48x12 = 105 g.i. = 28mph @ 90rpm

Is that crazy? It would be for me, but maybe not for you.

It works if your name is Boonen or Merckx or you ride in a vacuum.

Running the numbers is one thing, pushing those numbers is another... have experimented with a 100 gear inch drive and found that I go faster when I can spin at 120 rpm and not destroy my knees at 90... and it does not allow for any snappy acceleration, hills, or wind.

Worked with a messenger who insisted that his nearly 100 gear inches made him faster except he was probably the slowest messenger I ever saw... had no jump and by the time he got up to speed you'd be a mile down the road dropping off your next package.

Highest day to day gear I ever ran was 82 and was out for a ride working on my TT speed and found myself riding parallel to a course that had been set up for one of our many triathlons which I don't pay much attention to.

Ended up pacing a bunch of these guys for a few miles and got a few thumbs up from the riders as I wasn't dressed like a superhero and was riding a 30 year old steel conversion... and was not having any trouble keeping up.

Have been passed in the same way too... have been out there killing it and had a few people on fixed and geared bikes blow by me like I was parked.

They must have been on crack.

ok...
so you guys are telling me i am really better off spinning more @ lower ratio/inches? makes sense.
hope you didn't get me wrong earlier, i do keep up a purty damn quick cadence most of the time with my current set-up, but it is nice to sort of "lope" along & rest sometimes, especially on the long rides.
btw, i have cogs from 14t-19t, can't seem to keep myself from experimenting constantly & bigger g.i. just feels better to me.
well then, waddaya think about my 46x14, is it so turrible?

FWIW, we have a flat 10 mile TT series here, and when I've done it Merckx-style, I've run 52x15 (94 g.i.) on my FG. It's still pretty heavy if you get any kind of headwind, but that's the challenge of doing a fixed TT, right?

52x15...ummmm....i like that

There was an epic post around gearing and stopping without skiddnig that Ken Cox posted (recently?) I can't find it, but it belongs in this thread.

I was running 46x17 for a long time and then went to 46x18 and am very happy with it. I don't race, not in much of hurry to get anywhere so it works perfect for me. If I do trail riding on my FG I switch to a 19 tooth cog.

Isn't there an iPhone app that does this all for you?

what do you guys think about 49/16? im currently riding 49/17 but wanted a little more challenge and maybe a higher speed. thanks!

How long can you spin that 49:17 @ 90 rpm ?

How often do you spin it at 100... or 120 ?

If you are not regularly spinning out the gear you have now a taller gear is going to slow you down as your cadence will drop... think I have spoken often of riders dropping from an 80 gear inch ratio to one in the mid to high 70's and finding they got faster and could farther at higher speed.

I think it's stupid and you should learn to spin a lower gear ratio.

Recently dropped to 42/17 on my second bike/the one with a brake to accomplish two tasks; 1) Get better at spinning, and 2) climb a little easier.
So far so good :D

Track season is upon us here and for the next 4 weeks the guys will be riding 74 gear inches to develop their spin before they move up into the low 80's... considering here that the track is smooth and there are no hills and no wind that one has to deal with.

In the old days people started training by doing 1000 miles on a 74-76 inch gear and this is what was often used on the open road to knock down sub hour 40's... you have to spin that at 110 rpm or more for a full hour to knock this down and have to deal with wind and grades.

for anyone wanting to see the math behind that calculation.

it confused me until i learnt that gi is the diameter of the imaginary "wheel" not the circumference.

so let's see:

105gi x 3.14 x 90rpm = 29700 inches/minute.

29700 inches/minute x 60 (minutes) = 1782000 inches/hour.

1782000 inches an hour divided by 63360 (inches in a mile) = 28.125 miles an hour

there we have it, bang on target.

it's interesting that the 48x12 gearing means you're somehow driving an imaginary wheel 105 inches in diameter. that's a big wheel.

chain ring teeth x wheel diameter in inches / cog teeth = gear inches.

:)

Permit me to add to this discussion. Use the formulas referenced in the posts above to calculate what chain rings and cogs you need.

