Let’s say I have a 21 gear bicycle (Three forward sprockets and 7 rear sprockets). I want to start in the lowest gear and step up through all the gears until I get to the highest gear. How do I do that? Does the exact sequence depend on the gear ratio?
Typically, when I ride a bike like this, I will leave the front sprocket alone and step up and down the rear sprockets. Only when I find myself needing a higher or lower gear than is available using that method do I change the front sprocket, but maintaining a cadence often requires finer tuning than that. How is it done?
There is overlap between the front-back gear ratios, and it would depend on how many teeth your front gears and rear gears have (they vary from bike to bike). So, the exact sequence would depend on the gear ratio and you would have to do some interesting gear changes to go from one gear to the next in ratio order – start from the smallest in front, largest in back, maybe move the back down three or four times, then move to the middle in front and up a few in the back, back to the smallest in front and down a few in back, etc. At the extreme ends, you would probably just change gears in the back (after moving to the smallest or largest in front), but there would be a lot of strange stuff happening in the middle.
I know that there are electronic shifters – maybe they could be programmed to do what you’re after.
You may be able to replace your current sprockets for a set with closer ratios. Racing bikes generally have closer spaced sprockets than mountain or leisure cycles. Swapping a cassette is a 5 minute job if you have access to the right tools.
So, you’d start with the largest in the back (25) and smallest in the front (34), giving a ratio of 2.7. Then, you move to one smaller in the back, 3.0, then another smaller in the back, 3.3. One more time, and you’re at 3.6. Now, you have to move to the middle in the front and the second smallest in back, 3.9. Then, back to smallest in front, 5th smallest in back, 4.0. Then, you have to move the largest in front and largest in back, 4.2, then smallest in front, sixth smallest in back, 4.3, then 4.6. Then, back to the middle in front, 4th smallest in back, 4.8, etc.
You probably shouldn’t do that. It stresses drive train components unnecessarily. Some gear ratios are duplicated by using different shifter positions. Read about Cross Chaining.
If you’re smart, you really don’t want to do that. but I’m serious. Although there are 21 different sprocket combinations, there are likely about 12 different gear ratios in a practical sense.
First you calculate the precise ratios (I suggest converting to gear inches for the most useful figures). Then you do a lot of double shifts to go through them in order. And yes, the exact sequence will depend on the particular gear choices on your bike.
Actually doing this will let you experience what a pain in the neck it is to all those double shifts AND how useless it is, seeing as many of the shifts will give only a negligible change in actual ratio – a lot of work for little or no benefit.
Read Turble’s link to see how the method you describe is hard on the bike, and calculate out your ratios to figure the optimum shift sequence. If that’s not satisfactory, then changing out your sprocket sizes will be necessary.
ETA: On many (most?) bikes with three chainrings, the smallest front one is used only for steep hills. Most shifting is done with the two larger front rings.
You are already doing it right. If you wanted an easier way to maintain a certain cadence, you could go to a 10 or 11-speed cassette but that would probably take a new bike. You cold also get a tighter cassette like ticker suggests. However you’ll probably give up the easier gears for climbing hills.
There is a recent move to having only a single sprocket up front and 11 gears on the cassette in the back. You could easily step up through the gears on that setup.
On my hybrid bike, I only use the lowest chain-ring if I am climbing a very steep hill. Otherwise, it almost never gets used. I usually stay in the highest, but will shift to the lower one when going uphill.
I really don’t use all of my gears. I find that I stay in a range of them.
A truck driver with, maybe, sixteen gears to choose from will never ever use them all in sequence. In tricky conditions he may use a lot of the lower ones but when he gets to the open road he will skip two or three to get to the high gears.
Deciding which gear offered the best solution for the conditions was one of the skills a truck driver had to learn. Now that all this is done by computer, it got a lot easier.
You should try using the other front sprockets more often. The smallest front gear doesn’t just give access to lower gears, it makes the rear gear ratios closer together. If you are generally going slow or uphill, the smallest front sprocket will work better.
In general it is easy to shift the rear gears, and difficult to shift the front chain rings. This is because the chain must be moved where it feeds onto the sprocket, and this is under pedaling tension for the front. Thus pedal force needs to be reduced to near zero for front shifts.
So most riding is done by shifting only the rear gears. Front chainring changes are done only to accommodate large changes in grade, or wind.
Occasionally when riding a consistent grade, a slight optimization of gear ratio may be possible by switching chain rings. This was fairly common when 5speed rears were the norm. Chain rings were selected so that the smaller ring split the ratios provided by the large ring. This was known as “half step” gearing. If the small ring were instead made to provide as low gearing as possible (12 fewer teeth, normally*) it was called “alpine gearing”.
Nowadays, with so many cogs available at the rear, it is fairly rare to worry about where exactly the ratios of various chain rings fall…though spreadsheets make it easy to optimize for those that can be bothered.
*front dérailleurs become problematic to shift with more than 12 tooth difference in adjacent chain rings.
but I’m serious. Although there are 21 different sprocket combinations, there are likely about 12 different gear ratios in a practical sense.