Many thanks, GB. That's exactly what I was looking for!
(It also answers the question, viz. that pre-93 ones are indeed the same, which saves me about £40!)
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Many thanks GB. That's exactly what I was looking for! (It also answers the question viz. that pre-93 ones are indeed the same which saves me about £40!)
No, that does not mean they are the 'same'
Mazda list different part numbers, so there will be differences, probably in the compound of the pads.
this will, to a greater or lesser extent affect the brake efficiency/balance/wear.
all too often the vehicle manufactures spend a huge budget on getting components to work in a certain way, then the aftermarket find that something else will 'fit' so list one part number where the manufacturer lists a few.
brakes are one example, others include springs, dampers, thermostats, water pumps, alternators etc.......
these generic parts will in the main 'do the job' but may affect the vehicle operation, and reliability.
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Tony - I take your point, but I doubt that even Mazda spends a huge budget telling specialist suppliers how to do their job. The brakes in question are made by Akebono, and were presumably used on the more rapid editions of the (normally rear drum-braked) 323 because they meet the required spec and were already in the parts bin!
My Xedos has the same brakes as the 626 for the same reason, but I think it unlikely that Mazda have specified a special compound for the pads. If they use a different code, it is presumably to keep track of which vehicle they're being used for.
Equally, I wouldn't expect Mintex to use the same code for pads with different characteristics.
Edited by J Bonington Jagworth on 14/03/2009 at 15:20
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. If they use a different code it is presumably to keep track of which vehicle they're beingused for.
>>
No... I dont think they would bother doing that, what would be the point?
IF there were say, wear issues on a certain model of car, then that information would get to them through customer complaints, having different part numbers for identical parts increases stocking costs....
Equally I wouldn't expect Mintex to use the same code for pads with different characteristics.
No, exactly my point!
Mintex are no different to the vehicle manufactures, if there is a difference then you have to use a different code/part number.
I think you would be surprised how many different compounds are available...
here is a link to 'racepads' tinyurl.com/ava82d
I will say that in competition things are at the extreme end of being 'just so' but it should give you an idea of the reasons for having different compounds, even on road cars.
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Have to disagree with St and side with JBJ.
There are numerous examples amongst main dealers where 1 part number now fits x y and z etc.
I have lost count of the times I have been to the counter with the part label (including pads) and been told thats not available any more, we use zzzz now ! So a different number could just be a part where they have decided it fits more than originally intended.
There are numeous examples of the (identical) same parts in different packaging because it fits 2 different "value" motors. The same part on the value car is cheap and on the "prestige" car its over twice the price. (especially peugeot/citroen if you wish to question my accuracy).
Brake pads are available in different compounds occasionally (very occasionally) but not for general use; racing is totally different.
If mintex decided a different pad was needed, then it would have a different part number. They are designers (amongst many others) of braking systems for the vehicle assemblers.
I do, concede, that somethings are different between similar cars, but pads isnt 1 !
Edited by yorkiebar on 14/03/2009 at 16:15
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> I have lost count of the times I have been to the counter with the part label (including pads) and been told thats not available any more we use zzzz now ! So a different number could just be a part where they have decided it fits more than originally intended.
Yorkie... you should know the reasons behind that!
Part numbers ARE merged, normally when under testing, it is found that one part is suitable for other applications, do you really think its cost effective to use more than one part number where one would do?
with regards to the PSA group, they have been merging part numbers for a good number of years to reduce costs, years ago they DID use different part numbers on identical parts fitted on Peugeot and Citroen's, now on the whole they share part numbers (if not always prices.....)
>>Brake pads are available in different compounds occasionally (very occasionally) but not for general use; racing is totally different.
Yes as I said racing is different.... but look at 'identical' pads under different part numbers, and you will see different codes printed/stamped on them.
some of those codes will be production dates/batch codes, but other codes do state which compound is used on those pads.
If you dont believe me would you believe a Pad manufacturer?
tinyurl.com/bouthr (links to a Delphi pdf)
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>different "value" motors
Ain't that the truth! My firm did some work for a steering rack manufacturer, where the 'cross-reference' list made very interesting reading. The same racks were used in a range of vehicles, and as spares fetched widely different prices, according to the cost of the vehicle.
A lot of things are charged by what the market will bear, as anyone who has bought anything from Microsoft will attest!
(Example: www.pcwb.co.uk/catalogue/item/MSRTAB01 )
It's a webcam...
