Singlespeed & Fixed Gear "I still feel that variable gears are only for people over forty-five. Isn't it better to triumph by the strength of your muscles than by the artifice of a derailer? We are getting soft...As for me, give me a fixed gear!"-- Henri Desgrange (31 January 1865 - 16 August 1940)

Gear Ratio

Old 12-26-18, 12:34 PM
  #1  
Ride_Fast
Senior Member
Thread Starter
 
Join Date: Nov 2017
Posts: 83
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 53 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Gear Ratio

Hi everyone. My question today is what are the benefits of having a larger chainring? Also, for those of you who run big gears, what do you suggest? I currently run 48x15 and the next obvious one would be 48x14. But maybe that's still not a big difference for what I need. To give you an idea about my fitness level. Yesterday I pedaled an outdoor, windy, flat track going 20-21 mph for 1hr and 20mins, no water, no stopping, with at least 1 sprint for every 2 miles.

Last edited by Ride_Fast; 12-26-18 at 12:52 PM.
Ride_Fast is offline  
Old 12-26-18, 12:55 PM
  #2  
fietsbob 
coprolite
 
fietsbob's Avatar
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 40,997

Bikes: 8

Mentioned: 183 Post(s)
Tagged: 0 Thread(s)
Quoted: 6578 Post(s)
Likes: 0
Liked 69 Times in 62 Posts
wear spread over more teeth +1t on a chain ring is a smaller increase , than -1t on a hub cog..


you can do the Math Y/N ? Front T divided by rear T is a Ratio... 40/20 is 2:1 ...
fietsbob is offline  
Old 12-26-18, 01:19 PM
  #3  
79pmooney
A Roadie Forever
 
79pmooney's Avatar
 
Join Date: Oct 2014
Location: Portland, OR
Posts: 6,717

Bikes: (2) ti TiCycles, 2007 w/ triple and 2011 fixed, 1979 Peter Mooney, ~1983 Trek 420 now fixed and ~1973 Raleigh Carlton Competition gravel grinder

Mentioned: 88 Post(s)
Tagged: 0 Thread(s)
Quoted: 1548 Post(s)
Likes: 0
Liked 12 Times in 11 Posts
Many of us find "gear inches" and easy way to visualize gear ratios that the straight ratio fietsbob uses. It is also a language that has been around a ;long time. "Gear inches" (GI) is what a single wheel wopuld need to be to roll as far as one pedal stroke; in other words how far a high wheeler of 140 years ago would go (or a kid's tricycle). 70" is what a big high wheeler would be and also makes a nice all-around flat ground gear. Above 80" is starting to get big. 90s are full on race on the velodrome.

Your gear is 48 / 15 X 27" (roughly your tire diameter assuming common 700c) = 86.4", pretty big.

As for chainring size, bigger means bigger cogs also to achieve the same GI. Slightly heavier and very slightly more wind resistance but a little more efficient and long wearing. (An aside - running 1/8" chain, rings and cogs as opposed to 3/32" has many of the same advantages/disadvantages.) I run 1/8" and a 42 tooth chainring as I want to be able to go to good hill climb gears, am 65 yo and never had your kind of speed. In my racing days, the fix gear was primarily my poor weather/winter bike and after my first season of racing I rarely went higher that 42-15 at my strongest mid-season.)

Ben
79pmooney is offline  
Old 12-26-18, 02:40 PM
  #4  
fietsbob 
coprolite
 
fietsbob's Avatar
 
Join Date: Jun 2010
Location: NW,Oregon Coast
Posts: 40,997

Bikes: 8

Mentioned: 183 Post(s)
Tagged: 0 Thread(s)
Quoted: 6578 Post(s)
Likes: 0
Liked 69 Times in 62 Posts
that's only 1 step away multiply ratio by wheel nominal diameter.. ...

