Ming Cycle's reply to ST-QRS-001/saddle bolt request

Blackstridaaustria · November 30, 2010, 11:02pm

Dear forum members,

on 06.11.2010 I sent a request with two technical questions mentioning the Strida Quick Release Seat Molding and the Strida saddle bolt/nut to mingbike@ms9.hinet.net

As there was no reaction till 16.11.2010, I sent the message to info@vanmoof.com , who kindly forwarded it to Ming Cycle. Thanks to VANMOOF/The Netherlands!

Here is the message:

Dear Ming Cycle Team,

first I have to say many thanks to the whole team for crafting the famous folding bike Strida!

As an enthusiastic owner of a black 16" 2SD (original Schlumpf) and a brushed silver 18" SX, I was very happy to get the new quick-release-saddle system very soon from Vanmoof/Netherlands.
The QRS-001 seemed, at first sight, to be a wonderful solution to share the Stridas with my girlfriend and my sons, without the need to use tools for saddle height adjustment.

But then an annoying limitation was found: the splitting of the adjustment range in two parts (higher and lower) , which cannot be changed without tools (2mm Allen key, 6mm Allen key and/or 13mm flat wrench, depending on saddle bolt).

StridaJohn posted at Stridaforum:

…"The main disappointment for me is it only has limited adjustment … only about 10 - 12cm. It does not adjust all the way up and down the ‘seat’ tube. I was hoping that it could be used to share my Strida with my wife, without having to unscrew the seat clamps (or move pins). But for major adjustments the whole seat thing still has to be removed to move the pins ! Such a PITA ! "…

Quick Release Seat Molding ST-QRS-001

I believe there is a solution, requiring a seat pin with a special shape and just one hole in the seat molding. I want to test this at my own risk. Such experiments will cause the loss of any warranty, but this is definitely not the point. My first question is:

-Will a hole with a diameter less than 7,5 mm cause MAJOR decreases in the stability of the seat molding?
(the axis of the hole will meet the axis of the saddle tube at 90 degree angle, please refer to pictures QRSmod 01-03.jpg for exact position, marked red)

The second question is related to the saddle bolt (and nut), and has been posted by tszsiutong at HK Strida Club already:

hkstrida.org/forum/viewtopic.php?f=13&t=4086

I noticed the bolt material (marked KSFC M) is much different from the nut material (marked A2-70, stainless steel).
However, stainless steel may cause trouble, an effect called “galling”, and our experience affirms that.

Please refer here:

estainlesssteel.com/gallingofstainless.html

…“Thread galling seems to be the most prevalent with fasteners made of stainless steel, aluminum, titanium, and other alloys which self-generate an oxide surface film for corrosion protection. During fastener tightening, as pressure builds between the contacting and sliding thread surfaces, protective oxides are broken, possibly wiped off, and interface metal high points shear or lock together.”…

en.wikipedia.org/wiki/Stainless_steel

…“When stainless steel parts such as nuts and bolts are forced together, the oxide layer can be scraped off, causing the parts to weld together. When disassembled, the welded material may be torn and pitted, an effect known as galling.”…

-Will Ming Cycle supply a different saddle nut/bolt combination to solve the seizing (or galling) problem in the future?
(For my part, the problem is fixed with a lubricated titanium nut and bolt.)

Best regards,
BSA

Here the attached pictures:

QRSmod 01.jpg

QRSmod 02.jpg

QRSmod 03.jpg

On 18.11.2010 strida-global@strida.com replied:

I wrote back:

On 23.11.2010 strida-global@strida.com replied again:

This time I replied, on 25.11.2010:

Dear X.Y.,

many thanks for your reply.

I am sorry that my information was not detailed enough to explain what I want to do and what for.
Let us give it a second try, I will do my best to be more accurate.

Q1: I do NOT want to touch the frame TUBES of the Strida, no more ore bigger holes in any way.
Actually I meant drilling a hole (diameter less than 7,5 mm) into the PLASTIC material of the SEAT MOLDING.
Placed in the correct position (marked red in the attached paper drawings to be seen on pics QRSmod 01-03.jpg) , this hole will make the change of a (modified) seat pin from upper to lower position possible without the need of unmounting the complete seat molding (and the saddle) to change the positions of the seat pin!

[For better understanding please refer to picture seat pin 03.jpg, the drawing shows the original Strida and the modified seat pin. The modified pin contains a little magnet, which provides enough force to hold the 2mm Allen key safely for inserting the seat pin to the desired (upper or lower) hole of the rear tube THROUGH the plastic part of the seat molding. Here I have to notice that another little modification relating to the part QR locking mount.jpg is implicitly necessary. Of course the hole in the locking mount must have the same diameter as the one in the seat molding! As the modified seat pin has a diameter of 7,0mm, the hole must be 7,5mm, I mean.]

