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Old 2017-09-25, 02:14 PM   #1
GideupJimmy
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Loose Pedal Matter... my Sanity.

Hey all.... been riding Nimbus 36" for over 1 year on average 40km per week ... recently had tube changed at local bike shop.. when recommenced riding I stacked it due to peddle coming off the 150mm crank. . at first thought it was somehow connected to bike repair process. It happened again soon after (another stack) post tightening the pedal . The correct side pedals were in correct positions. Eg Right pedal screwed into Right crank... and noticed it loosening again for 3rd time this time after screwing into 127mm crank... (noticing both left and right pedals loosening)

It soon dawned on me that the frame of Nimbus was back to front.. I since rectified via unbolting wheel and correctly aligning to the frame...
What baffles me is since correcting the frame the pedal matter has disappeared.

When thinking about the wheel connecting to the frame, I don't understand how incorrect alignment could trigger pedal loosening. Don't understand any science here as long as the correct pedals are in correct crank side.

So thought to throw it out to the forum. As am now paranoid when riding checking pedal thread every couple KM plus carrying spanner and I am wanting to get back to normal...

The only positive is I thought it was a thread matter with the 150mm crank thread and moved to 127mm crank position and am finding this transition fine.

Appreciate any wisdom or logic please for my sanity ??... cheers Jimmy
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Old 2017-09-25, 02:37 PM   #2
sacherjj
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Left and Right cranks and pedals are threaded opposite. This is done so that the slight torque applied with the bearing on the pedals will tighten the pedals. If you have the wheel backwards, due to mounting or frame, you are putting force to unscrew the pedals. This really sounds like what you were experiencing. Was back to front making the pedals left to right?

Last edited by sacherjj; 2017-09-25 at 02:39 PM.
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Old 2017-09-25, 02:47 PM   #3
UniDreamerFR
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I will ask and say obvious things there:
When you fixed the frame that was back to front, did you also turn the saddle in consequence ? if you didn't, it's normal that you had this issue.

If the frame was back to front but the saddle was on the right direction according to the frame, (so the saddle was pointing backward too) you were just riding your wheel backward in the first place, which would obviously explain why the pedal were getting loose.
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Old 2017-09-25, 03:40 PM   #4
JimT
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Explaining this could get confusing with front and back of the frame and such. No matter what else, the bottom line is that when riding the right foot has to be on the right (R) peddle/crank and vise versa.
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Old 2017-09-25, 05:38 PM   #5
Mikefule
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The right pedal has a conventional clockwise thread. Screw it in clockwise to tighten it.

The left pedal has a left handed thread. Screw it in anticlockwise (US= "counterclockwise") to tighten it.

They took the wheel out to change the tube, and they put the wheel in back to front. That was careless of them. They should have known because bicycle pedals follow the same rule for the same reasons.

The reason that the pedals have opposite threads is because of a phenomenon known as "precession". It isn't simply friction in the bearings, but the way that the direction of pressure on the bearings changes during the pedalling action. If you pedal any significant distance with the cranks and pedals on the wrong side of the uni, the pedals will unscrew and may damage the cranks. I once wrote off a brand new crank like that in about 100 yards of riding.

If you were to set the uni up correctly and then ride BACKWARDS for a significant distance, the pedals would unscrew.

You cannot put a pedal in the wrong crank; it just can't be done (barring considerable amounts of brute force and crass stupidity) but it is very easy to get the cranks on the wrong side of the uni. This is something you should always check and double check whenever you remove and replace either the wheel or the cranks.
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Old 2017-09-25, 06:18 PM   #6
RHankey
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Here is an article that describes precession with an animated diagram which might help understand why pedals are threaded Right & Left.
http://blog.everydayscientist.com/?p=2655
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Old 2017-09-26, 01:11 AM   #7
GideupJimmy
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Still confused