(not into single speeds anymore.. but a 16:38, 26" wheel & a 16:53 in a 20" wheel [ IGH 11th of 14 is 1:1.in the hub ] is pretty close to rach other..
fietsbob is offline  
Old 12-27-18, 04:16 AM
  #5  
Mikefule
Senior Member
 
Join Date: Aug 2018
Posts: 75
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 27 Post(s)
Liked 2 Times in 1 Post
Changing the large chainring by 1 tooth is a smaller percentage change of ratio than changing the small rear sprocket by 1 tooth.

Bigger chainring and sprocket = smoother action, less friction, and less wear.

Smaller chainring and sprocket = marginally less weight and marginally less aerodynamic drag. Negligible effect for everyday riding.

Other considerations are simply what is readily available, and what looks better to you.

The gear inches thing is often a useful comparison because a simple comparison of ratios assumes that the two bikes being compared have the same wheel size.


You can of course look it up on a gear calculator online, but I think it is always nice to understand what is happening and to be able to work it out yourself. The calculation is easy enough:
  1. Take the number of teeth on the chain ring.
  2. Divide by the number of teeth on the sprocket.
  3. Multiply by the diameter of the driven wheel in inches.
Example: 49/17 x 28 = 80.7 inches.

This means that the gear ratio produces the same effect as if you were pedalling a directly driven wheel (penny farthing or unicycle) with an 80.7" wheel.

Technically, you should also factor in the length of your cranks, but as most modern bicyclists use cranks of 170mm +/- about 5mm, the effect is negligible. In the world of unicycling, we use cranks from around 75 mm up to about 170 mm and then it really matters.
Mikefule is offline  
Old 12-27-18, 02:12 PM
  #6  
Ride_Fast
Senior Member
Thread Starter
 
Join Date: Nov 2017
Posts: 83
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 53 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by Mikefule View Post
Bigger chainring and sprocket = smoother action, less friction, and less wear.

Smaller chainring and sprocket = marginally less weight and marginally less aerodynamic drag. Negligible effect for everyday riding.
Ok, this is actually what I wanted to know. Thanks.

For the experienced riders that have tried it all. What was your next move after 48x15? Did you make the obvious move of 48x14? The thing is you really don't know until you try it. Any suggestions?
Ride_Fast is offline  
Old 12-27-18, 02:20 PM
  #7  
TMonk
Not actually Tmonk
 
TMonk's Avatar
 
Join Date: Jun 2007
Location: San Diego, CA
Posts: 10,983

Bikes: road, track, mtb

Mentioned: 108 Post(s)
Tagged: 0 Thread(s)
Quoted: 864 Post(s)
Liked 31 Times in 14 Posts
I would suggest you focus on spinning your legs faster to produce more power/go faster instead of gearing up. Do you ride any hills?

Your listed speed and gearing puts you at about 80 rpm, which isn't super low but it's on the low end. If you could spin that gear at 90 rpm, you'd travel 22.5 miles instead of 20-21 in that same duration.
__________________
"Your beauty is an aeroplane;
so high, my heart cannot bear the strain." -A.C. Jobim, Triste
TMonk is offline  
Old 12-27-18, 03:31 PM
  #8  
REDMASTA
Senior Member
 
REDMASTA's Avatar
 
Join Date: Apr 2016
Location: Traveling through time, will return last week.
Posts: 556

Bikes: Bare Rum Sword Knuckle Runner

Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 208 Post(s)
Liked 3 Times in 3 Posts
get yourself a Big Zen chainring, all the cool flatlanders are doing it.
REDMASTA is offline  
Old 12-27-18, 04:58 PM
  #9  
IAmSam
Senior Member
 
Join Date: Oct 2012
Posts: 1,263
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 253 Post(s)
Likes: 0
Liked 1 Time in 1 Post
Apparently it is not what the OP was looking for but since it became part of the discussion...I used Gear Inches a lot to help me make decisions about my own drivetrain and everybody seems to be forgetting that tire size, which does effect the actual wheel diameter, should be included to more precisely calculate G/I. I'm pretty sure I've seen a formula somewhere that factors it in, but that's one of the reasons, besides being kinda lazy, why I am content to use one of the abundant gearing calculators available on the interwebz.

