What am I doing to cause my rear gears to slip?

[nickAKA]

It may be a fault that only the owner can replicate ,so the bike shop are unaware of what is happening. A usual no fault found, intermittent fault which is hard to pin down unless it happens when they are trying it out.
It sounds more likely that it is the freewheel slipping as I don't see how the chain would slip under normal conditions.
Perhaps the owner could ask the shop to check that it isn't the freewheel which is faulty. A simple solution would be to swap the wheel for another and see if it happens again.

Is the freehub slipping or is the chain skipping between cogs / jumping gears? it sounds like the latter to me but really need clarification...

 

[T675Rich]

Is the freehub slipping or is the chain skipping between cogs / jumping gears? it sounds like the latter to me but really need clarification...

I am not 100% sure but it feels and sounds like the chain is skipping between cogs, if it was the free wheel slipping would it only happen in a couple of gears? For example 1-1 is fine.

Can I ask what LBS means, I assume BS is bike shop but can't work out the L.

 

[vickster]

I am not 100% sure but it feels and sounds like the chain is skipping between cogs, if it was the free wheel slipping would it only happen in a couple of gears? For example 1-1 is fine.

Can I ask what LBS means, I assume BS is bike shop but can't work out the L.

Local

If the bike is new, get them to diagnose (on stand or riding) and fix

 

[guitarpete247]

Whilst on work stand they won't be able to apply as much force through the pedals as when you are on the road pushing uphill etc.

 

[nickAKA]

I am not 100% sure but it feels and sounds like the chain is skipping between cogs, if it was the free wheel slipping would it only happen in a couple of gears? For example 1-1 is fine.

So it's a triple ring on the crank, 8 speed cassette on the rear - let's assume you're in the 'big ring' (hardest) on the crank/front - can you change between all 8 gears on the rear cassette without the gears slipping/skipping?

 

[T675Rich]

So it's a triple ring on the crank, 8 speed cassette on the rear - let's assume you're in the 'big ring' (hardest) on the crank/front - can you change between all 8 gears on the rear cassette without the gears slipping/skipping?

Aye 3 at the front and 8 at the back. I can't say I have tried the full range with the big ring on the front as I usually have a decent pace up for I ever change into that so I usually have the back already quite high before I change. I'm not on the bike today so I think I will ride it to the LBS and try all the gear combos to see what happens.

 

[nickAKA]

If it's skipping lower range gears on the cassette in all the crank rings, I'd suggest resetting the rear derailliur from scratch (paying interest specifically to the cable tension) - it's not that difficut, just follow the GCN video earlier in the thread.
If it's just the smaller rings on the crank that are problematic, it might bring the front mech into play but would be exacerbated by poor setting on the rear derailliur. Is the chain noisy / does it rub on the front mech?

 

[Illaveago]

A stiff chain or lack of tension in the rear mech might cause the chain to jump the teeth on the sprocket but I would have thought the shop would have found that out straight away. It could help if you narrowed down which gears and situation create the problem.
Whatever the case I still think that it is a problem that the bike shop should sort out.

 

[roadrash]

Give it back to the shop and tell them to not bother ringing you until its right or if they cant manage that ask for a refund

 

[T675Rich]

If it's skipping lower range gears on the cassette in all the crank rings, I'd suggest resetting the rear derailliur from scratch (paying interest specifically to the cable tension) - it's not that difficut, just follow the GCN video earlier in the thread.
If it's just the smaller rings on the crank that are problematic, it might bring the front mech into play but would be exacerbated by poor setting on the rear derailliur. Is the chain noisy / does it rub on the front mech?

The chain doesn't rub on the front derailleur in any gear.

A stiff chain or lack of tension in the rear mech might cause the chain to jump the teeth on the sprocket but I would have thought the shop would have found that out straight away. It could help if you narrowed down which gears and situation create the problem.
Whatever the case I still think that it is a problem that the bike shop should sort out.

Gears 1-2 and 1-3 are the worst when going up hill, I don't use them on flats generally. 1-4 does it occasionally but above that is fine but I don't use them on some of hills as it is too hard.

I am going to the store tomorrow.

 

[screenman]

Am I the first to mention rear mech alignment, a common cause for slipping gears and one most people do not check, it should be the first thing to do. No point in trying to adjust something that is not lined up correctly.

 

[si_c]

A stiff chain or lack of tension in the rear mech might cause the chain to jump the teeth on the sprocket but I would have thought the shop would have found that out straight away.

It would also happen in all gears and every time the chain completed a loop, so easily identified.

To my mind there are a couple of things that you can check immediately to see if you can fix it.

1. Is the wheel properly seated at the back? Loosen the quick releases and wiggle the saddle side to side a touch and make sure that the axle for the rear wheel is located securely in the dropouts (the bits that hold the wheel in place). Then tighten up the quick release again - you don't need to unscrew anything, just use the lever. If the wheel drops into place at all, then that was likely the problem - you may now need to adjust the barrel adjuster on the rear derailleur as the gears will likely be worse now. (see this handy video)
   
2. The rear derailleur hanger is bent. This is very rare on a new bike, but it can sometimes happen if the bike was knocked during transit - if it is bent then the bike shop will either replace it with a new one (they're designed to break to stop something more expensive getting damaged) or they can realign it (bend it back into place). You can check this visually yourself by looking at the back of the bike. See this handy picture as a guide.
3. The cable tension is incorrect. This is by far and away the most likely scenario. I've had my bike running through the gears perfectly in the stand, not a missed or bad gear change. Once on the road though the whole system is under tension so things change - it's not the fault of the bike shop it worked for them - but it does mean that an adjustment needs to be made. Fortunately if you've watched the first video I linked to above, then you'll know how to fix it as it goes through all the things you need to do. If you're out on the road though you can usually fix it by turning the rear barrel adjuster a quarter turn in one direction and seeing if that fixes it, if not then try another quarter turn in the same direction and keep going until it's working ok, if it gets better but not perfect then next time you turn it, turn it half as much, if it gets much worse then turn it back in the other direction instead. It is very difficult to break anything doing this so you have nothing to lose.

 

[screenman]

You cannot check rear mesh alignment by eye, also it is very common for a new bike to have a much that is not aligned.

 

[gbb]

When my Bianchi Via Nirone C2C was quite new it did suffer from a slipping freehub occasionally, particually under load. A sudden loss of traction, cranks suddenly lurching forward for a split second, it's a difficult thing to explain exactly. No noise that shouldn't be there, no sense of the chain jumping cogs, changing gears, just a sudden loss, then re-engaging of drive.
It happened for a couple of months, very Intermittently, then went away never to return.

It's unusual tbh, but not impossible.

 

[Globalti]

Sounds like heavy grease causing the pawls to stick.