Bridgestone RB1 chain skips under load
 

Hello All,


I have a Bridgestone RB1 with a GPX rear derailleur. My rear wheel swallowed my derailleur, due to my own negligence.. the years seem to be flying by these days. The derailleur still looks tight, and frame end does not appear distorted. The chain distorted badly and seemed to have absorbed the damage. That chain was labelled SUNTOUR APII, and I couldn't find one on the Internetz. The chain is about 20 years old.. back when I was still handsome. Sooo I Amazon'd a ZONKIE chain that promised Suntour compatibility, and also met the approval of my digital caliper. Now my chain skips under load only on the smallest cog of my 7 speed cassette (Highest Gear? H setting screw sets this threshold). I got the indexing perfect and I ran a matrix of tests on the H setting threshold screw and noticed smallest cog prefers a wider reach (looser H screw), however my ability to return the bike to its former state is a complete FAIL. I'm reaching out for content knowledge.. to rescue a good bike with soul.. before I lose patience and buy a modern bike with parts support.. because --> Covid +19 lbs.


I'm new here, so please forgive my ignorances - Very thankful for relevant advice... I suspect the f'ing chain. It is a nice chain though. I don't know what I'm doing. I do know how to index gears and set derailleur thresholds. I don't know why I'm bragging when I'm a beaten man. I feel like that guy in the Twightlight Zone episode where he just wanted to read books and then broke his glasses.


Warn Regards- Sorry the pics won't upload - must be a resolution limit

The smallest cogs always wear out first. Probably time for a new one.

^This^ 20 year old freewheel and new chain? There's your problem. And you can't post pics til you have 10 posts. There are ways around it but photos aren't really needed when the answer is so obvious.

If you RD went into the rear wheel, there is a chance the RD hanger was bent. That won’t fix a worn cog, but it could be the cause of the skipping; especially if there was no skipping before.

The proper way to fix it is with a derailleur hanger alignment tool, which translates into taking it to a bike shop and have them do it. You may also have them check out the RD to make sure it is not tweaked.

If this doesn’t fix it and your 1st position cog needs to be replaced, Suntour is a can of worms. There is nothing current and you might have to try eBay and hopefully get lucky.

John

The small cog looks great, like it was machined yesterday. Thank you.

So free wheels change faster than chains? Do tire sizes change faster than rim sizes?

The wear to make a new cog unrideable with a new chain is so little it cannot be seen. (If you can see it, that cog is long past new chain compatibility, like years past.) You are describing the classic new chain on a worn FW/cassette. If some of us are a little curt in our answers it is because we've dealt with this 40-50 years ago and have been telling newcomers ever since. Nothing's changed in those years except the number of cogs, the bodies they sit on, the width and expense of the chains.

You have a compromised FW/cassette. Replacing the small cog will give it more life. Probably the next smallest will give you the same issue next chain. Now, if you want to start out right, go buy a new FW/cassette now (before you put any miles on the new chain with your current one. Worn cogs wear chains to fit very fast. That worn chain might work on your brand new replacement but it will make that brand new unit a well worn one in a few hundred miles. Go new on both, change chains frequently (there are dozens of threads on this website that will tell you how to measure chain wear) and your fine running replacements will go thousands of miles - if kept lubricated properly (dozens of threads there too).

I say FR/cassette because I have no idea which the RB1 uses and I'm about to to to bed. You need to replace your unit with the same or buy a new wheel (and maybe have to fuss with a bunch of other stuff).

Roger - will replace

I was not aware that a new chain can un-mask worn cassettes. An identical replacement cassette can't be found. I may slap on the old chain as a test while I shop for a modern bike. This is why we can't have nice, old things :-/

Thanks for your Knowledge All !!

FWIW: a new cassette and chain can also unmask worn front chainrings if they've been compromised by being ridden too far with a badly worn chain. Even steel chainrings (which typically last longer than alloy) can be destroyed by a chain that's been left on long enough to become badly worn and ridden in that condition too far.

In that case, the problem can recur even after a new cassette/freewheel and chain have been installed. Unfortunately, the fix is new chainrings (or a new chainring, if you ride mostly on one).

Don't ask me how I learned this. :)

It is a Suntour index drivetrain. The only replacements are co-op or eBay.

All this goes back to sending the RD into the wheel. That in itself can cause more issues that a mysteriously worn 1st position cog and cogs 2-7 are fine. If only the 1st is worn it would be a first for me.

John

Your call. And if you need a bike you can ride right away, getting an inexpensive one might be a decent option for short-term use.

But I'd recommend hanging onto the RB-1 and putting the time/effort/money into rehabbing it. The RB-1 is an extremely highly regarded bike - a classic even - with wonderful ride quality. (Disclaimer: I've never owned one, so the part about the wonderful ride quality is based on hearsay.) If it were mine, I'd consider re-doing it with a generally period-correct or even modern groupset.

You might not even have to go that far. If you're OK with friction shifting and the existing brakes/derailleurs/shifters are in good working order, a new Shimano-Hyperglide-compatible rear wheel/chain/cassette, new tires/tubes, new cables, and a general servicing might be all you'd need to end up with a very nice ride.

Again: your bike, so your call.

Bike store employees see cassettes or freewheels with worn-out 1st-position cogs fairly often. It's a consequence of casual riders finding the combination of the middle or inside chainring plus smallest cog comfortable for cruising around on flattish terrain. There are also riders who think that they can build leg muscles by treating the bike like a leg press machine, grinding away exclusively in the highest gear.

Agree that the alignment of the dropout should be checked, of course.

Thanks! I hadn’t thought that someone would primarily ride in a 13t/14t, but that would wear it out.

John

Funny, I wrote the post above, then went riding on a freshly built-up Pro Miyata yesterday on the sweet as-close-to-race 13-26 Sachs FW as my old legs will allow that I picked up slightly used. And under pressure, it skips on the middle 19 tooth. New chain, good Campy Chorus crankset.

What to do? Ignore it? Skip is manageable from a riding standpoint except this is a race bike. Shouldn't skip doing racing-like things such as aggressively muscling over a small hill. But - in line with this thread - it will stretch the chain which will put a quick few thousand miles to that sweet crankset. Maybe I could find a new or better 19 tooth cog. Extend the FW life but ignoring the warning that probably the rest of this FW is not far behind.

I've got another 13-26 on my farmers market bike. I'll measure that chain. It it's under 1/16" I'll swap these FWs. I know that one rides just fine and the chainrings on that 110-74 BCD crank are nothing special and easily to get.

You might be able to flip the cog. I know that the tooth profiles on 90’s Sachs Aris FW’s are directional. Plus the 4 tabs prevent it, unless you grind off one of the tabs.

I’d probably swap freewheels, flip the 19t, if possible, and see if it is acceptable for a farmers market bike.

You might be able to find a cog on eBay, but it is getting tougher.

John

Have to admit that pretty much describes me (large front, smallest two rear, mash hard) when I was less experienced and naive. May well have been a factor leading to needing a second knee arthroscopy.

With more experience - and after one destroyed crankset - I learned better and don't do that any more. It also might be why I've become quite a fan of Biopace chainrings; in my experience, they do seem to be noticeably easier on the knees.