Gearing change experiences/input - Diesel Forum

leros · 08-18-2006, 06:32 PM

I'm throwing this out there so that I can get some input from those of you that have done a gearing change because you have increased your tire size.

I am real close to doing a gear change in the next couple weeks but can't decide on what ratio, I only want to do this once and don't want to make the wrong choice. My friend changed his 3.73's out of his F-250 with 4.30's he likes the results of more power and his claim of increased MPG(2mpg). He is running 35" tires, lifted with no other mods. Mine is an Excursion with 3.73's, I'm running 35's, lifted with exhaust and a tuner.

I need to measure the circumference of my friend's tires to see what his "actual" diameter is as compared to mine. My tires, ProComp AT, say that they are 35-12.50 R17 but they acually measure 33.7". I don't remember what the stock tires measured, but I have it written dowm at home. I need to see what the RPM's were, running stock tires at freeway speeds and try to select the correct gear for my so-called 35's.

So my problem is, 4.11's or 4.30's? [img]/ubbthreads/images/graemlins/confused.gif[/img]

I tow a Toy Hauler about 8-10 times a year and drive to the river (about 4 hrs doing 75-80mph) not towing, all summer long. It's a weekend truck so I drive it all over, just because I like it. So I don't want the engine screaming down the freeway and my mileage to stink because I geared too high. Hopefully you guys have some personal experience you can share with me.

Thanks in advance.

PerryB · 08-18-2006, 10:12 PM

From a seat of the pants standpoint, you're going to like the 4.30's better and they will give better trailering performance as well. The only down side will come at speeds of more than 65-70 where the 4.11 gearset will get slightly better mileage. The first time I re-geared a 4x4 I deliberated long and hard between 4.10 and 4.56 (4.3 didn't exist for the application) and had convinced myself to go 4.10 when my dad opined that since the reason for the gear change was to get back accelleration and power lost to large and heavy tires, I should go for the lower ratio (4.56) as I would be happier with the outcome. In his opinion, the 4.10 gearset wasn't enough of a change to justify the effort and expense. As often happens the old man was right and ever since then, whenever I find myself stuck between ratio choices I opt for the lower set (within reason) and have always been glad I did.The difference in fuel mileage between the sets you mention will be in the 1-2 (at most) mpg range. P.S.-- I just re-read your post and realized we have a terminology difference. To clarify, when I say lower I mean mechanically lower, which is numerically higher. I'm advocating the 4.30 gearset.

GregsPSD · 08-18-2006, 10:23 PM

I dont have any input as to what gear to choose but whatever you choose if its a 4X4 make sure you change the front to the same ratio....

leros · 08-19-2006, 01:31 AM

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I dont have any input as to what gear to choose but whatever you choose if its a 4X4 make sure you change the front to the same ratio....

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Yes I know to change both, I forgot to mention it's 4WD.

Thanks PerryB for your comments and yes I was backwards when I said "geared too high". My mind knew it, my fingers refused to write it. I'm afraid of gearing to low, 4.30's, because with no trailer behind me I do drive 75-80. I really don't want to loose any more mileage. What to, what to do!! More homework and maybe some more helpful comments from you guys that changed gears.
I have noticed that alot of diesel guys don't change gears unless they go real big in tire size. The beauty of diesel power!

atasty39 · 08-19-2006, 03:07 AM

Thanks for saying to change the front gears also, I didn't know those had to be changed.

07HEMI4ME · 08-19-2006, 06:45 AM

[ QUOTE ]
[ QUOTE ]
I dont have any input as to what gear to choose but whatever you choose if its a 4X4 make sure you change the front to the same ratio....

[/ QUOTE ]

Yes I know to change both, I forgot to mention it's 4WD.

Thanks PerryB for your comments and yes I was backwards when I said "geared too high". My mind knew it, my fingers refused to write it. I'm afraid of gearing to low, 4.30's, because with no trailer behind me I do drive 75-80. I really don't want to loose any more mileage. What to, what to do!! More homework and maybe some more helpful comments from you guys that changed gears.
I have noticed that alot of diesel guys don't change gears unless they go real big in tire size. The beauty of diesel power!

