Chain blocking with 52/36 and 11-25

JohnnyRemo wrote:

Why would you be in 52x25 or 21 when you get the same ratios in the middle of the block with the 36 ring?

52/36 chainring and on an 11-speed 11-25 cassette it'll be:
11, 12, 13, 14, 15, 16, 17, 19, 21, 23, 25

Because if you're rolling along an undulating road in 52:19 (5.75m) and you need a few seconds of extra spin to get up a little gradient, dropping one gear into 52:21 (5.20m) or two gears into 52:23 (4.74m) is far more efficient than finding the equivalent in the 36 (36:15 / 5.04m so a fair bit lower) which involves one shift at the front and then 3 at the back or 36:16 / 4.72m (one front, two back shift).

You'd probably drop into the 36 for a more prolonged gradient, or for one that got steeper but for a short rise, it's perfectly reasonable to go to a bigger cog or two then back up to maintain momentum in the big ring.

Chain is too short which is the ultimate in stupidity - if you're hiring bikes out you pretty much assume that everyone is an idiot and you cater for that fact, not try and prevent cross-chaining by creating a second problem of locking a wheel up and stretching the mech beyond it's limit.

My road bikes (one running 39/53 with a 12-25 and one running 36/52 with 11-28) both work absolutely fine in all of their gears albeit the extreme edges are fractionally more noisy.

Mr Pennington wrote:

To prevent renters from cross chaining it sounds like the dealer intentionally shortened the chain. We know cross chaining adds wear and tear on the chainrings and cassette, so from the dealers perspective he doesn't have to spend monies to replace parts sooner than expected because of renters trashing his bikes.

The dealer risks the rear derailleur, hanger and chain from being damaged if he shortens chain to block the gearing up by unsuspecting renter. Cheaper to add a few pence to each rental and replace than risk the above.

Or he could fit Di2 to all his bikes and program no cross chaining-like me

Welsh boy wrote:

It might not be that the chain is too short, the rear mech might be too small.  As for this obsession with "cross chaining" there is no real reason why, as you say, you cannot use extremes for short periods IF your chainring/sprocket/rear mech combination is correct.

those two are not mutally exclusive.

the chain was too short, as evidenced by the blocking, the rear mech may also have been too small, which would mean that with sufficient chain for big big, the chain would slide opver itself in small small. This seems like a lesser issue to me as almost anyone would hear the noise realise they were in incorrect gear selectiob and rectify things, rathern than ripping the rear mech off trying to use big big with not enough chain.

SteveAustin wrote:

certain gear combinations just wont work. short-cage mech 52-36 and 11-25 will work if you dont run 52-25 which you shouldnt do anyway.

There's no reason why a 105 short cage mech won't work with 52-25. The capacity of a short cage 105 mech is 34t. That set up has a difference of 30t (52-16)+(11-25). So it could in fact run an 11-28 cassette and still be within its capacity. I've actually got an Ultegra short rear mech on one bike running 50-34 and 11-32. Way beyond its stated capacity but it works fine, the only caviat being that small chainring and smallest sprocket gives a sloppy chain but I never run that anyway. 

I don't advocate cross chaining, although in practice it doesn't really pose any problems. However the bike in question should never have been set up in such a way that the chain wouldn't cope with big chainring - big sprocket.

SteveAustin wrote:

certain gear combinations just wont work. short-cage mech 52-36 and 11-25 will work if you dont run 52-25 which you shouldnt do anyway. i wouldn't say the chain is too short, but if you want to run a  52-36 front cog youll need more need more chain, than the smallest combo can cope with. so its been set up to work on shortest chain length possible which wont work on the 52-25.    if the chain was longer it wont work on the smallest chain length as theyll be too much chain.

Needs a long cage mech to work with that spread of gears.

but you should never ever run big ring, big ring, twists the chain too much, and a worn snapped chain 50 mile from home is no fun..

Currently running Ultegra 6800 short cage with a 50-36 and 11-32, it runs fine in 50/32 as well as every other gear, 58cm frame with long stays too. You could do the same with the previous 6700 short cage model too. It most certainly would work with 52-25 no problem at all as I did 52/36-11/28 on my Raleigh Ti when I upgraded it.

Never ever? Well some of the manufacturers are saying that's not an issue and it would seem that the twisting you state causes a snapped chain doesn't seem to be a frequent issue, after all you're hardly ever in big/big anyway. 

SteveAustin wrote:

Needs a long cage mech to work with that spread of gears.

 rubbish

PP