Fastest possible drivetrain?

Question

I am looking for the ideal gearing to achieve good speed on a gravel bike when commuting. 2x11? 1x12? 3x12? 10-52? 11-50? How many teeth on the chainring? I know I could go faster if I get a road bike with aggressive gearing but my current bike is my favorite to ride so I just would like to get the most out of it. Its the Marin Bear Valley SE steel framed mtb from '93 with 135mm rear dropouts and 26" wheels, so its been my long time bike that I am reviving. Thanks

Answer 1

The gearing does not make you faster. It only allows you to pedal at an optimal cadence. Sort of like selecting the right gear in your car. Shifting to the highest gear does not make your car automatically faster if it forces the motor to run on very low rpm.

There is no single optimal universal gearing. Not even for gravel. With 1x11(or 12) you get the simplicity. With 2x11(or 12) you get a wider gear range. 3x gearing was mostly abandoned, but both 1x and 2x is widely used on gravel bikes. Mountain bikes mostly use 1x because they do not use that high gearing for high speeds on tarmac.

The optimal gearing really depends on the slopes you will be riding on as steep hills require low gearing. The heavier your baggage, the lower gearing you need. On the other hand, if there is a lot of good tarmac with gentle downhills, you will be glad for relatively high gears.

Very high gears like 50x11 or even 53x11 are for sprints on good tarmac.

For 1x the chainring should be somewhere between what you would use for 2x but the actual choice (if you can choose at all) also depends on the available cassettes for your derailleur and the gear ratio you need to achieve.

---

To give you some actual advice for a gravel bike: Go for a subcompact. It may be GRX or it may be something else, but smaller than the road cranks (e.g., 46-30 or 48-32). You can easily find steep hills off-road, steeper than even very steep roads. And a wide cassette like 11-32 or 11-34.

If you go for a road compact crankset 50-34, you will definitely want even larger sprockets in the back. That may be a problem for 9-speed or lower so you will be better served with 11 speed or even higher.

For a mountain bike I am less experienced in the modern combinations, but something even lower. Personally, I would now choose 1x for a MTB, if I had another bike for roads or faster gravel roads.

---

Finally, remember that a road bike does not get you faster because of aggressive gearing, it makes you faster because of good aerodynamics, the low rolling resistance with the road tyres and low weight of the bike.

Answer 2

... I know I could go faster if I get a road bike with aggressive gearing ...

This may be a misconception. With many drop bar bikes on paved roads, you can pedal as fast as you have the legs for. On most road-oriented gravel bikes specced with 48/31 or larger front chainrings and 11-34 (or larger) cassettes, you usually won't run out of gears if you have the legs to keep up. Exceptions may occur in really fast groups, or if you are trying to pedal on a steep descent (but in this case, chances are decent that you'd be better off coasting and tucking, unless you're trying to keep up with a fast group in a race/competitive ride). Some people spec drop bar bikes with chainrings like 46/30 to get more climbing gears, and it's more likely you'll run out of gearing in that case.

(NB: the discussion above assumes 700c wheels with 40mm tires; the OP's question has 26" MTB wheels, so the OP would be running a bit easier gear with the chainrings and cassettes stated above. There's something to say about that later. Also, the stated gearing is for Shimano or Campagnolo double drivetrains, which tend to be based around 11t small cogs and up to 34t large cogs (or you may be able to use some MTB cassettes for slightly lower gearing). SRAM's AXS groups are designed for smaller chainrings and a 10t starting cog; equivalents to the gearing above should be about 43/30 chainring, 10-36 or larger cassette.

With 1x drivetrains, you will trade off larger jumps between gears and potentially gearing at the high end. Having too large jumps between gears when you are trying to hold a group ride's pace can be annoying. It may fatigue you faster than with a double crankset, although many riders can potentially get used to this. However, your question may imply that your use case is for what some might all an all-road bike, e.g. you're traveling on paved and unpaved roads, and you only rarely encounter very rough gravel. In this case, you would benefit from more road-like gearing.

Subjectively, I would probably want 48/32 chainrings and an 11-34 or slightly larger cassette on a gravel bike for this use case. I might also consider a 1x with a 42t front ring and a 10-42 or larger cassette. Because I mainly ride road bikes and I like small gear steps, I'd be reluctant to get a 1x drivetrain with fewer than 12 gears for a more road-oriented use case. On gravel, especially rougher gravel, smaller steps are less important.

...Its the Marin Bear Valley SE steel framed mtb from '93 with 135mm rear dropouts and 26" wheels...

Unfortunately, there may be limits to the largest gears you can fit to your bike. The manufacturer probably stated a maximum chainring size, if you can still find it. Also, MTBs in that era were designed for triple cranks, and the chainring clearance for a current generation MTB or gravel double crankset may be less. I believe you can't mount road cranks to MTBs in general.

There isn't necessarily a need to go buy a new bike. You could try fitting slick tires to your current bike and seeing how you feel with it and its current gearing.

Answer 3

To add what everyone else is saying, start by measuring your speed, cadence, and ideally, power as well.

Cadence sensors that measure how fast you spin the pedals are relatively cheap. The data will help you to select an optimal gear. A good cadence is somewhere between 85-95 rpm. If you run out of gears with this cadence frequently, it is a good indicator that your drivetrain needs an upgrade.

The power meter is a pricey upgrade, however it will tell you exactly how much power you are putting out allowing you to optimize pedaling, gearing, and everything else to maximize the power transfer.

That all said, the low-hanging fruits likely are cleaning your current drivetrain, getting tires suited for your riding style, adjusting pressure, and watching a couple of youtube videos on how to get faster on the bike. Global Cycling Network has a few good videos on this.