EBB Adjustment Guidelines?

[keleher]

The thorn bike manual says adjust when "T1-T2" is between 40 and 60mm. The picture:

seems to indicate that T1-T2 is just the difference in diameters of the sprocket and chainring.

This makes no sense. My bike came w/ a 38-17, difference is around 100mm.

Clearly sag must be important here. But I'm not getting it from this picture.

??

[rualexander]

I think maybe the picture is misleading. What I presume it means is, if you hold the chain at the midpoint between chainring and sprocket, hold it top and bottom, and pull apart to measure T1, push together to measure T2, and calculate T1-T2.

[julk]

Thats it, T1-T2 is just the total sag.

Another way is adjust the EBB when the chain is loose enough to jump off over bumps.

[keleher]

Much obliged...

[stutho]

Thats it, T1-T2 is just the total sag.

Another way is adjust the EBB when the chain is loose enough to jump off over bumps.

How did you find out about my super secret method?    That is exactly what I do.

[pyjamas]

When I adjusted the EBB, at what felt like a comfortable tension I found the screws sinking into what seemed old holes, so I tightened the screws at that point.  However, I then found that T1-T2 = 40mm, the point at which I am supposed to readjust the EBB.

We are told to tighten the chain when T1-T2 >40mm<60mm.  Perhaps the really useful piece of information would be to know what T1-T2 should be after the chain has been tightened, so that we can tell what is the least difference before and after when it is safe to adjust without risk that the screws will slip back into old holes.  Anyone have an answer?

[julk]

Pyjamas,
I have just acquired a new Thorn Rohloff bike. My experience from my previous bike is that I will be adjusting the eccentric on the new bike only when the chain has gone really loose, almost certainly more than 60mm slack, and that way the rotation of the eccentric is enough to ensure that the bolts bite into a new bit of eccentric with no danger of slipping into previous holes or indents.
I will be leaving a bit of chain slack after adjustment as the Rohloff does not appreciate running with a tight chain.
Julian.

[lewis noble]

You say the Rohloff does not appreciate having a tight chain . . . does it damage the hub?? 

Lewis

[lewis noble]

To add to my previous post . . . I needed to take a link out of my chainm which had become so slack it came off on occasions - and EBB near the 'thin' part of it's shell.

A friend took the link out (I don't have a rivet remover and have never done it) but even at the 'rearmost' end of the adjustment, the chain is quite tight - though pedalling feels the same.  Friend says not to worry, it will soon wear in . . . . but in the light of previous post, I wonder if that will damage the gearing??

All observations welcome . . .

Lewis

[Paulson]

You say the Rohloff does not appreciate having a tight chain . . . does it damage the hub?? 

Lewis

There are reams of correspondence in this forum regarding this subject - I found it useful to read through them recently when I had the same quandry as you do.

I put a new, bigger chainring on and thus had to extend the chain length, which I did, I admit, as a novice, because although I've been tinkering with bikes all my life, I have never actually broken and reassembled a chain!!!

Lewis - re your question above - What I found was that the chain initially appeared very tight - and it made me despondent at the thought of having to start again and insert yet more extra links!  I had also wound the EBB back to the 'shortest' point to try and give the chain some slack.  I was really worried about this as I had visions of snapped Rohloff chains at the side of the road and worse......However after only 40 miles, the chain has enough slack in it to fall into the >40mm and <60mm banding.  I put 4 new links in and I can only imagine that they have extended under load a tiny bit.

I think that the rule of thumb expressed here is correct; unless chain looseness is becoming a real problem, just let it be......

[julk]

The Rohloff manual (page 48) has a recommendation for about 10mm slack for a newly adjusted chain.

I have seen in a post (cannot remember where) that no slack will put the internal bearings under some stress.

As Paul says, a newish chain wears very quickly at first and will give enough slack within a few miles. The wear should drop off dramatically after the first couple of adjustments.

[lewis noble]

Thanks Paulson - I weill be doing some short dayrides (commuting to / from my campervan to a music festival) next week so I will see how it feels after the week. 

Best wishes to all

lewis