Basically, yes. It was fitted to the 504 Estate I had and probably the
404's before that but I can't remember. Very simple device and exceedingly useful in a car where you are likely to get a considerable variation of loads.
Talking of Fiats, one of my first cars was a 1939 Fiat 500. Having the engine (such as it was) ahead of the front wheel axis and consequently being somewhat light on the back end with only the driver on board, sudden application of the brakes would result in the car instantly swapping ends. In those pre-seat belt days they probably reckoned it was safer for the driver if he had his accidents in reverse ;-)
I've already done that and posted my findings in this very thread:
Alas, the nay-sayers don't want to believe me, just as they won't believe a well-researched piece of journalism that will come up with exactly the same results. "You DON'T want to do it like THAT...!".
If my memory serves me right, you have a 404 coupe which may well not have had one anyway. To be honest I can't really remember whether any of the three 404 estates that I owned had the device or not, but the 504 certainly did. Actually now I come to think of it the first one had a worm drive axle and definitely no brake limiter, I don't know about the middle one and the last one had a hypoid axle (I think) and may have had a limiter. That would be about 1969/70 AFAIR. The 404 brakes had their own eccenticities, the front ones on my last two Estates being heavily servoed 2 trailing shoe in forward and reverse. Provided you remembered the necessary gentle application to re-align the shoes after a change from forwards to backwards and vice versa, otherwise you had 2 leading shoes with lots of servo. Does your coupe have these?
Good memory Ron, like a coupe but it a cabriolet ! The description on the worm and hypoid evolutions are right on the money. And yes the 404 has its on brake eccentricities, called "assisted" hydrovac - on coupe and cabrio at least - used on first generation 504 too which results in sudden HARD braking at slight pressure (really need to know this and get used to it). First time I lent the 404, my friend came back with a bump on his forehead. Not as bad as the DS "mushroom" though ... Actually the 404 is pretty stable even with the crazy brakes, my worst experience has been with an alfa ... that thing really slides around ...
Yes, "assisted" hydrovac it was - I'd forgotten that. Didn't Bendix have something to do with them? Once you had come an agreement with the things about which direction you were travelling in I found they worked very well. Most of the Peugeots I experienced around that time were Estate cars and they all rode, cornered and handled very well indeed. Unfortunately I think the engineers who really knew how to drive and thought it should be fun have now left the firm :-(
Exactly - think of what sitting over the rear axle in short cars does for traction at the rear end. If braking unloads the rear then the amount of traction reduces at the rear proportional to the reduction of weight. Bad thing *not* good. The illusional benefit of less weight at the rear will not reduce the amount of sideways "whip" as the mass of the vehicle (and surely momentum?) will remain constant. Remember, mass and weight are two different things - maybe the more practised physicists amongst us can elaborate?
Ever tried driving a Capri in the wet with and without rear passengers?
Mass is something that an object inherently possesses, something fixed and absolute for that object, and which mostly _resists_ change in motion.
Objects in deep space still have mass.
Weight is a force, caused by gravity, between two objects - it just happens that one of the objects is a planet! In the absence of a planet there is no weight, and on a smaller planet there is less weight. Weight mostly _causes_ a change in motion.
Objects in deep space do not have weight.
You have mass, but you >The illusional benefit of less weight at the rear will not
The so-called weight transfer is an illusion caused by the effects of deceleration on the suspension geometry, and the location of the centre of mass relative to the pitch centre. The rear end of the car still has every bit as much mass, and the tendency for that mass not to want to slow down or go round corners still applies every bit as much.
The message from Robert Pearce contains these words:
I am intrigued by why you consider the weight transfer an illusion. IIRC (from my schooldays more than 40 years ago) while the braking force on the front wheels will act at ground level momentum will act through the centre of gravity some distance above the road. The result is a couple that will increase the normal reaction at the front wheels and decrease that at the rear by the same amount. While I can (I think) see that a judicious applications of levers can eliminate any dive the weight transfer is real and could be demonstrated by any weight measuring device placed so as to measure it.
Inertia of course would still moderate any tendency to spin which I think is the implication of weight loss at the rear. Spin incidentally needs a couple to initiate it so provided the braking is absolutely uniform, the steering absolutely straight ahead and no extraneous forces (a very unlikely prospect act even if the rear tyres had absolutely no grip the car would not spin.
