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Old 07-22-2013, 08:59 AM   #34 (permalink)
aardvarcus
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Join Date: Apr 2012
Location: Evensville, TN
Posts: 676

Deep Blue - '94 GMC Suburban K2500 SLE
90 day: 23.75 mpg (US)

Griffin (T4R) - '99 Toyota 4Runner SR5
90 day: 25.43 mpg (US)
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Tire diameter comments-
Tall tires can be a cheap way to re-gear however there are prices to be paid in performance due to the added weight and the added distance the weight is from the hub center. For example, on my 2002 Celica I went 10% taller in tires with brand new 205/65/16 Michelin Energy Savers AS (205/50/16 stock). This was a stopgap solution and is working for now, but if money were no option this is not the route I would have gone. This tire swap cost me -$200, aka the tires needed replaced and I would have paid $200 more for the “correct” low profile size. The performance on the car is notably slower, more so than simply the 10% gear change would have affected, but the car is still fast enough for me.

My final drive is in the transaxle requiring a compete tear down to go from a 4.53 to a 4.3X or 3.94. Thus I cannot justify changing that gear, a $500 part and probably $500+ install as I can get a completely rebuilt transmission with this gear already installed for $2000. Better to spend the extra and get a fresh gearbox along with the final drive swap.

When my current tires or transmission wear out (whichever is first), my plan is to buy smaller 15” wheels, get stock sized lrr tires, and get a rebuilt transmission with the 3.94 final drive.

Tire weight comments-
On my truck, I have both light 255/85/16 mud tires on light wheels and heavy 285/70/17 road tires on heavy wheels. Probably a 30lb per wheel difference, 20lbs in the tires and 10lbs in the wheels. Exact same 33” diameter. The truck is noticeably slower on the heavy tire heavy wheel combo, much slower than just throwing 120lbs in the back. It seems crazy but I have found so far that my light Cooper Discoverer AS knobby tires get better MPG than the heavy Michelin LTX MS2 on short trips. Note that this is on a giant truck and we are talking a huge increase in wheel and tire weight. I cannot yet comment on long trips as I try not to take my truck on long trips if the car will suffice. Best MPG mod I have found.

Last edited by aardvarcus; 07-22-2013 at 09:05 AM..
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