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Old 07-11-12, 10:59 AM   #1
cvall91
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Replacing Cassette and Chain ring 10 speed

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 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. 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.

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Old 07-11-12, 11:57 AM   #2
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He's probably deluding himself. The drivetrain you have would allow a rider with regular pedalling skills to reach abt 35+ MPH before spinning out. Don't expect it to increase your top end.
Merely changing the cassette, and leaving the rings would get you up to 38+ MPH - assuming you have the legs for it.

If you're sensitive to cadence changes, you might improve your average a little from the 11-25 offering smaller increments than the 12-28. In which case you might as well go the whole hog and go for a corncob cassette.

Or swap the rings, and go for a 16-27 cassette instead. Theoretically, a little more efficient due to the bigger radiuses. IRL, your smallest sprockets will last a little longer.
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Old 07-11-12, 12:18 PM   #3
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Originally Posted by cvall91 View Post
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).

Quote:
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).

Quote:
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.

Last edited by Drew Eckhardt; 07-11-12 at 02:54 PM.
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Old 07-11-12, 01:00 PM   #4
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cvall91, I ride mostly flat land in my immediate area. It is just my opinion that compact cranksets are better suited for those in hilly areas. I used a 53-42 with both a 13-21 13-23 8S for years. After my knee injury I simply changed to a triple for hillier rides (sometimes with a 13-27 or 28). I liked the close ratios for riding with the A groups.

I'm with dabac WRT the efficiency of using a larger chainring/cassette combo. Also each rider can only maintain a certain ratio/cadence, regardless of how the gear inches are obtained.

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Old 07-11-12, 01:35 PM   #5
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Just get the 11/23 cassette.
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Old 07-11-12, 01:42 PM   #6
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Use this chart to figure out what you need. http://www.jbarrm.com/cycal/cycal.html in a 50-12 turni the cranks at 95 rpm you will be going 31mph. You need to be able to put out over 375 watts to ga that fast. If you can you can make a living racing a bike.
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Old 07-11-12, 01:55 PM   #7
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Quote:
Originally Posted by cvall91 View Post
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 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. Would switching these actually be that much of an improvement? I mainly do group rides in the 20+ speed group if that changed anything.

Thanks
No, it would not be an upgrade at all. With the 11 alone you will gain a gear that you will use mostly downhill, and changing to a 53 would add another one you will use mainlyh downhill. Adding high gears will never, never increase your speed.

I have never ridden with a group (and I raced cat 3) where anyone spun at less than 90 rpm (most were 100-120) At that cadence the 50/11 is 33 mph. the 53/11 moves that to 35 mph. More typical rpm's take you into the 40 mph realm. I raced a criterium where we averaged a blistering 29mph (fast for a cat 3/4 crit). I had a 48/13 high gear (on a loaded tour, so had a smaller chainring). I finished 6th because I was boxed out on the sprint.

For the type of riding you specify I do agree with the 39 small ring, as shifting will be crisper, less jarring, and you will have a greater selection of cruising gears.

Last edited by cny-bikeman; 07-11-12 at 01:59 PM.
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Old 07-11-12, 01:57 PM   #8
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Originally Posted by Drew Eckhardt View Post
No.

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 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.
THIS!