Edited by J Bonington Jagworth on 14/03/2009 at 16:46
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"Mintex are no different to the vehicle manufactures, if there is a difference then you have to use a different code/part number."
Which in my case, it isn't! Only Mazda are using different part numbers (for whatever reason) but Mintex don't, because it's the same part, AFAIK.
I've no doubt there are different compounds for different applications, in the same way that you can buy stickier tyres that last less well, but for general use, I would expect any difference in 'normal' pads to be insignificant.
Appreciate your thoughts, though. I'll know soon enough if the new pads feel different!
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This is perhaps a case where there is a good justification for Mazda keeping two part numbers. If the rear brake calipers are mechanically the same, one way to tailor the rear brakes for the different weight distributions of the two cars would be in making a different compound. So, the outline in the Mintex book would be the same, but, the pads would be different.
If the MX5 has proportionally more weight on the rear axle, the pads for an MX5 might have a higher co-efficient of friction, which might cause dangerous rear locking if used on a 323. If the car were mine, I wouldn't be taking the risk.
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Ok Nc
but the question is actually, are the pads specified to be the same? or are they the same shape?
2 different questions, 2 different possible answers.
If they are speicified to be the same then that is ok. There are countless examples of this!
There are also countless examples where the same shape is a different number.
The chance of a compound on a mazda pad actually being different enough is a seperate but unlikely matter though !
I have been to (probably) more brake pad factories than the average person and different compounds are fitted to the same vehicles too! Reason, because the pads arrive from various parts of the world, get boxed (including oe) and sent on. (this example is not mintex btw
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YB - this is the original question.
>>Does anyone know if Mk.1 MX5 rear pads will fit our old 323F GT?
Whether they will fit or not in a purey mechanical sense can be determined from the Mintex drawings, as answered by GB.
Whether they are correct for the application, however, cannot be determined from the outline drawings.
I'm not sure how visiting brake pad factories helps anyone to answer this question.
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"I'm not sure how visiting brake pad factories helps anyone to answer this question."
just to dispel the hype over the possibility of a different compund causing a problem !
hth
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the possibility of a different compund causing a problem !
How do you *know* that in this particular case Mazda's use of 2 different part numbers does not have a good engineering reason?
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>> the possibility of a different compund causing a problem ! How do you *know* that in this particular case Mazda's use of 2 different part numbers does not have a good engineering reason?
exactly the point im trying to get across..... Mazda design and build the cars...they know why they use the compounds they do, the patten parts makers dont have that info.... if it fits, it will do!
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Just had a surprize at the HUGE variation in prices for Mrs V's Mx5 front pads.
& there are variations available, depending on model & disc size, even before you start thinking about redstuff, yellowstuff, greenstuff, or whatever colour track day enthusiasts say you should have!!
£70ish from Mazda = them not getting the sale. £24 for Nipp Japanese, rather than Chinese imports, were chosen.
Will they last 50000miles, remains to be seen!!
& as a bit of a, 'did you know'... that if you want a rear llight unit, for early Discovery, it's cheaper to buy a Maestro van assembly, rather than LR part.
Same thing - different part number & packaging!!
VB
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"£24 for Nipp Japanese"
Which I have all round on the Xedos. They work fine.
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"Mazda design and build the cars"
But not every bit of them! Lots of parts, including brakes, are made by others. All Mazda, or any other manufacturer, will do is specify the requirement - I doubt they bother themselves with the formulation of friction materials, any more than they formulate paint.
Edited by J Bonington Jagworth on 14/03/2009 at 22:40
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>>is specify the requirement
That's the important bit, determining and defining the requirements to ensure the parts work correctly, it's the vital, responsible, and safety critical part of the process. If requirements are complete and well drafted, who exactly makes the parts is much less important, almost to the point of irrelevance.
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"That's the important bit, determining and defining the requirements to ensure the parts work correctly"
Which (I surmise) involves the manufacturer telling the brake manufacturer about the application (weights, dimension, power, etc) rather than how to do his job. Later testing will soon reveal if either of them got it wrong!
My point is that the manufacturer does not involve himself in the fine detail of standard component design, but will label up parts to suit his own inventory requirements. If he uses the same brake mechanism for two similarly powered cars, whose pads are given the same reference by an established OEM, it seems reasonable to assume that they are close to identical.
