Fitting Oka wheels

Dean, welcome to the club where everyone is happy, sweat free and can lift their arms past their shoulders for the rest of the day! I got one a while back and noticed a mate carries one with him, he's a tipper driver and he's doing big truck wheels! They are expensive but once you realise all the other things you can use them for, working on mechanical things in general becomes so much quicker and easier. When tightening i hand start, use the gun then when pulled up i tighten by hand if it's a critical bolt/nut etc but you do get a feel for how tight things are after a while and i can now usually just do it by feel with the gun. Be careful though as at the start i rounded a few nut and bolt heads. An impact driver with 3/8" drive can be useful for smaller nuts and bolts in the workshop etc.

Only thing is, Milwaukee don't make an OKA wheel picker-upper and/or mover! We should put in a suggestion to their research department!

cheers, alister

My two cents are...I'm far more comfortable with a torque multiplying tool which at least allows you to dial in the torque that you want,that way you can dial in as much pressure in your shoulder as a Holden wheel nut.
Cheers,joe

Milwaukee is well reputed.
I got a 400nM Metabo as I already had that battery platform.
Makes life easier...

Alister McBride wrote: ............................. Only thing is, Milwaukee don't make an OKA wheel picker-upper and/or mover! We should put in a suggestion to their research department!

cheers, alister

Perhaps the thread title should be altered to "Changing Oka Tyres" ? , I tried but couldn't

One thing that I'm increasingly aware of (as I age) is the weight of an Oka tyre/rim combo. At around 80 - 90 Kg it's no joke and any slip/mishap could lead to serous injury. On our recent trip I met up with a lovely lady in outback Qld who with her husband had owned Oka 66 ? and 110 ? in the past, but age/inability to manage heavy wheels was a major consideration in their moving away from the Oka. I understand exactly where they're coming from. It got me to thinking (a dangerous and rare occurrence according to Kaye).

The steel rim 325/85 R16 XML combo we were running on this years trip and our 'normal' touring 305/70 R 19.5's would each weigh in at the 80 - 90 Kg mark, both are mounted on steel rims. Changing to alloy rims would give a huge weight saving. When I changed from 305/70 R 19.5's on 'railway rims' to 315/70 R16's on Eagle Alloys several years ago the weight saving over six wheels was a massive 256 Kg, most of it un-sprung. This weight saving along with the smaller diameter wheels made the Perkins powered Oka a much better vehicle to drive. Half the weight saving was in the tyre the other half the rim.

With our 6BT powered Oka and standard Oka gearing the 38.7" XML's give a good touring speed but not necessarily a good touring ride. With standard gearing a Cummins powered vehicle could easily manage a larger diameter tyre but a bumper cut would most likely be needed to avoid fouling, especially with off road articulation. The 305/70 R 19.5's give an excellent touring ride, are as tough as the XML's but at around 36.7" are not as well geared for touring as the big XML's.

Dana do a 4.56 diff ratio (std. Oka is 4.88) which would improve matters but their next ratio at 4.11 is probably a bit high to be a viable choice with wheels of this size.

What I'm leading to here with all this 'thinking' is what about 4.11 diffs into 315/75 R 16's (34.6") tyres ? There's a formula out there for working this out but I can't seem to find it, I think Peter may have posted it a while back so a 're-print' would be nice .

The up side would be much lighter, easily manageable wheels, better un-sprung weight and vehicle handling with more mounting options of a smaller diameter spare/s. Downside would be less strong tyre construction (127 is the best I can find for 315's as opposed to 147 for the bigger tyres) and I'm unsure if the smaller 315's would tend to 'bog down' more readily in the soft stuff ?

