Araya Rims - concave - why?

[sherlylock]

In chatting to a fellow retrobike member last night whilst selling some Araya rims (nice to meet you Alex!). Talking about measuring rim wear on secondhand wheels - usually the method is to run a straight edge across the rim to see how concave they are.

But some (if not all) Araya rims from the early nineties have concave sidewalls by design, making them quite hard to measure for wear.

So why design a sidewall with a concave section?

The only thing we could think is it acts as a centralising feature for the brake pad (once it's bedded in presumably)?

Anyone got any other theories for the reason for this design?



Cheers!

 

[Raging_Bulls]

Alignment would certainly be a good reason.

As for measuring rim wear, I use an Iwanson caliper to measure the thickness of the side

From what I gather, rims generally become dangerous at 0.5mm. At 1mm I'll start looking for a replacement and once I reach 0.7 I'll either replace the rim or put the bike in storage until a suitable replacement rim has been found.

 

[Retro Spud]

Re:

I asked the same question on here only a few ago

viewtopic.php?f=1&t=315059


I've been told Campag followed suit, if you look at the page from the marketing blurb its a selling point !

 

[kingoffootball]

Slight increase in surface area of contact between pads and rim?

 

[danson67]

Given that straight faced rims tend to wear to concave, with maximum wear at the centreline of the braking surface, I suppose the idea was to spread the rim wear across the braking surface. That way there should be less risk of the rim bursting at the thinned out centreline, maybe?

I have some Campag Ateks with the concave sidewalls, and I can't say I've noticed any better braking that the flat faced stuff. They just look really tired as soon as the NOS shininess has worn off rather than waiting a few years for your Mavics to look that bad.

All the best

 

[hamster]

I think the other idea was to get the tyre beads further apart without a much wider rim which would add weight.

 

[sherlylock]

Yeah, some good theories here guys......loving the Iwanson caliper too - need to get me one of those!

 

[robdeanhove]

I had two thoughts:

1) As above, wider rim for less metal, so weight saved

2) It would tend to push the brake pad down, not up, as it wore, so reduced the risk of slit sidewalls as pads slide up the rim if you're rubbish at setting your brakes up or don't check them very often

3) If you're brake pads aren't perfectly at 90° to the rim, they might tend to slide up or down, a onave surface would cup (or hold) the pad in place better

4) It can't be for stiffness vertically a flat wall would be stiffer, not sure if they would claim turning stiffness? Look at a modern disc specific rim and it is often convex, so similarly curved, but outwards

To be honest, I don't know, but all of the above seem more realistic to me than many, many marketing claims I have heard for most other stuff!

 

[02gf74]

Cantilevers are pivoted so would engage a larger surface area before both pads and rim bed in.

V brakes have parallelogram link so contact angle is the same. That is for xt and xtr models. I dont think that is why manufacturers do flat sides but more likely the machinery is cheaper to do flat finish vs a curve.

 

[FluffyChicken]

Gives slightly larger contact area and helps reduce pad 'fall off' where it goes over the edge.

As far a wider bead are, the 395's are actually narrower at that point as the surface angle is positioned to push up into the tyre (much like M231's) but witha larger braking surface.

There should be a patent application somewhere.

Once they (maybe Mavic) started making it much wider (higher?) machined braking surface like on the 517/717 etc I guess there was little need for it and the expense of making them may have been too high (?), unlike the terribly small area you have on M231/230 etc.

Campag had a similar larger braking surface.

I used both and disliked Mavic for this very reason, so I maybe a touch bias
Araya were superior to the Campag though, mainly as the Campag seems to be a softer, less durable Alu and also as they always separated at the pins as they were not welded.

Araya and explanation

Campag and explanation