Q Can I upgrade my wheels and tyres on my all-wheel drive motorhome?

I have been a subscriber for around two years now, and you have been a great help in me choosing my new motorhome.

I’ve just taken delivery of a Hymer ML-T 580 based on the new Mercedes 4x4. The vehicle is fitted with stock 16in steel wheels and 225/75 R16 C summer tyres. The MIRO is 3,500kg with a MTPLM of 4,100kg.

The intention is to travel as extensively as we can in and out of season. We will predominantly be driving on paved roads, in a range of weather conditions, but will need to depart from the road where necessary, to get to and from our intended camping spot, which might well be over rough ground.

Additions such as snow chains are of course on my radar, but not the focus of my immediate needs.

I’m in the market for a suitable replacement all-season tyre. I’ve taken the decision to stick with the stock 16in rims, but increase the tyre width to as much as 265 if that’s possible on a 16in rim and there are no rubbing issues; which there shouldn’t be, given the ride height of the vehicle.

I’m also seeking a CP tyre rating as an added safety measure.

I’m finding the tyre market a bit of a minefield and would appreciate your advice on what’s available and the pros and cons I should be considering?

Stephen R Jackson A I will try to guide you through the options and will make you aware of the possible pitfalls and by the end of it we may be left with more questions than answers!

First, let’s talk about big tyres. You have probably seen vehicles shod with monster-truck-sized tyres, on relatively small wheels.

Where they can be fitted, they can be run at low pressures to provide the most grip in snow and mud conditions, but will need to be pumped up again to drive on the road and will provide a terrible amount of noise and the steering will be vague and unpleasant.

I think you may already have ruled that out!

In addition, when a tyre circumference increases, the gearing effectively changes so that an engine and gearbox that is optimised for use on paved roads will no longer be correct. Also, the speed indicated on the speedometer will be incorrect and may be recording less mileage than it should be.

You can fit marginally wider tyres at the same aspect ratio (profile) and go from 225/75 to 235/75 and only make a marginal difference to gearing and the other things, but the gains that you make are hardly worth it.

A better bet would be to change to, perhaps, 245/70 and (subject to availability and checking with your tyre provider) there may be little change in the rolling circumference.

However, you will have made the ride slightly worse and may notice ‘tramlining’ and less steering precision. There are always trade-offs to be made.

Low-profile tyres are less compliant, meaning that they are more rigid, and also absorb less of the shocks and bumps; so these get transmitted into the cab of the vehicle.

Another point worth noting is that rally cars that are negotiating snow, ice and even gravel are normally fitted with particularly skinny tyres so that they find more grip than wide tyres that act like skis.

The same can be said of wet weather aquaplaning... it can be made worse with wider tyres.

I know that you said that you may wish to venture ‘off the beaten track’ but to what extent?

The internal fixtures and fittings of your motorhome will feel the stress and strain of excessive twisting and vibration, not to mention your crockery, so bear this in mind.

The vehicle that you have purchased is (by all accounts) a very capable vehicle for travelling in almost all weather conditions and the extra grip and security that you have with four-wheel drive will enable you to confidently explore further than you would be able to in a two-wheel drive.

I would urge you not to make it unintentionally worse so make only minimal changes to optimise what is already a great all-round vehicle.

Michelin has now produced the first truly all-season tyre. I have seen it used extensively on cars and commercial vehicles and now it is being targeted at the motorhome sector.

It wears only very slightly more rapidly than a standard tyre and has the obvious benefits of being a winter 3PMSF (Three-Peak Mountain Snowflake) rated tyre and is acceptable as a winter tyre in the countries in Europe that require this during winter regardless of the prevailing conditions.

The CrossClimate 2 tyre is a bit of a marvel. It performs perfectly well in summer conditions, too.

I would not be too concerned about a ‘CP’ rating. Much more important is the load rating. This designates the maximum load on a given axle when fitted with the tyre in question, and a higher-rated tyre has a stronger construction. We used to talk in terms of ‘plies’, where a 10-ply tyre was considerably more burly than an 8-ply.

My advice would be to rein in your mountain goat expectations and replace your tyres with some all-season tyres of the same or slightly wider, but keep your sights on the load rating and go for the highest available.

There are some great Mud and Snow (M+S) tyres with huge knobbly tread patterns that may be beneficial if you venture off-road, but the ride will be loud, uncomfortable and you will use more fuel. You will also have to change them to drive in the winter in Germany (among others) unless you get a 3PMSFrated tyre.

At the end of the day, you have to decide how much compromise you are willing to accept for the whole year for what could be a very small proportion of the time. But then again, you could just get another set of wheels.

Stephen later replied to say he has opted for 225/75 R16C 121/120R Agilis CrossClimate tyres after speaking with Michelin. He would have liked the CP tyres, but they are not available in the required load rating.

Other tyre manufacturers produce all-season tyres so there are options, but some all season tyres have much lower fuel efficiency ratings than standard tyres. Watch out for this.

Nick Fisher