Difference in performance 31" Vs 33" ?

[Ruffstuff]

Hi Folks,
Can anyone tell me via first hand experience if there is a noticeable difference in performance when changing from a 33" tyre down to a 31" Tyre .
Vehicle is an 80 series Landcruiser 1hz, with aftermarket Turbo & Intercooler.
I originally had 31" all terrains before I had a camper and before the Turbo & Intercooler were fitted and went up to 33" Muddies when I was doing a lot more off-road work.
Now with a family & the camper in tow, the old 4.2 still lags somewhat, although I don't expect it to be a rocket ship.

The 33's are coming to the end of their life and I was considering going back to 31's if there was a reasonable performance advantage even though I love the look & off-road performance of the 33"s.
Thanks in advance,
Mark

[GeeTee]

yeah the lesser rolling circumference will make life easier for the engine and driveline and increase available grunt, especially at low speeds (off-road) and when towing. When actual speedo error is taken into consideration you'll probably drink less fuel, too

[DannyG]

Mark, I cant speak for everyone but in my instance (4.2TD as well) yes there is a significant difference.

My 33" muddys sucked more power and economy than I ever imagined, let alone all the extra load on the clutch and everythings else it effects.

I too am going back to 31" all terrains when my KM2's are worn out. I still do a lot of off roading but the old Patrol goes 99% of the places I take her muddys or not.

[BigJules]

As per the other comments, 31s will be easier on fuel and give you back some low speed oomph. However, I don't think I could ever go back; once you've seen your truck with 33s, the 31s will look too small. Borrow two and fit them to one side and see if you're happy.

The difference in running costs between 31s and 33s would be measurable but wouldn't buy you a beach house.

[GeeTee]

...but on longer treks its sometimes enough to pay for a few beers... or an unpowered  site. Every day!

[GeoffA]

When towing at a steady 100km/h, I've found I get exactly the same fuel consumption in 4th as I get in 5th.......and a lot more noise.......so I doubt changing tyre size would save much juice. In 4th, EGT's were lower, and it's easier on the gearbox.

I had 285/75x16 BFG A/T's for many years.........couldn't kill 'em. I went back to 265/75x16 BFG KM2's for a while, but quickly went back to 285 KM2's, 'cos I can. I had a set of GU alloys with 265/70x16 Cooper ST's briefly, and I hated the short gearing. It was revving it's head off. Mine just feels happier with longer legs.....it's easy to change down if needed.

KM2's take a little more to push along than the A/T's, but it's more something I feel when driving, than I notice at the fuel pump.

Like BigJules says, I reckon you'll be disappointed with the 31's. Maybe give the muddies a miss, and go with 285/75x16 A/T's......

 

[Symon]

I agree with the others, I recently went up from 31's to 33's and noticed the difference in get up and go and also at the bowser.

Like Geoff I now put along with the cruise set at 100k's and in 4th gear - especially when towing.  I use slightly more fuel this way but the 5th gear in the cruisers don't do much for you anyway, and you can feel the gearbox thanking you for it.

[dazzler]

Plus you may get a little longer out of the turbo'd 1hz before the head goes crack if its not under as much load.

[Hairs]

G'day Mark,
My 91 80 1hd-t runs 31x10.5x15's Bridgestone D/Duellers 604V's. This is the second set I've had. Speed is 2 k's over and I tow a pretty heavy camper and horse float.
Tow in 4th unless it is down hill or I have the wind behind me and I'm after a little extra fuel economy and then I'll push it into 5th.
Empty the 31's work well, I did think at the last set to move up to 32's but decided not to. yep, they would of given me a little extra in height, diffs bottom out where 33's have come through, which means I get hung up at times  I can live with that  .
I find the 31's work well.
Just my two Bob's worth.
 

[DannyG]

I had 285/75x16 BFG A/T's for many years.........couldn't kill 'em. I went back to 265/75x16 BFG KM2's for a while, but quickly went back to 285 KM2's, 'cos I can. I had a set of GU alloys with 265/70x16 Cooper ST's briefly, and I hated the short gearing. It was revving it's head off. Mine just feels happier with longer legs.....it's easy to change down if needed.

KM2's take a little more to push along than the A/T's, but it's more something I feel when driving, than I notice at the fuel pump.