If you're somehow exceeding the gearing of your recent-production bike, the coach of your pro team will probably let you know.
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Old 07-11-12, 02:17 PM   #9
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I think you need to talk to SOMEONE ELSE in your group!
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Old 07-11-12, 02:28 PM   #10
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Yea, I'm not interested in top end speed since I'll probably won't hit that on any given ride and I'm not planning on racing yet. I do notice a pretty big jump in some of the cogs which can be annoying. Apart from those couple of cogs I don't see how I can gain speed with the same efficiency. I basically never use the 4 bigger cogs in the back and only use the small chainring up front when starting from a stop. I just think I should be able to have more versatility instead of only using the same 3-4 cogs. Maybe this is the downside of riding on flats but a little more shifting in my rides would be nice.
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Old 07-11-12, 03:04 PM   #11
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Originally Posted by cvall91 View Post
Yea, I'm not interested in top end speed since I'll probably won't hit that on any given ride and I'm not planning on racing yet. I do notice a pretty big jump in some of the cogs which can be annoying. Apart from those couple of cogs I don't see how I can gain speed with the same efficiency. I basically never use the 4 bigger cogs in the back and only use the small chainring up front when starting from a stop. I just think I should be able to have more versatility instead of only using the same 3-4 cogs. Maybe this is the downside of riding on flats but a little more shifting in my rides would be nice.
Going to a tighter block will give you more versatility/variation and therefore better matching of speed vs. efficiency and that is where you may see increase overall speed, but the chainring change will do that also. Doing both a tighter block and tightening the chainring jump has the potential to create a lot of duplicate gears, so best to use Sheldon's gear calculator (just Google it) before deciding on the final setup. You also are significantly raising your low gear, but I doubt you will have a problem even with a 23 cog low, given where you live and your fitness.

Last edited by cny-bikeman; 07-11-12 at 03:19 PM.
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Old 07-11-12, 03:28 PM   #12
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Here's what you currently have:
http://home.earthlink.net/~mike.sher...no&TITLE=&HL=1

Here's what your guy suggested:
http://home.earthlink.net/~mike.sher...no&TITLE=&HL=1

But as someone said, just adding bigger gears doesn't make you faster - it does require more power to pedal in those gears.

As for me, the bike I ride around town to get groceries and go to work (in my work clothes) looks like this:
http://home.earthlink.net/~mike.sher...no&TITLE=&HL=1

People look at me like I'm an idiot when I'm grinding up hills in my shirt and tie at 48GI.
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Old 07-11-12, 08:16 PM   #13
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Going to a tighter block will give you more versatility/variation and therefore better matching of speed vs. efficiency and that is where you may see increase overall speed, but the chainring change will do that also. Doing both a tighter block and tightening the chainring jump has the potential to create a lot of duplicate gears, so best to use Sheldon's gear calculator (just Google it) before deciding on the final setup. You also are significantly raising your low gear, but I doubt you will have a problem even with a 23 cog low, given where you live and your fitness.
Yea I see what you mean. I looked at the links Tsmvengy posted (thanks btw) and saw the overlapping. I like the setup of just changing the cassette and leaving cranks alone. That way I can actually use more gears and make use of the granny gear while warming up or cruising.

Thanks for all the help, I'm gonna keep playing with Sheldon's calculator and see what i like best.
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Old 07-11-12, 09:44 PM   #14
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Yea I see what you mean. I looked at the links Tsmvengy posted (thanks btw) and saw the overlapping. I like the setup of just changing the cassette and leaving cranks alone. That way I can actually use more gears and make use of the granny gear while warming up or cruising.

Thanks for all the help, I'm gonna keep playing with Sheldon's calculator and see what i like best.
The overlap is a good thing because it both reduces ring changes that are accompanied with a rear shift and cuts their impact.

I ran 50-34 x 13-14-15-16-17-18-19-21-23 for way too long with exactly one overlapping gear (50x21 and 34x14) when you eschew the fully cross-chained combination. Any slower than 17 MPH I'd down-shift from the big ring 50x21 to 34x15 which is simultaneous pair of button pushes riding Campagnolo (but five lever actuations with Shimano or SRAM). Any faster than 19 MPH on the small ring I'd up shift from 34x14 to 50x19 with a simultaneous paddle movement plus a paddle movement (which could be three lever actuations on some Shimano levers). There's a lot of movement through that speed range on "flat" ground.

50-39 (add a 30 or smaller third ring for mountains that are too steep perhaps mixed with middle aged spread spread) worked a lot better.

Last edited by Drew Eckhardt; 07-11-12 at 10:14 PM.
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