Fixed gear problem: tight loose

[Too Tall]

Christophe? Anyone? What do you do?
I'm chasing my tail on this one. The setup is a brand new Sugino 75 crank, TA Pista rings and Sugino 75 BB. I can not for the life of me find a position on the crank or chainring spider combo that is "just right". The BB is fine, the hub is perfect. I've put the chainring in a few diff. spots and advanced the crank to the next taper face. No soap. The ring has poor run out not the crank / BB or hub...I measured.

OK I know the answer, call the supplier and cry. How common is this and what works for you? Do you pop for the goochie rings from Sugino?

[AHava]

There's only one way to do this - find the tightest spot on the chainring, and tension at that point to 'tight but not binding'. Any and all loosey-goosiness on the other end must be accepted as a fact of life. Perfection is unattainable.

Buena suerte,

Alex

[chrisroph]

Josh--Alex has it right. Its quite common and is related to chain ring intolerance. Grab your peanut butter wrench and spin the back wheel. Set the back wheel's horizontal position so the tightest spot is not too tight and then you should be good to go. That way, you will eliminate binding, which robs efficiency. Instead, you will have a place where the chain will be a little looser than ideal. Typically, with most out of tolerance rings, the difference between the tightest and loosest points on the ring will not be enough to cause any problems. Just remember that if the chain is too loose, it could come off, not a good thing during a track race. Some of my rings are slightly out of round. I've never yet thrown my chain. However, if the situation keeps you up at night or makes you kick the dog, beat the kids and fail to worship the queen, drop the green and buy some new rings. Also, every track has experienced mechanics hanging around. Grab one and ask him or her to look at your bike and tell you if they think it is a problem.

[TimB]

Josh,

I think Sheldon Brown has something on his site that may help - but if I recall correctly, it's under the section for tandem timing rings, not fixed gear. I ain't got time to look right now. The procedure involves loosening the chainring bolts some, and then something like whacking the chain with a hammer in the tight spots to re-seat the chainring on the bolts. [I've tried this in the past, with only minimal improvement.]

Okay, it was easy. The link is here: http://www.sheldonbrown.com/synchain.html

T

[Too Tall]

Christophe, yeah it's too loose even when adjusted pre suggestion darnit. Problem is I did drop my chain in a race two weeks ago. Oh what fun there was a sharp acceleration as the pack hit turn 3 and woopeeee....I screamed like is was chromosone challenged ;) and promptly headed for the grass...no carnage. I've ordered a DA ring and the supplier admits he does not sell alot of TA 1/8 rings..sheesh no wonder it was inexpensive. IN your experience are any particular brand of rings consistently better?

Tim, dewd....wasn't me who told you about that trick to balance timing rings??? Hmmmm. Actually I balanced your rings a few months ago...which is how long you've left your tandem in my shop!!!!! The spiders love it. All kidding aside ,spiders that is, you can not budge rings on the Sugino crank since the rear 1/2 of the chain ring bolt is a precision fit thru the crank arm AND the ring...it's frickin' solid...no movement. Double darn.

[chrisroph]

Josh---Whooh! Dropping a chain will send you quickly to the credit cards to buy some new gear so it doesn't happen again.The DA and Campy ($$$!) rings are uniformly excellent. I haven't used TA pistas. Most of my funky rings are older suginos. You'll probably solve the problem quickly with some new rings. Can you return the bad ring?

[TimB]

Josh,

I know, I know. One of these weekends I'll come by and free up your garage space. Of course, it's not like I'm a-goin' to ride that long bike any time soon unless I can find a guest stoker and KT gives the OK. Know anyone who wants to ride stoker and wouldn't mind towing a 2 year old to the playgound at Candy Cane City?

Whack those Spiders!

[Too Tall]

Sure sure. Doreen will do it. She loves your kids.

Yes, I can return the ring. The fellow is very nice to deal with and I told him I wanted to maintain a business relationship not cause a problem for him. I'm sensitive about that, small business survives on thin margins. My need for service and support far exceeds the cost of a friggin' chain ring. :cool:

[TimB]

So this got me to thinkin'...

On my Gunnar, I'm using an old DA square taper BB and DA (7210? the last generation to use the square BB) cranks. I'm using a Sugino 42t ring up front and a DA cog in back with 3/8" chain - i.e. road width.

Do we think the tolerance for these rings would be greater than for 'real' track rings? Because I get a lot-o slp in my chain. I've always just found the tightest spot and adjusted it there to be tight but not binding, which gives me lots of slack in the 'loosest' position,' but not so much I've ever thrown the chain. With a rear deraileur to tension the chain, you'd never notice such imperfections on a normal road setup.

Pondering...

[Too Tall]

My track coach taught me to hold the bike horizontal and spin the wheel fast. Listen and watch the chain. If you hear popping or it threatens to come off...nu gooot! If you want me to tweak your setup, can do....(cough) it's all too fresh in my mind right now :rolleyes:

[11.4]

I've found that while some chainrings are out-of-round, there seems to be even more trouble with crankarms milled out-of-round. After all, in a CNC'd world, the chainring can stay mounted, while a right crankarm has to be mounted and removed a couple extra times. Even if the bolt pattern is milled correctly with regard to the crankarm itself, the milling of the center spline or taper is anything but precise. Road standards tend to apply, where a derailleur takes up slight eccentricities, but this isn't very good on the track.

The good news is that you may have both an eccentric chainring and eccentric crank, and by rotating the chainring to match a different set of bolt holes it may offset problems. The bad side is that the crank arm is the problem.

[Too Tall]

Ever the astute teacher 11.4 :) I was able to isolate the chainring by indexing both and rotating to various positions and than doing vertical run out measurements. Haha, I used tape on a coat hanger and a long needle for my guage!!! I'd be very bummed if the crank was nuh goot. Ouch indeed. I've got a DA ring on the way....let's see what $90 gets me :rolleyes:

[11.4]

What seems to make the difference in tension on a fixie usually amounts to only a millimeter or so of displacement of the ring. Cumulatively the added circumference so created is enough to create the problem. This means that trying to measure the eccentricity of the ring (or crank) is hard -- you likely won't see it unless it's really excessive. And the difference can be in how high the teeth are milled, a minute offset in one of the mounting holes, etc., so you have to be sure you're measuring the right distance as well. Personally I've had problems with just about every brand, with Campy unfortunately the worst by a good measure, followed by the minor/odd brands, then Sugino, and finally Shimano. But none of them is perfect.

[chrisroph]

Good info here; I've had good luck with the eccentricity of my campy rings and have done worse with suginos. I suppose the important point is that all of the rings can create problems. Josh, I hope your DA ring runs true.