For years now I’ve been meaning to get into bikepacking, specifically by doing the Palouse to Cascades Trail, a 285-mile rail trail across Washington State. Having formerly been a railroad, the grade borders on completely flat and the surface is gravel (or, at the least the parts I’ve seen are). A so-called gravel bike makes a lot of sense. Although I have yet to pull the trigger on an actual bike, I wanted to share some notes from my research over the summer.
Terminology
[Note: I have a bad habit of using the term “pedals” to refer to the crank arms or crankset. I am aware that the pedals are just the small bits where you place your feet.]
A gear is a toothed device which uses the teeth to modify or transfer force. A cogwheel is a toothed wheel (a gear in the shape of a flat disc), often called a cog for short, although the individual teeth are also called cogs. A sprocket is a cogwheel which interacts with a chain. There are two sets of sprockets on a bike: the ones on the rear wheel are called the cassette and the ones near the pedals are called chainrings. Note that cassette is also the generic term for a group of sprockets.
On a chain, the distance between each link is uniform. This means that in order to describe the size of any sprocket that interacts with a given chain we only need to talk about the number of teeth that the sprockets have. “Teeth” is abbreviated “T”, so a sprocket with 51 teeth has size 51T. On a cassette, instead of listing off the size of each sprocket you only mention the smallest and largest e.g. 10-51T for a cassette whose smallest sprocket has 10 teeth and whose largest sprocket has 51 teeth.
The uniform link distance on a chain also means that, if two sprockets are connected by a chain and the sprockets are then rotated, the number of teeth moved by each sprocket must be the same. So, if your front cogwheel (chainring) is size 26T and your rear cogwheel is 52T, and you pedal the front cogwheel through one full rotation (26 teeth), then the rear cogwheel must have also moved 26 teeth, which is only half of a rotation since 26 is half of 52.
The gear ratio is the number of teeth on the chainring divided by the number of teeth on the rear sprocket. More intuitively, since the rear sprocket is attached to the rear wheel, you can think of the gear ratio as how many rotations of the rear tire you get for one rotation of the pedals. In our example, a full rotation of the pedals resulted in half of a rotation of the rear wheel, and so our gear ratio is one half or 0.5, which is the same as dividing the chainring size, 26T, by the rear sprocket size, 52T.
Of course, most bikes have multiple sprockets in the cassette and multiple chainrings, so rather than a single gear ratio the bike will have a variety of gear ratios, one for each combination of rear sprocket and chainring. The term “21-speed” often refers to a bike which has 3 chainrings and 7 sprockets in the cassette, for 3 x 7 or 21 total gear ratios or “speeds”. Similarly to cassettes, it is often helpful to compare the range of gear ratios on a bike by only examining the smallest and largest gear ratios, which are computed by dividing the smallest chainring by the largest rear sprocket and the largest chainring by the smallest rear sprocket, respectively. The lowest gear ratio determines how easy it is to ride the bike uphill, with lower ratios being easier, and the highest gear ratio determines the bike’s maximum speed, with higher ratios being faster.
The distance traveled by a wheel in one rotation is equal to the circumference of the wheel, which is calculated by taking the diameter and multiplying it by pi. In other words, C = πd. For a single rotation, common bike tire sizes 27.5″ and 29″ will travel 86.4″ and 91.1″, respectively. Beginning cyclists typically pedal at around 60 rotations per minute, so on 29″ tires they will travel 91.1″ per rotation × 60 rotations per minute × 60 minutes per hour ÷ 12 inches per foot ÷ 5,280 feet per mile or just under 5.2 miles per hour using a 1.0 gear ratio.
Since larger tires move farther in a single rotation, the gear ratio alone cannot be used to compare effort across bikes with different tire sizes. However, by simply multiplying the gear ratio by the tire diameter we can compute something known as the “gear distance”, a quantity which can be used for this comparison. Note that the gear distance is just the distance traveled by the wheel in one rotation divided by pi (excluding pi makes the gear distance calculation more approachable than distance traveled).
