Mtb geometry

Geometry, an In Depth Explanation. Feb 10, You must login to Pinkbike. Don't have an account? Sign up. Mountain Bike Geometry: An Overview Geometry is something you hear about all the time when talking about bikes such as, "I love this bike's geometry!

If you are a bit confused as to what exactly geometry is, then this blog should clear up any misconceptions you may have.

Introduction Geometry is the set of all the measurements on a bike. Geometry affects the feel of a bike more than anything else. No matter how bombproof you build it, it will still feel out of place and awkward because the geometry is geared towards cross country. Courtesy of Igz. Posted In: Stories Reader Stories. Some very good information in there. This will seventy be a help to people.

Good work. Brilliant one of the best tech blogs yet. Great i Didint know why geometry is so improtant in dh bikes. AqueousBeef Feb 10, at This is the measurement at the ground between the imaginary vertical line that goes through your front axle and the steering axis. This affects how the front end steers. Manufacturers take this into account, but riders need to think about what fork you put on a frame. It has to do with the axle to crown distance and the rake of the fork.

Very good article, i knew about geometry but not this detailed, Wicked post brule! Now I'll be more informed about wich bike I should choose, depending on the use and my mesurements. It'l probably make save a lot of money to poeple, they will choose the bike that perfectly fit them.

Good information. AqueousBeef Apr 12, at If you like my writing, I've just recently started a blog. Click to show your support! I'm glad that someone else realises this fact. But what you said is very true. Both of you are in the right, but all of this boils down to what you want your bike for.

2020 CyclingTips Gravel Bike Field Test: Is MTB geometry good for gravel?

It is easier to manual on shorter chainstay lengths whereas grip will increase on longer ones. The wise thing to do is to balance pros and cons against each other, so that you can make up your mind and come up with the right set up which will meet your individual needs.You need to look at whole range of measurements and consider how they interrelate. So what are the commonly seen metrics, which are the most important and how do they interact with each other?

This is generally taken from the centre of the bottom bracket where the cranks go through to the top of the seat tube where the seatpost exits the frame. It used to be the defining measurement when it came to bike sizing. So if a bike had a inch seat tube, it was a pretty safe bet the top tube was similar in length. As a result it offered a good indication of the fit and sizing on any bike.

Many brands still use the seat tube length to describe their size options 15, 17, 19 and inch for example. Other brands have moved on to simply calling their frames small, medium and large. Seat tube length used to tie closely with the top tube height, so choosing a smaller size gave you better clearance over the frame, but swoopy modern frame designs mean that even bikes with a longer seat tube can still offer loads of crotch clearance.

Now the main thing is to ensure that the seat tube is long enough to achieve a suitable saddle height but not so long that it makes it difficult to fit a dropper post. On bikes with curved or interrupted seat tubes, you should also ensure that that the seatpost can be lowered enough to achieve the correct saddle height.

This is another measurement that has become less meaningful as frames have evolved further away from the traditional double-diamond shaped hardtail.

mtb geometry

It still offers an indication of the cockpit length, but it mainly impacts on your position whilst seated and even then the measurement can be quite ambiguous. How can a seemingly fixed measure from the front of the frame to the seatpost become less significant?

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It all relates to the huge variation in seat tube angles that we encounter on modern bikes. For example, a bike could be quite short in the front end but gain a long ETT measurement by using a really laid back seat angle.

As soon as you stand, the bike will feel cramped and the short front end will be acutely obvious. On the flip side, a really steep seat angle can give a bike a short ETT measurement, even though it could be relatively roomy up front. Stack height offers a good indication of how high the handlebars will feel. Obviously the handlebar height can always be tweaked with headset spacers and different stems, but it provides an accurate indication of the starting point. This is the angle between the ground and the head tube at the front of the frame.

It offers an idea of how the bike will steer and many people fixate excessively on the head angle when looking at frame geometry. On flatter terrain it can feel more responsive and quicker to react to steering input. As the speed increases, or when you head downhill, the faster steering response becomes harder to manage and the bike begins to feel skittish and less predictable. At low speed and when climbing, a slack head angle 65 or degrees with Extra effort is required to pull your weight forward to stop the wheel flopping from side to side.

