Ducati Sporting Club

General - Motorcycle only Motorcycle Tech only please.

Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 22-Sep-2009, 05:34 PM
NBs996's Avatar
NBs996 NBs996 is offline
Registered Forum User
Ducati in my Blood
 
Posts: 4,728
Join Date: Sep 2003
Mood: I love my 996 xxx
Brake lines

OK, so you've typically got two different brake line setups for twin discs...
1. single line which splits above the mudgaurd to each caliper, or
2. two separate lines from master cylinder to each caliper.

Question is, what's the difference between the two, and what's the technical reasons behind the differences?

Answers on a postcard, or on this thread!
Reply With Quote
  #2  
Old 22-Sep-2009, 08:47 PM
Whele Whele is offline
Registered Forum User
Mille
 
Posts: 344
Join Date: Sep 2001
Mood: Meditating
If you have the single line which splits above the mudguard (set up 1) , all is fine until you rip the front mudguard from its mountings, then it takes the brakelines with it, (so the scrutineers at race meeting would have it)

The twin lines from the master cylinder (set-up 2) means if you boil your fluid in one calliper, the resultant air bubbles wont affect the breaking performance on the other calliper.

So In the real world – no difference.
edit - you could install 2 different internal diameter lines (on set-up 2) and have progressive bakes!

Last edited by Whele : 22-Sep-2009 at 08:52 PM.
Reply With Quote
  #3  
Old 22-Sep-2009, 09:32 PM
deej's Avatar
deej deej is offline
Registered Forum User
Ducati Meccanica
Bikes: have owned 748/853/916/749/853R/748/848 not sure whats next...
 
Posts: 2,244
Join Date: Sep 2004
Mood: excited about the changes made to averysmotorcycles.co.uk that are coming up
a good question that i'd be interested to see a more in depth answer to. the reason i ask is my 749 has the 1 down and 1 over the mudguard line not the usual twin line setup. under braking the bike feels real strong on the right side,even pulls slightly making the left feel very weak. would this be down to the line set up or something else
Reply With Quote
  #4  
Old 22-Sep-2009, 09:35 PM
Shazaam!'s Avatar
DSC Member Shazaam! Shazaam! is offline
DSC Club Member
Big Twin
 
Posts: 1,167
Join Date: Nov 2001
First consider what’s the same:

• The volume of hydraulic fluid that it takes to move the pistons from their retracted position to where contact occurs between the brake pad and the rotor disc.

• The pressure in the hydraulic fluid for a given braking force between the pads and rotors.

• The stiffness of a given brake line construction, that is, it’s resistance to expansion both circumferentially and longitudinally.


Now consider what’s different:

• The total length of brake lines that runs between the master cylinder and the calipers. Two lines are longer than a split configuration (which is the key to the answer.)

When you pull the lever to the master cylinder, a small volume of fluid is displaced that moves the caliper pistons. Then the pressure inside the brake lines increases as you squeeze harder - more force is exerted by the master cylinder and the brake pads are in contact with the rotor.

As the pressure rises inside the brake lines they expand and elongate. The volume of fluid that they contain increases and some of the force you apply to the lever is being used to expand and stretch the brake lines. This effect gives the feel at the lever what’s called a “spongy” feel. Said another way, you loose part of the pull harder - brake harder effect needed to modulate the amount of braking.

The longer total length of dual brake lines will undergo a greater increase of internal volume (which is less desireable) than a split configuration.

What’s interesting is that brake line sizes are commonly either -3 (3mm I.D.) or -2 (2mm I.D.). 2mm lines will expand less circumferentially than 3mm lines. So if you run two lines, use the 2mm size to negate the spongy effect of the longer line length. Two 2mm lines will move almost the same amount of fluid as one 3mm line so flow restriction is not a concern.
Reply With Quote
  #5  
Old 22-Sep-2009, 09:41 PM
Ghost's Avatar
DSC Member Ghost Ghost is offline
DSC Club Member
Big Twin
Bikes: Ducati 749, Phil Read Replica, DD 620
 
Posts: 1,830
Join Date: Mar 2008
Mood: 2011 DD Class 'B' Champion
Quote:
Originally Posted by Whele
If you have the single line which splits above the mudguard (set up 1) , all is fine until you rip the front mudguard from its mountings, then it takes the brakelines with it, (so the scrutineers at race meeting would have it)

The twin lines from the master cylinder (set-up 2) means if you boil your fluid in one calliper, the resultant air bubbles wont affect the breaking performance on the other calliper.

