Is it worth upgrading from a square taper crankset?
 

My entry-level road bike with Claris came with an FSA square taper crankset and BB. I was wondering if it was worth upgrading it to the Claris crank which is Hollowtech II. From what I've read, it's lighter and stiffer than square taper and looks a hell of a lot better, too. Also, I could feel the frame flex on my bike when sprinting, which causes chain rub (my front derailleur is properly adjusted), and was wondering if switching to HTII would help with that. Thanks in advance.

If you want a Hollowtech crank, just get one -- there's nothing wrong with wanting a certain look. But I seriously doubt you'll actually notice the weight, the stiffness, or any effect on frame flex.

Maybe... But not because of flex.

I was surprised at the expense and difficulty I had in finding a square tapper compact crank when I wore out the rings on my old UNIVEGA. Sure, its taken me years to wear out my crank so its not something to do often.

So upgrading to a Hollowtech will not only make you feel better, in the future you will have a broader range of replacement cranks to choose from.

Bottom bracket is one of those things you'll never notice (until it wears out). It's not like a saddle, tires, or bar tape. Ride it until you have to replace it.

Note that you'll need to replace your crank when/if you put a different BB on.

...

It could be frame flex that's causing the front derailleur rub, especially since this is an entry level bike.

Derailleur rub was a commonplace problem in the before time (before stiff aluminum and carbon frames became commonplace).

A properly assembled square taper bottom bracket should be trouble free for years and years. I don't notice any difference between square taper and external bearing BBs while riding, but I believe there might be a difference if an engineer calculated the stresses and deflections.

Something that can make a big difference is chainring quality - shifting on a set of FSA rings is significantly inferior to that on Shimano rings. that alone could be worth the trouble for the upgrade - new Shimano rings to fit the FSA crank will probably cost similar to a Claris crank & BB.

When I changed my 1979 Raleigh Comp GS from the old Campy Nuvo Record square tapers to a RaceFace Cadence 2 piece crank with the external cups, it convinced me that square tapers are dead.

If there is something odd about your bike that you have to have a certain chainline, then square tapers will let you get there. But then you have to play with spindle lengths, offsets and how different crank sets sit differently on that spindle. Not to mention the few different types of square taper.

It's just so much simpler to be two piece or a octalink or ISIS type crank and BB that engineered and standardized their fit so you don't have to worry about the many things you do with square tapers.

Yes this is all IMO. If any have an affinity for square tapers, that's fine with me.

This would be my reason to upgrade to a Hollowtech II crank. It probably would be a bit stiffer than the square taper crank that you have now but not noticeably lighter

I don't see how changing the bottom bracket and crank would have an effect on frame flex.

Oh wow, I never knew this to be the case. I thought they were all the same. I'm seriously considering upgrading now because of that. Front shifting has been pretty meh on Claris and I thought it all had to do with the short-arm derailleur design that was pretty stiff to actuate.

Having used both FSA and Shimano cranksets, I can't say that I've detected a difference in shifting quality.

Maybe the low-end FSA cranks are made to less precise tolerances? I have no experience there, I've only ridden the high-end FSAs.

I've used both Shimano and FSA, as well. I would give a slight nod to Shimano, but the difference isn't very significant at all. In the real world, both get the job done just fine.

Hollowtech finally made it all the way down to Claris? No more octalink? Frabjuous day!

"Upgrade" is a word often used on these pages when "change" is the most appropriate word.

I'm sure someone here will see that as an invitation. :)

The frame flex leading to the tire rubbing has little to do with the flex of the cranks. That is flex in the frame.

If you replace the ST bb with a hollowtech, you also need new cranks.

IMO, there is little to be gained by upgrading. The difference is there but not all that much. There are almost certainly better places to spend upgrade dollars.

Wait until you need to replace the crank or BB for other reasons.

If you have frame flex even the highest tech crank and the stiffest chainrings will still rub. You "might" get rid of some of the rubbing with very careful front derailleur stop screw adjustments and then cage modifications, but with indexed shifting if might be difficult and could make it worse. I have found a perfect test of a modification on a bike on a repair stand test, is not an indicator of success, since when you are powering through the pedal cycle with your power and weight AND if there is frame flex, your careful adjustments that remove the rubbing, may lead to over or under shifting.

Been there with FD rubbing on a vintage Peugeot. However, with the friction shifters you could tweak away the rub (usually)... :notamused:

Upgrading the crank and BB might help, but if not, you may wish to consider saving on the change and apply it to a new or used bike without the flex.

Rode a square taper crank for multiple decades with no flex/scrapping. Only time it would rub is when the BB tension needed some adjustment. Simple fix for the most part. Finally the BB races got pitting which prevented me from getting the proper pretension on the BB. Since the crank extractors had stripped out and both chain rings needed replacing any way, I found it cheaper to put in a close out Campagnolo ultratorque crank than to buy new rings and BB.

So no, you don't need to upgrade so much as check the BB tension.

Have you considered the low-end Claris derailer and shifter might be the cause of your issues?

Some FSA's I've ridden were "ughhh clank!" for the upshift & a "hrmmmmm swoop clunk!" for its downshift [2x system] & almost all the Shimano stuff was predictable with some minor shifting grunt. Once on the gear, both performed fine.

Would I swap out a square to something else if there's no obvious BB issue? Not in the current times, but would have 3 years ago quicker than a squirrel burying a nut.

I had a Claris groupset on my bike. I upgraded to a 105 groupset and a hollowtech BB. I don't notice any difference in the BB but I did love weight difference between both cranks and BB.

Some things are just worth quoting.

After many years of ST Campagnolo BB's I switched to Shimano external BB's a few years ago and I've had no problems in installation, removal and wear but can't claim to have noticed any difference in efficiency or shifting. A little observation is that Claris and Sora will both have steel inner rings which the OP might even prefer but pushed me towards Tiagra.

It's like going from a low end Tioga headset to a Chris King. No, you probably won't notice much difference but it is much nicer.

Nothing wrong with the mod bug, we all get it. Just embrace it.