Multiple Choice Driving Dynamics Quiz
29 February 2004, 06:15 PM
#31
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Nice one 
Have to say I was really clutching at straws with question 10, so there was a 75% chance that I'd get it wrong 
Quite impressed I got the rest right though, had to think about a few of them in terms of physical effect of weight transfer etc but gotta admit I was never 100% sure on some.
Well chuffed, now I've just gotta learn to put the theory into practice
Have to say I was really clutching at straws with question 10, so there was a 75% chance that I'd get it wrong Quite impressed I got the rest right though, had to think about a few of them in terms of physical effect of weight transfer etc but gotta admit I was never 100% sure on some.Well chuffed, now I've just gotta learn to put the theory into practice
29 February 2004, 07:03 PM
#32
Possible error in Webmaster's answers
Surely question 4 should have had an option d) Fuel surge?
This burning question has never been satisfactorily explored (or does it only apply on Scottish tarmac?).
This burning question has never been satisfactorily explored (or does it only apply on Scottish tarmac?).
29 February 2004, 07:53 PM
#33
Hi simon, good explanations on most, but i definately dont agree with your answer to 5 for the following reason.
When you place a heavy weight in the boot, you are adding weight outside of the wheelbase to the rear, this has the effect of raising the front of the car and lowering its grip levels signifactly, which will have a more detrimental effect on the cars handling than the loss of traction effect of increased load on the rear tyres.
If you would have said that the weight was toward the rear of the car but inside the wheelbase then i would have agreed 100% with you but as you said in the boot, which is outside the wheelbase, i dont.
I grew up rallying a hillman imp, a rear engined car outside the wheelbase, with a fuel tank mounted over the front axle, and as weight dropped at the front the tilt effect of the rear becoming efectively heavier induced major understeer. The same happens with the lambourghini Miura which is why they are a nightmare car to drive as the handling goes towards major understeer as the fuel tank runs dry.
Once you overcome the initial understeer issues, the chassis is then more liable to oversteer, which is why cars like the Imp and early 911 have snap oversteer tendencies, but the initial problem of understeer has to be overcome first, and that is why to be fast in cars like these you have to be brave and use weight transfer techniques more than conventional chassis designs.
I'll go with 10 but still think that is over simplified for an AWD car, but i agree with the basic principles, which is why i chose the same answer for a RWD car.
Good stuff, more of the same please.
When you place a heavy weight in the boot, you are adding weight outside of the wheelbase to the rear, this has the effect of raising the front of the car and lowering its grip levels signifactly, which will have a more detrimental effect on the cars handling than the loss of traction effect of increased load on the rear tyres.
If you would have said that the weight was toward the rear of the car but inside the wheelbase then i would have agreed 100% with you but as you said in the boot, which is outside the wheelbase, i dont.
I grew up rallying a hillman imp, a rear engined car outside the wheelbase, with a fuel tank mounted over the front axle, and as weight dropped at the front the tilt effect of the rear becoming efectively heavier induced major understeer. The same happens with the lambourghini Miura which is why they are a nightmare car to drive as the handling goes towards major understeer as the fuel tank runs dry.
Once you overcome the initial understeer issues, the chassis is then more liable to oversteer, which is why cars like the Imp and early 911 have snap oversteer tendencies, but the initial problem of understeer has to be overcome first, and that is why to be fast in cars like these you have to be brave and use weight transfer techniques more than conventional chassis designs.
I'll go with 10 but still think that is over simplified for an AWD car, but i agree with the basic principles, which is why i chose the same answer for a RWD car.
Good stuff, more of the same please.
29 February 2004, 08:21 PM
#34
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Question 10
What is the most likely effect on a car if you increase the rebound resistence of the front dampers
a) More front end grip under acceleration
b) More front end grip under braking
c) More rear end grip under acceleration
d) More rear end grip under braking
Answer c) More rear end grip under acceleration
This is a tricky one also. The reason for this is that increasing rebound resistence effectively lifts the front wheels off the ground (exaggerated, obviously) when the body of the car rolls backwards (under acceleration). This means that the weight of the car is being supported more by the rear tyres, which means more grip at the rear.
What is the most likely effect on a car if you increase the rebound resistence of the front dampers
a) More front end grip under acceleration
b) More front end grip under braking
c) More rear end grip under acceleration
d) More rear end grip under braking
Answer c) More rear end grip under acceleration
This is a tricky one also. The reason for this is that increasing rebound resistence effectively lifts the front wheels off the ground (exaggerated, obviously) when the body of the car rolls backwards (under acceleration). This means that the weight of the car is being supported more by the rear tyres, which means more grip at the rear.
you gave up too easily on that one !!I don't believe any of the Q10 answers are correct
It should be.... e) Less rear end grip under acceleration
Increasing the front rebound rate slows the rate of rise of the front of the car, this delays the rise in CofG height (which determines the weight transfer for any given longditudinal G force) This is why a typical drag race front shock has a 90:10 resistance ratio rating, 90 being the compression and 10 being the rebound, the aim being to get the front of the car to lift quickly hence increasing CGH and resulting weight transfer to the rear due to acceleration g force
Andy
29 February 2004, 08:27 PM
#35
LOL
I am still seriously hung over (mates stag night if you were thinking i am an alchoholic) and not upto a fight at braincell level yet.
