_ForceD_

So…using spare/used components I had on hand, and an old steel frame, I built up a road bike to keep at the vacation house so that I wouldn’t have to transport one back&forth. For the cranks, I ‘thought’ I had a matching set. But when checking to make sure they’re the same length, I guess I failed to make sure they’re a matching set. Upon riding the bike (at the vaca house), I noticed that the DS cranks is almost ¼ inch farther from the chain stay than the NDS crank is. Everything is assembled snugly and securely, and the frames isn’t bent. Neither of the cranks is rubbing on the BB shell, nor the chain stay. But apparently the two cranks have different angles. Nothing feels out of the ordinary when riding the bike. But is this anything to be overly concerned about?

Dan

Iride01 

More of a gap on one side than the other is generally okay and par for the course on many square taper and sometimes even with other types of BB's. But your crank arms should be 180° opposite. If they aren't square tapers then maybe you are just off a spline. If they are square tapers, then.... well that's one of the many gotcha's that rear their ugly head with square tapers sometimes. The square hole in them can be at different orientations for different brands, manufacturers or models. Square tapers came about when regions still had their own standards and no one cared if part of a crank made in another part of the world fit a crank made in their region.

Never mind, the word "angle" messed me up. When I came back are re-read your op, I see that you mean the angle of the arm going outward. Not the relation to the other crank arm orientation. But yes that too is dependant on the model and brand. On a crank with all it's own model parts that difference you are seeing is q-factor. Q-factor is how far apart the pedals will be from each other. I don't remember if it's measured from the outboard side of the hole, middle or inboard side going to the sane respective plane on the other crank.

But if only your eyes are giving you issues with it, then ignore it. Most people can tolerate a wide range of q-factor.

70sSanO

Not an issue if you don't notice it when peddling. It is nice to have the distance close to the same, but older bikes get challenged when going from asymmetrical to symmetrical bottom brackets. Even factory bikes were not always consistent DS to NDS..

John

ScottCommutes

To put some perspective, we're talking about 6mm on a vacation home bike that seems to ride fine. Nothing to worry about in my book.

_ForceD_

Thanks for the responses. Just to clarify, with regard to the centerline of the bike, the DS pedal is farther away from it than the NDS. Can’t notice it when pedaling.

Dan

wheelreason

I'm so disappointed, I thought this was going to be a "Can I use a square crankarm with a diamond one" thead...

zandoval 

There are certainly other differences between the bike you cant even notice...

Ya change your AO ya change your bike...

Still sounds like fun, fun, FUN...

79pmooney

No unless it bothers your knees or head. My knees like my feet to be as close together as possible. If I can, I set my bikes with the left crank just missing the chainstay paint. Back in the old days (1970s) many racer bikes came with left cranks nearly that close.

Now, perhaps we of that age are living in full denial and that our warped bike fit is the blame for society's ills now andthe reason so many of us have shrinks but I will continue on in the bliss of thinking that with happy knees, all is good.

JoeTBM 

Any chance that the NDS crank arm previously was on a bike that fell over and was bent inwards, I have seen some that were bent so bad that they hit the chain stay. If so, it may be possible to straighten (place on anvil of vise and hit center rise with a heavy hammer) or replacement NDS arm

andrewclaus

Usually the rider can feel that by a wobble in the pedal. I've seen that twice recently with Ashtabula cranks and I'm 50-50 with being able to straighten them with vise and hammer.

_ForceD_

Chance of the bike falling over onto the pedal/crank? That’s a high probability (in my garage). Chance that a 15-20 lbs bike bent a crank that is designed to withstand hundreds of lbs of pressure from the rider (out of the saddle cranking hard in a sprint or up a hill)? You’d have a hard time convincing me of that.

Dan

Road Fan

I'm like 79PMooney - I like my pedals close to the frame, same distance from the frame, and with front chainline that matches the rear chainline. Needless to say, I also need my chainstays to be symmetrical. After setting up a few bikes this way (wasn't quick or easy!) I could definitely run my fastest and jump my highest. So the benefit was clearly in my head, but that doesn't mean it was not totally worth my time!

Seriously, pedaling did feel better but I don't have any rationale for why that is the case.

As well, I would not attempt to hammer the crank arm to alter its shape. If it is aluminum it might crack. If it is carbon or other composite it is very likely to crack especially as it will be given cyclical stressing (due to pedaling) after being so assaulted. Cyclical stressing can take out a stressed aluminum chainset, as well. If it is steel it will probably not be brought closer to fracture, but I would want to align the crank axle with the pedal axle after the "repair," and that just adds stress to the steel arm. Besides, you will probably never get them actually parallel without making your own jig to control the work. I had a wobbly pedal on a bike about 60 years ago, and I could not stand it.

KCT1986

It's probably just a case of one or both of the arms not designed for the spindle length that it is currently on. Newer arms are designed with a curve outwards from the spindle to the pedal for more ankle clearance and to use a shorter (stiffer) spindle.

If it doesn't bother you, don't worry about it.

Another thing to possibly check is if the chainline is too far out. Based on the gearing combo that the bike is usually ridden in, this may cause noise/wear. Again, if not excessive, no worries.

70sSanO

There are a couple things. Some riders are sensitive to Q Factor and some are not.

I think Q Factor becomes more important as performance increases.

I ride more than one bike and the Q Factor of each one is probably different. Optimizing it would probably optimize my performance.

I also think the Q Factor of older square taper cranks was an accepted compromise compared to modern cranks.

John

Fredo76

A 1/4" difference is within the range of normal for a square-taper BB. If it doesn't bother you, it's fine.

JoeTBM 

Dan,

I am not trying to convince you or anyone else for that matter. I threw this out there as a possibility.

But I can tell you I have seen this twice, that a crank arm is bent in towards the frame on a donated bike. I can't tell you what caused the actual bending or how many blows it took to bend a crank that way but I can tell you it can happen.

The forces you are describing (hard pedaling vs a bang laterally) would seem to be very different even to this non-engineer.

KerryIrons

Yeah, but what about when pedaling?

70sSanO

LOL! That too.

I usually go back and edit out spelling errors. Missed that one.

John