Like BigJules says, I reckon you'll be disappointed with the 31's. Maybe give the muddies a miss, and go with 285/75x16 A/T's......

 

Geoff do you think the rolling resistance of the muddy tread is more then issue rather than the increase in diameter?

I went from highway tyres to KM2's and noticed a huge difference, thats why I am wanting to go back to AT's in 31's but Id much rather keep 33's if you think the AT's will be a decent improvement over the KM2's of the same size??

[Swaggie]

Ive always run 31 MTZ's,they hav taken me all over the High Country and not one puncture,Although i am right on tyre pressures...

Dont forget if you jump from 31' to 33's you could have an Insurance issue depending on your tyre placard...Also going back to 31's will save you a few bucks for each tyre...

So plenty of reasons to stay at 31's...

[GeoffA]

Geoff do you think the rolling resistance of the muddy tread is more then issue rather than the increase in diameter?

I went from highway tyres to KM2's and noticed a huge difference, thats why I am wanting to go back to AT's in 31's but Id much rather keep 33's if you think the AT's will be a decent improvement over the KM2's of the same size??

Yep, that's my experience, Danny. The road-noise that muddies make isn't happening for no reason.

Can't say I remember any issues going from the original road tyres to 285 A/T's, but it was a real long time ago.
The 285 A/T's certainly felt a good deal easier to push along than the 265 KM2's, but I really didn't notice any problems when going from 265 KM2's up to 285 KM2's.

When I first fitted the 285 A/T's I was concerned about legalities, so I did a bit of checking. The largest diameter tyre offered by Nissan as an option for the Series 1 GU is 245/85x16 (it's in the owners manual - Series 1 only). The OD of 245/85x16's allows fitment of 285/75x16's to Series 1 GU's. I checked this with an engineer, and he OK'd it, but I got him to certify it as well.....just in case I get queried. Only cost me $250....

Have you had the boost and pump timing on your TD42T looked at, or is it still standard?

[DannyG]

Yep, that's my experience, Danny. The road-noise that muddies make isn't happening for no reason.

Can't say I remember any issues going from the original road tyres to 285 A/T's, but it was a real long time ago.
The 285 A/T's certainly felt a good deal easier to push along than the 265 KM2's, but I really didn't notice any problems when going from 265 KM2's up to 285 KM2's.

When I first fitted the 285 A/T's I was concerned about legalities, so I did a bit of checking. The largest diameter tyre offered by Nissan as an option for the Series 1 GU is 245/85x16 (it's in the owners manual - Series 1 only). The OD of 245/85x16's allows fitment of 285/75x16's to Series 1 GU's. I checked this with an engineer, and he OK'd it, but I got him to certify it as well.....just in case I get queried. Only cost me $250....

Have you had the boost and pump timing on your TD42T looked at, or is it still standard?

Thanks for the info, I think Ill stick with 285's when I go back to AT's and see how it goes.

No mate havent even started the old girl for a month or two! Ill get Bathurst weekend out of the way then its full steam ahead getting a few things sorted starting with a rear diff oil change (it is starting to chatter when under load in the rear diff), an Injector service, and I need to look at the top of the gear box because it is getting hard to shift back from 5th to 4th and it has got stuck in 3rd momentarily a couple of times. Research tells me that it is something relatively easy to fix. Once I get those few 'must do' things sorted Ill start looking at the fun stuff Has yours experienced any of these issues yet?

[GeoffA]

Thanks for the info, I think Ill stick with 285's when I go back to AT's and see how it goes.

No mate havent even started the old girl for a month or two! Ill get Bathurst weekend out of the way then its full steam ahead getting a few things sorted starting with a rear diff oil change (it is starting to chatter when under load in the rear diff), an Injector service, and I need to look at the top of the gear box because it is getting hard to shift back from 5th to 4th and it has got stuck in 3rd momentarily a couple of times. Research tells me that it is something relatively easy to fix. Once I get those few 'must do' things sorted Ill start looking at the fun stuff Has yours experienced any of these issues yet?

Getting O/T.....PM coming your way......

[blackmav]

You could get 32s...

[meimarocu]

You could get 32s...

Got 32's like em, but makes it hard to get them in remote places.
And not many brands have 32's.
Cheers Ian.