I should get my books out, but i didnt want to have anything but my own memory for this stuff as its fun that way. I might be back.
I am still seriously hung over (mates stag night if you were thinking i am an alchoholic
) and not upto a fight at braincell level yet. I should get my books out, but i didnt want to have anything but my own memory for this stuff as its fun that way.
I might be back.
Last edited by johnfelstead; 29 February 2004 at 08:28 PM.
29 February 2004, 08:51 PM
#37
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john was probably just feeling a little off colour
What kind of pant-slip angle were you running?
As for how many I'd have got wrong, it'd be churlish to comment after the fact. However, I do feel that there's room for differences of interpretation/opinion on one or two, as, as written, they seem to assume that "all other things are equal", where in practice, all things are not equal. Another vote for more of the same though, good stuff!
29 February 2004, 08:58 PM
#38
LOL here we go.. this is what it's all about
Re : weight in the rear of the car.
Interesting thought about a reduction in load on the front tyres. It would interesting to measure the difference, but I would suggest that any reduction would be absolutely minute.
The most direct result of the adding of weight would be on the rear axle, but in addition on the increase in the polar moment of inertia which would also add to the oversteer tendency in this case.
In order to put enough weight in the boot to have a noticeable effect on the front tyre loads would mean the need for something SERIOUSLY heavy, and to be honest, by that time the car would be an absolute disaster to drive as the c/g and polar moment of inertia would be horrific.
----
Andy.F
Interesting theory
Unfortunately, the rise in c/g due to body pitch is next to zero in anything but the most unusual of circumstances. Think of it this way.. The weight of the car needs to be supported by the four contact patches. If during rearward pitch, the front tyres are being pulled away from the ground, the load they WERE supporting, needs to be supported by the rears.
All the best
Simon
here we go.. this is what it's all about Re : weight in the rear of the car.
Interesting thought about a reduction in load on the front tyres. It would interesting to measure the difference, but I would suggest that any reduction would be absolutely minute.
The most direct result of the adding of weight would be on the rear axle, but in addition on the increase in the polar moment of inertia which would also add to the oversteer tendency in this case.
In order to put enough weight in the boot to have a noticeable effect on the front tyre loads would mean the need for something SERIOUSLY heavy, and to be honest, by that time the car would be an absolute disaster to drive as the c/g and polar moment of inertia would be horrific.
----
Andy.F
Interesting theory
Unfortunately, the rise in c/g due to body pitch is next to zero in anything but the most unusual of circumstances. Think of it this way.. The weight of the car needs to be supported by the four contact patches. If during rearward pitch, the front tyres are being pulled away from the ground, the load they WERE supporting, needs to be supported by the rears.
All the best
Simon
29 February 2004, 09:01 PM
#39
rofl @ greasemonkey
Agreed re interpretation, although the disclaimers of "in the most likely cases", etc, etc. were there for that very reason.
In addition, as you are well aware, alomst any change in chassis set-up effects just about every other setting, so we need to stick to "all things being equal" type questions where possible I guess.
All the best
Simon
Agreed re interpretation, although the disclaimers of "in the most likely cases", etc, etc. were there for that very reason.
In addition, as you are well aware, alomst any change in chassis set-up effects just about every other setting, so we need to stick to "all things being equal" type questions where possible I guess.
All the best
Simon
29 February 2004, 09:27 PM
#40
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Originally Posted by Fat Boy
Surely question 4 should have had an option d) Fuel surge?
This burning question has never been satisfactorily explored (or does it only apply on Scottish tarmac?).
This burning question has never been satisfactorily explored (or does it only apply on Scottish tarmac?).
A particularly strong magnetic flux runs through the Citroen factory in Vigo where the Saxo is produced. This flux induces a unique, though normally harmless, magnetic charge in the cars' components as they run down the production line.
Under normal circumstances this charge is not noticeable, but under certain freak conditions, rather than attract paper clips and iron filings, it is known to attract spurious items of clothing, notably headwear or jackets with a curious check print, known in the scientific community as burberranus vulgaris.
Long term exposure to the Saxo's magnetic charge can result in a permanent magnetic realignment of the driver, and again while not usually harmful, problems can then result, including a long-term attraction to burberranus vulgaris.
