anga

Not easy finding 27.5" rims for rim brakes.
Does the Ryde Andra 321
https://www.ryde.nl/andra-321/
have sides flat enough for rim brakes? Rim profile below.

cyccommute 

Probably not. That’s not much of a flat. A simple Google search finds lots of options for a 584mm rim for rim brakes. The Zac 421 from Ryde is one example. Search for either 584mm rims or for 650B.

SoSmellyAir

Even if the disc rim is flat enough, the surface is not designed for rim braking or the resulting wear; do you really want to take that risk?

Andrew R Stewart 

The brake pads will wear into and conform to the rim's sidewall shape. Initial contact will be small and, as the pad wears away, slowly increase. Of course with minimal contact the stopping "power" will be small too

Rims have had specific machined brake tracks for only but a few of the many decades of rim brake use. So my initial thought is that it's fine to try disk specific rims w/ rim brakes. However I wouldn't expect the rim to last as long and (as I tried to explain) the performance might be less than acceptable (and another aspect will be the lack of a rim width control, as in machined tracks, will mean that the brakes might be somewhat grabby as the wide rim spots try to squeeze past the pads).

What I don't know but do wonder about is the rim side wall thickness and how any one disk specific rim compares to a brake tracked rim. But this is what I alluded to with my concerns about the rim's side wall lifespan. Andy

grumpus

Here's a few: https://hollandbikeshop.com/en-gb/bi...rim-27-5-inch/

Schweinhund

https://pacenticycledesign.com/produ...vet-rim-650b-1

Also available at Rene Herse

Schweinhund

https://www.renehersecycles.com/shop...ti-brevet-rim/

veganbikes

What search engines are people using "dontfindstuff.com"?

This is not an exhaustive list as there are plenty of prebuilt wheelsets using rim brakes for 650b and probably some stuff I couldn't quickly find or didn't already know about but this should give you a couple options:
https://www.ryde.nl/zac-421/
https://www.ryde.nl/andra-35/
https://www.velocityusa.com/product/rims/a23-650b
https://www.velocityusa.com/product/rims/dyad-584
https://www.velocityusa.com/product/rims/atlas-584
https://www.velocityusa.com/product/rims/a23-oc-650b
https://www.velocityusa.com/product/rims/quill-650b
https://www.somafabshop.com/shop/som...7#attr=408,771
https://www.somafabshop.com/shop/som...#attr=179,3574
https://pacenticycledesign.com/colle...vet-rim-650b-1
https://velo-orange.com/collections/...ts/voyager-rim
https://www.weinmanntek.com/product/8/2
https://www.weinmanntek.com/product/8/9
https://www.weinmanntek.com/product/8/10
https://alexrims.com/products/adventurer2/
https://alexrims.com/products/dm18-2/
https://alexrims.com/products/en24/
https://www.halowheels.com/shop/comp.../sas-27-5-rim/ (just anodized versions not powdercoated version)
https://www.renehersecycles.com/shop...lus-650b-rims/

Hondo6

If I recall correctly, the OP indicated in a previous thread that he's located in India. From what he's posted previously many items readily available in the US or Europe are prohibitively expensive if ordered on-line and shipped to him. I'd guess that's due to a combination of customs duties, shipping, and other taxes.

ClydeClydeson

This is not true. Frictional force between two smooth objects is given by the formula F=uN - the force is equal to the coefficient of friction (mu, represented by the letter 'u') multiplied by the 'normal' force - the force the pad is pressing against the rim. Contact size does not affect the equation. There might be other characteristics of the way the brake behaves that is affected by contact area, but contact area does not affect braking power.

veganbikes

The OP listed Ryde and asked about that rim so if they can get Ryde they have two options for rim brakes from them:
https://www.ryde.nl/zac-421/
https://www.ryde.nl/andra-35/

Andrew R Stewart 

I continue to learn from others here. While this explanation seems counter to my personal experiences I will heed it. Funny that so many brake pad companies seem to say otherwise (and, yes, I know of the power of marketing being greater than that of engineering)

I wonder about all the other applications of wider friction dependent systems that we all think work in a certain way. Like cars and their tires. Andy

Hondo6

Maybe, maybe not. I suspect he's able to get the rim he linked from an in-country supplier, and the link he provided was from the manufacturer's website to provide data regarding same for our review.

His source may not have the rim brake version and may not be interested in special-ordering it for him (or may not be able to get it). Or he may not have asked yet. Dunno unless he tells us.

Again: don't presume that US experience regarding purchasing things online translates to the same end result in other nations. Sometimes local policies and laws make a huge difference regarding cost and availability. That's particularly true if a nation is trying to develop local industries and has protectionist tariff policies on some items.

Case in point: based on the OP's previous posts, Wolf Tooth products are apparently prohibitively expensive in India if ordered directly from the US through Wolf Tooth's website - shipping and customs duties are more than the cost of the item, as I recall. Equivalent products ordered from Amazon India, presumably of local (or perhaps regional or trading-partner-nation) origin, are nowhere near as expensive.

anga

Hondo6 You are absolutely correct. Shipping (+ duty on shipping) is quite high for large but light weight items like rims. Fact of life. Have to work with this constraint.
Due to Covid, lot of suppliers went out of business. Otherwise Alex rims are usually available locally.
Bike24 has two 27.5" rims available + flat rate shipping of €20.
Zac 321 at 630 grams and Andra 40 at 850 grams. Both disc brake versions.

