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Ever since my aero road bike was stolen, I have been riding a cheap single speed bike on average 6 miles a day. The crankset was cheap and I recently switched to Sram Ominium 48t vs what the bike had 44t.

Overall the bike is faster but the chainring is on the larger side and i constantly have to standup if i am going up hill.

I feel like my lower back is getting stronger, but I am wondering what the physical advantages of a higher chainring on a single speed.

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    You've just pointed out the reason why gears were introduced! – Carel Mar 9 '18 at 8:47
  • Higher gear ratios are for flats or downhills. If you're riding up grades where that gear is too tough, then you have to compromise with a too-low gear ratio for the flats that helps in the hills, or suffer your way up the hills so your gear ratio gives you speed on the flats. There's no choice while riding a fixed gear/single speed, its only compromise. – Criggie Mar 9 '18 at 9:06
  • Bikes have replaceable rear cogs, if the gear ratio is too high you can switch to a larger cog. – ojs Mar 9 '18 at 9:07
  • In the days when derailleurs were forbidden on races, the cyclists had two different cogs on the rear hub. A mountain cog and a flat terrain cog. Gear changes were done at the side of the road by removing and flipping the rear wheel. Many single speed bikes of today have that possibility. – Carel Mar 9 '18 at 15:42
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    ...and the answer is, not much, it's the total gear ratio you should worry about. People just tend to flip out whenever single speed is mentioned. – ojs Mar 10 '18 at 2:28
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The efficiency of chain transmission decreases if one of the cogs has very low tooth count. Track cyclists often use high gear ratios, and large chainrings are used so that a reasonable sized cog can be used. Another reason is that when the cogs are larger, changing to one tooth larger or smaller cog changes gear ratio a smaller amount than with smaller cogs, so larger cogs allow finer tuning of the gear ratio. Both benefits are small, but in racing you use all advantages you can get.

For street singlespeed, the main reason to use large chainwheel is to make the bike look like track bike (isn't this why you bought the Omniums to begin with?). The other popular choice is 42t, because that comes standard with old road cranks and produces nice gear ratio for street use in combination with track cog.

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