My Bike
I already have a bike, actually: a Trek 8.3 DS, where DS stands for Dual Sport i.e. a hybrid bike. Basically, not really a road bike and not really a mountain bike, but something in-between. I’ve ridden it a couple dozen miles on the Palouse to Cascades Trail and didn’t recall having any issues, and I’ve got some panniers and other bits for hauling gear as well. However, I’ve also taken it out on some rough hiking/biking/horse trails out in the Ancient Lakes area of the gorge, and it was a disaster. A 14-mile loop and I probably walked the bike over half of it. Part of the problem was fitness, but the narrow tires lacked grip and I didn’t feel like the gears went low enough. I also lost a lot of skin due to rubbing against the handlebars (which was my fault for not wearing the proper gloves), but my hands also hurt due to a lack of hand position options on the flat bars. Oh, and the pedals kept ramming into rocks on the ground (known as a pedal strike), once so hard that the pedal was actually dented!
Since that fateful day I’ve been itching to replace the bike. Let’s tackle each problem individually:
Gearing
On the product page, the “Crank” for my bike is listed as “FSA Dyna Drive 48/38/28 w/chainguard” (aka 28-48T) and the cassette is a “Shimano HG31, 11-32, 8 speed”. The tires are “Bontrager LT2, 700x38c”, or roughly 29″ in diameter and 1.5″ wide (700x38c is a European standard and the units are “nominal” millimeters, so even though 700mm is 27.5″ it’s actually more akin to 29″). We can now calculate the following values:
- Lowest gear ratio: 28 ÷ 32 = 0.875
- Lowest gear distance: 28 ÷ 32 × 29″ = 25.375″
- Highest gear ratio: 48 ÷ 11 = 4.4
- Highest speed at 60 RPMs: 48 ÷ 11 × 29 × π × 60 × 60 ÷ 12 ÷ 5,280 = 22.6 mph
Now, let’s compare this gearing to the Kona Unit X, a steel-frame bikepacking bike. The Unit X has only a single 32T chainring in the front (known as a 1x or “one-by” drivetrain, popular on mountain bikes) and a 12-speed 11-52T cassette in the back. It also sports 29×2.6″ tires. This yields the following values:
- Lowest gear ratio: 32 ÷ 52 = 0.615
- Lowest gear distance: 32 ÷ 52 × 29″ = 17.846″
- Highest gear ratio: 32 ÷ 11 = 2.91
- Highest speed at 60 RPMs: 32 ÷ 11 × 29 × π × 60 × 60 ÷ 12 ÷ 5,280 = 15.1 mph
Since the lowest gear distance on the Kona is 70% of that of the Trek, I suppose that means it would be about 40% easier (1 – (1 ÷ 0.7)) to pedal uphill. It’s hard to translate that into something intuitively meaningful but I feel like that would be a noticeable difference.
At the high end, we’re giving up about a third of our top speed, but you’d still be able to travel 60 miles in a day with 4 hours of pedaling versus 90 miles with the Trek. As a non-bikepacker I can’t really say from experience whether that’s a dealbreaker or not, but poking around on the internet reveals that the mileage range for typical bikepacking trips is anywhere from 30-70 miles per day depending on conditions and conditioning, which means we’re still near the top.
On a side note, one of my biggest takeaways from researching gravel and bikepacking bikes is that for decades bike manufacturers have been trying to sell racing bikes with higher top speeds to weekend warrior wannabe athletes while ignoring the huge market segment of regular people who just want to ride around on mostly flat gravel and fire roads, away from traffic. The explosion in popularity of gravel bikes should be evidence that targeting the actual needs of casual users rather than elites is a recipe for success. In any case, by running the numbers against real-world usage as we did above, you can see that taking a hit on our top speed has a negligible impact on functionality.
Traction
The more tire that’s in contact with the ground, the more traction you have. This means that wider, and to some extent larger, tires have more grip, all else being equal. The Trek’s tires are an anemic 1.5″ wide and the frame only supports tires up to 1.8″. For reference, the classic mountain bike tire is 2.1″. However, these days gravel and bikepacking bikes often sport anywhere from 2.5-2.8″ wide tires and can even house “fat” tires that are 3″ or more. After renting a mountain bike with 2.5″ tires and returning to Ancient Lakes, I can confirm that the wider (and knobbier) tires make a world of difference. At 2.6″ the Kona’s tires are 70% wider than the Trek’s. Problem solved.
