Options for switching to compact crank
 

Hi,

I have a 2013 Cervelo S2 that I bought used a few years ago. It came with a standard (53/39) Dura-Ace 7950 crankset, but I'm looking to switch to compact. What is the best way to make this switch? Here are the options I've looked at so far:

• Replacing my crankset with a new or used compact Dura-Ace 7950; this seems inefficient, and almost everything for sale is $250 or more
• Replacing my chainrings; I thought this was going to be viable, but no one sells used chainrings and it's at least $250 to buy a 50t and a 34t ring (at which point I'd just buy a new crank and sell my old one)
• Replacing my crankset with something totally different; I was able to find, for example, a new-old-stock compact FSA SL-K 10-speed carbon crankset for $140. This issue with this approach is I'm not sure about BB compatibility

Any thoughts? I'd like to keep this as cheap as possible, and I'll likely be selling my current crankset once I make the switch. Thanks!

Danny

If you're goal is lower gearing, You might be better off replacing the cassette. It looks like you have a 25T largest rear cog. If you could get a cassette with a 32T sprocket it would make hill climbing much easier.

This will likely mean wider gear spacing. So check the progression first. Something like a 14- 16 - 18 - 20 - 22 - 25 - 28 - 32 might work well. Go lower if you have more then 8 speeds.

Thanks for the response! I will likely also be switching out the cassette, but that seems relatively straightforward. The crankset replacement is where I'm getting a bit tripped up.

Assuming you have the usual Shimano Hollowtech BB I would just get a new Ultegra or even 105 Compact crankset. You will have to lower your FD a smidge. You might want to shorten chain but that’s less critical.

Check EBay for good prices either new or gently used.

Thanks for the recommendation, that's a solid idea. On a somewhat related note, do you know if it's possible to use Ultegra FC-6750 chainrings with a Dura-Ace FC-9750 53/39 crankset? Instinct tells me no because that would be too easy, but they both seem to have five-bolt 110mm BCD setups. This is potentially viable because the Ultegra chainrings are way less expensive than the Dura-Ace ones.

Going from a 25 to a 32 might require a new RD, short cage to long cage.

Also not sure the bolt circle on a standard crank and a compact are the same which means you can't just change the chainrings.

My son is in the same situation with Sram Force having a standard crank and 11-25. Since he's no longer racing he's looking for a compact crank and wants to keep the close gearing of the 11-25 instead of a 11-28.

If you have a 7900 series crank with standard chainrings I am pretty sure that’s a 130 BCD. So you can’t just get compact chainrings.

The newer Shimano groupsets have the same BCD for standard and compact but Dura Ace 7900 and Ultegra 6700 are older generation.

Haha, that figures. So if I have to replace the whole crankset, do you think I should stay within Shimano or expand my horizons? I've found a couple used FSA SL-K options that are well reviewed and the same price as used Ultegra, but some say they don't work quite as well.

Thanks for the feedback. I'll have to take a look at my rear derailleur, I'm not sure what my possible cassette range is.

Just double check the fit and compatability before spending money.

Your call. Lots of people use FSA cranks and like them. As above make sure that whatever you get uses the hollowtech II bottom bracket.

Another consideration is an Ultegra 6800 or 8000 crank. These are 11 speed, but word on the street is they work fine with an otherwise 10s drivetrain. If cost too high just get a 105 series crank. They are perfectly fine for our purposes.

Whenever I do chainrings, either to replace worn rings or to revisit my ring selection (I switched from a 53t to a 50t years ago, to put me more into the center of my 12/23 cassette, and later tweaked it up to a 51t), I usually end up buying a whole NOS crankset, which is usually cheaper than individual rings themselves. I keep the rings and sell the crank arms on, unless the crank is an upgrade, in which case I keep the whole thing and sell the old arms. Strangely enough, I recently spent ages looking for the right compact crankset for my Campagnolo 10sp setup, finally found one and bought it, and then realized that I was happy with my current 51/39 crank, and there’s nothing in my locality that can’t be climbed with a 39/23. So, the NOS compact crankset is currently raising the tone of my parts box. I’ll no doubt start lowering my gearing as I age, but I’ll probably look at a 12/25 cassette before I switch to the compact crankset

What is the goal? If your normal riding has you using the larger cogs on the rear cassette, then yes that is an indication you need to change front or back. But if most of your riding you are on the higher ratio gears (smaller cogs), then what are you expecting to get from a compact crankset?

