Tech FAQ: TRP miniature V-brakes on Edge fork

Also: more Di2 gear range

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Editor’s Note: Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.

Dear Lennard,
I recently picked up a set of TRP 8.4 mini-V’s for a ‘cross bike I am building (I know it is late in the season — I actually got it for the rack mounts so that I could have a bike that can also carry my new son along).  In trying to install them on my EDGE cross fork, I found that the pins on the brakes do not line up with the holes on the fork.  I tried wiggling to no avail — it seems that they are just a little further out from the center of the mounting posts than the holes on the fork.  I tried a bit of force by hand, but that just chipped the clear coat on the fork.  Do you have any suggestions?  I thought about using a small drill bit to open the hole, but it seems like a risky idea.
― Jon

Dear Jon,
That’s a new one on me. I have the TRP CX9 mini-V’s on my Enve ‘cross fork; in fact, here’s a photo of me on it at Nationals. I have had no such problem installing it, and I’ve put it on and taken it off a number of times; the spring pin drops right into the hole.

I asked Jake Pantone, marketing and sponsorship director at Enve about it, and he said, “This is the first I have heard of an issue like this.” He did wonder if perhaps you have a fork that was a show sample or something that might not have gone through the normal drilling procedure that production forks do.

Since you say it’s an Edge fork, it must be a few years old, given that the brand changed to Enve a couple of years ago. So I’m going to make the assumption that this is not the first set of brakes you have had on that fork. That doesn’t necessarily mean that the holes are not mis-drilled, because the loose spring on many cantilevers makes it easy to line the spring up with a mis-drilled hole. However, it does indicate that they cannot be that far off, and the below tip could make the difference for you.

Lance Larrabee, marketing director for TRP, says, “I have not seen this problem with our brakes on Enve or any other fork. From time to time when installing brakes I have had to guide the pin into the hole using a small screwdriver.  Also, I’ve found sometimes it helps to loosen the brake pad before installing the brake arm as the pad sometimes overlaps the fork blade or seatstay forcing you to tension the spring a bit as you install the brake arm and spring pin.” Larrabee also sent the brake post schematic drawing. Check your fork’s spring hole location and dimensions against this.

If you still can’t get the spring pin to line up with the hole and the spring hole location is off, then I suppose you could move the hole over slightly with a round jeweler’s file. The base of the post should be aluminum. I suppose you could also use a slightly bigger drill bit and widen the hole; don’t drill more than a millimeter deeper than the length of the spring pin, though. I don’t think you would be able to start a drill bit of the correct size (2.4mm — see schematic) a bit off to the side of the existing hole, since it would tend to wander back into the existing hole and maybe snap off in the process.
― Lennard

Dear Lennard,
I am planning to do a 12-day fully-loaded tour on the Blue Ridge Parkway in April and hoping to use my current Felt CX bike, which has Dura-Ace Di2.

Question:  can I use and will it shift properly if I install a 30 x 42 (2×10) XTR or SRAM mtn bike crankset?

I need much lower gears than the 39 x 28 I currently have. Was hoping to be able to get a 30 x 28 low gear for the mtns. Will the front derailleur handle the smaller front chainrings?  Any other considerations or suggestions?
― Bob

Dear Bob,
Here’s what Shimano R&D director Wayne Stetina says about your situation: “Every MTB Di2 conversion uses an FD-7970F front derailleur with a clamp band adaptor and a 2X crank successfully.  Hint — get the 42/30 XTR crank; it will shift like a Dura-Ace racing double crank.  SRAM will only be rideable.  Also, you can re-space the MTB crank by swapping one bottom bracket cup spacer for 1mm spacers as needed, or use triple bottom bracket axle spacers to the non-drive side for narrower chainline on the 68mm-width road bottom bracket shell, since the 2X XTR axle is long enough for a 73mm bottom bracket shell.”

Another option might be to try a Shimano cogset not recommended for Di2, as a number of riders used on the Angliru climb in the Vuelta this past season. (The maximum cog size recommend by Shimano for Dura-Ace Di2 is 27 teeth.) I’ve heard of riders using Shimano cogsets topping out at 30 or 32. They said that they had to max out their b-screw adjustment (to rotate the cage way back so the upper jockey wheel won’t pinch the chain between against the largest cog). A trick for getting more backward rotation rear derailleur rotation to eliminate noise and roughness on the largest cog is to remove the b-screw and put it in from the opposite direction so the head, rather than the tip, contacts the derailleur hanger tab. You have to be very careful when trying a cog larger than the recommendation, as you wouldn’t want to ruin such an expensive derailleur by trying to make a shift that it couldn’t handle because the chain was too short.

If I had a Di2 bike, I’d try it and tell you what happened, but, alas, I do not.
― Lennard

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