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Dish.... How to caculate how much you need to go?
#1
I'm new to the term "Dish", and have been pointed to links about it...

I've done rims once before... in 1992. put fixed gauge near rim and made sure both sides were identical.

I am up against a rear wheel assembly where I re-positioned spacers and cones on the shaft.

I know the size of the spacer (2mm) but can only guess about the amount of change done to cones... as it was done once in error, and then a 2nd time (after spacer was moved to opposite side, based upon a 'calculated Chain-Line that was within .7mm of where I thought I was heading.)

How does one pre-determine how much Dish is needed -- "how far" to go?
If it's 3+mm do I attempt it all in one move, or two?

do I measure where the hub would be if it were adjacent to the tire, and measure back to the rim, and compare both sides to see what is needed?

This appears to be more complicated than Chain-Line adjustment.

???? Thanks for any comments...
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#2
Put the wheel in the frame, and measure how far from centered the rim is close to the cranks and brake bridge. NOTE: if your RD is the type with a claw on it that is clamped by the rear axle or Q/R, then you need to make sure that the rear axle is parallel to the BB axle.

Adjustments for dish should be in ¼ turn increments, loosen first, then tighten.

On my truing stand, I drop the wheel in, then center the rim side to side as I build the wheel.
http://forums.bicycletutor.com/thread-3834.html
Nigel
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#3
Nice Link!! I've got a video head eccentricity gauge that I'm going to put into 'new' service, as you did!!
Thanks...
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#4
There's no practical way nor any need to calculate ahead of time. Just do as Nigel suggests. You've dished properly when you can reverse the wheel in the frame and it stays centered between chain stays and seat stays. Or make sure the wheel is true first find three cans of equal height and support the rim horizontally with them on a *flat* surface. Measure the distance from the axle end to the surface, then flip the rim and compare. You have to loosen spokes on the side that has the larger distance and tighten the other side.
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#5
Does this 'reverse wheel and check for center' process work on rear as well as front wheel? (Still trying to get my head around this idea prior to starting in --- Obviously if I have a better idea of what I'm about to do, I'll be more successful with the implementation of it....



(11-27-2014, 12:59 AM)cny-man Wrote:  There's no practical way nor any need to calculate ahead of time. Just do as Nigel suggests. You've dished properly when you can reverse the wheel in the frame and it stays centered between chain stays and seat stays. Or make sure the wheel is true first find three cans of equal height and support the rim horizontally with them on a *flat* surface. Measure the distance from the axle end to the surface, then flip the rim and compare. You have to loosen spokes on the side that has the larger distance and tighten the other side.
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#6
(11-28-2014, 03:00 PM)JanJ Wrote:  Does this 'reverse wheel and check for center' process work on rear as well as front wheel?

Yes
Nigel
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#7
I would not have recommended that if it did not apply to the rear, as that's what we've been talking about all along.

All you need to know is that the goal is to have an equal distance laterally from the face of the locknut on either side to the rim face. It does not matter what's in between the locknuts. All you are doing is pulling the rim toward the side that has the greater distance.
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#8
Couple more questions.... My pre-adjustment measurements are not making sense..

If I put a tie wrap around frame, and cut it so the end of the tie just touches one side of rim... Then flip the rear wheel over..... and see where the 'pre-dish-adjustement' distance to the tie wrap end is... on the other rim...

Two Questions:
1. How much error is there before you consider it 'needing adjustment? (In mm)?
2. Once you start, At what point do you consider it's "OK"??? (In mm)?
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#9
1. I think the "soup can" method is more accurate. I can't make sense out of your question anyway - what do you mean by "other rim," and exactly how to your measurements not make sense to you? I would suggest you put the marker tie on the drive side if you have not already done that. There should then be a gap when you flip the wheel, and you have to move the wheel 1/2 of the difference.

2. If the diff is down to under 2 mm you're OK, but why not make it perfect?
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#10
with rear wheel where it is.... Tied a Tie wrap around left rear frame member, and cut it such that it just touched the left rim, as viewed from the rear.
Then, flipped the rear wheel around, and mounted it. and the tie wrap is basically in same place as it was before.. and tire is in center of frame as well.