A slack head angle can make a bike feel sluggish and lazy to steer on flatter trails. Once the speed rises or you point the bike downhill, a slack head angle will make a bike feel more stable.

As a side benefit, raking the front end out makes it easier for a telescopic fork to absorb square edged trail impacts. These days, with all of the complex frame shapes and suspension designs, the seat angle has become a tough thing to measure.

Regardless of how it is measured, you want a seat angle that allows you to achieve the appropriate position over the bottom bracket for efficient seated pedalling.Knowing a bike's geometry can help you understand how it will handle, feel and what comfort it can offer. It can also help you compare different bikes and help you understand what geometry you are best suited to. Most geometry charts can be found on manufacturer websites, although what the charts include vary.

Most manufacturers will at a minimum include size, head and seat tube lengths, top tube length, wheelbase and chainstay length. Many also include stack and reach measurements, but fork rake, bottom bracket drop and trail are not as common. It's one thing to know what the numbers are, it's another thing to know what they mean. This article spells out what each measurement refers to and how it is taken, along with how it influences ride quality and what you should be looking out for.

This information can be a little dry, but stick with us as it will help inform your future bike purchases and is applicable to any type of bike. Before we kick things off, here's a key chart that highlights the key areas of the bike that are used to take the measurements from. It's important to know straight off the top that bikes are not the same in terms of geometry and size. When manufacturers refer to the size of a bike whether it be via description like 'small', 'medium' or 'large' or via a measurement like '51cm', '54cm' or '56cm', those measures are not universal or governed by any standards, therefore knowing how to read a geometry chart is vitally important when comparing different bikes and manufacturers.

Bike frames are commonly measured in centimetres representing the length of the seat tube. A description of the frame size based on this measurement is then allocated, for example, a manufacturer may measure the seat tube length of a bike as 51cm, and then describe it is a 'small' frame. Therefore the quoted size of a bike isn't so useful when comparing across brands.

The two most fundamental elements of frame geometry are stack and reach. Knowing the bike's stack and reach will allow you to compare between different manufacturers and immediately know if it will fit you, regardless of how it is described or what the seat tube measurement is. Stack is measured vertically from the bottom bracket to the top of the head tube.

This gives an indication of how tall a frame is. For example, endurance road bikes will typically have greater stack than more race orientated road bikes. Reach is measured horizontally from the bottom bracket to the top-centre of the head tube. This gives an indication of how long a frame is. Looking to road bikes, performance race bikes will typically have a longer reach than endurance bikes to stretch a rider out, creating a lower frontal profile to improve aerodynamics.

Reach is also sometimes used to describe a rider's reach which is different to the frame reach. Rider reach refers to the rider specifically and is measured from the tip of the saddle to the end of the stem. Regardless of the frame reach, a rider's reach can be manipulated by changing the saddle set-back position and stem length. The head tube has two key measurements that will influence a bikes handling; the angle and the length.

Mountain Bike Frame Geometry Explained - Skills with Phil

The head tube angle refers to the angle of the head tube to the ground and will commonly be described as either 'slack' or 'steep'. A slack head tube angle requires more effort to steer but performs better at slow speeds. A steep head tube angle is found on performance road race, requiring less effort to steer which is better for high-speed handling. Mountain bikes will generally have a slacker head tube angle than road bike to provide greater stability on rough, technical trails.

The head tube length is measured from the bottom to the top of the head tube. Bikes with a long head tube raises the front end of the bike, putting the rider in a more upright position. Bikes with a short head tube lower the front end of the bike, reducing the frontal profile of the rider, improving aerodynamics. Fork rake or fork offset is a key factor in the handling of a bike.

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The amount that the fork is offset from this imaginary line is known as fork rake in road bikes, or fork offset in mountain bikes. Increasing the offset will make steering faster, conversely decreasing it will slow it down. Fork rake is only part of the steering story, as a greater fork rake will increase the wheelbase, which is prevalent on endurance bikes to create stability.

The below image shows an example of how an increase in fork offset or rake which reduces the amount of trail and as a consequence speeds up the bike's handling. Trail can be a complicated element of a bikes geometry to explain but stay with us as we'll try to break it down.Cycling culture is full of little idiosyncrasies.

