what exactly re-gearing does - Ranger-Forums - The Ultimate Ford Ranger Resource


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  #1  
Old 10-16-2008
OVERtheEDGE's Avatar
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what exactly re-gearing does

gotta prove my dad wrong on this so afew of you guys tell me what re-gearing my tuck is going to do for me. i have a 4.0 ohv, auto w/ 31s on it and planning to go to 33s next. i have a 3.55 gear and am getting a 4.10. so what is the 4.10 going to make a difference with? this guys my dad knows told him it wont make any difference at all in my truck. so tell me whats it gonna do.
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Old 10-16-2008
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It changes the axle gear ratio. Changes your final drive ratio.

Instead of the driveshaft spinning 3.55 times for every 1 rotation of the tire, it'll turn 4.10 times for every rotation of the tire. You'll gain better low end for starting out. And it'll drive more like stock (zippy?) compaired to a stock ratio with your tires. It makes it much more drivable and livable. I can't imagine how it'll be with 33's and 3.55's. it'll suck and your truck will be slow as snot. Something else it'll do, is that it'll keep the proper torque coming through the engine to drive the tires easier. An increase in gas mileage you should see because your engine is not working as hard to turn the tires. When an engine is working hard, it sucks the fuel down. Changing the gear ratio to a proper ratio, will put the engine in the 'prime' torque range to maintain speed w/o flat flooring it or downshifting. Stock like if you will.

Believe me, it'll make a HUGE difference having the correct gear ratio for the tire. I can't wait for my 4.88's!


Maybe math would change your dad's buddy's mind...

Highway RPM's(maintaining speed) = mph x final drive ratio x 336 /tire dia.

final drive ratio = axle ratio x trans gear ratio



Lets say your traveling 60mph in 5th gear(od) with stock 28" tires. .79 is an approx of your 5th gear ratio.

60(3.55x0.79) x 336 = 56538.72 / 28 = 2019rpm @ 60mph.

Add the 31's....

60(3.55x0.79) x 336 = 56538.72 / 31 = 1823rpm @ 60mph.

Add the 33's....
60(3.55x0.79) x 336 = 56538.72 / 33 = 1713rpm @ 60mph.



Notice what rpm your engine is running when you shift or the trans shifts? right about 2-2500k right?



Now...lets see what your Effective Gear ratio is... Effective gear ratio is what your truck FEELS like it's gear ratio is....

Old tire / New tire x axle gear ratio = Effective gear ratio(what it feels like your axle gear ratio is)

28 / 31 = .0903226 x 3.55 = 3.20 : 1

28 / 33 = .848485 x 3.55 = 3.01 : 1

Pretty gutless and highway cruising numbers there.



NOW....lets figure out what gear ratio is 'proper' for your truck given the tires...

http://therangerstation.com/tech_lib...tioChange.html

ok...well i couldnt find the calculation. But for my truck...stock 4.10's and 30.5's...and i'm rockin 35's. In order to have a factory feel while driving/factory ratio, I'd need a 4.66:1 ratio. But there isn't a 4.66:1 ratio avaliable....only 4.56 and 4.88.


Hope I helped convince your dad's buddy is wrong. lol.

Last edited by Fx4wannabe01; 10-16-2008 at 10:20 PM.
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Old 10-16-2008
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Sorry to threadjack but I dont understand that calculator I am running 32" tires with 3.73, I put in my numbers and got 3.73??? I must have done something wrong??? I am currently in the same boat debating 4.10s...
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Old 10-16-2008
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I ran 33's and 3.73's with a 4 banger and it sucked! Now I have 4.10's and still wish I had 4.56's
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Old 10-16-2008
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Quote:
Originally Posted by 98liftedranger View Post
I ran 33's and 3.73's with a 4 banger and it sucked! Now I have 4.10's and still wish I had 4.56's

hands on experience. listen to him.
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Old 10-16-2008
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I had 4.10s and 35's and my truck wasn't all that bad around town, but it would NOT hold 75mph on the highway. I hated driving the thing on the highway because it had absolutely no power whatsoever. Regearing changed that, its one of those must-do things when running larger tires.
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Old 10-16-2008
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Quote:
Originally Posted by richyrich View Post
Sorry to threadjack but I dont understand that calculator I am running 32" tires with 3.73, I put in my numbers and got 3.73??? I must have done something wrong??? I am currently in the same boat debating 4.10s...

Are you doing the 'Effective Gear Ratio' aka what it feels like your driving with? It's STOCK tire diameter vs. new tire diameter.

If it's the link for gears needed(which also gives you effective gear ratio), it's pretty self explanitory.