As for torque multipliers Joe I've never used one but I can tell you the large cordless impact wrench is very easy and repeatedly accurate to use with the torque sticks and much less force on the trigger than for a Holden wheel nut

Deano

I use a Milwaukee M18 FIWP12 (18V x 1/2") rattle gun for #196 wheel nuts. It is totally adequate for the job, but I also check them with a torque wrench.
I use a DIY winch to get the 80kg 305/19.5 spares up and down from their storage. The winch can be driven with a battery drill or by hand. I have not tried the rattle gun on it. They are too heavy to lift and I never do.
Cheers,
Peter

Deano that was partly why I fitted the 6 speed Allison, both 5th and 6th are overdrive, .71 and .61 respectively which keeps the 6bt at around 1800rpm at 100kph with 315/75R16 on Eagle alloys. That combined with the torque converter being locked most of the time even on gearchanges keeps the engine in its happy spot between max torque and power.

Peter_n_Margaret wrote: .............................I use a Milwaukee M18 FIWP12 (18V x 1/2") rattle gun for #196 wheel nuts.
Cheers,
Peter

The perfect tool for the job and my choice if I bought new. I picked up a good second hand 3/4" drive with similar specs with a couple of batterys and charger at a good price. I've fitted a semi permanent 3/4" to 1/2" adapter so I can still use my 3/4" skts for the "big stuff" . The torque sticks are a great invention and worth the effort IMO.

I found the gear/diff ratio RPM matrix I was looking for

Gear ratio Speed calculator

eg. At 100 kph with 315/75 R 16's (34.6") X 0.79 (5th gear ratio) X 4.88 (std Oka diff ratio) = 2350 rpm, with 4.56 diffs = 2180 rpm and with 4.11 diffs = 1980 rpm. At a more realistic touring speed of 90 kph = 1780 rpm and loafing along on good dirt at 80 kph = 1580 rpm with 4.11's in 5th and 2000 rpm in 4th.

As long as the Cummins can be tuned to give peak performance at say 1750 to 1950 rpm I reckon the combination of 4.11 diffs with 315/75 R16's sounds pretty good.

Deano

Peter_n_Margaret wrote: I use a Milwaukee M18 FIWP12 (18V x 1/2") rattle gun for #196 wheel nuts. It is totally adequate for the job, but I also check them with a torque wrench.
I use a DIY winch to get the 80kg 305/19.5 spares up and down from their storage. The winch can be driven with a battery drill or by hand. I have not tried the rattle gun on it. They are too heavy to lift and I never do.

Cheers,
Peter

I rather like the looks of ^that^
What is the model goof the lift? (A Shimano deep sea reel would work, if I was a fisher)

Peter and Sandra OKA 374 wrote: Deano that was partly why I fitted the 6 speed Allison, both 5th and 6th are overdrive, .71 and .61 respectively which keeps the 6bt at around 1800rpm at 100kph with 315/75R16 on Eagle alloys. That combined with the torque converter being locked most of the time even on gearchanges keeps the engine in its happy spot between max torque and power.

^That^ would have to be cheaper and easier than changing the gearing on each end?.
(I thought happy was defined as max torque for a constant load engine, or max BSFC?)


The 255 ZML are something like 10x35", but they don't seem to sell them anymore.
Low unsprung weight is always better. One a car is can be noticeable loosing 10kg, so gaining/loosing160kg for 4 should be much very notable..)

Yes it was very noticeable and other Oka owners with heavier wheel/trye combo's also comment on the smoothness and ride that you get with the lighter combo.
Most vehicles have a "sweet" spot usually somewhere between maximum torque and maximum power, it also changes with gearing and load. Of course major changes like engine and transmission can also have a major effect.

Not want to argue, but race cars often have their sweet spot higher than peak HP, and planes and ships, for instance, often use "Brake Specific Fuel Consumption" (BSFC) as their metric.

Whatever we chose for "sweet spot" can be justified, so then the question is how to we best get to the sweet spot?

I have the "Devon slicers" (16" LT) which are 8x32 (ish)... the RPM at ~1000 kph is ~2400 RPM, and it still seems to be ~17 lt/100km.
I am pretty sure, but have not checked, that it would be easier and cheaper to go to an Allison than the change rings and pinions .