Andra 40 comes with machined tracks but unavailable currently. The rim brake version is a machined version of the disc brake version. But heavy.

Just have to wait, I suppose.

ClydeClydeson

I believe brake pads and rotors benefit from increased size for heat dissipation and longer life, not for stronger braking. An overheated pad or rotor will lose braking power, but this is not directly caused by surface area.

Rubber tires are a slightly different animal because I don't believe road surfaces and tires qualify as 'smooth' as required for the formula - the rubber and thread and carcass of the tire deform around road irregularities so there can be a sideways component to the net forces between the road and the tire. Larger tires also handle heat better and wear longer than smaller tires.

ThermionicScott 

I debated whether to comment on this, but yeah, a lot of their rim-brake and disc rims appear to be the same extrusions. I'd have no concerns about using the "disc-brake" Andra 40 on a bike with caliper brakes -- in fact, one would get a thicker braking surface out of the deal.

anga

RIm weight is the issue.
How much does a 850gm rim impact riding?

Hondo6

A heavier rim will store more energy as rotational energy due to its larger moment of inertia, as well as more energy as translational kinetic energy. This will require slightly more power to accelerate to speed in a given amount of time, or (alternatively) slightly more time to accelerate to speed given a constant power input. At a constant speed on level ground, you should see essentially zero difference.

When accelerating to slower speeds, I'd be surprised if the effect was very noticeable. Since rotational and translational kinetic energy each varies with the square of rotational or linear speed, the effect will become more pronounced when accelerating to higher speeds. But the additional stored energy may assist in maintaining speed and/or a relatively constant power level in gently rolling terrain.

You can model each of those rims as a thin aluminum disk cylinder rotating around the axle of radius BCD and the rim's mass, calculate the rotational kinetic energy for each, then compare the totals if you want to see an estimate of the actual stored rotational kinetic energy difference. (To see the complete energy input difference, you'll also need to account for the translational kinetic energy at final speed of the mass difference between the two rims.) Presuming the rest of the wheels remain the same, that's the only difference you should see.

ThermionicScott 

They are heavy. Nearly twice as much as I prefer my 650B rims to weigh, totalling almost two extra pounds of weight that I wouldn't add to my bike unless I absolutely needed to.

But I was under the impression your options were limited...

anga

​​​​​
I have to import this, as well. No point getting a heavy rim, when I don't need the pros.
Waiting is an option, most likely!

Frkl

I have built a pair of Ryde Zac 421 (in 26") and they are very solid rims with a nice machined brake surface. They built true and round without any issues and are available very very cheap (about 15 Euro each, if I remember correctly). If you can get these in 650b, go for it.

Remerx also makes 650b rim braked hoops (https://www.simon-bikes.de/zubehoer/...-584-x-19?c=29). I have not used them but Remerx rims are sold by a few vendors I trust here in DE, so would risk it for 26 Euro, if you can't get the Zacs and must have silver.

I can't speak to your shipping situation of course.

Oh, the Andras are a rim for a really specific use-case. Do you need a rim made for fully loaded touring, remarketed for cargo e-bikes, with directional spoke drilling in extra thick aluminum instead of traditional eyelets? We have a cargo e- bike, and they are great there, where rotational mass is no issue, but I would not wish them on any normal bike, to be perfectly honest

jccaclimber

Friction is independent of surface area in the same way that saying lower spike count makes for a lighter wheel. In general it’s true if you can ignore other codependent variables. When you take the system level instead of looking at it in isolation there may be other significant contributors.

It ceases to become purely true when you:
1. Exceed the yield force of either side of your contact pair and start ripping the surface off (see skidding tires on cars).
2. Have curious things happen with vibrations/dynamics rather than purely rigid and static systems.
3. Have surface area based sources of force in addition to externally applied forces (eg. static attraction between two large sheets of paper, vacuum between two sheets of glass, etc).
4. Have the result of that friction change the system. For example, many consumer automotive brake pad materials don’t work very well when hot. Double the area and now you have half the temperature rise short term.
5. Externally applied force is dependent on that area. For example, a force applied on a large surface or rubber brake pad results in little squish of the material. If you apply to a tiny area on the rim you might get a lot more pad deflection—> lever movement before the same force is applied.
6. You are also differently sensitive to defects. A chunk of metal, rock, oily spot, lump in the rim, whatever, is going to impact that much larger a percentage of your system.

hokiefyd 

Given the same notional force applied to two different brake pads, one twice the size of another, is it an oversimplification to imagine that a larger brake pad distributes that force over a larger area so, while a brake pad that's twice as large as another brake pad has twice the surface area to apply friction, each square unit measurement of friction material also has half the force behind it...and the net sum of all this is zero (meaning, no effective difference in braking power)?

jccaclimber

In that case same force is going to be pretty close to same braking friction. I was just pointing out that as you take things to an extreme the rules break down. For example, readjust your pads that were hanging over the bottom of the rim to now sit just on that ridge or mate a new flat pad to a very curved rim and it starts to look a lot more like a line contact than an area contact. You could end up with a 10:1 or greater difference in area from what was intended, and a squishy and rapidly wearing brake system accordingly.