Trail Worthy Fab

Haf-E

Expedition Leader
I suspect that the drawing by Mitsubishi which shows the offset as being from the centerline to the outside edge of the wheel's center is incorrect - but since these are "dually" rims I suppose when used on rear, the mounting surface is on that side... hummmmm....

I would do the calculations using the backspacing - so much easier to measure than the imaginary "ET" offset spacing.
 

gait

Explorer
don't forget the thickness of the centre of the rim. I think its called the thickness of the disc in Mitsi drawings. Put another way, the mounting face of the rim is different if rim is reversed for front/rear. Or, from the above, the offset is different for the same rim depending on which face is mounted.

I haven't had to get into the detail but I would define offset (for the purpose of achieving equal front and rear track with the same rims) as from the centre line of the rim to the centre line of the centre (disc). Makes the calculation for same track front and rear a little easier. Alternatively define two different offsets, one for when wheel is on the front, the other for when its on the rear.

The other essential distance is the distance between mounting faces (bolt faces) for front and rear axles. At first glance, there's just enough info to calculate in the diagrams. Then I'd measure it.

I've always considered equal track front/rear as being distance between centre line of tyres is equal. I haven't a clue if that is "industry standard" definition.
 

1aquaholic

Adventurer
Haf-E to answer your first question the double beadlock rims being that there are bolts on the outside and a rock ring. So if you reversed one it would look very different from each other number one and the bolts would be facing in number two and The Rock ring would not fit over the brake drums number 3. I'll have a spare for front and rear but won't be able to mix them up.

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1aquaholic

Adventurer
Yeah definitely, thought a lot about that and I'm going to be very remote for long periods so want to have wheels uncase I bend or break one.

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ericvs

Adventurer
I suspect that the drawing by Mitsubishi which shows the offset as being from the centerline to the outside edge of the wheel's center is incorrect - but since these are "dually" rims I suppose when used on rear, the mounting surface is on that side... hummmmm....
I would do the calculations using the backspacing - so much easier to measure than the imaginary "ET" offset spacing.
don't forget the thickness of the centre of the rim. I think its called the thickness of the disc in Mitsi drawings. Put another way, the mounting face of the rim is different if rim is reversed for front/rear. Or, from the above, the offset is different for the same rim depending on which face is mounted.
That was my guess and how I based my cals. Funny thing is though, the part of the rim that touches the actual bolting surface is in the same orientation front and rear. i.e the front rim has the tire offset towards the truck and the inner rear dually is the same orientation, so the mounting surface front and rear is the 'inside' of the rim, not the outside as their offset dimension would lead you to believe.


I haven't had to get into the detail but I would define offset (for the purpose of achieving equal front and rear track with the same rims) as from the centre line of the rim to the centre line of the centre (disc). Makes the calculation for same track front and rear a little easier. Alternatively define two different offsets, one for when wheel is on the front, the other for when its on the rear.
I have to use two different offsets. Since the wheels he is looking at aren't reversible, this is a requirement.

The other essential distance is the distance between mounting faces (bolt faces) for front and rear axles. At first glance, there's just enough info to calculate in the diagrams. Then I'd measure it.

I've always considered equal track front/rear as being distance between centre line of tyres is equal. I haven't a clue if that is "industry standard" definition.
Yes, this is how I determined that too. Mitsubishi gives the track tot he centreline, so I did the same.


Alright, this is how I determined the numbers I got. I probably didn't have to draw it, but it seemed easier and would allow me to change the location of the wheels easier if we wanted.

Front:
Used the FT number (1650mm). Then I took the Offset of 135mm from CL to face of rim and subtracted the 9mm that it mentions on the tire portion. Did this on both sides and got a mounting face to mounting face of 1902mm.



Rear:
Same concept, used the RT (1542mm) and used the same 135-9 to get the mounting surface to mounting surface of 1542mm


Then, I used those two numbers as my basepoint. I think the thing I am unsure about whether the mounting surface of mounting surface is correct.

I then took the difference of those two and lined up the center of the front and rear tire. This gave me a track of 1722mm front and rear. I can then calculate the offset based on this number. I also split the offset between the two rims or I could reduce the offset on one and add it to the other while keeping the same track.



 
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ericvs

Adventurer
So after a call with Mitsubishi and some physical measurements, I am very confident that my numbers for mounting surface to mounting surface are accurate.

Next step is to ensure that the front offset measurement will work to clear all the suspension parts. As Amesz00 has mentioned, he is running 40s on his rig with no issues, so we *should* be ok, but I think a mockup is in order to really verify. If we need to adjust the front track to clear anything, it will be easy to adjust the rear track to match. More to follow.
 

ericvs

Adventurer
No need to over think it. The stock rims will serve you well.
That is just it though, stock rims are going away, so trying to figure out the correct offset for the new wheels. Also, if you aren't overthinking it, are you really thinking about it at all :sombrero:
 

1aquaholic

Adventurer
Ahhh the age old dual vs single argument. Nope, not touching that one! All I can say is I've over thought everything on my rig, it feels like a disease. Analysis paralysis.
 

unkamonkey

Explorer
I don't know but I have only one time when I got a rock stuck between a dual wheel and I drove them for over 40 years.
 

Haf-E

Expedition Leader
Haf-E to answer your first question the double beadlock rims being that there are bolts on the outside and a rock ring. So if you reversed one it would look very different from each other number one and the bolts would be facing in number two and The Rock ring would not fit over the brake drums number 3. I'll have a spare for front and rear but won't be able to mix them up.
I think you misunderstood what I was suggesting - if you use a bolted on wheel spacer on the rear between the brake/hub and the wheel - then you could use the same wheels front and rear. The stresses on the wheel bearing would be the same as with having different rear wheels with an extremely low backspacing to allow the track to align with the front wheel.

The wheels would always have the same orientation - so no "flipping" involved to mount a front wheel on the rear, etc.

Just seems like a better approach to me...

NOTE > I just did the calcs and if the the front wheels was staying with the same dimensions than the rear axle would need 7 inch spacers on each end - which sounds really crazy!
 
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ericvs

Adventurer
Alright, one more drawing. Based on a rough mockup, we have decided to try and line up the inside of the stock rim with the inside of the new rim, not the mounting surface, but the rim itself. This changes the offset a bit front and rear, but this should eliminate any clearance issues with the suspension parts that we determined could happen with the original offset I used. Again, not a pro at any of this, but this should work.

This is based on a 37/13.5R17 tire and 17x10" rim.



This will put the outside edge of the new front tire 4 1/4" outboard of the stock tire (which makes sense, since that tire is offset pretty far inboard by the stock rim.

This will also put the outside edge of the new rear tire outboard of the stock outer dually by 11/16".

Should give it a pretty mean stance!
 

gait

Explorer
just out of interest I measured outer edge of 285x19.5 front track with ATW reversible singles. About 1935mm vs your 2100. Just for comparison. Outside dimension of my box is 2100. Don't forget flares for the wheel arch, lest the rear view mirrors get dirty.
 
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