File photo: Jeff Barber.

Looking at an electric mountain bike, you can tell right away that it’s not the same as a 100% human-powered bike. The downtube is generally fatter to accommodate a battery, and there’s a tell-tale motor bulge in the bottom bracket area. Looks aside, electric mountain bikes ride differently too, and that’s mostly the point. They’re designed to provide assistance to make climbs quicker and easier, and the added weight affects how the bike handles on the trail.

But what about geometry? We wanted to know if eMTB geometry is significantly different from regular mountain bike geometry, and, if so, why.

Methodology 

Initially, we aimed to categorize the eMTBs we examined squarely in the trail bike travel category, seeking e-bikes with 130-140mm of travel. However, as we began researching different brands, their shorter travel e-bike offerings were pretty slim. 

To increase our bike pool, we decided to expand the travel range of the eMTBs we considered for comparison. We also wanted to ensure each bike had a non-electric bike that was either the same or very similar. In many cases, that was an easy task, with brands like Devinci offering their Troy trail bike and their Troy-E. With others, we had to match comparable trail and e-bikes, such as the Santa Cruz Bronson and Heckler SL, for example. 

For this analysis we looked for suspension travel numbers that were similar (if not the same), similar wheel sizes, and, of course, identical frame sizes. For this comparison, we examined size medium frames, or their equivalent number. The following bikes were compared:

Reach, stack, headtube angle (HTA), seat tube angle (STA), chainstay length, and wheelbase were all considered. While we wanted to include bottom bracket height in the comparison, some companies list “bottom bracket drop,” making a direct comparison difficult.

eMTB geometry vs. MTB geometry

Many of the bikes we compared were nearly mirror images of each other. The Orbea Occam and Rise fit this bill, with the electrified Rise being just 2mm longer than the Occam. The Ari Nebo Peak has a few millimeters higher stack than the Delano Peak, but other than that, it is almost identical across the board.

However, there were some interesting differences. The Rocky Mountain Instinct Powerplay has a nearly 10mm longer reach than the non-electric Instinct. However, just when we thought we were seeing a trend of longer reaches on e-bikes, the Canyon Spectral is 5mm longer than its pedal-assist version, which shares the same name.

Trying to compare 14 mountain bikes to 14 electric mountain bikes was dizzying. Fortunately, averaging the geometry totals gives a clearer picture of what we are looking at.

On average, the e-bikes are longer and taller than their non-electric counterparts. There was no difference between head and seat tube angles, perhaps signaling an end to the slackening of trail bikes.

The eMTBs have a 1.7mm longer reach, 3.1mm longer chainstays, and a 5.4mm longer wheelbase when averaged. They are also 2.2mm taller at the bars.

While determining average bottom bracket heights for all bikes was a challenge, it appears that bottom brackets are slightly higher on e-bikes than on their non-electric counterparts when examined individually. For example, the electric Canyon Spectral ONfly has a bottom bracket drop of 31mm, while the Spectral drops slightly more at 36mm. Similarly, the electric Pivot Shuttle SL has a bottom bracket height of 347mm compared to the new Trailcat LT with a bottom bracket height of 340mm.

But, it isn’t all e-bikes. Ultimately, six eMTBs had higher bottom brackets, while five showed no difference, and three were slightly lower than the non-electric version of the bike. But more on bottom bracket height later.

File photo: Jeff Barber

But why?

Joe Buckley is a product manager for Specialized, a company he has been with since 1997. Buckley worked on the first Levo eMTB that Specialized brought to market, and has had a hand in all the electric mountain bikes Specialized has released since.

And, for Buckley, he was a bit surprised the differences between e-bike and mountain bike geometry weren’t a bit bigger. 

While we initially may have had some theories on why e-bikes are longer and taller, such as companies taking an opportunity to update their geometry, Buckley provided a more practical reason.

“The most basic reason for being longer, historically, is that a motor takes up more space than a traditional bottom bracket, requiring more room needed for wheel clearance, pushing the chainstay to be longer than the comparative acoustic mountain bike,” Buckley told us.

Fitting the motor can bump the back and front of the bike out a bit, ultimately creating a longer wheelbase. The reason for a higher stack was more speculative in nature. 

Buckley explained that reach and HTA are relatively visible numbers, and brands typically don’t want them to deviate from current geo trends. Adjusting to a particular reach and HTA can lengthen other parts of the frame, particularly the front center (the distance between the bottom bracket and front axle). If this measurement gets too long, the bike can ride sluggishly. In many cases, adjusting stack height is the easiest option for achieving the desired reach and HTA without significantly altering other geo points.

However, the taller stack height we observed could also have a more straightforward explanation. Again, more room is needed for a motor.

While we didn’t include bottom bracket height in the comparison, Buckley pointed out that bottom brackets on e-bikes are almost certainly higher than those on their acoustic counterparts. Pointing to the Levo, he explained that this was for two reasons. First, they need to make enough space for the motor. Secondly, they know e-bikes are pedaling up and over rough and technical terrain where pedal strikes are prevalent. This is also why they spec e-bikes with much shorter cranks.

So, the extra length and height of e-bikes are primarily a result of the practical need to incorporate a drive unit. But, is there more to it? Are ‘longer’ and ‘taller’ making the eMTBs ride better? Should we expect this trend on every e-bike compared to a similar non-electric version?

“Ultimately, we are chasing what makes the bike ride the best, whether it’s an e-bike or acoustic,” Buckley said. “At the end of the day, you can’t pick a couple of geo numbers specifically and think you will know how a bike rides before getting on it. The ride quality is a sum of all the geos — plus kinematics, suspension tune, etc. Think of it as an apple pie. I’m not a foodie, but I don’t think anyone is basing their pie purchase solely on the type of sugar used.”