Here the desired function of the Strida QRS in steps, for example changing from upper to lower position of the seat pin:

open top and bottom Q/R lever

pull Q/R locking lever

slide seat molding in position with hole over seat pin, release Q/R locking lever

retract seat pin from upper position with 2mm Allen key (THROUGH the seat molding)

slightly pull Q/R locking lever and

slide complete seat molding with locking mount and locking lever to lower postion, hole in the seat molding over lower hole for seat pin, release Q/R locking lever

insert the (magnetic) seat pin with 2mm Allen key and make sure the locking lever fits onto the seat pin

lock top and bottom Q/R lever

Now the seat pin has changed its position from upper to lower WITHOUT un- and remounting of saddle and QRS.
There is no need to carry two 13mm wrenches with you, the time saving is enormous.

The question newly phrased, logically similar:
The top and bottom Q/R lever clamps MUST transfer the FULL weight force of the rider to the frame.
The seat pin and the Q/R locking lever mechanics MUST NOT transfer ANY weight force of the rider to the frame.
Is that correct?

Q2: The nut of the saddle bolt is marked A2-70, this is without any doubt STAINLESS STEEL!
The saddle bolt is made of DIFFERENT MATERIAL, which is marked KSFC M.

A simple test verifies the DIFFERENT materials: The BOLT IS magnetic, the NUT IS NOT!

Please refer to attached picture saddle bolt 01.jpg to see the markings.

Please refer to “A2-70” here:
volksbolts.com/faq/basics.htm
or here:
kqfastener.en.made-in-china.com/ … A2-70.html
bssa.org.uk/publications.php?id=42
or just google “A2-70”

Please talk to your technicians, they must know about “A2-70”!

And, partially, you are right, stainless steel contains chromium and molybdenum in various amounts as an alloying component.

However, the use of stainless steel, in combination with stainless steel OR non-stainless steel, WITHOUT lubrification MAY cause seizing or galling problems.
Nut and bolt will be “welded” together, and exactly this was mentioned in Strida forums, corresponding to my own experience.

The possible solutions for the problem would be, in my opinion:
a. To change the bolt to stainless steel (application of anti-seizing compound ABSOLUTELY necessary)
b. To change the nut to the same steel specification as the bolt, not stainless (I would recommend application of anti-seizing compound although NOT necessary)
c. To change nothing, in this case a small amount of an anti-galling/seizing product applied on the bolt would solve the problem for a long time.

[Working with stainless steels like Nirosta, V2A and Inox for over 25 years I would strongly recommend the use of the product below:
neverseezproducts.com/antiseize.htm ]

The technicians of Ming cycle actually have no information about seizing or galling of stainless steel?

I do not know what sort of bolt and nut you use at fabrication of the Strida, but both of my Stridas were originally equipped with this material combination, as I got them in hand here in Austria.

I would like to post our correspondence in Strida forums, maybe some member is able to enhance communication.

With kind regards
BSA

Here the newly attached pictures:

seat pin 03.jpg

Q/R locking mount.jpg

saddle bolt 01.jpg

This for now, here we have Wednesday 01.12.2010 0:00 am
I will post answers of Ming as soon as possible.

The reply on 02.12.10:

Dear BSA,

Thank you very much for your explanation!

Here are our comments -

If the pin was modified, it couldn’t be used for the other seat moulding (w/o QR).

If the pin was modified, the rear tube could be hurt by touching with seat moulding while open the QR.
3.The end user will have to buy the pin while they need a new QR seat moulding.
4.We don’t recommend to move the pin oftenly, because it may not be tighted enough, the hole may become bigger, all cause the safety problem.
5.The cost won’t be cheap to produce the new pin, must including the new mould & the M.O.Q. for 60 thousands.

Yes, the top and bottom Q/R lever clamps MUST transfer the FULL weight force of the rider to the frame. The pin is to fix the seat moulding and avoid it to move down & around. We tried to use the QR seat moulding without pin in the beginning, but it moves down somehow.

We don’t think it’s a problem to use 2 different material in bolt & nut, it is very common in the bicycle industry.
a) If changed the bolt to stainless, it would not strong enough.
b) If changed the nut to cr-mo, it would go rust very soon in some countries like Holland.
c) We used nylock before, but then it’s hard to be unscrewed.

Best regards,
X.Y.
MING CYCLE IND. CO., LTD.
mingcycle.com.tw

Dear members, what do you think?
Your suggestions, opinions or whatever are highly appreciated.

Thanks!

Blackstridaaustria

Binch_Shin · December 18, 2010, 1:17pm

Hello

Sorry for my late opinion…

With your new Height Adjustable System, it could be difficult to secure that the Seat Pin is always positioned properly. Even the checking seems difficult.
In the original system, ‘Setting the pin’ is the first step of the total assembly process

Binch

Blackstridaaustria · December 18, 2010, 9:39pm

Hi Binch Shin,

many thanks for your reply, better late than never!

