Make sure your bike is vertical and standing on a horizontal surface for an accurate reading.If there’s a kink in your seat tube, you’ll need to use a straight edge to follow the line between the bottom bracket shell and the top of the seat tube, then line up the phone with this.Most newer bikes will have tapered head tubes, so the angle of the front of the head tube will not be the same as the angle of its centreline.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.If you have straight fork legs, without an angle at their crown, the angle of the legs will be the same as the head tube angle, so you can measure this instead.
The differences are seemingly minute, but will show themselves in the ride.The only exception to this is on very small bikes, where the trail sometimes has to be increased to prevent toe overlap. You’ll find on endurance bikes, the bottom bracket drop will be lower to add to stability, because you’re lowering the centre of gravity,” says Allen.When designing race bikes, Allen has opted to spec shorter cranks for some riders, as low as 165 even for those close to 6ft in height. This is clear within the Specialized Venge charts where a size 49 has a trail of 63mm and a 52 cuts it down to 58mm, down to 52mm on a size 61cm.Some manufacturers, such as Canyon, have opted to reduce wheel size to counter this,Seat tube angle is simply the angle at which the seat tube sits, and it will have implications on set up.If the angle is too slack, on larger bikes the seat tube will extend too far backwards, which Allen says presents problems when fitting riders to bikes. Sign up to receive our newsletter! They’re exceptionally separate conversations.“If you’re deciding on a new bike, start by looking at it from a handling perspective. Now, more bikes have different fork lengths. finding the stack and reach of the bike correct for you requires several things you don't have.
Others have not.The good news is, we have the option of knowing stack and reach, and this will tell us how close the fit is for you. He was into gravel before it was even invented, riding a cyclocross bike across the South Downs and along muddy paths through the Chilterns. If updates to the geometry are made mid-project, the software can usually update the shaping to reflect these changes. Obviously if you’ve got a short chainstay on a large frame you’ve put the rider’s centre of gravity further back than on a smaller frame,” says Bowman Cycles’ Neil Webb.“Chainstays that are the same across the size range are usually a sign of a brand saving money by using one chainstay mould. 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.That’s the horizontal distance between the centreline of the head tube and the centreline of the seatpost. 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.Once, bikes all had horizontal top tubes. And obviously stem length.”Though sometimes expensive, handlebars can be swapped. I reckon it's worth talking about the Stack and Reach measurement that'll be very invaluable when it come to figuring out what size bicycle you need. Keep your numbers somewhere safe though: you don’t want to have to repeat the process. A 50s Colnago is equivalent to a 54cm top tube.Seat tube length is the straight line distance between the centre of the bottom bracket and the top of the seat tube.Again, it’s trickier than it sounds: some bikes like the Trek Madone have a considerable extension of the seat tube above the top tube junction while others use a seatmast, so it’s difficult to compare with an alternative’s dimensions.Plus, mountain bikes in particular 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 edge with the bottom bracket centre and the top of the seat tube and measure along this, if you’re not sure you’re following the right line.So we’ve seen that top tube and seat tube lengths are a bit of a minefield if you want to compare frames. Then move the level back and forward until the plumb line intersects with the centre of the bottom bracket spindle.
I'd rather have a moderate reach (430-ish for my 5'9" frame), and gain a bit of extra stability via longer chainstays. (Basic Right Angle Stacking Width) + 48 in. Use a carpenter's level to make sure that the floor in the area is even.