{thread snipped}.

As long as you can put enough force on the brakes to make the tire lock, there is no increase of "stopping power" as in "shorter breaking distance".

Of course if you can't get to the locking point with one system and can do so with another, there is a difference. And fading due to heat build-up could make the optimum brake strength harder to apply.

But if you can't lock the tires when you load the bike and under optimal conditions, isn't that an "engineering failure"? Using the right hydraulics, you can put any force on the brake. I can't believe Honda would not put enough reserves into the braking system to avoid this. But then again, maybe they didn't. GMC had plenty of problems with brakes on their SUVs in the 90s.

Has anybody ever refitted a '89 TA with dual front disk brakes and rear disk brake? Is that possible?

And while we're on the subject: My rear brake (drum) "sticks" a little. What can I do about it?

Mike from Colorado

89 TA

The reason this works is that the disk acquires heat from the conversion and then radiates that heat into the atmosphere as the it rotates into the air stream. The caliper also dissipates some small amount of heat but it is
relatively negligible.

Brake "fade" is the condition wherein the disk becomes so hot that it is not able to radiate its heat into the atmosphere before it rotates back to the brake pads. If it can not absorb any more heat because it has not dissipated enough from the previous rotation, the brake assembly will not be able to convert any more of the kinetic energy to thermal energy. This reduces or eliminates the resistance to the rotating, and hence forward, motion.

Historically, drum brakes were more prone to "fade" because of the closed design of the concave brake drum, the backing plate and the brake shoes trapped within. Note some of the extreme fin arrangements on some of the old racing drum brakes before disk brakes were adopted.

The boiling of brake fluid is a rare occurrence with modern materials and can be generally discounted I think. To boil the brake fluid the disk and caliper would have to be on the verge of melting. Fluid boiling was more prone on drum brakes because the brake cylinder was mounted on the backing plate inside the brake drum where much of the heat was trapped.

Curiously, cast iron disks are much better at heat transfer than stainless steel. Honda, when they first put disks on the original CB750 in 1969, chose stainless steel because it would not rust and therefore mar the looks of their newest tour de force. However, a much larger and weightier disk were the penalties for this aesthetic choice. I think the earlier Triumph triples had cast iron brake disks and always looked a bit shabby.

Twin disks are another compromise. As one person pointed out, if you can lock the wheel you have all the braking power you need. This is partially true. The question arises, when do you want to lock the wheel? At the top of the hill or at the bottom after the disk is well heated? Twin disks give twice the swept area for the kinetic/thermal conversion and twice the area for thermal radiation. This is a good thing but not without penalty. They also come with twice the unsprung weight which fights against good suspension compliance and handling.

There are some advantages to "feel" but I think this is a design issue more than a feature solely owned by twin disks. I think the main advantage of twin disks is that they "look cool". The racers have them so they must be the right thing to have, so goes the thinking. The fact that the racers have small cast iron units and put considerably more work on them should be compared to lugging around two hulking stainless steel units so you could pretend to be Rossi or whomever. Let's not mixup marketing with engineering.

Secondly, the original Transalp was a designed to be a "desert bike" more suited to the likes of the Paris-Dakar and Barstow-Las Vagas races. In fact, I vaguely remember that it did compete in the P-D race at least once but I could be wrong about this. The front disk and rear drum meant that the suspension could be the the best at what it was intended to do. The drum could be designed to be lighter and simpler than a disk with equivalent stopping power. The rear does only about 10% of the stopping generally and even less than that in the sand and dirt.

The front brake is more than adequate for a dirt bike and is lighter by half than twin disks so the suspension can absorb the ruts and whoops better. Having ridden my TA to the extreme and seen the Finnish videos I know this
is a much more capable dirt bike than most give it credit. Later models became heavier and more stylish at the cost of off-road capability. I would even suggest the increase to 650cc was to lug the extra weight around with the same performance.

And this is OK. Most riders want a P-D look but with a street bike ride. Look at how the BMW GS series has morphed from the very capable GS80 to the bloated cartoon that is the current GS model with the wanna-be aluminum luggage. Money talks and the manufactures listen. Take the V-Strom off-road? Only if I wanted to buy a lot of plastic!

This has all been rambling and [possibly?] pedantic but I hope I've offered some constructive insights. One slight consideration is that each of the twin disks are not quite as big as a single disk would be but since the reduction is an inverse exponential I think the comparison holds up well without a lot of math.

Saludos,

J.

As this thread has wound it way back and forth across the continents, I think I've forgotten the original question. For a
moment however, let me say something about "feel".