Yes, those are the "effects of deceleration...." that I mentioned. But the rear end of the car still has the same mass, and therefore still attracts the same gravitational force. Its _weight_ has not changed at all, there is simply an additional force being applied to counteract it.
When I called "weight transfer" an illusion, I in no way intended to imply there is no real effect, merely that it is not truly "weight" being "transferred".
Not by a properly designed weight measuring device that correctly accounted for all other factors involved. I never disputed the loss of tyre loading - indeed I have been strongly arguing that it is an important factor, and _very_ important to distinguish from the complete lack of any change of mass.
No! Inertia in this case does not help you, because inertia is directly linked to mass, and it is the mass which (in this case) _promotes_ spin.
... a likely story!
... ditto
Why do you consider that unlikely? Ever heard of cross-winds?
The message from Robert Pearce contains these words:
So you would argue that spinning some poor sod at 10g in a centrifuge doesn't alter his weight because the gravitational force hadn't altered.
I think you are reading far too much into the meaning of 'weight' while misinterpreting the meaning of 'illusion'.
I am not aware of any weight measuring device that does more than measure the normal reaction and in my view it would be wrong if it tried to do so.
Since mass is an inherent quality I see no reason for emphasizing the obvious at all.
Incidentally while weight transfer under braking is a significant factor in stability, particularly when cornering, it doesn't deprive the rear wheels of all loading. At a deceleration of 1g the c of g would have to be at a height above the ground equal to half the wheelbase to do that on a car with 50/50 weight distribution.
You and I appear to be speaking a different language. I used 'moderate' because the higher the polar moment of inertia the more force required. It is turning moment that promotes spin.
I think you have been carried away by your own mindset. Read what I wrote again. It is capable of 2 interpretations, in the first it is the whole scenario that is unlikely, in the second merely the 'no extraneous forces'. Either way it is the complete opposite of your understanding of it.
Incidentally cross winds have a lesser effect than weight transfer under braking as the turning moment is a function of the horizontal distance between the centre of pressure and the centre of gravity.
[my apologies for the typo below that might have served to confuse. I think the 'act' was the remaining part of some incomplete editing]
It is a condition of unstable equilibrium (but one where there is at least a chance of retaining equilibrium by steering) used as an example to illustrate that extraneous forces are needed to destabilize the situation. A point I think you implied some time ago (braking bias?).
It IS a condition of unstable equilibrium BUT there is no need for extraneous forces.... The unstable equilibrium is maintained by the ppor bloke's steering. At a second later road condtions (slope, adhesion, a pebble, etc. etc. ) car weight distribution, etc... push the car out of equilbrium ... think a bout it, you got to keep your hands an the wheel just to go right, no need for cross wind or cosmic wind there...
I would agree that most items metioned above are perhaps 'extreneous', but that is the way to a moot discussion IMHO the forces necessary to push the moving vehicle out of that most unstable equilibrium are intrinisic to any driving experience.
Of course I would! I know my physics, unlike you it seems. The poor sod is certainly subjected to very similar effects as he would suffer in a truly 10g environment, but it is _not_ weight. And it's your failure to recognise that distinction that makes you misunderstand the implications of so-called "weight transfer".
No, I think you are.
Then your opinion is broken. You're right that there are very few weight measurement devices that even claim to operate in the presence of extraneous forces. That's precisely why a sensible person never uses them in such a condition.
It clearly needs emphasising because you continue to treat something you call "weight" as being directly linked to mass, while simultaneously defining "weight" in such a way that it's blatantly not inherent.
When did I ever say it did?
And you are forgetting that it is the "equal and opposite reaction" to the deceleration which acts upon the mass. Extra "inertia" does not moderate because it comes from extra _mass_, which promotes the spin equally.
I could easily say the same to you, and with considerably more justification.
OK, but you seem to be arguing the opposite of what your (new?) intended meaning implies.
You're not comparing apples to apples there. I suspect you're also wrong
- the cross wind does not in itself apply a turning moment, it requires a difference in resisting friction from front to back. That's why a car at steady state will never be spun by a cross wind. However, a car under heavy braking can be affected by one.
Hang on, does that mean you are arguing that I was right all along?
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