Online calculators are available here:
http://software.bareknucklebrigade.c...it.applet.html (does not work with Google Chrome)
http://www.sheldonbrown.com/gears/

Your preferred gear inch will depend on:
- how fit you are
- how strong you are
- the terrain you do 90% of your riding
- the wind conditions for the majority of your riding
- how many skid patches you want (if that's important to you)


Since most riders cannot perceive a 1 gear inch difference, consider the following gear ranges with soft edges, not binary precision.

60-65 gear inches = good for older riders or weak knees or touring.

66 gear inches = good all round gear for flats and hills. Not too slow on the flats, not too hard on the hills and wind. Touring is even possible. Great acceleration from standstill.

69 gear inches = near ideal for most people and most applications unless you are exceptionally strong. City gear and hills are feasible.

70-73 gear inches = superb range. At 100 rpm, it produces 21.4 mph (34.5 km/h). At 100 rpm, the force required to turn the pedals is still relatively light. Anything is this gear range produces an excellent balance between acceleration, hill climbing, combating winds and flat road speed. Note that at 20 mph (32.2 km/h), approximately 80% of the power being produced by the human body is being used to overcome air resistance. This is why it is so hard to sustain any speed above 20 mph (32.2 km/h) during a daily commute. If you know how to spin, this gear range will not be slowing you down.

76 -81 gear inches = this range maybe useful in places where there are no hills and where riding with a slow cadence is preferred to riding with a rapid cadence. All other things being equal, one will sweat less pushing a larger gear with a slow cadence at low speeds (say up to 15 mph) versus a lower gear with a high cadence. All bets are off if you push a large gear with a high cadence! This range is also harder on the knees due to the pedal force required to turn the cranks. Acceleration from a standstill will be noticeably slower than gears in the high 60s and low 70s. It's a tall gear for city riding and sprinting from traffic to traffic light and intersections. Hills will also slow you down in a big way.

81 and up gear inches = velodrome racing gears in controlled conditions, and short term training applications.

These are my opinions only based on general observation, lots and lots of reading and learning from others who have gone before. I'm sure someone will say, "But I ride 92 gear inches and it takes me everywhere!". My reply would be, "Good for you. I hope you have money for the knee surgeries you're gonna need."

Find a gear low enough that allows you to climb the highest hill you need to ride on a regular basis and use that as a starting point for your singlespeed and fixed gear riding. With FG, you need to ensure the gear you pick is high enough that you can ride DOWN the tallest hill you've just climbed.

Best wishes,
Victor

Great thread and I enjoyed your post Squirrelli :)

I am a clyde and I just converted a bike boom 10 speed (29 lbs. with its original freewheel and derailleurs) to SS. I live in a hilly area and I'm running about 73 gear inches (46t chainring, 17t freewheel, 27 1 1/4" tires) and it works fine.

However, this bike has a steep seat tube which lets me stomp hard. I think I would probably want to go with lower gearing if I was riding a more relaxed geometry.

Great post, puppypilgrim.

Just ordered my first SS for round town and fun rides.. No big grinder climbs where I am riding.. Stock gearing is 46 / 16.. hafta see how that all works out.. Oh yeah, I'm 48

ah! cheers - i was wondering about that. it's good to know.

do you know why does the sheldon brown calculator asks for crank length? is that his own take on the gear inches calculation?

Crank length is a factor when you calculate using gain ratios and is not required when you calculate gear inches.

thanks again!

er, isn't that bicycle repair man? nice :)

Came across this when researching cruisers:
http://www.atomiccycles.com/coaster.html

The Coaster Brake Challenge recommends around 50 gear inches for racing cruisers. Note that most of their courses are hilly.

Here is a site to help determine crank length http://www.machinehead-software.co.u...alculator.html

Running 40x16 on my Primus Mootry. Looks like it's just a tick under 67 gear inches. Anyone else running a gear this low? I don't mind spinning but I really have nothing on downhills.

I am making a SS and was wondering if a BMX style gear would work for the rear?

Yes.

I just picked up a 39t FSA chainring and i'm going to be trying it out with either 16t or 18t in the back... never tried a gearing this low before... I usually ride 46x16 in the city with no hills...

Just built my first SS with a KHS frame and parts I had laying around. 42x17 doesn't need a chain tensioner and is OK for city riding, since I'm not concerned about speed. I'm 60, FWIW.