Sinker

Is a 52/39 crankset a compact?

When I started shopping for my first roadbike, I did a little research and decided with my age, weight, fitness level and no desire to race that a Compact crankset would be a good way to go for me.

I ended getting a Scott Speedster S40, and went with the Compact instead of the Triple.
So I've been riding the bike for a little over a week and am very happy with my choice. We've got some challenging hills in the area and I've been able to manage them. Maybe a little lower gear would be nice, but not critical. And since I'm still getting comfortable with descending, the tallest gear is plenty.

It was after today's ride that I actually noticed my crankset is 52/39, not the 50(or 48)/34 I expected for a compact! I just checked the Scott webpage, and sure enough they claim the Speedster S40 comes in either Compact 18spd or Triple 27 spd, and spec the compact as 52/39. Check it out: https://scottusa.com/us_en/product/16.../speedster_s40

I'm not complaining, because as I said I'm okay with the 39 for local climbs. But isn't 52/39 a standard road double? Of course I haven't measured; maybe my bike has the smaller (110mm?) bolt circle.

coasting 

not a compact. i have a 52/39 double. perfect for rolling hills. the climbing doesn't require anything less than 39/25 because no matter how tough the steepest bits are, they are never long. The downhill doesn't require anything bigger because before i run out of gears the descent if finished.

umd

It can be but almost certainly is not. Compact refers to the bolt circle diameter. A "standard" is 130 (campy is 135) and compact is 110. The smallest inner chainring you can get on a 130BCD crank is a 38 although 39 is more typical these days, whereas 42 used to be typical. A compact 110BCD crank often comes with a 34 or 36 inner ring. The outer ring on a compact is usually a 50 so that the jump from the inner to outer ring is not too large.

cooleric1234

While this answer is probably technically true I find that whenever people are talking about a compact crankset they don't mean the BCD, they're talking about the number of teeth on the chainring. A compact has 34 T in the smallest chainring (sometimes 36).

umd

Yes, I said that it almost certainly is not. It is possible to get "standard" sized chainrings for a compact crank but they are uncommon and the chance of a bike coming with one is virtually nil.

Kai Winters

Nope...not a compact at all. Old school standard.

Sinker

Thanks for the feedback. Like I said, as it turns out it's not a problem, just odd that they would advertise it as a compact.

Jynx

i doubt it but it may be a compact crank with standard rings.

Diesel-CAAD9

50/34 is the "normal" compact as far as tooth count...

i went with the 52/39 and i didn't feel i needed that 34 tooth ring... if i want to later i can just go to a 27-28 out back... there are some pretty steep hills in my area but i've managed them all so far aside from one...

umd

As far as 50/34 being a "normal" compact, my Giant TCR came with a 50/36.

Bah Humbug

Interesting; the Giant TCR I have right now has a 50/34 compact, which matches basically every compact I see.

umd

https://www.bikeparts.com/productinfo...817-58522.html

passerby

Sorry for the thread hijack, but I am in the market for a road bike which I am planning on racing in the future. Is there a big downside to a compact crank when racing? I really dont want to have to upgrade the crank, and would rather just buy a bike w/o a compact crank from the start if I know it will keep me from performing lower than I possibly could. Thanks a lot

rollin

Think about a cadence of 90-120 and think about the speed you would be going to max out a 50*11. If this seems too low then a compact may not be enough for you.

passerby

hahahahahaha you got me there. I really never even thought of that...thanks a lot

rollin

Not tying to be smart. There are some advantages of a standard. I have time trialed using my compact on very flat courses, I guess I'm just weak!

SteveE

Guess you're not not old enough. For me, "old school standard" would be 52/42.

Bah Humbug

Oh, I wasn't doubting you. Interesting to see though.

esammuli

I've raced (cat 2) with a 50-34 this entire season with no issues. The only time a compact would ever possibly be an issue would be a long, extremely fast downhill sprint and those are few and far between. Even then a 50-11 combo is approximately the same as a 53-12. I'll usually race with an 11-23 cassette and either a 12-25 or 11-26 during the off season.

BigBlueToe

Thank you. This is very informative.

Velodad

Not exactly. Compact= old school standard crank BCD with smaller rings.

Compact as defined by the late great Sheldon Brown: A double-chainring crankset that permits the use of smaller chainrings than will fit with the common 130 mm B.C.D.. Most "compact double" cranks use the old standard 110 mm B.C.D. which permits the use of chainrings as small as 33 teeth (more commonly, 34 or 36 teeth.)

Compact crank sets usually come with a 50 tooth chainring, and will normally go with an 11 or 12 tooth top sprocket in back.

110 mm B.C.D. double cranks with full-sized (52-42, 52-40, etc.) were common in the late'70s and early '80s, but they had become nearly extinct for double chainrings. The rebirth of this format, with smaller rings, was pioneered by Tyler Hamilton who used one of these in the 2003 Tour de France

Sinker

OP here...

I measured, and my bolt circle diameter is 130mm, so even more definitely not a compact. Wonder why Scott claims it is....

Velodad

If you read the fine print it will almost always say that the manufacturer may substitute parts. WITHOUT NOTICE.

umd

It's also possible that the shop that build it up swapped the part for whatever reason

nondes 

I had my 9-speed regular drivetrain swapped out to a 10-speed compact last winter. Out of curiosity I compared the 2 setups with the Sheldon Brown gear calculator and this is what I got: (compact on the right).

With the new 11 and 12-tooth cogs I am getting a greater proportional advantage at the top end of the range than at the bottom with the same size 25-tooth cog, despite the compact setup. I tried it in hilly country just last week - no serious complaints but on a 13% gradient I was hoping for a greater advantage at the low end. The message being to take a close look at the rear cassette as well as the compact crank when making this decision.