How to measure a bike frame: our complete guide to sizing a bike

If you ’ ra think of buying a new bicycle, or a beginning bicycle, understanding the winder measurements that define your skeletal system is significant to ensure that you get a machine that fits you and works for the type of riding that you intend to do .
ad
And if you ’ re planning to rent a bicycle, it ’ second useful to know your skeletal system ’ s key measurements, so you can make indisputable that your lease will be comfortable to ride and can be adjusted to fit .
not all manufacturers measure frame sizes in the same means, so you need to look at a few cardinal measurements to ensure that you ’ re comparing apples with apples.

Read on to find out how to size up your road motorcycle or batch motorcycle inning. besides check out our comprehensive guide to mountain bicycle geometry, which tells you how these measures affect manage ; flush if you ’ re a roadie most of the measurements are still as meaning .
We ’ ve besides got advice on how to choose the right size frame for road bikes and batch bikes and specific advice for choosing a women ’ sulfur bicycle .

Key numbers that define your bike

We ’ ll tell you below how to measure your motorcycle ’ mho :

  • Top tube length
  • Seat tube length
  • Reach and stack – and why they’re important numbers
  • Wheelbase
  • Chainstay length
  • Front centre
  • Seat tube and head tube angles
  • Bottom bracket drop
  • Bottom bracket height

What you’ll need to measure a bike frame

  • A tape measure
  • A clinometer to measure angles (there are free smartphone apps you can download)
  • A long spirit level (or you can use the clinometer app and a straight piece of wood)
  • A plumb line (or you can improvise with string and a couple of blobs of Blu Tack)

Most bikes, whether road or batch, are now measured in system of measurement units, but you may find some manufacturers that placid size mountain bikes in inches. Some brands, such as Moots, even mix the two !
We highly recommend you stick to metric unit units to keep things reproducible. If you in truth must, you can always divide centimetres by 2.54 to switch to inches .
You will normally be able to find a geometry chart for all sizes of a stream frameset on a godhead ’ s site. If your bicycle is distillery a current model, it ’ south worth taking a replicate of this because it will be more accurate than your measurements and likely a handy reference point down the credit line .

How to measure top tube length

Top tube measurement demonstrated on a bike frame

Simon Bromley / Immediate Media

once, bikes all had horizontal top tubes. now many bikes ’ top tube will have a gradient .
If you look at a bicycle geometry table, it will normally include the real top-tube length. But for a reproducible measure, careless of the peak tube angle, you need to measure the horizontal acme tube length, called the effective top tube length or virtual clear metro in many geo charts .
That ’ s the horizontal distance between the centreline of the head pipe and the centreline of the seatpost. Measuring it correctly will mean using your spirit tied or the clinometer app, to ensure that your quantify is actually horizontal .
many manufacturers size road bikes by top tube duration. That ’ s not true of batch bikes, where the frame size is normally marked S, M, L etc. That ’ s a system used for some road bikes besides : Merida ’ s road bikes go through S, S/M, M/L and L .
Of class, this measurement is up to each brand ’ s interpretation – Ridley ’ s size S frames have a top metro around 54cm, which is equivalent to many brands ’ size medium frames .
It ’ second worth noting that not all brands measure virtual top tube length in the same way either .
Colnago, for example, records the horizontal distance from the principal tube to a upright projected up from the top of the seat tube, so it doesn ’ t take explanation of the farther back projection of the seatpost and its numbers will come out smaller than other makers ’. A 50s Colnago is equivalent to a 54cm crown metro .

How to measure seat tube length

Seat tube measurement demonstrated on a bicycle frame

Simon Bromley / Immediate Media

Seat tube duration is the straight line distance between the center of the bottom bracket and the top of the seat metro .
again, it ’ mho trickier than it sounds : some bikes like the Trek Madone have a considerable extension of the seat tube above the crown tube junction while others use a seatmast, so it ’ randomness unmanageable to compare with an alternative ’ south dimensions .
Plus, batch bikes in finical often have a kink in the seat tube, so you don ’ t want to follow the line of the tube itself, which will be longer .
Line up your straight border with the bottom bracket center and the top of the seat tube and measuring stick along this, if you ’ re not sure you ’ re following the right line .

