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[sport]

H i put some 17/40/205 alloys on my corsa c the standerd alloys where 16/55/185 will my speedo inicate that i will be travaling a bit slower

[Danny]

are you sure they're not 185 55 15 standard?

if they are indeed 16, the 17's will mean you travel at 68.38mph when the speedo reads 70, as long as it was calibrated correctly when new for 185/55/16s

it's a difference of 2.31% and is perfectly legal (2.5% being the limit)

if they're 15's standard, it'll be 71.35mph when the speedo reads 70 when you change to 17s, a difference of 1.93% the other way, also completely fine

[Jimbob]

are you sure they're not 185 55 15 standard?

if they are indeed 16, the 17's will mean you travel at 68.38mph when the speedo reads 70, as long as it was calibrated correctly when new for 185/55/16s

it's a difference of 2.31% and is perfectly legal (2.5% being the limit)

if they're 15's standard, it'll be 71.35mph when the speedo reads 70 when you change to 17s, a difference of 1.93% the other way, also completely fine

I thought it was 0% for overread?

[Del Boy]

Shouldn't be over reading anyway really as speedos tend to show more than what you're actually doing anyway. My van though is spot on via GPS too and my mates Astra H is 5 mph out. Van had standard wheels on too.  :-/

[sport]

are you sure they're not 185 55 15 standard?

if they are indeed 16, the 17's will mean you travel at 68.38mph when the speedo reads 70, as long as it was calibrated correctly when new for 185/55/16s

it's a difference of 2.31% and is perfectly legal (2.5% being the limit)

if they're 15's standard, it'll be 71.35mph when the speedo reads 70 when you change to 17s, a difference of 1.93% the other way, also completely fine

Yes sorry thay where 15/55/185 And how accurate are sat navs

[Del Boy]

Sat Navs are spot on, as they're going via a live GPS signal

[the alarming man]

sat navs are ONLY accurate if you are travelling down a flat straight road

[Del Boy]

And the above must be straight & flat

[aaronjb]

And the above must be straight & flat

I knew a girl like that once.

[Del Boy]

And the above must be straight & flat

I knew a girl like that once.

[sport]

H i put some 17/40/205 alloys on my corsa c the standerd alloys where 15/55/185 will my speedo inicate that i will be travaling a bit slower

Hi also can any one tell me the tyre pressure for my 17/40/205 on a corsa
Front and rear thanks

[2woody]

that's quite a large difference - 4.4%

185/55 x 15 is 906wrpm
185/55 x 16 is 867wrpm

GPS is almost entirely accurate - trust it rather than your speedo