I simultaneously replaced my worn cassette, chainrings and chain on my road bike, but I’m experiencing an issue, whereby the middle chainring skips whilst running one of the two smallest sprockets on the cassette. It seems that the chain wants to move onto the large chainring.

The chainline seems fine – the chain sits pretty straight when in the middle chainring and one of the two middle sprockets on the cassette. I’m pretty sure that I have set the gears up correctly. Moreover, the issue was never present with the old components.

In terms of the components, I was previously running a 5600-series Shimano 105 triple set-up. As 5600-series is no longer in production, most of the replacements came from the 5700 series. Nonetheless, as far as I checked, all parts should be fully compatible.

Cassette:
Old: Shimano 105, CS-5600, 10-speed, 12-25T
New: Shimano 105, CS-5700, 10-speed, 11-25T

Chainrings (running on FC-5603 crankset):
Old: Shimano 105, FC-5603, Triple, 30T, 39T, 50T
New: Shimano 105, FC-5703, Triple, 30T, 39T, 50T

Chain:
Old: Shimano 105, CN-5600
New: Shimano Ultegra, CN-6600

By the way, I do appreciate that you shouldn’t run your chain in the two smallest sprockets while in the middle ring, but it’s more of a safety thing here. Inevitably, sometimes you end up in those gears, and when the chain skips, resistance disappears from under your feet, which can lead to all sorts of sketchiness.

Any ideas??? Thanks in advance.

Absolutely certain that the washers/spacers went back on in the right order on the middle chainring?

Absolutely certain that the washers/spacers went back on in the right order on the middle chainring?

No washers or spacers as far as I could see. Everything was just held together with chainring bolts. Shimano manuals appear to confirm this:

https://si.shimano.com/pdfs/ev/EV-FC-5603-2440B.pdf
https://si.shimano.com/pdfs/ev/EV-FC-5703-3004B.pdf

I reckon you’ll be fine once there’s a few miles on it – my fiver’s on new, (laterally) stiff chain and sharp edges on teeth and ramps/pins and nothing actually wrong

(you sure the chain’s the right length?)

I reckon you’ll be fine once there’s a few miles on it – my fiver’s on new, (laterally) stiff chain and sharp edges on teeth and ramps/pins and nothing actually wrong

(you sure the chain’s the right length?)

Yup, the chain is definitely the right length. I was also hoping that the drivetrain would ‘break in’, but after spending ages researching online, I finally came across this review on eBay:

Typical great Shimano quality, but beware of mixing this with 5603 chainrings

This chainring was bought to replace a worn 5603 39T ring. Since the 5603 rings are no longer available (anywhere!), I had to go to the 5703. Unfortunately, they are incompatible. Along with this ring, I purchased the 30T 5703 ring. After re-building the crankset with the two 5703 rings and retaining the 5603 50T ring, I discovered that they don’t play nicely together. I then consulted with my LBS and they told me they had encountered the exact same problem recently and that, worse, even replacing the 50T ring with a 5703 version wouldn’t solve it, as long as the crank spider was a 5603. According to Shimano, there should be no difference between the 5603 and 5703 spiders, but apparently there is. So I eventually replaced the entire 5603 crankset with the 5703, and of course that works just fine. So now this ring (and the 30T one) are spares – since they are getting harder and harder to find!

https://www.ebay.com/p/Shimano-105-5703-l-39t-X-130mm-10-speed-Triple-Middle-Black-Bicycle-Chainring/1300057350

Did you change the cable and outers?

And also, did you use an old quicklink to join the new chain? If so, buy a new quicklink.

The middle ring is definitely at the correct angle of rotation?

Just adjust the front derailleur with the barrel adjuster until it stops doing it. Do it on the fly if you have a barrel adjuster at the shifter.

Exploded diagrams don’t say that the rings are cross-compatible.

Did you change the cable and outers?

And also, did you use an old quicklink to join the new chain? If so, buy a new quicklink.

The cable outers are pretty new, but I don’t think they’re at fault here. No quick link, just using the Shimano pin.

The middle ring is definitely at the correct angle of rotation?

Visually, yes, but, of course, it’s very difficult to tell. I suspect that the there may be subtle differences in the FC-5603 and FC-5603 crank spiders, which may be at fault.

Just adjust the front derailleur with the barrel adjuster until it stops doing it. Do it on the fly if you have a barrel adjuster at the shifter.

Definitely not the cause of this. The problem persists even when the chain isn’t touching the front derailleur cage at all.

Is the middle chainring the right way round, i.e. the shifting pins on the inside to lift the chain from the small ring to the inner?

Also if the chain, cassette & rings were so worn they needed replacing you should probably swap the jockey wheels too as they won’t okay nicely with a brand new chain

Exploded diagrams don’t say that the rings are cross-compatible.

This is a very good point, I haven’t noticed the Interchangeability table previously. Definitely a point to note for the future. Thanks for pointing this out!

So I guess that it’s becoming increasingly apparent that the FC-5603 spider is simply not compatible with the newer FC-5703 chainrings. So annoying, looks like I’m going to have to shell out on a new chainset 🙁

So annoying, looks like I’m going to have to shell out on a new chainset

You’ll probably find a new chain set is cheaper than new rings anyway

Is the middle chainring the right way round, i.e. the shifting pins on the inside to lift the chain from the small ring to the inner?

Also if the chain, cassette & rings were so worn they needed replacing you should probably swap the jockey wheels too as they won’t okay nicely with a brand new chain

Yup, I followed the installation instructions to a t. All of the markings are in the right places. As for the jockey wheels, no, I didn’t replace them, but they look very unworn. Could be a factor of course, but I really don’t think that it’s at the core of the problem in question.

You’ll probably find a new chain set is cheaper than new rings anyway

…but sadly I already purchased the rings and it’s too late to return them, as they sat in my spares draw for about a year. I guess they’ll spend another year plus in there now, haha.

Try spacing the big ring out, or the whole chainset?

If you’re CBA.

Try spacing the big ring out, or the whole chainset?

If you’re CBA.

It could work, but I don’t think I want to go down that rabbit hole. I may never be able to get it to work perfectly. I’m still confused by why the rings aren’t interchangeable as they seem to fit perfectly. Anyway, a new chainset has been ordered.

Did you try rotating the middle ring? I’m just wondering if it’s that the shifting ramps/pins are fussy.

Guessing that the spider tabs are different thicknesses 5603 vs 5703.

Did you try rotating the middle ring? I’m just wondering if it’s that the shifting ramps/pins are fussy.

Nope, I haven’t tried that.

Guessing that the spider tabs are different thicknesses 5603 vs 5703.

That’s also what I thought, but once the chain is on the desired ring, it should work fine, regardless of which rings you use. As I said, the chainline looks fine. My guess is that the ring doesn’t rotate perfectly straight when installed on the old spider.

Did you try rotating the middle ring? I’m just wondering if it’s that the shifting ramps/pins are fussy.

How can the pins on the middle ring cause an issue when the chain is on the middle ring?

Pardon my brevity. I was referring to the configuration of ramps and pins on the chainset as a whole.