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Sideway movement of the rear wheel

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Sideway movement of the rear wheel

Postby Bietrume on Mon May 06, 2013 2:01 pm

Hi,

How much sideway movement of the rear wheel do you state when applying force on the pedals?
Standing still, when I apply the brakes and push on the pedal, I see the rear wheel tilting sideways by 3 to 5 mm. Is this normal and due to the cup spring used in the rear axle, or is part 338 probably bent like shown in following topic? http://www.stridaforum.com/forum/viewtopic.php?f=4&t=3421&start=15

I even have the feeling that when I don't pedal but move my buttocks sideways when riding downhill, it induces a tilting of the rear wheel causing on its turn a wavy trajectory :?
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Re: Sideway movement of the rear wheel

Postby Blackstridaaustria on Mon May 06, 2013 3:44 pm

Hello Bietrume,

there's no (visible) sideway movement at both of our Stridas.
But, they're both as good as new...

I think the cup spring can't be the reason for this movement, the spring is on the end of the right quarter of the rear axle.
(This quarter is in fact the axle of the bottom tube, not the axle of the rear wheel.)
The left half of the rear axle is the "real" wheel axle.
And the second (right) quarter is actually a left-handed thread plus a hexagon piece.
The complete rear axle is screwed in the seat tube from the left side, the bottom tube and it's "bearing" (part nr. 100-07) secured by bolt 373, washer and cup spring.

Supposed the left-handed thread is not loose, the sideway movement might also be generated by a backlash of the right rear joint, not only the wheel-axle joint at the left side, what do you think?

Hmm, I believe you should take a look inside, maybe first at the left for the 338 part...
I've original axles here, if you need dimensions for comparison please let me know.
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Re: Sideway movement of the rear wheel

Postby Bietrume on Tue May 07, 2013 6:31 am

Hi BSA,

Note that to state the tilting of the rear wheel, you should only apply the front brake and push quite hard on the pedal.
But I agree, I should take it apart to understand what's really happening. I will simultaneaously change the freewheel which is wearing quite fast: the teeth of the pulley are still OK, but the pawls don't engage well and the bearing shows a lateral play of about 1 mm...
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Re: Sideway movement of the rear wheel

Postby Blackstridaaustria on Tue May 07, 2013 6:36 pm

Yes, I see, front brake only...now it is possible to reproduce that movement, it is very small, maybe ~ 1 mm.

How many kilometres did your freewheel last this time?
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Re: Sideway movement of the rear wheel

Postby Bietrume on Wed May 08, 2013 2:43 pm

Hmm, difficult to say as I have no cycling computer anymore on my Strida.

I guess the freewheel lasted about 1000...1200km maximum (2.5 years). It is still the original one but it was causing me problems right from the beginning: high drag and bad working ratchet mechanism, especially after having ridden in the rain. :evil:

See also these topics: http://www.stridaforum.com/forum/viewtopic.php?f=4&t=3344 and http://www.stridaforum.com/forum/viewtopic.php?f=4&t=3243
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Re: Sideway movement of the rear wheel

Postby Bietrume on Mon May 27, 2013 7:41 pm

Today I removed the wheel to check what was wrong. Well... nothing :lol:

Part 338 is not bent and still ok:
Image


The sideway movement is actually due to the flexibility of the plastic rim:shock:

By pushing with my thumb the rim flexes by 4mm (check the edge between aluminium part and plastic part of the rim):
Image
Image

So this sideway movement appears to be normal on a Strida LT. I would be curious to know whether spoke wheels are stiffer than the plastic ones?

As I will order a new freewheel, I will order part 338 as well, just in case....
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Re: Sideway movement of the rear wheel

Postby Blackstridaaustria on Mon May 27, 2013 9:22 pm

Bietrume wrote:I would be curious to know whether spoke wheels are stiffer than the plastic ones?


Very good question, I think the first step must be the creating of a norm :twisted:

Yes, I really think so, no joke...did you try to squeeze a common body weight scale with a similar grip like that above?
I did and reached from 5- 25 kgs, depending on different ways to grab the scale.

Do you think it would make sense, preconditioned the axle is 100 % stiff mounted, to apply a defined weight (say 10 kgs iron attached to a hook) at the rim's edge?
Measuring of the wheel bending via clockwork would be easy then.
I've all kinds of Strida wheels (except 14 inch) handy and a comparison should be no problem,
but for a minimum standardization of the measuring method I'd appreciate your advice :D

Btw, I can't resist to mention that "bombproof" 16 inch Strida wheels were not built...by now...
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Re: Sideway movement of the rear wheel

Postby Bietrume on Tue May 28, 2013 2:34 pm

I agree with you, to properly compare the radial stiffnes of the wheels we need a pre-defined test set-up. What you propose is OK: 10kg applied with a hook on the rim edge.
Now the question: do we keep the force constant for all wheel diameter or do we keep the bending torque (force x wheel radius) constant? I think the force should be kept constant.