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My point is that the manufacturer does not involve himself in the fine detail of standard component design but will label up parts to suit his own inventory requirements. If he uses the same brake mechanism for two similarly powered cars whose pads are given the same reference by an established OEM it seems reasonable to assume that they are close to identical.
>>
normally only one part number per part, will be used by vehicle manufacturers, exceptions include where more than one supplier is used (but those part numbers will be linked as alternatives), there are also cases where 2 or more parts have been listed, but in testing it has been found that differences are so minor as to unimportant.
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>>the manufacturer does not involve himself in the fine detail of standard component design,
I think you might be surprised in this JBJ - some manufacturers do get very involved in the fine detail in order to implement cost down activities in an effective manner - the level of fine detail which suppliers will need to submit to a manufacturer before being considered for contract placement will be significant.
>>it seems reasonable to assume that they are close to identical.
I think that within the broad requirements of ECE regulation 90, yes, that's true.
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>>it seems reasonable to assume that they are close to identical. I think that within the broad requirements of ECE regulation 90 yes that's true.
If a variance of 30% is close to identical....(within plus or minus 15% of
the OE specification)
personally I regard that as a wide margin, I know I wouldnt be happy if my beer was served at -15% of a pint....although at +15% you would have to drag me out the pub!
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Sorry ST, I was being a bit of a weasel.
While regulation 90 might regard them to be sufficiently close, I'm not at all sure I would!
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No need to be sorry NC!
I dont know if you agree, but I would say that 99% of the time that +/- 15% wouldnt make any noticeable difference in normal driving, BUT its when the brown stuff hits the rotating device that things need to work as designed.
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>>BUT its when the brown stuff hits the rotating device that things need to work as designed.
Yes, definitely.
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"Mazda design and build the cars" But not every bit of them! Lots of parts including brakes are made by others. All Mazda or any other manufacturer will do is specify the requirement - I doubt they bother themselves with the formulation of friction materials any more than they formulate paint.
Oh get real!
do you really think cars are just thrown together from whatever bits can be found in the parts bin?
before you or I see a new model, they are subject to many hours of CAD testing - these days computer models are used to get the basic starting point, rig testing, track testing and then road testing, and then the vehicles are tested in service, and any problems found will be subject to yet more testing..
I know of one vehicle which will be subject to a recall, as a minor weakness has been found during rig testing - the car has been available for 3 years with NO ROAD failures, but as wear has been found the part will be replaced with a modified component.
Brake pads are subject to this level of design and testing as much as ANY other part of the complete vehicle - both by the vehicle manufacturer and their suppliers.
if existing parts can be used, then of course they will be - for reasons of cost as much as anything - but if its not right, it will get changed for something that is.
As a slight aside, who knew that fiesta/ka front lower arms are different, depending on whether PAS is fitted or not? any ideas why they may be different?
surely the addition of PAS wouldnt make any difference to the suspension?
But... it does!
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"As a slight aside, who knew that fiesta/ka front lower arms are different, depending on whether PAS is fitted or not? any ideas why they may be different?
surely the addition of PAS wouldnt make any difference to the suspension?
But... it does! "
simply the position of the ball joint in the arm; just slightly different !
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"one vehicle which will be subject to a recall, as a minor weakness has been found during rig testing - the car has been available for 3 years with NO ROAD failures, but as wear has been found the part will be replaced with a modified component."
I should hope so, but the reasons are more to do with potential liability than with altruism. All manufacturers remember the Pinto fuel tank episode...
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I should hope so but the reasons are more to do with potential liability than with altruism. All manufacturers remember the Pinto fuel tank episode...
That may or may not be true, but it does go to prove that ongoing testing brings benefits.
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"which might cause dangerous rear locking"
In which case, I would expect Mintex to supply it under different part numbers, which they don't.
The load on the rear wheels in most cars is pretty variable, depending on the cargo, yet rear brakes do not habitually lock up when lightly loaded, either due to some compensation device in the hydraulics, or simple reliance on the fact that the front wheels do most of the work thanks to the weight transfer under braking (and the overall effort required is proportional to the momentum).
I appreciate your concern, NC, but I'm not going to worry about it unless they feel very different.
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>>In which case, I would expect Mintex to supply it under different part numbers, which they don't.
Here's the important bit - *if* the pads are sold under the relevant ECE designation (they should be! & I think the relevant spec is ECE90), and the pads are marked up as being suitable for that model, then, yes, they're OK, because part of the testing to demonstrate ECE compliance is to demonstrate that the replacement pads are within a tolerance (plus or minus) of the OEM pads coefficient of friction.
