Spotted at Oban Ferry Terminal, waiting patiently until some Nomad decided to interrupt its muse!

I use a skier type lock for just a quick run into a store.  The red lock in the photo has a retractable cable in it.

If you just want a small cable with a couple loops on it, such cables have been sold for people to use to lock their saddle to their bike if they have a quick release seatpost and are concerned that the saddle and seatpost may disappear. 

A quick visit to the recent history of bike rims might help here:

When some manufacturer of bikes rather than rims invented the 29er, which is basically a touring or utility bike with wide balloon tyres, the technical side of ERTRO (European Tyre and Rim Technical Organisation), the industry body, was horrified to see some manufacturers, in a hurry to share in the new market created, cynically put 50 and 60mm tyres on 19mm and even a few narrower rims. ERTRO then urgently reminded everyone of existing guidelines, which were that the minimum rim width over the tyre bead-retainer ridges (not the outside of the rim) should be at least 40 percent of tyre width. Schwalbe, whose tyres many on the Thorn group regard highly, later published similar minimum rim width to tyre width recommendations.

The rim makers screeched to high heavens about not having the capital to invest in new molds and warehousing for a fashion flash in the pan soon to be overtaken by the next fashion flash in the pan, which is what many took the 29er craze to be in the beginning*, and ERTRO, an industry body representing the manufacturers, not the cyclists, hurriedly backed off and basically added an implicit "or whatever you like".

Thus the danger, to which in the original instance ERTRO responded, remained that wide tyres on unsuitable narrow rims would have to be more highly inflated, and would thus stand a greater risk of coming out of the retainer beads in high-speed cornering or even bursting the cheaper narrow rims apart.

Eventually responsible bike designers and manufacturers specified more and more wider rims as it became clear that the 29er had come to stay, as I forecast when it first appeared. The rim manufacturers responded with wider rims.

I tried a 60mm Big Apple on the 19mm no-brand Chinese rim into which an electric motor had already been laced, and nothing awful happened, except the bike was slower because the slight deformation of the Big Apple by the narrow rim put less rubber on the road, and on the downhills I slowed down considerably compared to my normal standard of letting her rip, because the bike didn't feel stable or particularly responsive to tightening the steering in corners (too much understeer). Perhaps not a big deal if you're poor and cannot afford the sometimes substantial premium for high quality wide rims; the likelyhood is that you will still think you're going faster than on narrower tyres, on which you could never approach the downhill speeds and security of a true 29er.

My personal opinion is that ERTRO's 40% of tyre width rims are still a bit iffy, but again, most cyclists have never gone as fast as you can go on 62mm tyres on rims with 25mm between the bead retainers, which are today relatively available and certainly comparatively cheaper than when the 29er was born, so most cyclists are likely to be satisfied.

The mental arithmetic sum for the minimum recommendation of 40% is rim width across the bead retainers times 2.5, thus if you have or can source a 25mm rim, 25mm x 2.5 = 62.5mm. Or, you have or can source 62mm tyres, you need a rim of (62/2.5)mm which rounds off to 25mm rim width across the bead retainers.

Below the footnote, there's a table of rim and tyre widths for the minimum ERTRO width recommendation to fit the widest tyre, both numbers in millimeters, in all cases where fragments remained rounded downwards because these rim widths are minima.

*Not me. For me the 29er was one of those very rare true engineering advances in bicycles -- it was clear me as an old racing car chassis developer that, if properly engineered, it would make for a faster, better-handling bike than the 37/38mm tyres I regarded as a poverty limitation on the bikes I had before the 29er; it also reflects my marketing background, because I further argued that if cycling were to grow, it would need to grow into sections of the population who didn't care the bat of the eyelid for the privations that came with bicycles but would demand both comfort and exceptional security for their commute or Sunday ride.

ERTRO Generalized
Minimum//Maximum
Rim Width//Tyre Width (all mm)
18//45
19//47
20//50
21//52
22//55
23//57
24//60
25//62
26//65
27//67
28//70
29//72
30//75
31//77

Strangely enough the SJS web site says that Andra 40 rims are suitable for 37 - 62mm tyres…….the same max tyre size as Andra 30 rims.

My complaint about the Andra 30 rims being pushed as a great expedition rim for wider tires like 57mm is that if I want to be able to lower the pressure for bad ground conditions, the rims are narrow enough that the bike feels too loose if I do that.  I only did it once and did not like the feel of the bike.  Thus, I feel I have to run the pressure higher than I would like on loose uneven ground on those tires because the rims are too narrow.  Too many times on steep uphills on loose gravel, my rear wheel lost traction and spun out and I came to an immediate halt.  And those hills are too steep for me to just get on the bike and be able to pedal up to speed with a full load, thus I had to push the bike up the rest of the hill.  But with lower pressure I am pretty sure that I would have had better traction with a larger tire footprint on the loose ground.

One of the times when I was ranting about this on this forum, Dave W (former SJS employee) told me I was completely wrong because the rim was good for up to 62mm.  But all he could say was that Ryde said so.  I think realistically, when manufacturers recommendations are too broad, the retailer should be willing to accept that.  I do not think any other rim manufacturer of a 19mm wide (internal) rim would suggest all the way up to 62mm.

Example, on my Lynskey I am running Velocity Dyad rims, I wanted a rim that would work well with 28 to 37mm tire width.  I considered the Mavic A719 and Velocity Dyad. 

In the end I picked the Dyad.  Rim internal width is 18.6mm, just a hair under the Andra 30 width.  Velocity recommends this rim for 25 up to 38mm tire width, which makes it just perfect for my tire preferences on my Lynskey.  That is a much more realistic appraisal of which rim would work best with which tires. 
https://velocityusa.com/collections/rims/products/dyad-rim-700c?variant=40783718350927

I had nothing against the Mavic A719, internal width of 19mm (same as Andra 30).  I already had owned a set of wheels with those rims.  Attached photo shows the max pressure recommendations from the sticker on one of my A719 rims, as you can see this rim was right in the range of tire sizes I wanted on that bike.   At this time my randoneuring bike has a Dyad (18.6mm internal width) on the front and a Mavic A719 (19mm internal width) on back, works great with 32mm wide tires.

I will never understand why Ryde says what they say for ideal rim width.

I wanted to run tires in the range of 40 to 50mm on my Sherpa.  I bought Salsa Gordo rims (no longer sold) with an internal width of 21mm, and they work great on that bike with that range of tires.

Rant over.  Sorry.  But this topic is the only topic where I have been unhappy when I followed the recommendation from SJS.