thorn chainguards

[PH]

EDIT - Part duplicated what martinf was typing at the same time, but different enough not to bother changing...

Ok but i don't want to change my chainring now, so i don't know if i can use a chainguard up to 38 t with my actual chainring 40 t .. ?   

Most probably not, the maximum T size will have the chain running just below the edge, the guard would at best be pointless if the chain was above the guard and if this wasn't the case with 40T it's hard to imagine why it wouldn't be advertised as such.
Chainring bolts - if you're currently running a single chainring in the outer position, you'll need to move it to in middle/inner position and put the guard where the chainring is now, this will need double bolts rather than the single you most likely have now. 
Also consider doing the above changes the chainline, if you wish to maintain the current one, you'll also need a different bottom bracket.

[Danneaux]

Agreed with Martin; when I make my own bash guards, I do so by filing the teeth from old chainring that are 6 teeth larger than the 'ring I am trying to protect.

The experiences related by others in this thread matches my own.

All the best, Julien,

Dan.

[mickeg]

It is not clear to me if this is for a Rohloff bike or derailleur bike with a double/triple? 

And if it is for a Rohloff bike, does it have a double crank? 

And if it is a double with one chainring on a Rohloff bike, do the chainring bolts have the little spacers that come with the Rohloff that allow you to use the double length bolts with a single chainring on a double crank?

In other words, we can't make firm answers without knowing what the situation is.

For my Nomad (Rohloff) bike which has a double crank, I cut the teeth off a 52T chainring to use as a bashguard with a 44T chainring, thus 8 teeth difference.  That was a bit bigger than it needed to be but it was functional so that is what I use. 

Touring where I use a 36T chainring on the inner position on a double crank, I use a 44T chainring as a bashguard because if I conclude that the 36 is too low, I can add a few links to the chain and use the 44 instead.  But it looks a bit odd to have two chainrings and no front derailleur.

If you have a chainring in the outer position on a Rohloff bike and move that chainring to an inner position, that will change your chainline a bit.  My chainline is off about 5mm because I run my chain on a chainring on the inner postion, but my chainline would be perfect if I had the chainring in the outer position.  I see a 5mm out of line position as not a problem, but I have no clue what you have on your bike.

[PH]

It is not clear to me if this is for a Rohloff bike or derailleur bike with a double/triple? 

Well, the question is based on a single chainring...
Given that I doubt it matters whats on the back, IGH, SS, 1X

[jul]

You didn't say what you wanted the chainguard for:

1 keeping trousers or legs clean
2 stopping the chain jumping off the chainring (IMO very unlikely with a Rohloff)
3 as a bashguard to protect the chainring from rocks

I sent this link in my precedent message ..
https://www.sjscycles.co.uk/chainsets/thorn-high-quality-alloy-chainguard-for-110-pcd-rings-up-to-38t-black/

But thanks for these responses. I would like this chainguard firstly to protect trousers

I've only one bike, it's a Nomad with rohloff


thanks

[jul]

Sorry i reiterate my question..

Can i use this Thorn chainguard (up to 38 teeth) with my future Surly chainring 36 t ?

https://www.sjscycles.co.uk/chainsets/thorn-high-quality-alloy-chainguard-for-110-pcd-rings-up-to-38t-black/

[martinf]

If it works for 38T it will work for 36T

[jul]

Ok Martin ..

But i noticed one thing.. if i add a chainguard, my chainring will take the inner position and it will touch my plastique bottle   



Also, to have a chain misaligned i'am not a fan, so maybe i'll add just spacers and basta 

[martinf]

If you want to fit the chainguard where the chainring currently sits, and the chainring inside of this, the best way is to fit a longer bottom bracket unit (boîtier de pédalier). If you choose the right length, you should be able to get the chainline correct (and not touch the bottle!).

If there is enough room between crank and chainring, cheaper would be to keep the chainring in the current position and use longer chainring bolts and spacers to fit the chainguard outboard of the chainring (closer to the crank).

[John Saxby]

Julio, if you're using a 36T or 38T chain ring, you could fit a Hebie Chainglider as a chainguard, without altering your chainline.

The Chainglider for the 38T ring will fit a 36T ring--I have one on my Raven. You have to cut out one part of the Chainglider, the piece covering the rear of the chainring, but it still works well. 

If you think that would be useful, I can send you a photo of the Chainglider on my Raven.

Cheers, John

[jul]

If you want to fit the chainguard where the chainring currently sits, and the chainring inside of this, the best way is to fit a longer bottom bracket unit (boîtier de pédalier). If you choose the right length, you should be able to get the chainline correct (and not touch the bottle!).

If there is enough room between crank and chainring, cheaper would be to keep the chainring in the current position and use longer chainring bolts and spacers to fit the chainguard outboard of the chainring (closer to the crank).

So it isn't obligatory to put my Surly chainring in the inner position ? (if i want to add a Thorn bashguard)

But how can i mesure if i have enought room between crank and chainring ?

John, maybe another day about to install a Chainglider, however i'm afraid to hear noise and also i like to see my chain 

[mickeg]

...
But i noticed one thing.. if i add a chainguard, my chainring will take the inner position and it will touch my plastique bottle   
...

If you bottle cage is one that can't be bent a bit to the side, buy a different cage that can.

If the cage is robust and hard to bend, take it off the bike and bend in a vice to avoid damaging the cage bolt fittings on the frame.

[martinf]

So it isn't obligatory to put my Surly chainring in the inner position ? (if i want to add a Thorn bashguard)

But how can i mesure if i have enought room between crank and chainring ?

No, you can fit the bashguard outboard.

You need the gap between the edge of the chain and the crank to be wider than the bashguard, ideally at least width of bashguard plus 2 mm each side to allow clearance between bashguard and chain and bashguard and crank.

I ran a chainguard outboard of the chainring on an old TA crankset with a single ring and rear derailleur gears to prevent the chain unshipping when shifting.

Old TA has a narrow gap compared with most modern cranks, but the chainguard wasn't very wide either.

[jul]

Ok fine.

So maybe i'll need to play with spacers to adjust clearance ..

I receive my Surly chainring soon, i will see better once at home, but i have not ordered yet the bashguard, i'm afraid not being able to install it. 

[martinf]

So maybe i'll need to play with spacers to adjust clearance ..

Probably. In the past I have sometimes filed down the aluminium alloy spacers on old TA chainsets to reduce the gap between 2 chainrings (for example to fit a triple on a fairly short bottom bracket axle or to improve shifting and chainline for the large and middle rings on a half-step triple).

Another possibility is to use a stack of washers instead of the spacers, done this to fit a chainguard outboard of a single chainring on a 5-arm crankset.

You will probably also need longer chainring bolts.