Hi guys,
I could do with some hands on feedback.
As some of you know I'm on this mission to get quality components at reasonable prices.
Shox and Plug leads now sorted, exhaust systems undergoing final testing - next on the list are brake discs and brake hoses [ St.St. Flexi ].
Question - what is the concensous of opinion re: Wavy vs Plain discs? [ K1100 ].
Folk quote lighter weight, better water dispertion, better cooling................ the only negative appears to be the price !!!!
We're currently having our Cobra Race car disc manufacturer look into the prospects.
The first Wavy disc pattern has been cut and we'll soon be getting the first road trial prototypes. After the trialling and any mods incorporated the pre-production discs will be trialled before production runs commence.
Early K1200s seem to be in the same boat [ ie lack of suitable components] and although I realise that there were [relatively] not that many K1200 bricks - why should we not?

Beachcomber,

You ask a very difficult question: wavy vs plain....
Not being an expert at all on brakes, I would question about the heat dissipation on a wavy disk. Unless the disk has a bigger diameter,the surface is less important. However, do the valleys cut in the disk would scoop extra air thus increasing the cooling down?
The shape of a wavy disk repels water when you break. Does a drilled disk accomplish the same (or close)? I believe that the original rear disk of the K100 (1983 - early 84) was drilled and BMW replaced it by a plain disk. Why?
The K100 being an old bike, most of us are trying to keep the look as close as the original (sometimes to the detriment of performances).

Hi Frog

"The K100 being an old bike, most of us are trying to keep the look as close as the original (sometimes to the detriment of performances)."

And the rest of us our doing our best to make them different / better !!!!!!!!!!!!!!!!!!

Hands up ANYONE whose bike is EXACTLY the same way it left the showroom..........not many [ if any ]. NO such thing as the perfect factory bike - so I guess we're all customisers, it's just the degree in which we differ.

I have NO problem with old Classic bikes being kept original for posterity, and I guess in several decades time the Kays might approach that status, in the meantime to a larger or lesser degree we will all keep modifying / improving our chosen rides.

Unfortunately [ ?? ] here in the UK the Kays took over as the Courrier bike of choice and most were abused to the point of - throw them away.

As to the Wavy discs - the stated "practical" enhancements seem to be irrefutable - as to if they're too modern for conservative tastes...........................

The question here is not one of aesthetics - but practicality.

Certainly the wavy discs are capable of dispelling more water, and would run cooler. Lighter weight is irrefutable helping with the gyroscopic effects of the wheel when changing direction.

The OEM rear disc cracking was made worse by the positioning of the drillings - that said, I've got a solid K1100LT rear disc that has cracked !

Well, here's my take on the subject. Solid discs from cast iron are a very effective design for a number of reasons - cast iron does not distort or expand very much at all under heat, certainly much less than steel, and very much less than stainless steel grades.
Energy from slowing the bike under brakes is dissipated as heat, so that's what we need to deal with and to this end it would be nice if the brake disc could get hot, then cool down (repeatedly) and still run true. Cast iron is very good for this purpose.
Drilling holes, milling grooves and slots etc can go some way to increasing the effective surface area to aid in better transferring heat, but as with any engineering solution there is always a compromise. In the case of the holes/slots/grooves it is most likely pad life that suffers to some degree, mainly due to dust inclusion and the fact that the brake pad travels across an interupted surface.
Slots, grooves etc also look "cool" and this is never better presented by anyone more than the Japanese, who are the masters of marketting.
BMW on the other hand are practical to the point of being boring (not so boring these days though), so my point in this case is the solid rear disc on the K100 and the "not the cool looking" radial slots in the front discs.
I suspect that the front disc slots are the result of much testing and the rear solid disc is the result of engineering design whereby the rear disc gets less load and the solid design sees longest wear life. This is the German logic that I see in so many industrial applications. In short, it may not always look pretty but it is mostly very effective.

steel melts at a lower point than cast iron, stainless discs are made to save weight racing purposes ,ie thinner ,cast iron is heavey and thicker ,the thin stainless wavey was designed more so for off road so the surface area would shift the dirt away from the callipers also provide more surface area as mentioned earlier . i see thinner discs as working well under lower speeds ,not much effort required to slow down therfore not alot of heat build up ,thicker discs would be better for faster speeds i think as there would be more friction and less warpage due to heat ,ive never seen the carbon fiber discs on a racing car but i imagine they would be prety thick also light weight . . . just in my opinion . . every one has there own veiws [img]https://2img.net/i/fa/i/smiles/icon_biggrin.png[/img]

Gentlemen, thanx for taking the time to respond.

