[Mattman]

I'm helping a friend build up a Large Surly 1x1 it will have an '03 XT crank and use the ES-71 bottom bracket. Who knows the correct size 73x110, 73x113 etc. Will it make a difference in the correct BB size if the chainring is run in place of the outer ring, or run in the middle position with a bashgaurd in the outer position?

 

[NoWay Ray]

Don't forget to add the trainer wheels, Matt! TR has a balance problem, which I'm not even sure trainer wheels can fix??? He can't wait to get over there though!

 

[Speedub.Nate]

I'm helping a friend build up a Large Surly 1x1 it will have an '03 XT crank and use the ES-71 bottom bracket. Who knows the correct size 73x110, 73x113 etc. Will it make a difference in the correct BB size if the chainring is run in place of the outer ring, or run in the middle position with a bashgaurd in the outer position?

You only have two choices with the ES71 bottom bracket, either 113 or 118mm.

113 will give you a 47.5mm middle ring and 54mm outer ring position.

118 will give you a 50mm middle ring and a 56.5mm outer ring position.

If you want to bump the middle ring out further, you can use the ES51 bottom bracket and run a 126mm spindle, which will get your middle ring out into the 54mm range. The ES51 adds ~50g of weight but is roughly the quality equivalent to a square taper UN50-series bottom bracket, nothing to avoid.

 

[Mattman]

Balance issues

Don't forget to add the trainer wheels, Matt! TR has a balance problem, which I'm not even sure trainer wheels can fix??? He can't wait to get over there though!

I just removed a nice set from my sons bike, not sure if they will reach the ground though. If he's like me though some device to keep the rear wheel on the ground may be needed also.

 

[TR]

Don't forget to add the trainer wheels, Matt! TR has a balance problem, which I'm not even sure trainer wheels can fix??? He can't wait to get over there though!

At least I dont have a 1x1 problem Ray.
When exactly are you going to actually buy that 1x1 that you keep saying is waiting at the shop for you.
At this rate you and I will be sitting at a nursing home together eating mushed up food through a straw and you will be telling this story about your 1x1 that is sitting at the LBS covered in cobwebs just waiting for you to go and buy it.

 

[Mattman]

Thanks, but I'm a bit slow?

You only have two choices with the ES71 bottom bracket, either 113 or 118mm.

113 will give you a 47.5mm middle ring and 54mm outer ring position.

118 will give you a 50mm middle ring and a 56.5mm outer ring position.

If you want to bump the middle ring out further, you can use the ES51 bottom bracket and run a 126mm spindle, which will get your middle ring out into the 54mm range. The ES51 adds ~50g of weight but is roughly the quality equivalent to a square taper UN50-series bottom bracket, nothing to avoid.

OK, so if we want to run an XT crank with a 34 tooth ring mounted in the outer position, are you thinking a 113 will be the better fit. This will be run with a singlespeed freewheel rear hub, so I'm thinking we need to nail the chainline pretty close on the front ring set-up. Basically I'm saying I dont know if I'm better off with a 54mm or 56.5 outer ring position.
I know that a small spacer is sometimes used at the BB to help the chainline. Thanks for the help, we're learning here.

 

[TR]

OK, I am going to ask a question to see if I understand this whole idea.
I am the guy who owns this Surly that Matt is trying his hardest to build in LA while I sit over here in Australia ultimately reaping the rewards.

Stop me if I have this completely wrong (which I just could have).

From reading the section about chainline in the FAQ it seems to say that we are looking for a 52mm chainline in a perfect world??
Therefore any of the 3 options put forward by Speedüb Nate will work but are dependant upon whether we use the middle or outer chainring position.
I assume that 2mm will not even be noticeable.
Is there any real benefit to using either the middle or outer chainring position??

 

[Speedub.Nate]

Basically I'm saying I dont know if I'm better off with a 54mm or 56.5 outer ring position.

That depends on the hub, but if it's 52mm like Too's saying, I'd go middle ring position, 121mm ES51 (puts the middle ring at 51.5mm) and then, depending on how critical your eye is, you could add a .5mm BB shim under the drive side flange to make it polish it off.

But if you want to stick with the 118 ES71, a 2mm difference isn't such a bad thing, and there are 1.5mm BB shims which will help your crank alignment without upsetting your Q-factor too much.