Tyre Size and Low Range

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Bit of a debate between me and a guy at work (a friendly debate) Can any one tell me if there would be a big difference when in low range when running say a 70 profile instead of 65 or 75 instead of 70 . Just talking to a bloke at work about it and he reckons the difference would be very noticeable especially when going down steep stuff low range ?? I had bigger profile on both my 90 series and didn't think it made that much difference, not that I noticed anyway. I said I would ask the question !! I know you have to give it a bit more on the black top but I would have only thought this was when you start to get into some serious rubber like 35s etc like some run on patrols/cruisers but then most change diff ratio's to make up the difference and or change over gears in there transfer cases to accommodate the bigger tyres....Cheers Steve

[barajak Senior Member Find all posts View Profile Close barajak]

I'm with you. It makes a difference in 4th & 5th high range but not noticeable geared down.

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

There is no difference at all, there is only about a 4kph difference at an indicated 100kph, meaning, that before the increase, your indicated speed at 100kph would actually really be about 96kph, but now with one size taller profile, and indicated 100kph would be a true 100kph..... what does that mean for low range, absolutely no difference. You will only notice anything if you went up from a 265/65/15 or 16 or 17 up to the next size tyre, being a 285/75/15 or 16 or 17.

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

So croozza, going from say a 265/65/17 (say a prado wheel for a good example) to a 265/70/17 there would be noticeable difference in gearing either high range or low range just a difference in speedo reading which I new about that bit as my old prado speedo changed......Im going to print the replys up to show him...............Cheers Steve

[Leethal Advanced Member Find all posts View Profile Close Leethal]

If there is a difference in High range (highway speeds) there will be exactly the same percentage difference in Low range (offroad speeds).
Going from 70 profile to 75 profile changes gearing by approx. 4% so on the highway (at roughly 100 km/hr) your about 4 km/hr faster for same engine rpm.
Offroad your Low range will be the same percentage "higher"
For example; a 90 series Low range is approx. 42.25:1 (1st gear 3.83 x low range 2.566 x diff 4.3) change to 75 profile tyres and the effective ratio is now approx. 40.9:1 ( 4% higher).
Will you notice the difference ... if you need to now use your brakes to control descents where before you didn't, then yes. Most likely you will not notice the change I would think. As for climbing if your engine has adequate power then that minor ratio "change" I would think would not be noticable.

As has been said, the greater the tyre diameter change the greater effect.

Lee

[Ghostriderhusky Senior Member Find all posts View Profile Close Ghostriderhusky]

I went from a 265/65/70 to a 285/70/17 ( 31-33)

And yes I do alot of hardcore steep rock crawling stuff . I noticed a bit of difference in low range when hill starting on reaaal steap stuff i needed to ride the clutch alot more. It's not bad enough to need a diff ratio change in my opinion , but when I go to 35"s I will be doing diff gears not long after

[Ghostriderhusky Senior Member Find all posts View Profile Close Ghostriderhusky]

On a 265/65 to a 70 , there would hardly be any difference

[croozza Avid PP Poster! Find all posts View Profile Close croozza]

So croozza, going from say a 265/65/17 (say a prado wheel for a good example) to a 265/70/17 there would be noticeable difference in gearing either high range or low range just a difference in speedo reading which I new about that bit as my old prado speedo changed......Im going to print the replys up to show him...............Cheers Steve

Lets say your off road in low 1st, you would be doing about 5 to 10 kph, with an increase in tyre profile, at those speeds equates to .2 to .4 kph, you will not notice any change at those speeds.

[Ozpat Advanced Member Find all posts View Profile Close Ozpat]

Steve, I went from original Grandcraps to BFG ATs 265x70x17, only noticable (big) difference is better grip.

Cheers, Jim.

[Andosan Junior Member Find all posts View Profile Close Andosan]

Difference in radius between a 265/65/17 and a 265/70/17 is about 3.5%. That means for a given engine speed you will be going 3.5% faster, but you will require 3.5% more torque. Unless you were measuring it I doubt you'd notice the difference.

[Peterpilot Avid PP Poster! Find all posts View Profile Close Peterpilot]

The actual difference depends on the tyre brand, type and construction. When I recently changed from a 265/65/17 highway tyre (775mm OD) to a LT265/70/17 Mickey Thompson MTZ mud terrain (810mm OD) the size difference is 4.3%, therefore I needed to adjust the speedo corrector by exactly 4.3% to get the speedo to read accurately.

I haven't noticed any loss of performance from the V6 on the road and in low range I suspect the difference would be even less. I'll put the theory to the test on the weekend

[Peterpilot Avid PP Poster! Find all posts View Profile Close Peterpilot]

Difference in low range was minimal

[glen_ep Addicted PP Member Find all posts View Profile Close glen_ep]

31's to 32's in low range would be a very small change.
However when changing from 32's to 33's, I noticed a huge difference on road.