biketocamp

Hey everyone. Hope I did this well. I rented an 8 speed bike with my girlfriend who doesn't ride. She needed help on how to shift and I decided to make a video on it in Central Park. Let me know your feedback! Enjoy!

Andrew R Stewart 

Sort of good but the terms are sometimes backwards. I suspect a remake will clean this up and smoothen out the delivery as well as round out the information. Andy

KraneXL

Just beware of common terms like "caught up in the chain'', or "playing around" (2:26) which aren't universally understood by everyone. One additional point is to remove your shades whenever addressing an audience.

steppinthrax

I have the same setup in terms of gears on my Trek (rear 8 front 3). However, I'm not real keen on the front derailleur use. I ride mostly in the city but keep the front derailleur on the largest cog. Now I notice he says to keep it in the middle cog? I'm a master on shifting in the rear, almost to a point where I only use a center section of the 8 rear gears in the city.

So how does the FD work in shifting? I imagine the larger outter gear is not the way to go all the time?

SBinNYC

You failed to emphasize that gears should be changed while pedaling and that the chain cannot be taut. This means that the rider should anticipate the gear change when approaching a hill not wait until he/she is already on it.

Andrew R Stewart 

Riders are taught to look at the gear system as front and rear when it's better, IMO, to describe it as upper and lower.

The rear der acts on the lower chain run. This stretch of chain is tension controlled by the rear cage's spring (and clutch if that's your bag). So the ability to push or pull the chain sideways, and also let it climb up off a cog's teeth before the chain can move sideways, is working against this spring loaded chain tension. That and the fact that the height differences (tooth counts, cog size) is generally fairly minor, maybe a 1/4"-3/8" AT MOST typically.

Now the front der acts on the upper stretch of the chain where the tension is controlled by both the rear cage's spring tension and that of the rider's pedaling force. Needless to say the rider's force can be far greater then that of the cage spring's. So to also push/pull the chain sideways the ft der needs either far more power or far less chain tension then the rider usually is applying (like when shifting during climbing). Add to this is that the height difference between front rings is usually far more then the rear cog differences and it's easy to see that the front der is doing far more work. It is up to the rider to aid this front shift by reducing their pedal force. We call this momentary reduction of pedaling force "soft pedaling". When I first got into der bikes (1968) we were taught that this soft pedaling was needed technique. Of course this loss of power is exactly what we are told is wrong to allow. It is this goal to not have to have the rider think and act accordingly that drives the industry to eliminate the front der.

I often describe bike stuff to customers with auto references, as many understand cars better then they do the simple bike. With a manual transmission, clutch pedaled car, and when shifting what does one do with the engine (the power of the car)? Does one turn off the engine (stop pedaling)? Does one floor the gas pedal (apply strong pedaling effort)? Or does one take their foot off the gas pedal (as they depress the clutch pedal) and reapply the gas after the shift is completed (soft pedal a few strokes during the shift)? But since our society seems to encourage the reduction of effort and thinking is just about every endeavor it's no surprise that many don't even know this. Andy

steppinthrax

Thank You

I understand the mechanical explanation you provided regarding the chain tensions of the front and rear der. However my question is more with technique. When and how should I use the front der. I've primarily been using my rear der all the time, however I keep my front der on the largest ring. I suspect that's not really the way to go. I keep hearing people you shift the front der when going up a hill because essentially it's giving you a new set of gear ratios for your rear. Of course you don't want to shift under tension.

Andrew R Stewart 

Well the answer is fairly simple, but simple doesn't mean easy to understand by everyone. These days the front shift provides a larger difference in cadence or gear ratio then a single rear shift does. So depending on where you are on the rear cogs and where you are on the front shifting one, the other or both might workthat moment. Do you want a lot of effort change? Shift the front. A more subtle change then it's the rear. But a couple or three rear shifts is much the same as the front. Since shifting the front likes to have less pedal force it's best done when you still have some forward momentum. If the change of cadence is too much for your legs to catch up to then shift the rear up a gear at about the same time (called "double shifting") . As this further reduced forward power (the rear shift also likes soft pedaling, although not as much as the front) doing this at the base of the hill or when going over the top of the hill is a common technique. Then when applying climbing power or in the excitement of a fast decent shifting the rear is easier to deal with.

