dsam2

So, I moved from Utah to Nebraska and now I am finding myself running out of gears on my compact crank (Sram Force 50x34) due to the flat squares that I am now forced to ride until I finish school and then I'm out of here. I have a second bike (rain/trainer/computer bike) that has mid compact rings (Sram Apex w/ 10speed red rings 52x36). I was thinking about just swapping the rings of the two bikes so I have the larger set of rings on my main bike. Can I just do this or do I need to replace the chain because of the larger ring diameter. Will I notice enough of a difference in gearing to bother with the hassle of the switch or should I just leave it be and be happy with what i've got. Also, the current chain on my bike has about 6500 miles on it, but it still has not stretched. I check it often and am shocked with how long it is lasting. Should I be concerned about it or just ride it till it stretches? Thank you for sharing your wisdom.

sch

Doubt you will notice much difference unless you are averaging 25mph. That is only a 4% change. You will have to raise the FD on the seat tube
for the larger ring. Chain length, sort of depends on how straightened out the RD cage gets when on the big/big combo, which presumably you
would never use (?) at the speeds you appear to be running. Change is feasible, not too likely to help. What cassette do you run? If you do change
the chain, good chance the cassette will need to be changed as well with that chain mileage.

dsam2

I have been fairly constantly swapping out wheel sets that each have different cassettes, so they have about half as much wear as the chain does. Both of the cassettes are SRAM PG 1070s. One is 11x26 and the other is 11x25 I believe.

Drew Eckhardt 

Make your sponsor buy you a more suitable bike.

50x11, 12, and 13 are nice 36, 33, and 30 MPH cruising gears (100 RPM for 1 hour or more) respectively.

For 5-10 minute efforts they're good for 39, 36, and 33 MPH respectively (110 RPM).

Sprinting they'll get you to at least 46, 42, and 39 MPH (130 RPM).

OTOH If you don't have a sponsor because you're not fast enough to run out of gears on flat ground you'll do better learning to pedal faster.

dsam2

The tone of your response aside, I get what your saying, and assume your straight forward answer is don't change your set up.

rm -rf

"Make your sponsor buy you a more suitable bike." He's kind of joking by saying that if you are spinning out a 50-12, which is 30.9 mph at just 95 rpm, that's Tour rider speeds.

A 52-12 is 32.1 mph at 95 rpm, about 1 mph faster than a 50-12.

Here's a chart from Mike Shermans Gear Calculator. It's 10 speed 12-25 cogs with 52 chainring in blue, 50 chainring in black, and 34 chainring in red. The 52 chainring is a little faster for a given cadence, about half of a rear cog shift.

At the chart's 85-95 rpm, either chainring is fine, even well past 25 mph.

Maybe try shifting to one easier gear than you are used to, and spin that much faster to maintain the same road speed. Get your legs used to faster cadences, which is often more efficient.



Chain wear
With over 6000 miles on your chain, that's a lot of miles. My Campagnolo chains tend to show very minimal "stretch" wear at 5000 or 6000 miles, using an accurate metal ruler, and are measuring well under 12 1/16 inch between rivet edges, still in the "good" range of wear. But I end up replacing them around that time anyway, since they are also wearing internally and are getting "too" flexible, making the shifting a little sloppy. (And I guess I worry more about a older chain like that)

I have a "chain checker" tool, that fits in between the rollers to measure wear, but I don't trust it as much as using a ruler, since it's measuring by pressing against rollers instead of measuring the actual distance between rivets.

dsam2

Thank you for your answer, it was very helpful. I think I will just leave it how it is. I will start thinking about a chain replacement soon though.

never_recover

Efficiency is about proper torque not cadence.. I'm sorry but I'm tired of seeing things like this for years...

Yes in a race you'll spin high RPMs to preserve your legs (it's instinctive whether you specifically train for it or not)...

But spinning 100 RPMs when you're at 70 or 80% FTP is ridiculous and inefficient...

The reason Pros seem to spin 100 RPMs all the time is because when you see them on TV... they're racing..

never_recover

Plus low torque / high RPMs for hours is bad for my rear end

zukahn1 

I see no issues with this swap your within 5% gear wise and 1 link or so chain wise so if the parts aren't tootal rough nackered you should be fine.

Drew Eckhardt 

The cadences producing the lowest measured EMG activity, perceived effort, and fatigue go up with increased power output.

I ride closer to 80 at an all-day endurance pace, 85 for a few hours, 95 approaching FTP, 105-110 on VO2max intervals, and choose to shift around 115-120 RPM sprinting but don't object to 130.

If you're riding at 70 or 80% of FTP on level ground solo you're going to be going closer to 20 MPH than 36 MPH, and at a more modest 80 RPM could hit 28 MPH using a 50x11 with many of us fine using 50x15 or 50x17 depending on how close our aerodynamics come to a barn door and how out of shape we are.

For 2000 miles or so, up to 145 miles at a time, with the totals suggesting avoiding fatigue is a big issue.

Drew Eckhardt 

When asked whether it was better to mash a big gear or spin a small gear, Eddy Merckx replied that it was better to spin a big gear which is a high toque, high RPM situation

fietsbob

The Pros , racing Paris Roubaix which is a pretty flattish profile , for them...

swap out the inner chainring .. for a larger one seen 53-46 combos,


but IDK , may do it to keep the return spring on the RD tightly wound.
in either chainring..

HillRider

Yeah, because he COULD do both at once. Most of us can't.

cny-bikeman

Mathematical speeds aside, nobody who is not a pro or elite amateur will get much use at all out of a gear higher than 110 inches (50/12). I did a 3 month, 10,000 mile tour with a high of 48/16 (only 5 speed freewheels available, too expensive to convert to triple, wanted close ratios - so 48/38 with a 16-28 freewheel). Even loaded I had few people pass me. I did switch out to a 14-24 for a couple criteriums.

zukahn1 

You are correct that modern race combo is likely 53-46 front and 11-25 rear. Which will give you roughly 120rpms at 120 inches for 32mph.

cny-bikeman

Not even close. An easy way to figure speed vs gear is that a 100 inch gear at 100 rpm is 30 mph (29.74) Therefore the 53/11 (a 125 inch gear even if you use 26" nominal wheel diameter) gets you 45mph at 120 rpm - 30*1.2*1.25.