Why the dealer tendency to chose sprockets with even number of teeth?

[silva]

That's something I noticed many times in the past, and today again, after visiting 4 shops to not find a 47t chainring.
Due to an unexpected repair result I wanted to get a 47t before the weekend so that I could refit the bike to my usage standards and also be sure this particular size doesn't void the frame.
It seems odd numbers of teeth are not popular among dealers. In the past my bikes also were delivered with even numbers teeth sprockets, without explicitly asking a particular number / gear.
So what am I overlooking? Do even numbers of teeth serve a particular purpose?

 

[Racing roadkill]

That's something I noticed many times in the past, and today again, after visiting 4 shops to not find a 47t chainring.
Due to an unexpected repair result I wanted to get a 47t before the weekend so that I could refit the bike to my usage standards and also be sure this particular size doesn't void the frame.
It seems odd numbers of teeth are not popular among dealers. In the past my bikes also were delivered with even numbers teeth sprockets, without explicitly asking a particular number / gear.
So what am I overlooking? Do even numbers of teeth serve a particular purpose?

Sprockets with an even number of teeth, are easier to produce, because of the tooling requirements, the manufacturing yields are higher, the prices are subsequently lower.

 

[andrew_s]

The pins, ramps and gates on chainrings are timed for changes to happen most easily when the cranks are vertical, when there's least tension on the chain.
If there's an even number of teeth, the pins etc ate identically positioned on each side of the chainring, so manufacture is a matter of turning the ring 180 degrees and repeating the same operation(s). With odd numbers of teeth there is no such standard angle, so, as rrk says, costs go up, and a small increase in manufacturing cost is a considerably larger increase in sale price, so competitiveness suffers.

As for 47T chainrings, TA make them (Spa Cycles in the UK)

 

[steveindenmark]

Would one tooth on a chainring make that much difference to you?

 

[silva]

So it's purely to cut production cost

The pins, ramps and gates on chainrings are timed for changes to happen most easily when the cranks are vertical, when there's least tension on the chain.

This reads like a technical reason I'm after with this topic. But I don't get it, can you explain it more clearly/detail?

If there's an even number of teeth, the pins etc ate identically positioned on each side of the chainring, so manufacture is a matter of turning the ring 180 degrees and repeating the same operation(s). With odd numbers of teeth there is no such standard angle, so, as rrk says, costs go up, and a small increase in manufacturing cost is a considerably larger increase in sale price, so competitiveness suffers.

As for 47T chainrings, TA make them (Spa Cycles in the UK)

On the other hand, the sale prices are typically just equal, regardless number of teeth, thus regardless odd/even.
The sites list a price for a model, and a dropdown to select teeth figure, and all places I checked/used so far, do not alter price based on that number.

I know where to find them, only that I wanted 1 piece just before this weekend, for a frame clearance check, before ordering more on the site I bought them before. Only that surprisingly none of the 4 shops I visited yesterday had 47t, with that particular element (tooth figure) as common reason. It wasn't the bcd or 1/8" width that they answered negative.

 

[silva]

Would one tooth on a chainring make that much difference to you?

Yes, my gear swap from 48/16 to 47/16 eliminated the chain tension variation growth (doubling) during use.
Wear concentration (48/16=no fraction) versus wear spreading. Also the more teeth the less wear per teeth. The bigger the contact surface in power transmission the less force per square surface unit and thus the less wear (but I'm limited upwards due to frame clearance due to wide tyres)
My current bike was delivered with a 3/32" instead of the requested 1/8" chainring. It wore out in a month, while the 1/8" mounted later on lasted 18 months, same rear cog, new and wider chain.
So this particular subject is for my case important - it reduces wear misery work and cost.

As said I'm hunting here a technical reason to chose even number teeth - economical aspects (cost) aside.
So a benefit, as in even number would reduce wear somehow.
I rather saw and also have read the opposite: increasing wear, especially in a no fractional gear worst case configuration.
So why then a tendency to chose precisely that?

 

[iandg]

Velosolo sell various rings 1/8 and 3/32 and different BCD

https://www.velosolo.co.uk/shopcrank.html

 

[raleighnut]

I thought 53-39 was standard for road crank these days.

 

[Racing roadkill]

I thought 53-39 was standard for road crank these days.

53-39 is referred to as a ‘standard chain set’ 50-34 as a ‘compact’, 52-36 as a ‘semi’ or ‘Pro compact’ other ‘oddities’ don’t have these terms applied.