Hey all appreciate the replies. Penny hasn't dropped as I keep thinking that Right foot on Right pedal is as simple as it gets. Whatever I did seemed to fix the issue. But still unclear on the science that how Right Foot on Right pedal can be different to Right foot on Right pedal subject to how the wheel slots into the frame...
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Old 2017-09-26, 04:01 AM   #8
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Quote:
Originally Posted by GideupJimmy View Post
Hey all appreciate the replies. Penny hasn't dropped as I keep thinking that Right foot on Right pedal is as simple as it gets. Whatever I did seemed to fix the issue. But still unclear on the science that how Right Foot on Right pedal can be different to Right foot on Right pedal subject to how the wheel slots into the frame...
It is not as simple as right foot on the peddle that happens to be on the right side of the uni. It is, right foot on the peddle that is marked with an "R" and is threaded into the crank with a right hand thread. As opposed to the wrong way, right foot on the pedal the is on the right side but is marked with an "L" and has left hand thread into the crank.

Some pedals may be marked differently. Maybe Right and Left or a grove in the left hand one.

Sounds like you have it correct now.

Jim
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Old 2017-09-26, 05:14 AM   #9
Mikefule
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Quote:
Originally Posted by GideupJimmy View Post
Hey all appreciate the replies. Penny hasn't dropped as I keep thinking that Right foot on Right pedal is as simple as it gets. Whatever I did seemed to fix the issue. But still unclear on the science that how Right Foot on Right pedal can be different to Right foot on Right pedal subject to how the wheel slots into the frame...
Right pedal can only fit into the right crank. Clockwise thread.

Left medal can only fit into the left crank. Counterclockwise thread.

Right pedal must be on the right side of the unicycle, with your right foot on it.

Left pedal must be on the left side of the unicycle with your left foot on it.

If you have the pedals on the wrong side of the unicycle - the pedals will unscrew as you pedal forwards.

The ways to have the pedals on the wrong side of the unicycle include:
1) Replacing the cranks and putting them on the wrong sides.
2) Taking the wheel out to replace a tube, then putting it back in the wrong way round.
3) Taking the seat off then putting it back on the wrong way.

It doesn't matter which way the frame is pointing. It is conventional to have the slot at the back, but for most conventional frames (not the Hatchet) the frame will work exactly the same facing either way.

The important thing is which way the pedal is turning on its spindle when you are pedalling forwards. If the pedal is under the wrong foot - that is, on the wrong side - then it will be turning the wrong way and will unwind.
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Old 2017-09-26, 06:31 AM   #10
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Quote:
Originally Posted by Mikefule View Post
The ways to have the pedals on the wrong side of the unicycle include:
1) Replacing the cranks and putting them on the wrong sides.
2) Taking the wheel out to replace a tube, then putting it back in the wrong way round.
3) Taking the seat off then putting it back on the wrong way.
Jimmy should always dobble check L/R when he gets his uni back from the bike shop. UniMyra learned this the hard way, and fell flat on his back off his 36'er after the LBF rebuilt his wheel and switched the left and right cranks.
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Old 2017-09-26, 09:25 AM   #11
Eric aus Chemnitz
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Wiki:Precession (mechanical) (with animation)
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Old 2017-09-26, 09:34 AM   #12
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Just for the record: Frames without brake mounts have no forward and backwards. It really does not matter. Most people have the slot for the seatclamp at the back, but that's really for no technical reason.
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Old 2017-10-01, 01:13 PM   #13
GideupJimmy
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Quote:
Originally Posted by UniMyra View Post
Jimmy should always dobble check L/R when he gets his uni back from the bike shop. UniMyra learned this the hard way, and fell flat on his back off his 36'er after the LBF rebuilt his wheel and switched the left and right cranks.
Hey UniMyra... can relate to the surprise of pedal falling off and then the crashing down part as Jimmy's elbow is still feeling it... UniMyra and Jimmy have something in common albeit on each other's other side of world...

Yep... the problem has not reoccurred and am back to normal. ...

Given jimmy did not change cranks but simply ( because it seemed to make sense at the time) took wheel out and turned it around plus rotated seat ... penny yet to drop as to how it resolved matter as Right pedal remained screwed in the right crank and left pedal remained screwed in Left Crank ......
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