Compact vs Standard cranks

briggsy2012

Calling all bike techies!

My main (and first road) bike came with a compact 50/34 170mm Shimano 105 crank, and over time I upgraded it to have 52/36 Q rings on it which I'm happy with.

As the 105 crank is looking a a bit shabby after a few winters use I'm planning to move it onto a winter bike I'm building, and then upgrade my race bike to Ultegra, maybe older 7800 Dura Ace, or even SRAM.

The question I have now is whether to go standard or compact on my main bike, but one consideration is that my Qrings are 110bcd.....

Obviously if I go standard I can't move my 110 bcd Qrings over, but at the end of day, what's the difference between compact or standard? I wonder as it seems you can put whatever 110bcd chain rings you like on a Compact even 53/39.....

Am I missing some vital piece of info? :-)

All advice gratefully received!

Cheers
Jon

imposter2.0

Search is useful - several current threads on this very topic....

viewtopic.php?f=40042&t=12953900

viewtopic.php?f=40013&t=12955366

viewtopic.php?f=40020&t=12788557

briggsy2012

Thanks Imposter,
I've had a look and to me they're basically saying it's all about chain ring size, and thats all.....

I asked my question because I was wondering whether there was another dimension to Standard vs Compact, as you can sometimes get a compact crank with larger chain rings than the usual 50/34.

So I guess I should stay with compact if I'm happy with 52/39 (would be happy to go bigger though) which is a bit of a pain as its not easy to find a decent 170mm arm length compact crank with 52/39 rings in the models I'm looking for. Which was why I was thinking about going Standard.

Cheers, we have answered my question....!

DiscoBoy

The bolt circle diameters are different. Compact is 110BCD and standard is 130BCD.

So, usually, standard rings (53/39) go on cranks with a larger spider with 130BCD, and compact rings (50/34) go on a smaller spider (110BCD).

Compact rings can't fit on a 130BCD spider.

Previously, standard rings were not fitted to compact (110BCD) spiders because they were too flexy. But now larger rings can be fitted to smaller, compact, spiders because they are stiff enough. Examples of this are your existing setup, and Dura Ace 9000 which doesn't come with 130BCD, only 110.

So, I guess your question was if your 110 BCD rotor rings will fit on a "standard" crankset, and the answer is no.

smidsy

You can physically fit whatever size ring combination you like if the bcd is right (110 for a compact spider) but you also need to factor in what tooth difference your FD can cope with.

Moonbiker

So I guess I should stay with compact if I'm happy with 52/39 (would be happy to go bigger though) which is a bit of a pain as its not easy to find a decent 170mm arm length compact crank with 52/39 rings in the models I'm looking for. Which was why I was thinking about going Standard.

Im confused, I read this paragraph several times & i don't understand what you saying

52/39 is a standard, so are you looking buy a new standard or a new compact 170mm arm crankset?

Grill

Moonbiker wrote:

So I guess I should stay with compact if I'm happy with 52/39 (would be happy to go bigger though) which is a bit of a pain as its not easy to find a decent 170mm arm length compact crank with 52/39 rings in the models I'm looking for. Which was why I was thinking about going Standard.

Im confused, I read this paragraph several times & i don't understand what you saying

52/39 is a standard, so are you looking buy a new standard or a new compact 170mm arm crankset?

He probably meant 52/38 which is still considered super-compact, as that's the biggest non-aero 110bcd Q-ring that Rotor makes (53/38 for aero version).

My advice is always unless you live somewhere pan-flat or are really strong, then go compact (or super).

Moonbiker

Never head of the term super-compact before.

52/38 is what I have on my bike because it was the only ring I could buy as a replacement for the 39t ring anywhere with 116BCD.

earthvspace4XTuUWcX

I would stick to a crankset with a PCD of 110, that way you can still use your Q rings, and basically you are not restricted to what chain rings you can fit. If you get a standard crankset (with a PCD or 130), then you limit your smallest chain ring to 38.