mikeread

This is not really a frame- building question but I suspect the people reading this section of the forum will be a bit more technically knowledgeable and able to give me some advice :-)

I have a winter/Audax bike which was my first and only frame build to date. It originally had Campag Centaur ergo levers, Shimano deep drop brakes and Mavic Open Pro rimmed wheels. The braking was good regardless of what blocks I used, which was usually the cheapest.

After a lot of miles I overhauled the bike and it is now running Shimano Sora levers (the older 9 speed ones with the washing lines) , the same Shimano deep drop brakes and the wheels now have Ambrosio rims. The braking is now scarily bad.

I have tried a few different brake blocks and the braking just feels wooden, there is no modulation at all.

Since the brakes have not changed I doubt they are the problem, Maybe the rim material makes a difference but I suspect, not much and they wouldn't make it feel wooden. So I can only conclude that the Sora levers are the problem and they pull more cable than the old campag ones.

Comparing the deep drop brakes to the current Ultegra ones, the mechanical advantage is 1.74 on the deep drop brakes (pivot to cable/pivot to brake block at lowest point in slot) and 2.3 on the Ultegra. Since my Ultegra brakes have the blocks only half way down the slot the actual MA is about 2.8. This explains the wooden feel and poor braking.

I am not happy riding the bike as it is and would appreciate your suggestions on how to improve the braking. I see plenty of bikes with Shimano levers paired with Shimano deep drop brakes, It must be possible to make it work

I am thinking:

Brake blocks - I will be ordering some more - Koolstop Salmon I believe are a good choice
Do all the Shimano levers have the same cable pull? Is there a better alternative?
Would the TRP or Velo Orange deep drop brakes be better matched to the Sora levers.? Do they have a better MA?
Could it be the rims?
Anything else?

Thanks

Mike

Andrew R Stewart 

Mike- I run much the same set up as you had (Campy Ergo pointed hood version, Shimano R650 calipers w/ OEM pads and Open Pro 700C rims). The wife has (Tiagra 4500 levers, Shimano R541 calipers w/ OEM pads and Open Pro rims 700C). We ride together frequently (although not enough) and she complains about hand soreness if the ride is long, bumpy or has lot's of speed controlled down hills. I rarely have hand issues. But our big difference is our hands. I've been a shop wrench for decades and she types away at work. Big difference.

I used to be on top of brake system leverage factors (since Frank B first published his findings in Bicycling years ago) but since have not paid too much attention to the actual numbers. Shimano has changed the relative leverages between their calipers and their levers a few times. I suspect Shimano will say something about cable friction and reduced lever travel bit others might suggest it's about shifting the playing field so their compatibility with other brand/design calipers is reduced. Here's another forum's discussion about this. Andy

Brake Cable Pull Ratios

mikeread

Thanks Andrew, the progressive/regressive issue is interesting. I have done a bit of measuring:

1 Looking at the Campag levers (the ones after the pointy tops), they are definitely progressive, starting at TDC and being on the way down when the pads hit the rim. Lever pivot to cable pivot is 18mm

2 The Shimano Sora are definately regressive as they reach TDC just as the pads hit the rims. Lever pivot to cable pivot is 21 mm

3 My new Ultegra levers pull very progressively, they are well over TDC with the lever at rest. Lever pivot to cable pivot is 36 mm but the cable pivot is well forward of the lever pivot (to make it progressive I guess) and distance from lever pivot perpendicular to the cable is significantly less. I cannot see much of what is going on inside.

This all makes sense with my experiences. I suspect the progressive/regressive differences between Campag & Sora makes a little difference and the greater pivot to cable distance of Sora makes some more. Add them together for much reduced mechanical advantage.

Looking at my Ultegra 11 speed set up, the lever must pull more cable but is also very progressive. So is the progressive element progressive enough to make them work with the deep drop brakes? They definitely work well with the Ultegra brakes but they are a very different design!

So now I have an idea why the brakes are rubbish but am no nearer to a solution.

If anyone has the TRP and/or Velo Orange deep drops and is willing to do some measuring, please let me know. It would be useful to know if the leverage is different.

Well done anyone who has read this far :-)

fietsbob

I have Kool stop brake blocks on all the bikes with rim brakes ,
rubber always hardens as it ages, so new ones will feel less 'wooden'

MA is Math, ratio of distances between

pivots (fulcrum) and work(pads), and effort (cable pull/housing push)

Cable pull ratio is a result of MA.. as is the cable pull demand... on the other end.


..

mikeread

Just a quick follow up for anyone stumbling on this thread with the same problem I had.

I eventually bought a pair of the TRP deep drop calipers. Being of more recent design I thought they would more likely be compatible with modern levers. Also I received assurances that the TRP brakes would work. All I got from Velo Orange was 'no-one has complained yet' !

Out of the box the TRPs had very strong springs, So strong that I replaced them with the springs from my old Shimano calipers before even trying them.. I may even make some titanium springs for even lighter braking, if I can get hold of some suitable wire.

The geometry is slightly different on the TRPs from the Shimano deep drops, the side pivot is lower giving more leverage. It doesnt look enough to make much difference but does.

Braking is far better than the Shimanos, I can now lock the back wheel and even pop it off the ground should I wish. The bike is now safe to ride :-)

Performance is still way off the utterly awesome Ultegra brakes fitted to my other bike, so please Mr Shimano can we have some deep drop Ultegra style calipers?