Braking from High Speed – Components

We’ve had some response regarding brake pads and discs, and whether these effect braking distances in any way, so here is a quick review of braking components.

Brake Pads

‘Softer’ pads with higher coefficients of friction require less lever effort for the same braking effect, but wear out quicker and can fade. Different construction of and materials used in pads can also effect the ‘feel’ during braking which is vital particularly on a track, and being able to sit the bike in it’s nose with one finger is great.

Make sure you buy a well known brand from a reputable source. I bought some ‘Armstrong Racing’ pads from Newark Auto Jumble some years ago, then went straight at the Esses at Donnington on a trackday. Very lucky to find the problem there, as I was off to the IOM on bike the following week. They were probably OK for normal road use, and of course may be OK now, but had I found the problem going down to the Creg on Mad Sunday…….

Brake Lines

Braided hoses, if not already fitted, can make a big difference as they don’t expand as much when pressurised, which makes the brakes feel sharper and uses marginally less lever movement. These do need to be properly made as they operate under high pressure. Most modern hoses are made to measure and swaged rather than you having to assemble your own fittings. Buying a bike fitted already with after market bolted hoses is always a risk that they have been assembled and torqued up properly. If in doubt change them. Again buy a major brand from a recognised supplier, and make sure they are certified correctly. See for example:-

http://www.helperformance.com/certification/

Master cylinders and calipers

The first bike we had which could stop with one finger, was an Aprilia Mille ‘Sound of Thunder’ bike, with the early Brembo racing radial calipers and master cylinder, which are now commonplace on top spec OE bikes. Absolutely amazing at the time. You can retrofit better master cylinders relatively easy (changing calipers usually mean changing forks, or some complicated bracketry for older bikes), but you need to be very careful to use the correct bore and displacement master cylinder, and adjust it correctly.

From experience, everything seems great tested statically, but if the master cylinder piston is not returning far enough, then the fluid cannot return to the reservoir , heats up and locks the front brake. Had this happen to a rider on a race bike with us a couple of years ago , as well as personally on an old TZ350 trying out a smaller bore master cylinder.

Brake discs

Also be very careful where you buy these safety critical parts. Here is a CB500 disc off a race bike where it has cracked and failed at Mallory – the rider was badly hurt.

IMG01910-20110716-1632

The same problem was found on a second bike the same day. These are non-floating cast iron, not the modern steel discs. However, steel discs can warp pushing the pads back, which you suddenly  discover when it takes two pumps to get the brake to work. The old thin fixed steel disc are very prone to this, so you need to make sure that pads are equally spaced and that the disc is not being bent when the brake is applied (another old TZ problem), which is why ‘floating discs’ were invented.

Some floating discs seem to wear the ‘spools’ very quickly, one side went recently on my GXR1000K7. You can here them ‘tinkling’  when you wheel the bike (some Italian bikes used to do this from new), but we cannot find what the service limits should be. You also sometimes get a ‘clonk’ initially when braking. If in doubt change them.

Modern sintered pads can wear out the discs quite quickly, so always check for bad scoring and minimum thickness (usually stamped on the disc).

Again buy OE or recognised brands from a reputable source.

Brake Fluid

Needs to be changed every two years on road bikes, more often for race bikes. Dot 4 is usually recommended, and there is a Dot 4 Racing with a higher boiling point for track bikes. The problem is you don’t know you have a problem until the fluid overheats and boils, as it absorbs water over time, and the brakes simply fail. There is also a new DOT 5.1 which has a longer life, not to be confused with DOT 5 which is silicone based and must not be mixed with any other brake fluid. DOT 5 doesn’t absorb water so has a long life, has a high boiling point, doesn’t act as a paint stripper, is better at very low temperatures, but is supposed to be more compressible making brakes spongy, and is not suitable for anti-lock systems.

Apparently some Harleys have DOT 5 fluid.

Always refer to your bikes handbook, only buy small bottles of fluid to top up and keep the caps on. For racing brake fluid, refer to the manufacturers advice for usage and frequency of changes.

 

What finally limits braking distances on a bike, is that braking forces much over 1 g have the back wheel in air, as the centre of gravity is so high, so braking harder flips the bike. This usually happens quite slowly, so riders have time to simply ease off the brakes.

 

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s