We all know I moved a 2mm washer from gear to non gear side, and adjusted both cones 2 times: Last one based on where I though it should be, and the first time both cone sides were adjusted with no indication of where they were... a beginner's mistake...

My confusion.... I'm not finding an error using the tie wrap procedure, which would seem to indicate that I'm the lucky-est person in the world... as it would seem that there is no adjustment needed! (Which is why I keep coming up with 20 questions.... to verify I didn't mus-interpret the procedure)...

Could you explain "Soup Can" in more detail?


(11-29-2014, 03:58 PM)cny-man Wrote:  1. I think the "soup can" method is more accurate. I can't make sense out of your question anyway - what do you mean by "other rim," and exactly how to your measurements not make sense to you? I would suggest you put the marker tie on the drive side if you have not already done that. There should then be a gap when you flip the wheel, and you have to move the wheel 1/2 of the difference.

2. If the diff is down to under 2 mm you're OK, but why not make it perfect?
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#11
(11-29-2014, 04:50 PM)JanJ Wrote:  .......Could you explain "Soup Can" in more detail?.....

Yes.

For 630mm bead seat diameter wheels (27")

Place three same size soup cans or similar cylinders (MUST BE SAME DIAMETER AND LENGTH, no dents), evenly spaced with centers on a 630mm diameter circle, on a hard flat surface. The center of the 630mm circle should have a cross hair, so that you can center the wheel. Place the wheel on the cans, with the center at the marked cross hair. Measure from the lock nut where it would hit the frame to the hard surface. Flip the wheel over, and repeat. The difference should be less than 2mm (±1mm).

With my trueing stand, I repeatable achieve better than ±1mm on average centering, ±0.15mm axial wobble (on the rim, tire are not that good) and ±0.25mm radial wobble.
Nigel
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#12
A bit of a correction. You do not have to be as careful as Nigel's procedure, which is an expansion of what I described in post #4. All you have to do is place each can so that it is in the same relative position under the rim, such as the outer edge of the can in line with the inside edge of the rim. They don't have to be equidistant, as the reason for three cans is that you only need three points to define a plane, and if the rim is true it does not matter where on the plane those three points occur. In practice it's best to have them fairly equidistant, but exact is not necessary.

As for your grand good luck, it could be that someone put spacers on previously without redishing. If the soup can method shows the wheel is dished, then be happy.
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#13
Well!! That Settles it!! I AM the lucky-est man alive!....

Don't know how I accomplished it.... Accurate mathematics, Dumb Luck, ______________
But.... I did the Soup Can test tonight... and I measure .6-.7mm difference! I'm going to leave it be for now...
Big Grin!

Offer to vote to make it May right now continues to be offered, as with exception to the cleaning out of the Motorcycle Saddlebags and put the MC helmets in their bags for winter, I am officially in PBS & PMS!!

Salt on the streets will do that!!!
Just for grins.... Do you bike folks who suffer PBS wait for the first warm spell after a good soaking rain (To wash salt away) before going out --- like us motorcyle folks?
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#14
what salt? Smile

CA doesn't use salt, even on I-80 over the Sierras.
Nigel
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#15
Midwest uses SALT!

The moment Salt hits the streets, I'm in PMS!!!

Does a number on frames and engine cases!!!

That's why I wait till a warm spell after a soaking rain before getting the bike(s) out! Wash it away, and dry the roads!


(12-04-2014, 04:51 PM)nfmisso Wrote:  what salt? Smile

CA doesn't use salt, even on I-80 over the Sierras.
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#16
I remember; learned to drive in Chicago area in the '70's; was in Minnesota in the '80's and part of the '90's and again in the mid '00's; before being recruited to come to San Jose.
Nigel
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#17
Did some classes at Ampex, Abekas in Redwood City, and Sony in San Jose... (70's -80's).. At that time, Loved it there...
Loved the Woodside Drive ride to Half Moon Bay....

Daughter now lives in Oakland
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#18
Weather is supposed to warm up this weekend....
If it remains dry..... I'm hoping to get in 3 rides....

1 motorcycle and 2 bicycle rides (to see how I did on repair)
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