Manufacturers throw a lot of hours and money into designing their electric mountain bikes. The majority of that expense goes to mountaineer geometry.
It is all about the design, angles, and positioning of the components of the bike. An e-MTB with bad geometry can be miserably painful to ride. But if done properly, the e-MTB is an utter joy.
So what is mountain bike geometry? In our MTB geometry guide, no stone will go unturned to make sure you leave reading this as a mountain bike geometry aficionado…
What Is Bike Geometry?
Bike geometry refers to the frame’s shape and structure, defined by measurements like angles, lengths, and the relationships between various parts. For e-MTBs, these measurements are crucial, as they determine how the bike handles under different conditions.
Key Geometry Terms to Know
Here are some essential terms every adventure seeker should understand:
- Head Tube Angle: The angle between the front fork and the ground; affects steering and control.
- Seat Tube Angle: The angle of the seat tube relative to the ground; influences pedaling efficiency.
- Wheelbase: The distance between the front and rear wheel axles; impacts stability.
- Reach: The horizontal distance from the bottom bracket to the head tube; defines how stretched out you’ll feel.
- Stack Height: The vertical distance from the bottom bracket to the head tube; impacts rider posture.
Mastering these terms helps you interpret geometry charts and understand how a bike fits your adventure style.
Which Factors Come Together for Mountain Bike Geometry?
Seat Tube Length
The seat tube length is one of the most important aspects of mountain bike geometry, and it determines who can ride a particular e-MTB. The seat tube length provides a minimum and maximum height where the seat can go – this is an important consideration for your height – if the seat doesn’t go high enough for tall riders, they won’t be able to ride comfortably.
A given length of seat tube can exclude some people from going for given bikes – clearly, if the limiting parameters of minimum and maximum were too narrow, then fewer people would be able to ride the bike so manufacturers try and offer a decent range of size. For riders who intend to do a lot of descending, how low the seat tube can go is important – most riders drop the seat post down for balance and comfort while flying downhill.
Top Tube Length
The distance between the seat post and the handlebars is the top tube length, which is an important aspect of e-MTB handling. If you are too hunched up between the seat and the handlebars, with little moving room, you will not be able to handle the bike very well.
Top tube length is one of the better gauges as to how much manoeuvrability the mountain bike geometry will provide you, from both the coming-up movement in the legs for pedal strokes to your arms with respect to handlebars.
Reach
Reach refers to the distance from the end of your seat down to the handlebars – only a little less distance, compared to top tube length. It is one of the important areas of mountain bike geometry that determines how you’ll ride the bike and be comfortable with it. If the reach is too long, you are likely to feel very uncomfortable and will put a lot of stress on your lower back and shoulders. You also won’t have full control over how the bike handles. A good amount of reach will allow a slight bend in the elbow while gripping the handlebars, which feels loose and comfortable and still makes it easy to manipulate the bike while stable. That is a very important feature of mountain bike geometry.
Stack Height
This means the distance between the center of the bottom bracket, by the pedals, and the center of the head tube, in the center of the handlebars. The stack height of an e-MTB can set your position on the bike – the higher the stack height, the more probable to sit back and upright to ride through more naturally, a more comfortable and more relaxed position.
If it’s shorter, you’re more likely to have a more aggressive, lower position on the bike, which maximises manoeuvrability.
ℹ️ Be cautious with your assistance use on hazardous technical sections – the bike’s heavyweight, combined with its immense power, could lead to a nasty accident if you aren’t careful or don’t have the strength to cope with it.
Down Tube Length
A bike down tube length is the distance between a bottom bracket, by your pedals, and the bottom of head tube, by your handle bars.
The overall size of the bike is determined to a large extent by this downtube length and very much determines the reach which you will have to reach the handlebars.
A longer downtube, along with a larger wheel size, provides even greater stability and feels more grounded. A shorter downtube typically leads to more playful e-MTBs, which can be easily thrown around with smaller wheels.
The length of the downtube also contributes to the strength of the bike: a long downtube increases the strength of the overall frame.
Front Centre
The distance of the bottom bracket, by the pedals to the front axle in the middle of the front wheel measures front center mountain bike geometry. This can actually give a longer front centre so that it would permit the bike to encounter and go through more obstacles and bumps.
It means the rider has to sit back further out with a longer reach toward the handlebars, for a more planted feeling on trail. A shorter front center allows more weight forward onto the handlebars and means harsh braking as well as obstacles cannot be managed as smoothly.
Chainstay Length
Chainstay length is the back axle to the bottom bracket’s distance, in the center of the rear wheel in a mountain bike. Thus, a longer chain stay provides better stability by giving one a more grounded feeling while positioning.
