Axle ratio

Great to hear edjunior, your experience is exactly what I am looking for.  I figured the same about the 4.30, it would give me some elbow room, but didn't realize about the legal limits.  I have an appointment tomorrow and they quoted me $1592 + tax to do the job.  They said there is a chance it could be a bit more if it needs new bearings, but with only 50K on it, they doubted that would be the case.  I'm not looking to break any speed records while pulling this thing, and as I mentioned, I only work 2 miles down the road.  I just don't need high end highway speed, nor the loss of towing power that comes with it.  In fact, when you read this, you have to wonder why anyone buys a truck with a 3.73 axle ratio. http://www.trucktestdigest.com/axle%20ratios.htm 

(I'm sure it has to do with the Gov. forcing car companies to squeeze every last possible drop of milage out of a vehicle, at any cost.  (Tow rating)

Jammer, you may want to look deeper into what axle ratio buys you.  Ford lists that with no other change than going from a 3.73 to a 4.10 your pull rating changes from 6800 lbs to 8400 lbs.  So it wouldn't be just saving your transmission.  I liken it to taking two 10 speed bikes, 1 with gears 4-10, and the other with gears 1-7, and seeing which 1 will climb a hill better.  You need less power to climb in 1st gear than you do in 4th gear.  But to better explain it,  you can see this directly when you compare a high end 10 speed with a "K-Mart" special.  Although both bicycles are called "10-speeds", the cogs on the rear end of the high end bike have a much lower gear, (or larger first gear rear cog).  When pedaling up a steep hill, my pedal revolutions are double what my sons are, (higher RPM's, ), but I can climb much easier than he can, even though his legs are stronger than mine.  He has to stop and get off 1/2 way up and walk.  We are both in "1st gear", but my axle ratio is much better than his.  He would much rather ride my bike especially when we are climbing hills than his.  Yes, he is already harping about a new bike.

Down the road when I replace this truck, I'll know what to look for the next time, but right now I just don't have expendable cash to buy both a new camper and a new truck.  There is also no cost difference when you order your new truck when choosing your axle ratio, they all cost the same, so do it right the first time.

Thanks,

Tom

The lower-numbered ratios ARE more economical on the open highway and it shows up clearly in the manufacturer's CAFE mileage testing. That's why the car makers make the standard axle the numerically lower one. 0.5 mpg is a big deal in the corporate fuel economy game, especially on a high sales volume vehicle like a half ton pick-up.

But averaged in with city driving mileage and towing mileage (where the 4.10 or 4.30 may actually improve mpg), you may not notice much effect over all. Given how you say you drive it, the numerically higher ratio ought to work well for you.

If you are not using the truck commercially, the "legal" issue really doesn't apply, since you are not subject to the GVWR regulations that apply to commercial operators. However, if you were in an accident that resulted in a civil suit, an opposing lawyer might  try to score points with the jury by claiming you were recklessly operating an "overweight vehicle".

Well, they are suppose to do the work on my truck today, but the shop looks awful busy.  I'll post back to everyone with my experience, (good, bad, or indifferent). 

I picked up the truck tonight and drove it home.  It's about 5 miles back to my house from the shop on secondary roads, but there is about a 2 mile section that is long and straight.  To be honest, I can't really tell they did anything.  I did notice at red lights it has a little more get up and go out of the gate, but when I got it up to 70 on the way home, it shifted normally and went into overdrive like it did before I dropped it off.  There was no roaring of the motor, and was pretty uneventful.  In hindsight, I wish I had opted for the 4.56 after driving it.  In fact if it weren't for the slight difference starting out at the red lights, and the box of 3.73 parts they put in the back of my truck, it's like they didn't do anything.  I checked my speedometer against my GPS unit, and they were pretty close to dead on all the way up to 70 give or take 1-3 miles per hour.  I checked the 4 wheel drive coming up the driveway, and everything seems to work fine.  I'm sure the tack must be running higher as someone listed above, but it's obviously negligible.  I guess I was expecting quite a bit more difference out of this change, and can only hope now that it will give me some extra pulling power that I was hoping for.  I guess according to Ford's specs, it will, so time will tell.  When I head in to work tomorrow, I will take it up to 70 again and record the tack reading.  Since I didn't do this before I took it in, I can only use the numbers above to calculate what it was reading before. 

