Ducato speedo inaccuracies.

[Guigsy]

Bigger wheels also mean more weight to spin up, so worse acceleration. And that your gearing is effectively a little bit taller, so you shift down to 5th on hills a bit more often.

 

[Carpmart]

The rolling radius of the tyres is the only factor that will determine the increase in accuracy for the Speedo. Rolling radius is determined by a combination of width of the tyre, size and profile. Therefore a 225/70/16 will have a different sidewall profile to a 215/70/16 and hence a different rolling radius. Tread depth also determines rolling radius.

Final drive from gearing and differential will also change with different rolling radius tyres.

All manufacturers quote the rolling radius of their tyres if you google it!

Unsprung weight, weight sitting outside of the spring/damping platform (primarily your wheels and tyres), also affects performance, less weight obviously being best, but on heavy and non performance vehicles, is of minor consideration unless you’re substantially increasing the weight.

 

[Happy Jack]

Bigger wheels also mean more weight to spin up, so worse acceleration. And that your gearing is effectively a little bit taller, so you shift down to 5th on hills a bit more often.

Yes Guigsy, one of the suppliers mentioned that.

 

[Happy Jack]

I changed from 215/70/15 to 225/75/16. My speedo now reads exactly the same as the gps.

Hi Silverman.
With 16" rims , how is your wheel arch clearance.
Especially on hard lock ?

 

[Landy Andy]

I swapped out my 215 15s for 225 15s. Speedo is now far more accurate, softer ride, and no additional cost as was buying tyres anyway. Although I have a dash mount readout for Speedo so use that.

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[1967bowesj]

Good morning all.
My Ducato 2016, 2.3 speedo reads 70 when the satnav says 65.
Running on 15" rims at the mo with 215/70/15 tyres.
Not a problem as I think I can adjust the overspeed warning.
But it would be good if it was accurate.
Added complication:-
Getting alloys, could stay with 15" and same size Falken 01, which are the tyres I fancy.
Load rating is 109/107, but speedo would still read high.
Other profiles are available but the size that puts speedo correct has poor load ratings, only just good enough.
Would like to go to 16" and 225/75/16 tyres.
Excellent load rating but speedo would read even higher!!!
Other profiles are available but again load rating goes down, although not as bad as 15" versions.
Really did want higher rating as it allows loser pressures to give a softer ride.
Axle weights in full trim are 1610Kg front, 1500Kg back
Can anyone think of any solutions?
Can the speedo be recalibrated and how ?
Have emailed 3 suppliers to for their recommendations.
Waiting for reply.
Am North East based.

Had the falken van 01 on last van and found them very spongy and soft on corners, floaty when passing or being passed. Wouldn’t have them again on a motorhome

 

[Happy Jack]

I swapped out my 215 15s for 225 15s. Speedo is now far more accurate, softer ride, and no additional cost as was buying tyres anyway. Although I have a dash mount readout for Speedo so use that.

Hi Landy.
I
Are the wheel arch clearances OK and no fouling of inner wheel arch panels on full lock each way ?

 

[Happy Jack]

Had the falken van 01 on last van and found them very spongy and soft on corners, floaty when passing or being passed. Wouldn’t have them again on a motorhome

Hi 1967.Hi
Think that's the first time I've seen bad press about Falken.

 

[Hettie's Crew]

Hi 1967.Hi
Think that's the first time I've seen bad press about Falken.

We have the EUROALL SEASON VAN11 Falkens in 225/70 15 on ours and can’t fault them.