I now offer six different wheel sizes for custom Bromptons, based on three frame sizes – it’s maybe a bit complicated, so hopefully this will help you choose the right size!
Changing between the two different wheel size in each frame size isn’t a big deal, it’s just a matter of rebuilding the hubs into different rims (assuming you have disc brakes).
Want to change the wheel size on your Brompton? You’ll need a rear gearing kit (Alfine, Rohloff, Enviolo or Kindernay), and front and rear disc brakes.
| Standard frame sizes: | These frame parts are dimensionally identical to original Brompton ones, so the bike folds exactly as normal, and normal spares and accessories will fit with no problems. |
 | 16″ (305): This is the smallest rim size, and it’s usually combined with fat 2″ Big Apple tyres – these are comfortable and less skittish on loose surfaces. The Big Apple tyres are becoming hard to find, but there are a few alternatives still available. |
 | 16″ (349): This is the normal Brompton wheel size, so this size will take all normal Brompton tyres. This is the only size that is compatible with the standard Brompton brakes rather than disc brakes. |
 | 16″ (305) Fat Bike: This is a special I’ve built a few times – it uses the smaller 305 wheel size, so can also use those tyres, but has special wide forks and rear triangle to use the unusual 16×3.0″ fat bike tyres. |
| Stretch frame sizes: | These frame parts are longer than standard, for larger wheels – so the folded size is a bit larger, and standard accessories like mudguards either won’t fit or have to be modified to fit. The riding position is a bit different with these frames, the bottom bracket (where the pedals attach) is about 3cm higher than standard. |
 | 18″ (355): This size is shared with the Birdy folding bikes, and can use either the fat 2″ Big Apple tyres, or knobbly mountain bike tyres. Standard racks and mudguards still fit okay. |
 | 20″ (406): This is the largest wheel size, so rolls very well, and is great for road riding – the fattest tyre that can be fitted is a 1.3″ slick. Because of the larger diameter, gearing is increased – this is especially useful if you want higher than standard Rohloff gearing. Standard mudguards fit, with modification. |
 | MTBrompton 20″ (406): This size uses the same rim diameter as the 20″ option above, but with fork and rear triangle made even larger to accommodate up to 20 x 2.4″ tyres! The bottom bracket height is 350mm, good for ground clearance – standard rack and mudguards will not fit. More about the MTBrompton here. |