When I now think back to the sideway movement of the wheel, I am not sure that the radial wheel stiffness contributes to it because the traction force is applied in the wheel plane. Either the wheel axle bends, either there is some backlash of the right rear joint as you suggested.

I hope your experiments will clarify things :)
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Re: Sideway movement of the rear wheel

Postby Bietrume on Wed May 29, 2013 8:07 pm

Freewheel and part #338 have just been replaced. The wheel still moves sideways, but now it is clear that the wheel moves together with the seat tube around the right rear joint. I verified the bolt (373?) and the tightening torque is still ok.
So there is nothing I can do I am afraid :cry:
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Re: Sideway movement of the rear wheel

Postby Blackstridaaustria on Wed May 29, 2013 8:35 pm

I mean a little bit of play is required for the rear hinge (for folding), but not that much as you wrote above.
Did you have a look at the plastic (?) part 100-07?
Maybe this part (and the corresponding holes of the bottom tube) widened out by the time?

However, I'm still very interested in the wheel stiffness, today I've prepared some parts for a first test and measuring results will follow asap.
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Re: Sideway movement of the rear wheel

Postby Bietrume on Fri May 31, 2013 6:48 am

I did not check plastic part 100-07, but I will do it and measure the different hole diameters.
I guess, I just need to take the rear right joint apart and not the wheel axle from the seat tube?

With so few kilometers ridden, and considering my low weight (67kg) and my normal physical condition, I wonder how I could have tortured the rear joint :?:
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Re: Sideway movement of the rear wheel

Postby Blackstridaaustria on Fri May 31, 2013 7:18 am

I thought in fact that you're a high-miler...

However, retracting of bolt 373 and releasing of belt tension should do, I mean.
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Re: Sideway movement of the rear wheel

Postby Blackstridaaustria on Fri May 31, 2013 4:11 pm

@ Bietrume:
Many thanks for the inspiration :wink:

Below the results of the wheel stiffness experiment;
but first a few words about the test setup:

Image

A common Strida rear axle was clamped firmly with a vise, the main measuring clock,
magnetically clamped to a ~ 25 kg steel plate, is touching the rim from the bottom, as close as possible to the weight.

Image

The feeler of the second measuring clockwork is in touch to the axle via an Allen bolt to check the axle bending.
The axle bent under load with all 16" wheels 1 tenth mm; the clockwork's arm is sadly too short for 18" wheels.

Image

The weight (a concrete drill core) of ~ 7,2 kilogram can be attached via a steel hook, below the hook an aluminium pad, for centering of the weight in the middle of the rim's flank and to protect the rim.
Applying the weight on different points of the rim (above and vice-versa the valve hole, between or directly above spoke nipples) did not affect the bending of the rim (much, within 1 tenth mm).

Image

Please note:
All checked wheels are rear wheels, except the LT plastic front wheel.
All Original Strida wheels (of course, except the LT plastic wheels :-) ),
were at least one time trued and their spoke tensions were corrected,
so the results might be slightly different to untouched Original Strida wheels.

Image

An amazing effect can be watched on the plastic LT wheels only:
Once the full weight is applied, the indicator of the clockwork doesn't really stop at the reached point - slow, but steady the indicator moves along :shock:
(I've stopped this test within 30 seconds or so...couldn't watch that, sorry...)
It has to be said that vice-versa the same effect appears:
Once the weight is detached, the clockwork's indicator will not stop at a particular point, for a short time it will move slowly further.
These movements were within a range of 3 tenth of a millimeter.

Bietrume wrote:I hope your experiments will clarify things :)


Do you think the above is clear enough?
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Re: Sideway movement of the rear wheel

Postby Bietrume on Fri May 31, 2013 8:34 pm

Very nice, thanks for this experiment. So it is clear that the LT rims are at least twice as flexible as the spoke wheels.

You applied a weight of 7.2 kg and with my thumb I probably applied double as much in order to reach 4..5mm deformation, seems logical.

The limited deformation of the axle also reassures me.
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Re: Sideway movement of the rear wheel

Postby Bietrume on Mon Jun 03, 2013 8:14 am

I took the rear right joint apart and measured the different diameters:
Image

The inside diameter of the plastic insert 100-07 is OK, but I can see that the holes in the lower tube are slightly oval. Which I don't understand, because that would suggest that the plastic insert is continuously sliding in the tube, which is definitely not the case as it was hard to get it out of the tube.

I also stated that the cup spring continued its abrasive work on the lower tube, even after I had rounded the sharp edges and put some grease some time ago. After a while there will not be enough tube material anymore :evil: .
I think I can get some spring steel shims at my job, that I will put between the tube and the cup spring. This should definitely reduce the wear.

BSA, could you please check the hole diameter of the lower tube of your Strida when you have the chance?
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