P4 Brake Fun!

Oct 10, 17 16:52

Post #1 of 27 (3445 views)

I've been trying to build up a super narrow P4, but have run into a hitch. The furschlugginer rear brake protrudes too far for the inner chainring to clear.

Now I could get a much wider BB and add some spacers on the drive side, but this would defeat the goal of achieving a narrow q factor, not to mention screwing up the chainline. I've also considered shaving down the brake pads to nothing and then tightening up the brakes. But when you tighten the cable up, 90% of the movement is on the non-drive side (the brakes don't pull symmetrically).

Any of you P4 geniuses have some thoughts on this?

My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers

Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 10, 17 17:08

Post #2 of 27 (3426 views)

Have you tested narrow Q?

I have but it was anomalous. Ie p5 and only 12 mm total ((6mm side)

I am still very interested but outside of a full structural redo of bb area or track cranks like you have, or custom bike like Walser or English very hard to do.

I thought you were 1X???

Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 10, 17 17:15

Post #3 of 27 (3411 views)

The best/easiest option I can think of is losing the inner chainring. There's a company out there that will do custom 1x direct mount chainrings though they're pricey and the lead times are kind of long... I'll try to track down the bookmark.

Re: P4 Brake Fun! [mauricemaher] [ In reply to ]

Oct 10, 17 17:42

Post #4 of 27 (3385 views)

mauricemaher wrote:

Have you tested narrow Q?

I have but it was anomalous. Ie p5 and only 12 mm total ((6mm side)

I am still very interested but outside of a full structural redo of bb area or track cranks like you have, or custom bike like Walser or English very hard to do.

I thought you were 1X???

Yeah, there is a definite improvement. Curiously, going from 131 to 121 gave as much improvement as 150 to 131. I'm guessing you hit some sort of inflection point with flow from the legs re-attaching when you get real close.

Yeah, I actually would like to do 1X. But it has the same problem, because the inside of the crank arms protrudes nearly as much as the inner chain-ring on the double.

GreenPlease wrote:

The best/easiest option I can think of is losing the inner chainring. There's a company out there that will do custom 1x direct mount chainrings though they're pricey and the lead times are kind of long... I'll try to track down the bookmark.

I've seen the suggestion elsewhere to drop the inner chainring. I may try that, though it means no powertap chainrings.

My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers

Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 10, 17 17:57

Post #5 of 27 (3366 views)

Get rid of the rear brake altogether. It's there for regulatory compliance only; it doesn't help you to stop the bicycle. And I speak from experience.

Citizen of the world, former drunkard. Resident Traumatic Brain Injury advocate.

Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 10, 17 18:07

Post #6 of 27 (3349 views)

I tested with Len Brownlee.

He pretty much only tests at 0 yaw. But his runs are very long IE 10 minutes and he does modelling at 3 different speeds ie plus minus 3mph so 27 30 33. Then does his own regression modelling.

The Q was very much an after thought, after I looked at other items much as possible within 2 hours, and I learnt about 10x more by watching others.

So not a definitive test.

Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 10, 17 18:08

Post #7 of 27 (3344 views)

install a center pull brake. make a custom bracket for it....and make sure you have a reliable front brake that dosnt 70% of the work anyway.

1X would be another way to go around this. how narrow of a Q factor can you acheive? i m curious to do something similar..

Jonathan Caron / Professional Coach / ironman champions / age group world champions
Jonnyo Coaching
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Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 10, 17 18:43

Post #8 of 27 (3292 views)

I once had 3 tt bikes and cannondale slice rs, and always fought against this funky problem.

Now I sold them all and bought a disc brake cervelo. I am extremely happy now.

Sorry for the not that needed info but what I wanted tell you is "there's no way to deal with fatty rim-pad clearance matter perfectly."

Stay home, stay healthy.

Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 10, 17 19:01

Post #9 of 27 (3273 views)

Bench grinder would be my first thought. It looks like the casting could be trimmed by a couple mm without sacrificing integrity. Second thought is 1x. It s a TT bike. What the hell you gonna do with the small ring? If you want a PT ring, just grind the little chainring teeth off.

Re: P4 Brake Fun! [jonnyo] [ In reply to ]

Oct 10, 17 20:03

Post #10 of 27 (3219 views)

jonnyo wrote:

install a center pull brake. make a custom bracket for it....and make sure you have a reliable front brake that dosnt 70% of the work anyway.