Another, less well-known symptom can present if the owner subsequently buys a car produced in a factory with a strong opposing magnetic charge, like, for example, a Subaru Impreza. The opposing charge in the bodyshell realigns the petrol in the tank, but when the magnetically oriented driver climbs aboard, it can quite literally be repulsed, bonding at a molecular level in the fuel lines, and resulting in the phenomenon commonly called fuel surge (but more accurately fuel solidification).
Needless to say, this phenomenon is most commonly experienced in areas with strong concentrations of ferric oxide, like Scotland.
Last edited by greasemonkey; 29 February 2004 at 09:39 PM.
29 February 2004, 09:29 PM
#41
i need to take you cross country in a cossie with a large server in the boot simon, it's hilareous how the car becomes an understeering pig then goes from understeer to snap power oversteer if you use a bit of weight transfer. I am sticking to my answer as i know from my own experience that is the practical effects i have seen in all the cars i have driven. You are right about the polar moments going nuts but thats half the fun of driving, or is that just me?
What would be cool would be to do a lot of these kind of quizes and then find out where people have disagreements and do practical tests on these points at bruntingthorpe to see who is correct, when they are put into practice.
I am sticking to my answer as i know from my own experience that is the practical effects i have seen in all the cars i have driven. You are right about the polar moments going nuts but thats half the fun of driving, or is that just me? What would be cool would be to do a lot of these kind of quizes and then find out where people have disagreements and do practical tests on these points at bruntingthorpe to see who is correct, when they are put into practice.
29 February 2004, 09:32 PM
#42
Originally Posted by greasemonkey
Another, less well-known symptom can present if the owner subsequently buys a car with a plastic fuel tank, like, for example, a Subaru Impreza. The plastic tank reduces petrol's normal immunity to magnetic fields, and thus it can quite literally be repulsed from the magnetically oriented driver, bonding at a molecular level in the fuel lines, and resulting in the phenomenon commonly called fuel surge (but more accurately fuel solidification).
but its a steel tank in an Impreza.
29 February 2004, 10:34 PM
#45
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Lol Simon ! It's not a theory, its the laws of physics !! Just because you stiffen a damper, you cant make the car transfer more weight to the rear, not in steady state which I presume your acceleration is ? or did you just mean a 'jab' at the fast pedal ?
If you can make weight transfer via any other means than
G x Mass x CGH / WB ......then I'll have some
Andy
If you can make weight transfer via any other means than
G x Mass x CGH / WB ......then I'll have some
Andy
29 February 2004, 10:51 PM
#46
Hi Andy
Correct, It's not in steady state, as the car body is in trasition, pitching backwards. Your theory is also transitional state as you are talking about the time it takes to move the c/g.
There are many forms of load transfer in vehicle dynamics that do not simple result in the formula you posted. Otherwise, there would be no way of altering the handling of a car, other than moving either the c/g, changing the mass, or the wheel base.
So..
During the pitching motion of the car, the dampers play a large part in the load transfer front to rear. The same as they do during the roll motion of the car from inside to outside.
All the best
Simon
Correct, It's not in steady state, as the car body is in trasition, pitching backwards. Your theory is also transitional state as you are talking about the time it takes to move the c/g.
There are many forms of load transfer in vehicle dynamics that do not simple result in the formula you posted. Otherwise, there would be no way of altering the handling of a car, other than moving either the c/g, changing the mass, or the wheel base.
So..
During the pitching motion of the car, the dampers play a large part in the load transfer front to rear. The same as they do during the roll motion of the car from inside to outside.
All the best
Simon
29 February 2004, 11:00 PM
#48
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Ok, I'll let you off I was talking about steady acceleration, so with your firm rebound damper I agree you would _initially_ get a marginal increase in grip just as you hit the pedal
Andy
I was talking about steady acceleration, so with your firm rebound damper I agree you would _initially_ get a marginal increase in grip just as you hit the pedal Andy
29 February 2004, 11:03 PM
#49
LOL
Thanks
But, you were also talking about a transitional state, not steady state, as you were saying that "Increasing the front rebound rate slows the rate of rise of the front of the car, this delays the rise in CofG height".
How is that to do with steady state? Or have I misunderstood something?
Cheers
Simon
Thanks
But, you were also talking about a transitional state, not steady state, as you were saying that "Increasing the front rebound rate slows the rate of rise of the front of the car, this delays the rise in CofG height".
How is that to do with steady state? Or have I misunderstood something?
Cheers
Simon
29 February 2004, 11:07 PM
#50
"Awe"
Greasemonkey,
I take my pants off to you. You may have problems with your Sti numbering system, but you certainly know your stuff with regard to fuel surge. At last, a deeply satisfactory answer to this worrying phenomenon.
A nation salutes you.
I take my pants off to you. You may have problems with your Sti numbering system, but you certainly know your stuff with regard to fuel surge. At last, a deeply satisfactory answer to this worrying phenomenon.
