Tyre width doesnt affect speedo rating - overall diameter including rims does

lets say 16's with tryes = 1000mm

18s with tyres = 1100mm

Thats where your 10% comes from.

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I am only an asshole on the internet :)

[SIGPIC][/SIGPIC]

ADRs were changed about a decade ago from +-10% to "read no less than" the actual speed travelled at, consequently all manufacturers set the speedo to read about 10% high.

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A nation of sheep will beget a government of wolves.

Aspect ratio (profile) is the tyre wall height as a percentage of the tyre width.
Therefore a wider tyre in the same profile will have a slightly larger diameter.
So yes a 225 will help.

But a 215/45/18 or 225/45/18 would get you closer to where you want to be.

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MY00 WRX. 89 Prelude. 99 CRV

Technically it does, because going from 215 to 225 therefore affects the width of your sidewall. Going from 215 to 225 in a profile of 40 adds 8mm to the overall diameter

However, as per my previous post/calculations it's a bee's dick of difference.

ps. Jez don't go buying new 225's as it will still tell you that you're doing 66 or 67km/h when you're doing 60km/h

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[I]trolololol[/I]

yeah I've read that the width does make a small difference, as can also the brand of the tyre. Certain brands may have a thicker sidewall profile etc. Difference is 1% or thereabouts

Thanks for the info.

Trolly i need new tyres anyway so looks like 225/40/18 is the way to go.

Will just have to live with it because i'm not soldering in a speedo corrector.

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Silver MY08 Betty.

+1 I asked dealer the same question. Apparently, they deliberately make the speedo reading 10% higher. If I were you, I won't worry about it. I have driven both my wrx and sti past speed cameras on fwy with speedo showing 110ish many times, never get a ticket.

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MY08 STI 422whp at 1.5bar on E85, built by Diversion Garage, assembled and tuned by EvoR

Update from new owner: 375whp at 1.4bar on 98, at Tokyo Motorsport

+200 'who cares'.

Sit on 60kmh on the speedo, actually doing 55ish kmh. No speeding fines. Roses are red. Sun is shining. Everything is grand.

All cars do this. You'd be hard pressed to find a modern car that is close to the actual speed shown on a GPS.

Remember that your GPS speed isn't super correct too. It is just averaging the time taken to go from spot to spot and depending on your equipment it can be incorrect too.

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[COLOR="Gray"]550Nm off a 2L... Just wish it was in the dak dak...[/COLOR]

Mine is the same after change from 215/45 18 to 225/40 R18.

Speedo is 10% slow.

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[COLOR=Black]Liberty GT Spec B tuned 240 HP & 372 Nm at the hubs.[/COLOR] "Instead of banning high performance cars - ban low performance drivers"

Mine is set like this.. Gps read 92 at 100 and about 54 at 60.. I like it

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06 sti