1x12 speed issues

[Kawasicki]

Hello everyone!

So I got myself a nice and cheap Giant XTC bike, that comes with a 1x12 drivetrain.

I am very pleased with it, except for the 1x12 drivetrain. If I shift into the big ring at the back the chainline is so severe that the chain drops off the front chainring. I measured the front chainline offset at 52.5mm...

The bike comes with a 30T Praxis Cadet crankset and a Shimano deore 10-51T cassette.

Have a look at this picture.... How on earth can the chain stay on the front chainwheel. The cross chain angle is nuts! All advice welcome.

[TGCOTF-dewey]

Check the plastic spacers on the bb. It's very easy to use too many, wrong side.

Usually tells you on the bb instructions and most have them online as pdfs.

[Kawasicki]

Cheers!

I will double check that Giant haven’t assembled it incorrectly.

Here is what it looks like up close. Maybe that spring washer seems a little too uncompressed.







The text on the crank near the bottom bracket…

[Master Bean]

Is the chain or chainring worn out?

[irc]

I use one of these on my 1*9 bike to stop the chain falling off to the inside.

https://www.ebay.co.uk/itm/Dente-di-cane-paracaten...

[Kawasicki]

Master Bean said:

Is the chain or chainring worn out?

No, the bike is nearly new.

[Kawasicki]

irc said:

I use one of these on my 1*9 bike to stop the chain falling off to the inside.

https://www.ebay.co.uk/itm/Dente-di-cane-paracaten...

Thanks. Would prefer it if the chain would just stay on. I was expecting a new 1x12 system to be as reliable as all the 2x and 3x systems I’ve used over the decades. Seems that may not be the case?

[Kawasicki]

Just googled 1x12 chain drops and found this…


https://www.reddit.com/r/bikewrench/comments/poj5m...


Maybe the Praxis chainring is to blame?

Just found this…

https://www.reddit.com/r/MTB/comments/pzqhfg/chain...

Edited by Kawasicki on Friday 25th August 05:28

[bobbo89]

Yeah the Praxis chainring uses the same offset tooth system as Blackspire with their snaggletooth rather than your usual narrow/wide. A chainline like that combined with a chainring that essentially pushes the chain over slightly every time it engages with a tooth is really only going to result in one thing.

They're the same fitment as Sram so fairly cheap and easy to swap out with a narrow/wide, just make sure you get the right offset.

[TGCOTF-dewey]

Kawasicki said:

Master Bean said:

Is the chain or chainring worn out?

No, the bike is nearly new.

Ah... I was going to ask if it had been converted from 3x9 which can cause problems.

But you say it's new.

AFAIK with press fit BBs you have no chainline adjustment so it's not a spacer issue.

If it's OE kit that's on the bike, I'd ping giant an email and ask them what their thoughts are - at least it's free.

The reddit post is interesting - no experience of praxxis rings as all mine are narrow wide, which do work.

You do also get a lot of lateral chain movement on a 12 speed by necessity so it may be fine. It's rare you're in 1st gear on a 12 anyway.

In gear 6 is the chain parallel with the front ring?

If it is, then it could well be the ring. Try a cheap narrow wide with the same crank interface as the crank arm - there are many standards to warn you.

[Kawasicki]

bobbo89 said:

Yeah the Praxis chainring uses the same offset tooth system as Blackspire with their snaggletooth rather than your usual narrow/wide. A chainline like that combined with a chainring that essentially pushes the chain over slightly every time it engages with a tooth is really only going to result in one thing.

They're the same fitment as Sram so fairly cheap and easy to swap out with a narrow/wide, just make sure you get the right offset.

Will look into getting another chainring! Thanks for the help!

[Kawasicki]

TGCOTF-dewey said:

Kawasicki said:

Master Bean said:

Is the chain or chainring worn out?

No, the bike is nearly new.

Ah... I was going to ask if it had been converted from 3x9 which can cause problems.

But you say it's new.

AFAIK with press fit BBs you have no chainline adjustment so it's not a spacer issue.

If it's OE kit that's on the bike, I'd ping giant an email and ask them what their thoughts are - at least it's free.

The reddit post is interesting - no experience of praxxis rings as all mine are narrow wide, which do work.

You do also get a lot of lateral chain movement on a 12 speed by necessity so it may be fine. It's rare you're in 1st gear on a 12 anyway.

In gear 6 is the chain parallel with the front ring?

If it is, then it could well be the ring. Try a cheap narrow wide with the same crank interface as the crank arm - there are many standards to warn you.

I would say gear 8 is the most parallel with the front ring. Definitely not 6!

I ride in 1st gear very regularly. I also ride in 12th gear regularly. I live in a steep sided valley!


I really appreciate the help. I will pop a query to Giant!

[GravelBen]

I've also heard stories of Praxis chainrings being prone to dropping chains, but no personal experience of them.

For what its worth chain drops have been very very rare with any of the 1x11 and 1x12 bikes I've had (Sram GX 1x11 & 1x12 and Shimano Deore 1x11).

[TGCOTF-dewey]

Kawasicki said:

I would say gear 8 is the most parallel with the front ring. Definitely not 6!

I ride in 1st gear very regularly. I also ride in 12th gear regularly. I live in a steep sided valley!


I really appreciate the help. I will pop a query to Giant!

I've just checked my son's 12 speed - and it's sat parallel on 8 too.

So almost definitely the chainring then.

[Kawasicki]

TGCOTF-dewey said:

I've just checked my son's 12 speed - and it's sat parallel on 8 too.

So almost definitely the chainring then.

Genuine thanks for your help

[Kawasicki]

That’s a crazy chainline….

[President Merkin]

I'll go chainring too. 1x12 drive is very wide but it's designed in. A good narrow wide chain ring grips the chain to account for the deflection. A chain device can help too, if the bike has a boss for one but you can also buy clamp on versions.

[TGCOTF-dewey]

Kawasicki said:

That’s a crazy chainline….

Same on my son's yeti. Note the more positive narrow wide engagement compared to yours.

[Kawasicki]

Just got a phone call from the bike retailer. They contacted Giant yesterday. Giant were already aware of the issue, they said certain bikes were incorrectly built and they will replace the front chainring with one with a 3mm offset.

Very fair and a logical potential solution, so I am pleased!

[Kawasicki]

TGCOTF-dewey said:

Same on my son's yeti. Note the more positive narrow wide engagement compared to yours.

Absolutely! Though it also looks like entire chainring on your son’s bike is offset a few mm inwards compared to mine!