Folding bike lock security depends on four parts working together. They are the hardened steel plates, the rivets that join them, the geometry of each joint, and the lock body with its key cylinder. Folding Bike Locks Explained is the broader overview of this lock format and where it fits. This article goes one level deeper into how each part resists a specific tool. Cutting tools are a common threat: in a 2015 McGill survey of Montreal cyclists, bolt cutters (10.3%) were among the commonly reported means of theft1. The weakest part sets the strength of the whole lock.
Quick Answer
What makes a folding bike lock secure?
A folding bike lock is secure when every part resists the tool aimed at it. That means hardened plates against cutting, protected rivets against cutting and drilling, a close fit against levering, and a pick-resistant cylinder. A US patent held by Ino Vision, Seatylock's parent company, names the joint as the weakest part, because bolt cutters can cut through the rivets2. Independent attack tests then show whether the whole lock holds.
Key Takeaways
- Hardness shrinks what a cutter can cut: one maker rates its 36-inch bolt cutter for 14.3 mm of soft material (HRC-31) but 11.1 mm of hard material (HRC-48)3.
- One folding lock patent, held by Ino Vision, identifies the joint as the weakest part, because bolt cutters can cut through the rivets2.
- Plate thickness alone does not settle security: the policing guide describes cutting, levering, striking and picking as separate attacks4.
- Independent testing judges the whole lock: the ART test house runs more than 20 tests, including a cutting test and an attack test5.
Folding Bike Lock Security Basics
Folding bike lock security is a chain of separate defences, and a thief only needs to defeat the weakest one. Folding locks are chains of flat steel bars joined by pivots, usually rivets, so the bars fold into a compact bundle for carrying2. Opened out, the same bars wrap around a bicycle and an anchor. That design gives the format its reach and its compact frame carry, and it also creates more joints than a U-lock has.
What are folding bike locks made of?
A folding lock has four working parts. The plates, which patents call link members, carry most of the steel. Ino Vision's patent describes link members made of a material hardened and dimensioned against cutting, such as a hardened steel alloy2. The rivets act as hinge pins between the plates. The lock body sits on the last plate and houses the locking mechanism, and the key cylinder inside it decides who can open it.
Which attacks do thieves use on locked bicycles?
The US problem-oriented policing guide on bicycle theft describes cutting, levering, striking and picking as attacks on locks themselves4. Its authors list tin snips, bolt cutters, hacksaws and angle grinders as the cutting tools in use4. Survey evidence points the same way. In the McGill survey, bolt cutters (10.3%), hacksaws (4.5%) and crowbars (2.3%) were other commonly reported means1. Most victims surveyed (52.3%) do not know the means by which their latest theft happened, so the true share of each tool is uncertain1.
For a folding lock, this mix means no single specification proves security: the plates, the joints and the cylinder each need their own answer.
Folding Lock Plate Thickness and Hardened Steel
Plate thickness sets how much steel a cutter must cross, while hardness sets how much steel a given cutter can cross at all. HRC is the Rockwell C hardness number, a dimensionless value in which the final letter names the Rockwell scale used for the test6. Higher numbers mean harder steel, and harder steel resists the wedge-shaped jaws of a bolt cutter.
Why hardness changes what a bolt cutter can cut
A bolt cutter maker's own ratings show the effect of hardness directly. Apex Tool Group rates its 36-inch H.K. Porter cutter for 14.3 mm of soft material (HRC-31), 12.7 mm of medium material (HRC-42) and 11.1 mm of hard material (HRC-48)3. Moving from soft to hard material removes 3.2 mm of rated capacity from the same tool3. The 24-inch cutter is rated for 7.9 mm of hard material (HRC-48)3. These are ratings for stock in each hardness class, not results on any lock.
The same scale places very hard steel above those classes. Very hard steel, such as chisels and quality knife blades, runs from HRC 55 to HRC 666. Ino Vision's joint patent gives examples of protector steel ranging from a Rockwell C hardness over 20 to over 602.
Why thickness and hardness must be read together
Thickness and hardness work in the same direction. A thicker plate increases the steel the jaws must cross, and a harder plate reduces the steel a given cutter can cross. Neither figure is useful alone, which is why a specification should state both. Case-hardening is a heat treatment that hardens the surface of steel while leaving the core tougher. Lock makers often case-harden shackles and chains so the surface resists cutting while the less brittle core absorbs impact7. If a folding plate is case-hardened, the same logic applies: a cutter must first bite through the hard skin.
A plate thickness figure carries weight only beside a hardness statement and an independent cutting test. A thick plate of soft steel gives a bolt cutter more metal, but metal of a hardness it is rated to cut.
