Quick question about geometry of Thorn Nomad Mk3

[tt2cycletours]

I am considering getting a new touring frame, but trying to find one with the highest bottom bracket I can find.

Does anyone know when Thorn state bottom bracket drop on their frame geometry information, if this figure is to the centre of the EBB and therefore you can actually achieve a significantly higher or lower height than stated? Or do they provide data assuming the bb will be in the highest most point and provide data with the expectation?

Some of frame makers out there actually state the EBB is a way of adjusting bb height to suit as well as for chain/belt tensioning.

Thanks.

[PH]

I would assume it's measured from the centre, it wouldn't make much sense otherwise, but I'd question if there's much height adjustment.  For one thing, you should only use the top arc of adjustment so I doubt the difference between the lowest and highest points was more than 3mm.  Then more obviously you have to use it for the intended purpose of adjusting the chain, so there isn't a lot of choice.  Tyre and pedal choice is going to have more effect than the EBB adjustment.
I can't remember the numbers, but the Nomad frame being designed for three wheel sizes means it needed the BB height for the smallest, that makes it pretty high on 650b and even more so on 700c.   I was considering one a couple of years ago but wanted to stick with 700c, it was the high BB put me off, it's quite a difference to my other bikes and although it might have been fine I decided not to risk it.

[mickeg]

... For one thing, you should only use the top arc of adjustment ...

That was the case with an eccentric that the pinch bolts would create small dents in the eccentric, thus it was a bad idea to create those where the eccentric was thin.  Example, the Mk II Nomad.

Is that criteria still valid on the Mk III Nomad where the eccentric shell diameter is shrunk to firmly grip the eccentric in place?

I have not been keeping up on Mk III details since I am happy with my existing fleet.  Thus, i have not researched this.

[PH]

... For one thing, you should only use the top arc of adjustment ...

That was the case with an eccentric that the pinch bolts would create small dents in the eccentric, thus it was a bad idea to create those where the eccentric was thin.  Example, the Mk II Nomad.

The advice is the opposite, keep the the thin part at the bottom to restrict water ingress, which may mean only using the bottom arc, in either case the throw only uses one half of a full rotation.

EDIT - Had to look at mine to work that out...

[mickeg]

Water ingress???

[PH]

Yes, from the manual

Note that the eccentric should be rotated in a clockwise direction so as the thin part of eccentric is at the bottom of the shell, this helps prevent ingress of water through the slots.

The thin side is solid, the thick side has a cutaway central portion, which would leave a cavity behind the slots. Of no concern on a set screw type as it doesn't have slots cut into the BB shell.

[mickeg]

Yes, from the manual

Note that the eccentric should be rotated in a clockwise direction so as the thin part of eccentric is at the bottom of the shell, this helps prevent ingress of water through the slots.

The thin side is solid, the thick side has a cutaway central portion, which would leave a cavity behind the slots. Of no concern on a set screw type as it doesn't have slots cut into the BB shell.

Now I understand.  Thanks.