anyone running 38/17 gearing on a Nomad MKII?

[revelo]

If so, what is the initial chain length you use and where is the EBB positioned?

I'm asking because my 42/17 gearing had me with an initial chain length of 52", with the EBB screws positioned under the front hole (thus less than half of the EBB available for tightening), and the 36/17 gearing has me with an initial chain length of 50", with the EBB screws positioned under the rear hole (thus more than half of the EBB available for tightening), and I believe 40/17 has an initial chain length of 51" with the EBB screws positioned near the rear of the EBB (thus almost the entire EBB available for tightening).

What I don't want is to have the EBB screws positioned all the way towards the front of the EBB, so that no further tightening is possible and a link has to be removed as soon as the chain stretches any more. I'm not planning to switch from 36/17 to 38/17 regardless of the answer, but it would nice if the answer was such as to put my mind to rest and dissuade me from even considering such a switch.

[julk]

I am running a 38x17 combo on my expr.
The chain is 50" with the eccentric fully back with all the adjustment left to use as the chain slackens.
The centre bottom bracket axle to centre rear axle distance is a midge's wing or two over 18".
Julian.

[Dave Whittle Thorn Workshop]

I'm not at work till Monday and hence cant check the drawings at the mo, but i'm fairly sure the Nomads are not the same length chainstay for every size.

[revelo]

I'm on a Nomad MKII 590M. Manual says chain stay length on the 590M Nomad MKII is 466mm (18.3"). My crude measurement just now with a tape measure is 468mm (18.4"). Both of these are clearly more than a midge's wing over 18" (457mm).

The chainstays on the Nomad MKII 590M would thus appear to require almost 1" longer chain than on julk's expr. If julk has the EBB positioned fully back (all adjustment available for tightening, none for loosening) when installing a fresh 50" chain with 38/17 gearing, then 51" on the Nomad with 38/17 gearing could have the EBB either same as Julk (a good place for an initial chain) or else positioned at the opposite extreme (a bad place for an initial chain, IMO, since it requires removing a link on tour when the chain lengthens, which is a nuisance). Can't be sure without actually fitting a new chain on a 590M Nomad MKII.

Maybe Dave can settle this authoritatively. Has Thorn shipped any Nomad MKII 590M size with 38/17 gearing? If so, what size initial chain and how was the EBB positioned initially?

[NZPeterG]

Hi I have a New Chain and 38t chain ring just sitting here to fit to my Nomad (17t rear) so do not know!
But fit the EBB is haft way its OK because you can cut the chain once the chain gets some wear..

Pete.......
 

[Dave Whittle Thorn Workshop]

Maybe Dave can settle this authoritatively. Has Thorn shipped any Nomad MKII 590M size with 38/17 gearing? If so, what size initial chain and how was the EBB positioned initially?

We dont record this sort of info i'm afraid.

[revelo]

Hi I have a New Chain and 38t chain ring just sitting here to fit to my Nomad (17t rear) so do not know!
But fit the EBB is haft way its OK because you can cut the chain once the chain gets some wear..

Pete.......
 

Hi Pete,

When you do get around to fitting that chain, please tell us the initial chain length (in inches), where the EBB screws were positioned (relative to the two holes in the side of the EBB) and also the size of your Nomad. And it's a Nomad MKII right? Since the Nomad-X has slightly shorter chainstays. Chainstay length is important and varies between MKII and X and also between different sizes.

Yes, of course it's possible to shorten the chain. But that's something of a nuisance and opens the possibility of botching things if the master link has become jammed and you damage either the master link or the rest of the chain while trying to unjam it. I don't feel like carrying a pair of Master Link pliers on tour. Yes, I know, a damaged chain can be fixed using some spare links and a couple of master links, and I carry all that, but this whole mess can be avoided by simply starting the tour with the EBB screws positioned at the middle or rear of the EBB, so there is plenty of EBB for tightening as the chain stretches.

I'm probably going to stick with the 36/17 gearing no matter what, since very low gears are useful to me, I've discovered. However, if it turns out that the 36T chainring allows lots of dirt into the 38T Hebie chainglider that i'm experimenting with, then I might consider switching to 38T. That's why I'm asking about initial chain length and EBB positioning. It's a question of one possible problem (dirty chain because chainglider doesn't work right, so that I have to carry chain cleaning fluids) versus another possible problem (need to shorten the chain while on tour and thus the possibility for problems if the master link jams).

Thanks,
Frank Revelo

[Dave Whittle Thorn Workshop]

I'd rather have a setup nearly at the front when brand new, then you can bed the new chain in (they usually stretch a bit in the fist few hundred miles) and then shorten 1 link and know that for your tour you have full travel available on the eccentric.

Just my 2p, there isn't really a right and wrong on this one.

[revelo]

This is related to question of whether to replace chains frequently (as is recommended for derailleur systems) or infrequently (Andy Blance's system).

Case 1: Very long tours (over 5000km). Since you probably don't want to carry a bunch of chains and the tour may be to parts of the world where buying quality chains is a problem, then what Dave suggested might be optimal. Start with a fresh chain, sprocket and chainring, then let them all wear down together over the course of the tour, adjusting the eccentric as needed, without ever removing links from the chain.

Case 2: Tours under 5000km. In this case, it is possible to use cheap chains and replace the chain after each tour, so as to minimize wear to the more expensive sprocket and chainring, and also eliminate the need to clean the filthy chain after each tour. So far, I've taken 4 tours for a total of 8000km and replaced the chain 3 times (and also 3 oil changes). The 17T sprocket and Thorn aluminum 42T chainring showed very little wear, even though the chain was dirty throughout most of these tours. Evidently, the dirt (though very thick) was mostly on the outside of the chain. Had I attempted to clean the chain after each tour, rather than replacing it, and done a poor job with this cleaning, I might have pushed that dirt inside the chain where it might start to wear the sprocket and chainring. The problem with what Dave suggested is that it requires a couple of hundred miles of shakedown rides after installing the new chain and before starting the tour, in order to get the chain to stretch enough to allow adjustment, and arranging for that might be a problem for someone like me who has little time between tours.