BobbieB - all the aftermarket discs we hve checked are stainless with a high carbon content. They are also the same spec as OEM dics [ 5mm thick ] - not thinner as you suggest.

I'm certain that part of the appeal of wavy discs is purely aesthetic / desire to be different.

However, I haven't seen an PRACTICAL negatives yet .....................

I was going to throw in the aesthetic comment as it would be a typical Japanese marketing exersize, assuming they started it.
As for the engineering side of things are they used on GP bikes? If any performance improvements were to be had then that is where they will be seen.
As few of us travel at GP speeds and if you prefer the look of the wavy discs, and there are some radical ones out there, then go for it. As I keep saying as far as accessories go we are now spoiled for choice.

As we are not racing and hence travelling at such speed with such heavy repeated braking that the discs and callipers are overheating the key question for me is can one get the same retardation effect from the same pressure at the hand or foot with a wavy disc as one can with the standard BMW disk. Given that wavy discs look ugly I am with Bert why would one do put them on? I do not think that track performance is the issue we need to look at here for road bikes just can we get the same retardation effect for the same brake pressure and the same or less wear on the brake pads. Does anyone have factual figures about braking effect for a given piston pressure in a calliper with standard BMW disks versus the alternative wavy discs?
Regards,
K-BIKE

Excluding the 4V I would suspect any modern disc caliper setup wavy or not should be light years ahead of the discs on the 2V K's.
My current wallpaper is the latest model Ducati Multistrada with the front wheel and brakes very prominent. Granted they are not wavy discs but 6 piston calipers and bigger rotors on a bike significantly lighter than our K's has got to provide some awesome stopping power.

phil_mars wrote:I was going to throw in the aesthetic comment as it would be a typical Japanese marketing exersize, assuming they started it.
As for the engineering side of things are they used on GP bikes? If any performance improvements were to be had then that is where they will be seen.
As few of us travel at GP speeds and if you prefer the look of the wavy discs, and there are some radical ones out there, then go for it. As I keep saying as far as accessories go we are now spoiled for choice.

Phil,

you're waaaay behind the game - GP bikes haven't used steel discs for years - just like F1 cars - they're carbon.

Wavy discs were de-rigeur for off road and Motard as they got rid of the muck and water quicker [ a plus for road use ?]

K-Bike - One man's ugly is ........................... A stock Brick is hardly a thing of aesthetic beauty!

True, we're not all rushing around at warp factor 3 - but you load up an LT with rider pasenger, full to overflowing panniers, tank bag, top bag ............. and I'll bet you'll be glad of better retardation when that Trabant pulls out on you on the Highway.

I'm not trying to convince anyone of the aesthetics of a wavy disc - that is pure personal choice [ K Bike ] - I just wanted to know if anyone could see any practical negatives. Seems not?

beachcomber wrote:

phil_mars wrote:I was going to throw in the aesthetic comment as it would be a typical Japanese marketing exersize, assuming they started it.
As for the engineering side of things are they used on GP bikes? If any performance improvements were to be had then that is where they will be seen.
As few of us travel at GP speeds and if you prefer the look of the wavy discs, and there are some radical ones out there, then go for it. As I keep saying as far as accessories go we are now spoiled for choice.

Phil,

you're waaaay behind the game - GP bikes haven't used steel discs for years - just like F1 cars - they're carbon.

Wavy discs were de-rigeur for off road and Motard as they got rid of the muck and water quicker [ a plus for road use ?]

K-Bike - One man's ugly is ........................... A stock Brick is hardly a thing of aesthetic beauty!

True, we're not all rushing around at warp factor 3 - but you load up an LT with rider pasenger, full to overflowing panniers, tank bag, top bag ............. and I'll bet you'll be glad of better retardation when that Trabant pulls out on you on the Highway.

I'm not trying to convince anyone of the aesthetics of a wavy disc - that is pure personal choice [ K Bike ] - I just wanted to know if anyone could see any practical negatives. Seems not?

Don't think I mentioned the word steel in my post I was referring to the design not the material they were made from, and assuming there was some advantage to be had from a different shape disc then that is where you would find it.
In actual fact if you want the utmost in engineering you should look to the aviation industry and see what they need to slow down a few hundred tons travelling at over 200 mph.

Ahhh sorry Phil reading 2 mails at the same time - however - carbon discs work on a totally different principle so removing material [ as in wavy ] would be detrimental.

I do not see how I could have better retardation than I have right now since moderate hand and foot pressure will engage the ABS and stop the bike quickly. Even without ABS a motorcycle or car for that matter cannot stop any faster than the retardation rate at which the tyres lose grip on the road surface. So any change in the disc will not make my bike stop any quicker than it does now.

