Setting B gap

[Giff]

With the “new” white SRAM B gap guage does the setting have to be measured in the sag position ?
Has anyone got s suggestion of the best way to put the bike in sag if you are on your own?
Thanks

 

[Pyr0]

let the air out of the shock until it compresses to the sag point?

 

[Mikerb]

The B tension only really has to achieve 2 things. First it it has to be set so that the guide wheel does not hit the largest cog or get so close that the chain jams, and second that is allows just enough chain length between the guide wheel and the largest 2 or 3 cogs to enable is to be directed onto those cogs by the mech. So I have never used a guide tool or set the bike at sag to do that, instead just focused on getting the best gear change, and that varies depending on whether the chain is brand new or "broken in" ( done with the back wheel hanging in a bike rack).
At SAG the rear axle is usually closer to the chainwheel meaning less tension on the mech clutch, so the gap will grow, but some rear triangles actually describe a rearward arc initially applying more tension on the mech clutch. That rearward arc will almost certainly be before the SAG point so it is worth watching the B gap during the shock travel at the begining of its stroke if you have that design. I would do that with the bike on the ground and a suitable weight slung from the saddle.

 

[RickBullotta]

The B tension only really has to achieve 2 things. First it it has to be set so that the guide wheel does not hit the largest cog or get so close that the chain jams, and second that is allows just enough chain length between the guide wheel and the largest 2 or 3 cogs to enable is to be directed onto those cogs by the mech. So I have never used a guide tool or set the bike at sag to do that, instead just focused on getting the best gear change, and that varies depending on whether the chain is brand new or "broken in" ( done with the back wheel hanging in a bike rack).
At SAG the rear axle is usually closer to the chainwheel meaning less tension on the mech clutch, so the gap will grow, but some rear triangles actually describe a rearward arc initially applying more tension on the mech clutch. That rearward arc will almost certainly be before the SAG point so it is worth watching the B gap during the shock travel at the begining of its stroke if you have that design. I would do that with the bike on the ground and a suitable weight slung from the saddle.

My experience has been that using the tool is actually somewhat important. Even if you clear the largest cog on the cassette adequately, I've found that inadequate or incorrect gap will make for slow or inconsistent shifting down to smaller cogs. Worth using the tool. And in terms of sag, this is where having an assistant during the 30 second b tension adjustment process helps a ton.

 

[Giff]

Thanks for the replies and suggestions. I am fitting an SRAM AXS and it seems to suggest that the B setting is quite critical in initial set up.

 

[Mikerb]

My experience has been that using the tool is actually somewhat important. Even if you clear the largest cog on the cassette adequately, I've found that inadequate or incorrect gap will make for slow or inconsistent shifting down to smaller cogs. Worth using the tool. And in terms of sag, this is where having an assistant during the 30 second b tension adjustment process helps a ton.

I agree....I was not saying that tool is not a useful guide but I do not need a tool to assess 10mm or 15mm....I can do that by eye! ...and yes my adjustment is always fine tuned by checking the gear change especially going down the cassette from the largest to probably 3 rd largest cog. I also made the point however that a new chain will be a lot stiffer ( sideways movement) than one that has broken in so the b gap can be different initially and need tweaking after a few rides.

 

[RickBullotta]

I agree....I was not saying that tool is not a useful guide but I do not need a tool to assess 10mm or 15mm....I can do that by eye! ...and yes my adjustment is always fine tuned by checking the gear change especially going down the cassette from the largest to probably 3 rd largest cog. I also made the point however that a new chain will be a lot stiffer ( sideways movement) than one that has broken in so the b gap can be different initially and need tweaking after a few rides.

Interesting - thanks for the tip on the chain stiffness! Just replaced one. I'll follow your suggestion and check it again after a couple rides. Thanks!