Would there be any advantage to switching out my Tiagra crankset with an Ultegra? I'm hoping I could use my compact chain rings, but don't know if the crankset is interchangeable and beneficial.

Which version of Tiagra, which version of Ultegra? 9- or 10-speed?

What bottom bracket do either use?

What kind of advantages are you seeking? The Ultegra crank is a bit lighter and stiffer than Tiagra and has a greater bling factor. All of these advantages would be diminished by using the Tiagra chainrings, if that is even possible.

I think he wants to swap the Tiagra and instal Ultregra. I think the Ultegra, from his post, is a compact, whereas the Tiagra is not.

If your current crankset needs replacing, sure, replace it with the best you can afford. If there's nothing wrong with it, consider whether you're suffering from upgraditis. There's nothing wrong with changing something just because you want something 'better' as long as you're honest with yourself about why you're doing it.

+1
.... Provided it fits and works with your other components (which is what you were asking...)

As for compatibility, you might also check on the bicycle mechanic's forum as this type of thing can get pretty technical. Also, pictures and specific model numbers could help (for number of bolts, etc...)

You will have to be sure the bottom brackets do match as said. There are two of each crank sets as doubles, Ultegra 6700, Road Double, 130mm BCD, 53-39T or 52-39T, Ultegra 6750, Compact Double, 110mm BCD, 50-34T. The bottom bracket for the Ultegras is FC6703, width=68/70mm

Tiagra 4500, Road Double, 130mm BCD, 53-39T, Tiagra 4550S, Compact 110mm BCD, 50-34T.

Make sure you have the same BCD for the spider of the Ultegra as the Tiagra has on your bike. Tiagra Bottom Bracket, SM-FC4500, width=68/70mm. If you have the Tiagra compact crank set make sure the Ultegra is the FC-6750. The 52-36 is becoming popular as a mid-point between the road Double and the Compact Double. So both Tiagra and Ultegra list the same numbers for the Road Double as they list for the Compact Double. The widths are the same for Tiagra and Ultegra for all four crank sets as are the chain line measurements @ 43.4mm.

It should be doable and Shimano and others make an assortment of chain rings you can choose the gearing from to suit your needs.

Here is their website so you can see what will work for you:https://bike.shimano.com/#. Hope these help you.

Bill

Any bike that the Tiagra crank fits will also take the Ultegra. If the BBs are not the same, get the one that works. It may even come with the crankset anyway.

BD and jesseh627,
The Shimano site indicates that they both come with a bottom bracket, the numbers I gave are for separate order of the bottom bracket for the Tiagra. Ultegra does list the bottom bracket number as SM-BB6700 on the website, it is not listed as a separate item or link. The bottom bracket number link for Tiagra is in the same link as the crank. I take this to mean that the bottom brackets come with a crankset for both groups. the Ultegra is a Hollowtech II construction with Hyperglide Ultra-thin for 10 speed, the Tiagra is Hyperglide Ultra-thin for 9-speed.

My experience in swapping 10 speed 105 in place of 7 speed RSX says the narrower 10 speed will work with the Tiagra if it is the 9 speed. I am ot sure of any difference in the widths for Shimano's 9 and 10 speed Hyperglide. Again, check the website for your application and what you want to accomplish first, please.

Bill

Well, I'm immediately over my head. This is a new bike, Specialized Roubaix...all I know is it is a 10 speed Tiagra compact, not sure of the model. I have the opportunity to pick up an inexpensive ultegra crankset but never thought of all the complexities. I'll do some more digging to see exactly what I have. I've emailed Specialized to find out bottom bracket specs. Thank you, all for the fast response and great information!

Jesse,
Just forget all the numbers I threw at you, if the Roubaix has a Tiagra and uses the Tiagra, the Ultegra should work provided they are close in year of manufacture. 10 speed Ultegra is relatively new and if the Ultegra is close it should work. If it has the bottom bracket with it you are golden. Sorry for all the numbers and complexity I used. I am an engineer and plead guilty to having Engineer's Disease, bad. I over thought this one, best of luck with the swap and please let us know how it goes if it gets done. Happy New Year.

Bill

Mate, if it's new, leave it alone. Shimano keep improving their kit every year and I think you'll find that the current Tiagra is pretty darned good. Use your money to build a companion bike for the Roubaix, do up an old bike or build a shopping bike or something

If it is a Tiagra compact, run with it. Tiagra is a very serviceable groupset. I don't think you can carry the chainrings on the compact Tiagra over to the road Ultegra, so that answers your original question.

But (and there is always a but), if you can pick up the Ultegra crankset for cheap, and it comes with the BB, get it and put it away until you think you've outgrown the compact, which is possible if you are in a flat part of Texas. If you are near Austin, for example, though, definitely stick with what's now on the bike.

Aha. 10-speed Tiagra to 10-speed Ultegra. This would be an easy swap that won't require any other changes, if the Ultegra is also a compact double. Shimano road threaded outboard bottom brackets are interchangeable. And your main benefit would be small weight loss and a prettier crankset. Maybe the shifting would be a bit snappier, but this is hair splitting.

And for Rowan's information, Tiagra offers only compact and triple cranksets.

Personally, I' buy a new bike before upgrading anything on a 10-speed Roubaix that wasn't broken.

I believe the only significant difference in performance would be the bling factor

Think others have put my opinions.

I wanted to dig into this, from a general knowledge standpoint (as in I have none, and want to learn) So are you saying that (for instance) an ultegra 175 34/50 crankset will fit both in a bike that was designed with bb30, and the same crackset will fit in a bike with an english BB, and all you need to do is change the BB not the crank?

I can't quite follow your meaning. What I was saying is that if your bike now has a 10 sp Tiagra crank, an Ultegra crank will also fit since they would use the same type of BB, either English or Italian depending on which threading your bike has (probably English). To put either crank into a bike with a BB30 shell would require some kind of adapter which would work with either one. But a BB30 crank will not fit into a frame with an English or Italian threaded BB shell.

Not correct, see my first reply for the number for the standard road double Tiagra crankset, 53-39 chain rings and a 130 BCD. The Compact and Road Double use the same BB and have the same spindle length and chain line measurement (again see my first reply.)

And, I agree with the fact that Tiagra is fully serviceable and totally reliable and is a great shifting crank set. I'd run it for ever, personally. Tiagra and 105 are my choices for Shimano groups, good bang for the buck and well engineered. Disclaimer: I run SRAM on my CAAD 10 4, just had a lot of Shimano components over the years, I personally like the RSX 7 speed on my R500 Cannondale.

Bill

to simplify, will a given crank fit into bikes with different bb...so the crank part itself is no different (as in different length, diameter something) just the bb is different.

so for instance I have a giant defy with an ultegra crank. it has a bb30. Can I take that crank off the giant, buy a english bb and install it all on a new bike that needs the english bb (rather than buying a whole new crank and bb)

If your bike has an Ultegra crank and a BB30 BB shell, then it has to be using an adapter since all Shimano cranks are designed to fit threaded BB shells, not oversized. So yes, you should be able to use the Ultegra crank on the new bike. Whether you will need a new BB depends on whether the Giant's adapter utilized the standard Shimano BB or not. New Ultegra BBs run about $30.

Thank you, Bill. This is all new, so I get overwhelmed quickly. Thanks for all the help! Happy New Year!

definitely sticking with the compact! Between the wind (always), and the hills, I need all the help I can get.

thanks!

To this point....my Masi came with Dura Ace about 7 yrs. ago. Very nice kit. This year I bought a cyclocross bike with 105. The 105 shifts smoother than the old DA.