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How Much Will Tyre % Size Afect Aceleration And Speedo

RS444

By RS444,
in Four Door Family & Wagoneers

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GoldZilla Grand Master

GoldZilla

Posted
Posted

Seeing as you have an RS-Four (and hence, all wheel drive), the only thing you really need to worry about is that you use the same sized tyres on all four wheels, or you will eventually cause serious (and expensive) issues with the transfer case on the gearbox.

Your tyre placard says 195/60/16? I'm sure mine says 225/50/16 or around that...

Anyway, do a search on the forums (or on the net in general) for tyre size calculators. There are quite a few mentions of them even within this part of the forums, so it won't be hard to find references to them. It will give you the best diameters to aim for if you need to replace your tyres and want the same or similar rolling diameter.

Have you got access to a GPS navigation device with speed read-out (the newer, the better)? If you have, use it to get an idea of how much difference there is between what your speedo says and what the navigation device tells you. Speedometers are usually set up very optimistically and often read a speed higher than what you are actually travelling. I replaced my standard Stagea wheels and 225/50/16 tyres with V35 Skyline wheels and 245/40/18 tyres and the speedo is now a LOT closer to what it should read. It used to read 60km/h when I was actually doing about 54-55km/h, and now it's only below by 1km/h or so. I've checked this on 3 different navigation devices for comparison's sake (before and after), and all told me the same thing...

KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

My door placard says 205/55/16 so you are probably looking at the 15in sizes.

Your tryes are about 3% smaller so your speedo will be a little more optomistic then usual. Acceleration should be marginally better but not so you would notice it. Similarly fuel consumption should be fractionally worse.

As GoldZilla says when you next change your tyres try to find ones slightly bigger than standard and your speedo will be more accurate.

I am using 235/45/17 and they are quite a bit bigger than stock but my speedo is just about spot on. The Stagea final drive of 4.3 is qute low so the bigger the tyres the better!

  • 1 year later...
  • 1 month later...
rosella Community Regular

rosella

Posted
Posted

I just replaced tyres on my M35. It came with 225/45/18 and the web specs state 225/55/17. I've used an online calculator and I went for 245/45/18 and they fit nicely under the guards too. Pictures will follow shortly when it stops raining. BTW, the speedo accuracy improved from being 7.01% too fast to 2.6%. This was based on the daily drive of 228km.

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