How can I fit a bigger rear tyre when limited by the front derailleur? I've recently bought a hardtail, just an entry-level bike, but I've only got entry-level skills.  The tyres it came with are WTB Nano 2.1". They aren't exactly ideal for the sort of conditions we have in the UK in winter (lots of deep mud, wet tree roots, muddy rocks etc.) and I'd like to fit something (i) knobblier and (ii) a little wider.

At the front this is easy, something like a Maxxis Shorty 2.3" or Magic Mary  would easily fit.  At the back, there's also plenty of room except behind the front derailleur



where there's about 3&nbsp;mm (and that filled up with mud today)

There are 2" tyres for mud, but they're reputed to have a harsh ride on anything else, and not grip well on wet rock/tree roots -- something I need at my skill level as my lines aren't up to much and I don't always carry enough speed. 

This is the only bike I've owned with a top-pull FD.  And I can see why they've used one rather than have cables under the BB getting coated in mud and even bashed.  But it takes up much more room than any of the bottom-pull FD's I've got.  Is it because it's a cheap FD? Because it's a triple? It's an Altus 3&times;9 drivetrain.

Is there an upgrade that would gain me a few mm? 



As an aside: I picked it up in a hurry, lightly used/ex-rental and without a test ride, for around half the shop price. I'm happy with it apart from this, and assumed that I might upgrade consumables (perhaps as they wear out). I looked at the specs in detail to be sure the fundamentals were there, but is there any way I could have spotted this?
Put a larger tire on the front and don't worry about running a larger tire on the rear. 

Back when North Shore BC riding was just starting to take off (i.e., 1990s) we often did this setup as we were equipment limited. At the time the "thinking" was that it was bizarre ride a tire bigger than a 2.0 anything but a dedicated race downhill bike. So we would often swap a fork and run bigger rubber up front as there was clearance issues in the rear. Now  25 years later and anything less than 2.3 is pretty much considered anemic for most riding. 

Anyway, the mismatch tire size works fine. The front is where you are often traction limited as you brake and steer with this tire.  A small rear tire may mean a bit harsher ride (i.e., higher pressure with all other things equal) and a tad less traction, but you can afford this compromise on the rear.

Plus, one tire is cheaper than two, and if any one asks just tell them the setup is more aero (#AeroIsEverything - /sarcasm).