Thread: perentie 6x6 my new toy

33s should fit without a problem, just be careful which rim offset you get, some offsets will scrub on the front flares, not sure about rear.
You need to get tyres and rims with an appropriate load rating for what is a bloody heavy bit of kit too.

Put some pics up of the new rig oh and make sure there is some engine pics to

Just for giggles, I threw on some 32s to see how they fit. Tyres are 32x11-15s on 15x8 rims with zero offset:






I don't mind the look, and I'm sure 33s would look just as good, even better.

The rear has bucketloads of clearance, and even under heavy articulation I don't think you'd come close to scrubbing anywhere. The Assault Pioneer has the "Project Bushranger" rear body which features a valance with footholds that your Air Defence doesn't have, so you'd have even more clearance.



The standard rims have 22mm of Pos offset, while these 15x8s are zero offset. This means that the inner face of the tyre is in the same location as the standard tyres. I'd suspect you'd have room to go to 13 pos offset rims and still not scrub. In this pic, I have a standard wheel on the intermediate axle and a 32x11 on the back. You can just see they're aligned:



This shows the outer edges. The 32x11 sits inside the valance:




On the front, the zero offset means that the tyre will clear the chassis components on all lock and articulation, as it has the same inner clearance as the stock tyre. However face sits well outside the flare and although I didn't get the chance to twist it up, I suspect it would foul the flare or the guard. A bit of suspension lift would perhaps get around that. To keep it legal, you'd need to add wider flares. I would do anything for love, but I won't do that.



Then, if you've lifted the front, what do you do with the rear? The vehicle does sit a little nose down, so an inch at the front won't look out of place, but any higher and you'd have to do something with the back. The shame of it is you don't need ANY lift at all in the back for clearance, it's just to level the vehicle. Having to replace 4 heavy leaf springs just for making it look nice is a bugger, not to mention expensive. I don't normally like extended shackles, but in the rear is the only place they be acceptable. 2 inch longer shackles will give you an inch of lift.



The problem with this is the pinion angles, particularly on the rear axle.


The intermediate axle pinion angle will be improved, but it doesn't need it as it has a longer driveshaft at a shallow angle. The rear pinion angle will be worsened, and it has a short driveshaft coming down from a pillow block bearing at a steep angle! What to do?

Also, the design of the rear bogie suspension can cause issues if the tyres are too large.





Unladen, the rear axles are 940mm apart. When loaded with up to 2 ton payload and under full articulation, the design of the load sharing rocker means that as the leaf springs flatten, the axles move closer together.


As an example, I will use the dimensions of BF Goodrich KM2 M/T tyres (as they are what I would choose!). The 33x10.5-15 is 826mm in diameter, while the 255/85-16 is 840mm. With the 255s, you will have 100mm between the tread of rear and middle tyres unladen. Loaded up and under full flex, they will come very close to touching and locking together. Any larger tyres will almost certainly lock under articulation of the rear suspension.


As mentioned by Isuzutoo-eh above, the rating of the wheels you choose will be important. Just as important is the tyre rating. My preference would be for the 255s before the 33x10.5s for their higher load rating (1550Kg at 80psi Vs 1180Kg at 50psi), and then fit them to 130 Def 6.5 rims.

There is no emoticon for the level of jealousy I feel!!!!!

Nice purchase!

Originally Posted by 303gunner

Also, the design of the rear bogie suspension can cause issues if the tyres are too large.

...

Unladen, the rear axles are 940mm apart. When loaded with up to 2 ton payload and under full articulation, the design of the load sharing rocker means that as the leaf springs flatten, the axles move closer together.


As an example, I will use the dimensions of BF Goodrich KM2 M/T tyres (as they are what I would choose!). The 33x10.5-15 is 826mm in diameter, while the 255/85-16 is 840mm. With the 255s, you will have 100mm between the tread of rear and middle tyres unladen. Loaded up and under full flex, they will come very close to touching and locking together. Any larger tyres will almost certainly lock under articulation of the rear suspension.
...

I can see some people modifying the suspension to allow larger wheels to be fitted.

And if people are wondering about the "Valence" that I'm talking about and the clearance over the rear wheels, here's a comparison between the Air Defence rear body and the Assault Pioneer. While it appears to hang lower and foul the rear tyres, as shown in the pics above, it doesn't come anyway near them.


These pics also show how increasing the diameter of the rear tyres would reduce the clearance between them. There's not a lot of room to play with.