciated.
I might need to buy myself some meccano.... unless you can suggest an alternative for modelling with!
best
D
Lego is excellent for this sort of thing. I recently built a model of a live axle setup with a panhard rod to demonstrate to my son.
Sam_68 - 2/7/14 at 06:29 PM
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.
v8kid - 3/7/14 at 05:57 AM
quote:Originally posted by Sam_68
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!
scudderfish - 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
scudderfish - 3/7/14 at 06:40 AM
Here's another more informative vid
britishtrident - 3/7/14 at 07:25 AM
quote:Originally posted by v8kid
quote:Originally posted by Sam_68
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
v8kid - 3/7/14 at 08:33 AM
quote:Originally posted by britishtrident
quote:Originally posted by v8kid
quote:Originally posted by Sam_68
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!
Sam_68 - 3/7/14 at 07:08 PM
quote:Originally posted by v8kid
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.
Simples?
[Edited on 3/7/14 by Sam_68]
Sam_68 - 3/7/14 at 07:23 PM
quote:Originally posted by scudderfish
Here's another more informative vid
Amazing to think that a tiny company like Lotus were achieving this over 30 years ago, isn't it?
Think where we might have been if the FIA hadn't effectively smothered it at birth by banning active suspension in F1...
CNHSS1 - 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
Sam_68 - 3/7/14 at 08:18 PM
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.
smart51 - 4/7/14 at 09:08 AM
For balance, here's a different point of view from an autocar test driver.
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.
CNHSS1 - 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&RSam_68 - 4/7/14 at 04:10 PM
quote:Originally posted by britishtrident
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...
... and beam axles both ends, of course, so it didn't have any problem with jacking.
You could tell it had a beam axle at the front, mind you, from the steering feedback but I guess it's a personal thing whether that
bothered you or not. I could never quite decide whether the crudity of it was annoying, or charming!
Smart51 is right though - it's easy to take up a negative attitude against body roll without really considering why you think it's a
problem. Fair enough if you need to maintain a stable aero platform on a single seater, but the old Lotus Elan was very soft in both bump and roll,
yet it remains a joy to drive that makes most modern 'Seven' types look like fidgety boneshakers in comparison.
quote:Originally posted by CNHSS1GWJs Raptor is a lovely design both F&R
As it happens, quite a bit of my early modelling and analysis to develop a personal understanding of how monoshocks function was based on the Raptor,
as I have access to the CAD drawings of the car. It is a lovely design, but I admire the PCD Saxon (also by MBO) even more - it's a jewel.
Martin Ogilvie is a hugely under-rated designer, in my opinion, who deserves a lot more recognition.
Sam_68 - 4/7/14 at 04:30 PM
quote:Originally posted by CNHSS1...Most hills SS use mega soft rear ends with a 3rd spring setup to stop it dragging its bum like a dog with
worms...
Have you by any chance seen the rear end of the latest Empire (with Willem Toet aero package)?
I haven't had much chance to get out to the Hills this year, and I only managed to catch a very brief glimpse of it at Prescott as the rear cover
was going back on. What I think I saw was a 'fully floating' transverse monoshock (ie. giving no roll resistance at all - even
from the road springs).
Discussion with the driver suggested that this may indeed be the case, though he was either completely clueless about the suspension set-up of his car
or (more likely!) playing dumb to avoid giving too much away...
I don't suppose you've seen enough of it to confirm?
CNHSS1 - 4/7/14 at 07:31 PM
I have a couple of mates running Force cars, LM and PT so have seen them develop more. When Lee Adms was running the raptor I was struck just how
simple and u cluttered it was, looked easy for a clubman to work on and maintain too, looked like a small component count and ran 3rd spring via bump
rubbers GW junior said it was purely to be lighter than a spring and most decent damper firms have data sheets for their bump rubbers (think raptor
ran ohlins or penske iirc).
I've seen the empire in its semi closed form a few events and subsequently in its tunneled and full aero form (looks like darth vaders weekend
track toy lol) but never seen it with the bodywork off tbh. It does look well sorted, not the car that's being stripped and fiddled with every 5
mins. I shall pop up to loton next weekend as its 3 mins fromhome but im not competing so will take a camera and have a squint. Wi post up if i get
any pics.
The idea of the floppy rears probably not as daft as it sounds given an uber stiff front end, should give mega traction off launch and out of the
tight cambered corners, thinking of Pardon at Prescott especially, thats one that makes most single seaters look like tesco trolleys!
