Compact Campagnolo 4 arm crank - building a 50/36

Discuss light weight issues concerning road bikes & parts.
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OrPe
Posts: 251
Joined: Wed Oct 18, 2006 10:15 am

by OrPe

Hi,
I have a new record compact crank coming. I live in a flat area so the 34 will definitely be on the small side.
I see the chainrings are matched (50/34, 52/36,...).
Will shifting quality be harmed on a 50/36 combo? How bad? Priced to get both rings is... a bit higher than I’d like to spend. 36 alone is much cheaper.

Thanks
Oren


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Priit
Posts: 39
Joined: Wed Jan 27, 2016 9:22 am

by Priit

Shifting quality for 50/36 will be ok, maybe even better feel than with 34.

by Weenie


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corky
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Location: The Surrey Hills

by corky

If you’re riding mainly flats ....why not go for the 52/36?

AJS914
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Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

If you live in a flat area, why not just go 52/36? Or, if you really like the 50 I wouldn't worry about the 34 because 99% of the time you'll be in the 50 anyway.

FlemishCompact
Posts: 76
Joined: Wed Feb 12, 2014 11:56 pm

by FlemishCompact

AJS914 wrote:
Tue Aug 06, 2019 9:53 pm
If you live in a flat area, why not just go 52/36? Or, if you really like the 50 I wouldn't worry about the 34 because 99% of the time you'll be in the 50 anyway.
OP mentioned that pricing was prohibitive.

AJS914
Posts: 3387
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

He also said he also bought the crankset so it's not 100% clear what he's doing. I'm thinking that he already bought a 50/34 and wants to add a 36 to it.

The other thing is that a 36 doesn't buy you much. For example a 34x16 is the same gear ratio as 36x17. With a 34 you basically put it in one cog smaller in the back and you have the same ratio as if you had a 36.

joejack951
Posts: 587
Joined: Fri Feb 18, 2005 6:50 pm
Location: Wilmington, DE

by joejack951

My flatland bike has a 50/34 crank and 12-25 11 speed cassette. Single tooth shifts in the rear from 12 to 19. A headwind on a bridge makes having the 34 worthwhile.

JoO
Posts: 167
Joined: Thu May 04, 2017 7:30 am

by JoO

I have used 50/36 on campagnolo 5 arm crankset. 36t ring from stronglight. Worked very well. Strong light also makes a 4 arm version, perhaps worth a try, it is cheaper than a campagnolo 36t.

joeyb1000
Posts: 197
Joined: Thu Mar 03, 2016 8:37 pm

by joeyb1000

Stating the obvious, the paired chainrings means that no matter where the chain is on the small chainring, half of the pins will catch the outer link of the chain and lift it up. So, this affects upshifts only, has minimal effect on downshifts and no effect when just riding along.
I haven't done 50/36, but I have done 52/34 and 52/39 using a "52 for 36" large chainring. The 52/34 worked better than I expected, but not as well as the paired 52/36. The 52/39 was about the same as the 52/36. I assume that the lack of pin allignment was made up for by the reduction in gap between the chainrings.
The choice is yours. Given that some special Italian scientist spent a lot of time matching those chainrings, it seems a shame not to try them as intended.

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OrPe
Posts: 251
Joined: Wed Oct 18, 2006 10:15 am

by OrPe

Thanks guys.

I have bought a NOS record 4 arm crank real cheap. it is 50/34.
buying a pair of chainrings will more than double (!!!) the price i paid, given two rings cost ~200$. which is... prohibitive.
i'll try riding it as-is and to adapt.

thanks again
Oren

graeme_f_k
Shop Owner / Manufacturer
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by graeme_f_k

Priit wrote:
Tue Aug 06, 2019 9:44 pm
Shifting quality for 50/36 will be ok, maybe even better feel than with 34.
Not correct.
joeyb1000 has it almost exactly right.

On the teams we do run other chainring combinations than those that we specify for normal end-users but generally the rings are "SC" and are modified away from the ones that we make for production.

The problem that you have to work with, is that the teeth on the inner ring need to be positioned correctly with reference to the ramp that initially "collects" the outer link plate of the chain.

The matching of the 52 and 36 means that the teeth on the 36 that are profiled to "release" the chain best are positioned in the right place with reference to the ramp on the 52. Because of the difference in circumference between a 52 and a 50 and the consequent difference in how the FD interacts with the ring, the ramps are, with reference to the fixing points of the chainring, in slightly different places on a 52 and a 50 ring. Look at the backs of the rings and you can see it. Hence, the "release teeth" on the 34 and 36 are also in slightly different places with reference to the chainring fixing points - so mixing the rings outside of the intended pairings means that the ramps can't work exactly as they should. On the SC rings, this is adjusted but even so, we know that shift performance is not the same as the fixed pairings that we make for final customers.

The old adage that the closer the rings were in size to each other, the better shift you would get, is still true but only within the context of rings with pretty generic ramping and pinning - TA rings, say, where the ramps and pins are designed to work "averagely well" regardless of inner and outer ring sizes work better where the ring sizes are closer. Where rings are very specifically made to be used as a pair, it's no longer really true unless the chain has very little radial distance to travel. No doubt a 48/52 pair would work very well, as in that case, the ramps and pins are doing very little. At the other end of the scale, a 34 / 53 pairing where neither ring is even remotely working in the way it was intended will shift comparatively badly, especially under torque. Shifting will need more force to be applied to the chain by the FD and will probably leadt to more force being applied to the lever by the user - the end result, more wear and tear on the chain, the back of the big chainring, the inside of the FD and the shifter.

Since probably the mi- to-late 1990s, chainring ramping and pinning has been evolved to the point now, where non-spec ring combinations can work "OK" but the stress that is transferred to all the other shifting components is increased.

The FD design also plays it's part - the "gate" that the chain passes through has to have the correct width and be positioned correctly both for upshifting but also in order to control the chain for downshifting. The wider the chainring range, the bettwr the control of the chain has to be, especially as the cassette sprocket size differences increase - this is the reason why the shifting regime and set up on 12s is different to 11s post 2015, which was itself different to pre 2015 11s. The wider ranges of cassette offered meant that the way the chain needs to be controlled as it drops from the big ring to the small, especially on 50/34 and now, even more so on 12s 48/32, changed.

If the OP is looking at 11s, I'd go 52/36 with a 12-up cassette, rather than 50/34 with an 11-up. Little will be given away at the "hard" end of the gearing range but the chain will be less tightly wound around both sprockets and chainrings so the system will be more efficient, having less rolling resistance and there will be less wear and tear as the wear that does occur will be distributed over more teeth. The smoother rolling is why the six-day guys would always pick, say, 52 x 13 over 48 x 12, for instance.
A Tech-Reps work is never done ...
Head Tech, Campagnolo main UK ASC

graeme_f_k
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by graeme_f_k

joeyb1000 wrote:
Wed Aug 07, 2019 3:00 pm

The choice is yours. Given that some special Italian scientist spent a lot of time matching those chainrings, it seems a shame not to try them as intended.
Absolutely.
If Campagnolo could get the same performance and make a 34 and a 36 ring that worked equally well with a 50 outer, they likely would - it would be a considerable marketing win over the opposition. The problem is, it doesn't work that way for anyone ...
A Tech-Reps work is never done ...
Head Tech, Campagnolo main UK ASC

by Weenie


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