Rod, You should find out what wheel radius they are using to determine the BB height. Obviously, different tire sizes will result in different BB heights. An Atlantis is your size would have a BB drop of 80mm. Using a skinny tire (340mm wheel radius) on the Atlantis the BB height would be 10.25". Most likely you don't intend on using a skinny tire on this Mercian given that you want a copy of a rough stuff frame. Mercian seems to have good customer service so they will likely give you the numbers I have requested. The information that you've given so far leads me to believe the drop is too much but let me know when you here back from them.
On a side note, I wish frame builders would deal in BB drop rather than BB height given that drop is constant regardless of tire choices.
Curt Goodrich
Minneapolis, MN
> Hi all,
> I have a 65cm c-t frame on order with Mercian Cycles. I wanted it built
> to the same geometry as a Rivendell Atlantis, which is almost the same
> as Heron touring frame. I just received a note from Grant at Mercian
> that says the following:
>
> One of our frame builders has just started to check your frame on his
> frame jig and found that the bottom bracket height has come out at
> 101/8" this is 1/2" less than we would normally build such a frame. Are
> you sure this height or bottom bracket drop is correct? Do you want us
> to proceed with the build?
>
> I know Rivendell favors a lower bottom bracket height, is this something
> Mercian is just not used to or is there something else out of whack?
>
> Any and all suggestions would be really welcome.
>
>
> Thanks!
> Rod Kronenberg
> Fort Collins, CO