Flat bar cross bike based on drop bar frame
 

Hi all,

Want to build a flat bar cross/commuting bike. I know I probably need to go with a longer top tube if I'm using a frame intended for drop bars. A 53cm top tube is my sweet spot for drop bars - allows me a 10cm stem with comfortable use of the whole bar. My standover using the rivendell "book jammed up into crotch" method is 80cm. Of the frames I'm looking at, one is 53cm top tube with 77.5cm stand over. The other is 54.5cm top tube with 79.5cm stand over. Obviously, for a cross frame, the more stand over is desirable, but for flat bars, the top tube needs to be longer. If it were just for road use, I wouldn't worry, but as it will be stopping at lights and used off road, stand over is important.

I know lots of people will say stand over isn't important, but habing none at all worries me a bit. I have road bikes with 78cm stand over which touch "soft tissue", but not firm against pubic bone.

I suppose what I'm getting at is, could I go with a frame the same size top tube as my drop bar bikes, and make it fit with a flat bar?

Incidentally, had to explain this dilemma to a customer in theshop I work in, who wanted a flat bar on his road bike which already had a 12cm stem... Hoping as I use a 10cm stem I might have more leeway to play with.

Any ideas much appreciated.

Sb

One thing that has occurred to me is that on a flat bar conversion the bar's ideal position would be mid-way between the "virtual" tops, hoods and drops of a drop bar, in a sort of compromise between those 3 main drop bar positions...

What's your height? I'm 170 cm and I ride a medium flat bar gravel road/adventure bike which is roughly 54 cm.

I'm 173cm, with v short arms and v small hands (arms shorter than my dad's, and he's 166cm) so tend to size down to get adequate reach, and thus compact frames have a LOT of seatpost showing! I tend to go for traditional horizontal frames with 52-54cm top tubes with drop bars (ideally 53cm) so am anticipating needing over 54cm tt for flat bars...

But as I said, stand over concerns me when sizing up to get reach for flat bars..

What's your bike's stand over height? Have you got clearance?

Of course you can, and this is what most people do since the primary dimension is usually the seat-tube length. You can always get a longer or shorter stem to adjust for reach. You can also get seat-posts with varying amounts of set back or none at all to further fine tune reach. 'Stand-over' is a bike dimension. Riders do not have stand-over, they have 'inseam' and done properly inseam is measured barefoot, but when riding it will likely be in shoes of some kind. My vintage road racer is impossible to straddle barefoot, but it is quite easy to do so in cycling shoes. It's a very big frame but I still need about 4.5" of seatpost showing. If I wanted to make a flat bar road bike out of it I would not go looking for a different frame with a longer top tube I would simply buy a longer stem. Around 20mm longer usually does the trick.