Larger Tyres and distance travelled

[drgtr]

Larger Tyres and distance travelled

[the evil twin]

How long is a length of string...

Use your GPS to see how far your odometer is out.
It will usually NOT be by the same amount the speedo is in error.
Best way is to travel, say 10k's on the Odo (the further the better) and see how far the GPS says you have gone.

Other option is over a known distance of say 100 K's of road markers

[drgtr]

Thanks Evil Twin.

Is there a formula to calculate differences though?

say from 31 inch to 35 inch rolling diameter and how much it should be out percentage wise?

Also would I be right in my assumption I would be travelling more physically now then what the odometer will show?

[the evil twin]

Thanks Evil Twin.

Is there a formula to calculate differences though?

say from 31 inch to 35 inch rolling diameter and how much it should be out percentage wise?

Also would I be right in my assumption I would be travelling more physically now then what the odometer will show?

The percentage will be 4/31sts... IE 13%
The problem is this... hardly any 35 inch tyre is actually 35 or any 33 actually 33.
Many 33's are often only a tad over 32 and most 35s will actually be around 34ish

I usually work in 5% for each 2 inches change as it is easier and will be awful close... and yes... you will be going further on 35's than your Odo thinks you are.

[MB]

As ET kindly mentions 5% Drgtr is very close I find too on each tyre 2” increase. It also appears for me IIRC that each diff ratio change adds another roughly 5% atop from a trucks OEM plated diffs. 3.9s to 4.1s to 4.3s etc....
Changing from plated stock 4.1s to 4.3s and 35” BFGs tyres seems to be 10% for me according to highway markers as ET also suggested. Best to good GPS check for yourself would no doubt be safest and or drive like me at a grandpa 15% under pace :-) !


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[drgtr]

Wealth of knowledge as always and appreciated

Thanks guys.

[the evil twin]

Agree with MB... 5% is a golden number when 'guesstimating' what will happen to a Patrol when you change things.
Bigger/smaller tyres - 5% per 2 inches speedo, odo, fuel economy
Diff ratio - 5% per step speedo, odo, fuel economy
Full Roof rack - 5% worse fuel economy
Fully loaded Truck for touring (usually about 300Kg over GVM) - 5%
Full 750 Trailer - 5%, add another 5% for each additional 750Kg

Doesn't always hold true but will be awful close most of the time

[threedogs]

In the tyres specs they should have a distance for the rolling diameter.
Good luck running the 35"s

[drgtr]

Its been great running the 35s lol

Its amazing how well the TD42 on 4.3 diff ratios run it.

So on the Speedo when it shows 90kmh Im really at 104kmh on the GPS and at 95 Kms Im really at 110kmh

So its 15 percent difference.




Low speed I can feel the mud chunky treads
Higher speed Its noisier but still smoothish.
Slight driveshaft vibration if I dont load the clutch starting off on low rpm sometimes.

Originally at 110 kmh I was at 2670 rpm with the 275 75 16 (5th Gear)
Now at 110 kmh Im sitting on 2180 rpm with 315 75 16 (5th Gear)

Im using less fuel already. I dont even get out of 4th gear in the suburbs.
I dont even need to rev past 2000 rpm as it is still comfortably in the torque band.


Im very happy overall.



So if the odometer shows I have done 100kms distance do I add the difference of 15 percent on top for the distance too? to get the real distance travelled?

[MB]

I do get confused easily Drgtr mate and will have to defer to ET here. +\- tyres/diffs etc....
I do know that a BFG Km2 muddie varies shiploads from fresh to sand tyre worthy :-)


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