How to adjust drivetrain so I don't pedal empty air?

You might know what I'm talking about: coast a bit, then start a pedal stroke, and there may be zero resistance for a part of the cycle (let's say 30 degrees) like you're pedalling empty air. Then the pedals gain purchase and there is some resistance indicating your effort is actually going to the wheels.

I figure this problem is in the freewheel or the internal gear hub. Which would it be and how do I adjust them? Also, does this problem have a Googlable name?

This wouldn't be a problem except at high cadences I keep losing purchase, or don't get any purchase at all.

• Is this by any chance a coaster brake hub?
– ojs
Jun 3, 2021 at 14:37
• How high a cadence are you talking, and what speed is your bike going at the time? It's one thing if you're crawling along at 10km/h and a completely different thing if you're flying along at 45km/h. Jun 3, 2021 at 22:07
• You mention "loss of purchase" of foot on pedal I presume. Do you use cleats/clipless shoes, or toestraps, or do you use platform pedals with flat shoes ?
– Criggie
Jun 3, 2021 at 22:51
• s/gain purchase/engage/g Jun 4, 2021 at 8:22
• To a certain degree, this is both normal and unavoidable: When your feet are at rest while coasting, you obviously need to accelerate them to match the speed of your bike before the freewheel can engage. Obviously, it becomes a problem if the freewheel takes too long to engage, but you cannot expect to feel resistance right from the off. Your pedals are not some kind of generator that generates power at any speed, they are mechanically linked to your rear wheel, and if you don't pedal fast enough to keep up with the rear wheel, you cannot expect any resistance from the pedals. Jun 4, 2021 at 8:31

I can think of three things that could contribute to the pedal stroke "floating" before it engages:

1. A hub with a high number of "degrees of engagement," or low number of "points of engagement." Hubs have a ratcheting mechanism inside that allows them to freewheel when they're not receiving power from the cranks. The points of engagement refers to the number of places the ratchet can catch and deliver power. When you apply power to the cranks, the ratchet slips until it finds the nearest point of engagement. If your hub has a low number of points of engagement, it can slip quite a bit, leading to the "floating" feeling before it catches. Generally, cheaper hubs have lower number of points of engagement than more expensive hubs. "Degrees of engagement" is the angle between your "points of engagement." DT Swiss offers an explanation of their star ratchet with pictures here.
2. If you're coasting fairly quickly, you need to get the drivetrain up to the same speed as the wheel is going before you can apply any power. This is easiest to experience if you winch yourself up a hill in a very low gear, then coast down the other side - when you go to start pedalling again, you're still in the very low gear, and you spin out quickly (feeling no resistance) until you shift up. To avoid this, you have to remember to shift while you're descending, or shift near the top of the hill.
3. I have accidentally over-lubricated a hub, where the grease actually prevented the hub from engaging for part of a pedal stroke (the grease was holding the ratchet open). The solution was to take the hub apart and clean half the grease out, then the hub operated normally.
• Thanks for describing #2, that's definitely an issue on top of #1 (which I also notice). I've been staying in one gear due to a broken shifter. Thought it should be possible to add speed even if the chain is going slower than the wheel. Shows what I know. Jun 3, 2021 at 13:35
• #3 might also happen if the grease in the free-hub has become sticky due to age and keeps the pawls from engaging in a speedy way. Jun 3, 2021 at 18:19
• Point 1 can also be a dirty freehub in which not all the pawls are moving properly. In that case it's a sign that it's time to service the freehub (doable but a bit fiddly and can need odd tools). If you don't, and the last pawl jams, you won't be able to pedal Jun 3, 2021 at 18:38

You are referring to your freehub’s angle of engagement. That is, how many degrees does your pedal need to travel before the freehub engages and transmits your power to the drivetrain.

Here is a primer by Matt Wikstrom of Cyclingtips on freehubs, and it does cover this topic. The bad news is that you can’t change your existing hub’s angle of engagement unless there is an upgraded freehub with more points of engagement. I think only DT hubs may have these upgrades available. Otherwise, you would need a new hub or rear wheel, which is obviously a costly endeavor.

To elaborate, there are pawls in your freehub body, e.g. in the picture below.

The pawls are spring loaded. When you are pedaling, the pawls engage teeth in the freehub body.

More teeth or more pawls means more points of engagement, I.e. your pedal covers a smaller angle before the freehub engages.

Now, if you are a road cyclist, I would caution that points of engagement are not an issue for us. We don’t coast very much. This point applies to most gravel cyclist. For mountain bikers and gravel cyclists on very rough terrain, you do often have to coast and backpedal to reposition the pedals, and many points of engagement are a definite advantage in this style of riding. However, as I said, you cannot alter the points of engagement in an existing hub unless it’s a DT.

• Some pawl-style hubs also allow you to add more pawls to increase POE. More POE is also not necessarily better in every circumstance as it exacerbates pedal kickback. Jun 3, 2021 at 20:25