Can confirm the 6800 11 speed crankset works with a 10 speed drivetrain. Currently running this setup on my road bike (the 10 speed components are 105). Had to make the chain a little smaller, lower the front derailleur, and re-tune the derailleur. All together, it wasn't hard.
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Dave

What would be the real disadvantage between new Tiagra 4700 and 6800 in this case?

About 250g. But certainly an option.

Good ideas, really appreciate it.

I'll probably end up just selling the current Dura-Ace crankset since it's got a 130mm BCD, but that's definitely a great approach.

The goal is to increase cadence by decreasing gear ratio. On most of my rides I find myself spending 50+% of the time in the lowest gear ratio (1.39 for me), and it still often isn't enough.

I think I may end up going for this if I can't find a solid used Ultegra 6700/6750 crankset, I appreciate the input.

Your cheapest option is to just get another Shimano compact crank and lower your FD. You likely will also have to shorten your chain.

As noted, your current crank cannot accommodate smaller rings due to the larger 130 BCD. And changing cassettes may require a different RD or a derailleur hanger extension.

The FSA crank is fine, but you may also need to swap the BB. I cannot recall if FSA 24mm cranks work on Shimano BBs, and do make sure you buy a 24mm FSA crank, not a BB30.

Swapping threaded BBs is not hard to do, if you have the tool for it, which also isn't terribly expensive.

True, but do the latest gen Tiagras have any reports of broken crankarms as did the Ultegras are/were?

I guess to get back to one of your original questions.... Since your current crank is a hollowtech II, I've found that trying to find just the rings alone to not be much less than buying a new crank set with the rings you want.

Unless you are super concerned with weight, a Tiagra crankset will do you well.

I've also found that I can buy a brand new crankset for the prices people are asking on eBay and elswhere for used. You just have to google and look at a lot of online vendors to find the one that has a real deal. Amazon is unlikely to be the place for finding deals on a name brand crankset.

You can buy a crankset just to get the rings and then sell the bare cranks to recoup your money.

You can get one for $105 with 172.5mm arms. https://www.bicyclesonlineshop.com/p...10sp-chainset/

You can't do that. Standard 5 arm road cranks have a 130mm Bolt Circle Diameter which won't fit rings smaller than 38 teeth. Compacts have 110mm BCDs small enough to accomodate 33T.

You don't want to do that. Shimano, Campagnolo, and presumably SRAM do a better job sculpting their rings for fast shifting. FSA does not.

FSA engineering is sometimes bad. They've sold cranks with bottom brackets that were too wide, so it wasn't possible to properly bottom the crank arms on their tapered splined interfaces leading them to wobble and fail. They've sold cranks with fat hollow carbon fiber arms that interfered with achieving proper front derailleur rotation.

Good points, thanks. That's what I'm thinking right now. I've been researching my derailleur and I probably couldn't get anything larger than a 30T in there, but I might make that switch if the crank doesn't do it.

Yep, I've been doing a lot of Googling to try and find the cheapest price. I unfortunately can't swap the ring because of 110mm BCD vs. 130mm, but I will be selling my old Dura-Ace crank; it seems like I might actually be able to make some money off of this transaction if I get a good enough deal on the new crank :)

Yeah, I've been reading a lot of reviews of these FSA SL-K and K-Force cranks and they all seem to break. A bit mind-boggling given they cost a small fortune...

Thanks for the tip about the cheap Dura-Ace crank, but I'm fairly certain that website is a scam. I Googled it a while ago and it seems like it's pretending to be bicyclesonline.com, a reputable dealer. There are reports of people making orders and getting fake shipping numbers but never receiving anything.

IME, cranks are the wrong place to economize. My thoughts are to get a new crank and new BB to match.

https://cimg3.ibsrv.net/gimg/bikefor...afc621ce28.jpg

Wow, way to hammer the point home :lol:

Why a new BB? I will probably end up going for another Shimano Hollowtech II crank anyway, and the current BB has got under 1,000 miles on it.

Your BB should be ok. My Ultegra 6700 BB crapped out at about 40,000 miles. YMMV.

Wow, good to know. Maybe in 40 years I can reach 40,000 miles :foo: