TromboneAl

I put a new and different (Willful Neglect Corrosion resistant chain) on my bike, and got a chain skipping problem that only occurred when I had a 38 tooth chainring as my small ring on the front. Switched back to a 39-tooth chainring, and the problem disappeared.

I can either stay with this setup, or get a new chain, put the 38T back, and try to resolve the issues.

The climbing seems slightly harder with the 39T, but perhaps that's just a placebo thing. It's only one gear inch different.

Do you think climbing really is harder with the 39T? Should I just HTFU?

Are there advantages to a 39 tooth ring?

Please do not respond with "Do whatever YOU want to do, why do you need us to tell you?"

Front: 39, 53
Rear: Shimano HG51 8-Speed Cassette (11-28T)

fietsbob

shall we bring another mattress, princess, is that pea still bothering you?

Gerryattrick

Phew! I thought it was another bike accident thread.

Number400

Ha! Yuck, yuck , yuck!

NOS88

It seems possible that the smaller circumference of the 38 makes a difference. If a link were just a bit stiffer than the others it might cause it to skip. But, I’m not sure this makes complete sense, because the rear cog has much smaller circumferences than your 38 up front. I’ve got to tell you, this is one that would drive me crazy until I knew why what was happening was happening. The other possibility is that new chain ring is not designed to work with your current setup. Is the new one designed for an eight speed system? In terms of should you just HTFU, you can do that with a 38 or 39 tooth up front if that's your goal. Just push harder. But, your post leads me to believe you want the 38.

oldbobcat

Or the smaller circumference of the 38 may have caused the chain to hit a chainring bolt that was machined just a little too close to the valley between two teeth. For one tooth, you can guess at my recommendation.

TromboneAl

My current theory is that sometimes the wider chain hadn't shifted all the way over onto the small chainring when I applied pressure. Perhaps the 9-speed I had prior to that shifted faster, so it was never "in between" when I mashed.

The 38 tooth ring (got it used from LBS box) has this on it: FSa 38T 130 mm BCD 7075/T6

Tell me how an 8-speed chainring would be different from a 9-speed.

Thanks,

Al

NOS88

9 and 10 speed chainrings have the teeth ever so slightly farther to the right than a 6, 7 or 8 speed chainring (according to Sheldo Brown that is:https://sheldonbrown.com/speeds.html) . Try flipping the chainring and see that that solves the problem.

Dudelsack 

Either way is a dumptruck full of awesome. It's all good. YMMV.

B. Carfree

Are you sure the 38T ring isn't just so worn that it can't properly hold the chain? By the time the teeth get pointy, it's long gone.

As far as which would be the better choice between 38T and 39T, there are two things I consider.

1. Is my low gear low enough for me?
2. Which one creates the greatest "gap fill" gearing relative to the big ring. Graph the gear inches with a log scale and see where the 38T and 39T gears sit relative to your big ring.

TromboneAl

Oh, that''s a neat idea.

Yes, the 38t one isn't worn.

I'll look into those other things and ride for a while with this.

skilsaw

What solution costs the most money?
Go with that. Isn't that what cycling is all about anyway?

oldbobcat

This certainly cuts to the chase. Thanks.

B. Carfree

Oh drat. Yet another thing I've been doing wrong all these years.

jyl

HTFU is clearly the answer :-)

It'll make a man out of you!

rydabent

b carefree +1

The simple answer is that the 38T chain ring may just be worn out. One tooth smaller is no reason at all that the chain has problems. Just look at it logically. Look at all the 30 tooth grannies and smaller that work fine if not worn.

TromboneAl

True, that would be a good explanation. But it just doesn't look worn enough to me -- what do you think?

big john

If the chain is worn to the 39 it might skip on a new ring. If you buy a new chain you might need a cassette, too.

oldbobcat

My money says the skips are happening when rollers of the chain pass through the valleys that are directly over bolt holes, especially the one at 1 o'clock in the top photo. Notice what looks like extra wear between those teeth. Then notice the imprint left by the crank spider where it is attached. The chain is riding so low that plates are hitting the end of the crank spider, causing the chain to jump. It doesn't happen on the 39t ring because the ends of the crank spider are farther from the chain.

A chain with worn rollers will ride even lower, exacerbating the effect. Get a new 38t ring, preferably one with all the bolt holes beneath teeth instead of valleys. Or, if you insist on using this ring, file a half-millimeter or so of material from the ends of the crank spider so the chain will clear it, if you're not at all worried about compromising the strength of the crank. I'd be worried, though.

NOS88

Good eye!

oldbobcat

There's a reason why most chainring manufacturers stop at 39t on a 130 mm crank. Clearance.

Just because somebody makes a part doesn't mean it will work. Well maybe it will, for some applications, for that short window when everything is brand new.

fietsbob

with a 53t big ring , 39t is 14 less.

TromboneAl

OK, that's a theory worth throwing some money at, and I'm finally understanding what ThermionicScott said in another thread. I might just put the 38T back on to eyeball it and see if that's what's happening.

The problem didn't happen until I put a new chain on (8 speed instead of 9), but perhaps that new chain is slightly different.

fietsbob

TA, in 110. sells a 33t chainring , to use it they machine the ends of the crank spider with a clearance notch..

the clearance modification , can be done with a steady hand and a sharp file. .. in this case as well..