Bicycles come in all sorts of shapes and sizes. The size of the frame you buy should be dictated by your body measurements, but when you're choosing your next bike you should also consider the type of riding that you are planning to do (cycle touring, off-road bikepacking, mountain biking, commuting etc). Bikes come with different wheel sizes, and different types of handlebars and pedals. Your saddle also needs to be chosen and fitted correctly to prevent saddle sores, pain and potential injuries. An incorrectly set up bike can lead to pain in the wrists, shoulders, lower back, thighs and knees, and cause injuries in the long run, especially if you ride on it for multiple days back to back. This post describes several things worth considering when purchasing your perfect bike, and a few measurements that will help you set up your bike correctly.
The wheels
Bikes these days come with 26", 27.5" or 29" wheels. Mountain bikes were originally designed with 26" wheels, however modern bikes are sold with 27.5" or 29" wheels and it really is down to personal choice. A 27.5" wheel is more agile and easier to turn, but the 29" wheel makes the bike more comfortable and gives it more power. The 29" wheels also allow more trail contact and stability. Moreover, a smaller wheel may be a better option for a smaller rider, as it will allow more clearance to fit the seat post bag. The tire thickness is also something to consider when purchasing a bike - thicker tires give more stability and roll easier over bumpy tracks, but the trade off is more friction on the road which makes them a bit slower. There is a level of give in the modern frames however, some gravel bike frames won't take really chunky tires and the set up on some of the cross country mountain bikes may not allow for slicker tires due to the positioning of the breaks.
The handlebars
When bikepacking, you will travel long distance, often for days at the time. It is therefore important that your bike is comfortable. Gravel bikes often come with different grips that allow changing riding positions on longer journeys. If you prefer to ride with flat handlebars, you can purchase ergonomic grips with wrist support and bar-end horns that allow change of position. These are not expensive and help protect your wrists on long bumpy rides.
The saddle
The importance of choosing the right saddle width cannot be emphasized enough. If you ride on a too narrow seat, it can result in lower back pain and more serious injuries, a saddle that is too wide will lead to saddle sores and pain at the back of your thighs. Most bikes are sold with standard narrow male saddles, and often with low quality cheap saddles as it is accepted that most people have their own preference. In order to find your perfect saddle size, you need to measure your sit bones (or ischial tuberosities), which are the bones on either side of your pelvis on which your weight rests when you're seated. To measure your sit bones you will need something that you can make an indentation in (a piece of corrugated cardboard for example). Place it on a flat chair and sit with your feet tilted up (raised heels, toes on the floor) for a few minutes to leave an impression. Find the deepest indentations that your sit bones left and measure the distance between them. The average sit bone width for men is 60-160mm and 90-170mm for women. Add 20-25mm to this measurement for your ideal saddle size. The saddle size also tends to be narrower for more aggressive racing style of riding where you don't sit on the saddle for so long, and lean forward more instead. Saddles come in different shapes and sizes, and it is good to try out a few first (several bike shops actually allow to test drive a saddle). Long nose saddles have been around for a while and there are many models to chose from. They tend to me more comfortable for flat riding and sitting more upright. Short nose saddles are a relatively new invention that tends to be preferred by women as they work better with female body geometry. However, they also allow more aggressive riding, are more aerodynamic and more comfortable in an attacking, uphill riding position. The angle of the saddle is also important and can be influenced by the saddle type and by personal preference. The general rule is to adjust saddle angle so that the front two-thirds of the saddle are parallel to the ground. If you feel pressure at the front of the saddle, tilt it down by up to 1 degree and try again. If changing this by up to 3 degrees does not improve things, you may need to look for a different style of the saddle. If you find yourself sliding slightly forward or with pain in your thighs, try tilting the saddle back by up to 1 degree.
The pedals
This is another controversial topic. Should you ride in cleats, or clip-less? As with anything to do with bikepacking, this is a personal choice. Riding in cleats means that you use the power of your muscles not only when pushing on the pedal but also when you pull up, so it makes riding more efficient. The counter argument is that in a rugged terrain, unless you are an experienced rider, it may be difficult to unclip in case of a fall. Another argument for clip-less used to be that in a bikepacking scenario you will more than likely need to cross rivers and push your bike through some sections of the trail. In the past, shoes fitted with cleats were rarely waterproof, and came with standard rather slippery soles. However, these days Shimano and others make boots that are fully waterproof and fitted with hiking Vibram soles, and Five Ten make excellent waterproof boots with grippy soles for those who choose to ride clip-less. Waterproof socks are also a good addition to the bikepacking wardrobe.
Helmet and head gear
A well fitted helmet is really important. It protects your head when you fall, and with the rugged terrain and steep descents on the more adventurous off-road bikepacking routes, it is likely that at some point fall you will. A bikepacking helmet should be relatively light and allow head ventilation, and come with a peak to shield your eyes from the sun, rain and the mud. As you will be camping in the Scottish wilderness, a white helmet can help spot the ticks and brush them off before you put the helmet back on your head. You will also need glasses (sunglasses and a pair of clear glasses) to protect your eyes from mud, wind and the flying critters, and a strong headtorch for night riding and camping.