Some of them we love and respect, like the fact that a water bottle is a water bottle in all walks of life except when on a bicycle.

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Others can be infuriating — and the inconsistencies within geometry charts definitely fall into the latter category. The geometry of a bike is hugely important when it comes to selection.

However, since every brand seems to have its own secret squirrel method of displaying and itemising geo, actually putting the numbers to good use can be confusing. In the past, brands would leave potential customers to determine how long and low, or short and high, a bike was based upon the top tube and headtube length.

Then, stack and reach arrived and the vast majority manufacturers have incorporated the standard. Stack is the vertical distance from the centre of the bottom bracket to the mid point at the head tube.

Reach is the horizontal distance from the centre of the bottom bracket to the middle of the head tube. Now, more bikes have different fork lengths. And obviously stem length. Though sometimes expensive, handlebars can be swapped. Stack is less easy to manipulate without making changes which can negatively affect handling. Stack and reach sits on a sliding scale, finding what suits you is something you can perfect by trying a range of bikes, and knowing which numbers suit you — or of course booking in for a pre-purchase fit.

Head angle is the angle at which a line would travel through from the head tube to the steering axis, to hit the floor. The number is the relationship between the head tube angle, and the fork offset — so how far the axle of the fork sits out from the crown of the fork. If you were to extend that fork trail, it will slow handling down and make the bike more stable. The differences are seemingly minute, but will show themselves in the ride.

The only exception to this is on very small bikes, where the trail sometimes has to be increased to prevent toe overlap. This is clear within the Specialized Venge charts where a size 49 has a trail of 63mm and a 52 cuts it down to 58mm, down to 52mm on a size 61cm.Modern mountain bike geometry has highly evolved over the last few years to give us some super fun bikes that seem to do everything better.

In most situations, these improvements help make us better riders and mask our deficiencies. The two I overhear most are that wheelbases are getting too long and that the seattube angles are too steep. The latest modern geometry is a longer wheelbase, slacker headtube angle, steeper seattube angle and longer reach. Compared to a mm travel bike from 3 years ago things have changed a lot. This geometry is found on many of the current mountain bikes but many of the larger brands are taking conservative approaches.

The Norco Fluid we tested earlier this year is a prime example of modern mtb geometry found even at the entry level mm travel full suspension price point. Basically, these changes make mountain bikes more fun on a wider range of more aggressive terrain — both up and down. Larger diameter 29 and wider wheels and tires and better suspension allow us to go faster.

So the need for more stability from slacker headtube angles and longer wheelbases gives us more stability at those faster speeds. These geometry updates also reflect modern trail design — Flow trails, bike parks, enduro etc. Increasingly the flowier open terrain is being preferred by more riders.

Until I started riding modern geometry bikes I was a bit skeptical of how the changes might affect my riding style. I speculated the changes may affect how well the bike pedals and handles tight terrain. This is true for me not only on the downhills but also on the steeper uphills. The steeper seattube is something that I really notice while climbing.

mtb geometry

The additional traction and comfort just makes going up a little bit easier and more pleasant when shit gets really steep. The longer reach, wheelbase and more slack headtube angles are noticeable going down when more precise control is needed.

The bikes practically beg to let the hell off their brakes more. Even with wheelbases that are much longer I feel like I am able to corner better in tight terrain than on bikes from a few years ago.

I believe this is due to longer droppers letting you greatly lower your center of the gravity. From technical steep climbing and cornering to steep and rough descents I do feel I am a better rider aboard modern geometry bikes. The Transition Smuggler feels sure-footed on an ultra wide range of riding from slow speed tech to wide open and loose.

There are those who may see a little less benefit especially from the extreme end of modern geometry. Those with flatter and really tight terrain may find some of the new bikes not quite as agile. Or they may not notice much improvement.Hard-core mountain bikers love to geek out about mountain bike geometry, spouting off numbers about things like reach, head tube angles, and wheelbase — but what do these number mean, and how do they affect your ride?

mtb geometry

This is where geometry numbers come into play. They are a standardized set of measurements that can tell you how aggressive a bike is, how it will fit, and what kind of riding it will be best for. For instance, a large Santa Cruz mountain bike may fit like a medium Giant bike.

