How To Measure The Size Of A Bike
If you lot're thinking of ownership a new cycle, or a outset bike, agreement the key measurements that define your frame is important to ensure that you lot get a machine that fits yous and works for the type of riding that yous intend to do.
And if you lot're planning to hire a bike, it'due south useful to know your frame's key measurements, then yous can make sure that your rental will be comfortable to ride and can be adjusted to fit.
Not all manufacturers measure frame sizes in the same manner, then you demand to await at a few fundamental measurements to ensure that you're comparison apples with apples.
Read on to notice out how to size upwards your route bicycle or mount bike frame. Besides bank check out our comprehensive guide to mountain bike geometry, which tells you how these measures affect treatment; even if you're a roadie about of the measurements are still every bit significant.
Nosotros've also got advice on how to choose the right size frame for route bikes and mountain bikes and specific advice for choosing a women's bike.
Key numbers that ascertain your bike
We'll tell you beneath how to measure your bike'due south:
- Top tube length
- Seat tube length
- Reach and stack – and why they're of import numbers
- Wheelbase
- Chainstay length
- Front centre
- Seat tube and head tube angles
- Bottom bracket drop
- Bottom subclass summit
What you'll need to measure out a cycle frame
- A tape measure
- A clinometer to measure angles (there are costless smartphone apps you can download)
- A long spirit level (or y'all tin can use the clinometer app and a straight slice of wood)
- A plumb line (or you can improvise with string and a couple of blobs of Blu Tack)
Most bikes, whether road or mountain, are now measured in metric units, but you may find some manufacturers that however size mount bikes in inches. Some brands, such equally Moots, fifty-fifty mix the two!
We highly recommend yous stick to metric units to keep things consistent. If y'all really must, you can always carve up centimetres by 2.54 to switch to inches.
You will normally be able to find a geometry nautical chart for all sizes of a current frameset on a maker's site. If your bike is still a current model, it'due south worth taking a copy of this because it will be more accurate than your measurements and likely a handy reference down the line.
How to measure top tube length
Simon Bromley / Immediate Media
One time, bikes all had horizontal top tubes. Now many bikes' top tubes will have a slope.
If you look at a bike geometry tabular array, it will normally include the real top-tube length. But for a consistent measure, regardless of the top tube angle, you lot need to measure the horizontal elevation tube length, called the effective meridian tube length or virtual top tube in many geo charts.
That'due south the horizontal distance betwixt the centreline of the head tube and the centreline of the seatpost. Measuring information technology correctly will mean using your spirit level or the clinometer app, to ensure that your measure is really horizontal.
Many manufacturers size road bikes past acme tube length. That's not true of mountain bikes, where the frame size is usually marked S, G, 50 etc. That'due south a system used for some route bikes also: Merida'south road bikes go through S, S/Chiliad, 1000/L and L.
Of course, this measurement is up to each brand's estimation – Ridley's size Southward frames accept a acme tube around 54cm, which is equivalent to many brands' size medium frames.
It'southward worth noting that non all brands mensurate virtual summit tube length in the same way either.
Colnago, for example, records the horizontal distance from the head tube to a vertical projected up from the top of the seat tube, and so information technology doesn't take account of the farther astern projection of the seatpost and its numbers volition come out smaller than other makers'. A 50s Colnago is equivalent to a 54cm peak tube.
How to measure out seat tube length
Simon Bromley / Firsthand Media
Seat tube length is the direct line distance between the heart of the bottom bracket and the elevation of the seat tube.
Once more, it's trickier than it sounds: some bikes like the Trek Madone have a considerable extension of the seat tube above the pinnacle tube junction while others use a seatmast, so it'south hard to compare with an alternative'south dimensions.
Plus, mountain bikes in particular often accept a kink in the seat tube, so you lot don't want to follow the line of the tube itself, which will be longer.
Line upwardly your direct edge with the bottom bracket center and the acme of the seat tube and measure forth this, if you're not sure y'all're post-obit the correct line.
How to measure out achieve and stack
Simon Bromley / Immediate Media
And then we've seen that top tube and seat tube lengths are a scrap of a minefield if yous want to compare frames. For more consistency, most manufacturers will now show reach and stack values for their bikes.
These have the advantage of beingness contained of frame design and measure the perpendicular distances between two fundamental contact points: the bottom bracket and the summit of the head tube.
We've published a more detailed explanation of why achieve and stack are important hither.
In brief, the reach is the horizontal altitude between the two. To measure it, you'll demand your spirit level again.
