Bicycle Mechanics - Wheel alignment paradox please help!!1

Here's the mega problem!!
1. For some reason or other, the rear tire is almostly perfectly aligned BETWEEN the chainstays.. its smack on the middle... HOWEVER, when i view it from above through the brake posts, its more toward the left brake post!!

How is it possible that the tire can be aligned between the chainstays, but not betwwen the brake posts?

Note that this rear wheel has NO wobble...

2. If i tighten the drive side spokes, so it aligns the tire (with reference to brake posts), wouldnt it screw up the alignment with the chain stays (which is already perfect)

3. Finally, (this is the killer problem), the drive side spokes ALREADY seem to be in tighter tension than the non drive side! i know so coz they make a much higher pitch when i pluck them... so if i FURTHER tighten them, wouldnt there be problems from a super tight drive side, and a loose non drive?


Sorry for the many many questions again....

Thanks so much!

It could be that the axle mounts are not in alignment, causing the wheel to be crooked in the frame.

Your frame is bent.

What model bike is it and which way to the drop-outs go? Horizontal or Vertical? It IS possible for the rear wheel to be centered in the chain stays but off-center in the seat stay if your rear axle isn't fully seated. However, if you're sure the axle is properly seated you probably have a frame problem.

Let me cut to the chase: Take your bike back to the dealer if you just bought it and let them figure out what's wrong.To satisfy your curiosity, here are some answers to your questions:


Originally posted by jpow
Here's the mega problem!!
1. How is it possible that the tire can be aligned between the chainstays, but not betwwen the brake posts?

Assuming the rear wheel is properly seated in the drop-outs, it's called a mis-aligned frame. You can check your frame & drop-out alignment with a tape measure and string. There are more accurate and sophisticated ways, but this usually works "well enough" to clue you into a potential problem.

Drop-out alignment:
1. Measure the distance from the center of the drop out to the center of the bottom bracket spindle on each side of the bike. They should be the same length.
2. Measure the distance from the center of the drop out to the center of the seatpost collar on each side of the bike. They should be the same length.

Rear triangle alignment:
1. Tie a piece of string around the left rear drop-out and wrap it all the way around the head tube then back to the right drop-out and tie it off.
2. Measure the distance between the string and your seat tube on each side of the bike. They should be the same.
3. Repeat the process at the brake boss/bridge - tie a string to the left boss, wrap around the head tube and then tie off on the right boss.
4. Measure the distance between the string and your seat tube on each side of the bike. They should be the same.

If any of these dimensions are not the same on either side of the bike you're frame is mis-aligned. Next step depends on if it's a new bike under warranty or not.


. Finally, (this is the killer problem), the drive side spokes ALREADY seem to be in tighter tension than the non drive side! [/B]

This is normal; don't be alarmed. With the exception of tandems and perhaps heavy-duty touring or Downhill racing bikes, the rear wheel of a bicycle is "dished" to compensate for the cassette's placement. Dishing results in the drive side spokes being at a much higher tension than the non-drive side spokes. Here are some pictures of rear wheels that illustrate what "dishing" looks like:

http://www.mtbreview.com/spotlight/wheelset/symmetry.shtml

Let me suggest that you NOT adjust the tension on your spokes.

Could it be something as simple as the brakes are not properly aligned and one pad is closer to the rim than the other? Depending on the brakes installed you may be able to re-center them by adjusting a screw (I know you can do this with Ultegra brakes)

Zack

thanks for the great replies guyS!!! really appreciate it... im a new bie so learning as much as i can now..


if it IS frame misalignment, (this is a pretty old frame)

is it dangerous to ride?

the wheel seems to be off center from the brake posts by abt 1-2 mm....

but its aligned at the chainstays and it doesnt wobble...


Thanks!!

DUH?

if the wheel is true to the frame (i.e.:paralell) then you're bike has been DISHED to compensate to meet the chainline (chraining's to cassette).

Originally posted by jpow
im a new bie so learning as much as i can now.. if it IS frame misalignment, (this is a pretty old frame) is it dangerous to ride?

Take it by your Local Bike Shop for a good tune-up and once over and have them give you a recommendation. That will give you AND me piece of mind.

... and if it's a good shop you should be able to ask plenty of questions about your bike that should help bring you up on the learning curve.

The dish on your rear wheel is probably incorrect. When this happens (and it's common) you tend to hold the wheel so that it lines up with the chain stays and the top part of the wheel leans toward one of the seat stays.

If this is a new bike, the shop where you bought should fix it for you for free. Frankly, if it was my shop, I'd have been embarrassed to have let the bike go out that way in the first place.

THanks for the replies guys!! after proper measuring, i realised it was INDEED improper dish...

well i tightened the drive side spokes 1 turn each, and magically it got aligned!!

damn im such a newbie.. heehe

anyway, anyone knows HOW MUCH tighter the drive side spokes can be compared to non drive?

Due to the dish, my drive side is quite tight, whereas the non drive side are much looser....

how much a difference is safe?

i don't want to go overa pot hole and have my wheels collapse...

thanks!

The dish tells the tale.

The difference in spoke tension is what creates the dish in your wheel. When you have the wheel aligned so that the rim runs true to the frame, that's how much tension differential you HAVE to have between the right and left sides of your rear wheel.

Now here's where it gets interesting. If you don't have enough tension on your left side spokes, the ones that are relatively slack, you are going break spokes. The key to successful wheelbuilding in the age of 8 and 9 speed freehubs is to get enough tension on the left side spokes in absolute terms. Doing this means that the right side spokes have to be very tight indeed.

thanks for the reply again, spoke wrench (an apt nickname!!)

is there anyway to figure out how much "absolute" tension the non drive side shd have?

do i need to get a tension gauge?

also, on a slightly different topic, how much wobble is usually acceptable for a race ready bike? i've done my best to true my wheels, but its STILL not absolutely perfect.. i'd say abt 0.5 - 0.8 mm off....

Measuring tension on a rear wheel is done with the drive-side spokes. They are tightened to 120 kilograms of force per centimeter squared. *whew* Once the wheel is dished and radially correct, small adjustments are made to keep the tension even, called tension balancing. Depending on the gauge of spokes, tension can vary on the non-drive side. On a well built wheel, non drive-side spokes can measure 30-40kgf/cm2 less than the drive side spokes!

No wire spoked wheel is ever perfect. It's only a matter of how precisely you can measure. If you can get the wheel within a millimeter of true in both side to side wobble and out of roundness, I think that's pretty good.

Trueing for side to side wobble is actually pretty easy. Once you have much out of roundness, it's hard to get rid of it. I find that building the tension into the wheel in small increments is the way to minimize out of roundness.

in relative terms, how many kgf/cm is lets say... 1 turn of a spoke worth?

would 1 turn = 1kgf/cm?

i havent read all the posts but i currently ride a frame that's not aligned(salvaged POS- i can't seem to force myself to toss the frame). i don't advise it although personally i haven't had any problems (took it for only a handful of rides as of yet).