Fitting 285 or 33 inch tyres

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

Like a lot of people, I have a set of 265/70/17s on on speedy rims with the extra offset. 2inch lift and no rub. Have talked to others with standard rims and there is a little rub on full lock for them. Just an opinion but I do not think I would enjoy anything bigger diameter with the automatic gear box behaviour. Has anyone changed diff ratios with bigger tyres to overcome this problem? Is it an easy mod?

Not a 120 but mines an auto with 33's.... and I did change the diff ratios shortly after the upgrade. TBH the biggest negative impact the 33's had was on braking performance, second to that would be take offs from zero where the auto's torque converter slips longer than original. After upgrading diff ratios the initial take offs and torque converter slipping improved, and after a transmission cooler installed the general gear changes improved. The labour costs for diff ratio installation is high so it's best to combine with locker installations.

Hi Amts,
I think you will find that the latest research / report shows the larger the footprint / surface area the better the tyre Off road. And has shown the larger the diamiter tyres are better than wider. I think this is one of the reasons manufacturers are creating tyres with stronger sidewalls , not just for protection, but so the tyres bags length ways and not sideways when running lower pressures.
It might depend on which report you read, but the latest ones I have including tests from 4wd action have shown this.

'Wider better offroad' is way to generalised, and I wouldn't trust 4wd action's research. I could easily say rubber compound has significantly more impact on grip than surface area - but that would be over-generalising as well. It all comes down to what you want from the tyres. I'd agree with amts's point where wide (LOW PROFILE) tyres are beneficial for cornering stability on road. For offroad however, it depends on what surface you want to traverse, as there is no perfect tyre for everything.

Speaking from experience, my last tyre change was from 255/85R16 BFG KM2's to 255/85R16 Maxxis Bighorns. With the Bighorns I immediately noticed reduced grip on road, on dirt and on rocks. However, the Bighorn's tread is exactly 206mm wide vs the BFG's 182mm (12% wider). In this case wider proved worse, but I presume the compound has much more to do with it.

One of the biggest arguments people have for wide tyres is to keep the vehicle on top of mud. However, I've noticed in USA there's an increasing number of mud vehicles using super skinny tractor tyres, because the large lugs can spit out the mud easier, as opposed to getting clogged up.

At the other extreme, if we look at Artic trucks, it's clear that wide/huge wins on snow.

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Hi Amts,
I think you will find that the latest research / report shows the larger the footprint / surface area the better the tyre Off road. And has shown the larger the diamiter tyres are better than wider. I think this is one of the reasons manufacturers are creating tyres with stronger sidewalls , not just for protection, but so the tyres bags length ways and not sideways when running lower pressures.
It might depend on which report you read, but the latest ones I have including tests from 4wd action have shown this.

That's right. The larger footprint comes from having a longer footprint. If the footprint area is the same, the one with the longer footprint will have better performance offroad. So say instead of going with 285/70R17, it is better to go with 265/75R17 (assuming such a size exists).

Also mud tyres generally have narrower tread width compared to AT or HT tyres, even though they are 265 wide in the tyre size spec. So if you are looking at why some say their tyres rub and others don't despite fitting the same size tyre, it is due to the tread width and how square the shoulders are. eg. my Wrangler MT/Rs have round and narrow shoulders and they don't rub on full lock. But some BFG ATs do. These are 265/70R17 tyres.

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

The only reason I went for a 275/65 over the 265/70 was that the former was the only legal option at the time. As things seem to have panned out I will definitely be looking at the 265/70 next time around. The extra 10mm width over stock is meaningless only the 14mm increase in diameter was important.

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

Hey Mule

Are you able to elaborate on the auto gearbox issues with the 265/70/R17 tyres? I am about to pull a trigger on a new 150 D4D Auto and am really keen to put this tyre size on (same size as I currently have on my Jeep Wrangler in an ST Maxx - has been a great tyre size to balance road v's off road). I am really concerned about the extra 3.5% rolling circumference impacting performance and auto transmission behaviour. I intend to tow a 1tonne camper trailer off road (I want these tyres for better traction) and do a lot of highway driving.