Your reasoning about rear locking is way off the mark!
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Here's the important bit - *if* the pads are sold under the relevant ECE designation (they should be! & I think the relevant spec is ECE90)
I think NC, it is E90, for vehicles registered after September 1999, and the tolerance is I believe is 15%, which IMO is a wide range, which would allow patten parts to be used on a wider range of models than manufacturers own specs allow....
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>>the tolerance is I believe is 15%
>>used on a wider range of models than manufacturers own specs allow....
That the range was so wide hadn't registered with me until your post - thanks.
So, although it's legal to supply and fit these pads, I very strongly suspect that a rear axle pad which is close to the extremes of the regulation 90 requirements will cause the vehicle to no longer meet the requirements of regulation 13 - specifically see Annex 10, where the requirements to demonstrate adequate brake force distribution are described.
www.unece.org/trans/main/wp29/wp29regs/r013r6e.pdf
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That the range was so wide hadn't registered with me until your post - thanks.
No problem NC.. I will admit Im quite enjoying getting my teeth in discovering some of these specs/regulations, Ive been stagnating in my job too long!
Whilst I have never been as knowledgeable as yourself, in my dim and distant past I used to have to know more than I do today.. if that makes sense?
ah... how I miss the 80's when I had my fingers in motorsport, and modified cars......
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>>if that makes sense?
Alas, yes!
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Surely the rear braking is pretty minimal on a 323? I'd think twice about the brakes on the front of a car if there was any doubt but the back is glorified handbrake territory only. I'd fit the pads and be done with it. For all the hand wringing that is going on surely the tyre choice would have at least an equal effect on braking and we all know that you can go as cheap or expensive as you like without being officially told off.
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>>Surely the rear braking is pretty minimal on a 323?
Yes!, to avoid locking of the rear axle - the danger being that too much braking on the rear axle makes the car unsafe. So unsafe that there's lots of regulations in place to try to prevent it.
These regulations are entirely consistent with the tyre makers advice to fit the best tyres to the rear.
One of the problems is that most people have experience of locking the front and rear wheel on a bicycle, where the danger is reversed. IF you lock the front tyre on a bike, you're probably about to fall off, whereas in a car, locking the front wheels is quite benign, and prior to the requirements to fit ABS on all cars, there were no regulations in place to prevent locking of the front brakes in cars.
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Surprising that so many cars have had so many different brands of pads fitted without reported problems.
Surprising too that so many oe pads can come from different sources (they do, I have proof) without affecting the braking issues.
At no point has anybody recommended fitting unkown brands ( a different point entirely), just that common sense needs to be used sometimes!
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Surprising too that so many oe pads can come from different sources (they do I have proof) without affecting the braking issues.
Yes, and as you well know, no matter who supplies the manufacturer they have to comply with the vehicle manufactures specifications! At no point has anybody recommended fitting unkown brands ( a different point entirely) just that common sense needs to be used sometimes!
No, they havent im glad to say... but dont forget that common sense also includes if it seems too cheap - it will be!
some pattern parts are absolutely fine, others arent, I myself use them, but... I had some mid range pads in a fiesta (wouldnt give the cheapest a thought) and they were fading and smelling going down hills, at 30mph.... I tell you now, I wont be using them again!
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"some pattern parts are absolutely fine, others arent, I myself use them, but... I had some mid range pads in a fiesta (wouldnt give the cheapest a thought) and they were fading and smelling going down hills, at 30mph.... I tell you now, I wont be using them again! "
Likewise, I will never fit oe pads to certain cars (ka for example). After market ones are far better on this car, even HJ car by car agrees. I can name plenty others too, so I always use top 4/5 aftermarket brands; unless customer wants dealer supplied (very rarely)
Lets not get into the paranoia that only dealer supplied parts are good enough is all !
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>>After market ones are far better
If there is such a difference, how can the spurious parts be compliant with regulation 90?
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Are ferodo/delphi/mintex etc spurious?
I dont think so !
Who ensures the pads meet the spec required? The car "assembler" (note not manufacturer) or the parts suppliers?
Edited by yorkiebar on 15/03/2009 at 14:16
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>>Are ferodo/delphi/mintex etc spurious?
