Wheel diameters and how they affect mileometer

[e31shrew]

Hi all

I have searched the forums and found a few similar questions but this has another slight query!

My Bongo has after market 17" alloys on. Tyres are 225 45 17. I appreciate that it will probably show a 5% error in speedo reading [ as most cars have a built in 10% error, its no great shakes!] When coming down the motorway last week after picking it up, I was doing 65, whereas SWMBO was following at 60.

Problem is that the distance to the garage to collect was 35 miles, yet the mileage shown when we got back was nigh on 60! Do the speedo and mileometer run from differing sources?Perhaps its not quite as economical as I thought!

[wonkanoby]

are you sure its a milometer

my speedo card reads mph

but trip and milage are in km

[mikexgough]

This will help you....

[e31shrew]

This will help you....

Thanks Mike. I did use that from a previous thread to work out that the reading would be around 5% out on the speedo. Intrigued by the previous answer though. So the speedos can be MPH whereas the mileage and trip can be Kilometers? Blimey. It was sold to me as having done 96000 miles so perhaps its only done 58000!
Theres no KM sign next to the mileage figures though

[e31shrew]

Just found a previous long thread re this so thanks for all the help!

Doesnt seem to be a set rule re this. So it looks like the odometer is reading kms.

Cheers all

[francophile1947]

It all depends on whether you speedo is chipped or just has a new face. If the speedo only goes up to 110, it's a new face and the odometer will be reading in kilometres.
Those size tyres will make your speedo read that you are doing just over 4% more than the standard tyres i.e. speedo reads faster than you are actually going. See here for a calculator http://www.tyresave.co.uk/tyresize.html
Incidentally, that size tyre is hard to get with a sufficient load rating for the Bongo - have you checked that they are at least 92 on the front and 96 on the rear?

[e31shrew]

The plot thickens! Now I haven't got the faintest idea of the supposed mileage! Speedo goes up to 110mph. Just checked the previous MOTs. The first one I have, from 2007 [ year of import ] shows the mileage reading in KMS....92000 or so. Next two, show readings of 94000 and 95000 approx, in miles!
Would you think the odometer is reading kms from that info, and its just a mistake, on the latter MOTs?
As I said before, it's definitely over reading by at least 40% on recent journeys.

[wonkanoby]

yeah

i had to take mine back and get it changed to km this year

[francophile1947]

The plot thickens! Now I haven't got the faintest idea of the supposed mileage! Speedo goes up to 110mph. Just checked the previous MOTs. The first one I have, from 2007 [ year of import ] shows the mileage reading in KMS....92000 or so. Next two, show readings of 94000 and 95000 approx, in miles!
Would you think the odometer is reading kms from that info, and its just a mistake, on the latter MOTs?
As I said before, it's definitely over reading by at least 40% on recent journeys.

It's a mistake - the "mileage" will be in kilometres. The MOT station has just taken the reading and assumed it's in miles.
Did you check your tyres load rating? If they're too low, it may invalidate your insurance

[e31shrew]

yeah

i had to take mine back and get it changed to km this year

Do you think I could take it to any testing station or would it have to go back to the one that did the last test?

Thanks for your help

[e31shrew]

Did you check your tyres load rating? If they're too low, it may invalidate your insurance [/quote]

I'll whizz out with a torch now!

Thanks again

[e31shrew]

Just checked...94 all round so need to get at least a couple of new ones! Just a thought though. I take it that the 'official' plate on the door stop, would have been based on the vehicle carrying 8 adults in MPV format. Would the original ratings still apply after the car has been converted to 'campervan' to carry a max of 4 persons? I guess my small kitchen weighs less than 4 x 125kg adults, albeit perhaps slightly chunky grown ups!

[francophile1947]

Pass It's just that the insurance companies have a nasty habit of ducking out of claims nowadays, so is it worth the risk?

[Tony C]

Both speed & mileage overclock by 10 percent on my V6 fitted with 16" alloys, have checked it out against both satnav & another vehicle, put it down to rubbish chip.

[francophile1947]

Both speed & mileage overclock by 10 percent on my V6 fitted with 16" alloys, have checked it out against both satnav & another vehicle, put it down to rubbish chip.

What size tyres have you got?