If one is comfy with math it's easy to create a chart of the gear ratios. On one side there's the cassette cog sized in order. On the other scale there's the chain ring(s). Simple division give you the ratio. Then by looking at specific cog/ring combos one can see the progression or the near duplication of these ratios. There are many on line apps for this, although I do this with a hand held calculator being of that generation. Back in the day we would tape onto out stems a small paper chart wit the ratios. Some of us would try to shift through the gears sequence, most find that all the double shifts are a hassle and find their own flow of shifting which works for their style and manor. Andy

steppinthrax

Thanks, Now I understand.

So it seems like the FD provides COURSE adjustment while the RD provides FINE adjustment. While at the same time the FD requires less tension on the chain, whereas the RD can have more, however you should try to minimize tension either way (i.e. don't shift uphill). My other question which you might have answered is that there are EQUIVALENT gear ratios between the front and rear. Meaning you should have the RD and FD in different gear selections that both provide the same exact or similar mechanical advantage. I don't know what those are on my bicycle, I'm assuming I can find this with the calculator you indicated. But this continues to explain why you can't simply multiply the FD by the RD to get the number of speeds your bike has and that it's pretty misleading. People who don't cycle tend to say I have a 24 speed (i.e. 3 x 8). I further understand that there are gears you shouldn't be using when the chain it at an extreme angle (such as the largest RD cog and the largest FD cog which would put the chain at a large angle to rub against the FD cage).

Andrew R Stewart 

Yes, I think you would find that some of your 24 "speeds" are dups (or very close) of each other. And that one nor the other of a dup set will have the chain in a less angled run. Or one will be easier to shift into from the ratio ine is currently in.

The absolute best, no math and no counting dirty teeth, way to see what gear ratios really do is to do a roll out for each cog/ring combo. You'll need a long enough tape measure, a couple of pencils/pens/nails and your bike (oh, and a paper and pen to record your findings). Shift the bike into the small front ring and the largest rear cog (your lowest uphill gear). Place the rear wheel so that the valve is at the ground and place one of the markers on the ground right at the valve. Place the cranks so one is exactly at the bottom of the stroke. With your hands roll the bike forward while also turning the crank around one full rotation. Stop when that same crank arm is again at the bottom and mark the rear wheels contact point with the ground. You have found out how far forward the bike goes in this gear for one rotation of the crank. Measure and record. Repeat for each cog/ring combo. You will end up with 24 measurements of how far each gear allows the bike to travel. This is an analog version of a ratio chart. You will see that some gears are nearly the same travel forward as another gear is. These are your duplicates.

In the USA we refer to a gear ratio in what's called inches of development. This is what the imaginary rear wheel diameter would need to be to result in the bike's travel forward IF the cranks were directly connected to that wheel (much like a kid's tricycle or a unicycle has). You will see that in your fastest downhill gears the virtual wheel diameter is many times your leg length and would be impossible to straddle and pedal if you didn't have cogs and rings. In Europe where the metric system rules (bad pun) they use the distance the bike travels forward as the gear reference (once again showing how much more sense the Metric system makes). Andy

cny-bikeman

Forgive me, but I don't think it's done well.

First, the smallest rear cog is not the "low" gear, as should be obvious by the fact that the shifter position is labeled "8". You also use incorrect terminology in other places. One helpful guideline is that he further you go out from center on front or rear the higher is the gear.

Secondly, the high gear does not necessarily "give you top speed". The last thing you want to do is imply that one shifts to a high gear in order to go faster. In fact riding the top gear can result in slower speed, as well as more strain on your knees and parts.

Third, posts above explain more about how to shift, but just as important is knowing when to shift. The best approach is to aim for a comfortable cadence (revs/min of the crank) and shift in order to keep that cadence and pressure on the pedals as consistent as possible, but at a rate of over 1 rev/sec (typically 75-90rpm). If you or the bike goes from side to side then shift to an easier/lower gear. One does not need to know what ratio one is in, what is best for a given speed, etc.

As for the front derailleur, I think coarse adjustment is a poor way to describe its function. It's better to think of it as controlling what general range of gears one is in - low, middle or high. Then the rear is used for fine adjustment within those ranges, which do overlap.