Sideway movement of the rear wheel


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? [url]Photos of Stridas in Hong Kong]

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 :confused:

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.


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…

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?

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. :imp:

See also these topics: [url]My Strida doesn't like cold weather] and [url]Assembly problem?]

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

Part 338 is not bent and still ok:

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):

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…

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

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 :smiley:

Btw, I can’t resist to mention that “bombproof” 16 inch Strida wheels were not built…by now…

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 :slight_smile:

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:

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.

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 :question:

I thought in fact that you’re a high-miler…

However, retracting of bolt 373 and releasing of belt tension should do, I mean.

@ Bietrume:
Many thanks for the inspiration :wink:

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

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.

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.

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).

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 :slight_smile: ),
were at least one time trued and their spoke tensions were corrected,
so the results might be slightly different to untouched Original Strida wheels.

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 :open_mouth:
(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.

Do you think the above is clear enough?

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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.

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

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 :imp: .
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?

It’s a bit tricky to measure the inside diameters exactly with a usual sliding caliper, I mean.
So, I’d say the bolt side is minimally oval (~ 0,05 mm).

The axle side is definitely oval, in the same direction (red arrow) like yours for ~ 0,1 mm.

I’m sure the plastic part is in fact sliding in the tube, it was hard to pull out, yes, but the high forces inside of the joint will be able to move the plastic part easily - the “levers” (seat and bottom tube) are 75 cm, respectively 90 cm long!
Btw, didn’t measure the inside diameter of the plastic part, it’s looking as good as new:

I was also thinking of to put something below the cup spring, but a matching washer, or shim, has to be strong (and of a certain thickness).
Doing that will increase the force of the cup spring, don’t you think so?

So you have similar holes and axle dimensions as on mine!

I see that your bottom tube is as damaged by the cup spring as on my Strida :frowning:

I was thinking to a washer of 0.5mm thick, made out of spring steel. These parts are used as valve shims in shock absorbers and are quite hard (harder than aluminium anyway). The shim being not coated, I will paint it.
As the bolt 373 is tightened to torque, the force should not be higher than without washer, the bolt will only extend with 0.5mm more to the outside.

Oh, f…, yes, I didn’t recognize the torque, thank you :blush:


I was actually wrong in my statement about the torque :blush: . And you were right when you wrote that adding a washer would increase the spring preload. The sketch below shows that bolt 373 is actually torqued against axle 340 end. So the cupped spring preload is purely dependant on distance X (spring built-in length).

I think I now have an explanation for the angular movement of the wheel on my bike: the sharp edges of cupped spring 367 eat the surface of the bottom tube and of washer 364 away (as can be seen here), which increases the cupped spring built-in length. These springs are very stiff, which means that a small variation of their built-in length greatly affects their preload.

I have not checked the dimensions of the cupped spring 367, buit I think they are close to these ones: inner diameter: 12.2mm, outer diameter: 28 mm, thickness: 1.25mm, total height: 2.1mm

In a catalogue ( you find out that when you compress such a spring by 0.64mm, you achieve a force of 2083 N. If you now compress it by only 0.38mm, the force drops to 1395 N.

So, the wear/deformation that can be stated on both bottom tube and washer 364 will make the preload of the cupped spring drop sensibly.

Looking now to the exploded view of the Strida in the manual, you can see a washer 363 between cupped spring 367 and the bottom tube. According to me, this is a flat washer that prevents the wear of the tube and also increases the preload of the spring. I wonder why they have removed it.

I get mad when I see that such cheap parts and poor design can affect the functioning of this otherwise nice bike. :imp: :imp: :imp:

This poor design has following consequences:

  • Irreversible damage of the aluminium bottom tube.
  • Clicking noise
  • Angular movement of the rear axle + wheel : this can trigger the belt to jump on the flanges of the freewheel and definitively damage the belt.
  • Bad guidance of the rear wheel: it accelerates the wear of the rear tire and causes bike instability.

I sincerely hope that these problems have been solved on the EVO3, as its high price should go together with a high quality level.

Dear Bietrume,

thank you so much for research, explanation and the excellent drawing!

Your conclusions are indeed coherent and comprehensible and they also explain the different part numbers of the exploded drawing.
(I was totally wrong to think that there could be two cup springs in that place - as stated erroneously in the post here)

This is anyway a highly important discovery - which should be definitely reported to Ming - and it should be investigated why the washer is missing.

For the cup spring:
Recently we’ve reordered a few springs, therefore it was easy to measure the real dimensions of 5 unused original springs;
inner diameter 12,3 mm, outer diameter 23 mm, thickness 1,7 mm, total height 2,9 mm
So - due to more thickness - the force of the original cup springs might be much higher than the amounts of the example from the catalogue…
(Interesting detail at the “Group2; 1,25 up to…” - radiused edges - aha!!)

According to Bill there are only two “washers” below the rear wheel bolt of the EVO…
Last week arrived finally a few EVOs Vienna, I’ll check their rear bolts asap.

Anyway we should tell Ming our opinion about the cup spring!
Honestly, I don’t have much hope, but maybe Ming cycle has learned meanwhile to respect and follow the advice of experienced customers.

[i]I want to beg here also for assistance of technically versed Strida users and dealers!
Ask the Ming cycle technical support about the frame damage, clicking noises, movement of the rear wheel and the missing washer 363 of your Strida.

Please report here in the forum if your Strida does have the big washer 363,
I would really like to know if the washer was mounted on older versions…