It depends. If they were approached by the manufacturer to provide OEM parts for a particular model, then, they will be in possesion of enough information to make the parts without having to reverse engineer, or guess what the specification was.
If they have to reverse engineer the parts, they can never obtain any idea what the nominal specification was or obtain any information about the tolerances allowable from nominal. They are guessing.
>>Who ensures the pads meet the spec required?
A test house authorised by the ECE - the parts supplier is responsible for submitting the parts for test, and controlling the parts manufacturing process thereafter.
>>(note not manufacturer)
I don't know where you get this rather naive idea from!
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"I don't know where you get this rather naive idea from!"
Then I am surprised at you. You know as well as I (or maybe better) that "systems" are sourced by the assemblers and then built into the cars. Most vehicle design now is mostly just that, shape design !
You cannot agree that anything other than oe is acceptable. I often find it is or better !
So we disagree again.
Bored now, sorry.
Pay your money, take your choice !
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Yes, vehicle manufacturers buy in parts and sub-systems. They have been doing it for years.
In fact I can't imagine that the manufacturers of any complex item have only deliveries of raw unprocessed materials at one end of the factory, and finished goods coming out of the other. (Ford's Rouge plant was perhaps quite close to this though)
To call a vehicle manufacturer an assembler is to place zero value on a significant slice of the work done and risk taken by a vehicle manufacturer. Yes, the visible thing that you see is the assembly line, but without the other more hidden work of the manufacturer, there would be nowt rolling off the end of it.
>>Most vehicle design now is mostly just that, shape design !
If anyone imagines that developed and tested vehicle designs spring from the felt tips of vehicle body designers, then their view of vehicle design and development is somewhat narrow.
>>You cannot agree that anything other than oe is acceptable. I often find it is or better !
I have wasted too much time in fitting spurious parts which haven't worked properly only to have to replace them later with proper parts to advocate them. Yes, there are occaisons when you might know that the OEM spark plugs on a given car were Bosch, or that the glow plugs were Beru, and then, it's not a great risk to fit hose parts - this, I do myself (I don't buy everything from the dealer!), but when I don't know who the OEM was, I stick to genuine parts, because I *know* they meet the manufacturer's specifications.
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Lets not get into the paranoia that only dealer supplied parts are good enough is all !
I dont think you will find ive ever said that....
what I have said, is manufacturers own parts (dealers HAVE been known to supply aftermarket parts) are the only ones that have been tested and approved to be of the specification set by the manufacturer for the vehicle the parts are listed for.
as I have said, I have in the past worked with dealers, factors, done some work in the field of motorsport, and modified cars... I do realise that in certain cases the original fitted parts are not the 'best' for the application, ie racing touring cars on road pads would be hopeless...
but to say 'part A will fit' so fit it without a second thought is not IMO a safe option.
IF part A is listed by the manufacturer of THAT part for THAT vehicle, then it should be suitable (if not then you will have comeback if and when problems occur) however, IF it is NOT listed for THAT vehicle, then they may well be a reason it is not suitable.
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"fit it without a second thought"
If I was doing that, I wouldn't be here! :-)
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"fit it without a second thought" If I was doing that I wouldn't be here! :-)
Very true! In fact you probably wish you hadnt asked lol!
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"you probably wish you hadnt asked lol!"
I certainly didn't think it would be quite so controversial!
For the record (and in case it wasn't clear from the original question) I am buying Mazda 'genuine' parts - the question was to do with the compatibility.
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"on a bicycle, where the danger is reversed"
What an extraordinary statement! Locking brakes on bikes is more serious because of the stability problem, but locking the front wheels is worse in any vehicle because you are no longer able to steer. Locked rear wheels may not help (unless you're a rally driver) but they are a lot less likely to put you through the nearest hedge!
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>>What an extraordinary statement!
No JBJ. Locking the front wheels in a car is benign. You have comparatively ages to feel that they are locked, and modulate the brake pressure accordingly.
>>but they are a lot less likely to put you through the nearest hedge!
Sorry, but this is completely and utterly wrong. If the rear wheels lock, the vehicle can swap ends quicker than most will be able to catch it. Bear in mind this is likely to happen in an extreme situation, not being deliberatly provoked as in the rally situation.
The situation is reveresed, because locking the rear wheel on a bike is not likely to send you off, whereas locking the front wheel usually does.
