TallRider

I just replaced my 12-year-old front wheel with Sun M13II rim, with a newly-built wheel with H+Son TB14 rim, because I wanted a wider rim.
It's striking how much the braking is strengthened by the new rim. I wouldn't expect such a difference. Same brakes and pads. Only factors I can think of:

• machined braking surface of the TB14
• different aluminum alloy and coefficient of friction with the pads
• old rim surface may have gunk on it (but I'd cleaned it with acetone and scoured it recently)
• angle of contact might be slightly better on the wider rim, although with a single-pivot sidepull brake I don't think the angle would be meaningfully changed

Thoughts? I've never thought machined braking surfaces should matter much, especially after some riding and braking, but perhaps that's relevant (or is until I've ridden and braked on the rim for a bit)

FullSpeedAgain

I guess with use the brake surface get's polished so the friction coefficient gets lower. When trial cyclist used rim brakes, they sandpapered it.

Maybe your new wheel's rim is more rigid so less braking force is lost by flexion when the brakes press it

TallRider

I hadn't thought of the surface being smoother mattering - machined braking surfaces are smooth in the direction of travel for rim against paid. But that might play a role as well.

I highly doubt that either double-walled rim is flexing inward enough under braking force be create a noticeable difference. Maybe this happens with some single-wall rims, but I suspect that mechanism is rare in recent decades.

fietsbob

Actually my Mavic SSC, CD treated rim (A Hard Anodizing) braked better
once I Scoured the anodized surface off and exposed the base aluminum

[EX 721, 559 size FWIW]





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TallRider

The H+Son rims I have are just machined bare aluminum; I don't have the hard anodized version. Should have mentioned that.
So I'm comparing bare aluminum to bare grooved aluminum and wondering what is so different.

fietsbob

groove? if only 1, when it's gone replace the rim,
you wore it down to the level of wear indicator..

TallRider

No, I just mean the tiny grooves/channels of a machined brake track.

TallRider

Turns out there's more gunk on the old narrower rim than I'd expected - I cleaned it off with an acetone rag tonight, and I got plenty of aluminum/rubber dust, the residue of braking.
Plus the narrower brake pads, which had worn in for a wider rim, didn't have much contact area on the narrower rim
So maybe there's no real difference here after all.

2manybikes

josephn1990

Its because of the wider rims

TallRider

What about wider times could matter to braking force, beyond pad contact angle?

TallRider

I opened the caliper qr after installing the new wheel, which puts the brake pads the same distance away from the rim as with the narrower rim and closed qr. So that issue is accounted for.