Anybody got a handle on this?
The wheelchair guys get very interested in it but I'm struggling to find anything of direct relevance to cars.
(Haven't checked the SAE yet)
Effect of toe and camber on rolling resistance
Started by
Greg Locock
, Aug 29 2004 02:08
12 replies to this topic
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#2
wegmann
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Posted 31 August 2004 - 22:00
The only thing I know is that when camber increases from zero to 3 degrees, the tire spring rate decreases. This could possibly mean that the rolling resistance goes up, but I can't guarantee that at all.
There might be something in Race Car Vehicle Dynamics by Milliken & Milliken, if you have it.
If your application is the skinny roundish tires on wheelchairs, maybe motorcycle data would be more relevant?
There might be something in Race Car Vehicle Dynamics by Milliken & Milliken, if you have it.
If your application is the skinny roundish tires on wheelchairs, maybe motorcycle data would be more relevant?
#3
Greg Locock
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Posted 31 August 2004 - 22:27
No this is for cars.
Milliken includes graphs for induced drag (as he calls it) for toe variations, but not camber. I'm half inclined to use the old camber=5*toe relationship to work back to a guess.
I don't like his data much, at zero toe he shows 0.6% rolling resistance for one tyre, which is achievable, but not in a conventional passenger car tyre.
Anyway for his least unlikely curve he shows that 2 degrees of toe (say 10 degrees of camber) the rolling resistance increases from 0.9% to 1.5% (edited, I'd converted from toe to camber incorrectly)
Milliken includes graphs for induced drag (as he calls it) for toe variations, but not camber. I'm half inclined to use the old camber=5*toe relationship to work back to a guess.
I don't like his data much, at zero toe he shows 0.6% rolling resistance for one tyre, which is achievable, but not in a conventional passenger car tyre.
Anyway for his least unlikely curve he shows that 2 degrees of toe (say 10 degrees of camber) the rolling resistance increases from 0.9% to 1.5% (edited, I'd converted from toe to camber incorrectly)
#4
wegmann
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Posted 01 September 2004 - 14:25
Sorry, I looked through everything I have. I don't have any data with camber vs. rolling resistance, but let me know if you find anything.
#5
desmo
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Posted 02 September 2004 - 03:58
Assuming a reasonably elastic tire carcass, I can't intuitively think of why realistic camber changes would significantly affect rolling resistance, although, intuitively again, it seems likely toe changes might.
#6
Fat Boy
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Posted 02 September 2004 - 05:40
Interesting subject here.
There isn't much to be found about this subject. Chuck Hallum wrote some SAE papers about his tire model. The one I have in front of me is titled "Understanding Race Tires", reference number 983028. His model is all about the heating of the tire due to sliding it across the pavement.
Let me quote, "The fascinating thing about camber force (alone) is that the surface particle strikes and leaves the ground at the same point. There is no slip. Without slip there is not contact patch heating. Camber side force is generated with no contact patch frictional heat, only internal damping heat. Camber force is almost free of heat generation."
The logical conclusion is that if no heat is generated, no additional energy is expended by increasing or decreasing camber.
Toe is a different matter. While Hallum doesn't specifically cover toe, he does cover general drag due to tire slip %. It has to act in the same basic way. If I were to guess, I would say that drag due to toe is some sort of Sin function where small toe setting do not make a large difference, but as the angle is increased, the drag increases significantly.
I went to a presentation by Hallum right before he passed. He was quite clever, but, in general, I think he was just a bit off base on his tire model. A lot of his theory was 'Gospel According to Chuck' rather than conclusions based on experimentation. The experimentation that needed (needs?) to be done isn't cheap and most people don't want to pay for these types of tests for purely scientific reasons.
In practical application, I nearly always balance my toe setting (specifically the rear toe) with the speed of the circuit. High speed circuits get less toe; low speed circuits get more. If you run a high toe setting on a high speed circuit, you will see a reduction in top speed. Camber on the other hand does not seem to effect top speed at all. Often, I'll end up running higher camber settings on a high speed circuit because it makes the car better in high speed corners. I've never seen camber effect straight line speed a bit.
There isn't much to be found about this subject. Chuck Hallum wrote some SAE papers about his tire model. The one I have in front of me is titled "Understanding Race Tires", reference number 983028. His model is all about the heating of the tire due to sliding it across the pavement.
