Wider wheels for my Hymer 654

[Deeski]

We've got a 92 Fiat Hymer 654 and want to put on some wider/custom wheels. Has anyone done this and have some advice to offer? Do you know if by putting a wider wheel on we restrict the wheel from turning properly in the arch. Current wheels are 195/75 16 and have seen a set of Ally 205/75 16 (Fiat branded). However, would love a set of steel slotted mags . . . any thoughts, comments, advice would be appreciated.

[Derek Uzzell]

Deeski:

 

You appear to be referring to tyre-size rather than wheel-size.

 

Tyre-size is specified in a mixture of metric and Imperial units - for example, a 195/75 R16C tyre would have a width of 195mm and a 'depth' of 75% of that figure, and would have been designed to be fitted to a 16" diameter wheel. Wheel-size is normally specified just in Imperial units - for example 8.5x20 would indicate a wheel with a width of 8.5" and a diameter of 20".

 

Application-wise, tyres tend to be more flexible than wheels. Based on Michelin's technical handbook, a 195/75 R16C tyre could be used on 16" wheels with a rim-width from 5.0" to 6.0", with 5.5" being preferred. A 205/75 R16C tyre could be used on 16" wheels with a rim-width from 5.5" to 6.0", with 6.0" being preferred. So, in principle at least, you ought to be able to swap your present 195mm-wide tyres to wheels with a rim-width that was probably intended for 205mm-wide tyres.

 

However, there's much more to a wheel than just width and diameter. A wheel may well be make-of-vehicle-specific - for example, a wheel intended for a Ford may only fit a Ford and be unsuitable for a Fiat, Mercedes, VW, etc. A wheel may also be model-specific - for example, a 16" wheel designed for a 2008 Ducato could easily be unsuitable for a 1992 Ducato (and vice versa).

 

Before power-steering became the norm for light commercial vehicles, a relatively narrow tyre (and wheel to match) was often chosen by the vehicle manufacturer to keep steering effort tolerable. I don't know if your motorhome has power-steering, but, if not and you are considering upping the tyre width as well as the wheel width, then you must anticipate heavier steering as a consequence, particularly during slow-speed manoeuvring. For what it's worth, changing from 195/75 profile tyres to 205/75s would also increase the vehicle's overall gearing by around 2.5%.

 

I remember a "Which Motorcaravan" test report of an Arto motorhome factory-fitted with (optional) alloy wheels, where the wheels' increased width (or offset) caused the rear tyres to foul the vehicle's rear wheel-arches. So it's not just the front wheels you'd need to be careful of when it comes to clearance limitations.

 

Realistically, provided that the Fiat-branded wheels will actually fit on your motorhome's wheel hubs, and their wheel-rims are only a bit wider than your present ones, and the width increase is 'symmetrical' rather than offset, and you don't intend to increase the tyre size beyond 205/75 profile, and there's plenty of clearance currently evident (front and rear) around suspension/brake components and within the wheel arches, then you should be OK swapping to the alloy wheels (Well, maybe!!) But I'm afraid the only way to be sure is to make the change, then load up your Hymer fully and see if anything rubs when steering and/or braking heavily.

 

Personally, I wouldn't conceive of doing what you are proposing to an elegant motorhome of mature years. Ignoring the cost and uncertainty involved, I think it's like suggesting to your favourite granny that wearing a string-bikini would make her look more sophisticated.

 

(Incidentally, what's a "steel slotted mag", please? I used to own a Reliant Scimitar that had wheels (made by Dunlop I seem to recall) with alloy centres and chromed steel rims. Awful things they were - though they looked snazzy - but I don't think I've seen anything similar on motorhomes, just all-steel or all-alloy.)

[Deeski]

Thanks Derek for your very detailed reply - I appreciate the time it must have taken. We are digesting all the information. Our current wheels are incredibly narrow, the wheel hubs horribly pitted and, due to a recent blow out, we need to replace one anyway so we thought we might treat her to a shiny new set all round. Indeed, not a decision to rush into so we appreciate all your feedback. Oh and slot mags were popular in the 70s and made by Wolfrace I believe - probably not unlike those on your Scimitar.

[George Collings]

I am broadly in agreement with Derek. It may improve the looks but altering wheels/tyres from standard is a highly experimental. I would anticipate rear wheel / arch fouling when cornering at speed to be more of a problem than at the front where wheel arch clearance allows for full lock at low speed.

At the rear body roll simultaneously compresses the rear springs and brings the wheel arch towards the top of tyres inner sidewall.

 

At the front the inner wheel normally moves through a greater angle than the outer (Blame a early 19th century horseless carriageway designer named Ackerman who invented a still widely used sytem to avoid wheel scrub). The most likely points of front wheel fouling are the rear inner sidewall and outside wall at the front of the wheel.

 

Alloy wheels your size are worth perhaps as much as £50 +as scrap and a tempting target for metal thieves who use brutal methods to remove security bolts.

 

Consider having the steel wheels cleaned up ( possibly sandblasted )and repainted before the new tyres are fitted and fit some fancy wheel trims.

 

Go steady, sudden overdoses of TLC might make the old girl think she is up for sale.

 

 

[Guest Tracker]

You could try an internet search of commercial vehicle breakers for replacement wheels and you would then have the luxury of being able to repaint them at your own convenience and to your own standard prior to refitting as well as saving lot's of loot to spend on diesel.

 

There is also a wheel bearing issue with wider wheels and given the wide body of a motorhome heaven knows what extra stress could be placed on the bearings.

 

As you don't drive a motorhome like a roadster, well I don't, well not very often then anyway, and given that fuel economy is better on narrower tyres you could find wider wheels having a small impact on fuel consumption too?