Lights
Good bike lights are definitely needed on the spring and autumn bikepacking journeys when the days are quite a bit shorter. The escape routes will likely be on the roads and lights make you more visible to the cars that pass you. A strong front light is also essential for night riding (which is an absolute joy in itself and a great way to spend an autumn evening). Invest in a good set of lights that are waterproof, have a strong beam, long lasting battery and are rechargeable so that you can plug them into your power pack and recharge on the go.
The frame
Frame size
Historically, bike sizes were measured by measuring the length of seat tube from the bottom bracket to the top of the seat tube (or a variation thereof). However, modern bikes have different geometries which makes it a bit more difficult to decide what size frame to go for. For example, a compact-geometry bike with a 52cm seat tube could feel the same as a classic-geometry bike with a 60cm seat tube, which is why when you test ride some bikes you may feel that you are "between sizes". This is why some of the measurements you will see below give you the "effective" length which accounts for the different bike geometry. Modern bikes are often sold in Small, Medium and Large frames which are often not standardised across the manufacturers. This is why it's good to be aware of a few simple measurements that may help you find your perfect bike.
Frame material
Most bikes these days are made from either aluminium or carbon, however, steel and titanium bikes are also available. Aluminium tubing is shaped to bear the weight correctly and welded together. Aluminium is quite stiff and strong but relatively light which makes it a great material for all types of bikes. However, it is also prone to fatigue, unlike steel and titanium, and when it fails, it can be difficult to repair. Carbon frames are generally lighter than aluminium, but also more expensive. Carbon polymers are a strong and adaptable material that can be molded into all sorts of shapes. Carbon frames are made of sheets of carbon fibres held together with epoxy resin. Carbon has the highest strength-to-weight per ply, but it's strength depends on the direction, so in a bike frame it is stacked at multiple angles. You may see "modulus" being mentioned when you shop for a carbon bike - the higher the modulus the higher the strength of the bike. This is accomplished by different layering of the carbon sheets and generally means that the higher modulus frames tend to be more expensive. The disadvantages of the carbon frames are that they cannot be reamed or tapped to provide threads to screw in additional components which makes fitting things a bit more difficult and means that they are generally not compatible with panniers unless you can mount them on a thru-axle. Carbon fibre is also easy to crush which is why carbon bikes often have metal reinforcements in the sensitive areas. If you had a bash or a crash on your carbon bike, get it inspected to assess any internal damage before riding again. Steel bikes used to be the norm but these days they are a bit less common. This is mostly due to their weight, however, they do have some advantages. Steel is much stronger and more durable than aluminium or carbon, and can be repaired easily when it fails, which is why steel bikes are often chosen by round the world tourers. The downside is that steel can corrode, so the tubes need to be painted both on the inside and the outside, and maintained. Titanium has appeared on the backpacking scene over a decade ago as a wonder lightweight material to produce camping accessories. Titanium bike frames are lighter than steel but tend to be heavier than aluminium or carbon. They are very strong and durable which is why the titanium bikes are sometimes called "a bike for life". However, they tend to be expensive.
Bike measurements
Bicycle manufacturers often list several measurements on their bike specifications list. These can help you choose the frame that is right for you and the type of riding that you prefer to do. As you can see from the image below, different lengths of certain frame elements can lead to more or less aggressive position when riding. The lengths usually given by the manufacturers are illustrated on the figure below. You can also use online calculators to work out the lengths that are best fitted to your riding style and geometry (for example: https://www.wrenchscience.com/pages/fit-system/)
Seat tube length (A)
The seat tube length is measured from the centre of the bottom bracket to the top of the seat tube. You may also see the term "seat post effective" measurement which is the distance between the bottom bracket and the point at which a virtual horizontal top tube would intersect the seat tube. In the past, the seat tube length used to be the main measurement used when sizing the bike. These days, it is used to determine the lowest seat position and by how much can the seat can be lowered using a dropper post. Seat tube lengths can be given as C-T (centre of the bottom bracket to the top of the tube), C-TTT (measured from the centre of the bottom bracket to the junction of the seat tube and the top of the top tube), or C-C (measured from the centre of the bottom bracket to the junction of the seat tube and the centreline of the top tube). The seat tube length is useful in determining the length of seat post needed to correctly position the saddle height. To set up your saddle at the correct height, take your inseam measurement and multiply it by 0.883 - this is the distance you should have between the top of your saddle and the centre of the bottom bracket. Work out where your sit bones sit on the saddle and adjust the distance between this point and the centre of the bottom bracket. If your saddle is too high, you will likely rock from side to side when riding. This will result in hip pain, saddle sores, and may also affect your shoulders and arms, as you will most likely transfer too much weight onto the handlebars. If your saddle is too low, you will likely get pain in front of your knee and in your back, and you will lose some of your pedalling power.
