All I know is, that if you want to hoon about like a mad thing at times, you need to know what you are driving and how differetnly they react and need to be driven.
not that i ever hoon about ever you understand.
|
|
So where can you find out what the weight distribution of your car is?
|
Possibilities include;
Look in your handbook, ask the dealer, ask the manufacturer, ask to use a VOSA weighbridge, and measure it yourself, ask to use a weighbridge at a scrapyard, etc, etc
|
always best to have a few bags of sand in the front hood of an old beetle.
also helps when you weigh the things in because it ups yourpound per tonnage
|
|
|
Possibilities include;
It might be useful to drive the thing round a few bends under various weather conditions and degrees of acceleration and deceleration.
That may not give you the exact weight distribution, but if you have sensitive trousers it will certainly give you some idea. However, since weight distribution, while important, is far from being the only factor determining a car's behaviour in corners, it will give you something more useful: an idea of how the jalopy actually behaves in corners.
|
That's an interesting observation, NC, and one that immediately strikes me as both correct, and now you mention it, obvious.
Would another way of putting it be that the car goes round a corner because all four wheels are no longer aligned in a fore and aft direction, soit is not possible for the moving vehicle to continue rolling along in a straight line without some of the wheels scrubbing the road.
The scrubbing effect will exert a turning moment, the final result of which will reach equilibrium when each wheel alters direction so as to minimise the force it experiences. So the combined effect will be that the forces on each wheel will be equalised.
Hence it is not meaningfull to say that any pair is actually exerting the turning effect - they all are?
So if the rear wheels were on casters, the car would not steer because it would be impossible to transfer any force to them?
|
Tyres on my Focus hatchback wore fairly evenly all round.
Suggests to me the back wheels do a similar amount of work to the front.
|
>>So if the rear wheels were on casters, the car would not steer
Or, perhaps, if the rear tyres had less tread than the front ones?
;>)
Has anyone ever been expelled from this forum?
|
>>Hence it is not meaningfull to say that any pair is actually exerting the turning effect - they all are?
>>So if the rear wheels were on casters, the car would not steer because it would be impossible to transfer any force to them?
Yes, absolutely Cliff, I agree with both points you make - that's a good way of putting it.
|
Wasn't there a big argument a while back (from one contributor anyway) about whether a car with castors at the back could get round corners? (FWIW I'm in the "no" camp).
While I wouldn't defer to Clarkson on these matters, I think "bunkum" is a bit harsh. Given the front biased weight distribution of a FWD, the front wheels are transmitting more cornering force. They also have to get the power down, and do by far the biggest part of the braking. So apart from the cornering force and their role in the balance, not really that much for the rears to do except keep the back end off the floor...
Experience suggests that hard driving hammers the fronts much more than the rears.
Most of everything else Clarkson says is bunkum though.
|
The front wheels of a front-drive car propel the car, make the initial steering effort, carry in most cases more than half its weight and of course deploy most of the car's braking effort when it is travelling forward.
It seems perverse therefore to claim that they don't do most of the work. It may not be quite as perverse as it seems, NC just about manages to convince us, but perverse all the same. All you have to do is look at the size of the bearings, brakes and shock absorbers compared to the back ones which have little to do by comparison. Or the wear rate of the front tyres in say a V6 front-drive Alfa Romeo.
Obviously these components are bigger and wear out faster because they have the same amount of work to do. Stands to reason (not).
The whole point about angrily citing perfect theoretical smooth-road neutral cornering is that it doesn't tell anyone but an engineer anything of practical use. In real life a more intuitive approach gives better results, irksome as that may seem to a theory man.
|
Both Lud and Manatee really should re-read my post - they've both mis-interpreted it.
|
mis-interpreted it.
... not without an element of volition in my case. Sorry NC...
:o}
|
>>... not without an element of volition in my case
or mine ;-)
|
Obviously these components are bigger and wear out faster because they have the same amount of work to do.
All I can say is that on the FWD cars I have owned, the front tyres wear about 3 times faster than the rears. I think that proves adequately that they 'do more work', which I rationalise by (a) traction wear, especially under heavy acceleration, and (b) steering wear, where the fronts scuff more because they point further from the line of travel than the rears (especially on a car with built-in rear passive steering).
|
All I can say is that on the FWD cars I have owned the front tyres wear about 3 times faster than the rears.
So why have a 4wd in the first place?
|
All I can say is that on the FWD cars I have owned the front tyres wear about 3 times faster than the rears.
So why have a 4wd in the first place?
Taking your question at face value, FB: FWD = Front-wheel drive, not 4WD. Nuff said?
|
|
Tyres on my Focus hatchback wore fairly evenly all round. Suggests to me the back wheels do a similar amount of work to the front.
>>
Suggests to me that you don't thrash it around like a maniac with both feet on the pedal!
J. Clarkson wouldn't understand ackerman steering if it hit him on the nose. nor it seems would anyone else on this thread.
|
Tell us all about Ackerman steering Farmer Boy - I'm intrigued.
|
Here's a bit of fun about Ackerman steering;
i949.photobucket.com/albums/ad338/Number_Cruncher_...g
As you'll see, the information given in many textbooks about Ackerman steering is actually a bit duff.
|
Here are the notes for the graph:-
The graph shows changes in track rod length which would be needed to maintain true rolling conditions as corner radius varies.
The intersection is the distance behind the front axle where the projection of the line joining the steering axis and the outer track rod end intersects the vehicle centreline.
Many text books suggest this point should be near the rear axle, i.e., 1 wheelbase behind the front axle. The graph shows this is not true, and for true rolling, an intersection about 0.6 wheelbases behind the front axle gives much less error.
|
|
|
|
|
So where can you find out what the weight distribution of your car is?
At home. Use the bathroom scales, a stout board, and a brick.
|
If shopping trolleys had fixed rear wheels they would corner properly, because the back wheels could then exert a useful force.
Similarly if a car had casters (I've looked up the word and "o" or "e" is correct) on the back it's much-vaunted front wheel drive would not "pull you round the corner" but merely change lanes in a straight line.
(Or imagine a car balanced by a gyroscope with no rear wheels!)
|
If shopping trolleys had fixed rear wheels they would corner properly because the back wheels
Do you know why shopping trolleys have casters on all wheels? Just try steering a line of about 20 and you'll find out!
|
|
Costco trolleys have fixed rear wheels and steer like a car, I would not like to try driving a car with castors on the back. Probably be like well worn rear tyres in the wet.
|
|
|
|
If shopping trolleys had fixed rear wheels they would corner properly because the back wheels could then exert a useful force.
No they would not.Steering input is at the rear so fixed rear wheels would necessitate scrubbing sideways or twisting about the longditudinal centre line,very hard on the wrists with a loaded trolley.Fixed wheels at the front would work better,a bit like an old fashioned dumper,but they took a bit of practice to get used to the rear wheel steering. On a flat smooth surface castors all round enables the greatest manouverability.
|
|
I find the Costco type trolley far easier to control than a standard "4 castor" trolley, thats why SWMBO "drives" the standard ones, she drives as though her car is on 4 castors anyway. And no she does not read this!
|
|
|
|
|
|
|
|