Folding Bike Lock Rivets and Anti Tamper Rivets
Folding bike lock rivets are a documented weak point. Ino Vision's 2020 US patent states that the weakest part of the folding lock is the joint, because bolt cutters can cut through the rivets2. The patent's named inventor is this article's author. The plates may be hardened, yet the hinge pin between them is a separate part with its own exposure.
How anti tamper rivets protect the joint
Anti tamper rivets are rivets fitted with hardened guards that stop a tool from reaching the pivot pin. In the patent, a protective sleeve stops the bolt cutter from cutting the joint member, and a cap stops drilling through it2. One example is a ring that may rotate freely around the rivet, which makes tampering with or cutting the ring very difficult2. Another example places a hardened plug in a recess at both ends of the rivet, so a drill bit meets hardened steel first2.
Seatylock's product description for the Foldylock Forever lists oversized drill-resistant rivets. A patent records a design and its intent, and it is not test evidence for any product. The joint still needs an independent attack test behind it.
When a product page says only "riveted", treat the joint as the open question. Look for a stated rivet guard on both faces and an independent attack rating that covers the whole lock.
Folding Lock Joints Under Leverage and Twisting
Folding lock joints face a second threat besides cutting: leverage, where a bar or the bicycle itself turns the lock against its anchor. The policing guide describes the attack plainly:
"Thieves will use the gap between the stand and the bike left by a loosely fitted lock to insert tools such as jacks or bars to lever the lock apart."
Shane D. Johnson, Aiden Sidebottom and Adam Thorpe, ASU Center for Problem-Oriented Policing4
The same guide notes that thieves even use the bike frame as a lever, rotating it against the stand until either the bike or the lock breaks4. Every hinge in a folding lock is a point where that twisting load concentrates. A lock that wraps the frame and anchor with little slack leaves no room for a bar and less freedom for the frame to rotate.
Length is therefore part of joint security. The right length closes around the actual frame and the usual anchor, without loops of spare plate. The guide on how to choose a folding bike lock covers matching length to frames and racks.
Choose the shortest length that still reaches your frame and your usual anchor, because spare length becomes working room for a pry bar.
The Lock Body and Key Cylinder
The lock body holds the locking mechanism, so it has to resist striking, drilling and picking rather than only cutting. The policing guide warns that a lock left touching the ground invites a hammer and chisel4. It also notes that thieves can insert tools into the keyhole to pick a keyed lock open4.
Disc tumbler locks are cylinders that use rotating slotted discs, instead of spring-loaded pins, to block the plug until the right key aligns them. They are generally harder to pick than pin tumbler locks sold at a similar price8. Their known destructive weakness is drilling, which can disable the mechanism by destroying the sidebar8. Fitting anti-drilling plates is the documented countermeasure8. Seatylock lists an automotive-grade lock cylinder on the Foldylock Compact, so buyers should confirm the cylinder type and any anti-drill feature on the product page.
Daily handling matters here too. A lock body that sits clear of the ground when locked reduces the hammer-and-chisel opening, and that habit costs nothing at the rack.
Treat the cylinder as the lock's front door: hardened plates mean little if a pick or a drill opens the body in less time than a cutter needs.
Folding Lock Parts Matched to the Attacks Against Them
Each part of a folding lock answers a different attack, and the cited sources name both sides of each pairing. This cross-walk maps every part to the attack documented against it, the defence documented for it, and what a buyer can check on a specification sheet or certifier listing.
| Lock part | Documented attack | Documented defence | What to check |
|---|---|---|---|
| Plates (link members) | Cutting with bolt cutters, hacksaws or angle grinders4 | Hardened steel: a 36-inch cutter is rated for 11.1 mm of hard material (HRC-48)3 | A stated hardening process and an independent cutting test |
| Rivets (joint members) | Bolt cutters cutting through the rivets2 | A sleeve against cutting and a cap against drilling2 | A visible guard on both faces of every rivet |
| Joint geometry and length | Levering through the gap a loosely fitted lock leaves4 | A close fit that leaves no gap for jacks or bars4 | A length that closes around frame and anchor without slack |
| Lock body | A hammer and chisel when the lock touches the ground4 | Locking with the body clear of the ground4 | Room on the anchor to lock off the ground |
| Key cylinder | Picking through the keyhole4 and drilling the sidebar8 | Disc tumblers resist picking; anti-drilling plates resist drilling8 | The cylinder type and any anti-drill feature |
| Whole lock | Timed attacks with specific tools5 | An attack-test star rating from 1 to 55 | The exact model on the certifier's own listing |
Read the table from the bottom up when shopping. An independent rating covers the whole lock, and the rows above it explain where a lock without one is most likely to give way.