1X would be another way to go around this. how narrow of a Q factor can you acheive? i m curious to do something similar..

With 1X campy track crank and 103 BB, I get to ~120 on a P3C. No matter what I do with the P4, I'm pretty sure, I can't get below 130.

grumpier.mike wrote:

Bench grinder would be my first thought. It looks like the casting could be trimmed by a couple mm without sacrificing integrity. Second thought is 1x. It s a TT bike. What the hell you gonna do with the small ring? If you want a PT ring, just grind the little chainring teeth off.

I just showed the 2X because it demonstrated the problem better. It actually clears just as well as the 1X. But if I ground down the little chainring, it would actually fit better -- and I would have a Powermeter. That's a really interesting idea. Thanks!

My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers

Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 10, 17 20:09

Post #11 of 27 (3209 views)

Grind off some of the brake.

Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 10, 17 20:18

Post #12 of 27 (3203 views)

Picture from the bottom pointed up?

This looks fixable to me, at least up to a point.

What rear wheel?

Re: P4 Brake Fun! [Richard Blaine] [ In reply to ]

Oct 10, 17 20:30

Post #13 of 27 (3189 views)

Richard Blaine wrote:

Get rid of the rear brake altogether. It's there for regulatory compliance only; it doesn't help you to stop the bicycle. And I speak from experience.

Thread hijack: I'm sure this was at least partly tongue-in-cheek, but I just upgraded my P4 to the v2 rear brake and it made a difference. For sure there's a lot more stopping power with good front brake (DA) + v2 rear brake than just the front brake alone.

Re: P4 Brake Fun! [chicanery] [ In reply to ]

Oct 10, 17 20:56

Post #14 of 27 (3170 views)

chicanery wrote:

Picture from the bottom pointed up?

This looks fixable to me, at least up to a point.

What rear wheel?

The photo is from above. I haven't decided on a rear wheel yet. I got one of these cranks:

http://www.short-bike-cranks.com/short-crank-specs

If I can make it work by paring down the inner chainring of some Powertap chainrings, it broadens the wheel choices a little. Otherwise it's probably a Hed disc with a narrow rim and Powertap hub.

My latest book: "Out of the Melting Pot, Into the Fire" is on sale on Amazon and at other online and local booksellers

Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 10, 17 21:00

Post #15 of 27 (3167 views)

I meant, can you post a picture from the bottom.

I have a 23mm HED disc with Powertap if you need it. I don't actually have a need for the narrower version.

Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 11, 17 0:18

Post #16 of 27 (3088 views)

I'd go full single 1x setup and grind off the back of the bolt tabs on the cranks if needed. 120mm might be a bit too narrow for power production so maybe not much if any penalty overall.

AeroCoach UK
http://www.aero-coach.co.uk

Re: P4 Brake Fun! [jkatsoudas] [ In reply to ]

Oct 11, 17 7:02

Post #17 of 27 (2963 views)

jkatsoudas wrote:

Richard Blaine wrote:

Get rid of the rear brake altogether. It's there for regulatory compliance only; it doesn't help you to stop the bicycle. And I speak from experience.

Thread hijack: I'm sure this was at least partly tongue-in-cheek, but I just upgraded my P4 to the v2 rear brake and it made a difference. For sure there's a lot more stopping power with good front brake (DA) + v2 rear brake than just the front brake alone.

My post was, in fact, mostly jocular. But when riding my P4 I actually always assume my rear brake isn't going to help me. I have a SRAM Red front brake and don't ride in the Alps, so I've never been in too much trouble with that assumption.

And sorry for being uninformed, but what's that v2 brake you mention?

Citizen of the world, former drunkard. Resident Traumatic Brain Injury advocate.

Re: P4 Brake Fun! [jens] [ In reply to ]

Oct 11, 17 7:19

Post #18 of 27 (2941 views)

some other good ideas for sure, just to add my thoughts though.