So In the real world – no difference.
edit - you could install 2 different internal diameter lines (on set-up 2) and have progressive bakes!

That statement is not true as the hydraulic system is common so air would be in the system causing loss of feel at the lever.
Reply With Quote
  #6  
Old 22-Sep-2009, 11:17 PM
paynep's Avatar
DSC Member paynep paynep is offline
DSC Club Member
Ducati Meccanica
 
Posts: 2,081
Join Date: Jun 2001
Mood: Wet wet wet
Quote:
Originally Posted by Shazaam!

What’s interesting is that brake line sizes are commonly either -3 (3mm I.D.) or -2 (2mm I.D.). 2mm lines will expand less circumferentially than 3mm lines. So if you run two lines, use the 2mm size to negate the spongy effect of the longer line length. Two 2mm lines will move almost the same amount of fluid as one 3mm line so flow restriction is not a concern.

Now that is something I'd never considered. And maybe why I've never managed to get the brake setup on my 851 to feel as good on track days as my identically padded/disc'd/calipered/master cylindered old 888.....

Just goes to prove that you can still get good info from the DSC site.

Cheers Larry


Paul

11th year in DD #68 and getting slower by the year

M800 & 620SSie DD racer
Reply With Quote
  #7  
Old 23-Sep-2009, 12:20 AM
NBs996's Avatar
NBs996 NBs996 is offline
Registered Forum User
Ducati in my Blood
 
Posts: 4,728
Join Date: Sep 2003
Mood: I love my 996 xxx
Thanks shazaam, that's just what I was thinking.

I've been a bit curious as to why a twin setup is considered by some to be some kind of performance upgrade, when theoretically all it does is make the lever action softer. Thought I might be missing something!

I've got the twin setup on the 620 for just this reason, I've come to prefer a softer lever with a bit more travel between on and off, and lets me fine tune me braking pressure easier.
Reply With Quote
  #8  
Old 23-Sep-2009, 09:10 AM
skidlids's Avatar
DSC Region Organiser skidlids skidlids is offline
MotoGP God
 
Posts: 18,200
Join Date: Apr 2002
Mood: Its ONLY a Bike Club
As mastercylinder/lever ratios can be matched to either setup, the standard setup on bikes from the factory will also be considering costs and possibly weight as the 916 style setup with the short hose T-ing off across the mudguard must weigh less than 2 full length hoses with the extra banjo fitting and double banjo bolt.

Most of my bikes have a T piece just above the bottom yoke so there is only about 200mm of single brake line, so not alot lost on the hose expansion/softening effect over the standard system and only a little bit saved over the two seperate hose setup. But then mostmy brake setups are fitted to either Brembo or AP Radial Mastercylinders, the AP giving the best setup with its adjustable ratio


Checkout the Desmo Due Paddock on Facebook
Reply With Quote
  #9  
Old 23-Sep-2009, 02:13 PM
MLC Racing's Avatar
MLC Racing MLC Racing is offline
Registered Forum User
500SD
 
Posts: 620
Join Date: Jun 2006
Mood: Moto Guzzi are the new Ducati??
Thumbs up

I may be wrong but I always understood that ACU rules insist on the '1 line for each caliper from the master cylinder' arrangement. The single hose and splitter was road use only!
Reply With Quote
  #10  
Old 23-Sep-2009, 02:19 PM
skidlids's Avatar
DSC Region Organiser skidlids skidlids is offline
MotoGP God
 
Posts: 18,200
Join Date: Apr 2002
Mood: Its ONLY a Bike Club
Quote:
Originally Posted by MLC Racing
I may be wrong but I always understood that ACU rules insist on the '1 line for each caliper from the master cylinder' arrangement. The single hose and splitter was road use only!

Dave the ACU rules say the Hose must split above the Bottom yoke

So you have the choice of two seperate Lines coming from the M/cyl or a single line from the M/cyl to a T piece above the top yoke and then a line down to each caliper

With either setup having a cable tie holding the two together below the line of the bottom yoke has been known to fail scrutineering


Checkout the Desmo Due Paddock on Facebook
Reply With Quote
Reply
  
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes
Postbit Selector
Switch to Vertical postbit Use Vertical Postbit

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Recent Posts - Contact Us - DSC Home - Archive - Top
Powered by vBulletin 3.5.4 - Copyright © 2000 - 2019, Jelsoft Enterprises Ltd. - © Ducati Sporting Club - All times are GMT +1. The time now is 09:49 AM.