Adhere a plumb line to the end of the level. If you lot're using Blue Tack, brand sure that the blob at the terminate of the string is fairly symmetric and your cord hangs down directly otherwise your measure out may exist off.
Align the top edge of the level with the centreline of the superlative of the caput tube. So move the level back and forward until the plumb line intersects with the heart of the lesser subclass spindle. At present just measure the distance between the pinnacle of the plumb line and the head tube and you've got your reach.
Another option is to button your bike up against a wall, measure the altitude to the top of the head tube and the distance to the bottom bracket, then subtract one from the other. You'll however need to brand sure that your measurement is horizontal though.
The stack is the vertical distance betwixt the lesser bracket and the acme of the head tube. And then in one case you're prepare upward to record your reach, you should also exist able to measure your stack, post-obit the plumb line.
An alternative method is to measure the vertical distance from the ground to the elevation of your head tube, then mensurate the tiptop of your bottom bracket from the ground and subtract this.
Both reach and stack are quite fiddly to capture; y'all'll probably need a second pair of hands if you use the plumb line method and information technology'south worth repeating to ensure you're consistent.
How to measure wheelbase
Simon Bromley / Immediate Media
Your frame's wheelbase is the distance between the front and rear axles. Information technology'southward a primal determinant of a frame'south ride quality and will vary with frame size likewise.
It's fairly piece of cake to mensurate, although you need to set the fork straight ahead or your measurement volition be incorrect.
Like reach and stack, it'southward worth repeating the measurement several times to make sure yous get the same number. Accuracy volition also be increased if you measure the wheelbase on both sides of the bike and take the boilerplate because this will compensate if the fork is non quite directly.
How to measure chainstay length
Simon Bromley / Immediate Media
Chainstay length is ane of the 2 components that make up your wheelbase and, again, contributes significantly to your frame's handling characteristics. A frame with shorter chainstays volition typically feel more lively than one where the stays are longer.
The chainstay length is the directly line distance betwixt the middle of the lesser bracket axle and the centre of the rear dropout, so it'south fairly easy to mensurate with a ruler.
How to measure front center
Simon Bromley / Immediate Media
The other component of the wheelbase is the forepart centre. That'southward the equivalent of the chainstay length merely measured from the axle to the front end dropout.
Again, it affects handling, besides equally toe overlap with the front cycle. It'southward not frequently quoted by bike makers, merely BMC, for example, shows it on its geometry charts.
Notation that the wheelbase is not the sum of the chainstay length and the front end middle, as neither of these is measured horizontally.
How to measure seat tube and head tube angles
Simon Bromley / Immediate Media
The seat tube and head tube angles are two of the nigh important factors to determining treatment, with more upright tube angles typically leading to more nimble handling. Your clinometer app will come up in useful here.
If yous've got a direct seat tube, y'all can measure the seat tube angle by lining upward your smartphone and reading the number off the clinometer app. Make certain your bike is vertical and standing on a horizontal surface for an accurate reading.
If there'southward a kink in your seat tube, you'll demand to use a direct edge to follow the line between the bottom subclass shell and the top of the seat tube, and so line up the telephone with this.
Most newer bikes will take tapered head tubes, so the angle of the front of the head tube will non be the same as the angle of its centreline.
You can go shut to the latter by belongings your phone at the bending of the centreline, or by using a straight border to line upward with the centres of the elevation and bottom of the head tube.
If y'all have directly fork legs, without an bending at their crown, the angle of the legs will be the same as the caput tube angle, so y'all can measure this instead. Again, information technology'southward important to have the bike standing vertically.
You can as well mensurate head tube angle past lining up the clinometer with the steerer extension above the head tube.
How to measure out bottom bracket drop
Simon Bromley / Firsthand Media
The bottom bracket drop is the difference between the elevation of the wheel axles and the centreline of the crank axle.
You tin mensurate it past finding the height of the rear axle and the height of the lesser subclass, then subtracting one from the other. Information technology's some other key measurement quoted by bicycle brands on their geo charts.
How to measure out bottom bracket meridian
Finally, the bottom bracket peak is the altitude from the ground to the centre of the lesser subclass shell. So that'due south quite easy to measure, although exist careful to keep your wheel direct upright for an accurate reading.
Unlike bottom bracket drop, it will be afflicted (slightly) by your tyres too, then inflate them to your usual running pressure.
Then at present y'all've got all the measurements you need to size up your frame. Keep your numbers somewhere safe though: you don't want to have to repeat the procedure.
How To Measure The Size Of A Bike,
Source: https://www.bikeradar.com/advice/buyers-guides/how-to-measure-a-bike-frame-our-complete-guide-to-sizing-a-bike/
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