 

[Ajax Bay]

I think the OP is taking the fact that a few shops didn't have a 47t ring when he wanted it out of proportion and trying to think 'why?' when actually the fact was that the shops didn't have a 47t ring with that particular BCD and number of bolts - reason? not many riders want one (specifically) so why stock it. He then extends to odd numbers query to sprockets - which I guess is only of interest to single-speed aficionados - clearly there are loads of odd-number toothed sprockets on very many cassettes.
https://singlespeedcomponents.co.uk...-sprockets/products/dicta-fixed-gear-sprocket
I think it's the case that a 47t chainring is an infrequent choice across the cycling world, and confess I couldn't understand why a 46t or a 48t would not suffice. Most people are not that picky ("my usage standards") and how would a 48t or a 46t "void the frame"?

my gear swap from 48/16 to 47/16 eliminated the chain tension variation growth (doubling) during use.

I don't get it, can you explain it more clearly/detail?
@andrew_s has suggested a good reason (with rationale) for even numbered chainrings being preferred from a manufacturing PoV.

 

[Deleted member 26715]

So what am I overlooking?

The number of beers you have drunk?

 

[iandg]

I think the OP is taking the fact that a few shops didn't have a 47t ring when he wanted it out of proportion and trying to think 'why?' when actually the fact was that the shops didn't have a 47t ring with that particular BCD and number of bolts - reason? not many riders want one (specifically) so why stock it. He then extends to odd numbers query to sprockets - which I guess is only of interest to single-speed aficionados - clearly there are loads of odd-number toothed sprockets on very many cassettes.
https://singlespeedcomponents.co.uk...-sprockets/products/dicta-fixed-gear-sprocket
I think it's the case that a 47t chainring is an infrequent choice across the cycling world, and confess I couldn't understand why a 46t or a 48t would not suffice. Most people are not that picky ("my usage standards") and how would a 48t or a 46t "void the frame"?

I don't get it, can you explain it more clearly/detail?
@andrew_s has suggested a good reason (with rationale) for even numbered chainrings being preferred from a manufacturing PoV.

I am when I ride fixed - I own 42,43 and 44t* chainrings and a set of sprockets from 15 to 21.

edit* - and a 48t

 

[midlife]

Yes, my gear swap from 48/16 to 47/16 eliminated the chain tension variation growth (doubling) during use.
Wear concentration (48/16=no fraction) versus wear spreading. Also the more teeth the less wear per teeth. The bigger the contact surface in power transmission the less force per square surface unit and thus the less wear (but I'm limited upwards due to frame clearance due to wide tyres)
My current bike was delivered with a 3/32" instead of the requested 1/8" chainring. It wore out in a month, while the 1/8" mounted later on lasted 18 months, same rear cog, new and wider chain.
So this particular subject is for my case important - it reduces wear misery work and cost.

As said I'm hunting here a technical reason to chose even number teeth - economical aspects (cost) aside.
So a benefit, as in even number would reduce wear somehow.
I rather saw and also have read the opposite: increasing wear, especially in a no fractional gear worst case configuration.
So why then a tendency to chose precisely that?

You wore out a chainring in 4 weeks, blimey that's going some!

 

[silva]

Velosolo sell various rings 1/8 and 3/32 and different BCD

https://www.velosolo.co.uk/shopcrank.html

I'm well aware - I ordered all the replacement stuff for my new bike there.
But since it came to a surprise to me (I wasn't told) that my bike would lack a chainring when repaired / delivered back, and I wanted to bring back the bike to usable state this weekend, I wanted to find a chainring in a short notice, but couldnt find avail in any shop within range, which came as a surprise to me.
I'm about off too, gonna try a couple other shops in nearby city. Trouble also was/is that the dealer that repaired the bike apparently wasn't that sure whether or not a 47t ring would void the frame, and ordering a single ring from Velosolo to try costs > twice as much due to shipping and bank fees.

 

[silva]

You wore out a chainring in 4 weeks, blimey that's going some!

Yea, if you want to know brand/model it was an 48t Surly stainless steel 3/32" one, with a KMC S1RB chain running on it, under a 5 mm wrong chainline (that I didn't know at the time - it took 52 weeks to finally discover thanks to help on a forum, after having seen X times the dealers I-don't-know-nothing-never-seen-before-face after asking why the chain hung 45° tilted, lol).
Since I found better ring and chain, as proved by an 18 month life under same usage regime.
Apparently, stainless steel, in this case the cheapest grade 304, is quite soft, aluminium 7075T6 beats it. And ofc the 1/8" width and thicker teeth and wider chain also helped to reach that 18 months. I would like a good steel grade chainring, the weight surplus is for my application neglectable. But so far unable to find, just look at how hard it is to find an aluminium one.