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I've got a Cervélo S3 disc w/ a hanger that requires a 17 mm spanner.

In the event of changing hanger when on the road; what would a preferably small and light spanner be?

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  • 3
    The Cervelo S3 is an aero road racing bike. In a road race, if you need to change your hangar, you are likely out of contention entirely. In a longer supported event like an audax ride, is the S3 necessarily the best type of bike? I don't believe that many multi-tools will have a 17mm open end wrench...
    – Weiwen Ng
    Aug 5, 2021 at 13:48
  • 3
    I would not carry a tool for this. It is too big (not just heavy - at least for the adjustable.one, but also bulky). If you bend the hanger, you will still get home in some gear. If you break it completely, you will improvise a fixie and carefuly get home (or to the nearest train station) as well. If it was installable with a multitool and fit my saddle bag, I would bring it, but not at this cost. Aug 5, 2021 at 16:17
  • 2
    @carel I've tried that, and its not particularly easy. If the chain's not exactly right, it will climb up or down the cassette.
    – Criggie
    Aug 5, 2021 at 20:29
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    Pic? I want to see what kind of monkey business Cervelo invented here.
    – MaplePanda
    Aug 6, 2021 at 5:29
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    @MaplePanda: This is strange anyway, because RD-hangers are generally held by 2-3 screws through the drop-out.
    – Carel
    Aug 6, 2021 at 6:19

4 Answers 4

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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.

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  • 3
    Good points about the extra versatility of adjustable spanners as straightening devices! Aug 5, 2021 at 14:03
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    The problem with small adjustable spanners is the hard limit on nut size. That's why I chose instead to add to my toolbag 12 cm long pipe wrench pliers. They can probably grab something 30 mm wide. Sure, the grip will be suboptimal, and may even damage a tight nut, but in an emergency I find its versatility crucial.
    – calofr
    Aug 6, 2021 at 6:27
  • You could also buy a 6" adjustable spanner and adjust the size of the handle (using an angle grinder). With a little care you could probably reshape the wrong end into something useful, as I did with a metal tyre lever when I needed an 11mm spanner
    – Chris H
    Feb 28, 2022 at 20:25
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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

enter image description here

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.

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    There are plenty of cheaper single-ended cone spanners out there too, that con't carry the Park surcharge - One might also choose to narrow the handle rather than cutting it short, to retain leverage.
    – Criggie
    Aug 5, 2021 at 18:22
  • I've definitely considered cone spanners due to their weight and form factor. I'll likely get this one: cdnm.bike-discount.de/media/org/orgb_R/orgid_33/thumbs/… And then cut it and use a 10mm hex from the multitool for torque.
    – T0TTE
    Aug 6, 2021 at 6:18
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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).

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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.

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  • Wow! Might be the answer :)
    – T0TTE
    Aug 14, 2021 at 19:24

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