Tyre Size Increase

Submitted: Monday, Jun 23, 2014 at 17:03
ThreadID: 108461 Views:1295 Replies:3 FollowUps:0
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Gday all,

Looking at moving from 275/65 R17 (OEM tyres) to 285/70 on a 3.0 CRD Nissan Patrol.

After info from anyone who has fitted this size as to how drivability may have been affected, particularly when towing?

Thank you!

Lester
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Reply By: Robin Miller - Monday, Jun 23, 2014 at 19:22

Monday, Jun 23, 2014 at 19:22
Hi Lester

You probably know they are seriously underpowered car as is , but a lot of people do that change and live with it.

You don't say if yours is auto or manual - if its manual just drive it and use the next higher gear all the time and it drives like that. (I.E. start of in 2nd instead of 1st.)

Now if its an auto this is harder but drive it with the snow mode switch engaged - not quite the same thing but will give you the idea.

I have those sizes amongst the wheel sets I have and run standard wheels and tyres as much as possible.

But mine is the auto 4800 petrol and loss of torque doesn't worry it much but the 285 wheel set of mine weighs over 5kg more per tyre than standard
and this mass has to be accelerated up and down and slows the car down.
Having the auto box beefed up recovered most of this.

So can't really advise you as not sure what you wish to achieve and there are different options.

For instance I wanted max body ground clearance and by carefully looking at what limits it I ended up changing slightly the side steps which was worth more than 1 tyre size increase combined with rubber spring spacers.

Robin Miller

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AnswerID: 534885

Reply By: Ross M - Monday, Jun 23, 2014 at 20:47

Monday, Jun 23, 2014 at 20:47
The 40mm dia increase will over gear it and sap rear wheel torque to some extent.

If towing it wouldn't be a good thing as what you are after there is retaining applied torque to the rear wheels, not lessening it.
It is slightly over 5% increase, so Speedo "over read" will be closer to true but ODO will under read if currently correct.

With a CRD, if it takes the engine load into a different area of it's electronic fuel map it may suddenly be over a reasonably efficient level and begin to use more fuel than you think.
A trial of someone else's wheels would be good to do there before deciding.

Also wider wheels take more to push along, purely because of the width. The wide roller effect.
As Robin mentioned, more mass of rubber = more weight of tyre.

I can't see a benefit for you in doing it. Unless the tyres are free.
AnswerID: 534890

Reply By: FatGaz - Wednesday, Jun 25, 2014 at 17:43

Wednesday, Jun 25, 2014 at 17:43
Hi Lester,

That change will give you better float if driving on sand and will give you better clearance for off road work.
It will also rob you of power at the tyres which will effect towing.
As already mentioned, your speedo and odo will change (may actually be closer to true).

The problem is, some states will only allow a small variation from the size displayed on your tyre plackard (usually on the door). This may make your vehicle un-roadworthy in those states unless you have an engineers cert otherwise.

In my opinion, I like a slightly oversized tyre. But I don't tow heavy loads.
AnswerID: 534989

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