And to be precise, seeing as how it was just mentioned that crankarm length ought to be included in one's gear calculations - No, that is not any part of figuring Gear Inches (or the European/Metric equivalent - "Meters of Development"). It is Sheldon Brown's gear measurement system called "Gain Ratio," which is the distance travelled by the bike divided by the distance travelled by the pedals during one turn of the crank, that does bring crankarm length into the equation....
IAmSam is offline  
Old 12-28-18, 08:59 PM
  #10  
Ride_Fast
Senior Member
Thread Starter
 
Join Date: Nov 2017
Posts: 83
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 53 Post(s)
Likes: 0
Liked 0 Times in 0 Posts
Originally Posted by TMonk View Post
I would suggest you focus on spinning your legs faster to produce more power/go faster instead of gearing up. Do you ride any hills?


Your listed speed and gearing puts you at about 80 rpm, which isn't super low but it's on the low end. If you could spin that gear at 90 rpm, you'd travel 22.5 miles instead of 20-21 in that same duration.

I practice spinning as well. I have a spare wheel with a 17 on one side and 16 on the other. All of my strava segments are very similar from 17-15 except for top speed, but usually the "average speed" is always 20-21.


No hills, I live in Florida. I do enjoy climbing though whenever there's a bridge.

Originally Posted by IAmSam View Post
Apparently it is not what the OP was looking for but since it became part of the discussion...I used Gear Inches a lot to help me make decisions about my own drivetrain and everybody seems to be forgetting that tire size, which does effect the actual wheel diameter, should be included to more precisely calculate G/I. I'm pretty sure I've seen a formula somewhere that factors it in, but that's one of the reasons, besides being kinda lazy, why I am content to use one of the abundant gearing calculators available on the interwebz.

And to be precise, seeing as how it was just mentioned that crankarm length ought to be included in one's gear calculations - No, that is not any part of figuring Gear Inches (or the European/Metric equivalent - "Meters of Development"). It is Sheldon Brown's gear measurement system called "Gain Ratio," which is the distance travelled by the bike divided by the distance travelled by the pedals during one turn of the crank, that does bring crankarm length into the equation....
Tire size 25mm and crank arm length is 170. 28's are becoming really popular and I've thought about trying them out.

Last edited by Ride_Fast; 12-28-18 at 09:05 PM.
Ride_Fast is offline  
Old 12-28-18, 09:36 PM
  #11  
TMonk
Not actually Tmonk
 
TMonk's Avatar
 
Join Date: Jun 2007
Location: San Diego, CA
Posts: 10,983

Bikes: road, track, mtb

Mentioned: 108 Post(s)
Tagged: 0 Thread(s)
Quoted: 864 Post(s)
Liked 31 Times in 14 Posts
Originally Posted by Ride_Fast View Post
I practice spinning as well. I have a spare wheel with a 17 on one side and 16 on the other. All of my strava segments are very similar from 17-15 except for top speed, but usually the "average speed" is always 20-21.


No hills, I live in Florida. I do enjoy climbing though whenever there's a bridge.
Nice, glad to hear you've got some experience and know what you want. The 48/14 is certainly a big jump up and is large enough to compete in endurance events at outdoor velodromes, just something to keep in mind.

For some context, I race a 51/15 in the Men's A's at the outdoor velodrome in San Diego, which is a similar gear to 48/14. It's certainly big enough for me to score points in races sometimes against national champs, former world champs and (occasionally) professional road cyclists. But there are guys who ride bigger gears and I happen to prefer a lower, "spinny" gear than some people. As with everything else YMMV, just providing some context. Needless to say the races are fast.
__________________
"Your beauty is an aeroplane;
so high, my heart cannot bear the strain." -A.C. Jobim, Triste

Last edited by TMonk; 12-28-18 at 09:40 PM.
TMonk is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.