How to Judge Folding Bike Lock Security With Independent Tests
Independent certification is the most consistent way to compare folding bike lock security across brands, because each scheme applies one test method to every lock it certifies. The Dutch ART scheme is a clear example. Its test house runs more than 20 tests, such as the freeze, dust, corrosion, endurance, cutting, tensile strength and attack tests5. The attack test determines how many stars, from 1 to 5, an ART lock receives5.
The star bands describe the tools used. For 3 or 4 stars, the lock must withstand opening attempts for a few minutes with specific tools5. Because the attack test is run on the complete lock, that single rating reflects plates, rivets, joints and cylinder together.
A rating belongs to an exact model. Check the certifier's own listing for the lock in question, such as the Foldylock Elite, rather than a badge on the box. For the wider question of when a folding lock is enough for the parking risk, see are folding bike locks secure.
Use the parts in this article to understand a rating, never to replace one. A lock with a published attack rating beats a lock with impressive parts and no independent test.
Frequently Asked Questions
Can bolt cutters cut through a folding bike lock?
They can if a weak part is exposed. Ino Vision's patent names the joint as the weakest part of the folding lock, because bolt cutters can cut through the rivets2. Hardened plates shrink a cutter's reach: one maker rates its 36-inch cutter for 11.1 mm of hard material (HRC-48)3.
Can thieves drill out folding lock rivets?
An unguarded rivet can be drilled, which is why protected designs cap it. Ino Vision's patent places a hardened plug in a recess at both ends of the rivet2. Its examples for guard steel range from a Rockwell C hardness over 20 to over 602. Look for a guard on both faces.
What does an ART star rating mean for a folding lock?
It is the result of the ART attack test, which gives a lock from 1 to 5 stars5. The rating covers the whole lock, so plates, rivets and cylinder are all in play. The test house runs more than 20 tests, covering durability, weather resistance and attack resistance5.
Does the key cylinder affect folding lock security?
Yes. The policing guide warns that thieves can insert tools into the keyhole and pick a keyed lock open4. Disc tumbler cylinders tend to be harder to pick than competitively priced pin tumbler locks, and anti-drilling plates can be installed to resist drilling8.
Why should a folding lock fit closely around the bike?
A loose lock leaves a gap that thieves fill with jacks or bars to lever the lock apart, according to the US policing guide on bicycle theft4. Folding locks have several hinges, so a close fit around frame and anchor removes both the gap and the room to twist.
Limitations and Edge Cases
- The bolt cutter figures are one maker's ratings for its own tools, by material hardness class; they describe stock, not folding lock plates.
- The joint patent records a design and its intent. It is not evidence that any particular product passes an attack test.
- The theft-method shares come from a 2015 survey of Montreal cyclists and may differ in other cities1. Power-tool attacks belong to the wider Folding Bike Locks Explained overview.
References
Methodology: the figures were compiled from a peer-reviewed theft survey, a policing guide, a bolt cutter maker's published ratings, a granted US patent and the ART certification scheme, plus three encyclopedia entries on hardness, case-hardening and disc tumbler locks, each read on October 20, 2026. Michael Shenkerman holds editorial responsibility, and the article compiles published figures only.
- Transportation Research at McGill (TRAM) - Breaking into bicycle theft: Insights from Montreal, Canada, by Dea van Lierop, Michael Grimsrud and Ahmed El-Geneidy, International Journal of Sustainable Transportation, 2015.
- Google Patents - US10766553B2, Folding bicycle lock with joint protection, inventor Michael Shenkerman, assignee Ino Vision Ltd, granted September 8, 2020.
- Apex Tool Group (Crescent) - H.K. Porter PowerPivot Bolt Cutters, max cut capacities by material hardness in inches, product sheet ATG-3866.
- ASU Center for Problem-Oriented Policing - Bicycle Theft, Problem-Specific Guides Series No. 52, by Shane D. Johnson, Aiden Sidebottom and Adam Thorpe, 2008.
- Stichting ART - Over het keurmerk (About the ART quality mark), accessed October 2026.
- Wikipedia - Rockwell hardness test, sections on scales and typical values, accessed October 2026.
- Wikipedia - Case-hardening, section on uses, accessed October 2026.
- Wikipedia - Disc tumbler lock, section on lock picking, accessed October 2026.
Conclusion
A folding lock is only as strong as its weakest part, and the joint is the part Ino Vision's patent singles out. Hardened plates, guarded rivets, a close fit and a pick-resistant cylinder each answer a named attack, and an independent attack rating shows whether they hold together.
See the overview in Folding Bike Locks Explained for how this lock format fits everyday parking and carry.
