Spider slipping on crank?

Riding home from work last night skidding to a stop at some traffic lights there was this crunching sound and what felt like my chain slipping, then when I set off under pressure the same thing.

Thought my chain must be slipping for some reason, but rather than stop to sort it I just wanted to get home figure I could sort it there.

Next time I tried to stop via skidding same thing happened, then once again when I set off. Checked chain tension but it seemed ok.

Made it home, then this morning reset my chain tension. Set off down my street, tried to skid and same thing.

It seems that the crank is slipping round the inside of the spider - they're older sugino road cranks by the way.

Anyone had this problem before? and is there any way of fixing or is it new crank time (really can't afford this option though...)

My first thought was loose chainring bolts. But the problem could be elsewhere. Have you retightened your lockring just incase?

http://www.londonfgss.com/search.php?searchid=4142833

It is definitely the spider slipping - not the cog/lock ring, not chain slack. You can see that the spider has moved as the arms are in a different position to the crank arm.

Is there any way of fixing this?

What cranks do you have? Sounds like you need new ones.

Some sugino ones - from the early 70s I think .

This is what I feared - just wanted to check if there was a cure for it.

I was pulling away from the lights at the south end of commercial road on sunday, lorry driver behind me honked so i thought i'd accelerate hard. My chain suddently lost tension and when i pulled over this is what i saw. just thought i'd share

you can polish that out

Sounds like you need new ones.

+1
That goes for Rauri too ;)

http://www.londonfgss.com/search.php?searchid=4142833

Sorry - no matches. Please try some different terms.

?????

I do skid but not very often. I always cringe slightly at the damage it must cause my bike every time I do it!

do you have a picture?

I lied!!! i feel terrible... even though I had my lockring and cog well tightened up and loctited too , under the pressure of skidding on some of tha red painted cycle lane stuff it was violently loosening making a horrible noise, rather than just smoothly unscrewing a little like it did before. found this out by marking my spider and crank with marker, then forcing it to skip, and checking to see if the marks still lined up.

Had a token lockring, and was tigtening up with the old hammer and screwdriver method to try and sort it, managed to split/snap the lockring... gutted. Would've been way more gutted if it hadn;t cost £2.99 from evans. time to get a lockring spanner me thinks.

Luckily got a flipflop hub so was still able to go ride.

New question: Does running a small chainring/cog (I've been running 42-14) put a lot more strain on parts than running a bigger chainring/cog with a similar gear inch?

Fucking knew it.

At least you got it sorted.

I think the theory goes if you spread the wear over more teeth, stuff will last longer? Also smaller cogs have higher angles of chainwrap or some shit so I think that might exacerbate the wear.. feel free to research and confirm/deny these theories. I can't remember if they were fact or musings.

smaller chainring and cog causes them to wear faster yes.

I understand the parts wear faster - this may be a ridiculous question, but i meant like does having a smaller chainring/cog put more (unscrewing) force/strain on parts (like the spider, or unscrewing the cog) than a larger setup?

Tell me if this is daft.

I understand the parts wear faster - this may be a ridiculous question, but i meant like does having a smaller chainring/cog put more (unscrewing) force/strain on parts (like the spider, or unscrewing the cog) than a larger setup?

Tell me if this is daft.

The smaller cog could put less force as the leverage is less isn't it?. The opposite of using you wheel rim to get best leverage with that Rotafix method.

Probably doesn't make any difference though as I know fuck all about physics :-)

so you are asking if chain tension is higher?

The smaller cog could put less force as the leverage is less isn't it?. The opposite of using you wheel rim to get best leverage with that Rotafix method.

Probably doesn't make any difference though as I know fuck all about physics :-)

Yes, but somehow I was thinking that with less teeth, there is more pressure exerted on each tooth, reuslting in a greater force to unscrew it, rather than more teeth with the pressure spread between them?

I also have very little knowledge of physics...

I'm no physicist, but I imagine in most cases there are only a few of the teeth on the sprocket putting any real force into the chain. Imagine a chain pulling on the sprocket; the first tooth will take the strain and any later teeth are just guiding the chain around, then the next tooth engages with the chain, taking the tension off the first one.
Obviously as chainrings and chains aren't exactly perfectly sized there must be some strain taken by other teeth...
But, as a larger chainring (more teeth) means each tooth is further away from the pivot point, then the force required to turn the wheel is less as the leverage is greater. So less force, less wear, presumably.
So, in conclusion yes but not for the reason you propose.

waits for someone who knows what they are talking about to come and prove me completely wrong

well i suppose a larger cog would exert more force unscrewing as the torque would be greater for a given chain tension, but chain tension varies with the sizes of the cogs/chainring.

my mind is boggled! ha