jhgold

Hello fellow cyclists, this is my first post here so sorry if its already been asked. I've ordered a 160mm Shimano 105 crankset but want to keep the current chainring because I prefer the current gearing of 52/36 as opposed to 50/34 which is what the 160mm is coming on. I know the arms can be replaced as I have seen just the spider arms for sale on eBay etc. I was wondering if someone could point me to any guidance and torque settings etc as I cant find anything online! Thanks!

schwim

At the 1 minute mark, he begins removing the non-drive side crank arm. I will say that I've never needed the tool he's using for the tension nut. I've always been able to get it removed easily with anything handy I can lock into the nuts spline.

mstateglfr 

Hollowtech/HT2 describes a bunch of different cranksets all with different chainring shapes and BCD sizes.

First off, is the design of your current crankset the same as your new 105 crankset? Meaning, do they use the same bolt design and spacing? If yes, it's worth discussing further. If no, any further discussion on how to do what you want is pointless.

dabac

The right - drive side - arm is permanently bonded to the bottom bracket axle.

To reach your goal, swap the chainrings over.
To succeed with that, you need the bolt circle and bolt count to match. I can’t tell from here.

jhgold

Hi, yeah its exactly the same model just a different crank arm length.

Iride01 

If you look on the backside of most any Shimano crank arm, near the hole for the pedal will be the part number. Plug that into the search box here at Shimano's tech doc site and you can find most everything you need to know.

https://si.shimano.com/

If there is a DM for it, that will give you the most useful information.


But for the most part, just remove the left crank and slide the right crank and everything else out the other side. Be sure you understand about the stopper plate on the left crank arm. Especially for when re-installing the left crank arm.

mstateglfr 

Remove the rings from your old crank and put them on your new crank. Tighten to 13nm...or basically 'really tight'.

PeteHski

This^
It was an odd question worded the other way around, given that the 105 crank arm is fixed.

SoSmellyAir

I have a related question: Does either crank arm need to be removed to install different chain rings? Or can the crank be left in place? There is a bike I want but it only comes with 52/36 while I would rather use 50/34.

mstateglfr 

Again, different cranksets have different spider shapes. What you are asking may be possible one one, but not modern ones I have worked on.
Even if it is possible, I dont know why anyone would keep the crank arms attached to the bike. On a Shimano crank its 2 bolts to undo for removal. On a Praxis crank its 1 bolt to undo for removal. Such a simple removal process seems like the obvious way to handle changing chainrings since you then have easy access to the rings and bolts.

Iride01 

IMO, related question should be in it's own thread. And in the Bicycle Mechanics sub-forum where this thread should have been. Again, IMO, I'll get over it! <grin>

For Shimano 4 spoke road cranks it's a toss up for me which is easier. But the chain rings can be removed and replaced without removing the crank from the bike. I've done it both ways to replace the chain rings. The time saved by not taking the crank out of the bike is probably lost by the tad more trouble of getting the crank turned to access the ring bolts for removal and replacement.

The OP's question revolves around them getting a crankset with different size arms that they wish to use. So they have to remove the cranks from the bike regardless.

Apparently the OP couldn't find a deal on one with the ring sizes that they desire and are going to have to swap their current rings to the new crank. That shouldn't be any issue since the OP has a choice of when to install the rings.

However from one model and series version to the next the profiling on the ring spokes might not match the profiling on the crank spider. I have that issue with the Ultegra R8000 rings I use on my 105 5800 crank. But no one but me and the mechanics at the bike shop have ever said anything about it. That is purely cosmetic.

SoSmellyAir

My bike has a 110 BCD spider so it was relatively simple to upgrade chain rings (from FSA to Shimano 105). Until your post above, I did not know -- but now I do, after further research -- that Shimano Hollowtech crank spiders and chain rings are not necessarily forward and backward compatible between generations.

Because I have a Cannondale SI crank in a BB30A bottom bracket, the removal of the crank arms is a bit more involved. So I had not realized that it is easier with a Shimano Hollowtech crankset.

cxwrench

That would make a difference in whether you bought the bike or not?

SoSmellyAir

No, I have not yet bought a new bike. Yes, the installed chain rings would affect my purchase decision, because:
(1) it is an expensive bike;
(2) 12 speed Ultegra 50/34 chain rings are relatively expensive and not yet widely available; and
(3) I need optimum gearing to make the best use of my meager power.