How to select the fenders for my bike I inspected the tires of the bike and found their size: 700 x 40  - 28 x 1 5/8. Which probably means, that the diameter is 28 inches and the tire width is 40 mm (I measured with a ruler).

I found, that people recommend SKS Chromoplastic fenders and they have many sizes: http://www.ebay.com/itm/SKS-Chromoplastic-Road-Racing-Bike-Mudguards-P35-Black-/380993168162?pt=UK_SportGoods_CyclAcces_RL&amp;hash=item58b4f66322

The seller says, that the fender is for 700C (which is probably my size), but the width is not specified. Maybe, 'P35' means 35mm tire?

Should I select the fender exactly for 40mm or buy a little bigger?
Mudguards can be measured in a few different ways, so different brands may vary. And it seems the SKS model numbers and names have recently changed, so some websites may still refer to the old names.

For SKS Chromoplastic, 'P35' refers to the width of the mudguard. For it to fit, the guard has to be a bit wider than the tyre, probably at least 5mm more. From the SKS website, the Chromoplastic 35mm is designed to fit a 700 x 20-28 tyre.

So for a 40mm tyre, you should look for a 50mm mudguard. Or a bit wider if your tyre is particularly wide or knobbly. SKS do make a Chromoplastic P50 (also known as 'Hybrid' size), designed for 38-45mm tyres, so that would fit fine. Or another option would be the SKS Bluemel B53, which is 53mm wide so fits 700 x 38-47 tyres.