Bigger tires on a diesel truck [ Archive] - GasSavers.org - Helping You Save at the Pump

Well, I've tried downsizing tires on the Blue Beast, from 265-75R16 to 235-85R16. The new tires are a hairsbreadth taller than stock but narrower. I haven't seen much improvement in mileage.

I have been thinking of going in the opposite direction. BFG makes huge all-terrain 305-75R16 tires. Now I know that the tread on these tires is not aerodynamic and they are heavier. But it will effectively gear the truck about 8% lower for a given speed. The effective axle ratio will go from 3.73 to 3.47.

What's the group's opinion? Will big mud tires make my mileage go up or down?

Yes it will effectively make your gears taller, but the RR of big, knobby mud tires will eat up all of your savings and probably some extra.

-Jay

I agree with Jay.

I wonder about engine efficiency in diesels...is RPM as important? Based on the little I know, I'd guess that it's more important, but still not enough to offset the RR of big mud tires.

Tall, high-pressure highway tires, OTOH, might do the job.

Yep. I agree. Some "E" rated highway Michelins would be nice.

-Jay

Yep. I agree. Some "E" rated highway Michelins would be nice.

-Jay

The existing 235-85R16 tires are Michelins. They're rated for 80 psi, I keep them at 90. I wish they had helped mileage more, but nothing seems to help the Blue Beast's mileage significantly........

18 mpg average is pretty decent for a "one ton" truck, even with a diesel engine.

Don't forget that if you change your tire diameter, it will throw off your speedometer and odometer, so you'll have to calculate that in when figuring MPG (or adjust your ScanGauge).

Did you adjust your odometer readings for the new taller tire? If you went 100 miles on the old tires...the new ones might be traveling 104 miles but the odometer will still read 100. Taller-skinnier tires at higher pressures would be you best bet.

The difference in tire height in miniscule. An odometer correction of just 0.2%

If they're rated at 80 PSI then you've already got E rated tires. If you have E rated Michelins aired up to 90 PSI then I think that's all you can do as far as tires goes... Look elsewhere for mods. You've already hit the point of diminishing returns on your tires. I don't see any signifigant FE gains from different tires.

-Jay

I always figured diesels would be good candidate for larger wheels. They make insane amounts of torque. If you just going down the highway unloaded, or even a light load you may only be using 300 ft-lbs. of that 480 lb-fts. of torque your producing. That leaves you 180 ft-lbs. to play with, without increasing the amount of fuel its burning. I'd look into American Force Wheels. They make some mighty big wheels with basically street tires, instead of those insanely wide mudding tires.

Stay with the 235s. 265s are about the same.

Going bigger will result in lower MPGs. Hundreds of guys have tried it and bigger tires are your enemy.

Big tires have much higher rotational inertia and hurt you every time you pull away from a light. Slowing down the engine for a given road speed is a good idea, but anything that adds to the "flywheels" reduces MPG.

This is one thing the factory engineers did absolutely right. Leave it alone.

Stay with the 235s. 265s are about the same.

Going bigger will result in lower MPGs. Hundreds of guys have tried it and bigger tires are your enemy.

Big tires have much higher rotational inertia and hurt you every time you pull away from a light. Slowing down the engine for a given road speed is a good idea, but anything that adds to the "flywheels" reduces MPG.

This is one thing the factory engineers did absolutely right. Leave it alone.

I'm way jealous of your 24-27 mpg..... from a 1 ton. Where did you get the fastback fairing? I can't find one. Snugtop makes a rounded cap, but not for F350s.

I'd love to re-gear the truck to 3.08 too, but I'd have to do both axles since my truck is a 4x4. And maybe put in a front positraction unit. How much did a single ring and pinion cost?

I made my fastback fairing out of stuff found in my garage. Plywood, one-by lumber and rubber floor runner turned upside down.

If all goes well I'll make a better one this winter. Probably fiberglass with faired in mounts for CCTV so I can lose the elephant ears.

For a4 the best ratio you can get is 3.55:1. Not worth it unless you are ruuning OEM 4.10s.

But for a 4x4 maybe a GV overdrive would work. Those are good for instant 4 MPG. They are salty but if you are high-mileage they pay off fairly quickly. I drive 25,000 miles per year, but the 4x2 adapter is low-volume therefore outrageously expensive. 4x4 adapters are high-volume and semi-reasonable.

But for a 4x4 maybe a GV overdrive would work. Those are good for instant 4 MPG. They are salty but if you are high-mileage they pay off fairly quickly. I drive 25,000 miles per year, but the 4x2 adapter is low-volume therefore outrageously expensive. 4x4 adapters are high-volume and semi-reasonable.
Finally went to the GV site. Pretty cool stuff, but enough to make my head hurt. Someone put 285/75's on my X, and I'd prefer to be back to stock (265/75) or narrow (235/85). But I like the RPM's at 60 to 65. Would be interested in a little more ground speed with the same RPM's. Hmmm...

keep in mind when going to narrower tires that, assuming same PSI, they're gonna belly out more thus effectively eliminating the small % gain in diameter. if you went from 265s at 35-50 psi to 235s at 90 psi then it may not matter.

Well, I've tried downsizing tires on the Blue Beast, from 265-75R16 to 235-85R16. The new tires are a hairsbreadth taller than stock but narrower. I haven't seen much improvement in mileage.

I have been thinking of going in the opposite direction. BFG makes huge all-terrain 305-75R16 tires. Now I know that the tread on these tires is not aerodynamic and they are heavier. But it will effectively gear the truck about 8% lower for a given speed. The effective axle ratio will go from 3.73 to 3.47.

What's the group's opinion? Will big mud tires make my mileage go up or down?

To echo the others...down 4sho. you could try a 255/85/16. Be careful of the wider taller tires. Any overdrive gains are negated by the increased RR and weight.


I've got a '97 PSD 1ton. Since 2002 I've increased the fuel mileage doing a number of things specific to this vehicle.

Learned to drive speeds that lock up the torque converter. Mine locks at 45mph but after it locks it won't unlock until I drop below 40mph.

Went from 285s to 265s at 80psi.

I added an open element intake (tymar),

a chip made a big diff too. Weird enough the best fuel mileage gain is on the hottest setting of the chip.

Removed my bug guard (not really vehicle specific).

and I don't drive on trips of less than 10miles unless I have to. The owners manual actually says not to cause the motor won't get up to operating temp.

I use a block heater on a timer for at least 1.5hours before starting it on days I have to drive it (generally only in the winter). Cold truck really gets back mileage.

One other thing...I try to never get the rpms over 1600. I believe that my motor has 425ft/lbs of torque at 1600rpms:eek:


Good luck with it.

PS The best fuel mileage I ever got was a trip to SD from WA in a really hot July a few years back I was getting about 560miles before each fillup whereas usual around here is 425 before a fillup. Extended freeway driving in hot weather seemed to be the ticket (I was generally doing about 80mph too as the montana speed limit signs are just there to satisfy the feds:D )