The main thing that keeps me thinking this tyre size will be fine is that a lot of guys seem to be running them and I cant find any threads reporting major issues (or diff ratio/transmission mods required to run this size)

I have investigated changing the diffs ratios - getting the correct C&P ratio for this car seems to be the difficult part. I am now thinking that a chip and exhaust upgrade may provide some compensation.

I know this is my first post, however I almost want to start a new thread on what issues (excl. suspension/rubbing - this is well covered) people have had to overcome as a result of fitting 265/70R17 tyres and how they overcame them....

Cheers

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

Argh - scratch that - found a good thread (in the 150 section....)

[Mule Member Find all posts View Profile Close Mule]

Hi Farmgate. I assume there are no significant programming changes in the 150 D4D auto from the 120 but I don't know. In the 120 with the bigger diameter rubber the auto box has crap programming such that it does not hold lock up in 5th gear at 100km/hr with a slight head wind or carrying a little something on your roof or trailer or caravan. I do not know if it is to protect the lock up plate or just to give a lower gearing but it is a pain in the bum and wallet for the extra fuel. It behaves a little better at 110km and even when a little slower at 85-90km but again depending on how much accelerator required to maintain speed. Cruising with an Oz tent on the roof with the 265/70/17s is a constant pain with the auto moving in or out of lock up in top gear with every little minor rise in the road. You are constantly trying to feather off the accelerator to stop it wanting to shift out of lock up. You just want it to lock in and cruise but no such luck with prado!!!!!!

[Mule Member Find all posts View Profile Close Mule]

Glen, Thanks for the information. You say "after a transmission cooler installed the general gear changes improved." I am curious in what way it improved?

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

Thanks Mule - that does sound like it could get painful. I will see if I can get some of the 150 guys to share their experience with this size - hopefully there are some differences in the 150 that help.

[Kalb Lurker Find all posts View Profile Close Kalb]

Hey guys. I've got a 120 series and I'm running 2" lift. I've got 0 offset 17x8 CSA sunnies with 285/65/17 ATs. Initially they rubbed, whilst new, but that went away quickly. I want to change to 285/70/17 (32.7") just want to know for certain they'll fit with minimal or no rubbing. Don't mind a bit under full lock / compression situations. Was thinking about putting in 10-20mm strut spacers to level out the front end, but from what I'm reading it's not height that's the issue, it's width, and I would have thought going 0 offset would have eliminated that?

Cheers in advance.

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From my reading, 0 offset is too far. +20 to +15 offset is more in the ballpark.

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

Glen, Thanks for the information. You say "after a transmission cooler installed the general gear changes improved." I am curious in what way it improved?

It's difficult to explain exactly, but I definitely noticed the gear changes were clearer, felt quicker to change and stronger. Another way to say is less slop. I noticed it most when climbing very steep roads like the Bells Line of Way at Kurrajong or out of Kangaroo Valley.

Now that I think back, before the cooler, the transmission would occasionally act incorrectly, ie, refuse to kick down gears on steep climbs and result in crawling speeds, and/or overheat. It was rare but happened enough that I'm 100% certain the cooler resolved those issues. Never happened since, even now with the supercharger.

Goes to show the AT overheat indicator on the 90's comes on too late, the temperature is already negatively affecting the transmission.

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

did you end up fitting 285/70/17's? I'm currently running 275/70/17 with no rubbing just wondering if i go to 285 next time I'm due tyres.....

[Marlan Gounden Lurker Find all posts View Profile Close Marlan Gounden]

Hi Guys,

I've just taken the plunge and fitted 285/70/17s with a -12mm offset rim. More than enough clearance to the strut and UCA's but ever so slight rub against the front mudflaps on full lock. Its an easy fix. Pics to follow. Tyres are Maxxis 762's with MT classic III rims.

[Guest Close Guest]

Hi Guys,

I've just taken the plunge and fitted 285/70/17s with a -12mm offset rim. More than enough clearance to the strut and UCA's but ever so slight rub against the front mudflaps on full lock. Its an easy fix. Pics to follow. Tyres are Maxxis 762's with MT classic III rims.

-12 or +12?

[Marlan Gounden Lurker Find all posts View Profile Close Marlan Gounden]

negative offset. -12mm. New rims are 42mm further away from UCA.