Chain length on shimano axs

[Sander23]

What's the proper way of sizing your chain when running shimano with axs?

On my old drivetrian I just kept the chain on 121links.
Now I replaced my chain and followed the shimano method biggest sprocket + chainring +6 link is about 126 links.
Put the chain on and adjusted my bgap to 41mm ND my chain looks like this
View attachment 20240522_201928.jpg
Imo this doesn't look right chain looks like it's to big.

Maybe bgap wrong?

 

[steve_sordy]

There are at least six different ways to do it, but for all of them, you need to fully compress the rear suspension to check that the any rearward movement of the axle during compression does not overtighten the chain. If you don't, a deep compression might rip the mech clean off.

I do this:

Put the chain on the largest cassette gear (assuming a 1x set up). Adjust the chain so that the lower mech arm is pointing forward at 45 degrees. For hardtails it's job done, but for full suss you need one more step: the shock compression.

Either let out the air in your shock or get a heavy mate to compress the bike for you. I think it's better to let the air out because then there is no heavy weight tensioning the chain and maybe damaging the mech. If the bike suspension is of a type where the rear axle moves rearward during compression then the chain will tighten and move the mech. As long as the suspension can be fully compressed without jerking the mech you're good to go. Otherwise, you need to add two 1/2" links and test again.

This may still end up with a chain that looks a bit slack, but at least you know that you are not going to rip the mech off.

 

[BuckSaw]

The quickest way to size a new chain (assuming that you haven't changed to a different sized cassette, chainring, or derailleur) is to lay the new chain out beside the old chain and remove links from the new chain. I do this when I'm working on my own bike. If I'm working on a customers bike I typically follow the chain sizing procedure of whatever chain I'm installing. Your chain does look like it has one too many links though, and by links I mean an inner and outer link. I would do what @steve_sordy suggested and confirm the chain length through the suspension travel before removing links. If it's still slack at full compression I would remove a link and check again. I haven't seen a written procedure for chain sizing when mixing Shimano and SRAM drivetrain components.

 

[Sander23]

I have never had a bottom out on the 51T, usually when I have a bottom out I'm half way or up to the smallest sprocket.

Can the mech get ripped off when I'm in the smaller sprockets if the chain is to short?

I'm afraid that I'll get alot of chainslap when it's like this.

 

[steve_sordy]

I have never had a bottom out on the 51T, usually when I have a bottom out I'm half way or up to the smallest sprocket.

Can the mech get ripped off when I'm in the smaller sprockets if the chain is to short?

I'm afraid that I'll get alot of chainslap when it's like this.

It's a calculated risk. You will be balancing one thing against another. You know how and where you ride better than anyone else.

 

[Sander23]

It's a calculated risk. You will be balancing one thing against another. You know how and where you ride better than anyone else.

I don't want to cut it to short because it's an expensive xtr chain.
This is the length with full travel.

Chain on the biggest sprocket

Chain on the 2nd largest sprocket

 

[steve_sordy]

@Sander23
That's a new one!
It had never occurred to me not to cut a chain to the correct length just because it was an expensive one.

PS: You don't have to throw away the bit you cut off, keep it in your pack for when you damage the chain. Doing so has saved me many a time from a walk home (or somebody else).

 

[Sander23]

@Sander23
That's a new one!
It had never occurred to me not to cut a chain to the correct length just because it was an expensive one.

PS: You don't have to throw away the bit you cut off, keep it in your pack for when you damage the chain. Doing so has saved me many a time from a walk home (or somebody else).

I meant cut it to short.

 

[steve_sordy]

I meant cut it to short.

Then add back in the bit you've cut off! Magic links are just that, magic!

 

[Shark58]

This is the length with full travel.

Looking once again at the fotos you provided I believe I now found the reason for your slack chain.

The process to determine correct chain length is very similar for SRAM or Shimano.

• compress the shock to reach maximum length of your chainstay
• mount the chain on the largest sprocket and the largest chainring, but don’t thread it through the derailleur
• add a defined number of links at the connection point following the guide

See screenshots from Shimano manual:



It looks as if you have done the measurements with the chain through the derailleur and that will give you a much longer chain.

About B-Gap adjustment.
Best practice recommendation for mixed installs is to use the process from the manufacturer of your cassette and chain. This will ensure smooth shifting. And in B-Gap adjustment SRAM and Shimano do differ. Unfortunately you can’t use the easy way for Shimano, because you don’t have a Shimano derailleur with its markings. You will need to use the old method by shifting to the largest sprocket and then position the rear wheel so that the lowest tooth of the sprocket is opposite the highest tooth of the pulley. Measure the distance between both teeth. Adjust the B-Screw to set that distance to 5-6mm.

