Fiat ducato wheel sizes (1 Viewer)

[Douglas]

I am due to buy a new set of tyres and it occurred to me that I would like to change my wheel size from 15 with 5 stud to 16 with 5 stud.

Is there such a wheel and is it legal?

The present tyre size is 215/170R15C 109/107R

Doug...

 

[haganap]

HI Doug,
I have 16 inch on my 2.8 and used to have 15 on my 2.0. From my understanding they can not be interchanged, however I was only told this when I wanted to do the same. I was told that the stud pattern is different but like I said only told and never tried.

I can recommend the Dunlop av9 tyres though, loads cheaper than full scale camping car tyres and amazing grip.

 

[rainbow chasers]

Changing sizes are fine as long as they are the same all round OR larger ones on the driven wheels.

Couple of factors to take into consideration however, the larger diameter will mean possible fowling on the inner arch when in full lock - this can be cured by adjusting the stops - but would give you a larger turning circle. It would also DECREASE your accelration, but INCREASE your top speed - which is why boyracers fit bigger wheels! Decrease in acceleration on a motorhome isn't really what you want, as it will be more of an effort pulling away - but will mean that you would have marginal benefits of slippery surfaces. You speedo would be slightly out as it will mess up the vss signal.

You would have a van effectively with a larger turning circle, slower acceleration, and more expensive tyres gaining a higher top speed.

You then have to look into tyre height - you need a commercial reinforced side wall tyre. These will not be available for your vehicle in standard guise, so you will need a lower profile. Finding a low profile commercially rated tyre will be a job! Low pros will be no good - motorhomes put too much strain on a commercial tyre as it is - the sidewall and height are used when cornering or under load. In fact most motorhomes actually run partially on the sidewall or tyre edge due to the weight and cornering.

The easily available direct fit will be alloys, but you will need to mate a lower profile commercially rated tyre...you may find one, but they may end up being more expensive.

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[400ixl]

When you increase the wheel size you tend to reduce the profile size to keep the rolling radius as close as possible to the original. This is what as it was termed "boy racers" do when they increase the rim sizes.

This means that speeds stay consistent and the speedo remains reasonably accurate.

So for example, for your 215/70/15 tyres, 215/65/15 tyres will only be 4mm out and your speedo 0.59% less accurate.

There can be downsides though.
Wheels weigh more than tyres, so the unsprung mass increases which decreases acceleration very very slightly)
The lower profile makes for a harder ride
Sometimes the alternative profiles make for a more expensive tyre (can at times be cheaper)

The things you need to get correct on any new set of wheels other than the rim and trye size are:

PCD (e.g. 5*98) which is the number of studs and the distance between them
Offset (e.g. ET48) which is the distance between the hub face and the centre line of the wheel.
Centre Bore (e.g. 56.1) which is the size of the centre ring to locate the wheels to the hubs. Sometimes if it is larger than you need you can get a spigot ring to reduce it.

Not looked at what the settings are for the Ducato is it is possibly different for ages, models and engines.

 

[Douglas]

One of the reasons I was thinking of larger wheels is that with the Michelin that I have at the moment I am running at 80psi to get the correct tyre shape and it makes for a hard ride. So maybe what I need is a different tyre profile that will allow me to run at a lower pressure.

Wheels and tyres are not something I know much about so I am guessing?

Doug...

 

[rainbow chasers]

The reason you run a higher pressure is due to the weight of the vehicle.

If you take your base vehicle - ducato for example - running 3.5t is actually fully laden for the base vehicle. Imagine driving a van loaded up to the gunnels - that is effectively what a motorhome is. This is why you need the higher pressure to stiffen the tyre and allow for the weight. It also aids stopping the vehicle, by keeping the surface area in contact with the road and coping with forward weight distribution.

If you run at low pressure, you will introduce your sidewalls to the road, particularly during cornering where the weight is thrown to one side. This will cause tramlines on the inside of the tyre (where the rim contacts the tyre carcass or cornering/deceleration) - and eventual blow out, as the side walls are no where near as robust, or thick as the surface area. Bow outs cause not only in convenience, but possble skirt damage as they explode, or even a crash.

If you search for underinflation on google, I am sure something will be about to explain it better.:thumb:

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