Technical FAQ: Broken shifters, rider flexibility, and more

This week, Lennard Zinn answers questions about a broken SRAM Force shifter, rider flexibility, and more

Repairing SRAM Force levers

Dear Lennard,
I had a recent incident with a sink hole that stopped dead my front wheel, causing the bike to endo (and me too, straight onto my collarbone … oh well, it was 30 years coming, I suppose). The bike seemed to have landed straight on the 2010 SRAM Force lever blades. There are no marks anywhere on the bike aside from scratches on the levers, plus a crack in the composite body of the left lever, at the inside point of the lever pivot, which seems to be press fit into the body sort of like a rivet. I am attaching photos of the crack, both with the cracked piece of the lever body missing, and with it simply pressed back in place (without any bonding, just press fit like a puzzle piece).

My question is this: can I safely repair the chipped lever body piece, perhaps with regular super glue or with carbon fiber repair resin? Since it will need to hold the brake lever blade pivot, this is a safety issue, not a cosmetic one. In its current state, the lever still works perfectly; it shifts normally, and it brakes normally as well — on a repair stand. I’m not riding this in its current state.

If super glue is all that is needed, I can certainly perform this myself. If you recommend carbon fiber resin, I can ask my friends at nearby Van Dessel, where they sometimes repair Van Dessel frames in-house. Last issue: if you think this can be bonded, should I push the lever pivot out of the way (i.e., outboard, since the crack is on the inside of the left lever) when bonding, or bond the composite piece with the pivot in place (and thereby presumably bonding the pivot in as well, rather than simply pressed in)?
— Greg

Dear Greg,
I’ve done enough gluing and repairing of little pieces like this that I think I can definitively say that neither method you’re proposing would hold very well. There just is not enough surface area to adhere to. Super glue on the broken edges or even resin and carbon layered over the crack will not re-mold the area into a single piece. It would need to be re-melted and molded into that shape to have its original strength. Applying the brakes tends to force that pin back against the lever body, but side loads and crashing on the lever will tend to yank the pin right out the front.

Unfortunately, SRAM does not sell lever bodies alone, so you can’t rebuild this lever like you could with 8-, 9-, 10-, and early 11-speed Campagnolo Ergopower levers. And I don’t think that SRAM offers an aftermarket lever-body-and-shifter assembly sans brake lever, either. To have a totally safe lever, you probably have to buy a new DoubleTap shift/brake lever unit.
― Lennard

Feedback on bottom bracket threads

Dear Lennard,
The technical term for what you described in your BB thread answer is here.
— Ray

Dear Ray,
Thanks! That’s an awesome moving illustration of it!
― Lennard

More on mixing components

Dear Lennard,
Since you have reported the 11-speed Campy cassettes will work with the Shimano shifters and derailleurs, how about using a Campy freewheel on those Mad Fiber wheels? This will save Brian and others from having to throw away wheels when going to 11-speed. The downside is having to buy a new Campy freewheel.
— Devin

Dear Devin,
You are correct; that would work fine, and in retrospect, I wish I had mentioned it. Maybe you meant this by the word “freewheel,” but Brian would not only have to buy a Campy cogset, he would also have to buy a Campy freehub body. On wheels for which Campagnolo freehub bodies are available and 11-speed Shimano-compatible freehub bodies are not, this is a good solution. But assuming Brian could get an 11-speed Shimano-compatible freehub body to fit that wheel, the Campy 11 solution offers no economic advantage.
― Lennard

Titanium vs. carbon

Dear Lennard,
I was reading your response to the Technical FAQ: Giving up carbon for old titanium, and the writer stated “I’ve been told that it will be like trying to convert a 69 Camaro into a 2014 Corvette,” which makes me curious about Titanium vs Carbon. Is that a fair comparison, other than weight and the material characteristics of the two materials? If they are set up the same, shouldn’t they both be Corvettes? And would there be a big difference between a 1” vs. a larger headtube, if they are both carbon forks?
— James

Dear James,
Well, I suppose you could make the argument that “it will be like trying to convert a ’69 Corvette into a 2014 Corvette.”

And yes, my experience with cyclocross bikes with fork shudder indicates that there is a substantial stiffness difference between a straight 1-1/8” carbon steerer and one that tapers down from 1.5” at the crown to 1-1/8” at the top. And the 1” steerer would undoubtedly be less stiff than the 1-1/8” one already. So yes, there would be a big difference in stiffness. That said, titanium bikes of that era with 1” steerer forks generally performed quite nicely, which was what I was trying to say by recommending against replacing his Litespeed’s head tube with one that will accept a bigger steering tube.
― Lennard

Is there a downside to shorter stems?