I replaced my '89 TA's front (OEM) hydraulic brake line with a Galfer stainless steel unit. Immediately gone was that "spongy" feel. Actuation was crisp and I felt there was a direct relationship between finger effort and stopping "power".

This may be a 1st step to improving the TA's "braking". Certainly less expensive @$50 than a double disc retrofit. One should also consider (in evaluating braking power) whether there is any air in the brake line.

In fact this may be even a better 1st step. Mity-Vac (sic?) make a hand pump brake bleeder that sells for $20 in most auto US parts stores. That and a fresh bottle of the appropriate DOT fluid is a great investment.

As most US TA's are a dozen years old, its safe to say most have never had their fluid changed. A quick look into the sight glass on the reservoir that looks like maple syrup is indication it needs to be changed. Brake fluid is clear and that's what you should see.

I change my yearly.

Dave Steven

Dave is entirely correct in this.

To expand the subject a bit further. Stainless steel brake lines are not made of stainless steel. They are basicly the same rubber lines [although sometimes with teflon liners] ENCASED in a braided stainless steel casing. It is the casing that prevents the rubber brake line from expanding under pressure. Sort of like a girdle on a fat girl. Thus, all the effort you apply to the brake lever is directly transfered to the brake cylinder and hence the pads. This is the better "feel" you get from them - what you put in is exactly what you get out, Not minus the brake line swell factor.

Dave is also correct in that any brake, single disk, twin disk, or drum, is going to give crappy performance if it is not maintained well. Brake fluid should be changed yearly or at least bi-yearly. The calipers should be dismantled at that time and the pistons pressed out and examined. For the small cost I suggest that the piston seal o-ring be replaced. When you reassemble it all be sure to clean and grease the pins and/or pivots the caliper rides on. Finally makes sure the wheel rotates freely without drag. If not the master cylinder on the handlebars may need to be rebuilt. However, if you change your brake fluid regularly this is rare. The clearances on a disk brake are very small and even the tiniest bind in the system can cause a "grabby" brake.

Why does brake fluid change to syrup? Normal brake fluid is hydroscopic. This means that it absorbs moisture out of the air. Modern master cylinders have those little bellows devices to prevent this but nothing is perfect. An alternative is to use silicon brake fluid which is not hydroscopic but which absorbs money out of your wallet at a much faster rate. I've seen discussions arguing against it but it has worked well for me.

So, if you want the best brakes listen to Dave. Get SS brake lines and use some winter day when you can't go riding anyway to disassemble your brakes and tune them up.

The next time you have one of those "Oh Shit!" moments your brakes will be your best friend and you'll be glad you gave them all that attention.

Chau, J.

>>main advantage of twin disks is that they "look cool". The racers have them so they must be the right thing to have, <<

ok, so we're agreed on everything but this point. maybe an SV650 can get by with a single rotor, but not any GSX-R. it would be crimminal (esp in the US!) for mfgs to sell some of the bikes out there with any less braking power than they do. a lot of these machines are capable of speeds deep into the triple digits and you know some idiots out there get their jollies by going fast in straight lines. imagine how much trouble you could get yourself into with your VF1000R if you had only one rotor up front. that disc would have to be as big as the wheel to reign in that horse from ton-up speeds. not that you would ever go there.... ;-)

my question is, why would anyone try to say that TAs don't need any more braking power? when can a skilled rider ever have too much?
kev

Hi Kev, glad you remember my VF-R. Too bad we never got to run together with my new race compound, low profile Metzelers. Your little Hawk GT would have appreciated my triple disks then so that I wouldn't run over you in every
turn! =;^)

To reiterate a point, every design is a trade off. A bigger gas tank means greater range but more weight to move around in the turns. Twin disks means more braking power but less suspension compliance. I was talking about the TA design when I stated that twin disks were overkill for the design purpose. I remember a rather exciting trip down the
Kankamangus highway from the summit with you, and I don't think either of us were in danger of overheating the brakes. How much faster do you think you could go on that bike?

A Hyabusa is another design with it's own requirements. Flat paved roads, a la autobahn, at very high speeds are it's design environment. Consider the trade-offs. Weight, wheelbase, steering rake and trail are all increased for stability at high speed at the cost of fast steering response and side to side transients. A CBR954 would eat it alive on the Ortega highway but lose on the freeway.

Somebody mentioned the Buell with the rim mounted disk brake. The trade here is that the hub and spokes can be made much lighter because they no longer have to support the torque of the braking force from the disk out to the
rim.

So, how much brake does the Transalp need. I think that you and I have proven, on several occasions, that the single disk is sufficent. How much does an RC51 need? Probably just a little bit more if you or I are on top of it. :o)

Can't wait to go riding together again.

J.