Let me quote, "The fascinating thing about camber force (alone) is that the surface particle strikes and leaves the ground at the same point. There is no slip. Without slip there is not contact patch heating. Camber side force is generated with no contact patch frictional heat, only internal damping heat. Camber force is almost free of heat generation."
The logical conclusion is that if no heat is generated, no additional energy is expended by increasing or decreasing camber.
Toe is a different matter. While Hallum doesn't specifically cover toe, he does cover general drag due to tire slip %. It has to act in the same basic way. If I were to guess, I would say that drag due to toe is some sort of Sin function where small toe setting do not make a large difference, but as the angle is increased, the drag increases significantly.
I went to a presentation by Hallum right before he passed. He was quite clever, but, in general, I think he was just a bit off base on his tire model. A lot of his theory was 'Gospel According to Chuck' rather than conclusions based on experimentation. The experimentation that needed (needs?) to be done isn't cheap and most people don't want to pay for these types of tests for purely scientific reasons.
In practical application, I nearly always balance my toe setting (specifically the rear toe) with the speed of the circuit. High speed circuits get less toe; low speed circuits get more. If you run a high toe setting on a high speed circuit, you will see a reduction in top speed. Camber on the other hand does not seem to effect top speed at all. Often, I'll end up running higher camber settings on a high speed circuit because it makes the car better in high speed corners. I've never seen camber effect straight line speed a bit.
#7
Greg Locock
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Posted 02 September 2004 - 06:58
I like the path of the carcase argument, but that leaves me a bit puzzled as to what exactly is causing the side force to be generated by camber?
Well, I think the sideforce is a result of the overturning moment needed to twist the carcase flat to the road , which will obviously increase as the wheel is leant over. But I'm not convinced!
Well, I think the sideforce is a result of the overturning moment needed to twist the carcase flat to the road , which will obviously increase as the wheel is leant over. But I'm not convinced!
#8
Ben
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Posted 02 September 2004 - 15:01
I suppose for the effect of toe just find the lateral force for the slip angle created by the toe and multiply that force by the sin of the slip angle to find the drag force.
Not sure about camber, will re-read the Hallum papers again and check Pacejka's book.
Ben
Not sure about camber, will re-read the Hallum papers again and check Pacejka's book.
Ben
#9
Greg Locock
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Posted 02 September 2004 - 22:37
Reimpell and Stoll has an equation for estimating the increase in rolling resistance due to toe, which uses a geometrical argument similar to what you propose, and too many greek symbols.
If my guess above is correct it explains one puzzle - why doesn't camber need a slip angle to generate thrust (unlike toe). So I'm getting more comfortable with it.
So, if the tyre's cross section is stiff in torsion we'd expect more camber steer.
I've got a 2 1/2 hour session with one of the local tyre companies today, I'll try and remember to ask them about this. It could be answered inn 20 minutes on their Fltattrac machine, and it is not the oddest question I've ever asked.
If my guess above is correct it explains one puzzle - why doesn't camber need a slip angle to generate thrust (unlike toe). So I'm getting more comfortable with it.
So, if the tyre's cross section is stiff in torsion we'd expect more camber steer.
I've got a 2 1/2 hour session with one of the local tyre companies today, I'll try and remember to ask them about this. It could be answered inn 20 minutes on their Fltattrac machine, and it is not the oddest question I've ever asked.
#10
red300zx99
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Posted 03 September 2004 - 01:17
Greg, whats the oddest question you've asked? 
#11
Greg Locock
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Posted 03 September 2004 - 11:16
OK, the manufacturer is pretty persuasive that camber has no significant effect on rolling resistance, but they haven't done the experimental work.
#12
RDV
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Posted 08 September 2004 - 05:36
quote:
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wegmann-The only thing I know is that when camber increases from zero to 3 degrees, the tire spring rate decreases. This could possibly mean that the rolling resistance goes up, but I can't guarantee that at all.
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This is a geometric effect... imagine a beam(tread) held up by two springs (sidewalls)
the amount of deflection at 0 camber (both springs support tread) will be less (giving higher apparent spring rate) than if one sidewall is carrying more of the load (with tire cambered).. . this in turn causes more heat generation as the sidewall flexes , and also increases rolling resistance drag. The wider the tire , the bigger the effect, ditto the lower the aspect ratio per deg of camber.