But "pretty sure" can be cured... How much are those Allison autos, and what is required for a swap?

It would be cheaper to change the diff ratios )) You will need a more powerful engine than a Perky plus the bits to join that engine to the Allison, then bits to join the Allison to the transfer case, then new/ refurbed/retubed tailshafts to join the transfer case to the diffs. Then there will be new vehicle specific transfer case mounts built to suit your vehicle and whatever transfer case you fit.
Once all the mechanical stuff is done then there is the wiring and TCM, shifter, transmission cooler etc to get it all working, once it is working then you have to "tune" the TCM to operate the Allison correctly with your vehicles weight and configuration.
Old school diesels usually have a rev range that they are happy to run at all day and this is usually the spot where best fuel economy is achieved, all the ones I've ever dealt with are usually between max torque and max power, they aren't race car engines!

Yeah you are probably right...
The changing of the ring and pinion is not cheap, so I suspect that the Allison swap must be a lot of £€$ ?

Back on topic....
I can see how the 12.5"x37" may be great in sand and dirt, but also suspect that the unsprung weight would favour a 10"x35" or something lighter.
But with load ratings etc, it is all a bit confusing and a lot of variables.

Hey Deano. 39.5 / 13.5/ 17 Gladiator. Looks like a chance, but I'm not sure on 17" wheels yet.

DarrenWebster303 wrote: Hey Deano. 39.5 / 13.5/ 17 Gladiator. Looks like a chance, but I'm not sure on 17" wheels yet.

Golly-G those are large!

Hi Darren, yes I've looked at these, with std. 4.88 diffs 2050 rpm for 100 K's or 1850 rpm for 90 K's. They have a good load rating at 131 but polyester sidewalls compared to the Michelin steel belted side walls. American racing Baja's are load rated and a good price so at around $800 a corner plus spares who is going to be the first to 'have a go'

The same end result (2060 rpm @100k's & 1850 rpm @ 90 K's) can be attained with a diff ratio change to 4.56 and with 315/75 R16's. Parts only ratio change is about $600 per axle including new bearings, Hankook MT's (124 rated) can be got for around $290 and rated alloys for around $240 so at $1660 per axle or $830 a corner cost is about the same.

I'm considering going 4.10's which is a more difficult ratio change as a new rear carrier is needed. This will give 1960 rpm @100 K's and 1775 rpm @ 90 K's but am unsure if this is 'a bridge too far'

.Deano

Deano it might be a bridge too far with a manual gearbox but would be similar to 6th in the Allison which does have a torque converter which is locked most of the time, just turn the wick up a bit on the 6bt!

As Peter said the 6bt will do just fine. With 37’s i’m doing 1770 at 100 and fully loaded it handles it. When cruise control is engage I will nearly get full boost before the Allison will down shift so it’s pretty much on the boil. I just experimented driving from Taree to Darwin at 1700 about 95 instead of 100. I wanted to see the difference in fuel economy. It did down shift a bit more but it never felt like it needed more rpm. If I’m in hilly stuff and only doing 80 I will lock out 6th just so it doesn’t up shift when I ease of. I’ve found the Cummins to be far more comfortable at revs below 1900. Anything higher just seems a waste. It’s just a different animal to the Perkins it revs more freely and grunts better at lower revs. So choosing tires is so much easier. If it was mine I would do what I could to get the revs right down. With a manual if you gear it right up you will be more inclined to go back to 4th and take the load of 5th on the steeper hills.
Rob

How did the fuel economy go on that test Ralley?

With a tailwind it was about 18 on the flat and about 20 over the range. This is with no passengers but about 2t of trailer. I usually do about 19-20 at 100km/h. It’s about 20-21when loaded.

I was more inclined to go the other way Deano, for the tyre hight/ ride/ clearance side of thing, as you know, I do like to go where it probably should not go...