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Discussion Starter #1
Stock tires were 265/70/17 (BFG Trail), and this winter I went to **** Cepek FCII's, 285/70/17

Aftermarket tire is 3.5% larger, a little heavier, and has a max tire pressure of 65 psi. Load carrying capacity is the same as the E rated stock tire however tire pressure was 75 psi front and 80 psi rear.

So, I won't bother with the actual mileage numbers but with the switch, I consistently get 9.5% less mileage with the aftermarket tires. This is taking into consideration the difference in rotation as well.

That is a combination of highway, bush roads, 4x4 and in 4x2.

Gearing is the 3.55.

So, I am still OK with that as it is still about 8-10% better than my 6.0 leaker in fuel economy but with more power and torque.

Also, the safety factor on the road is huge. I had the tires siped and there is no comparison on all condiditions other than dry pavement. 35-40% of my mileage is on gravel road conditions, mud, ice and snow so I am much more comfortable with the FCII's and more than happy to use a little more fuel.

Anyhow, thought some of you wanting to change tire size would like to know my findings.

Oh, the TPMS's had to be reprogramed for the new PSI's.

Super Moderator
4,247 Posts
^^What HE said^^^

Wider tires = lower MPGs
Deeper lugs = lower MPGs
More noisy = lower MPGs
Lower inflation = lower MPGs
Heavier loads = lower MPGs
Taller tires = lower MPGs (either/or because the vehicle is TALLER and/or not programmed for the current N/V ratio)

Even changing from one MODEL of tire to another in the same BRAND can affect economy, this is significantly due to differences in belt lay-out and compounds.
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