Topic: Would this be a dangerous thing to do, or just a silly thing to do?

[Autoground]

I have a set of 520 sprockets and chain, sitting around going to waste. The sprocket teeth are 14/33 for a gear ratio of 2.35.

I have a 1980 CB650 with a 530 chain on 16/39 sprockets for a gear ratio of 2.45.

HYPOTHETICALLY, if my sprockets went bad or my chain broke... what would happen when converting to a modern 520 chain with smaller sprockets?

The speedometer would lose accuracy. What other oddities would unfold?

[Alan F.]

Sounds doable. Why would your speedometer lose accuracy?

[Mantree]

You would loose a little acceleration and gain some top end but hardly enough to make a big difference your speedometer is run off the front wheel so unless you change your front your speedo won't be affected.

[Autoground]

So there's nothing dangerous about it? I just lose chain tensile strength?

I imagine there's a small change in the pathway of the chain from front to rear sprocket. I wonder if it would cause the chain to bump anything.

Re: the speedometer I read that somewhere else, so it probably refers to a bike with a different kind of speedometer? Maybe I shouldn't trust everything I read.

[Alan F.]

Some speedometer are driven by a cable from the front hub, later some were I think cable driven from the transmission (?) and eventually they weren't cable driven anymore but run by a signal from a sensor on rotating internal engine parts.

[Mantree]

If I remember the last time I worked on a 650 I think it was a hub driven but I might be wrong. Some bikes (normaly shot driven) will run off a hal effect sensor in the rear drive.

[scunny]

The speedo on the 650 is driven off the front wheel.

[newday777]

So there's nothing dangerous about it? I just lose chain tensile strength?

If you don't consider the broken chain wrapping around your rear sprocket and locking the rear wheel at speed dangerous....well.......

I had a chain break on my 750 back in the late 70s which wrapped around the rear sprocket instead of spitting out the rear of the bike to the ground. It was a skidding stop at 45 mph into the dirt apron of the road, this after a 100 mph pass just before...... It was a YEHAW moment in my life of many miles.

[bryanj]

A modern 520HD chain is equally as strong as a 1980's 530 standard chain BUT  note the HD part

[Alan F.]

Would a 14 tooth front be considered too small for a 650? What's stock?

[Autoground]

17

[Alan F.]

I won't claim to know if 14 is too small.
When switching to a smaller front sprocket the radius the chain bends around becomes smaller.
There is a point where one tooth too small will cause greater chain wear than one tooth higher.

I'm not qualified to tell you if 14 is cool or not though.
Maybe one of the knowledgeable 500/550 guys knows?

[bryanj]

I would sayyes 14 is too small, 16 was too small for a 750

[grcamna2]

A modern 520HD chain is equally as strong as a 1980's 530 standard chain BUT  note the HD part

This. 

Keep it properly lubed and adjusted correctly and it'll be good for it's useable life.

[Tim2005]

I would keep an eye on clearances when you fit this- the sprockets are smaller diameter by quite a bit, so there's a risk that the chain would then rub on the swingarm or other parts

[Autoground]

Note that the chain type is also changing, not just the number of sprocket teeth. This is all a conversion to a 520, with a 520 chain. Do the worries about wear still apply, o were you thinking about it as an alteration to the traditional 530 gearing?

[Alan F.]

530, 525 and 520 chains all use a link length of .625" pin center to pin center.

It's the width of the links that narrows.

The seat-of-pants appearance of a gearing change will not be affected by swapping from 530 to 525 or 520.

In a pinch (after the apocalypse or just on a long road trip) with a bike converted to 520 sprockets, you could swap on a 525 or a 530 chain in a pinch and continue riding. This will not be universally advisable, but it will work.

[robvangulik]

The weight of the chain is less, so the forces going around tight bends will be less too, compared to a 530 chain.