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A common answer when people ask about frame size/geometries is to go to the local bike shop and ask to try the bike. No discussion of course, in an ideal world, it would be better to be able to try a bike for a longish tour "in its environment" before buying it.

But that answer for me is not so "obvious": unlike a pair of shoes, where you can quickly evaluate if the shoe has nasty contact points, a bike can be set up/customized: you can fine tune the position of the saddle; components like the saddle, grips, or tires can make a big difference in how a bike feels (especially for first impressions) and can be easily swapped. Even trying the bike of a friend might not be entirely representative: they can have swapped/upgraded some components, have an older/different version, or have a different frame size. The geometry is also something that is difficult to evaluate "objectively".

The offer in bikes in also huge, and it's unlikely that the shop will have the exact model you want for trying (even before the pandemic), most of the time they will give you another one saying "it's very similar". Also, if you can try the same model, they might give you a better version than the one you attend to purchase, which can lead to some form of disappointment (especially with entry level bikes, where the components will make a huge difference in how a bike feels). Or they might not have the good size. Or you can only ride it on the parking, which might not be representative if you want to purchase a down-hill MTB.

The question is double:

  • what should be the attention points when trying the bike itself?
  • if a shop can't have the exact version of the bike, on what would be better to compromise when choosing the bike to try (frame size, components, even brand it's a bike are similar components)?
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For me, there's two things to consider when trying a bike at a shop.

  1. Can i have a proper test ride (1hr+ over a range of terrain). I want to find out how the bike climbs, how it descends, how it feels in the corners, what it's like over rough surfaces.
  2. Do they have a bike with the same frame I intend to buy (doesn't necessarily have to be the exact same model).

If I can't get both of those things, it's not worth the effort.

A good test ride can be especially difficult to get for a mountain bike. I've found for MTB then a really valuable resource is to try and get signed up for a 'demo day' which often give you the chance to try multiple bikes in one day.

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  • It goes in the same direction than the "why I asked the question". I have the impression that going online from manufacturers that are "online first" (that are making sure that sizing is consistent and with 30 days return policy) may have more "value" than purchasing from a LBS, assuming that one knows what one wants. LBS have other advantages though (mostly service and advice). I was not aware of the "demo days", seems interesting too.
    – Renaud
    Aug 4 at 7:13
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First you want to test ride the bike with your optimal saddle height.

Two questions related to bike fit:

  • Can the handlebars be moved to an acceptable height? Most good bikes today have ahead stems so you can't simply untighten a bolt, move the bars and tighten a bolt but you must also re-adjust the headset. If the handlebar can't be moved high enough, consider a larger frame; if the handlebar can't be moved low enough, consider a smaller frame.
  • Is the handlebar at an acceptable distance from the saddle? If it's too near, consider a larger frame; if it's too far, consider a smaller frame.

Sometimes you may not find a fitting bike using these methods and you need to swap the stem.

Other than that, I'd be looking at the opportunity to attach everything you need (lights, are there eyelets for fenders, does the U-lock fit in the main triangle, can you fit a kickstand, are there eyelets for rear rack). Then take a hard look at the geometry. My two concerns about geometry are if the chainstays are long enough (if not then panniers hit your ankles when riding) and if the bottom bracket drop is suitable (if bottom bracket is too low you'll hit the pedals to ground on corners, if bottom bracket is too high it's hard to mount and dismount). You should also check the standover clearance but usually that won't be an issue with modern bikes that have sloping top tubes.

The components can always be changed, but one of the most expensive components to change are the wheels so if the wheels have a suitable rim width, and enough many spokes to make them durable, it's always better. Extra points for hub dynamo should you need one. Also a wide enough range cassette could be good to have, because if it doesn't, you may need to change not only the cassette but also the chain to a longer version and rear derailleur to a longer cage version. With MTBs I'd also check that there is a large enough chainring.

With road bikes, I'd also be looking very hard at tire clearance. On other types of bikes (touring, gravel, cyclocross, MTB, hybrid) this usually isn't an issue.

The suspension characteristics of the bike should match what you need because suspension forks are long and rigid forks are short, so it isn't realistic to swap a suspension fork to a rigid fork that would be way too short for the geometry. I always prefer non-suspension bikes, and if I ride offroad then the suspension is obtained by choosing a fatbike with plenty of low-pressure air volume in tires.

Today the market seems to have decided that it's all disc brakes. I'm not entirely sure I agree with this decision, because rim brakes are good enough for 99% of purposes and actually often more rigid than disc brakes, offering a very nice braking feel. The only drawback of rim brakes is that in wet conditions, it takes two wheel revolutions (4.3 meters) to have full braking, but then again at 7 m/s speed you have 14 meters of reaction time. In anticipated stops, you already have cleared the rim of water in advance by lightly applying brakes early so the 4.3 meter penalty doesn't apply. In stops you have considered possible, you usually have lightly applied the brakes before you may have to stop, so the 4.3 meter penalty doesn't apply. The only problem is that in completely unanticipated stops your reaction time increases from 14 meters to 18.3 meters, hardly something to complain about. But it's very hard to find reasonable rim brake bikes today. About the only ones are road bikes that have no more than 23mm tire clearance (and to have reasonable tire clearance you need to choose disc brakes).

Don't compromise on the frame size unless your optimal size is inbetween two sizes (in which case you can choose either of the two), or if the sizes are closely spaced (2cm) in which case there probably are two that fit good enough.

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  • “if bottom bracket is too low you'll hit the pedals to ground on corners” This also depends on the pedals. Platform pedals are usually wide which makes ground hits more likely. If you plan to use (narrower) cleatless pedals it might not be an issue.
    – Michael
    Aug 3 at 8:50

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