Horizontal top tube length (B)
The top tube length can also be measured in several different ways: Actual (C-C) measured from the centre of the seat tube to the centre of the head tube, Effective (HT-T) which is the length of an “imaginary” level tube extending from the centre of the seat tube axis to the top of the head tube and Effective (TT-C) which is the length of an “imaginary” level tube extending from the centre of the seat tube axis to the point where the top tube intersects with the centre of the head tube. The length of the top tube is one of the factors that determines the reach of the bike and if the riding position is is “extended” or “compact”. Knowing this length helps work out the final riding position.
Steering angle (C)
Also known as the steering axis or the head angle, defines how your bike will behave in the rougher terrain. If you'd like a bike that is agile and quick to turn, opt for a steeper angle (higher number), and choose a wider angle (slack, or lower number) for more comfort and stability over agility. The steering angle will also depend on the type of the bike you are riding and will impact on your riding position. It is important to note as well that the smaller bike frames come with the risk of toe overlap (the tendency for the rider's toes to catch on the front wheel during wide turns) which is sometimes results compensated by the manufacturers by reducing the head tube angle to place the front tire farther from the pedals, which could compromise handling compared to a larger bike of the same model.
Seat angle (D)
The seat angle defines how you sit over the bike. A steeper angle shifts your centre of gravity forward and helps you tackle the uphill, and a slack angle means more weight on the rear wheel which is more comfortable for riding on the flat trails but may make steering the front wheel more difficult when riding steeper uphill. For example, triathlon and enduro bikes have seat angles in the range of 75-80 degrees, off-road bikepacking and gravel bikes are around 73-74 degrees, hybrids and touring bikes are in the range of 72-73, and commuter are between 70 and 73.
Head tube length (E)
This measurement defines how upright you will sit on your bike. The longer it is the more upright you will sit, shorter heat tubes will lead to a more extended position. As a rule of thumb, the handlebars should be at the height of the saddle (or higher), unless you are an aggressive rider. This measurement is given not counting headset cups, steerer tube, or spacers, from the bottom to the top of the head tube. Touch your elbow to the nose of the saddle and reach forward towards the handlebar. If your bike is set up correctly, the horizontal distance from your fingertips to the stem’s handlebar clamp should be between two and four fingers’ width. You can use spacers to modify this, do bear in mind though that that can lead to shortening of the horizontal reach to the handlebars.
Chainstay length (F)
This is measured from the centre of the bottom bracket to the centre of the rear wheel axle. Similar to the steering angle, this length will define how your bike handles, with short chainstays giving you more agility and longer chainstays leading to smoother riding. Longer chainstays are al also better for good climbing and smooth rolling and are favoured by trekking and enduro bikers, whereas tricks, wheelies and jumps require a shorter chainstay. Shorter chainstays give you a more aggressive riding position and quicker handling but also make it easier to lift the front wheel which may not be desirable bikepacking. Longer chainstays give smoother rides, more rear clearance for luggage and a more upright position.
Wheelbase length (G)
Measured from the axle of the front wheel to the axle of the rear wheel, this measurement also impacts on the bike's stability, Short wheelbase bikes are more agile and longer wheelbase bikes are more stable.
Bottom bracket drop (H)
Measured from an imaginary line intersecting the axles of each wheel down to the centre of the bottom bracket. A higher bottom bracket is better for mountain bikes and biking on rough terrain as it increases your ground clearance whereas lower bracket, often seen on commuter bikes, may improve handling by lowering the centre of gravity and make mounting/dismounting easier.
Fork length (I)
This is measured from the fork crown to the axle along the steering/head tube axis. However, as many modern bikes have a Fork offset (K), another measurement is given for the Axle-to-Crown, measured in a direct line from the fork crown to the axle. Knowing this measurement may help you work out your bike's geometry. Fork travel (L) is the maximum length that the fork can shorten by when fully compressed, and varies between 80-200mm. Cross country hard tails usually have 80-100mm travel, trail mountain bikes are built with 120-160mm travel, enduro bikes have 150-180mm travel and downhill mountain bikes have 180-200mm travel. The "give" in the suspension provides comfort from the bumps of the rough terrain, but it may affect the mounting of bikepacking bags. It can also dissipate some of your pedalling energy, which is why on most bikes the suspension can be locked when travelling on the road. Gravel bikes can be fitted with stem suspension instead, which gives between 20-30mm travel. These do not usually lock which may result in a slight bobbing feeling when cycling uphill.
Standover height (M)
Standover height is the measurement of the space between the rider and the bike. It is important for safety and for when you're mounting and dismounting the bike. It's usually measured vertically from the centre of the bottom bracket to 150 mm from the top tube to seat tube junction. You should have at least an inch of clearance between your bike’s standover and your inseam, and a bit more if you are riding a mountain bike to help with the unexpected dismounts on uneven terrain. Too much standover height can also lead to bottom-outs and falls.
Reach (R) and Stack (S)
Stack and reach are measurements used to describe the bike geometry. These measurements will help you determine your optimal riding position and tweak things if necessary. The reach is a measurement of how long the frame is, and is measured horizontally from the centre of the bottom bracket to the top of the headtube. It can be adjusted slightly by moving the saddle fore and aft by 3-5cm. Stack is the measurement of how high the frame is, measured vertically from the centre of the bottom bracket to the top of the headtube. It can be adjusted by adding head tube spacers.
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