Hand Comfort
The Trek sports flat handlebars, standard on mountain bikes. Wide flat handlebars have the advantage of better steering control, however, they also lack hand positions, which contributes to discomfort or even tingling and numbness over time. As some who struggles with poor circulation in extremities, this is a big issue for me. These days many touring bikes, such as the Breezer Radar X Pro, have drop bars which curve downward, offering a variety of hand positions. The downsides of drop bars are that the components are more expensive and that, being narrower than flat bars, the steering is less precise. They also require more maintenance in the form of handlebar tape.
One upgrade that I’ve already made to the Trek are Ergon grips, “horns” of various size which attach to the ends of your flat bars. I went with the largest GP-5 but I think the more modest GP-3 (which is more of a nub than a horn) would have sufficed. Another option would be an entirely different handlebar design, such as the Jones H-Bar, which offers all sorts of possibilities beyond even drop bars.
Separately, I had mentioned that by not wearing gloves my hands had been rubbed raw while riding the Trek around. However, a good pair of gel cycling gloves is also supposed to help a lot with hand discomfort. I picked up what I believe are Gyro Bravo gel gloves from a bike shop in Moscow, Idaho and, while they solved the abrasion problem, I still had tingling while wearing these and using the Ergon grips. I’m thinking that this may just come down to training, in the same way that seat discomfort goes away as you ride more.
Pedal Strike
As a reminder, pedal strike is where the pedals run into an obstacle (say, a rock) while in a lower position. In Ancient Lakes, where many trails are old Jeep track and rocks are everywhere, not only did this happen several times but I once hit a rock so hard that the pedal was bent. The obvious solution to pedal strike is to get the pedals higher off the ground. One way to accomplish this is just to get larger tires, say, moving from 27.5″ to 29″, but since I’ve already got 29″ tires I can’t really do much more (although, wider tires will necessarily lift the bike up higher than narrower ones).
The other option is frame design: the bottom bracket is the bit that the axle of the pedals and chainrings go through, and a higher bottom bracket means that the pedals will necessarily be higher off the ground. In practice there are two measurements for the bottom bracket (abbreviated BB) placement. The first is the BB drop, which is the distance that the bottom bracket sits below an imaginary line connecting the centers of the two wheels. The other measurement you’ll see is the BB height, which is the height of the bottom bracket above the ground. The drop does not take tire size into account whereas the height does. Performance-wise, a lower bottom bracket lowers the center of gravity, increasing stability.
I couldn’t find the BB drop for the Trek, which was released in 2015. However, the latest version of that bike has a 60mm drop. For comparison, the Unit X has a 65mm drop and the Radar X Pro has a 75mm drop. At first glance those look worse, however, given that their tires would be about an inch thicker and one inch is 25.4mm, they should actually be higher off the ground than my Trek.
Conclusion
After renting what I believe was either a Rocky Mountain Growler 20 or Soul 10 and repeating part of Ancient Lakes, here’s what I learned:
- Lower gears definitely help with climbs, but, fitness is still the primary concern
- Gel gloves alone do not solve hand comfort issues with flat bars
- Wider tires make a night and day difference when it comes to traction
- Wider tires also let you roll right over most obstacles, eliminating pedal strike concerns
- I am not in good biking shape
- I could use some actual biking shoes
Given the frame limitations of my Trek, no amount of upgrading is going to solve the traction issue; a new bike will be necessary. However, Ancient Lakes is much more rough than trips I’d actually like to do along the Palouse to Cascades Trail. Given that we’re almost to the end of summer and that my lack of fitness is still holding me back from longer days, I think it’s best to put off a purchase for now (which is easy given that bike inventories are crazy low) and concentrate on building up experience with my current bike rather than moving on to something new.