bigger tires, now down on power?

[SSell]

So my plan is to run this fuel out, change fuel filter, get a scan for fault codes (none found with the key/on/off thing). was beating the truck on freeway yesterday, fan seems to be cycling when I really wouldnt expect it to----low moan at freeway speed that climbs and falls off independant of engine or roadspeed. How can I check for a fan clutch problem? These are electrically cycled now , not just locking up when the engine is really hot, right?

 

[Bob4x4]

A 3. 73 geared auto truck will feel a significant change when towing a 10k trailer with a taller tire. The 3. 73's by them selves are too high for the mountain roads on a stock truck

 

[AMink]

Don't forget that you weren't going as slow as your speedometer indicated if you didn't change it for the bigger tires. I don't know how much difference it is, but it will be a little. Start cheap. Check your air filter and your fuel filter first, then move into the more expensive stuff. Good luck.

 

[diesel_driver]

A few years late to the party, but I'm getting ready to increase tire size and just did the calcs for proper gear sets. My stock gears are 3.73. If I switch to 37" tires, I need to change my gear sets to a 4.88 ratio. That will bring me back to an effective 3.93 ratio. If I switch to a 4.56 gear set, my effective ratio would be 3.67. Both ratios are available for the AAM 9-1/4" and the 11-1/2".

I don't tow that much weight, a 20' x 8.5' enclosed hauler for my motorcycles (roadrace) and assorted gear. I'm thinking the 4.56 ratio would be a good compromise. Anyone have any input?

 

[BILTIT]

Try it with stock gears, you might be ok.

I know when i jumped to 35s with 3.73 gears i can feel the difference for sure but i still tow 7000+lbs through the mountains without issues. I just manually drop out of OD more often.

 

[GrantP]

Try it with stock gears, you might be ok.

I agree. I'm running 35's with 3.73 and driveability is fine, admittedly I don't tow heavy but I do tow at high altitude when I do...probably only 6k totally loaded. These engines have so much torque the gear change may not be necessary. My next set will be 37's and I'm not really concerned about it. If anything I may go to 4.10s but in my opinion 4.88's are serious overkill. I'd go with 4.56 if you you have any issues towing your trailer. You might also consider the strength difference of the different ratios, sometimes numerically higher ratios will have a smaller pinion gear.

https://www.ringpinion.com/Technica...ontent/parts/ringandpinions//size_matters.inc

 

[Prairie Dog]

I made the same change to 75/285's and it did make a significant difference to power - most noticeable when towing. The next time I went to 70/285 and it was much better.