24r21 tires on m1070

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New member
Hartland, Wisconsin
New to this forum so learning where to post questions. Sorry if this question shows elsewhere as well.

Another question re: M1070.
Want to put 24r21 tires on an M1070. Have seen pictures and videos with these tires installed. All are off road. As these are approx 6” wider than the stock 16r20s, will this make the truck illegal on the highway? It seems the most common 18” wide rims are 80/20 offset. Does that mean that 80 % of the additional 6” is pushed outboard making the overall width the stock 102” plus 80% of the extra 12” for an overall width of 102+9.6 or 112”? Not sure how the offset thing works vs stnd 10” rims. If it is width problem, how do these trucks get around on public roads? Are there tricks? Thanks again for the help.


Staff Member
Super Moderator
Steel Soldiers Supporter
For a 21x18 wheel with a 80/20 offset the backspace would be about 16-1/2", if mounted dished-in.
Now, the backspace of the stock 20x10 HET wheel only has 13 inches, and I really doubt that there is much room left, for a wheel moved further inwards.

From a few pics I have, it seems that those extra wide tires/wheels stick out more than just 6". The fender extensions are at least 9 inches wide.
untitled 6.jpg

Anyway, since I was curious too, I made a little diagram (all to scale) to compare the stock wheels/tires with the 24R21s on such 80/20 offset wheels.
Provided that a wheel with that much backspace could even be used, the wider tire still would move outward about 4-1/2" - which means over-width, already.

16.00R20 vs. 24.00R21 tires.PNG
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