Keep your numbers somewhere safe though: you don’t want to have to repeat the process.Fundamental measurements so you can compare frames like-for-likeAgain, it affects handling, as well as toe overlap with the front wheel. So once you’re set up to record your reach, you should also be able to measure your stack, following the plumb line.You can also measure head tube angle by lining up the clinometer with the steerer extension above the head tube.Thanks! As you no doubt already know from your own experience, the range of what's acceptable can be very broad. For example most Tektro brakes have 39-51mm for short reach brakes, 47-57 for medium, and 55-73 for long. As ever, I'm not sure there is a "correct" STR for any given rider. Sign in to manage your newsletter preferencesAn alternative method is to measure the vertical distance from the ground to the top of your head tube, then measure the height of your bottom bracket from the ground and subtract this.Unlike bottom bracket drop, it will be affected (slightly) by your tyres too, so inflate them to your usual running pressure.Like reach and stack, it’s worth repeating the measurement several times to make sure you get the same number. I have also found that seat tube angle and head tube angle make a big difference in my personal comfort or ability to ride a particular bike. The reach would decrease and the stack would increase but the combined measurement (reach + stack) would be the same. There are essentially 3 different reach classes for dual pivot brakes, but manufacturers vary in the exact numbers. It is typically the opposite in modern mountain bikes these days with more emphasis on 'long/low' so the reaches are very high, but stacks are much lower than my custom frame.Sorry, but your mention about your Enigma stack is incorrect. It’s another key measurement quoted by bike brands on their geo charts.If you’re thinking of buying a new bike, or a first bike, understanding the key measurements that define your frame is important to ensure that you get a machine that fits you and works for the type of riding that you intend to do.Align the top edge of the level with the centreline of the top of the head tube. Great subject and well written, thanksAll very interesting, and I'm quite certain not one of my bicycles is the correct STR for me. It’s a key determinant of a frame’s ride quality and will vary with frame size too.And if you’re planning to rent a bike, it’s useful to know your frame’s key measurements, so you can make sure that your rental will be comfortable to ride and can be adjusted to fit.Paul has been riding since he was a teenager and has been writing about bike tech for almost five years. Now many bikes’ top tubes will have a slope.In brief, the reach is the horizontal distance between the two. Again, it’s important to have the bike standing vertically.You can get close to the latter by holding your phone at the angle of the centreline, or by using a straight edge to line up with the centres of the top and bottom of the head tube.The seat tube and head tube angles are two of the most important factors to determining handling, with more upright tube angles typically leading to more nimble handling.