Sifaw

Hello there,

i have a roadbike with a 73mm bb shell and i recently bought a tiagra compact crankset that has a 110mm bolt circle lenght and the thing is i cant get enough of it to come out the other side to properly attach the left arm of the crank

This is rly upsetting because as far as i can tell shimano only makes 110m length cranks for compact 2 ring, the only solution i see is getting a new 3 ring crankset for about 100€ and this would mean i have to change my sti shifters and possibly the front derraileur aswell... are there any other options? thanks.

fietsbob

you need a BB for that MTB width BB shell .. which at 73mm is what it is..

Sure of your measurement accuracy? BB shell Road bikes are generally 68mm wide, or if Italian (made there just not sounding like it) 70mm..

If in over your skill set, enlist a bike shops experience..

Sifaw

i measured the shell myself its a 73mm shell on the frame.
how is another bottom bracket going to help? the one i have came with the crankset, its a bb-rs500 70mm (no spacers) and it attaches fine on the frame.
Would buying a 73mm give me more space to attach the arm? are the cups thinner or something?
thank you for answering.

Andrew R Stewart 

Option 2 is to cut down the shell and retap/chase then face the shell to 68mm. (He says knowing nothing but the bike's shell width). Andy

Marcus_Ti

You need the right crankset for your frame. Short of destructive modificiation (refacing the BB down to 68mm), that is your only option.

Without metal work, your Tiagra cranks won't work.

Leisesturm

The o.p. is also confusing bcd (bolt circle diameter) (110mm) with spindle length (unknown), and, as Bob says 73mm is not a recognized standard BB length for roadbikes. Not that it matters! Bottom bracket spindles are available in a dizzying variety of shell lengths and spindle lengths and something can be found that will fit (and for a lot less than 100 euros) if the o.p. can determine exactly what they need.

Edit: it would appear that Tiagra cranksets need HollowTech II bottom bracket cups. I assume you already have a spindle? (24mm)
https://www.universalcycles.com/shop...0&category=347

HillRider

You need a crank made for a 73 mm bottom bracket shell. Tiagra is a road crank and made for a 68 mm (or 70 mm if Italian ) shell and the spindle isn't long enough for a 73 mm shell. You need an MTB crank/spindle made for that shell width or, as Andrew noted, have the shell faced down to 68 mm, which won't be easy.

Hollowtech II cranks have the spindle built into the driveside crank arm and they aren't changeable. The OP needs another model crank with the proper spindle width, either an MTB Hollowtech II or a suitable square taper compatible crank.

To the OP: a press-fit bottom bracket will not work with a threaded bottom bracket shell. You need the correct crank.

Sifaw

ok that is what i tought but i have seen the same frame of my bike using a claris compact crankset (110mm) and it says on the site bottom bracket: press-fit.
is it possible to fit a press fit on a threaded shell? if so would press fit give me more space?

Marcus_Ti

Go to a bike shop.

Based on your questions, you're in way over your head

GrainBrain

What make and model is your bicycle? How about a picture?

Sifaw

i built the bike myself the frame is a cube attain 2017

going to the bikeshop its not something i wanna do as i would like to learn how to fix this myself

fietsbob

Want to mill down the faces of the BB shell to be 70mm ? a well equipped bike shop has the tools.. To buy your own, they sell for about $400



https://www.cube.eu/en/2017/road-tri...knyellow-2017/

called the shop where you bought it yet?






/....

Sifaw

cutting my frame is not something i wanna get into id just rather replace the shifters derraileur and crankset to a 3 ring one (shimano makes 3 ring cranks for road with 130mm)
but still it bugs me that the same frame (cube attain simplest model) is on that website with a

• crankset Shimano Claris FC-2450, 50x34T
• Bolt Circle: 110mm

Marcus_Ti

Which is why I say go to a shop. All of the things you report don't add up, between what you say you measure and what the frame spec online is.

A) If the BB is actually 73mm then a 105 or Tiagra crank will not work. Period. We know 105 works, because the stock Cube 2017 105 model has well 105. Per Cube's own tables

B) You say you have "bb-rs500 70mm (no spacers) " that "and it attaches fine on the frame."....well firstly that bb is 68mm and not 70mm. Secondly the frame specification says that frame takes a pressfit BB and not a threaded BB at all. That BB part number and your frame (per Cube's data) 100% cannot work with one another.


