Standard vs 33" tyres and fuel economy

[D@niel]

Hi guys, how much difference in fuel economy is there going from standard 265/65/17 (30.5") up to 33" tyres on a gen4 3.2 diesel. And how much power do the larger tyres sap? Thanks

[kiwi1973]

Few things you should be aware of here:

Will they actually fit without rubbing? This may be determined by the wheel offset you have. You'll likely need the clearance offered by a bullbar to the front of the front tyres and may need to do some trimming to the mudflap area to the rear of the front tyres.

Assuming they fit ok, some of us can get away with 32" tyres without affecting torque converter lockup, but 33's are pretty likely to interfere with TC lockup. And this is where fuel economy will be impacted quite a bit, as well as transmission temps.

If you really want to go with 33's to do it properly you should consider re-gearing the diffs. I'm assuming you have an auto? If so you have 3.9 ratio diffs. Diffs from a diesel manual are 4.1 ratio, for from a petrol model 4.3 ratio. It would be interesting to see what anyone running 33's on 3.9 ratio diffs has to say about their experience. With diffs re-geared the issues of torque converter lockup and most of the fuel economy issues will be mitigated.

Another thing to consider (and I'm still pondering this one myself rather than pre-concluding), is it really worth going to 33's over 32's?! 33's over factory size offers about 1 inch of extra ground clearance, but offers only 1/2 an inch over 32's (265/70/17 or 265/65/18). The 1/2 inch gained with 32's has few compromises for most, but that last 1/2 inch of clearance going to 33's brings with it compromises requiring changed diff ratios to properly rectify. Whether that's worth it is up to the individual.

Although that final 1/2 inch of clearance seems negligible, it could actually be enough to make a difference in especially deep ruts, or sections with especially big rocks.

Whilst the extra clearance afforded by 33's is clear advantage, it's not clear that for overall 4wd touring the 33's are necessarily the better choice. I'm going to assume the choice here is between 285/70/17 and 265/70/17 to keep this simple. With a Gen 4 long wheel base the only options for a 33" equivalent are to go wider as well as taller. So you're going 7.5% wider to get 3.5% taller. Whether this matters too much is open for debate, but generally it is considered that going taller offers traction advantages, whereas going wider doesn't and may actually offer up some compromises. That said, 285 is not all that 'wide' in the overall scheme of things.

In my view in some respects 265/70/17 is a bit of a sweet spot for a Gen 4 Pajero, as it is strictly taller than factory size and no wider. Some online calculators will tell you that this is 31.6 inches, but depending on the manufacturer and tyre you can get close to a true 32" tyre. Cooper ST Maxx is about 31.85" and STT Pro is 31.93" for instance.

[Hatto]

Good answer!

[starjunk]

Great answer!

Learnt something new today. Thank you kiwi1973

[kiwi1973]

A few further thoughts on this issue - (it's an issue that I've looked into fairly thoroughly!)

I said earlier that with a Gen 4 the only 33 inch equivalent options were to increase width more than diameter. This is true with 17 inch rims, though with 18 inch rims one could consider 275/70/18. Compared with 265/70/17 or 265/65/18 this is 5.1% taller for just 3.8% wider. However, this offers less increase in sidewall height, is an uncommon size and may be an expensive size.

Other drawbacks of 33 inch tyres, and their mitigants, include:

Decreased braking efficiency. This could be rectified through fitting a different compound brake pad, such as EBC Green Stuff.

Modifications needed to fit 33 inch spare on rear door.

Additional stress on steering and suspension components. Pajero's are quite robust in construction - the additional stress could mean some components don't last as long as they might otherwise, but in the overall scheme of things I don't expect service life of wheel bearings and components will become in any sense unacceptable.

After researching all the pros and cons to fitting 33's I've yet to fit new tyres and could go either way. I have concluded thus far that there's really nothing wrong with 265/70/17 - they'd be a fine size to stay with. That said, many of the compromises associated with fitting larger tyres I'm about to separately overcome anyway. I'm building a new rear steel bar that can easily be designed to give sufficient space for a 33 inch spare on the rear door. Whilst in the process of looking into swapping in different ratio diffs I recognised that it would make sense to find a rear diff fitted with the optional diff lock (which my Paj doesn't have). Indeed, I became so attracted to the idea of gaining a diff lock that I think I'd like to proceed with this regardless whether I opt for the 33 inch tyres or not (retrofitting a diff with factory diff lock is the most cost effective way to get a diff lock).

So basically I reached the conclusion that 32 inch tyres are probably the sweet spot, but since it appears I'm about to separately overcome most of the compromises anyway, then I could still consider the 33's.

One further point to make - for someone who had their heart set on 33's but didn't have the budget right now to re-gear diffs, a TC lockup kit could be used to overcome some of the issues. It's not the ideal solution.

[D@niel]

Wow cheers for the in depth responses mate. I've decided to go for a 32" anyway, I still want to be able to fit the spare on the rear door without hassle and keep power loss to a minimum and fuel effiencecy up! My factory tyre size is 265/65/17, I'll be keeping to the 17" rims. Cheers mate

[shortiegetdown]

Thanks heaps for all that information! Do you know what the ratios should be for. 3.2td auto?

[redbruce]

Thanks heaps for all that information! Do you know what the ratios should be for. 3.2td auto?

MY16NX and earlier is 3.917, MY17+NX is 3.692.