Review: Zefal 4947B K-Traz U17 & Cable Extension U-Lock

Review: The K-Traz U17 Cable is a U-lock with a loop made from very high resistance steel and a 120 cm cable that guarantees extra security for the wheels and saddle

Zéfal, a French company with a long history dating back to the early 20th century, originally gained its reputation through pneumatic pumps. However, today, their product range has expanded to encompass a wide array of cycling accessories, including pumps, water bottles, mudguards, locks, bags, and smartphone holders.

At the forefront of Zéfal’s anti-theft offerings is the K-Traz U17, a robust U-shaped bicycle lock with a 1.20-meter cable designed to enhance bike security.

Special FeatureAnti-theft
Lock TypeKey Lock
Item Dimensions LxWxH3.94 x 1.97 x 5.91 inches
MaterialHardened Steel

Product Overview

The Zéfal K-Traz U17 is among the most durable options within the Zéfal anti-theft lineup. This U-lock model stands out for its resilience and is available both as a standalone unit and with an additional 1.20-meter cable, which we are reviewing here. The U17 features a steel roll bar and operates with a key lock mechanism, with three keys included. Furthermore, it comes with a convenient frame attachment support for easy transport.

The retail price for the Zéfal K-Traz U17 with the cable attachment is €52.95, while the version without the cable is priced at €44.95, though actual market prices may vary slightly.


Weight1.67 kg
Anti-theft typeu
Attachment to frameYes
Number of keys3

Construction & Design

The K-Traz U17, like most U-locks, boasts a substantial size, measuring approximately 30 x 18 cm. While it’s not overly bulky, it’s still large enough to be carried in a backpack comfortably, especially considering its manageable weight of 1.58 kg.

Transportation is made more convenient by the included frame attachment support, which can secure the lock to various tube sizes ranging from 20 to 80 mm. Although this support holds the lock securely in place once installed, some concerns linger about its long-term durability due to less-than-stellar finishing.

The lock itself has an attractive appearance, coated in black rubber primarily to protect the bicycle frame from potential scratches during use. However, this rubber coating tends to show wear and tear relatively quickly, affecting the lock’s aesthetics while not compromising its functionality.

Unlocking the device is straightforward with the key lock mechanism. The key insertion is smooth, with minimal resistance. A protective cover shields the lock from water and dust intrusion, consisting of two movable metal pieces. This design ensures you won’t forget to secure the cover, but the seal might not be entirely waterproof.

U-shaped locks like the Zéfal K-Traz U17 offer versatility in securing different parts of your bike, including the front wheel, frame, and attachment point. With an internal length of approximately 23 cm, it provides sufficient space for such attachments, although chains or folding locks may offer more flexibility in this regard.

A notable feature of the K-Traz U17 is the additional cable it comes with. This cable enables you to secure the rear wheel or extend the lock’s reach, adding complexity for potential thieves. However, it’s advisable not to rely solely on this cable as the primary point of attachment, but rather to use it in conjunction with other security measures.


Like most manufacturers, Zéfal offers its own security evaluation scale for its locks. The K-Traz U17 Cable obtains a score of 17/20 on this “in-house” scale, one of the highest. The 14 mm diameter of the anti-theft bar keeps it away from break-ins attempted with simple pliers and even bolt cutters. Ours will have left only superficial marks on the Zéfal lock.

No anti-theft device is truly inviolable, it is better not to forget that. Our protocol continues using a Bosch Professional GWS 18V-7 cordless angle grinder equipped with a 4 Ah battery. An easy-to-carry tool that bike thieves have now added to their arsenal.

Faced with our grinder, the steel hoop of the K-Traz U17 lasted less than 40 seconds. A fairly average result for an anti-theft device in this category. For its part, the cable lasts around twenty seconds between the jaws of a bolt cutter and only 4 seconds under the disc of a grinder.


The Zéfal K-Traz U17 Cable is a fairly practical anti-theft device to use on a daily basis and easy to take anywhere. This U is certainly not the most resistant on the market, but it is well complemented by the cable which adds difficulty for possible thieves.

While the lock’s U-shaped design and cable provide decent security for your bike, it’s important to note that it’s not completely impervious to determined thieves equipped with power tools like angle grinders. However, it still offers a reasonable level of protection for everyday use and is convenient to carry with its included support for attachment to your bike frame.

Keep in mind that no bike lock is entirely theft-proof, and the effectiveness of any lock depends on various factors, including the determination of thieves and the tools they use. Therefore, it’s essential to take additional precautions and not rely solely on one lock to protect your valuable bicycle.


  • Resists pliers and bolt cutters.
  • Don’t damage the frame.
  • Attachment to the frame possible.
  • Additional cable is addable


  • Cumbersome.
  • Restrictive U format for certain bikes.
  • Average resistance for a U.