tyre sizes

[Guest pete]

Need to replace tyres on my motorhome and have read a promobile test result that gave high marks to Continental vanco 4 seasons. I am having trouble sourcing these in my size, 205/70/15 but have been offered 215/70/15. My base vehicle is peugot boxer and I am concerned about the effect of the extra width on full lock. advice appreciated.

[Guest Derek Uzzell]

1. Where did you find the promobil test results please? 2. Are you still looking for advice? Or have you now swapped your tyres?

[Guest pete]

Promobil results are on www.motorcaravanning.co.uk/vehicles/tyretests Not bought tyres yet so still open to advice.

[Guest Derek Uzzell]

OK, Pete, let's begin with the tyre-size change. I've checked with a chunk of a Fiat 2002 handbook I happen to have and with Michelin's van tyre technical booklet. Both indicate that 1994-onwards Fiat Ducatos (which means Peugeot Boxers too) with 15" wheels can be fitted from new with 3 alternative tyre-sizes - 195/70 R15C, 205/70 R15C or 215/70 R15C. In fact, with Ducato/Boxer-based coachbuilt motorhome designs, more normally than not the converters specify Fiat's "camping-car package" that includes Michelin's XC Camping tyres in 215/70 R15C size. So, in principle, everything points to you not having clearance problems if you fitted 215/70-section tyres to your motorhome instead of the present 205/70 ones. What about in practice? I don't know if your concerns about potential full-lock problems with larger section tyres are based on having measured the current clearance and found it minimal, or because (like me) you have an apprehensive and pessimistic nature. The circumstantial evidence suggests there should be adequate room for the larger tyre, but, if you have found that clearance is tight at the moment, I strongly suggest you stay with 205/70 tyres. If you haven't checked the current clearance yet, it would be common sense to do so, making sure there is plenty of space between each tyre's inner/outer sidewalls and the bodywork or suspension/braking components. (As you have recognised, any clearance problems will most likely be at full-lock.) However, also check there is plenty of room above the tyre-tread. You should do this for rear wheels as well as front wheels, just to be sure, and you might also consider whether a tyre-size increase would have any impact on spare-wheel storage. (I'm assuming you are proposing to replace all 5 tyres.) I can't offer very educated guesses as you haven't provided anything to go on regarding the make/model/year of your motorhome or of your present tyres (except for the size). Going to 215/70-section tyres would raise your 'van's gearing and affect speedometer/odometer readings, but only marginally. Effort at the steering-wheel would increase, but would only be a serious consideration if your motorhome did not have power-assisted steering. Braking and road-holding should theoretically improve, but if you noticed this you would be a better (and braver) man than I. I thought you were probably referring to the information on the motorcaravanning.co.uk website, but, as promobil magazine has published more than one tyre-related report, I felt it best to check. This particular report was published in June 2002, so the data have now aged 3 years. Although I've not read the original promobil article, I believe its objective was to compare Michelin's XC Camping 'motorhome' tyre with alternatives. With ultimate load-carrying capability as the priority, in 2002 there was no genuine alternative to XC Camping for vehicles with 15" wheels (and that's still pretty much true). Promobil would have chosen 215/75 R16C tyres (as fitted to Fiat Maxi chassis vehicles with 16" wheels) because alternatives to XC Camping were available in that size. But these alternatives were heavy-duty '10-ply rated' designs (I refer you to my posting of 05/02/2005 for more on that.) Tyre manufacturers tend to use a limited range of brand-names. For example, for their ordinary light-commercial-vehicle tyres Michelin use "Agilis", but this name covers 4 'normal' sub-species (Agilis 41, 51, 61/81 and 101), plus another 2 specialist patterns (Agilis 41/51 Snow-Ice and 61/81 Snow-Ice). The reality is that, while all these tyres are branded "Agilis", each discrete grouping of tyres (that's 6 in all) has differences in construction and a totally different tread design. The promobil report revealed that Michelin's Agilis 101 pattern in 215/75 R16C size performed comparatively poorly in wet-conditions tests, but that doesn't mean an Agilis 81 205/70R15C or 215/75R15C would have performed similarly badly. By the same token, it means there is no guarantee that a comparative test of 15" 205/70 or 215/70 8-ply rated tyres would have placed Continental Vanco at the head of the list. What I'm getting at is that, if I owned a hefty motorhome fitted with 215/75 R16C tyres and wanted to replace them all, the promobil report would definitely encourage me to choose Continental Vanco. But, if my motorhome had 15" wheels, the choice would be less clear-cut. Indeed, if I habitually ran the vehicle near or beyond its maximum permitted axle-loadings, I'd probably opt for XC Camping for its tolerance of high-load/overload conditions, despite its dismal showing in the promobil test. Horses for courses, as the saying goes... I glanced at the Continental website but didn't spot a reference to the "Vanco 4 Seasons" pattern. I did notice, however, that the normal "Vanco" pattern (that was superior to 4 Seasons in the promobil test) is marketed at 215/75 R15C size with two load/speed ratings - 106/104R or 109/107R. It's probable that your present 205/70 tyres have a load-index of 106/104 (or lower), but you should check this is so. Whatever replacement tyre you opt for, it should have a load-index equal or superior to that of the tyres being removed. Has this confused you? The truth is, as nobody appears to have done a comparative test of 15" van tyres, I believe you are perfectly justified in making the assumption that the excellent performance of 16" Continental Vanco tyres shown during promobil's testing will cross over to the 15" versions. Whatever the case, Continental is a very reputable make and their tyres are fitted as original equipment by major vehicle manufacturers (eg. Mercedes), so I'm sure Vanco tyres would serve you well.