BB difference

[jim55]

I need to replace my bottom bracket and what's on there is a square taper kind .
IV got a set of tiagra cranks that use a hollow tech BB fitting ,so was Gona fit them as changing BB anyway.is there a diff between 105/ultegra / tiagra apart from price,the width of shell is 68mm so surely any model as long as it's 68 mm would do ,,eh?🤔

 

[Ajax Bay]

No - any Hollowtech II BB will do you.

 

[ianrauk]

And you'll find absolutely no performance difference between the three.

 

[jim55]

Cheers guys 👍

 

[Cycleops]

You'll need a Hollowtech wrench to fit the BB.

 

[coldash]

The various Hollowtech BBs need different tools to tighten them. The Shimano RS500 cups are bigger than the more expensive Shimano BBs, so make sure you get the right tool for the BB you buy (and I got the cheaper RS500 and it is fine)

 

[Ajax Bay]

The BBs with a smaller diameter come with an adaptor (in the box) for the old size tool to which @coldash refers.

 

[Smokin Joe]

The various Hollowtech BBs need different tools to tighten them. The Shimano RS500 cups are bigger than the more expensive Shimano BBs, so make sure you get the right tool for the BB you buy (and I got the cheaper RS500 and it is fine)

Or simply buy another square taper BB which are more reliable and less of a faff than Hollowtech.

 

[Big John]

This'll be the first hollowtech II BB fitted to this particular bike? If so, according to the Haynes Bike book, they recommend you have the shell re-threaded and re-faced before fitting the BB. Not many folks carry those sort of tools in their toolbox so it's either a trip to the lbs OR ignore and carry on regardless. The book, sadly, doesn't say what the consequences are of not re-threading/re-facing. Maybe others can throw light on that one.

 

[coldash]

Or simply buy another square taper BB which are more reliable and less of a faff than Hollowtech.

Great advice unless like the OP you want to fit HT cranks

 

[Smokin Joe]

This'll be the first hollowtech II BB fitted to this particular bike? If so, according to the Haynes Bike book, they recommend you have the shell re-threaded and re-faced before fitting the BB. Not many folks carry those sort of tools in their toolbox so it's either a trip to the lbs OR ignore and carry on regardless. The book, sadly, doesn't say what the consequences are of not re-threading/re-facing. Maybe others can throw light on that one.

Misalignment causes premature wear on the bearings.

 

[coldash]

This'll be the first hollowtech II BB fitted to this particular bike? If so, according to the Haynes Bike book, they recommend you have the shell re-threaded and re-faced before fitting the BB. Not many folks carry those sort of tools in their toolbox so it's either a trip to the lbs OR ignore and carry on regardless. The book, sadly, doesn't say what the consequences are of not re-threading/re-facing. Maybe others can throw light on that one.

IMO, some of that is a bit purist. I’m not convinced that the re-thread bit is at all necessary unless the threads have been damaged (and why would they be if a properly fitted Square taper had been properly removed. The re-facing is in case the shell edges aren’t parallel. If they are out, the HT BB cups would not align properly which would cause bearing wear (and potentially other problems)

As it happen, I recently did the same thing that the OP is considering on a Giant Scr that I use on the turbo. The square taper BB was rough and I wanted to fit shorter cranks. Got a set of 165 Soras, checked the shell face using calipers (it was fine) and fitted a RS500 HT BB. The cranks spin smoothly and it isn’t a difficult job.

 

[Mr Celine]

And you'll find absolutely no performance difference between the three.

The tiagra BB fitted to my Roubaix wore out after 4000 miles. I replaced it with an Ultegra one which is still showing no sign of wear after 17000 miles.

 

[jim55]

Or simply buy another square taper BB which are more reliable and less of a faff than Hollowtech.

Can't refit the square taper kind I have IV mangled it in vice to get it off ( unless I was to buy new chainrings ,it's throwing money away when I have a set of brand new tiagra hollow tech sitting there

 

[Gunk]

I wouldn’t personally bother recutting the threads, unless they’re damaged. I’ve just recently fitted a new Hollowtech BB and it does come with the plastic tool adapter.

I just cleaned the threads thoroughly with brake cleaner and small brass wire brush. I always assemble them dry. I just grease the shaft of the crankset as I have removed them before and shaft has been rusty