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It is a compromise, and you must make the decision, and Maybe make some changed in the way you drive.... driving 75-80mph or Towing performance. Im my mind, you have to give a little to get a little.

hope that make since

trx416ex2nv · 08-19-2006, 12:41 PM

i put the same size tires on mine and went to 4.30's

leros · 08-20-2006, 03:49 AM

[ QUOTE ]
i put the same size tires on mine and went to 4.30's

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Any other input, mileage change, towing mileage change, how is freeway driving? Are you happy with the 4.30's or do you think that you should have gone with 4.11's? Can you give me just a little more? (well as much as possible [img]/ubbthreads/images/graemlins/grin.gif[/img])

06PSD4ME, I understand what you are saying, I only drive those speeds on the open highway NOT towing. I realize I will have to change my driving habits. I might put my stock wheels/tires back on to do some tests on the highway.

leros · 08-21-2006, 11:35 AM

Just a bump to try and get some other experiences, anyone?

Thanks,
Steve

mistman · 08-21-2006, 04:02 PM

Mines stock w/4.30's and I'm getting decent mileage at 70-75 mph. In fact I seem to do better around 70 then at ~60ish (my dash mileage guage shows an increase). I've gotten around 15-16 mpg average since the day I got it, it did dip to below 15 for a while but now is creeping back toward 16 (I calculate by hand) as I'm approacing the 10k mark. It's an '06 4x dually without any re-flash's. My step dad has an '05, same everything except gear (he's got 4.10's) and he gets much worse mileage than I do (but he does a lot of in town driving, mine is all hwy). I didn't know if I would like the lower gears or not but wanted the extra grunt, at this point I'm very happy with them and I run stock size tires. You may even want to go 4.56.

leros · 08-21-2006, 04:42 PM

Thanks mistman for the info, I know for sure that 4.56 gears would be too low for my application. I think my little 6.0L would be screaming down the highway for sure! My 35" tires don't measure much larger than my stockers so if I were running 38" or 40", 4.56's would work (but then I'd probably be asking 4.30 or 4.56?).

It's alot of money to me (for doing both axles) and I don't want to do it twice so I'm trying to see from the guys on here that did change their ratios, with tires my size. One guy said he changed to 4.30's but didn't say anything else about it? Oh well. Thanks again.

lightningfast2 · 08-21-2006, 04:43 PM

i have an 03 with cooper tires that are 315's. i installed 4.30 gears and my mileage went down bad on the road. i went from 19 to 14-15. towing in town went up 1-2mpg with my 7x16 open trailer with lawn equipment.

me, im wishing i would have went with 4.10's since now im killing my fuel mileage on the road at 75-80 empty.

comes down to how much weight you tow and how often. i'm looking now that i'm going to have to go with 37's to get my gear ratio back to stock so i can get my fuel mileage back empty.

Just my opinion.

Scot

leros · 08-21-2006, 05:23 PM

Thanks Scot for that feedback, that's exactly what I'm afraid of. I pull a trailer that's about 8500# and my power is pretty good especially with the chip, just looking to get it closer to stock ratio again and maybe grab back some mileage.

lightningfast2 · 08-21-2006, 05:34 PM

now there is one thing with the 4.30's. when you hit the go pedle, IT GOES. you get a noticeable throw back and when it hits about 60, to me it pulls hard. top end i have yet to really see what it will do. i loved my 3.73's and the 315's empty on top end.

i'd think long and hard. one way that might help you is to put some stock tires back on, drive around for a day or so, then tow with it. get the feel of what it's like again to tow with stock gearing. if you still feel that it's under powered, do the 4.30's. I put my 315's on when i only had 8k miles on my truck. i replaced the gears at about 45k and now have a little over 50k. 37's are way higher in price for tires but i don't want to spend $1400 minus what i could sell my 4.30's for to change to 4.10's

Scot

leros · 08-21-2006, 06:18 PM

[ QUOTE ]
i'd think long and hard. one way that might help you is to put some stock tires back on, drive around for a day or so, then tow with it. get the feel of what it's like again to tow with stock gearing. if you still feel that it's under powered, do the 4.30's.

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That's exactly what I need to do, I still have my stock tires/wheels. I did put them on a couple months ago while having my 35's balanced. I drove to Arizona with the stockers on and picked up about 2mpg, but the stock tires aren't as wide as the 35's either. I did not tow with the stock tires at that time.