I also think the K100RS is one of the best looking bikes I have ever seen, that's why I ride one. If I liked something with wavy discs I would buy it. So given it won't make the bike stop faster and looks ugly why do it?
Regards,
K-BIKE

KBike guess we'll agree to differ - however, none of your responses gives me any insight as to the practicalities - just your opinion of what is ugly and what is beautiful [ eye of the beholder and all that].

Better retardation, etc.,etc. - under perfect conditions Your discs never get wet, never overheat ...................?

You have a beautiful looking bike and perfect brakes - I guess you will not be looking for Wavy discs then?

BTW - I ride a Kay because they're cheap and cheerful and I can change them to what I want inexpensively - "best looking" was not even a consideration.

Don't you have Ducati's where you live?

We have very many Ducati's around here but I still don't think they look as good as the K100RS if I did I would be riding one they are very easy to buy both new and second hand and not unreasonably priced.

All discs get wet but with the holes in the standard disc that does not seem to be an issue since as I have said before one can brake hard enough to cause the ABS to operate or if ABS is not present to lock the wheels both in the wet and the dry.

So the crunch is do wavy discs stop the bike in a shorter distance than the standard discs and pads in the wet? In the dry?

I suspect they have appeared on bikes as a ad man driven marketing exercise not because they are better, since as was mentioned above if they were beneficial then at the very least big aircraft would use that design and so would GP track racing bikes. Do wavy discs wear the pads out faster? I would love to see some factual comparisons between stopping distances with each type. With twin discs up front as standard I have never had a hint of fade even after some spirited riding with heavy braking.

Without some actual benefit my feeling is why change? If there was measurable improvement then I would seriously consider overriding the aesthetic objection and using them. Is there any factual info about improvements?
Regards,
K-BIKE

That's more like it KBike - a logical argument - not just "I don't like it".

OK now we're having a serious debate - the manufacturer in question has been making discs for however long - we [ Realm ] have been using this manufacturers' discs [ not wavy ] for our Race cars and road replicas for 25 years now.

He does have full testing facilities, which naturally we will take full advantage of.

It seems that NO ONE who has responded negatively can give me a back to back comparison - only what they THINK - AND most seem to be based on looks ......................

And I guess unless the respondants are braking engineers, that will be a matter of opinion.

I was hoping to hear from someone who has gone from stock to Wavy or vice-versa and could give some genuine hands on feedback.

In the World of progress [ or not in your view ] - "I don't like the look" becomes a secondary consideration.

OBVIOUSLY these discs would not be aimed at your dyed in the wool BMW traditionalist - most of whom think that anything without two opposing cylinders is heresy.

BTW - I've got a pal who thinks his Trabbant is the most beautiful car in the World - and to him I guess it is.

Beachcomber, I did a bit of research and did find a general bike forum which actually had users which posed the same question and had members who had swapped from conventional to wavy discs with no conclusive opinion other than brake pad wear was horrendous.
Unfortunately I can not remember the forum but will keep browsing.
Now you mentioned GP bikes use carbon brakes and are not wavy because they use a different process? So care to elaborate?
It appears however Superbikes are not allowed to use carbon brakes so are wavy discs used in that arena?
The other information I gleaned which you may have mentioned was that they first appeared in the off road arena as they are better at removing mud but that would also suggest a use in the supermotard area.
I suspect there is also a very slight advantage to gained in the reduction of unsprung weight. Perhaps the only real option is for you to fit them and tell us the difference. or there is always the Carbon option at 1000gbp ea!!
And Jeremy I agree the 16V RS is a great looking bike but the Ducati ST3 is not too shabby either?

Question - what is the concensous of opinion re: Wavy vs Plain discs? [ K1100 ].
That was what was asked at the biginning of this thread, so "opinions" in my book are what people think, and that's fine.
I have already offered my thoughts, but not bothered with too many facts, however, it is a very sobering thought when one thinks of some of the potential consequences associated with experimenting with alternative brake designs and materials.
A guy lost his life at Bathurst some years back, after experimenting with his own brake disc design. I'm sure there are plenty of other examples as well.
Some things are better left alone, especially when they already perform satisfactorily.

Cost is the only factor for me. 3 bits of metal with holes in and a price that reflects this.

Thanx as always to all who took the time.....................

Wedge - that's what started all this off !! We pay £70 for a 3/4" wide vetilated disc. which also has grooves in each face [ Cobra race Car]. So why am I being asked £120 for a 5mm SINGLE disc. for a bike ?
Quantity cannot be the issue, as we only produce 20 Cobras a year [ 80 discs].

Same issue with the shox, Plug leads, etc.,etc.

One regrets the loss of life of the racer who lost his life - do we know what his qualifications were to produce his own brake discs and do we know what caused the accident?

