Strida Bike’s Rear Hinge Explained
For Strida Fans, the Strida bike’s rear hinge has often been a topic for discussion. Some Strida owners may call it the ‘achille’s heel‘ of the Strida bike’s design and other owners may never experience a problem.
This blog post is my opinion of the Strida bike’s rear hinge based on my personal experience and discussions with other Strida owners.
The Strida Bike’s rear hinge is the connection of the bottom tube and the seat tube at the rear wheel of the Strida bike. The rear hinge makes it possible to fold the Strida bike. Depending on the weight of the rider and the amount of applied pressure on the pedals, there can be a significant force applied to this hinge. The other cause of force is the action of folding the bike and placing the bottom tube inside and beside the front tube. This action is the common way to fold the Strida bike. The Strida EVO model includes a Strida frame clip which holds the bottom tube to the front tube without the compression required to place the bottom tube inside and beside the front tube.
The Strida Bike’s rear hinge parts are, a thin nylon flat washer, steel cup spring, a small steel flat washer, and a bolt.
The nylon washer fits between the bottom tube and the seat tube and provides a smooth pivot when the tubes are folded.
The steel cup spring rests against the bottom tube with the end of the axle in the cup spring’s center hole. The compression of this cup spring provides the torque to hold the bottom tube tight against the seat tube. This cup spring is compressed even more when the Strida bike is folded and the bottom tube placed beside the front tube.
The small steel washer fits between the cup spring and the fastening bolt. The pivot point when lifting the bottom tube to fold the Strida bike is between this small washer and the cup spring.
The bolt that holds the rear hinge joint tight is the last part. This bolt is torqued 18 – 20 Nm and locked with a thread locking compound to prevent it loosening. This amount of torque applies the correct amount of compression on the steel cup spring to hold the Strida rear hinge tight when riding or folding the Strida bike.
How well does it work?
The above explanation is how the Strida bike’s rear hinge was designed to work. If the pivot point when folding is not between the small steel washer and the top surface of the cup spring, for example due to slightly out of tolerance parts or inadequate grease between these washers, then a problem will develop with this hinge. The problem is that the next part to move is the steel cup spring against the softer aluminum tube. The manufacturing of the steel cup spring can leave a very sharp edge, this sharp edge cuts into the softer aluminum tube and will wear a groove. This wear in the aluminum tube will eventually loosen the rear hinge. A Strida owner may first become aware of this situation when they hear a creaking noise, the steel cup spring moving against the aluminum tube can cause a creaking noise heard with each pedal stroke. This creaking noise can be transmitted up the seat tube and sound as if it is coming from the seat mount or the ball joint at the top of the Strida triangle.
If this condition of a loose rear hinge is not addressed then other problems may develop, the hole for the axle in the plastic end cap in the bottom tube can be enlarged. As well, the hole in the bottom tube that the end cap fits into and the axle goes through can also become enlarged resulting in more movement in the rear hinge. With enough movement the drive belt may twist and with a few twists will break.
I think it is important for Strida owners to check the operation of their Strida bike’s rear hinge. To check, keep your eye on the rear hinge when folding and make note of which part moves. The movement or pivot point should be between the small steel washer and the cup spring. The cup spring should not move and the bolt head should not move.
Rear Hinge Upgrade Kit
Strida Canada West’s rear hinge upgrade kit includes, nylon washer, Strida part # 166-1, bolt with thread locking compound, Strida part # 373, spring washer Strida part # 367, small hard washer, replacement for strida part # 364, 12x25mm stainless steel thin washer, small packet Never Seez compound, wooden toothpicks for Never Seez application, gloves for personal protection.
The rear hinge upgrade kit that I have developed has three changes from Strida’s original parts.
One, the small flat washer is a harder steel washer that does not deform with the applied torque.
Two, the steel cup spring is a Strida washer without the sharp edge. By grinding off the sharp edge there is less chance the cup spring will scar the aluminum tube. Grinding off the sharp edge also creates a larger and rough surface contact area with less chance of the cup spring moving on the aluminum tube.
Three, a thin stainless steel washer that is placed between the steel cup spring and the Strida aluminum tube. This washer is to protect the tube from damage.
With the kit I have included a small packet of Mariner’s Choice Never Seez compound to be applied to the top of the cup spring and the bottom of the small steel flat washer with the included wooden toothpicks. The Never Seez compound will insure that these two parts will move easily together and maintain the correct pivot point. I have chosen this product because Mariner’s Choice Never Seez offers “unparalleled resistance to water washout and the best protection in continuous high moisture environments both above and below water lines” as per their product information. This product may cause skin irritation so care needs to be taken. For this reason I have included one pair of protective gloves with this kit.
Installation of the Strida Canada West rear hinge upgrade kit requires a 13 mm wrench or socket to remove the bolt holding the existing cup spring and small washer. The bottom tube and the seat tube then need to be pried apart to clean and replace the nylon spacer washer. This nylon washer should be lubricated with the supplied Never Seez compound. After the bottom tube is replaced on the axle the this stainless steel washer and new cup spring can be fitted on the end of the axle. Apply the included Mariner’s Choice Never Seez compound on the surfaces where the cup spring and the small steel washer meet. This is the pivot point and the Never Seez compound will insure these parts move as they should. To install the new bolt the same 13 mm wrench or socket is required, ideally the bolt should be torqued 18 to 20 Nm as per the Strida manual page 20. If you do not have a torque wrench then you may want to have a bike shop tighten this bolt for you. If you do not use a torque wrench then be careful not to over tighten this bolt and compress the cup spring, 18 to 20 Nm of torque does not take a lot of pressure to apply. It is very important to check that the bolt does not turn when folding, if this happens then it will not take long for the hinge to become loose. I recommend that you check this bolt for looseness on a regular basis. I do this by watching the rear hinge when I fold and unfold my Strida. I watch that the pivot point is correct and that the bolt does not turn. The bolt supplied with the rear hinge upgrade kit is coated with a thread locking compound.
After installation I would wait two hours before checking the pivot of the rear hinge and testing the bike. This will give time for the thread locking compound to cure. When folding a Strida bike I often check the pivot point for the correct movement.
If the parts are within tolerance, and the joint is assembled correctly, and there is a long lasting grease between the small washer and the cup spring .. then the Strida rear hinge joint will generally last for years.
For some Strida owners the rear hinge joint might be the Strida bikes ‘achille’s heel‘ but I believe with the right parts and some preventative maintenance there is no reason why a casual rider or an everyday commuter should not enjoy many years of pleasure from their Strida bike.
Further notes and links
This thread in the Strida Forum is a discussion regarding this topic. The thread includes the experience of a Strida owner who has needed to repair his rear hinge. The parts and technique he used were developed by Strida Forum contributor BlackStridaAustria, AKA Chris D which are detailed here at this link.
October 10th 2015, I have added the thin stainless steel washer to the rear hinge upgrade kit. This washer may be optional if you would like your Strida bike to be more original. I think the added protection provided by this thin washer is a good reason to consider it’s use.