[Recommendation] I'm in-between sizes!

Just looking at the geometry stats for the 49cm versus the 52cm there are a couple of things to note (http://allcitycycles.com/bikes/space_horse). The reach (lateral distance from bottom bracket to centre of the top of the head tube) of the two sizes are very similar (only 3mm difference which is squat). Although the seat tube angle is steeper on the smaller bike which will move you further forward.

The larger size has a 16mm larger stack (vertical distance between bottom bracket and centre of the top of the head tube). These aren't big differences especially if you have a few spacers under the stem with the smaller size.

Other differences which are more likely to be noticeable are the handlebar width (40cm versus 42cm), the stem is 90mm versus 100mm and the crank length 170mm versus 175mm.

The handlebar width is important as you will feel this difference, check your existing bike to see what the handlebar width is and if you think you can handle the change.

The longer stem on the larger bike will put the handlebars a wee bit further away which will require you to stretch a bit further. Fine tuning a bike sizing by changing the stem length is possible although as others have pointed out you can't make large changes here, maybe a cm or two before affecting the handling.

The crank length could be an issue. And by issue I mean it could cause you knee pain. 175mm cranks are rather long for someone 5' 7" (I'm 6' and use 175mm) which will require your legs to travel a wider circle. Not by much, you may not even notice it, but then again, maybe your knees will. Again, check your existing bike (the length should be imprinted on the inside face of the crank arm) and decide if the extra length in the crank arms might be an issue for you.

/r/bicycling Thread