 

[Sander23]

Looking once again at the fotos you provided I believe I now found the reason for your slack chain.

The process to determine correct chain length is very similar for SRAM or Shimano.

• compress the shock to reach maximum length of your chainstay
• mount the chain on the largest sprocket and the largest chainring, but don’t thread it through the derailleur
• add a defined number of links at the connection point following the guide

See screenshots from Shimano manual:
View attachment 141130
View attachment 141133

It looks as if you have done the measurements with the chain through the derailleur and that will give you a much longer chain.

About B-Gap adjustment.
Best practice recommendation for mixed installs is to use the process from the manufacturer of your cassette and chain. This will ensure smooth shifting. And in B-Gap adjustment SRAM and Shimano do differ. Unfortunately you can’t use the easy way for Shimano, because you don’t have a Shimano derailleur with its markings. You will need to use the old method by shifting to the largest sprocket and then position the rear wheel so that the lowest tooth of the sprocket is opposite the highest tooth of the pulley. Measure the distance between both teeth. Adjust the B-Screw to set that distance to 5-6mm.

Thanks that's usefull info. On the bgap side

First picture is chain only on the biggest sprocket and chainring and shock fully compressed.

Seccond pictures where to show the bgap distances.

But according to those pictures my chain should be even longer?

If I measure it on biggest sprocket and chainring without any full shock compression I measure 6 links

 

[Shark58]

First picture is chain only on the biggest sprocket and chainring and shock fully compressed.

You mean on this photo the chain does not go through the derailleur and around the two pulleys?

The B-Gap on the second photo is clearly much larger than 5-6mm.

 

[Sander23]

You mean on this photo the chain does not go through the derailleur and around the two pulleys?

The B-Gap on the second photo is clearly much larger than 5-6mm.

Yes that's what I mean.

The bgap on 5-6 mm is way off on this setup.

 

[Shark58]

Did you find a solution?
What bike is this, make, model, year? And what was the original drivetrain before you put the Shimano 12x plus SRAM AXS on?

For comparison I took some pictures from my bike. This is a pure SRAM AXS install with chain length checked by the SRAM method. Chain wrapped around largest sprocket and chainring without going through the derailleur, pulling both ends tight and adding two links where overlapping started. This is one inner and one outer link, making it much shorter than the Shimano process. After then threading the shortened chain through the derailleur and closing it, this is what it looks like (ignore the mud, we had a lot of rain recently):

Largest sprocket (52t), gear 1


Smallest sprocket (10t), gear 12

 

[Sander23]

Did you find a solution?
What bike is this, make, model, year? And what was the original drivetrain before you put the Shimano 12x plus SRAM AXS on?

For comparison I took some pictures from my bike. This is a pure SRAM AXS install with chain length checked by the SRAM method. Chain wrapped around largest sprocket and chainring without going through the derailleur, pulling both ends tight and adding two links where overlapping started. This is one inner and one outer link, making it much shorter than the Shimano process. After then threading the shortened chain through the derailleur and closing it, this is what it looks like (ignore the mud, we had a lot of rain recently):

Largest sprocket (52t), gear 1
View attachment 141366 View attachment 141367

Smallest sprocket (10t), gear 12
View attachment 141369 View attachment 141370 View attachment 141371 View attachment 141368

My bike is a haibike fullnine 10, came with shimano xt slx with a chain of 121 links.
Now the chain is 126 links using the sram method with sag( wich was 1 link shorter then the shimano method).

I tried adjusting it to 5-6 mm but that doesn't work. I adjusted it till I had some good tension and came on a 41 mm

That last picture of yours has alot more then 5-6 mm or am I wrong?

The chain tension is good now I think. I did had to adjust the micro adjust up to 22 though( on my previous cassette it was at 15)

 

[Shark58]

That last picture of yours has alot more then 5-6 mm or am I wrong?

Probably due to the odd angle of view. Also the chain gap is measured with the shock in the sag position but my photo was taken without any weight on the bike.

Here is a very good instruction video from SRAM‘s YouTube channel. Measuring chain length starts at minute 3.

I checked the geometry data for your bike and it has a really long chainstay (477 mm). With that and 38t chainring plus 52t sprocket the chain length calculates to 224 or 226 links including the lock. The only difference from the original Shimano system is the largest sprocket having 51t. This should not need a shorter chain. Not clear why your original has only 121 links. It must at least have been 122 because you can’t have an uneven number of links in a closed chain.