A question on Rim dynamics

[Nev62]

I am replacing the 6" rims and 235/75R15 tyres on my 4b with 8" rims and 32/10.5 tyres.

1. The centre hole in the rims of my 4b is 93mm. New rims is 109mm (is this Landcrusier or Patrol, box says Landcrusier). Guessing this will place extra stress on the studs, any other problems?

2. The offset causes the new rims (without tyre) to protrude 22mm outside of the guard (with tyre I'm guessing 50-55mm) and push the centre-line out around 20-25mm each side from standard. Will this cause a problem? (on the plus side, extra stability )

3. Current tyres are 28" and new tyres will be 32". If I get 10-12% more power at the rear wheels, will this compensate for the larger diameter tyres and heaver rims.

4. Would I be better off going 7" rims with 30.5/9.5 tyres? (is the extra 3/4" clearance worth it?)

[J Top]

To me clearance is only a same part of larger tyres.
The increased footprint with tyre pressure drop,both width ways and long ways, is a huge benefit as well as the floation , sidewall flex aspect .
J Top

[-Scott-]

I am replacing the 6" rims and 235/75R15 tyres on my 4b with 8" rims and 32/10.5 tyres.

1. The centre hole in the rims of my 4b is 93mm. New rims is 109mm (is this Landcrusier or Patrol, box says Landcrusier). Guessing this will place extra stress on the studs, any other problems?

Yes, extra stress. No problems beyond the potential to snap studs.

2. The offset causes the new rims (without tyre) to protrude 22mm outside of the guard (with tyre I'm guessing 50-55mm) and push the centre-line out around 20-25mm each side from standard. Will this cause a problem? (on the plus side, extra stability )

Aside from increasing your track beyond the legal maximum for an IFS vehicle, you will affect your scrub radius (heavier steering, additional loads on steering components, potentially uneven wear patterns) and throw more additional load to your wheel studs. The extra height of the tyres will probably help compensate for some of the extra scrub radius.

3. Current tyres are 28" and new tyres will be 32". If I get 10-12% more power at the rear wheels, will this compensate for the larger diameter tyres and heaver rims.

It will help, yes. I expect you'll notice it most at low revs, trying to get the car off the line. I went from approx. 29.5" to 33" and really notice the difference - but I'm happy to live with it, because I love the performance off-road.

4. Would I be better off going 7" rims with 30.5/9.5 tyres? (is the extra 3/4" clearance worth it?)

The extra 15% of rolling radius will have many effects on suspension and drive train which was not designed for it. 30.5" tyres won't be as bad in terms of wear, but you never get something for nothing.

I think you will use the extra 3/4" - just do it!

Cheers,

Scott