New KMC 8-99 Chains Skipping

[IronMac]

phopwood: Yes, same amount of links as the old chain.

il padrone: the old chain was over 12 inches...maybe 1/8 over...and I used two different rulers to measure stretch.

here are some pics of the current setup and it is gear 6 according to the shifter.

[phopwood]

From a visual point of view all looks ok, I can't see the chain line, but if the chain line is out, on the tensioner you will see wear lines on the inside of the tensioner where the chain rubs..

Can you describe the skipping.

Also how tight is the spring on the tensioner, push the tensioner up towards the chain stay and see how tight it is.

Peter

[IronMac]

Ok, no wear lines anywhere that I can see. I shone a flashlight down starting from the sprocket and followed the chain through the flywheels and out. The chain does not rub against anything so far as I can tell.

The skipping is usually a one or two skip where it seems something has not caught and it occurs only when you're really putting some pedal to the metal.

And I can't budge the tensioner. It's rock solid from the left, the two holes, the nut or bolt, down to the wire. The only part that can be moved is the hanger with the lowest flywheel. Even then, pushing upwards to move the hanger you are in danger of tipping over the whole bike.

[phopwood]

Hi,

I confess without seeing and playing with the bike I am stumped.

If you can rotate the pedals forwards with the bike supported in some way you may be able to see why the chain is skipping.

It might also be worth checking your hub shifter tension just in case your hub is causing the problem.  But if it was the hub I would expect a slip rather than a skip.

All the best.

Peter

[IronMac]

Thanks Peter for the effort.

I may have to email Rohloff with a link to this thread to see if they have a suggestion.

[JimK]

It does sound like a new chain on an old sprocket. My current chain started off noisy and then moved into just shifting a bit under load and now all the parts have worn themselves into compatibility. The whole process took a few hundred miles.

If you're talking about little shifts, like the pedals move a quarter inch, I would say just keep riding and see how it evolves. If you're talking about big shifts, where the pedals move maybe 30 degrees or more around the circle, that would not be a worn sprocket and would seem to require more attention.

[IronMac]

Thanks Jim for the latest reply and it concurs with what Rohloff just emailed me back. They are pretty sure that the sprocket has worn just enough for there to be an incompatibility issue.

Thanks everyone for taking the time and making the effort to help me with this.

Will report back when all of the stuff arrives.

[phopwood]

Mac,  did you ever get this all sorted out.

Peter.

[IronMac]

Thank you Peter for the question. I was hoping that I could report success but here is what has happened.

I finally received a sprocket three days ago because Bike24 was moving their warehouse and held up all orders by over a week. It then took its own sweet time to arrive here in Singapore.

I had ordered a 15 tooth sprocket because that was what was on my Bike Friday invoice. Lo and behold! They had installed a 13 tooth sprocket!   

Grrrr.....I could not believe it! They only build bikes with 20-inch and smaller wheels yet they put down a 15 tooth sprocket on the invoice! I had seen mention of the 13-toother for 20-inch wheels but thought that BF knew something that I did not.

Can I still use the 15-tooth sprocket? I don't know if it will overstrain the hub or not. According to BF's invoice, the front crank is a 53-tooth but I would take that with a grain of salt.

[Danneaux]

Hi Mac!

I'd suggest counting the teeth on the chainring first so you'll know for sure what you're dealing with in choosing your ratios.

Here's Rohloff's take on the matter: http://www.rohloff.de/en/technology/workshop/sprocket_ratios/

Smallest permissible sprocket ratios

The primary sprocket ratio used with the Rohloff SPEEDHUB 500/14 (e.g. 42:16) converts the slow rotational speed at the crank into a fast rotational speed at the rear sprocket and reduces the input torque for the Rohloff SPEEDHUB 500/14 in the same proportion. To prevent overstraining the hub, a minimum factor of 2.10 must be used. This minimum factor equates to a primary transmission ratio of:- 36:17, 34:16, 32:15 and 28:13. These SPEEDHUB 500/14 ratios resemble a derailleur transmission of 20:34.
Larger chainrings can be used without exceptions.

A 53x13 gives a ratio of 4.07. Used with 406mm wheels, the range will be from 21.2-111.7 gear-inches.
A 53x15 gives a ratio of 3.53. Used with 406mm wheels, the range will be from 18.4-96.8 gear-inches.

In answer to your question...

Can I still use the 15-tooth sprocket? I don't know if it will overstrain the hub or not.

I think you'll be fine.

Best,

Dan. (...who lives on the bike route about 2mi/3.2km from their factory door so sees a lot of 'em)

[phopwood]

As Dan says I think you will be fine.  Let us know how it goes.

Peter.

[IronMac]

I'd suggest counting the teeth on the chainring first so you'll know for sure what you're dealing with in choosing your ratios.

Hahahahaha (bitter laughter here)

The NWT has developed a metallic "shushing" sound while pedalling after the mucking around. Pretty sure it is not serious but it is going back on the stand and I will install the new sprocket then. Assuming of course that it is a 53-tooth chainring and not some weird-a$$ number.

So far, this bike has turned out to be a hangar queen. If it is not the Rohloff, it is the pedals; if not the pedals, it's the Supernova wiring; if not the lights, it's the Chris King headset; if not the headset, it's the fenders, etc. It's worry upon worry upon worry about what's next to fix.

Thanks Dan and Peter!

[Andre Jute]

A 53x13 gives a ratio of 4.07. Used with 406mm wheels, the range will be from 21.2-111.7 gear-inches.
A 53x15 gives a ratio of 3.53. Used with 406mm wheels, the range will be from 18.4-96.8 gear-inches.

Not only can you use the 15T sprocket, Mac, you should. Nobody needs a 112 inch gear on a Bike Friday, whereas the 18.4in low with the 15T sprocket will be rather useful on utility bike even in Singapore.

[IronMac]

Sorry to keep everyone in suspense but I was finally able to ride the bike and it's a success!!!  Woohoo!

Changing the sprocket was a bit tough and I think it's because there was no grease in the threads. Well, at least none that I could detect. I also did not want to bang my knuckles while kneeling over the small wheel. But off it came in the end.

The ride now is silky smooth, there is hardly a sound and I keep thinking I need to get my hands on what KMC is using to lube up their chains! Shifting is excellent. As an aside, my hub makes very little noise and it's been that way for the longest while.

Thanks everyone for your input...much appreciated!   

[phopwood]

That is great news week done to you, one less thing to worry about. 

When was the last time you changed the oil on the hub.

Peter