Dear Lennard,
I notice in your response to the “long legs, short torso” guy, you didn’t address his statement (which I bet $2 he heard from a shop person) about a shorter stem adversely affecting the handling of the bike.

I’ve heard this SO many times (I bike shop a lot with beginner females) and it kinda drives me crazy that comfort might be sacrificed for some theoretical handling issue.

Do you have any experience/knowledge on this topic? I’d love to see it addressed in one of your VeloNews columns, then I could say to the shop “experts,” “Lennard says …”
— Ray

Dear Ray,
Well, given that Fisher Genesis Geometry is exactly that (a longer top tube coupled with a shorter stem, as well as a shorter chainstay), I don’t know that you need any further evidence that bikes can handle well with short stems. Furthermore, downhill bikes often have little stubby stems, and racing them requires precise handling.

With a shorter stem, your total steering lever is shorter, so the same input to the handlebar results in a proportionally larger deflection of the front wheel. This is not necessarily a negative thing, but when Chris wrote, “The short stem undoubtedly affects the bikes handling/steering characteristics,” I suppose it is a rational assumption to make that he is inferring that the change in handling would be negative.
― Lennard

Using rider flexibility in bike fitting

Dear Lennard,
When we did our research on frame sizing to determine our stack and reach curve, [we found] that flexibility often played an even larger role in fit that torso/leg length ratios. Everyone thinks it is very mechanical from a torso/appendage measurement perspective, but changes in torso angle due to flexibility bring viable reach length back very, very, very quickly. I agree you headed him in the right direction, but it surprises me that RIDER flexibility isn’t mentioned as a key metric. Also, getting fit first and then choosing a brand/model as there are so many different stack/reach combinations available today is like saying “56cm” is just too abstract these days.

I think many taller pros could be faster/healthier with a slightly more conservative bar position as they just don’t have the flexibility to maintain their current fits. If you look at them from the side, there are a considerable percentage where their sacrum stays nearly vertical in the drops and they do all of their flexing in the mid- to upper-spine, reducing the size of their chest cavity and affecting their breathing and compromising the back/power on longer stages … let alone chronic issues over time. I think this is one of the reasons brake lever hoods have climbed up the bar curves so dramatically on pros’ bikes and they spend so much time in the hoods. The second cause/effect is often running their frame a size small, no spacers and a long stem (130-140mm is not uncommon), putting way too much weight on their front tire and removing any ability for fore/aft weight management in braking and cornering … degrading their handling capability, which, if they aren’t the best bike handlers, isn’t helping their cause. Andy Schleck could be an example; on the MTB side it could be Ryan Trebon. I believe there is a high likelihood they are being penny wise and pound foolish in their fits … elbows can always bend to get you lower when you need it.
— Anonymous former bicycle product manager

Dear Anonymous,
Good points. Yes, rider flexibility is key for bike fit. And given the amount of space I’ve dedicated here to stack and reach over the years, I certainly ought to have brought that up in my answer to Chris.
― Lennard

Stack heights

Dear Readers,
In re-reading that March 11 posting, I cringed a bit at my statement that the headset spacer stack is “not to exceed 100mm (four inches).” I should have said that, while it should never exceed 100mm, you should stay within the fork manufacturer’s stack-height recommendation. Stack recommendations vary from fork to fork.

We used to sell hundreds of Alpha Q Z-Pro forks, which was a fork I developed with True Temper for tall riders. It had a 450mm-long carbon 1-1/8” steerer that had about double the wall thickness of most forks. It also had a glue-in insert to reinforce the steerer under the stem clamp. The maximum recommended spacer stack for Z-Pro forks was 100mm, and that was present in my mind when I wrote that.

Stacking up a lot of spacers under a stem should not be taken lightly, and eliminating them in some cases should not be either; some manufacturers require that there be at least one spacer between the headset and the stem. Fork steerers breaking above the headset was an issue for George Hincapie in the 2006 Paris-Roubaix, and it has long been a pet concern for Cervélo founder Phil White.

Now that Alpha Q is no more (nor is Serotta, who made us similar forks with double-thickness 450mm carbon steerers for a number of years), and we still make frames for big guys needing long steering tubes, we have ENVE make us special forks with 400mm steerers. Unfortunately, ENVE can’t increase the steerer wall thickness, so we had Wheels Mfg. make us 122mm-long glue-in inserts. These are one-piece, slightly longer versions of the inserts that came with Alpha Q forks and that still come with 3T forks. This insert alleviates a worry I had about customers in the 300-pound range overloading the top of the fork steerer or about customers who choose to run a very tall stack on an ENVE fork.
― Lennard