The oversize-tire Odyssey

[payaso del mar]

figured I may not the be the only one interested in mounting bigger rubber, so...

I wanted to convert to 15" wheels to give me more tire selection, especially in AT-tread rubber, more load capacity, and more ability to roll over offroad obstacles.  I bought the 15" steelies from a later model 2WD Tacoma...same bolt circle and center bore.  I'd been agonizing over what size tire to buy and was even considering getting a $10 throwaway tire mounted.  looked at 215/75, 225/75, 235/75, and 235/70.

finally figured out I could use the current rear tires (27x8.0-14) to get at least an idea*....since I don't have the torsion bars in the truck right now, it was easy to raise the wheel to top of travel with a jack to simulate hitting the Mother of All Bumps....if you're going to have clearance issues, it will usually be at the top of wheel travel.  still haven't decided whether to index the torsion bars down one spline to raise body slightly.

it looks like a 28" diameter tire will clear but I don't think I'd go with much more.  so the Dueler A/T Revo2s in 235/75 are out, since they're almost 29" diameter.  pity, as I'm on the 2d set on my Taco and LOVE these tires in all conditions.  I ended up deciding to go with a set of Firestone Destination ATs in 235/70.  28" diameter, 1896 # load capacity, treadwear rating 460, great reviews on Tire Rack. 

I'll let y'all know how they work out generally and if I have any clearance or gearing issues.  and will post pix of the clearance on the current 27s once I find my camera.....

*rough idea, since the offset on new wheels is very different than old ones

[zero]

I take it you don't have a 6 lug full-floater in back.   Only wheels around that are bigger with that bolt pattern are 16" and 17" and most are two-piece split-rim.   Last thing I'd want on my Toyota is bigger rubber.  Just drops the MPGs down and that is why I have it.

[payaso del mar]

no, the 5 lug it is.  I kind of regret not buying 16" Jeep wheels for it...still MORE selection of modern rubber.

I realize there's a possibility it won't help the mpg any, but I don't think it's going to hurt things that much. I lost about 1 mpg going from HT tires to AT tires on the Taco, but the tradeoff in offroad capability was well worth it, and I suspect this will be the same.  larger tires don't always "just drop the MPGs" any more than larger engines automatically do....it's a tradeoff between gearing, rolling diameter, rolling resistance, and tire/wheel combo weight.  as in a lot of areas, there's been a lot of tech improvements since 1985, and some (admittedly only a few) of them can help this old crock act more like a modern vehicle.

 i'll let you know what #s I see when I get the new tires on....I track mpg on every tankful, just as an early-warning diagnostic datum.  maybe I can stand to do a tankful or 2 on the old rubber to get a "before" figure.  Those 27x8 LTs on the rear are pretty heavy as it is. 

[payaso del mar]

so new 27 x 8.5-14 LTs would be 30# each and turn 778 revs/mile.  the 235/70-15s are 31# each, so not a huge weight difference, and they do 745 revs/mile.  I already suspect i'll be regearing when I swap the '91 axle in.

we changed our subie from 205/55-16s (an AWD car with 6.3" ground clearance?  really?) to 215/60-16s.  gas mileage stayed about the same despite the heavier tires, I suspect due to the effective regearing from the larger diameter rubber.  gained nearly 1/2" of ground clearance at the cost of some transient response, but my wife isn't an autocrosser, she just wants to get there.

[zero]

6 hours ago, payaso del mar said:

 

we changed our subie from 205/55-16s (an AWD car with 6.3" ground clearance?  really?) to 215/60-16s.  gas mileage stayed about the same despite the heavier tires, I suspect due to the effective regearing from the larger diameter rubber.  gained nearly 1/2" of ground clearance at the cost of some transient response, but my wife isn't an autocrosser, she just wants to get there.

I hope your Subaru has an automatic trans and not a manual.  The last two Imprezas I had were 5 speed manuals and had terrible gearing with standard size tires. Geared way too high and very hard to get started even on a slight grade.  If anything, they needed smaller diameter tires.

[payaso del mar]

5 speed manual, but they must have regeared it since earlier Imprezas....turns about 3500 at 70.  also, it's the 2.5 engine in the Impreza chassis so it has decent suds for 3000# car.

here are some clearance pix, with the 27x8.5-14 LTs and suspension "topped" out against the bump stop......ie, this is about the worst case scenario and equivalent to hitting a huuuuge bump.  so for those of you running 14" wheels, yes, 27x8.5s will fit just fine.  these clearances will change slightly with the different offset Tacoma wheels.

 

[payaso del mar]

finally, there's been some discussion about whether hub-centric wheels (fit pretty tightly to the center bore, so the lugs aren't carrying the whole weight and torque) are important.  I tend to think it matters.  my wheels are far from fitting tightly to the hub, as you can see from pic.  what you probably can't see in the other pic is how the lug nut holes have elongated slightly from the wheel moving.  now these were on the rear so they were dealing with engine torque, the wheels are the Cheepest of the Cheep white-spokers, and who knows how well the previous owners kept the lug nuts torqued....but there it is.  if your wheels don't fit the hub tightly, be SURE you keep em torqued correctly.