Recently I've been riding my cyclocross bike with 23C tires as a road bike substitute, but
the BB (bottom bracket) position feels high and a bit odd.
That said, this is only "compared to a road bike,"
and it's actually normal in itself, so I decided to measure exactly how much difference there is.
↑This is a Ridley Crossbow.
The seatpost doesn't look very long, but that's because
the 520 size is measured center-to-center, and center-to-top is around 550mm.
It's also because the top tube is horizontal.
I run a string through the center of both hub axles.
Ideally you'd have two people do this for much greater accuracy,
but this time I'll just tape the string down.
↑The string is taut.
The shortest distance from this string to the BB center
(the perpendicular line segment from the string to the BB center)
is the chainstay height.
I hold a ruler against the string.
By eye, I'd say it's around 59mm.
The actual geometry chart for this frame also shows 59mm.
Road bikes usually come in at just under 70mm or so.
Fixed gear bikes are typically around 45mm.
The smaller the number, the higher the BB position, which means saddle height increases from there—so
the shallower the chainstay (smaller number), the higher your foot reach becomes when putting a foot down from the saddle.
At 59mm, this frame leans more toward the road bike side,
but since cyclocross bikes run about 32C tires,
the saddle height above ground increases further, making the foot reach even higher.
On a road bike, when you straddle the saddle and put one foot on the ground,
you typically touch down around the cleat area of your shoe,
but with fixed gear or cyclocross bikes you end up more on your toes.
With cyclocross, the tire thickness adds to the chainstay height effect.
Based on feel, the foot reach on my cyclocross (when equipped with cyclocross tires)
felt more like a fixed gear bike, so I thought it would be shallower.
One more thing about chainstay height and foot reach.
I ride a fixed gear on rollers, and when I place my foot on the roller frame stand during mounting,
on a road bike my foot lands around the ball of my foot,
but on the fixed gear I'm on my toes, which makes that first pedal stroke less stable.
That said, what really matters about chainstay height
is how it affects handling during riding (especially in corners and descents), and foot reach
is really not a big deal.
the BB (bottom bracket) position feels high and a bit odd.
That said, this is only "compared to a road bike,"
and it's actually normal in itself, so I decided to measure exactly how much difference there is.
↑This is a Ridley Crossbow.
The seatpost doesn't look very long, but that's because
the 520 size is measured center-to-center, and center-to-top is around 550mm.
It's also because the top tube is horizontal.
I run a string through the center of both hub axles.
Ideally you'd have two people do this for much greater accuracy,
but this time I'll just tape the string down.
↑The string is taut.
The shortest distance from this string to the BB center
(the perpendicular line segment from the string to the BB center)
is the chainstay height.
I hold a ruler against the string.
By eye, I'd say it's around 59mm.
The actual geometry chart for this frame also shows 59mm.
Road bikes usually come in at just under 70mm or so.
Fixed gear bikes are typically around 45mm.
The smaller the number, the higher the BB position, which means saddle height increases from there—so
the shallower the chainstay (smaller number), the higher your foot reach becomes when putting a foot down from the saddle.
At 59mm, this frame leans more toward the road bike side,
but since cyclocross bikes run about 32C tires,
the saddle height above ground increases further, making the foot reach even higher.
On a road bike, when you straddle the saddle and put one foot on the ground,
you typically touch down around the cleat area of your shoe,
but with fixed gear or cyclocross bikes you end up more on your toes.
With cyclocross, the tire thickness adds to the chainstay height effect.
Based on feel, the foot reach on my cyclocross (when equipped with cyclocross tires)
felt more like a fixed gear bike, so I thought it would be shallower.
One more thing about chainstay height and foot reach.
I ride a fixed gear on rollers, and when I place my foot on the roller frame stand during mounting,
on a road bike my foot lands around the ball of my foot,
but on the fixed gear I'm on my toes, which makes that first pedal stroke less stable.
That said, what really matters about chainstay height
is how it affects handling during riding (especially in corners and descents), and foot reach
is really not a big deal.