Posts
451
Joined
11/19/2017
Location
Pittsburgh, PA
US
Edited Date/Time
1/1/2019 6:05am
So im not even close to happy w the front brake on the 18 250sx I just got. The lines and caliper and rotor are fine but its got the typical cheap Chinese master cylinder squish that a lot of new road superbikes are coming with these days. Like my new gsxr 1000 was similar level of junk so swapped it for a Brembo rcs 19 and that fixed the lever feel and reduces the squishiness and inconsistencies of it.
I saw a Supermoto rmz450 at the local shop that had a 16x19mm bamboo master and the lever didn't even move, it just worked on pressure instead of any amount of level travel, not looking for quite that much but it would be better than what it is now.
Ideas?
*note, its bleed just fine and yes I know its normal and you probably think its the best system out there but it just isnt sorry
I saw a Supermoto rmz450 at the local shop that had a 16x19mm bamboo master and the lever didn't even move, it just worked on pressure instead of any amount of level travel, not looking for quite that much but it would be better than what it is now.
Ideas?
*note, its bleed just fine and yes I know its normal and you probably think its the best system out there but it just isnt sorry
Lever should be fully engaged maybe 15mm in, otherwise, air.
Had my brand new 2017 sit for 2 month in the garage with 8h on it, got back, brake was unusable. Bleed it, and as good as new. Can also happen if you lay the bike over so air slips in.
what other master cylinders are people running? just supermoto stuff?
The Shop
Illl have to check out the prior year master to swap
The rear brake lever action is perfect. Have it set so there’s maybe 1mm of free play then it’s enguaged and it hardly moves
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Ful…
There's a lot of info here:
https://www.oppracing.com/category/1012-brembo-oe-oe-front-brake-master…
What is the stock 18-19 clutch master piston, any negative in upgrading to larger piston?
Actually, you have to consider the entire system starting with the force at the lever. A larger master requires more force on the lever to produce the same braking power, everything else being equal. The new Brembo stuff ('14-'19) uses a 10 mm master with 24 mm caliper pistons. If you do the math, that's a hydraulic ratio of 11.52:1. The '09-'13 KTM brakes used a 9 mm master with 24 mm calipers, i.e., a hydraulic ratio of 14.22:1. So, for the new stuff the force applied at the master is multiplied 11.52 times and for the '09-'13 brakes the force is multiplied by 14.22. The larger the master (for a given caliper size) the less line pressure (braking force) for a given lever effort. The trade off is that the higher the hydraulic ratio the greater the distance the master cylinder piston must move to develop a given pressure. You can apply the same principle to the clutch.
Interestingly, when Andrew Short was on KTM in '13 he wanted a stronger brake for outdoors, so he used the '08 master (10 mm) and '08 caliper (28 mm) for a 15.68:1 hydraulic ratio.
Pit Row
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