Well, that all sounds about right.  Another thing you should notice is, when you are crusing kinda slow (15 - 20 mph), and punch it (coming onto a freeway or something similar), when the tranny downshifts, the RPMs will really shoot up high.  This lets you know you are getting into the power in a hurry.  And it will, or should, give you a pretty good jolt. 

And like you said, everything else was pretty inconsequential.  But being able to get your load up to cruising speed easier will really be nice once you get a chance to test it out.

What I would do if I were you, I would leave the truck the way it is and try towing were you normally will be towing. If you feel you need more torque, then try a shift kit and changing the shift points with a programer. Now days, they sell programers that will have pre-set settings for performance, economy and towing.

Just as a follow up, I couldn't be happier with the performance with the new 4.30 gears.  As edjunior pointed out, there is quite a bit of a jolt when I step on it hard at a red light compared to when I had the 3.73 gears in it.  It really gets up and goes from a stop.  The new TT should be here in the next couple weeks, so I guess that will be the REAL test.

Thanks everyone!

Glad it seems to  be working out. Let us know how the fuel economy question goes - hard data is always welcome!

I know I am late replying to the topic, but to help the next guy........

To simplify the gearing for non tech guys:
when referring to gearing in an axle think of it like this, when some one mentions 3.73, that means that it is 3.73 turns of the drive shaft before one complete turn of the axle shaft. so when you do a mild up grade from 3.73 to 4.10 you went from 3 3/4 turns of the drive shaft to 4 1/8 turns of the drive shaft before one turn of the axle shaft the differnce is less than half of a turn of the drive shaft. Typically this will not affect your gas mileage or engine rpm's drastically, but a small boost of low end torque is immediately noticed, and once compared to a stock unit the difference is very noticable.

Going from a 3.73 to like the poster put in his truck 4.30 is approximately 1/2 of a turn of the drive shaft to one turn of the axle shaft more. Which is a pretty good increase in torque. Once you start getting to the 4.55, 4.88, 5.13 is when you start really noticing the rpm, torque, and fuel mileage differences.

Like in my rock crawler, I am powering 44" tall tires with a stock 4.0 6 cyl. It is all through gearing. My transmission has a lower 1st gear than most stock ones, my transfer case has twice the low gear than a stock one ( stock: 2.3 to 1; mine: 4.0 to 1), and my axles are super low gearing of 6.71! Top speed for this jeep in 5th gear is 55 with the engine screaming at 3200 rpm's!

Dang Rusty...thanks for that laymen's definition of the ratio numbers!  That makes things much clearer (I think I actually understand it!).  I too look forward to the numbers and experience after pulling the trailer.  My numbers above are all concrete, all hand calculated (well, an iPhone app anyway) as I had no truck computer telling my the mileage I was getting.  I kept all the numbers for the mileage I was getting (I tend to be a bit of a packrat!...even in the electronic age).  But every person is different, and all driving conditions are different.  My 15 - 16 mpg came driving 35 miles to work and back (70 miles round trip) on a freeway where I could put cruise control on at 65 mph for 95 percent of the drive both ways.  Very little "city" driving.  Even in the local driving I did, I still maintained that mileage.  The towing mileage really varied due mainly to the weather conditions (wind!).  I got the 11 (actually 11.1) towing between home (just north of Houston) and Glen Rose (just south of Ft Worth) in near perfect weather conditions.  I only got 8.6 on the return trip because I had a bit of a headwind.  Just a small headwind can greatly reduce the mileage, regardless of the gearing you have.

I am  glad that the info could help........ Also, I live 25 min from Glen Rose.... Lovely place it is!

One more thing to keep in mind fella's, a change in the axle gearing also means a change in the speedo..... You should always let the shop doing the work know, that you need either your computer set for the correct axle ratio + tire size, or the proper speedo gear. If the shop that does the work is un- able to do this then IMO they are un-capable of doing the work right. If your cpu or speedo gear does not match your new gearing, it can lead to in-accurate speedometer reedings, higher mileage reading than the vehicle actually has.

Make sure when having the work done to not use a shop because of their price, use a local shop with a high priority reputation. A poorly set up ring and pinion will only lead to disaster, especially when towing. If the back lash of the r & p ( ring & pinion) is not set right it will start to wear very fast, and if the pinion gear is not set to the right depth it can burn up bearings causing very expensive repairs to seals & bearings!

DFW Rusty said:

One more thing to keep in mind fella's, a change in the axle gearing also means a change in the speedo.....

Click to expand...

