Sideway movement of the rear wheel

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:

Hi BSA,

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 (http://www.bellevillesprings.com/disc-springs-din-2093.html) 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.
[/i]
contact@strida.com

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…

Hi BSA,

I’m glad you agree with my findings. :smiley:

So the cupped spring of the Strida does not have standard dimensions, this is really strange. It is maybe made according to Chinese standards :question:

Coming back to the contact surfaces of the cupped spring, here is what you can find on the same website as the one of the catalogue:

I wonder also why washer 364 has a stange shape when used. Is it a flat washer when new or is it also a kind of cupped spring? In the first option, it looks like the steel is much too soft for the loads it has to stand…

Hello Bietrume,

“agree” is not the fully correct expression, it was more like an enlightenment…

Unfortunately I’m really busy at the moment - the heating equipment in one half of my apartment is out of order and it’s getting cold here - therefore just a short interim report:

Should be possible to find out, but will take some time…

For the catalogue citation:
Thanks again, didn’t see that!
Hmmm, if we would now simply put hardened steel washers above and below the belleville (cup) spring then would the spring load raise…
…maybe too much for the bolt 373?
What do you think?

Today I could take a quick look at three original brandnew Stridas, EVO, SX and LT:
All of them equipped with the new EU-conform frame, the EVO was taken out from the original box.
Guess what?
NONE of the three was equipped with more than TWO “washers” below the bolt 373 :unamused:
(At the weekend it will be time to check two more EVOs and look at the washer 364.)

Btw, could you please tell us your meaning to this post?

Yes, that is a solution I was thinking about. If you want to keep the same preload, then you have to put a small washer of the same thickness as all the hardened washers you are adding, between bolt 373 and axle 340. Then the spring built-in length will not change. You just have to make sure that bolt 373 is screwed far enough into axle 340. If it is too short, use a longer one.

I now see that my sketch was wrong :imp:

I thought washer 364 was centered on axle 340, but it is actually clamped between nut 373 and axle 340. So if you add a washer under the cup spring you need to add another washer 364 but of the same thickness to keep the same spring preload.

In my case, I want a higher preload, so I will not add an extra washer 364.

Calm down, most of us will not have realized that :smiley:
The drawing is still very good, I was quite unsure about this detail and therefore I wanted to disassemble a few bolts at the weekend.
Seems that we need in sum three washers to reach the target of a fully functional rear joint…

I’m also quite unsure how to proceed with this post because it will belong to several known issues of the rear Strida region. To merge the posts is not that good, I think…maybe pin this post and edit with links to the other posted problems…

Well the proposed solution is less simple than I thought: the distance ‘X’ is only 2mm. The cup spring thickness is 1.7mm, so it can only be compressed by another 0.3mm before being completely flat. It is not advised to push a cup spring until it is flat as the stresses in the spring become too high.

Adding a washer under the cup spring is therefore not advised, if the washer is about 2 mm thick (like the stainless steel one I found in a DIY shop), the cup spring will not be centered anymore and bolt 373 will not be screwed against axle 340.
Overtightening the bolt will damage the cup spring.
Adding a third washer between axle 340 and washer 364 is not ideal because it will not center perfectly and the inner edge of cup spring 367 will not be well guided.

On my bike, I replaced the soft steel washer 364 by a stainless steel one, which seems to be a much harder material. The original washer was quite deformed/worn out, and my first impression today is that the rear wheel swing movement has been reduced by almost 50% by bringing the preload of the cup spring almost back to its inital value.

Had no chance to examine more Evos, sorry for the delay :blush:
But I’ve found a good pic of a 3.0 Strida’s rear area- there is an additional washer below the cup spring!

For this pic I’d like to get the permission to use it from [size=150]florian[/size] - are you still here?
Please look at your mailbox…

Yes, perhaps not ideal…but if the thickness of the third washer is below that of the cup spring and the outer diameter very close to that of the axle it should work, I believe.
The third washer should fit inside of the cupspring; imaginable as some kind of axle elongation - shown in red color below.
(I’m here also thinking about a method for easy retrofit - a longer axle, like mentioned by Xentrax here, would be the better solution, but it would also need much more effort for exchange.)
Hope you don’t mind that I’ve used your image for illustration:

I agree with your ‘3 washers’ solution. However, for a retrofitting solution, the difficulty will be to find standard stainless steel washers with the proper dimensions (diameters and thickness).
You can of course order custom washers made by laser cutting or etching but it could be quite expensive, especially if you have to buy the raw material in large quantity :confused: