Fixed gear alteration
 

Experts, grateful for advice re: gears. I have a bike with fixed gears to run around town. Currently set up as 44 tooth chain ring and 18 tooth freewheel cog which is just to light a push. Is the easiest option to fit a 16tooth freewheel cog to get a bit more pressure on the pedal?
Thanks,
T

You would go faster/farther for the same turn of the pedals. You would also lose a bit of hill climbing ease.

What is your cadence? A moderate/higher cadence at speed is usually preferable to a slow grind.

Thanks Base2, My cadence around town about 70rpm..

The rear axle will shift back 1/4” if you reduce the total tooth count by two. Is there room for that?

If that would be an issue, another option might be a 42 chainring and 16 tooth cog which is still more gear inches than you run currently but, with the removal of one chain link, should put the rear axle about in the current position.

Otto

You don't have a fixed gear.

What you have isn't a fixed gear, it is a single speed...You could try putting on a 46 tooth chainring up front, which would also move your rear wheel forward a little bit so make sure you have enough room between the tire and the frame or you could use a 16 tooth rear cog....What you have on there right now 44 x 18 is about 65 gear inches which is pretty good for urban riding in traffic with frequent stop and go .

70 rpm is a pretty low cadence. You might do better to practice spinning faster. Higher gear ratios don't always translate to faster speeds.

By swapping out the 16T rear cog with an 18T you'll increase your speed by about 13% at the same cadence. But it will require about 13% more effort for headwinds and hill climbing. I'd probably opt for a 17T sprocket for 70 gear inches. This will provide over 6% more speed, But will require less effort then the 18T sprocket would.

If you feel you can deal with a headwind with a 16T sprocket (approx. 74 gear inches) then go for it. I use my 38T chainring w/18T rear cog (55 gear inches) for some headwind and hills on my 3 x 7 speed bike. Of course that would not work on a single speed bike...Too slow the rest of the time. At 65 years old riding perhaps 3 - 5 hours per week, I could live with the 44/18T gearset (66 gear inches) that came with your bike. I'd be willing to sacrifice a bit of speed to have a low enough gear to be comfortable with headwinds and hills.

Yup. Getting cadence up to a much more desirable 90 rpm would give 29% more speed vs 13% when switching from 18 to 16. You go to higher gears when you are spinning out the existing gears. And a taller gear, by itself, will not make you faster. Putting out more power makes you faster.

Thanks Charlie, Phil, Kerry and Wolfchild!

This is worth repeating (a second time), with some data. I've been riding a long time and have a naturally lazy cadence, 60 or 70, and haven't felt that it was a horrible thing because I don't strain and am not trying for speed records. I don't ride single speed and I do have a computer on my bike, so I started playing with gearing to see what changes in cadence would do in real life. What I have generally found is that when I feel like I'm in a good place I intentionally shift down a gear anyway just to see what happens. What happens is that my speed jumps UP a couple of MPH! Which was totally unexpected. This happens very consistently! As a result, I am trying to crank a bit faster, get a bit less less lazy. I can't say that it's more work, but keeping up that cranking speed requires some attention because it's against my natural tendency.

You won't be able to test this on your bike, which is why I'm commenting. Keep the larger gear; you'll be glad you have it when there' a hill.

It’s definitely more work to pedal faster, but it lowers the force and required pedal strength.

The internal power requirement of pedaling is an increasing function of cadence and the published data from Formenti’s group appears to increase as the cube of cadence.

Still, the difference between 70 rpm and 90 rpm is only like 0.3W/kg and in many, but not all, riding situations it makes for faster riding.

Otto

Hmm... my cruiser has a 44/17 and it doesn't seem to climb as well as my SS with 48/16... at least not as fast. And it has a 650b wheel on the back.

I understand why a high cadence might be the best option when max power levels are required, Like making that burst of speed to the finish line in an important race, or climbing a hill fast, But for those of us who are more interested in the shear pleasure biking for adventure and moderate excersize who have no intention of generating the high power an athletic racer attains, a cadence in the 60 to 70 rpm is perfectly acceptable and far more efficient then a high (80 - 90 rpm) cadence.

That said, I would probably keep the gears the same on the ops bike because a 60 - 75 rpm cadence is the speed range I would be most comfortable in on the mostly flat land where I live.

At low to moderate power levels, a 60 - 70 rpm cadence doesn't put any unusual strain on our muscles or knees. It is not grinding. Sometimes while pedaling against some wind at moderate intensity with my 55 gear inch cogs on my comfort bike, I am perfectly satisfied with a cadence of about 60 rpm. It was both very enjoyable and provides good excersize for a 65 year old man.

At times when I'm feeling more energetic and increased my intensity a notch, about 70 rpm just feels right. I have seen many younger and more athletic riders cruising at about the same cadence.

Yes