![]() The stack is the vertical distance between the bottom bracket and the top of the head tube. You’ll still need to make sure that your measurement is horizontal though. Now just measure the distance between the top of the plumb line and the head tube and you’ve got your reach.Īnother option is to push your bike up against a wall, measure the distance to the top of the head tube and the distance to the bottom bracket, then subtract one from the other. Then move the level back and forward until the plumb line intersects with the centre of the bottom bracket spindle. If you’re using Blue Tack, make sure that the blob at the end of the string is fairly symmetric and your string hangs down straight otherwise your measure may be off.Īlign the top edge of the level with the centreline of the top of the head tube. To measure it, you’ll need your spirit level again.Īttach a plumb line to the end of the level. In brief, the reach is the horizontal distance between the two. We’ve published a more detailed explanation of why reach and stack are important here. These have the advantage of being independent of frame design and measure the perpendicular distances between two key contact points: the bottom bracket and the top of the head tube. For more consistency, most manufacturers will now show reach and stack values for their bikes. ![]() So we’ve seen that top tube and seat tube lengths are a bit of a minefield if you want to compare frames. A 50s Colnago is equivalent to a 54cm top tube. It’s worth noting that not all brands measure virtual top tube length in the same way either.Ĭolnago, for example, records the horizontal distance from the head tube to a vertical projected up from the top of the seat tube, so it doesn’t take account of the further backward projection of the seatpost and its numbers will come out smaller than other makers’. Of course, this measurement is up to each brand’s interpretation – Ridley’s size S frames have a top tube around 54cm, which is equivalent to many brands’ size medium frames. That’s a system used for some road bikes too: Merida’s road bikes go through S, S/M, M/L and L. That’s not true of mountain bikes, where the frame size is usually marked S, M, L etc. Many manufacturers size road bikes by top tube length. Measuring it correctly will mean using your spirit level or the clinometer app, to ensure that your measure is really horizontal. That’s the horizontal distance between the centreline of the head tube and the centreline of the seatpost. But for a consistent measure, regardless of the top tube angle, you need to measure the horizontal top tube length, called the effective top tube length or virtual top tube in many geo charts. If you look at a bike geometry table, it will usually include the real top-tube length. Now many bikes’ top tubes will have a slope. Once, bikes all had horizontal top tubes. If your bike is still a current model, it’s worth taking a copy of this because it will be more accurate than your measurements and likely a handy reference down the line. You will usually be able to find a geometry chart for all sizes of a current frameset on a maker’s site. If you really must, you can always divide centimetres by 2.54 to switch to inches. We highly recommend you stick to metric units to keep things consistent. Some brands, such as Moots, even mix the two! Most bikes, whether road or mountain, are now measured in metric units, but you may find some manufacturers that still size mountain bikes in inches. A plumb line (or you can improvise with string and a couple of blobs of Blu Tack).A long spirit level (or you can use the clinometer app and a straight piece of wood).A clinometer to measure angles (there are free smartphone apps you can download).Reach and stack – and why they’re important numbers.We’ll tell you below how to measure your bike’s:
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