My 93 F-250 has a 410 rear end with a 9.3 diesel. At 2000 RPM I am doing 60 MPH. I need new tires and was thinking of getting larger tires than the existing LT235-85R16 10PR so I could decrease the RPM. I do not want huge off the road tires. I would like to change out the 410 to a 373 but can't afford or want the headache. Does anyone have any suggestion of a larger tire that won't rub when I turn the wheel?
Thanks
Tom D

 

I am running 33 inch tires on my 94 4x4 ext cab and all I had to do was shimm the front bumper out 1 inch

 

Don't forget by adding "bigger" tires most bigger tires are also wider, more rubber you have on the ground, higher will be fuel consumption....


2000RPM at 60 is right on the money for fuel economy and constant power in these engines!

I take it you wanna go faster and keep the RPM's lower?

 

Only way to go faster and lower RPMs is go with the 3.55 gear ratio. Your not gonna get any better than that. I dont think there is a lower gear ratio for these trucks than that (I could be wrong). It you wanted to swap axles it would be 3.31, but that is a new axle and idk if it will match to this truck.

 

I have seen a 3.08 ratio but to me that is just silly. If you have a truck use it to haul/pull stuff, lots of heavy stuff.

 

I'm not trying to go faster, I would like to get a little better mileage. Empty I get around 15 mpg highway and 12 in town. If I put a load on her, it drops to 10 mpg on the highway.

 

You should be getting much more! How long has it been since it was tuned up...if ever?


What's the mileage on the truck?

 

agree.spend the money on tuning rather than tires.......well since you need tires too though..thats gunna smart a little.
search U-haul/ebay injector pumps here in the idi section to help keep cost down.if the ip/injectors have under 100k.when was the last time the engines been timed?
id stick with the 235's.
i see you have a large trans cooler.whats your normal trans operating temp at the pan/test port?
over cooling the girl,hurts FE.
keep it at 150 minimum.may want to block some of that massiveness off when your not towing.

when was the last time you had a front end alignment? how did the old tires ware?
when was the last time the diff was flushed? consider synthetic?
when was the last time you repacked the wheel bearings? consider synthetic?
trans fluid changed regularly? TC properly locking and unlocking? lockup just after 3rd.unlock when you let her coast downhill etc?
brakes or hubs feel real hot after an hr drive?
how many miles on the truck and various parts/history etc?

 

My truck is stock as far as I know. It says it has 3.55s in it but I am at 1900 RPM at 60MPH with cruise control on, empty.

This probably isn't a good thing to do but I can almost stand on the brake pedal and push the accelerator to the floor and still run 20MPH in first gear. These engines have immense amounts of torque! I think someone swapped in 4.10s in my truck but I have no way to prove that unless I take off the diff cover again and inspect the ring gear.

 

Where is the ratios coresponde to the door tag code anybody got the chart i want to know what mine are i think i got 4.10s to

 

And Tom man your doing great on the mpg with the 9.3L diesel you posted is in there thats alot of dicplacment lol

 

3.08s can't be found anymore anyway it seems. All the aftermarket suppliers stopped making them. My truck does fine for towing what I need, and it will consistently deliver 24 MPG @ 55 MPH (US gallons) when empty. Why 3.08s? - thats why. Although unless you have the dana44 front end (assuming a 4wd), you can only go as low as 3.55 anyway (3.54 in the case of the dana)

A few questions I should ask are:

How long is your average trip? Short trips (10 miles or less) will get bad MPGs no matter how good your tuning is.
What is your proportion of highway verses city miles? If you spend a lot of time in the city in stop and go traffic, then keep the 4.10s. If you spend a lot of time at constant highway speeds, then go for the gear swap. 3.55 will make a noticeable difference in fuel economy, although don't expect anything earth shattering. For days when you are towing, expect to drop to 3rd more often.

Don't get taller tires than the 235/85/16. Even those aren't quite ideal, but they are at least narrow for their height. If your truck is 2wd, then I would expect you to be able to reach 20 MPG already on a good day at 55-60 MPH (for trips of ~30 miles or more where the engine and the rest of the powertrain spents most of its time at operating temperature).

 

I put new injectors in about 15K miles ago. I never had the timing checked. It's hard to find a diesel mechanic who can set the timing on an old IDI 7.3 diesel CORRECTLY. I live on the Florida Space Coast and I'm still searching.

 

I agree. The trans runs too cool. At best 170F without towing. I have approx 127K miles on it.
Needs ront wheel brgs packed. Diff and trans recently flushed. TC works fine. I have not touched the alignment. The tires wear excellent so I will not "wake a sleeping giant"

 

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