Mechanics and Fixing Any Questions Answered

4.3mm at widest point.

M4.5 is a thing, I'd be surprised to see an imperial small fastener on Shimano.

Excellent thank you, will get a 4.5mm bolt ordered and will report back.

Just replaced a Tiagra 4500 chainset that someone had borked all the crank bolt threads on, with a new Claris one because that's all I could find with the same ratio. It's a road bike, which inexplicably has a MTB HT2 BB in it. The old crankset had a 3mm spacer on the NDS, and the new crankset comes with the same spacer. However, I cannot get the NDS crank arm on at all with the 3mm spacer in place. If I take it off, the crank fits as I'd expect and there's no play.
I assume the spindles are different length for some reason? But why would the new Claris one come with the spacer?

It also has one drive side BB 2.5mm spacer. The chainline isn't great, bit noisy. I should probably remove the BB spacer and add the NDS 3mm spacer, right?

HT road triples come with an NDS spacer to balance the crank spacing.

If you remove the BB spacer the MTB tube inside will be too long. Your best bet might be to move the BB spacer to the NDS and ignore the crank one.

Oh yes, forgot about the tube - I'll probably do that then

is there a reliable hack to measuring your disc brake rotor wear without one of those slotted tools?
I have some manual verniers but hear they’re not too reliable for this as the margins are so thin

I have some manual verniers but hear they’re not too reliable for this as the margins are so thin

I’d suggest that if a person struggles to read rotor wear on a vernier caliper that is a person problem, not a vernier caliper problem.

Correct: no BB spacer needed on 68mm BB and road crankset.

The tube will be fine, or just trash it.

if a person struggles to read rotor wear on a vernier caliper that is a person problem

Depends a bit on the wear, if there's a ridge at the perimeter it's hard to get a good measurement with an ordinary caliper. Time to get the micrometer out, or a caliper with rebated jaws designed specifically to get past the perimeter ridge

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That’s fair.

Tbh it’s not something I’ve ever done. I think with the negligible cost of new rotors, if I was concerned enough to think about measuring them, I’d just go ahead and replace them.

with the negligible cost of new rotors, if I was concerned enough to think about measuring them, I’d just go ahead and replace them

Yeah, that was my first thought too🙂

How's this for a full length but minimalist mudguard design, for a rim brake bike? A flat strip of carbon fibre, 30mm wide. It's stiff but it bends a little if you force it. It's attached to the brake bolt in the usual way. The stays are just fishing line. The lines are pulled tight so the strip bends to form the usual circular shape. The tension in the strip holds the lines taut. Might it work if the stiffness of the strip is just right?

Might it work if the stiffness of the strip is just right?

It's rather unlikely to form a circular arc of the desired radius. Assuming it's a physics problem rather than a serious engineering proposal, so ignoring any imposed loads from actually venturing outside a gravity free vacuum chamber, and equally assuming the fishing line is has zero flexural stiffness but infinite longitudinal stiffness and that the brake bridge end of the strip is perfectly rigidly constrained to be tangential to the tyre clearance arc, you just have to solve for the lowest energy configuration given a known length of the springy strip and the known coordinates of the fixed end of the fishing line. It's a large deformation cantilever problem but with the end load vector determined by the axis of the fishing line, which is well beyond my level of maths.

I normally just replace once an obvious lips appear/felt, as it’s more economical to replace pads and rotor than just pads (which likely to wear out quicker on tired rotors)

a physics problem rather than a serious engineering proposal

I have no desire to start a mudguard business. But I've already got the fishing line, so if I happened across an interesting strip I might risk it for a biscuit.

Every fender I’ve seen made from flat stock has loads of side spray.

So the rider gets wet feet?

Picture water escaping from the sides of the fender along its entire length. Basically your upper half will escape most of that, the rest of the side spray will hit everything else, of course that’s better than not having any protection. Fenders have compound curves for a reason.

So the rider gets wet

FTFY.

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Sounds like the stem bolts are the problem, that's what's holding everything together when riding, if you've no extra torque to spare with them then add some carbon paste to the stem/steerer interface.

What torque should I apply to a steel compression cap so that it doesn't come loose?

If it's loosening with 4-5Nm applied after clamping the stem, the issue is most likely, as you suspect, the plug shifting in the steerer bore. I think before trying to find a solution, you need to be sure of what exactly the problem is. Take accurate position measurements of everything when you initially set the bearing preload, and then take the same measurements after it has come loose. You want to know if the plug is getting closer to the top of the steerer, and it might only need to be 0.1mm movement. You'll probably want a depth micrometer, or a foot that spans the steerer diameter for your vernier caliper.

When I first dreamed this up I envisioned glueing fishing line on the underneath edges of the strip. Do you think this would redirect all the side spray?

I doubt it, but in the spirit of enquiry do it and report back.