Ford Powerstroke Diesel Forum banner

Run 37's without re-gearing? Good? Bad? meh?

16K views 29 replies 13 participants last post by  Eagle 33 
#1 ·
Considering a 6" lift... With that, Im interested in how important it is to re-gear to 4.10s if I run a 37 with it. Truck is stock with 3.73s, I don't tow much, just a small camper and a car occasionally, nothing more than 5000-6000 pounds. If i run the 37's without going to 4.10s will that wreck the tranny, or just make the truck a total dog when I'm towing? Kind of a rookie question I know, never ran a lift/tires this big on anything before and of course im doing homework on my own but Im looking for your input...
 
#2 ·
Well I got an 8 inch lift with 38's on it and I also got 3.73's. I have never towed anything yet so I couldnt tell you how good it is while towing but unloaded or stuff in the bed it isnt horrible. My intake, exhaust, superchip probably help with that but I dont have any issues. But I would imagine it might hurt while towing. Someone else can chip in. And I am still get approximatly 13 MPG with purely only stop and go so. Thats my experienced. If I boost launch it will still smoke the 38's on accident lol
 
#3 ·
Without re-gearing, you'd really hurt the MPG on the setup. I've also heard that a 6" lift (which is what I have) will still rub on 37" tires (which is what I want). I don't think the transmission would be a factor, provided you have a good tow tune that tunes the transmission. I don't tow anything, but I've listened to what others have said and this is what I've taken from the majority of conversations.

Good luck!
 
#4 ·
Im starting to lean towards the 6" with 35x12.5s but keeping my options open. Super diesel, is that your set up with 35's on it in your sig?
 
#5 · (Edited)
Yep, sure is. 35s look a tad small on my truck to be honest... but I've just recently started hearing that 37s rub on a 6" lift. Looks like I'll have to go bigger on the lift to fit 37s without rubbing and/or trimming - which I'm not gonna do. So, I'll stick with 35s for now.
 
#9 ·
Yeah, i do kind of like the small goofy look if the tires are poked out a bit. weird i know. but yeah 4.10s with 35's wouldnt be much fun except leaving stop lights. Would result in pretty poor gas mileage on the highway. Dont feel like spending the money to regear if I'd be best off to go with 4.30s.
 
#10 ·
I know I'm comparing apples to oranges, but my 6.0 came with 3.73's and the tires were 34" in diameter from the factory. Aftermarket 35's with rims are a little heavier and wider and you'd notice a difference in performance going to 4.10's, but the cost of re-gearing doesn't really make this a good decision IMO. When I went to 8" of lift and 37's, I drove on the 3.73's for a couple of months until my TruTrac showed up. I went to 4.30's and the truck is turning slightly higher rpm's at highway speeds, but I would absolutely recommend re-gearing if going 37's or bigger. Not only to try to get back to the engine rpm's "sweet spot," but to offset the additional weight of the tires, rims, and lift kit (and the decreased aerodynamics of a lifted truck).
 
#12 ·
gears and tires

I think you guys are a little confused on lifts, tires, and gearing. I am not here to put anyone down, I just want to share what I have learned though years of off-road and building Jeeps. I understand that these are two different vehicles but the principals are pretty much the same. There is a mathematical formula for the selecting of gears to tires, here is a link that can walk you though it Gearing Up for Taller Tires! · Superlift · www.superlift.com in our trucks the main reason for regearing with larger then factory tires is to save the final drive ratios of the transmission,with the lower rpm the transmission will be pulling overtime shifting between 5th and 6th gear, you also want to regear to regain the performance and mileage lost by the added rotational weight that you put on the vehicle. You can get by with not regearing on 35's but fuel mileage and performance will be degraded. Here is a video to look at and think about FUBAR BIG TIRES KILLS TRANSMISSIONS - YouTube I don't agree with everything this guy says, but he explains this point pretty well....
 
#14 ·
It all makes perfect sense:rofl: ill be keeping the stock gears and going with 35's with the 6" lift. Thanks to you all for confirming my thoughts and learning me a bit too. :thumb:
 
#15 ·
I run 37's with a 3.73 and while I haven't been disappointed in my towing (Nothing heavy, motorcycle trailers, cattle trailers etc.) I am dissatisfied with my highway mileage. I'm lucky to get 13MPG going 70 down the interstate and probably likely to get 12-12.5. That would be my biggest motivation to regear, especially if I do go to 40's when these tires run out. What does a regear to 4.30's normally cost?
 
#17 ·
^^ how much that run you?
 
#19 ·
Snake your right I do agree that 4:30 is too low for 35's and a V8. I personally would look more to the 3:90 to 4:11 range of gear selection. OP I just called my contact in 4wheel-parts of Dallas and was quoted 1700.00 for a complete re-gear. That included parts labor and fluids.
 
#20 ·
I went to 4.56's on my 37's and didn't like it. I wish i had just done 4.10's or left them alone and put a tuner on it.

I towed my baja outlaw which was about 6000-7000lbs and it wouldn't shift into over drive with the 3.73's. It would at 90mph though....

Take off was AWESOME with the 4.56's though. However, it wasn't bad with the 3.73's.

I only changed mine for towing the boat.

In HINDSIGHT - i would have just done a 4" lift and 35's - tuned it and never regeared it.
 
#21 ·
you must have an 8" lift to run 37's or a 6" with trimming being done for that size tire, it will be much cheaper and less hassle in the long run to do a 6" lift with 35's. no regearing needed for that setup.
 
#22 ·
thats the way im leaning now. maybe down the road jump down to a 3.90 or 4.10 as mentioned before but i dont think im gonna have that extra $1700 off hand right away.
 
#23 ·
Yeah, I have a 6" with 37's and even with what seems like excessive trimming, she still rubs when it's turnedf if the road isn't perfectly smooth. I've heard you can even get away with a 7" lift much more successfully than a 6".
 
#26 ·
I forgot to mention earlier that some guys will need a speedometer recalibration or an after-market tuner like the SCT so that you can change the tire and gear parameters. Not doing so will throw off your speed and mess with the ECM. I believe that the dealerships can adjust up to 35's, hope this helps.....
 
#27 ·
i run 37s with the stock 3.73s and i wish i had some 4.30s, especially when towing. i know my around town mileage would pick up and it would be easier on all other parts, ie: tranny. but if im going to do it i will do it right by changing out both diffs and front and rear at the same time which is going to cost a pretty penny
 
#28 ·
I run 295/65/20's that come in at 35.4. I would really like to throw a set of 4.30's in it. As it sits now the truck wants to run at 80-85mph and I have to really pay attention to keep it down to 70. Also with a bigger turbo you really need to keep your revs up some to keep the turbo spooled up. If I was going to 37's I'd really consider 4.56's, and 4.88's with 40's.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top