Does Going 650b Actually Get You a Bigger Tire?

The advice is everywhere: if you want fatter tires, drop to a smaller wheel. Smaller rim, more room in the same frame, more rubber under you.

It is often true. It is also completely pointless on a third of the frames we can check, and there is no way to tell which kind you own by looking at it.

We hold manufacturer geometry and clearance for 53 bikepacking frames. 17 of them publish a maximum tire width for more than one wheel size, which means we can measure the swap directly instead of arguing about it. Across those 17 frames, dropping from 700c/29in to a smaller rim gains an average of +10.4 mm of tire width.

That average is close to useless, and the reason it is useless is the interesting part.

The three groups

Of the 17 frames that publish both:

• 11 gain width. Some of them gain a lot — Salsa Beargrease goes from 76 mm to 102 mm, which is 26 mm more tire.
• 6 gain nothing at all. Identical maximum width on either wheel size — the swap is wheels you paid for and rubber you didn't get.
• 0 lose clearance. Whatever else is true, the swap doesn't cost you tire width on any frame here.

So on 35% of the frames we can check, the standard advice buys you exactly nothing. It won't hurt you — but a wheelset is not a cheap way to learn that.

Every frame that publishes both

Frame	700c / 29in	Smaller rim	Change
Salsa Beargrease	76 mm	102 mm	+26 mm
Salsa Heyday!	76 mm	102 mm	+26 mm
Surly Bridge Club	47 mm	71 mm	+24 mm
Salsa Blackborow Frameset	76 mm	97 mm	+21 mm
Salsa Timberjack	53 mm	71 mm	+18 mm
Surly Midnight Special	42 mm	60 mm	+18 mm
Surly Karate Monkey	64 mm	76 mm	+12 mm
Surly Ogre	64 mm	76 mm	+12 mm
Surly Grappler	64 mm	76 mm	+12 mm
Salsa Warbird	45 mm	51 mm	+6 mm
Salsa Flyway	50 mm	51 mm	+1 mm
Salsa Fargo Ti	76 mm	76 mm	0 mm
Salsa Journeyer	50 mm	50 mm	0 mm
Salsa Fargo Steel	76 mm	76 mm	0 mm
Salsa Stormchaser	50 mm	50 mm	0 mm
Surly Straggler 650b	50 mm	50 mm	0 mm
Surly Preamble	41 mm	41 mm	0 mm

Why a third of frames gain nothing

A smaller rim leaves more room between the tire and the frame in one specific place: the top of the arc, where the tire passes the seat tube and the chainstay bridge. Drop the rim 38 mm in diameter and you drop the top of the tire by 19 mm, which is real vertical room.

But that is only the binding constraint on some frames. On others the tire runs out of room sideways first — at the chainstay yoke, where the stays split around the bottom bracket. Width there is fixed by the frame, and it does not care what diameter your wheel is. A frame built with a narrow yoke and generous vertical clearance gains nothing from a smaller wheel, because the yoke was always the limit.

That is the whole explanation for the spread in that table. Frames designed around a big wheel tend to be vertically constrained and gain from the swap. Frames designed around a fat tire tend to be laterally constrained and don't.

One caution when you read a maker's chart yourself: forks are routinely cut for more rubber than the rear triangle, and some brands publish the fork figure right next to the frame figure. Salsa lists the Flyway as 50 mm frame and 57 mm fork. The frame number is the one that decides what the bike clears — quote the fork number back to yourself and you will buy a tire that doesn't fit.

The fender tax

The other clearance number nobody quotes at you: 8 of our frames publish a maximum with fenders and without. Fitting fenders costs an average of 4.6 mm of tire width.

Frame	Cost of fitting fenders
Salsa Warbird	−7 mm
Salsa Vaya Frameset	−7 mm
Surly Ogre	−5 mm
Surly Grappler	−5 mm
Surly Midnight Special	−4 mm
Salsa Stormchaser	−3 mm
Surly Straggler 700c	−3 mm
Surly Long Haul Trucker 700c	−3 mm

Three to seven millimeters does not sound like much until you are choosing between a 45 mm tire and a 38 mm one. That is the difference between a tire that floats on gravel and one that cuts into it, and it is the actual trade you are making when you decide to run fenders on a tour.

Worth saying plainly: most frames don't publish a with-fenders figure at all. When a maker gives you one number, assume it is the fenderless one.

What to do with this

If you are thinking about a wheel swap to get more tire, the order of operations is:

• Find your frame in the table above. If it gains, the swap does what you want. If it is in the neutral group, you are about to buy a wheelset that changes nothing about your tire width.
• If your frame isn't listed, check the maker's chart for both wheel sizes. If they only publish one, that is itself an answer — the other size was not a design priority.
• Decide about fenders first, not last. The fender question changes your maximum tire width before the wheel question does, and on most frames it costs you more than the wheel swap gains you.

The short version

Going smaller-rim gains an average of +10.4 mm across the 17 frames that publish both numbers, but the average is a bad guide: 11 frames gain and 6 gain nothing. Whether your frame is limited vertically at the seat tube or laterally at the chainstay yoke decides which group it lands in, and the only way to know is to read its chart. Fenders cost you 4.6 mm on average, which is often more than the wheel swap wins.

Every frame in these tables has its full published geometry and clearance on its own page, with the manufacturer's exact wording and the date we last checked it.