A nation salutes you.
29 February 2004, 11:15 PM
#51
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Ok, going back to transients, I still maintain that the increase in CGH _can_ result in greater weight transfer than a quick tug on the unsprung mass.
Again, it all depends on the car but you must have seen these drag cars with the very soft front dampers that allow the nose to leap up, that's all about lateral transfer due to CGH.
If in your car you only accelerate for a few milliseconds then stiffer rebound is the way to go
Again, it all depends on the car but you must have seen these drag cars with the very soft front dampers that allow the nose to leap up, that's all about lateral transfer due to CGH.
If in your car you only accelerate for a few milliseconds then stiffer rebound is the way to go
29 February 2004, 11:58 PM
#52
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Shock!
Originally Posted by Fat Boy
Greasemonkey,
I take my pants off to you. You may have problems with your Sti numbering system, but you certainly know your stuff with regard to fuel surge. At last, a deeply satisfactory answer to this worrying phenomenon.
A nation salutes you.
I take my pants off to you. You may have problems with your Sti numbering system, but you certainly know your stuff with regard to fuel surge. At last, a deeply satisfactory answer to this worrying phenomenon.
A nation salutes you.
As for the STi numbering system, I have no problems with it, it's the dull b&gg*rs who get it wrong who have the problem!
Anyway, what's the obsession with pants? First Simon's asking about them, and now you're desperate to take yours off. Has everyone got a pant fetish today???
01 March 2004, 10:51 AM
#53
Andy
(This is a useful debate IMHO).
You state that if you only accelerate for a second then stiffer front rebound is the way to go, and yet you say that the drag car is the way to go also?
By your first statement I assume you are agreeing still that during the rearward pitch transient of the car body, the increased rebound resistence of the front does indeed transfer more load rearward?
If this is the case, we are in agreement that the statement is true during transients, so what effect could the dampers have during steady state?
All the best
Simon
(This is a useful debate IMHO).
You state that if you only accelerate for a second then stiffer front rebound is the way to go, and yet you say that the drag car is the way to go also?
By your first statement I assume you are agreeing still that during the rearward pitch transient of the car body, the increased rebound resistence of the front does indeed transfer more load rearward?
If this is the case, we are in agreement that the statement is true during transients, so what effect could the dampers have during steady state?
All the best
Simon
01 March 2004, 11:54 AM
#55
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"If in your car you only accelerate for a few milliseconds " was my quote, not a full second Simon !!
Quote Simon - "during the rearward pitch transient of the car body, the increased rebound resistence of the front does indeed transfer more load rearward?"
It doesn't actually transfer more load, it just allows the SAME LOAD to come off the front end _quicker_
This however ultimately delays the rise in CGH which WOULD increase the overall load transfered......so it's swings and roundabouts.
This is typical of trying to look at the effect of some adjustment in isolation, for example the increased rebound rate may result in jacking down of the front end on a bumpy surface, further reducing rear end grip under acceleration......but you know that anyway
I think the key to less ambiguity is ensuring the question is applied to a specific spec of vehicle. If this question was applied to a circuit car running stiff springs then I would agree with your answer, if it was applied to a drag car, I'd disagree. On a road car it could fall either way.
Andy
Quote Simon - "during the rearward pitch transient of the car body, the increased rebound resistence of the front does indeed transfer more load rearward?"
It doesn't actually transfer more load, it just allows the SAME LOAD to come off the front end _quicker_
This however ultimately delays the rise in CGH which WOULD increase the overall load transfered......so it's swings and roundabouts.
This is typical of trying to look at the effect of some adjustment in isolation, for example the increased rebound rate may result in jacking down of the front end on a bumpy surface, further reducing rear end grip under acceleration......but you know that anyway
I think the key to less ambiguity is ensuring the question is applied to a specific spec of vehicle. If this question was applied to a circuit car running stiff springs then I would agree with your answer, if it was applied to a drag car, I'd disagree. On a road car it could fall either way.
Andy
07 March 2004, 10:34 PM
#56
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Here's mine - have to say guessing a bit on a couple as my experience is all either on road or loose surface!
1: a
2: a
3: b
4: c
5: a
6: a
7: c
8: b
9: b
10: a
11: e
1: a
2: a
3: b
4: c
5: a
6: a
7: c
8: b
9: b
10: a
11: e
07 March 2004, 10:36 PM
#57
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NUTS!!! Just noticed that there were further post and 2 more pages of them!! well I'd better check the answers and see just how much of an idiot I made of myself!!!
07 March 2004, 10:44 PM
#58
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MMM good fun!! Have to say I agree with John Felstead on Q5 - I too used to have a Hillman Imp Sport with various mods but by far the most effective for making the damn thing go round corners was the bag of cement that was situated in the front (boot). Witout it understeer was HUUUUGE problem!!!
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