pgoat

I did some searches and saw lots of threads but still have questions about my commuter bike:

mountain bike, bought new in 1993, used offroad lightly/moderately for a few years and then put away for a decade or so.

I pulled it out in early 2006 or so and started using it for commuting. The first thing I did there was swap the fat knobbies for 1" slick tires; by summer 2007 I realized the original 7-spd gearing was way too low for street. The original chain was also pretty worn by then, so I took the bike in for a tune up and got a new drivetrain:

we swapped the gearing from the original 46/36/26 crank up front to 46/35/24. The original cassette was a wide-spaced 13-30t Shimano Hyperglide "G", which I switched to a close spaced 13-23t. We used a new chain, of course...just a basic OEM brand.

I mostly live in the middle ring as my commute is only 7 miles and mostly stop and go, with tons of traffic lights, stop signs, traffic and peds to go around, etc. I have little chances to use the big ring and I do need to save my knees (I'm 44) so I started using the granny ring twice a day to cross a bridge over the East River. I had been using the 36x30 before but wanted a closer spaced cassette for the street....So we kept the 24t granny and swapped the rear for a narrow Shimano Hyperglide "I-L", 13-23.

After a few months riding (all new chain, chainrings, cassette), mostly commutes and one or two metric centuries, possibly 500 miles, tops, I decided in the fall of 2007 I still wanted higher gears. I bought a backup wheelset and put a 12-21 Hyperglide cassette on there and have been using that ever since.




Fast forward to the present: about a month or so ago I started having skipping when I stood up to honk (starting off at lights, accelerating past cars, etc.) in the 35x12. Then it started getting worse, and then started happening in the 46x12 too.

I measured the chain from 2007 and sure enough it is stretched at least 1/8" over. I slapped a new SRAM chain on two days ago and cleaned everything off. To my eye the cassettes didn't look bad, but yesterday on its first run, the new chain was slipping like crazy...I understand that the cog teeth could be worn to the old chain. But today I threw the original 13-23 cassette I got in 2007 on and while it is not as bad, it still slips unless I keep it on the big ring. The 46t seems to work fine with all the cogs, even the 13t. The middle ring works ok with the largest cogs (21t, 23t), but starts to slip even in the middle of the cassette. The granny ring is very slippy unless I am calmly climbing in the 21 or 23. Anything jerky or intense on the pedals and it skips.

My questions:

*I understand how the 12-21 cassette I used from late 07 to early 09 - probably about 2000 miles - could have worn from the old chain. But would the original new 13-23 cassette also be too worn for a new chain? As I mentioned, it has maybe 500 miles or less on it, albeit with a different chain, but one that started out new together.


*would the fact that it is a SRAM chain on a Shimano Hyperglide cassette matter?


*Would the length of the chain have anything to do with this? I was wondering if shortening it would make a difference. I should point out I had no skipping issues until a month or so ago, so I guess that isn't likely. btw, I shortened the new chain I just put on to match the new chain installed in 2007...no idea whether the shop used my old original chain with the 13-30 cassette as a guide or resized big/big, etc.


*Finally, while I have no problem spending the money on a new cassette, I hate to do that if it isn't the real problem...is it possible I just made bad gearing choices here? Maybe I just don't need a granny on this bike, and should just live with the bigger chainrings and get larger cogs?


any sane replies are welcome

ryanwood

in my experience drives train components need to be upgraded simultaneously in order to maintain optimal operating conditions.

There really isn't any fool proof solution for slipping chains, but it sounds like you are still dealing with worn drive train parts not playing nicely with new parts.

It could be somthing like a bent rear dr or dr hanger that is simply being exasperated by swopping out components.

My recomendation is to take it into the shop and ask them to check it out.

Mr. Underbridge

Is it possible that running the new cassette on the new chain wore it out pretty quickly? It's possible that by the time you did your test on the less-worn cassette, the chain had mated to the worn cassette.

As long as you got the correct chain, it shouldn't.

Possible. If the chain's too long, then the derailer might have to open too far to provide tension for the chain. When using the small cogs, possibly combined with a B-screw that's backed out too far, you could end up with fewer chain links contacting the cogs than you'd like. That could make skipping more likely. More importantly, it could also accelerate wear of the drivetrain. You could adjust the B-screw and shorten the chain to an appropriate length to see if it minimizes the effect. I go with enough chain to wrap around the big-big combo, plus two links. However, there's a good chance that you've done damage to the new parts in the interim.

No, those gearing options are legit. They shouldn't skip. That said, you could probably go with larger cogs and larger chainrings, preserving your gear ratios, and have a drivetrain that will be less susceptible to these effects. Say, a 14-27 rear and standard 30/42/52 road triple. But as it is, your gearing is similar to my MTB (except less range in the rear). It should work.

I hate to say it, but I'd probably get a new chain and new cassette, just for peace of mind so you know for sure there's no issues. Just make sure to get the chain length right, and check that B-screw.

m_yates

My advice is to replace the cassette with a brand new one.

I recently replaced the chain on one of my bikes and it started skipping like crazy, but only in the middle gears that are my favorites. I took it to the bike shop, and the mechanic sold me a new cassette. After I put that on, the skipping went away. The mechanic could notice wear on the cogs, even though they looked like new to me.

pgoat

Thanks - just to be clear, I used the brand new chain only one day (14 miles) with the old worn 12-21 cassette, on Tuesday. This morning's 7-mile commute was the maiden voyage for the 13-23 cassette.

I haven't messed with the B screw at all.

I will say that when in the big/big combo the derailleur is stretched with little wrap on the upper pulley, but it isn't parallel to the floor or anything (more like pointing diagonally from 10:00 to 5:00), and the chain is not super taut. In the little/little combo it is hanging lifelessly.

I also should have mentioned; although my bike came with a 13-30, the DX rear derailleur is a short cage (road?) model, stamped Max 28t. would that influence your cassette choices? I factored that in when I originally changed to a close spaced cassette in '07, plus I just like the close jumps on the street....I would have preferred a true one-tooth jump straight block corncob 13-19....but not sure if that is a no-no here?

Mr. Underbridge

Then I might try shortening the chain and seeing how it works with the 13-23 cassette. If you've got that much excess chain, that could be the problem.

pgoat

well, on the way home the big ring slipped not at all and the granny hardly...the middle ring is the one tat was slipping like mad - and I think it was skipping the the chainring...so I am assuming the worn out chain trashed that ring too, since I spend so much time in it.

Guess I'll start checking my chain more often now.

I checked my two road bikes and they both have stretched chains....groan