Elantr025

Hi,

Im currently having a Gunnar Sport build up and the shop is suggesting a FSA 48/34
compact crank, NOT a 50/34.

So what is the difference between a 48/34 and 50/34 compact crank? Which would
provide a more comfortable ride?

I am an avid recreational type ride, im NOT a racer and im NOT a tourer, sort of
in between and mostly ride on flat terrian.

Thanks

Menel

Never seen a 48top chainring compact, 50 is the general standard, it's just mean you have a bit less top speed potential, and the chainrings are closer together so super crisp shifting.

Difference sounds like it will be negligible in your case.

vladvm

48/34 is usually cyclocross set up the other is road compact crank. Both might rob you of top speed. I suggest get the standard 39/53 since you are in flat area, even the standard 42/52 would be ok. Changing the rear cassette with 11-28 would be another option.

BikeArkansas

I just finished a Gunnar Roadie about a month ago. I went with all Ultegra components and am satisfied with the 50-34 compact crank. However, this set up does not shift as well as the one I had with the 48-34 on a previous bike. By shifting, I mean on the crank only, not the cassette which shifts VERY well. That said, this Ultegra shifts way beyond my ability to ride, so there are no real complaints.

R900

It's a cyclocross crank, unless it's a cyclocross frame and you plan on doing some cyclocross, I would go with a standard 50/36 or 50/34 compact.

DaveSSS 

There is no value is using a compact on flat terrain. Just get a 53/39 with a 12-23 or 12-25 cassette.

kayakdiver

Flat riding... can't see a reason to not just go with a standard crank.

thcri

Two Teeth?? Seems to me there is not much difference??

rm -rf

Compact cranks will overlap the big and small chainring at a different speed range than a standard crank. So it partly depends on what are your typical flat road speeds, and your typical cadence.

Here's a chart from Mike Sherman's gear calculator showing the difference between a 48 and 50 chainring at the normal 80-95 rpm cadences. Blue=50, Black=48, Red=34. For example: the 50-21 combination is about 15mph at 80rpm and 17.5 at 95 rpm. You can see there's not a huge difference between 48 and 50.



You want to avoid the 34-12 and the 50-25 cross-chained combinations. So the front chainring switch is often in the range of 15-18 mph.


39-53 chainrings move the speed range to faster speeds. But you lose the low end gears. Any hills that slow you down below 10 mph will be more difficult, grinding up at low cadences instead of sitting and spinning up.

SpongeDad

I would take the closer ratios of 48/34 or 50/36 over 50/34, especially if your on flat terrain. Take a look at rm's data above and pick something that allows you to ride comfortably in the big ring in the middle (e.g., the 19 tooth cog) of the rear cassette on the flats.

tFUnK

i know of someone who races cat 3 and consistently finished with the front pack on group rides who rides with a 48t. less top end speed for sure, but perhaps more useful coverage of the small jumps from 12t-17t.

gregf83 

A 50 tooth big ring allows you to stay in the big ring and around the middle of the rear cassette under a greater range of wind conditions. It requires less shifting back and forth on the big ring.

banerjek

The bike ride will be very similar, though going with the 48 will provide slightly closer gear ratios when you're in your big ring as well as lower the speed you need to be in to use it effectively.

Don't listen to these guys that say it will limit your speed. If you run a 12/27 in the rear, you don't spin out until nearly 40mph and there's no way in hell you'll get anywhere near there on flats. Even going downhill (when gravity is doing most of the work) it's going to be a minor issue if at all. In the unlikely case it makes a difference, it will be so small as to be unimportant and it will definitely be less important than the likely benefits you'd get from running a smaller ring.

In all honesty, a 46/36 might be even a better fit for you. That would spin out about 37mph and give you more overlapping gears over the rings and closer ratios in the big ring.

The thing to know about riding 50/34 is that if your cruising speed is below 20mph but above 16mph, you'll either be at the top of the small ring or the bottom of the big ring. Much better to get rings where your natural speed is in the middle.

Fat Boy

banerjek,

+1

knobster

I have this crank on a couple of my bikes. I like the 48/34 more than the 50/34 mainly due to shifting. I find that the jump is easier to shift with. A more desired range for me is the 50/36. Shifts like a dream.

knobster

I agree with everything he's saying here. One of my bikes has a triple 48/38/26 which I use for dirt roads and trails mainly and I really love the 48/38 combo. If I needed lower gears such as the 46/36, this would also be a great combo.

DaveSSS 

Yes, I rode a 50/34 with a 12-27 11 speed (my mountain riding setup) on flat roads this year. I rarely even used the little ring, since the 50/25 is useable. It seemed a little odd to hardly ever use the little ring.

Elantr025

Thanks guys....
BUT i am ONLY a recreational rider! NOT a racer! Im more a C rider and cruise at around 14mph or so.

jdon

Then I too would agree with banerjek.

grwoolf

50/34 with a 11/28 in the back is a good combination for me. If I'm not riding hills or major winds, I'm always comfortably in the big ring. The 50 - 11 combo is just as good as a 52 - 12 on a traditional crank for top end. There is no reason to get into the small ring as long as you are keeping it above 14-15 mph. If you don't mind a little cross-chaining (which I don't), it's no problem running the 50 - 28 for short climbs, etc. The big thing you'll miss is the 16 tooth in the rear, which is a gear I'd like to have, but it's all about trade off's.

DRietz

Just as a note - a lot of people here are stating that 48/34 combo's are a very cyclocross-y combination and it's also a very classic touring set up, although there would usually be a very small gear after 34, around 28 or 26.

Yay for useless facts...

DinoShepherd

Right. C-X is normally (and there is a lot of room around normal) 46 - 36 with a 12-27(or so)

revchuck 

Yup. This is my range, unless I'm in a paceline. I'm usually using either a 34/14 or a 50/21 combination (12-27 cassette). I've considered changing out my 50 tooth big ring for a 48, since it would basically move me one cog to the right on the cassette, but decided it wasn't worth the expense.

531phile 

I agree. If you do a lot of climing compact has its advantages, but for flats, stick with 53/39. I got a compact 50/34 and on the flats I'm basically on the 50 teeth 75% of the time.

rm -rf

Then the 48 & 34 chainrings will work great for you. Even the 48-12 high gear is a faster gear than my climbing cassette's top gear of 50-13, and I rarely miss having a faster 50-12.

You can cruise on the 34-15 or 34-16. And shift to the 48 chainring if you get a tailwind or slight downhill, and want to go 17+ mph.

(The 39-53 standard cranks would work, too, but then you wouldn't have low gears for any hills on your ride. And the gears are closer together in speed when using a 34 compared to a 39, so you can get the exact cadence you want to use)