A shorter chainstay tends to push your weight forward on a bike, which is good for traction and improved climbing ability. Shorter chainstays can also give a more responsive ride and can manipulate from left to right faster.
Meanwhile, a chainstay which is long pushes your weight back to the bike’s rear and is beneficial for going downhills. Chainstays are one of the most critical components of mountain bike geometry.
Wheelbase
The distance between both axles, in the middle of the front and rear wheel, is the measurement for the wheelbase on an e-MTB. A longer wheelbase gives more stability out on the trail, providing a larger surface area and the potential for a longer downtube.
A longer wheelbase brings a much greater traction; it results in a very smooth riding experience and makes the overall bike much stronger. It will open up the possibility of carrying larger weights and cargo.
Head Tube Angle
The head angle is the angle between the headtube and front axle/ground. In case of a steeper angle, it is very likely to make the bike play more and easier to maneuver, while a slacker head angle MTB will offer a lot more stability and a more grounded feel.
You will probably see a steeper head angle in a bike that is for difficult and technical terrain with a lot of sharp turning and fast-moving sections. Downhill bikes, which take on more lumps and bumps and need more stability on those gnarly descents, are likely to have a slacker head tube angle.
Standover Height
That literally explains itself – stand over height is the distance from the top tube to ground as you stand over it. Obviously, this means so much in terms of balancing when stationary, but perhaps even more important for balancing and pedaling. And if you get the standover height wrong, that can feel unstable while cycling.
What’s a Good Geometry for a Mountain Bike?
There is no such thing as good or bad geometry for a mountain bike. Everything depends on the type of riding you want to do and your body mechanics. Different disciplines of riding require a different kind of geometry, and certainly you can get good and bad geometry for different disciplines of MTBing and e-MTBing.
Downhill Mountain Bike Geometry
They come with a slacker head tube angle, longer wheelbase and longer downtube that provide stability out on the trail as well as some robustness. They feature a lower bottom bracket and longer chainstay and also longer reach. All this creates that planted feeling.
Enduro Mountain Bike Geometry
Enduro bikes are a sort of downhill base, but the head tube angle is more slacker and longer, but with shorter chainstays. This makes them climb much better, and they are more manoeuvrable. They have a steeper seat tube angle for a better climbing position but still have a longer reach for stability on the short, sharp descents.
Cross-Country Mountain Bike Geometry
Cross country bikes possess a higher head tube angle than other styles to enable excellent handling along with steeper seat angles for enhanced pedalling power as well as effectiveness. These bikes have smaller wheelbase and chain stays for further speed and agility along with reduced traction.
Enduro Mountain Bike Geometry
Enduro bikes are a sort of downhill base, but the head tube angle is more slacker and longer, but with shorter chainstays. This makes them climb much better, and they are more manoeuvrable. They have a steeper seat tube angle for a better climbing position but still have a longer reach for stability on the short, sharp descents.
Trends in e-MTB Geometry
The e-MTB market is evolving rapidly, with exciting trends in geometry:
- Progressive Geometry Designs: Modern bikes feature slacker head tubes, steeper seat tubes, and longer reach measurements for enhanced performance.
- Mixed-Wheel Setups (Mullet Bikes): Combining a 29-inch front wheel with a 27.5-inch rear wheel is gaining popularity for its balance of speed and agility.
- Integrated Design Features: Brands are refining geometry to seamlessly integrate components like motors and batteries without compromising handling.
Expert Tips for Adventure Seekers
Test Ride Before You Buy
A geometry chart can give you the numbers, but only a test ride will reveal how the bike truly feels. Focus on comfort, control, and how well the bike suits your preferred terrain.Check Manufacturer Size Guides
Sizing is critical when it comes to bike geometry. Use manufacturer-provided guides to choose the right frame size based on your height and riding style.Make Small Adjustments
Minor tweaks, such as changing stem length or handlebar width, can drastically improve your experience on the trails.
Final Thoughts
Mountain bike geometry is of paramount importance. Every e-MTB has a different geometry, and this is specifically tailored to the discipline that the bike is designed for. Riding a bike with the wrong geometry, in the wrong discipline, will be very uncomfortable – in some cases it will lead to crashes, injury and a thoroughly unpleasant day at the pedals.
Make sure you know styles of riding you want to have before buying an e-MTB. Use our comprehensive guide of geometry to help find a bike in the right way, because today, several producers offer a wide range of possibilities for adjustments of various parts of a frame, tailored either to your body and trail requirements for the particular race or terrain.
