What size should I ride in BMC if I ride a M in Giant?

[Chiasson]

Some people told me to downsize to 51? They measured me at 53 cm at a shop and told me I'd be 54cm for a Specialized and 51 in BMC. Wouldn't it be too small? They didn't had any in stock. I’m 5’9 3/4

 

[Angliru]

I've checked them out and the BMC's seem to have longer top tubes than the typical frame. I'm about 5'-10" also and figured I would need about 51-52. Back in the day I used to select my frames by the seat tube measurement until I figured the virtual top tube measurement was better for my own bike fit and it's worked out well for me ever since.

 

[geobob]

I built a big database of bike geometry to help answer this type of question - search for your current bike, then compare it side by side with the ones you're interested in. It's at geometrygeeks.bike

I've always found comparison with your current bike to be by far the best guide. The 'named' sizes between brands vary too much to be useful.

Good luck!

Bob