Originally Posted by
waddo
Thanks for the clarification. But now I really don't understand! My wife's Specialized with flat bars has and effective top tube length of 55.5cm. She finds it quite comfortable and her position relatively upright. To have the same top tube length on the Surly she would need the 54cm frame! In fact the choice is between the 42 and 46. So I cannot understand comparing the top tube length on both bikes.
Things seem more confusing than ever ;(
The top tube length of a flat bar bike should be longer than that of a drop bar. This is because more length needs to be tacked on to a drop bar bike for the reach to the levers. A flat bar has its shift and brakes basically right at stem length. A drop bar has its brakes out another habdful of cm from the stem(how far will vary based on drop bar style).
Based on the stack and reach of the Sirrus, a 52cm LHT would be closest. But the standover height is too high at that frame size.
This assumes your wife rides an XS size Sirrus for size comparing.
Perhaps a sloping top tube touring bike frame is needed?
Otherwise, you could size down on the LHT and have a lot of steerer spacers plus a long stem to compensate.
This approach, a huge spacer stack, is actually pretty common on LHTs(based on all the pics i see). Its as if the geometry doesnt work for a lot of riders, but they still use the frame because its a solid value for the price and features.