If locking the front wheels is so dangerous in cars, where are there Constructiion and Use regs, and ECE regs to prevent it? There aren't any, because it's truly rear axle locking which is dangerous.
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"where are there Constructiion and Use regs, and ECE regs to prevent it?"
Presumably absent because it's more difficult to provoke. Rear wheels are relatively easy to lock under hard braking because of the weight/load transfer (which can be 100% on a bike) while the same phenomenon tends to keep the front wheels turning.
I couldn't agree less with your assertion that front wheel locking in a car is 'benign'. Ploughing straight on with no steering is a lot harder to correct than a wayward back end, IMHO!
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>>a lot harder to correct than a wayward back end, IMHO!
If you lock the front wheels up, nothing happens, you have time to react, and release the brakes a bit. There's no instability, the car doesn't suddnely spin. The situation can be regained without needing racing driver reflexes.
If you lock the rear wheels at speed, the car swaps ends before you know what's happening.
It's a completely different situation to provoking some rear wheel sliding by being over enthusiastic with the throttle in a RWD car. In that circumstance, you're expecting something to happen, and you are ready with the right response. If you find the rear wheels lock under braking, it's likely to surprise you.
>>Rear wheels are relatively easy to lock under hard braking
Yes, on a bike, I agree, and on a bike, it's not as much of a problem as locking the fronts. On a car, rear locking should be something that most contributors to this site have never experienced (they would know about it!)
If it were just me going on about rear locking on cars, then your objections might have more ground. But, it's also the C & U regs, the ECE regs, and the fact that motor manufacturers spend money on expensive devices like load sensing valves to prevent rear locking. Prior to ABS, front locking was not regulated at all - no money was spent. Are they ALL wrong?
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"load sensing valves to prevent rear locking"
Which are there because of the variability in load on the rear axle. In a conventional layout (front engine/drive + rear boot or hatch) this can vary by a factor of 2 or 3 (even more in a pickup), and while I accept that locking wheels with a heavy load in the back could be hazardous, it's also rather less likely. I fail to see why under normal circumstances a car with locked rear wheels should suddenly 'swap ends' without some severe provocation. I have done it, exiting a roundabout too fast on snow, but that was with all four wheels locked, no grip and a big rotational component. One thing it taught me was only to brake hard in a straight line!
If a bike, with its short wheelbase and small polar moment of inertia, can cope with rear wheel locking relatively easily, then why not a car? Apart from the need to stay upright, the physics is just the same.
"Prior to ABS, front locking was not regulated at all"
How could it be? ABS was the only remedy.
Edited by J Bonington Jagworth on 15/03/2009 at 23:28
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>>I fail to see why under normal circumstances a car with locked rear wheelsshould suddenly 'swap ends' without some severe provocation.
I can and does happen. Come on JBJ, British legislation, European legislation, and the compliance of vehicle manufacturers by fitting expensive brake valves - you're trying to tell me they're ALL wrong, and you're right? You can't be serious!
If a bike with its short wheelbase and small polar moment of inertia can cope with rear wheel locking relatively easily then why not a car?
My point was that front locking on a bike is even more dangerous.
>>Apart from the need to stay upright the physics is just the same.
There are surprisingly few points of commonality between motorcycle dynamics and car dynamics.
"Prior to ABS front locking was not regulated at all" How could it be? ABS was the only remedy.
I don't mean regulated in the sense of regulating the brake pressure, I mean regulated via legislation. ABS on the front was not the only technical remedy, load sensing valves on front axles were always an available engineering solution - although off the top of my head I can only think of one vehicle so equipped (and that specification was to stop a different problem).
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"I don't mean regulated in the sense of regulating the brake pressure, I mean regulated via legislation. ABS on the front was not the only technical remedy, load sensing valves on front axles were always an available engineering solution.."
I knew what you meant, NC! Load sensing isn't anything like ABS, which (as I know you know) senses wheel rotation. Restricting the available braking force on the front wheels without that input would be fairly unhelpful.
I'm not arguing specifically with the legislators, whose output is also focussed on goods vehicles and the behaviour of trailers under braking. It was you who described 'swapping ends' under braking, which might be true of an artic with its mass concentrated on the rear axles, but I have to tell you that I spent a short time last year balancing the handbrake linkage on my car, the simplest test for which was to yank it on while moving, thus locking one or both rear wheels (only in the wet, though). All that happened was that the car continued in a straight line...
