What is the maximum lift that I can go for an F-250/F350 without changing the gear ratio? Or let me ask this first; is it possible to lift a crew cab /long bed pickup without changing the gears?

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FYI, I’m looking at buying F250/F350 crew cab long bed ASAP.

Thanks,

VJ

 

The gears you use depend on the tire size...not the amount of lift...

 

Ho, I’m sorry, let me rephrase the question again. What is the biggest tire that I can go for?
FYI, 2003 Ford F350 7.3L Engine.
Thanks,
VJ

 

Well, that kinda depends on what factory gears you have..are they 3.73's or 4.10's?

 

ghunt, Thanks for replying,
I had a look at this truck(F350 -2003 -7.3 L ) at a dealership in PA last week. I’m not sure what the exact gear ratio is. Can please be kind enough to tell me which ratio is better for bigger wheels.
Thanks,
VJ

 

Well, depending on how big you wanna go with the tires...honestly 4.10's are probably your best choice. With a diesel, 4.10's should be ok up to at least a 36" tire, maybe bigger. My brother ran 4.10's on his old F-150 that had 36's on it and he said they worked pretty well.

 

Thread moved to SuperDuty forum.

-Matt

 

your speedometer will be really off, if you keep the same ratio and upgrade size. it will really put alot more stress on the driveline, and reduce the torque to the wheels. it would be good for highway though, it will allow you to go faster with the same engine speed as before. if you have 3.73's now, and like your acceleration (most PSD's have the 3.73 because of their supreme torque), then i would upgrade to 4.10 or 4.30, depending on wether you go to a 35'' tire or a 37'' tire. if you have 4.10's now, and want a 35'' tire, i would say 4.30's would be good (stock size p265's are 31.6'') if you want a 36+, i would say to go to 4.56 or even 4.88 for more acceleration. the higher the number, the lower the speed and fuel mileage, and higher engine speed. but larger tires will compensate for that.

 

Use the calc in my sig to figure out you gearing needs. The gear ratio has nothing to do with speedo accuracy, the tires do this. The speed is read off the tone ring and will read correct regardless of gear ratio. The bigger tires are what makes your speedo wrong.

 

Vijay,

You had posted in another topic area about looking for a truck. I had posted about a v-10 x-cab 4x4 with about 8 inches of lift and 37" tires. Did you ever get that post. I would prefer the diesel (which I have) but others like the gas engine. Just wanted to make sure that you saw that post.

The truck was at Auto Outlet USA in Danville, Va--Riverside Dr Location.

The phone number to the other location is 434-799-8721. I cant find the Riverside location number.

Good luck with your truck purchase.

 

I appreciate all your replies,
Stroking_it7.3 & BFR250SD,
I might have some more question, may be silly, but I will ask you ASAP.

Powerkleen,
I did Email AUTO OUTLET USA asking for photos since they have not posted any photos online (www.autotrader.com). I will wait to hear from them. However I will be looking for trucks in PA all weekend; any leads other that Paul Burns auto? Ho, damn it is going to be a rainy weekend…sucks!
Thanks,
VJ

 

I got the whole deal with the gear ratio and tires size now. But everything goes around the preserving amount of torque you need/ was-at-factory setting. But my issue is quite different, I do not worry about torque at all, I need good highway mileage, decent acceleration with bigger tires & lift kit and that’s all. No business of hauling or pulling etc. What is best ratio for me without stressing engine on long term use?

One other thing I want to know is; what does it mean to say that the gear ratio is 3.73 or 4.50. What does this number signify? Mechanically where do you get this number from (I mean there has to be numerator and denominator with some relation to horse power or cubic capacity or something similar)?

Thanks,
VJ

 

VJ, A gear ratio of 3.73 (Which is what just about all diesels have) means that the driveshaft must turn 3.73 times to make the tires turn 1 time. You can get the gear ratio by looking at the tag on the rear axle. I just bought a crew cab long bed and just ordered a 6.5" lift, and plan to run 37" tires.

 

Correct me if I’ wrong,
If I keep the gear ratio a constant factory and add a bigger size tire then I should have some mileage improvement at the cost of torque and little overload to drive shaft right?
Is there a handy mathematical formula for calculating the torque loss? I think this should help me determine who much I have lost in terms of towing capacity. Also, how do you translate torque to towing capacity?

 

Vijay,

Use the calculators in my sig and it will show you what the tire changes do to your trucks driveability.

Adding bigger tires will not improve your mileage, unless your truck was severely overgeared to begin with. If you use the engine and tranny outside of it's intended operating range, your mileage will suffer, as will your tranny. Gears are needed to compensate for this and keep everything in it's optimal range.

Yes you can mathematically figure out the torque loss to the ground. Take the torque ouput of the engine, multiply it by the torque converters amount, then by the transmissions ratio (in which ever gear you would like), then finally by the rear end gera ratio. This will tell you what you are getting back there. Then subtract about 10 - 20% for frictional and mechanical losses through the drivetrain. Remember to use the calculator in my sig to figur out your effective gear ratio with the tire change.

You also have to keep in mind that with big tires, something is gonna suffer, be it power, economy, acceleration, etc. You have to get gearing that is appropriate for the application to maintain these.

Again, use the calculator in my sig and it will tell you where you need to go with this.