Effective Top Tube Length
The effective top tube (ETT) length is the simplest way to determine a bike’s size. That said, just because the ETT is the same between the two bikes, it doesn’t mean the bikes will have the same reach.
Seat Tube Length
Seat tube length isn’t too important for most people with the exception of those who need additional standover clearance (often smaller riders). Again, it’s best to compare bikes based on their stack and reach measurements if you can.
Head Tube Length
Long head tubes are common on touring bikes in order to prop the bars up high without the use of excessive headset spacers. Head tubes are often 40mm+ longer than the equivalent road or cyclocross bike