Sadly, I am not able to fully understand what you mean with “positioned properly”?

There are two holes in the frame tube, the upper and the lower possibilities to insert the seat pin.
To be more precise, we actually have four holes because the tube is hollow.
So, let’s say we have two holes pointing in driving direction and two holes are pointing backwards.
The seat pin will be mounted in any case (regardless of original or modded version) through one of the backward holes, which contain the threads for the seat pin, at first.
Once the backward hole is passed by the seat pin, there are certainly just two possibilities left:

The seat pin WILL NOT find the corresponding, forward pointing, hole.
That means the tip will bump against the inner diameter of the tube, the thread of the pin will not find its corresponding thread, it will be possible to turn it around a little, but not to fix it properly. Furthermore, if the seat pin has been mounted “that wrong way”, it will be impossible to mount the Q/R seat molding (using original parts) or it will be impossible to move the seat molding up or down (using a modded seat molding). Also the Q/R locking lever needs the tip of the seat pin for correct function, but more about that below.
The seat pin WILL find the corresponding hole.
The small conical area at the tip of the seat pin supports this action, the seat pin’s thread will find its partner in the hole without any problem, and the bolt can be fixed properly by turning clockwise.

So, in my opinion, the seat pin might be mounted in just two ways:
“Positioned properly” or not, absolutely regardless of what seat pin or seat molding has been used!

Yes, checking might be difficult when the seat pin is blackened…

Below, the inside of the Q/R locking lever (red) with attached Q/R locking lever safety hook (black) can be seen:

In correct mounting position the Q/R locking lever sits on the tip of the seat pin, secured with the plastic hook. The tip fits in the round, deeper hole inside the arrowed shape.
If the seat pin is not in its proper position, the Q/R locking will slip to the top of the Strida, each time unlocked, and loose its functionality or fall off.

Yes, according to the manual, page EN-4, chapter “Installation”, step 1 :
“Ensure the seat pin is fully tightened.”

The installation process in 18 steps will be equal, whether original or modded version.
The 8-step process mentioned above belongs to the height adjustment of a modded version only!

More comments on this topic are highly appreciated!

Best regards

BSA

Binch_Shin · December 19, 2010, 2:32am

I have two thoughts:
1. if you insist Easy Movable Seat-pin then your idea is the best solution including less modifications. There would be no structural imperfection (that I could point out )
2. Ming Cycle Engineer’s advice is considerable : #4.We don’t recommend to move the pin often, because it may not be tightened enough, the hole may become bigger, all cause the safety problem. Following my engineering experiences, aluminum thread doesn’t lead its bolt precisely through itself… sometimes it’s hard to notice Going Wrong…

Binch

Blackstridaaustria · December 19, 2010, 9:36pm

Hi Binch,

Knowing that you are a mechanical engineer and designer, your words are a precious affirmation, thanks!

True for sure, but where is the problem?
Might this be caused by missing lubrication?
I think the biggest problem is the inappropriate material pairing, in this case aluminium/steel.
This sort of material pairing, just like stainless steel/aluminium or even stainless steel paired with stainless steel, always tends towards galling or seizing without using an anti-seizing lubricant.
(That’s exactly what I mentioned about the saddle bolt/nut combination, and I am really surprised that Ming’s technicians have never heard about such things - point 7. of Ming’s reply.)

Ming’s engineers are certainly trustworthy, but one thing makes me really perplex, at point 6.:

“Yes, the top and bottom Q/R lever clamps MUST transfer the FULL weight force of the rider to the frame. The pin is to fix the seat moulding and avoid it to move down & around. We tried to use the QR seat moulding without pin in the beginning, but it moves down somehow.”

Dear Binch, please correct me if I am wrong, but in other words this means:

Sometimes, caused by “somehow”, DOES the seat pin transfer ANY WEIGHT!
Otherwise the seat pin would not be able to stop the slipping process…

I hope to keep your interest running…

BSA

Binch_Shin · December 29, 2010, 6:49pm

Hello BSA

I think the problem is originally from the low strength of aluminum… As you know, the thickness of rear-tube is very small. The length of thread is quite short The thread can be easily spoiled by a mere force. So I agree Ming’s advice, “Don’t change the pin position often.”

To analyze this mechanical matter, a recommendable approach is to choose knowledges of Static Friction. Before the seat-moulding slips actually (with an actual velocity), the seat-pin would take a small portion of weight. Physically : WEIGHT = Big frictional force of moulding + Small shear force on seat-pin

I have been waiting for a Height Adjustable Seat for a long time. I wanted it because lower seat is safe for running down and higher seat is helpful for climbing up. And now Ming’s solution is satisfactory. (but I didn’t buy it yet )

Although I am not in the Strida business, your demand seems not usual… not acceptable for many of Strida riders. Sorry to say this

Binch