This is why it is important to compare other specs when choosing the right size for you. There are a number of measurements that are important in determining mountain bike sizingtwo of the most important are reach and stack.

Reach: The reach measurement is the horizontal distance between the bottom bracket and the center of the head tube. Stack: While reach is a horizontal measurement, stack is the vertical distance between the bottom bracket and the center of the head tube.

This is primarily a gauge of seated pedaling position and relative handlebar height. This can be adjusted to a degree, with headset spacers and handlebar rise for increased stack height. For mountain bikes, where geometry is based on the aggressive riding standing position with the seat down, reach trumps stack as the primary fit dimension.

Head Tube Angle: Head angle, or head tube angle, is the angle between the front fork of your bike and the ground. Although there are other design aspects that affect the front wheel, fork offset, trail, etc… this is the key metric that the industry uses to determine front-wheel characteristics.

Think of the angle of a chopper bike vs a scooter. The chopper is super slack, while the scooter is as steep as it gets. A slacker head angle will, in general, be more stable at high speeds as well as feel more comfortable on steeper downhill terrain. Conversely, your bike will steer less precisely on uphill terrain. Bikes with steeper head angles feel like the front wheel is planted and can steer nimbly on uphill terrain, while feeling twitchy and unstable on fast downhill terrain.

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There are a lot of factors that contribute to the wheelbase length on a bike including head tube angle, reach, and chainstay length. Total wheelbase is something of a culmination of all of these factors.

The Basics of Mountain Bike Geometry – How To Get The Angles Right!

This is also one of the biggest differences you get when sizing up or sizing down your mountain bike. The gist of wheelbase is that increasing the distance will increase stability, whereas shortening wheelbase will make a bike more maneuverable. Take note of where that increased wheelbase is coming from Head tube angle? What does this mean for me? These numbers are just the beginning though, the best way to figure out what will be most suited to you is to get out there and ride!Where will the longer, lower, slacker trend take us?

By Seb Stott. If you look at the history of mountain bikes, they have gradually evolved from barely modified road bikes into the stretched-out and stable machines of today.

Stems have got shorter, wheelbases have lengthened, head angles have been slackened and bottom brackets dropped — all with the aim of improved handling. Because geometry has so consistently gone in one direction, bikes at the forefront are simply described as progressive. If you ignored that history it would be tempting to see this incremental change as merely a fad.

A few more millimetres here, a degree less there — just enough to convince buyers that their current bike is obsolete and they need a new, more up-to-date version.

But I would argue that this lengthening trend in geometry — while it certainly helps sell bikes — has also been the most universally beneficial change in the history of mountain bike design.

Tweaks such as Boost axles, extra gears or the latest suspension layout offer marginal benefits at best, whereas geometry defines a bike. Even the highly divisive issue of wheel size is trivial by comparison. A longer frame reach allows for the use of a shorter stem without putting the bars on your lap. This makes for faster, more predictable steering and a more confident position on steep descents.

A longer cockpit also allows for a steeper seat angle without feeling cramped. Mondraker led the way with its Forward geometry bikes way back in The Spanish company started off with 10—20mm stems, but has since softened that stance to 30mm.

The result was awesome stability and control, enough to override many other issues with the early bikes. The disadvantage of this increase in reach is a corresponding increase in wheelbase, which can make these bikes harder to manoeuvre on certain flat corners. Though our experience of riding long bikes tells us this is far less of an issue when experienced from behind the handlebars than you might imagine from behind your keyboard.

In this sense, they increase stability. At the same time, they make it easier to change direction of lean when negotiating fast corners. In this sense, they also make the bike more agile. The disadvantage of lower bottom brackets is obvious: ground clearance. To some extent, this can be remedied with shorter cranks and smaller chainrings. But there are still limits. For this reason, downhill bikes have more or less universally agreed upon 63 degress. Some trail and enduro bikes have got close to this in recent years.

Since then, slack has become mainstream. Its That bike has won virtually every race that matters since it was released. So where will it end?

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