It is hard to help you, because what you say you have is not what the manufacturers of the individual parts say you. Which means you are measuring incorrectly and/or using the wrong part numbers....or have knock off parts (like say a frame from EBay that wasn't actually made by Cube).

Sifaw_

First of all thanks for all the awnsers, let me try to clarify by posting some pics
I understand the bb at 68/70mm is not perfect for the shell but i removed the protective cilinder and the cups attach perfectly to the threaded 73mm shell

HillRider

An English (aka BSA) threaded frame has the same threads no matter what the shell width so your bottom bracket will indeed thread in perfectly but the cups will be too far apart if it has a 73 mm shell.

That Shimano BB-RS500 bottom bracket is made for a 68 mm shell width if English threaded and 70 mm if Italian threaded and not both at once. Italian threads are completely different from English threads.

You've already said the crank you have has a spindle too short to work with your frame and have been told NO Shimano road crank is going to work with it if it really has a 73 mm shell which is at odds with the 130 mm rear drop out spacing as most 73 mm shells are used on MTB frames with 135 mm dropout spacing. This whole thing is very strange.

As recommended above you seem to be in over your head and need to have someone who understands more help you in person.

Sifaw_

so you are saying not even this 105 will work?
also isnt the dif between that 68/70 bb to a proper 73 bb just the length of the black cilinder?

Kontact

The red line you have marked "110mm" isn't the right part of the crank that is 110mm. 110 is the bolt circle diameter - the diameter of a circle that runs through the chainring bolts.


68 English or 70 Italian are the standard road BB shell widths for frames. 73mm is the standard MTB BB shell frame width, and it was adopted along with 135mm rear hub spacing to give more clearance for mud and wide tires.

The OP is trying to put cranks designed for road bicycles into a frame designed for MTB cranks. There are plenty of exceptions to what is considered to be in whatever category these days in terms of the frame, but the crank generally is going to be for one shell width or the other. If you have a 73mm frame, you need a crank with a spindle for that frame.

dedhed

https://www.merlincycles.com/blog/bu...oad-chainsets/

dedhed

Some good illustrations here. This guy seemed to have the same issue.

Hands On Bike: Avanti Inc 3: Special Crankset Setup

Sifaw_

i say again.. i have measured the spindle to be exactly 110mm, and it did say bolt circle 110mm aswell on the site.
So u are saying that the 105 is not going to work cuz even tough it has a larger bolt circle it will have the same spindle as the tiagra and all other shimano road cranks??

HillRider

Bolt circle and spindle length are completely different things and not related to each other. Yes, a 105, Ultegra, Dura Ace, Tiagra or any other Shimano road crank will NOT WORK with a 73 mm bottom bracket shell. Period. End of discussion.

Sifaw_

OK THANKS, this was very usefull but it still doesnt solve the mystery of how the hell cube is selling attain frame bikes with double cranksets
I will quote the important part that solves the problem for any1 interested:
"This was the final solution which I thought of. I found a road triple crankset, and measured the spindle length to be 112.5mm, which is 2.5mm longer than the road double or Alfine crankset. I also used a MTB BB, which have BB cups of 10mm wide on each side, instead of the 11mm of a road BB. Together, I managed to get an extra 2.5+1+1 = 4.5mm of spindle length on the left side!"

Kontact

The bolt circle is immaterial, but your use of the measurement "110mm" is creating confusion because no one measures the spindle on Shimano cranks the way you did.

Instead, Shimano refers to the spindle length by referring to the cranks compatibility with the BB shell width - either the crank is for 68 or for 73. You can adapt a 73 crank to a 68 bike with spacers.


Don't refer to the issue you are having by measuring the spindle length - no one knows that measure or uses it.

And bolt circle diameter has nothing to do with your problem, either.


All the Attain bikes I just looked at online either that had discs listed Press-fit BBs. Where did you get the idea Cube was using road cranks with 73mm threaded BB shells?

Sifaw_

m8 i own a 2017 Attain frame bought from bike-discount.de and it HAS a 73mm Threaded BB shell, this is a fact.
So unless its possible to adapt it to a press-fit bb i dont understand how they put those cranks there.