Ahh, not true in our case Rusty!  Folks on the F-250 website explained it all in more technical talk, but because of where our speed sensor is (VSS), with just a gear change, the speedo does not require updating.  Only with a change in tire size.  I can find the specific link, but I can verify (as I think explorer777 can also), that no update was needed.  I actually changed out my entire rear end with one that already had the 4.30 gears in it.  But I put the same tires back on, so still nothing needed done.  I'm not sure if that's for just Fords, or any of the newer vehicles, but definitely not needed in our case.

I am by no means an expert, but a gear change has the similar affects to the speedometer as a tire size change. They both alter the over all -drive shaft spin to tire spin ratio-. I am not saying you are wrong, but I am saying that you may want to re-check your sources. Or better yet, check your speedometer with a gps. I am not saying this to be right, I am saying it to keep the extra miles from showing up on your odometer....

My question to the guys on the f-250 forum would be, how would the vehicle know to counter set for the gear change with out changing the axle ratio setting on the cpu or changing the speedo gear?

EX: jeep- if you geared the axles from a 3.73 to a 4.10 that is a .37 drive shaft increase per revolution of the tire. So for every revolution of the tire you have gained .37 extra drive shaft spin, that adds up fast when your drive shaft only spins 4.1 times per tire revolution. Atleast on jeeps anyways, the speedo gear reads the revolutions of the driveshafts, and since the drive shaft is now spinning more times per tire revolution it will have a pretty significant affect on your odometer and speedometers read outs!

Like I said, I am not debating to debate, I am just making sure that everyone gets the right info.... I would highly recomend re-checking your resources for your sake...... And If I am wrong, I would like to see the info about the way it works on fords. I am a big tech info goober, and love learning new things......

Gotta go with a fellow crawler Rusty on this one. Tire size and axle ratio changes both require a speedo recalibration. I only know of one type VSS that measures wheel speed and I don't think Fords run a CAN BUS system but I could be wrong. I gues the bottom line is if the VSS is on the output shaft then Rusty is right. If the VSS uses the tone ring from the ABS then it would read axle shaft speed and only care if you change tire size.

wayne

Fords do not require the speedo to be recalibrate when swapping gears, atleast the 92-97 F150-F250-F350's and 99+ superdutys don't.  I regeared my 94 F150 from 3.08's to 4.10's and my father did his old 94 F350 from 4.10's to 3.55's, then his old 99 F350 from 3.73 to 4.56's.  We didn't have to mess with the speedo or computer at all.

Okay, I tested mine with GPS, and drove it for a year and a half without having anything else done.  Here is the reason:

"Speedo is read after the differential on the axle tube, so tire size affects it but not gears."

Kinda what I said above...the location of the VSS.  And explorer also compared his to GPS.  So, no difference with just gears.

And if anyone is interested, here is the link to the F-250 forum when I got my 4.30's done and Bilstien shocks at the same time.

http://www.ford-trucks.com/forums/757387-new-shocks-and-a-4-30-a.html

Hi Guys, edjunior is right.  When they finished my Ford F-250, they told me I didn't need any other adjustments, but I checked my speedometer with my GPS anyway for my own satisfaction.  Sure enough, it was spot on with no changes.  I too kept the same tires on it.  What they "told" me was, that because Ford put that ratio in some of their other trucks, the on board computer recognized it and made the adjustment automatically.  They use the same computer for multiple axle ratios, (or the same subroutine at least for you computer geeks out there.)    I won't argue that point, as I don't know, but at least with Ford, it seems you don't need any other work done.

I stand corrected..... That is interesting that ford would put the speedo on the axle housing, although is probably the best spot for the most accurate reading. I agree, if it is on the axle after the 3rd member, then y'all are right it will not require a change/ update to maintain accurate readings!

It makes sense to put the speedo sensor on the axle, especially when there are many transmission and ratio options.  Less chance to get the wrong speedo gear or program.

zukIzzy said:

Gotta go with a fellow crawler Rusty on this one. Tire size and axle ratio changes both require a speedo recalibration. I only know of one type VSS that measures wheel speed and I don't think Fords run a CAN BUS system but I could be wrong. I gues the bottom line is if the VSS is on the output shaft then Rusty is right. If the VSS uses the tone ring from the ABS then it would read axle shaft speed and only care if you change tire size.

wayne

Click to expand...

Me too...  You have to change the parameters in your computer.  This is easy to do, but it does not adjust itself!