Back pedaling/reversing causes gear down shift

[martinza]

Whenever I'm in the lowest (biggest) gear (1x10 Shimano Deore) and I either roll back or pedal backwards, my chain starts to climb down the casette towards the highest (smallest) gear.

 

This is bloody frustrating if you're on a steep uphill, you stop or fall over, try to align the pedals to get going again and then KACHRKIKIGHIGK!!!: the chain was 5 gears down and you just put full power on to get going.

 

It does look like the wheel is correctly aligned. The gear shifts up and down are really smooth.

 

Any reason why this happens, and ideas on how to remedy?

[DR ◣◢]

Was this an issue from the start or a recent development?

[capediver]

Guessing here but maybe look at adjusting the B screw on the derailleur....this happened to me on a previous bike and found the B screw adjustment was way out...just before you do try, note the present setting and number and directions of turns so you can reset it back if it's not the issue.

[Butterbean]

Might be chain line related, had this issue before.

[DR ◣◢]

Had this with a KMC chain that had some wear. Reason i’m asking if it did it from the start.

[martinza]

It is second hand bike that has done this from the start. But chain wear is something I should check then, thanks.

 

I was also thinking it has to have something to do with chain line. As the deraileur is guiding nicely when going forward, but there is nothing to guide when going back, so in some ways it makes sense that the chain would want to go to whatever position is "0" alignment with the chain ring...

[Quagga]

Measure from the center of your seat tube to the chain ring. If more 50mm then your chain ring is not in the correct place.

 

Maybe people doing 1 x conversions uses the wrong chainring or does not use the correct spacers

 

Or if you have a long straight edge. Place it against the cog in the middle of the cassette. Let’s say gear 5/6 and you chain ring should be inline with that cog.

[martinza]

Measure from the center of your seat tube to the chain ring. If more 50mm then your chain ring is not in the correct place.

 

Maybe people doing 1 x conversions uses the wrong chainring or does not use the correct spacers

 

Or if you have a long straight edge. Place it against the cog in the middle of the cassette. Let’s say gear 5/6 and you chain ring should be inline with that cog.

 

Okay, the straight edge route makes sense, I'll try that. But if it is straight in the middle, gear 5/6, would it not make sense then to drop when not guided by the derailleur? The bike is a stock standard Trek Stache 5, I expect they would have the spacers right. 

[DieselnDust]

Whenever I'm in the lowest (biggest) gear (1x10 Shimano Deore) and I either roll back or pedal backwards, my chain starts to climb down the casette towards the highest (smallest) gear.

 

This is bloody frustrating if you're on a steep uphill, you stop or fall over, try to align the pedals to get going again and then KACHRKIKIGHIGK!!!: the chain was 5 gears down and you just put full power on to get going.

 

It does look like the wheel is correctly aligned. The gear shifts up and down are really smooth.

 

Any reason why this happens, and ideas on how to remedy?

 

 

this is normal for 10speed and 11speed drive trains. They were never designed to cope with the extreme chain angles of 1x.

There is no easy remedy either as a narrower chain with make the problem worse. The best remedy is a dedicated 1x12 drivetrain

[PhilipV]

My shimano 1x conversions have always done this. 10dp and eleven 11sp.

I was warned about it before I did the conversion, but adapted to it quickly enough that it became a non-issue.

[ChrisF]

Interesting ....

 

 

Currently have 3 bikes that are 1x11 Shimano.  One bought new like this.  They other was bought as a 1x9, and changed to 1x11.  Third bike was a 3x9 bike, changed to 1x11.  

 

None of them drop a gear when back pedalling.

[DieselnDust]

Interesting ....

 

 

Currently have 3 bikes that are 1x11 Shimano.  One bought new like this.  They other was bought as a 1x9, and changed to 1x11.  Third bike was a 3x9 bike, changed to 1x11.  

 

None of them drop a gear when back pedalling.

What is the size of the largest sprocket on the cassette

[DR ◣◢]

Same on my side. No issues in the past with 1x conversions. 

 

My 1x12 with the Sunrace, KMC, and SLX derailleur was the first. It stopped when I switched to the XTR derailleur and XTR chain. Still on the Sunrace cassette. 

 

My money is on chain line. 

 

Edit: Trek Stache 5 is a boost 148 frame with stock 1x10 drivetrain. 

Is the front chainring still the original? I think it was a 28t FSA. 

If this was changed then the wrong chainring could have been used which will cause a chain line issue.

Edited January 26, 2021 by DR ◣◢

[Mojoman]

My shimano 1x conversions have always done this. 10dp and eleven 11sp.

I was warned about it before I did the conversion, but adapted to it quickly enough that it became a non-issue.

I have this issue but only when the bike is on the stand and I turn the crank backwards to clean and lube up the chain...on a ride I have no problems....

1 x 10....

[ChrisF]

What is the size of the largest sprocket on the cassette

 

Uhm ....    I seem to recall ....

 

Giant - 36 front, 42 rear

 

Titan - 30 front, 46 rear

 

Mongoose - 32 front, 50 rear

 

PS - last two are 26" with shorter chain stays, so should have even worse chain angles.

[MrJacques]

Why are you pedaling backwards?