Swopping 15" to 16" wheels Forums

mrtrilby

Our motorhome has 15" wheels fitted, and seems incredibly low geared - 70MPH is at 3000RPM but the speedo is over-reading and its more like 60MPH at 3000RPM.

I have a note from the dealer about getting the speedo swapped for one that reads correctly, but swapping the speedo won't help the gearing.

Consequently a good option that occured would be to swap the 15" wheels for 16" wheels - both appear to be standard fit on a 2005 Ducato. That would hopefully up the gearing enough to make the speedo read right, and hopefully improve economy a little. The only downside I can see is that the tall reverse gear would become even taller.

Does anyone know if 16" wheels come up for sale cheaply second hand very often, or am I dreaming? Alternatively is there a decent market for lightly used 15" wheels and tyres (tyres have about 4k miles on them)?

travelman868

I would be very careful of changing from 15" to 16" wheels.

The rolling radius between these sizes could creat a major difference to gearing and make the van undrivable.

The tyres on 15" are very often 195 whereas on 16" they may well be 205 or 225/ 75

I would sit down with the sizes of tyres you are thinking of fitting and do the maths.

loddy

Travelman
You have only quoted the width of the tyre, what you should do is talk to a friendly tyre fitter and compare rolling radius and then some basic maths should give you an Idea, you may stay with 15 rims

Loddy

safariboy

Is the suspension set the same for both wheel sizes? Both sizes may be available but are the vehicles the same?

Safariboy

teemyob

Hello There,

You need to consult the tyre bible.

This >

gm6vxb

If your present van has 215/70-15 tyres and you change to 225/70-16 tyres then you will increase speed from 60 to 63.47MPH at the same engine revs.
Have a play on

witch

witch

sorry wrong link in my previous post Embarassed

But if you have 185 x 70 x 15" wheels at 60 mph changing to 225 x 70 x 16" would give you nearly 68 mph. close to what you want.

John

Pugwash

Howdy,

The 244 series Ducato like your 2005 model (not sure about the present 250 series) had two gross vehicle weights. Many were 3500kgs to fit with European and newer UK driving licences, others were "uprated" to 3850kgs. Some were turned out by Fiat as 3850, others were done "aftermarket" by motorhome builders for example Hymer. There is a Fiat protocol for uprating these chassis, one of the requirements being the fitting of 16" wheels which enables tyres of sufficient load carrying capacity to be fitted. There are other requirements of course, the suspension for example, but to the best of my knowledge no change was made to the final drive ratio and the brakes also remain the same. I'm unsure if the rolling distance of the 16" wheels was brought back to the same as the 15" by different profile tyres - this could be the case.

If you really want 16" wheels try ringing round a few dealers. Someone may have asked for alloy wheels to be fitted and the dealer may have some 16" steel wheels available. The stud spacings and offsets should be the same so there shouldn't be any problem with them hitting anything. You can also find out what tyre size is standard on the 3850 chassis and work out it's rolling distance to see if it's very different to your 15" tyres.

Good luck,
Pugwash.

mrtrilby

Thanks for the thoughts.

For interest, our van is plated at 3500kgs, and runs 215/70/15 at the moment. Both the Hymer and FIAT manuals also list 215/75/16 as suitable.

The speed calculator suggests it'll see approximately 5MPH increase in real speed versus indicated speed at 70MPH which would be enough to bring the speedo back to within legal limits, but possibly not enough to have any meaningful effect on economy or engine noise.

The van has oodles of power to pull with 16" wheel, although as I said earlier, it might be a bit tall in reverse for low speed reversing (it's already too tall IMHO).

I'll try and pop in at a dealer and see whether 16" wheels turn up second hand very often. It doesn't sound like there's much point in throwing much money at it though.