Cannot seat into low gear when climbing

[Maherees]

Hi all,
this has defeated some of the finest minds today on our bike ride and is something I have wrestled with a good part of the year.
I have a Sram Rival 1 set up whereby my actual largest cog on the rear seems to be bigger than my chainring, anyway no matter how many times I reindex on the bike, on the stand, when I'm actually out on the road and have to go up a steep hill I have great difficulty selecting the lowest gear - it seems to jump out and in, so eventually i have to select a higher gear - which really is not desirable.
I'd appreciate any pointers?
Thanks

 

[DCBassman]

If indexing won't fix it, likely something is bent, the mech hanger usually.

 

[Maherees]

If it was would i need to buy a new one or can it be fixed?

 

[T.M.H.N.E.T]

Is it being limited by the limit screw

 

[Ajax Bay]

Size of chainring (just one)
Range of cassette please? ie 11-34
On the stand with the cable unclamped and 'L' limit screw unscrewed a turn, can you push the derailleur cage so it touches the spokes?

 

[Maherees]

The cassette is a SRAM Rival 11-42T and the chainring is 40T. I have checked the L and H screws quite a few times. BUt of course, setting it up on a bike stand is not the same as using out on the road.

 

[Ming the Merciless]

What’s the angle of the derailleur cage with it in bottom gear? Is the chain line correct?

 

[Maherees]

I'll have to check that tomorrow when I out it back in workstand.

 

[Ming the Merciless]

If you can post some pictures from the side and front and back that’d help.

 

[roubaixtuesday]

Follow this to the letter would be my suggestion.

https://www.parktool.com/blog/repair-help/rear-derailleur-adjustment

Most likely causes IMO

L screw
Cable tension
Wear: jockey wheels, chain (in that order)
Damage: hanger, derailleur (in that order)
Wear: derailleur

Just guessing of course.

 

[SkipdiverJohn]

The frame is flexing under load.

 

[Lovacott]

My gears behave very slightly differently under load so after indexing at home, I take the bike for a spin with a few hills chucked in and make minor adjustments on the road. You should only be talking about a quarter of a turn of a limit screw and/or a barrel adjuster at the most.

 

[raleighnut]

I'd go for frame flex too, add in the awful chainline of a 1x gear system in the innermost cog and I'm not surprised 0ut jumps out of gear under heavy loads then re-engages when the load is less.

 

[Gunk]

My gears behave very slightly differently under load so after indexing at home, I take the bike for a spin with a few hills chucked in and make minor adjustments on the road. You should only be talking about a quarter of a turn of a limit screw and/or a barrel adjuster at the most.

I set up first on a stand and then pop the bike on a Turbo to finish off the final indexing adjustments. You’ll be surprised with the difference riding under load makes, what feels perfect on a bike stand is completely different when ridden under load.

 

[figbat]

This is why I put the Tiagra shifter with barrel adjuster on my 1x10 gravel bike build, so small adjustments are easy to make on-the-fly.