The guys we are using have been producing speciality discs for over 35 years - and not a single product related death. You see Dennis, there's that word again "satisfactory" [ OK - satisfactorily ] - not excellent, outstanding, but .. the satisfactory, the ordinary the mundane.........................

Phil - that's my initial concern - logic dictates that the internally swept "waves" would perhaps cause wear. But then - if the surfaces are perfectly flat [ and these are ] it should make no difference. Cooler running brake discs should give the pads an easier life - but will they?

Carbon discs rely on the swept area for their efficiency - as I Imagine the aircraft brakes already mentioned.

Carbon discs are outlawed in the regs for Superbikes - as the system has to be road orientated. As you know - carbon discs don't work at low temperatures - ask an F1 driver after a few laps behind the safety car !

Off road was the place they [ Wavy discs ] grew to prominence due to better debris / water cleaning.

There is a benefit from the lower weight due to the lower gyroscopic forces encountered when flipping rapidly from one side to the other. However, I suspect that I am not that rider anymore !

The wavy discs WILL go ahead to be tested and even as we speak the pre-production samples are being tested in the lab ready to be let loose on a road bike. I will be the first test pilot and then I'll hand them over to a long term Kay owner, who is also a courrier and will put starship mileages on them far quicker than I will - and he rides a lot harder than me!

WAVY DISC TEST
14 October 2004 - Grand Prix Racewear
A recent test carried out by MCN shows that there is no advantage to using wavy type brake discs. It can be found on page 18 of their October 13 2004 issue.
The test compared the performance of wavy discs against normal type discs. The test was carried out using a MotoGP-spec 2D datalogger, onboard a 2004 Suzuki GSXR-600 road bike.
Here is the data;
- Braking distance - stopping from 80mph to 0mph
OE disc = 46.76m
Galfer disc = 46.83m
After the discs had all been bedded in, all three versions produced very similar results. The distances were measured after hitting the brakes as hard as the rider could when he reached 80mph. They were close enough for the error tolerances of the datalogging system, so there was no real difference in total braking distance.
- Braking Lever Pressure -
OE disc = 12.3bar
Galfer disc = 18.6bar
This was measured to see how hard the rider had to squeeze the lever to stop in a set distance. The wavy discs required the rider to use more pressure, possibly due to a smaller average pad contact area. The Galfer discs took the most effort.
It also shows that the wavy disc will heat up and cool quicker, which can lead to inconsistent braking.

www.grandprixracewear.com


Just something I came across.

This from a different forum than I was trying to find but does give some real world experience: http://www.ducatisti.co.uk/forum/technical-help/39984-wavy-discs.html

As for experimenting with different brakes and while I am as cautious as they come if it was not for someone trying something new and different we would still be living in caves.
Everything we do has some element of risk and in theory the greater the knowledge we possess the further those risks are reduced which then becomes a calculated risk.

So fortunately for us someone somewhere has tried something new and given us the bikes we now have or would like to have.

AT last - thanx Avenger a reasoned [ albeit old and secondhand] respone.

I stopped taking MCN many years ago as I found their style to be similar to the Sun / Mirror etc.

I've just requested a back issue of Performance Bike magazine with a similar back to back testing using modern equipment. This issue should be relevant as it's around 12 months old.

However - from the MCN results it appears in the dry [ ? ] conditions there is no appreciable difference in retardation. And as to wear, we don't have the answer from a short test - although my first thoughts were - probably more wear. Initially I thought from the edges of the "wave" - but of course on reflection that's not so as the surface presents a perfectly flat contact path. Overheating / warping? Well we seem to manage that quite well with OEM discs [ oh yes and cracking ]. Heat dissapation from running many cycles can be tested in the manufcaturer's lab without any guesswork required - and without risking life and limb!

That still leaves the other specifics of lighter wieght and potentially better water / debris clearance. That won't affect me personally as I don't ride in the rain these days.

I've just been re-reading [ 100th time ! ] the Tony Foale / Vic Willoughby bible - "Motorcycle Chassis Design - theory and practice". Plus a couple of modern referrence books - and the lighter weight / gyroscopic force argument seems to be valid. Did MCN conduct any slalom tests - or was it just a straight line braking excercise?

Thanx again Avenger for taking the time.

BTW - your company wasn't / isn't connected with my old buddy Alan Eisner is it?

The higher brake pressure required looks like a bad thing.
Regards,
K-BIKE

Anyone who is prepared to lug 600 lbs + of bike can surely manage a little exrta pressure?

Maybe we should look at servo assist for the limp wristed?

However, I think you've nailed your colours well and truly to the mast KBike - keep the bike as God and BMW intended - a thing of perfection.