Road Cycling - Gear Ratios

Forgive me for asking the obvious, I am a newbie.

I'm riding a Jamis Aurora. It is my first road bike and it's definitely geared "higher" than my GT mountain bike. If it were geared any lower I'd have trouble on some of the longer climbs.

I see gearing expressed as, say, 52/12. I'm assuming that means 52 teeth on the front chainring, 12 on the back? I'm going to count mine to see what my high and low is. What's best for road riding? What do you all use?

There is no "best" ratio for road riding. It depends on what speed and cadence you're trying to maintain, your strength and your abilities and training. Most road bikes have 39/52 up front and a cassette of 12-25 on the back. I have 11-23 on the back.

I find that I cruise most comfortably in a 39x16 at about 30 km/h, which means I'm pedalling at around 100 rpm. On a ride today, I was using my 52x17 to 52x15 ratios for quite a bit of time, while riding in a group with a bunch of elite racers. At that point in the ride, we were moving at 40-45 km/h.

Few recreational cyclicts will ever use a 52x12, let alone 52x11. I don't use the biggest gears [big ring smallest cogs] all that often, but I have been known to sprint above 55 km/h in the flats and, though I don't spin a 52x11, I can certainly push it out of the saddle for a couple of minutes. I have spun out at my highest gear in a demented descent, trying to make an attack on my stronger training partner work. It didn't, but I saw 85 km/h at that time, anyway.

So... In answer to your question, there is no "right" gear. Find a comfortable cadence [say, 90 rpm] and chose the gear that allows you to spin with the most speed without too much effort.

I don't think that explanation can be improved upon.

For most mere nonracing mortals, a top gear of about 100 inches, such as 52/14 or 48/13, is adequate. Yes, optimal gearing is highly personal, depending on one's preferred cadence, strength, typical terrain, typical load, etc. As you ride, notice which gears you tend to use. In particular, do you often wish you had something lower? higher? Do you never use your lowest gear, or, as I do, save it for a killer climb at the end of a long ride? Do you ever spin out your top gear, or are you, as I am, afraid to go that fast?

Interesting. I just counted my teeth. 52 is the largest chainring, 12 is the smallest in the rear. So, 52/12 I guess is the proper way to say it. I manage to spin that out on long descents... guess I need something "bigger"? Should I go smaller in the rear or larger in the front?

Ditto with respect to cadence. I would make keeping your ideal cadence your highest priority, and then build your gearing to suit it.

I personally like higher cadences, which dictates using lower gearing. I do 100-120 rpms on the flats and 80-100 on the hills. A 39-26 would give you a speed of about 15 km/h at 80 rpms. What kind of grades you can conquer with your gearing also depends on your strength, fitness, and weight.

To help evaluate your gearing, you may find useful a set of Excel worksheets that I wrote up. You'll find them here: http://www.uni-bonn.de/~jmlee. Please read the instructions.

Cheers,
Jamie

On my chain ring I have a 53, 39 and on my cogset I have 11, 12, 13,14,15,16, 17 19 and 21 and I would usually used the ratio 39 x17 it gives me the cadence that would make my bike riding very intense

Originally posted by siliconwafer
Interesting. I just counted my teeth. 52 is the largest chainring, 12 is the smallest in the rear. So, 52/12 I guess is the proper way to say it. I manage to spin that out on long descents... guess I need something "bigger"? Should I go smaller in the rear or larger in the front?

Now see that's interesting. If I spin out a gear on a descent I just coast.

The problem with going for a bigger gear to cope with spinning out on descents means you either move all your gearing higher and less useable on the flat) or you have bigger jumps to your lower gears (which can affect your cadence)

Originally posted by siliconwafer
Forgive me for asking the obvious, I am a newbie.

I'm riding a Jamis Aurora. It is my first road bike and it's definitely geared "higher" than my GT mountain bike. If it were geared any lower I'd have trouble on some of the longer climbs.

I see gearing expressed as, say, 52/12. I'm assuming that means 52 teeth on the front chainring, 12 on the back? I'm going to count mine to see what my high and low is. What's best for road riding? What do you all use?

To calculate chain inches take the chain ring divide by the rear cog and multiply by 27. At 100 rpm with 100 chain inches, you will cruise 30 mph. So if you spin at 90 rpm that means at 100 chain inches you will cruise at 30 times .9 = 27 mph. A 52/12 times 27= 117 chain inches which at .9 rpm is about 32 mph.

Really, very few cyclists spend anytime at all riding at speeds over 30 mph. What is more important is figuring out if you have the gearing for the local hills. A 39/25 times 27 is 42 chain inches. At 90 rpm that is 11 mph but you can turn over 80 or even 70 rpm seated on a hill and that makes for 9 mph seated. Out of the saddle you can probably get down to 5 or 6 mph. And that will do pretty steep hills. However, if you have long sustained climbs (over 1 mile) or hideously steep ones that you want to ride, I would go with a triple.

Gear inches (chain inches ??) are a useful way of comparing the actual gear ratio from front chainring to rubber.
no of teeth in chainring/no of teeth in rear cog x wheel diameter.

For your road bike the wheel diameter would be 27, for your MTB it is 26.

I find the best way to think about gears is that they match my power output and my chosen cadence for the conditions ( gradient/windspeed/load/road surface etc).
If you want to get scientific, you can get a heart monitor and ride at a particular heart-rate and cadence. Use your gears to keep both these factors at their optimum, and the speed will take care of itself.