A couple of years ago, we posted about our appreciation for the "one bike, two sets of wheels" approach. Since then, our love for this has only grown. Based on what we heard this weekend at the Flow State MTB festival, there is a lot of interest in the concept.
As with everything "bike," it's not as simple as that. Getting a set of mountain bike wheels, like the Hotfoot or soon-to-be-available-again (if what I'm told is true) RaceFace ARC 30s, for your road bike obviously runs into problems with tire clearance, but you might run into trouble in the other direction in subtler ways.
Let's say you have a mountain bike and you want to do some road riding on it. I'm all for this, as this was how I spent all spring (aka "mud season") in Vermont. I'm "lucky" in that my mountain bike's axle spacing is 100mm front and 142mm rear. This makes my mountain bike something of a fossil (though I do love it so), but it makes switching between gravel wheels and mountain bike wheels simple from a wheel fit perspective. I change the front axle diameter and go from "gravel wheels for the gravel bike" to "gravel wheels for the mountain bike" and back easy peasy.
Now I realize that I'm off track of the "one bike, two sets of wheels" deal here, but a lot of people reading this own mountain bikes, and "two bikes, two sets of wheels" is REALLY versatile for those of us who live in places where it gets really f-ing cold, because a mountain bike with big road, or light tread gravel, tires is a weapon in cold early spring. Why? Because travel speeds are lower, which keeps you closer to base and keeps wind chill down, you can layer more but it's less obtrusive than on a drop bar bike, and... MITTENS! Any educated ski lift operator will tell you how great Axeman mittens are. They are cheap enough to be liftie-wallet friendly, and WARM and durable. I have a pair for skiing, and a pair for dog walking and riding the mtb when it's freezing. Add some hand warmers and even if your hands get as cold as mine do, you're good down to any reasonable riding temp.
(same wheels as below, with different gravel tires)
Back on track. If your mtb has boost spacing, it's still easy to get a set of wheels built up with rims like HED Belgium G or the soon-to-be-available-again (if what I'm told is true) RaceFace Arc 25s and boost hubs, and use them with like 45mm road and/or gravel tires. Why do I say "like 45mm..."? Because you don't want your two sets of wheels to be that different in diameter. Why? Well in the extreme case, if you went from say 2.4" mtb tires to 23mm road tires, you'd have pedal clearance issues. The bike would lose about 1.5" of height, and even though mtb bottom brackets are higher than road bottom brackets, that's too much height to lose. For another, your handling would get all wonky. Warn your dentist before you try to ride such a setup no handed.
This way, all early spring for me
Similarly, with using a gravel bike for a "road bike sometimes, gravel bike the other times" approach, you want to keep your road and gravel tires somewhat similar. I use 30mm (actual) road tires and 40mm (actual) gravel tires on my gravel bike (which got re-christened as a gravel bike from a cx bike a bit ago). The handling difference is there, I notice it, but it's manageable. And it moves in the right direction - the handling is a bit quicker with the road tires on it. That step magnitude works out great. With road tires on, that bike might not be my ultimate choice for a technical crit but it would be far from bad, and for any group ride or gran fondo or whatever, it's amazing. With the big gravel tires on, it gets me anywhere I might wish to go where I wouldn't rather have the aforementioned mountain bike under me.
My particular setup for the gravel/road duo happens to be Cafe Racers for road and RCGs for gravel. And they work wonderfully. The HED Belgium G and Belgium+ rims make perfect complements to this, as do several other rim combos. As I do, you can go with the same rim width, or you can go bigger for the gravel and slightly narrower for the road set (as you would with the HED combo above).
There's also the tactic of going a little more splash on the primary set and reining the budget a bit for the secondary one. You can use hubs, spokes, or rims to do this - carbon hubs on the primary, alloy on the second. White Industries on the primary, Bitex on the secondary. Bladed spokes on the primary, round on the secondary. It's easy to put yourself through a little conjoint analysis (fancy marketing word) and decide which traits optimize your use and enjoyment of each set.
If your gravel wheels decide to be 650b, then you can go big big on those tires relative to your road tires. A 700c wheel with 28s is somewhere about the same as a 650b with 42s, so even if you take your 650b set up to 47mm, the handling differences from one to the other will be subtle and appropriate.
So the big takeaways - look out for axle fit if you're "two bikes, two sets of wheels, four great setups" curious, and keep tire sizes within sight of one another.
If you keep those simple guidelines in mind, you can extend the heck out of your bike's use cases, and you just might find the N+1 rule to look more like N=1.