"There are surprisingly few points of commonality between motorcycle dynamics and car dynamics"
I was talking about simple laws of motion - momentum, inertia, friction, etc. AFAIK, the same apply to both.
Edited by J Bonington Jagworth on 16/03/2009 at 12:31
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>>All that happened was that the car continued in a straight line...
Two things.
1) Yes, if you are already going in a straight line, and there's nothing acting to yaw the vehicle.
2) You were provoking the response and were ready for it - perhaps even correcting at the steering wheel.
A car with its rear wheels locked *is* dynamically unstable, while if the front wheels are locked the car remains stable.
Try it. Take a model matchbox car, and a smooth inclied surface. Lock the front wheels, and the car will roll/slide down the slope, and within sensible limits is insensitive to exactly how the motion is begun. Lock the rear wheels, and, unless you set the car off exactly at right angles to the slope, it will swap ends fairly quickly to the dynamically stable situation of the front (formerly rear) wheels locked.
While the legislation does cover all vehicle types, it is applicable to cars.
Yes, of course Newton's laws still apply, but the modes and types of instability are completely different for cars and bikes.
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"Try it"
I did, and I concede the point, counter-intuitive as it seems. I have to say that the model with some front weight bias (a rough approximation to a modern FWD car) carried on in a straight line for longer, but I can't argue with your thesis! Where does all that yaw come from?
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>>counter-intuitive as it seems.
Yes I know exactly what you mean. When I was first presented with these views and arguments on the braking section of a vehicle design course, I initially struggled to accept the material being presented in largely the same way.
It was a little time before I began to accept it and see how it fitted in with both legislation and practice, and some of my dodgy experience with a car which I had badly modified.
In the most striking incidence, I had used a rear axle from an estate car to obtain different gearing on a saloon car, but I had not considered that the brakes were larger, and controlled by a load sensing valve on the estate, whereas I plumbed them straight in on the saloon. In normal driving, it was fine, you couldn't tell, but in an emergency stop on a fairly gradual, but wet bend, I found how quickly the car changed ends!
>>Where does all that yaw come from?
Surprising isn't it!, Although playing with toy cars seems a bit daft, it's quite a good illustration of how the ability of the rear axle to provide grip is necessary for stability, and demonstrates that the rear wheels do far more than simply support the body of the car.
>>I did, and I concede the point
A credit to you JBJ for coming back and posting up what you've seen. Thank you.
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Thank you, NC. I'll believe you sooner next time!
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"Your reasoning about rear locking is way off the mark!"
I didn't think it was that bad. Perhaps you can elucidate..?
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yet rear brakes do not habitually lock up when lightly loaded,
Yes, because of the regulatory input on brake design.
The British C & U regulations just say that rear wheel locking should be prevented. So, you could, if making a car for the UK only have rear brakes which barely apply (as long as minimum MOT standards are met), and be OK.
The ECE regulations are much tougher to meet. Not only do they specify that the rear axle brakes should not lock, they also specify minimum performance for the rear brakes (best visualised in terms of the adhesion utilisation graphs in Annex 10 of regulation 13).
So, rear locking is avoided at the design stage - but, no-one but the OEM knows how much margin there is before rear locking happens - it could be 20%, in which case, the 15% allowed by ECE regulation 90 is safe, but, if the margin is less than 15%, non OEM rear brakes could cause rear locking.
My practical concern is not that non-original replacement rear brakes are poor - I'm more worried about them being too effective.
>>simple reliance on the fact that the front wheels do most of the work thanks to the weight transfer under braking
Yes, the fronts do more work - this bias towards the front is designed in, and weight transfer is included in the design.
I would be happier if ECE regulation 90 said that for front brakes, the replacement parts had to be -0% to + 15%, while for rear brakes, -15% to +0% - then, rear locking would definitely be avoided in all cases.
You will not pick up by feel if replacement rear brakes are dangerous. In normal driving, with good anticipation, and gentle braking you would not get into the regime where rear locking can be lethal. Finding an emergency half way round a wet corner is where the problem might manifest itself (been there, done that, had to wash the underpants!). Short of doing a series of emergency stops on surfaces of differing mu values, you would not find the problem.
That rear locking has serious consequences, and is difficult to detect makes it especially dangerous IMO. A bald tyre, or bulging sidewall is obvious and visible. A spongy brake pedal can't be missed, but, too much braking on the rear axle lies dormant until you really need the brakes to work properly.
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