Does wheel size alter gear ratios?

[kokomo]

Change the Diff Ratio and all order will be restored...

Did it on my Brothers Surf HIlux..

Easy and cheap..

Go see a mechanic

[Noelm]

as a general rule, you do NOT change the diameter of the wheel and retain the same "profile" tyre, you get a tyre that has a lower profile and the 'rolling" diameter remains almost the same, so what I am saying is,,, if you had (say) 15" wheels and had 75 profile as in your tyre size as 15 X 265 X 75 when you go to (say) 17" wheels, you would then fit 17 X 265 X 65, that will ,maintain the overall diameter, these dimensions are "just for instance" and you will need to go to a good tyre service and ask for proper advice, or, you can alter the speedo drive, as this is what is done on cars that are available with various wheel sizes and diff gear ratios from new, or you can just do it and put up with it, but remember speedo readings could bring you undone at speed cameras and stuff!

[ak73]

or just fit a speedo corrector kit from Jaycar for $50

[snatch]

Get a gps and test your speedos current accuracy. I found that when I fitted Bridgestone duelers to my D40 that to get a tyre that fitted I had to go slightly oversized. It actually corrected my speedo as it was slightly over indicating with the standard factory rubbish.

Going to an oversized tyre increased my 2000rpm speedo reading from 97 to 100kph and when tested against a gps it was accurate. In other words the circumference of the tyre eincreased by roughly 3 %. Hope this helps.

[Orrsum]

Get a gps and test your speedos current accuracy. I found that when I fitted Bridgestone duelers to my D40 that to get a tyre that fitted I had to go slightly oversized. It actually corrected my speedo as it was slightly over indicating with the standard factory rubbish.

Going to an oversized tyre increased my 2000rpm speedo reading from 97 to 100kph and when tested against a gps it was accurate. In other words the circumference of the tyre eincreased by roughly 3 %. Hope this helps.

thanks for that, its what i was getting at, my speedo overstates my current speed by approx 6km/hr. i can get bigger tyres for the current rims its just that i have come accross some 17inch ones at a really good price.

thanks again.

[White Pointer]

i am wanting to upgrade my Navara wheels from 16 inch to 17 inch and go from a 255/70/16 tyre to a 265/70/17.

Somebody told me that if i increase too much i will not be able to move off the mark when towing due to the fact that it will alter the gear ratio.
can anybody explain this to me or offer some advice.

G'day,

Make sure it is legal according to the owner's handbook or the tyre placard. If not, you will need a modification plate to recompliance your vehicle. This is critical for insurance.

The tyre seller should be able to tell you the rolling diameter of your OE W&T and the ones he wants to sell you. They have to be exactly the same! If you are buying a set of 5 it is not so critical, except make sure it fits. But if you are keeping one of the originals as a spare, and the diameter is different, you will blow up your diff if you put it on.

The low profile tyres will be softer and may run power pressure. They will stake easier and may not have the load index rating to maintain your carrying capacity, including towing loads.

White Pointer