If most of the pull is nds, you could add a stop the to bottom of the ds chainstay to keep the arm from moving out past where you need it. Then shave the brake pad down on the ds to whatever you need to make up the difference. That way you still pass the "brake check."

ymmv of course

My Blog - http://leegoocrap.blogspot.com

Re: P4 Brake Fun! [Richard Blaine] [ In reply to ]

Oct 11, 17 10:15

Post #19 of 27 (2879 views)

Richard Blaine wrote:

And sorry for being uninformed, but what's that v2 brake you mention?

Some time around late 2010 or early 2011 Cervelo figured out that the original rear brake on the P4 sucked and released an improved version of it. Depending on what year P4 you have, you may or may not already have the v2 brake. If you have a 2009 or 2010 P4 with the v1 brake, the upgraded brake is available from Cervelo. IIRC, it's ~$200-something for the brake and another $70-something for the new brake cover (the cover for the v1 brake will not fit on the v2 brake).

Re: P4 Brake Fun! [jkatsoudas] [ In reply to ]

Oct 11, 17 12:16

Post #20 of 27 (2789 views)

jkatsoudas wrote:

Richard Blaine wrote:

And sorry for being uninformed, but what's that v2 brake you mention?

Some time around late 2010 or early 2011 Cervelo figured out that the original rear brake on the P4 sucked and released an improved version of it. Depending on what year P4 you have, you may or may not already have the v2 brake. If you have a 2009 or 2010 P4 with the v1 brake, the upgraded brake is available from Cervelo. IIRC, it's ~$200-something for the brake and another $70-something for the new brake cover (the cover for the v1 brake will not fit on the v2 brake).

I have an April 2011, one of the last ones made. And if that's the "improved" brake, I shudder to think what the original was like.

Citizen of the world, former drunkard. Resident Traumatic Brain Injury advocate.

Re: P4 Brake Fun! [Richard Blaine] [ In reply to ]

Oct 11, 17 12:23

Post #21 of 27 (2777 views)

The two brakes are interchangeable on the frame, which defines all the relevant pivot points. So there's no difference in leverage, for example.
The main difference is, the new one is easier to work on, so it should be more likely to get set up and adjusted right.

Damon Rinard
Engineering Manager,
CSG Road Engineering Department
Cannondale & GT Bicycles
(ex-Cervelo, ex-Trek, ex-Velomax, ex-Kestrel)

Re: P4 Brake Fun! [Richard Blaine] [ In reply to ]

Oct 11, 17 13:14

Post #22 of 27 (2730 views)

I have a 2011 P4 also and V2 of the brake. I thought someone had finally figured out a solution to that crappy brake. I do like the idea of taking the brake off completely.

I'd love to figure out a way to throw on a Tri rig brake. I have a buddy who can fabricate just about anything so if anyone has any suggestions...I'm all ears.

Re: P4 Brake Fun! [TriathlonJoe] [ In reply to ]

Oct 11, 17 14:48

Post #23 of 27 (2667 views)

TriathlonJoe wrote:

I have a 2011 P4 also and V2 of the brake. I thought someone had finally figured out a solution to that crappy brake. I do like the idea of taking the brake off completely.

I'd love to figure out a way to throw on a Tri rig brake. I have a buddy who can fabricate just about anything so if anyone has any suggestions...I'm all ears.

I'm going this route, just need to find someone to fabricate it.

Basically, it will be a metal horseshoe. The 2 ends of the horseshoe will bolt in directly where the current brake bosses are. Then, at the top of the horseshoe, will be another bolt into the frame where the P4 brake has its brake "rocker" bolted into the frame. So now you have 3 very solid connection points directly into the frame.

Then, again at the top of the horseshoe, have a hole drilled out for a standard, single bolt rear brake. You'll need some spacers to make sure everything clears, but it seems like it would work very well.

Let's chat a design, and see if you buddy can make one for each of us :)

Alex Arman

Strava

Re: P4 Brake Fun! [doublea334] [ In reply to ]

Oct 12, 17 8:23

Post #24 of 27 (2540 views)

Sounds good. Send me a PM when you get a chance. I already sent your idea to my friend. He likes it and thinks it's doable. The only thing is that he's about 2 hours away from me.

Re: P4 Brake Fun! [TriathlonJoe] [ In reply to ]

Oct 12, 17 9:12

Post #25 of 27 (2510 views)

Count me in on this adaptor. I'm sure there are a few of us with P4s that are willing to pitch in for this solution.

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