I suspect from data I've seen that it is a second order effect compared to toe, but there is some drag, at LeMans there is a gain in top speed even with as little as 1 deg less camber. (On fronts.. rears adjust more in the 1/2 deg range), these run on 19 or 18 inch rims with quite stiff carcasses. F1 tires o lot less sensitive as 13" and high aspect ratio.
Usual range of adjustment +/- 1deg max will not show it... you need big chunks of camber to notice it in other formulae... and radials will be more sensitive than crossplies.
quote:
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Fat Boy-Let me quote, "The fascinating thing about camber force (alone) is that the surface particle strikes and leaves the ground at the same point. There is no slip. Without slip there is not contact patch heating. Camber side force is generated with no contact patch frictional heat, only internal damping heat. Camber force is almost free of heat generation."
The logical conclusion is that if no heat is generated, no additional energy is expended by increasing or decreasing camber.
--------------------------------------------------------------------------------
...er, correct as far as no heat (ok, very little) generated at contact patch, but sidewall flex and internal hysteresis will generate a reasonable amount of heat, the energy of course will be part of the total drag budget...
one of the tricks to generate heat in too-hard tires in usual UK winter conditions is to cram a lot of toe and camber to bring them up to a temp where they will begin to work... (obviously in formulae where tire heating is banned)
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wegmann-The only thing I know is that when camber increases from zero to 3 degrees, the tire spring rate decreases. This could possibly mean that the rolling resistance goes up, but I can't guarantee that at all.
--------------------------------------------------------------------------------
This is a geometric effect... imagine a beam(tread) held up by two springs (sidewalls)
the amount of deflection at 0 camber (both springs support tread) will be less (giving higher apparent spring rate) than if one sidewall is carrying more of the load (with tire cambered).. . this in turn causes more heat generation as the sidewall flexes , and also increases rolling resistance drag. The wider the tire , the bigger the effect, ditto the lower the aspect ratio per deg of camber.
I suspect from data I've seen that it is a second order effect compared to toe, but there is some drag, at LeMans there is a gain in top speed even with as little as 1 deg less camber. (On fronts.. rears adjust more in the 1/2 deg range), these run on 19 or 18 inch rims with quite stiff carcasses. F1 tires o lot less sensitive as 13" and high aspect ratio.
Usual range of adjustment +/- 1deg max will not show it... you need big chunks of camber to notice it in other formulae... and radials will be more sensitive than crossplies.
quote:
--------------------------------------------------------------------------------
Fat Boy-Let me quote, "The fascinating thing about camber force (alone) is that the surface particle strikes and leaves the ground at the same point. There is no slip. Without slip there is not contact patch heating. Camber side force is generated with no contact patch frictional heat, only internal damping heat. Camber force is almost free of heat generation."
The logical conclusion is that if no heat is generated, no additional energy is expended by increasing or decreasing camber.
--------------------------------------------------------------------------------
...er, correct as far as no heat (ok, very little) generated at contact patch, but sidewall flex and internal hysteresis will generate a reasonable amount of heat, the energy of course will be part of the total drag budget...
one of the tricks to generate heat in too-hard tires in usual UK winter conditions is to cram a lot of toe and camber to bring them up to a temp where they will begin to work... (obviously in formulae where tire heating is banned)
#13
RDV
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Posted 08 September 2004 - 05:59
re quoting Hallam
On Pacejka's latest book the bristle tire model figures quite heavily... take the same analogy to camber..
as a given particle of rubber strikes the ground, it will move i.e. slip as the carcass has a different rolling radius due to deformation , but maintains its perimeter due to belt rigidity ... if I've explained myself well... so considerable slip.... even when in a straight line
-"The fascinating thing about camber force (alone) is that the surface particle strikes and leaves the ground at the same point. There is no slip.
On Pacejka's latest book the bristle tire model figures quite heavily... take the same analogy to camber..
as a given particle of rubber strikes the ground, it will move i.e. slip as the carcass has a different rolling radius due to deformation , but maintains its perimeter due to belt rigidity ... if I've explained myself well... so considerable slip.... even when in a straight line
