Originally Posted by cvall91
Couldn't find anything in search so sorry if there actually is something.
I recently got a new road bike and the current gears are 12-28 in the back and 50-34 in the front.
I'd swap that for 12-23 12-13-14-15-16-17-18-19-21-23 since that feels so good on flat ground.
Speaking from experience 34x23 (which would be close enough to 39x25 or 26) is enough to get a fit rider without middle age spread over anything in the Colorado rockies and to enjoy spinning up most of it. Down in Florida loosing the lowest gear probably wouldn't be a bit deal.
I'd throw a 39 inner ring on too to cut front shifting . Although making the small end of the cassette perform like the cogs are two teeth smaller doesn't seem significant, some back of the envelope calculations show the effects are huge and explain anecdotal reports of peoples' front shifting increases moving from road triples with a 39 middle ring to compact doubles with a 34.
Using the rider aerodynamics from Gibertini and Grassi's paper with .4m Sd and .760 Cd riding on the hoods, a 75 kg rider/bike combination, and .004 CRR a pleasant 100 RPM in 34x13 gets him up to 20.5 MPH at 172W. With 39x13 he gets up to 23.5 MPH which is a 250W effort - 45% harder. If the rider were like me with a 235W threshold power the 34 ring is only good for a zone 2 endurance pace on flat ground while 100 RPM in 39x13 is getting to a VO2 max intensity.
This effect is amplified by people's desire to increase their cadence as power increases. While 110 RPM at an endurance pace feels like you're spinning air, going anaerobic it feels pretty natural. That makes the small ring useful up to 25.8 MPH and 317 Watts which is a zone 6 anaerobic effort for me.
Things get even more dramatic comparing a xx - 39 - xx triple to a 50-34 compact. The 39 ring is between where the 50 and 34 rings would be and chain angle isn't too extreme getting to the last cog. More power, 125 RPM still feels good, and the combination allows for 31.8 MPH / 575W sprinting effort without leaving the small ring.
I'd probably skip the 53 ring which usually goes with the 39 since speeding up past the small ring would become a 4 cog change which is two right levers shoves versus the single push with the 50 ring. I change rings a lot more often than I end up going down-hill in the small speed range between 50 x smallest isn't enough but 53 x smallest would still be usable (like having a starting cog one tooth smaller).
I was talking to someone in my group about his wheels and said that before the wheels, a big upgrade will be changing the gears. He said to get a 11-25 cassette and switch the chainrings to 53-39. He said I'll easily get a 2mph gain and much cheaper than wheels.
As a couple of data points:
Eddy Merckx dominated the classics with a big gear of 52x13, with feats like spending 140km off-the-front all the way to the finish on a Tour de France stage. 50x12 is half a gear bigger. You do _NOT_ need the 11 cog which would net 1.5 gears bigger than Eddy.
I don't have an especially good spin, although with the right tail-wind or down-hill I could spin a 50x13 30 MPH for over an hour and 50x12 33 MPH. For 10 minutes 33 and 36 MPH would be pleasant. Sprinting down-hill I'd prefer 't a bigger gear after 38 and 41 MPH respectively although 42 and 46 MPH are possible.
I've used a 50x13 big gear for 16 years including 10 in the Colorado Rockies (there are a small number of descents where I might apply more power, but lots of flat places where one tooth jumps through the 17 or 19 cogs feel great).
I live in South Florida so 99.9% of my rides are on flat roads. Would switching these actually be that much of an improvement? I mainly do group rides in the 20+ speed group if that changed anything.
No, although a 12-23 may feel better and a 39 inner ring will let you spend a lot more time on the small ring.
While people made do with things like 52-42 x 13-26 in the six speed era there's no reason to just "make do" when you're willing to spend $100 on your hobby.
I've been riding cassettes with one tooth jumps through at least the 19 cog since upgrading from 6 to 8 cogs and realizing that a road triple would let me have a low gear like 42x28 for the mountains west of Boulder, CO and corncob for the plains east without swapping depending on which way I or my group decided to go that day (50-40-30 x 13-14-15-16-17-18-19-21). It's really great.