What 17 mm spanner for roadside repairs?

Two most useful spanner sizes on a bicycle are usually 15 mm and 17 mm. They also usually require a lot of torque (for pedals and bolt-on axles), and it makes sense to have them in a form of properly long spanners.

However, an open-ended spanner that would combine these two particular sizes is hard to buy. A solution that I saw is to get a more common 15/16 mm spanner, or 15/14 mm spanner, and machine one of the slots to be wider to 17 mm. This saves weight and space: instead of carrying two spanners and use them one-sided, carry only one 15/17 mm.

If additionally flattened, the same 17 mm spanner could be used for cup-and-cone adjustments of certain hubs.

My personal solution to this problem is to carry a small adjustable spanner. The one I have is about 15 cm long. Its jaws are officially rated to up to 15 mm, but in reality it opens up to about 19 mm or more. Such a spanner is heavier than a non-adjustable one, but it is also more versatile (I also use it for 8 mm on my odd custom rear axle).

Roadside repairs are generally made with the smallest adjustable wrench that has enough jaw opening.

I have a 4" adjustable wrench that I carry always. It has, however, only 15mm jaw opening and even if it opened up to 17mm, it would not necessarily have enough leverage to torque properly a 17mm nut/bolt.

So, my recommendation is to find a 5" adjustable wrench if you can, and fall back to 6" adjustable wrench if you can't.

I don't recommend a fixed spanner. Someday you'll have rim sidewall damage that requires an adjustable wrench to fix, or your brake disc gets bent (an adjustable wrench can fix it too in a pinch). Or if you don't have anything other than 17mm nuts/bolts on your bike, someday you might be riding with someone else who happened to have a non-17mm nut or bolt and by choosing to carry an adjustable wrench instead of a fixed spanner you could save their day.

Of course, at home you don't use an adjustable wrench ever except perhaps for rim sidewall damage. Disc brakes are straightened with the proper tool and 17mm bolts and nuts are torqued with a fixed spanner.

If it doesn’t require too much torque, get a cone wrench like this one:

https://www.parktool.com/product/double-ended-cone-wrench-dcw-3#tabbed-section

They are pretty flat and lightweight. You could cut off the 18mm end if you don’t need the length.

Why do you feel the need to carry a wrench for the derailleur hanger in the first place? Personally I don’t think a bent or broken hanger is likely, especially not on a road bike. I keep a spare hanger at home since they are hard to get, but I wouldn’t bring it on a trip or even training ride. Even if your hanger is bent it usually only messes with your shifting but doesn’t make the bike completely unrideable.

If you’re feeling rich, a titanium adjustable wrench like this one would be awesome: https://countycomm.com/products/adjustable-wrench-titanium-6-inch-nsn-pending

Lightweight but also functional.