How to measure reach and stack

Stack and reach measurement demonstrated on a bike frame

Simon Bromley / Immediate Media

So we ’ ve seen that top tube and seat tube lengths are a piece of a minefield if you want to compare frames. For more consistency, most manufacturers will nowadays show reach and stack values for their bikes .
These have the advantage of being independent of frame design and quantify the plumb line distances between two key contact points : the bottom bracket and the top of the head tube .
We ’ ve published a more detailed explanation of why compass and batch are important here .
In brief, the range is the horizontal distance between the two. To measure it, you ’ ll need your spirit level again .
Attach a plumb line to the end of the level. If you ’ re using Blue Tack, make certain that the blob at the end of the chain is fairly symmetrical and your string hangs down neat otherwise your measurement may be off .
Align the lead border of the flat with the centreline of the top of the head tube. then move the level back and forward until the plumb occupation intersects with the center of the bottom bracket spindle. now just measure the distance between the top of the plumb line and the head tube and you ’ ve got your range .
Another option is to push your bicycle up against a wall, measure the outdistance to the peak of the heading tube and the distance to the bottom bracket, then subtract one from the early. You ’ ll still need to make indisputable that your measurement is horizontal though .
The push-down list is the vertical distance between the bottomland bracket and the top of the head metro. then once you ’ re set up to record your scope, you should besides be able to measure your batch, following the plumb line.

An option method is to measure the vertical distance from the ground to the top of your head pipe, then measure the acme of your buttocks bracket from the footing and subtract this .
Both reach and smokestack are quite fiddly to appropriate ; you ’ ll credibly need a second base couple of hands if you use the plumb occupation method and it ’ s worth repeating to ensure you ’ re consistent .

How to measure wheelbase

Wheelbase measurement demonstrated on a bike frame

Simon Bromley / Immediate Media

Your frame ’ sulfur wheelbase is the distance between the front and rear axles. It ’ s a key deciding of a frame ’ randomness ride quality and will vary with frame size besides .
It ’ sulfur fairly easy to measure, although you need to set the fork neat ahead or your measurement will be incorrect .
Like reach and stack, it ’ second worth repeating the measurement several times to make certain you get the like act. Accuracy will besides be increased if you measure the wheelbase on both sides of the bicycle and take the average because this will compensate if the fork is not quite directly .

How to measure chainstay length

Chainstay length measurement demonstrated on a bike frame

Simon Bromley / Immediate Media

Chainstay length is one of the two components that make up your wheelbase and, again, contributes importantly to your frame ’ s handling characteristics. A human body with shorter chainstays will typically feel more full of life than one where the stays are long .
The chainstay length is the directly line distance between the center of the bottom bracket axle and the center of the buttocks dropout, so it ’ sulfur fairly easy to measure with a rule .

How to measure front centre

Front centre measurement demonstrated on a bike frame

Simon Bromley / Immediate Media

The other part of the wheelbase is the front man center. That ’ s the equivalent of the chainstay length but measured from the axle to the front dropout .
again, it affects handling, adenine well as toe overlap with the front wheel. It ’ s not much quoted by motorcycle makers, but BMC, for model, shows it on its geometry charts .
note that the wheelbase is not the summarize of the chainstay length and the battlefront center, as neither of these is measured horizontally .

How to measure seat tube and head tube angles

Seat and head tube measurements demonstrated on a bike frame

Simon Bromley / Immediate Media

The seat tube and steer tube angles are two of the most significant factors to determining wield, with more upright metro angles typically leading to more agile handle. Your clinometer app will come in useful here .
If you ’ ve got a square seat pipe, you can measure the seat tube lean by lining up your smartphone and reading the number off the clinometer app. Make certain your bicycle is vertical and standing on a horizontal surface for an accurate read .
If there ’ s a curl in your seat tube, you ’ ll need to use a uncoiled edge to follow the line between the bed bracket blast and the top of the buttocks tube, then line up the phone with this .
Most newer bikes will have tapered head tubes, so the slant of the front of the capitulum tube will not be the same as the angle of its centreline .
You can get close to the latter by holding your telephone at the angle of the centreline, or by using a straight edge to line up with the centres of the lead and bottom of the head tube .
If you have straight crotch leg, without an angle at their peak, the fish of the legs will be the lapp as the question tube angle, so you can measure this alternatively. Again, it ’ randomness authoritative to have the bicycle standing vertically .
You can besides measure head tube angle by lining up the clinometer with the helmsman extension above the promontory tube .

How to measure bottom bracket drop

BB drop measurement demonstrated on a bike frame

Simon Bromley / Immediate Media

The bottom bracket drop is the remainder between the altitude of the wheel axles and the centreline of the crank axle .
You can measure it by finding the acme of the back axle and the stature of the bottom bracket, then subtracting one from the other. It ’ second another key measurement quoted by bicycle brands on their geo charts .

How to measure bottom bracket height

Bottom bracket height measurement demonstrated on bike frame

finally, the bottom bracket altitude is the distance from the ground to the centre of the penetrate bracket shell. So that ’ second quite easy to measure, although be careful to keep your bicycle straight upright for an accurate read.

Unlike bottom bracket neglect, it will be affected ( slenderly ) by your tyres excessively, so inflate them to your common run coerce .
ad
so now you ’ ve got all the measurements you need to size up your frame of reference. Keep your numbers somewhere safe though : you don ’ deoxythymidine monophosphate want to have to repeat the march .

Related Posts

Leave a Reply

Your email address will not be published.