Shimano band-on front derailleur question.

[Pointy boy]

This may be a stupid question, but…
I’m about to install a Shimano band-on front derailleur. It came with adapters for smaller seat tubes, but I don’t need to use them as I have a 34.9mm seat tube.
So my question: the front band has a recessed shape (see photo) whilst the the rear band has a smooth face. Won’t this recessed side damage the seat-tube, in a way that the flat/faced side (or an adapter) wouldn’t? Or is this a non-issue?
Thanks!

 

[raleighnut]

What is the frame material ?

 

[All uphill]

If I remember correctly one of the adapters supplied fits neatly in the recess of the band. When tightened only the adapter makes contact with the seat post.

 

[Pointy boy]

What is the frame material ?

Aluminium.

 

[Pointy boy]

If I remember correctly one of the adapters supplied fits neatly in the recess of the band. When tightened only the adapter makes contact with the seat post.

No, just comes with 2 adapters. The clamp is 34.9, with adapters to take it down to 28.6 and 31.8.

​

 

[raleighnut]

Aluminium.

Should be OK as long as you don't overtighten, could have been a problem with a Crackbon frame

 

[Wheelspinner]

I've usually used a small strip of old inner tube cut to fit those clamps to any frame, aluminium or carbon or even steel. Avoids clamp marks to a fair extent and protects paint in the event you need to move the derailleur up or down to adjust for different size chainrings.

 

[wafter]

That doesn't look like a Shimano item; if it's a cheapie may well be that they expect you to fit it with no inserts which I'd certainly not be doing, looking at the inside of that clamp.

 

[Webbo2]

I have only bought one Shimano clamp on front mech in recent years a 105 and I’m pretty sure it was solid on both sides of the clamp.

 

[Vapin' Joe]

That doesn't look like a Shimano item; if it's a cheapie may well be that they expect you to fit it with no inserts which I'd certainly not be doing, looking at the inside of that clamp.

It doesn't look like it to me either unless the inserts are missing and I wouldn't fit it to an aluminium tube.

 

[wafter]

As fortune would have it, I have in my hands the adaptor off my ill-fated CdF 20 project; it's a Shimano SM-AD91-M, is solid cast alloy and contains c. 1-1.5mm thick plastic inserts marked for use on 28.6mm tubes.. so wouldn't fit a 34.9mm tube even with the inserts removed.

IIRC the other one I bought for my marginally less ill-fated CdF 30 came with two inserts - one for 28.6mm and one for summot a bit larger (maybe 31.8mmm?); IIRC it's listed as fitting 34.8mm so it seems they intend it to be fitted with nothing separating it from the seat tube (again, bugger that).

Futher digging reveals Shimano list two:

SM-AD91-SM: 28.6mm with insert, 31.8mm without
SM-AD91-L: 28.6mm with insert, 31.8mm with smaller insert and 34.8mm without

I'd not entertain the idea of fitting anything without some form of cushioning (PVC tape maybe?) and certainly wouldn't be using something as illustrated in the OP that's evidently pressed and has just two narrow bands of contact.