Tyre Size Question

[Blitz_boy]

Hi guys, I'm getting my V35 coupe complianced. The factory tyres are a 45 series (225 front and 245 rear)

But for compliance I've been told I need to fit 40 series tyres as this is whats on the Aussie placard.

Is this drop in profile going to affect the car at all? Will it through out the speedo?

[scathing]

It will throw out the speedo, theoretically.

This tool is a good to work out what changes will happen as you change profile. At the "stock" 100km/hr (which generally isn't accurate anyway) you'll be doing 96km/hr. Which is sweet FA, honestly. Given that the OEM speedo overreads, you'll find that this new size is closer to "true".

I went to a 285/35 R18 wheel. According to the above tool, I should have lost 3.1% of my diameter compared to a 245/45 R18 (which is the OEM 350Z size). However, when I compare the speed to my GPS and those helpful electronic signs on freeways, at 110km/hr my digital speedo is now 1-2km/hr higher than their indicated speeds.

Why don't you try to source a 350Z placard instead, and that way you can keep the stock tyre sizes?

[Blitz_boy]

Thanks for that. I would like to keep the 45 profile but thats the evidence pack that the compliance workshop has.

Sounds like it will be fine.