Quote:
Originally Posted by RazorsEDGE View Post
I had 4.10s and 35's and my truck wasn't all that bad around town, but it would NOT hold 75mph on the highway. I hated driving the thing on the highway because it had absolutely no power whatsoever. Regearing changed that, its one of those must-do things when running larger tires.
Pretty much exactly what i was trying to say. lol. Wouldn't hold power because the RPM's were too low to provide enough torque to keep moving/holding speed.
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Old 10-16-2008
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What were the original tires on it? You will need that info to get a ratio of than than the 1:1 you achieved. Usually it is not worth the cost to regear only one step difference. The MPG will not be enough to justify the cost and time.
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  #9  
Old 10-16-2008
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Quote:
Originally Posted by richyrich
Sorry to threadjack but I dont understand that calculator I am running 32" tires with 3.73, I put in my numbers and got 3.73??? I must have done something wrong??? I am currently in the same boat debating 4.10s...
You need to put in your new tire diameter, old tire diameter, and current gear ratio. The calculator calculates the suggested new gear ratio. Old tire diameter should be whatever tire came stock on your truck.

For example: my truck came stock with 205/75r14 tires. A 205/75r14 is 26.1" tall (calculated as follows): [(205*.75*2)/25.4]+14. This would be my "old tire diameter" I put in the "new tire diameter" which is whatever tire size I'm planning on moving up to, and the current gear ratio I'm running (which is stock, 3.45).

If I wanted to find out what gears to run for 33's, I would enter the following:

New Tire Diameter: 33
Old Tire Diameter: 26.1
Current Gear Ratio: 3.45

I'm not sure what you're trying to calculate richyrich, but we'll assume you're trying to calculate the gear you should have in order to run those 32's. First you need to find out your stock tire size. Since you're a 98 4x4 I'm going to assume something like 235/75r15. That calculates to 28.9", so we'll put in the following:

New Tire Diameter: 32
Old Tire Diameter: 28.9
Current Gear Ratio: 3.73.

Click calculate and that gives us 4.13 to return to stock.
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  #10  
Old 10-17-2008
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I would recommend 4.56's over 4.10's for 33's.

I have a 4.0L SOHC with an auto on 33's and I'll tell you it's slugish compared to my 32's I had.

Last week I ran up to Georgetown, up in the mountains, and couldnt get my truck over 55 uphill... I'm looking at re-gearing myself for the reason I just don't have the power to push em with the ratio I have.
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  #11  
Old 10-17-2008
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what those guys told ya ive run 31s 32s and 33s now on my ranger which is the 4.0L SOHC 5spd auto with 4.10 in the axles, with the stock 31's truck was real peppy off the line spun em really easy, lost a little power with the 32s but didn't notice any low end power problems, got a little lower rpm (not much) on the high way, with the 33's i have to down shift on a 6% grade and get my foot into it to keep 65/70mph it wont pull hills in overdrive very well any more, still spins em but i have to try. also thanks to the torque multiplier effect you get from the torque converter. if i had the money i would go to 4.56 and lock the rear, or get a manual. auto doesn't shift like i want it to. damn computers
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Old 10-17-2008
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do any of you guys know what the gears on a 99 2.5l 5spd are stock? Furthermore, was there any changes verses the 2.3l 5spds?
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  #13  
Old 10-17-2008
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Quote:
Originally Posted by Melt View Post
do any of you guys know what the gears on a 99 2.5l 5spd are stock? Furthermore, was there any changes verses the 2.3l 5spds?
On the sticker on your door there is a code. That will tell you what axle you have. See here: http://therangerstation.com/tech_library/Axles.html
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  #14  
Old 10-17-2008
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Quote:
Originally Posted by jeffb502 View Post
On the sticker on your door there is a code. That will tell you what axle you have. See here: http://therangerstation.com/tech_library/Axles.html
Same thing goes for the original stock tire size. On that door sticker.

Decoding a metric tire size into a standard inch tire size...
http://therangerstation.com/tech_lib...nch_Tires.html
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  #15  
Old 10-17-2008
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Quote:
Originally Posted by jeffb502 View Post
I'm not sure what you're trying to calculate richyrich, but we'll assume you're trying to calculate the gear you should have in order to run those 32's. First you need to find out your stock tire size. Since you're a 98 4x4 I'm going to assume something like 235/75r15. That calculates to 28.9", so we'll put in the following:

New Tire Diameter: 32
Old Tire Diameter: 28.9
Current Gear Ratio: 3.73.

Click calculate and that gives us 4.13 to return to stock.
Thank you Jeff thats exactly what I was asking for

Im replacing my 7.5 with 3.73' rear dif this weekend and had to decide by tomorrow between a 8.8 open 3.73(the cheap route) or a 8.8 LS 4.10 out of an '04. I think I'll go with the 4.10 even though its gonna cost a lot more since I will also have to change the front dif gears now as well. Hope it's worth it...
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Old 10-17-2008
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Just so you know...i got a 30k used front 4.10 dif for $75 at a local junkyard.
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  #17  
Old 10-17-2008
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The RPM's and off the line acceleration will feel more like stock.

Aside from the increased rotating mass, a stock tire (28.5) to a 33" tire is an increase of roughly 15% in circumference. Going from 3.55 to 4.10 gears is roughly the same increase in mechanical advantage.
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  #18  
Old 10-17-2008
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Everything that's already been said is true...plus remember poorer fuel economy. On stock tires with 4.10, I'm running about 3,000 rpm at 70 mph in a 4.0 liter OHC.

An engine spinning faster will nearly always require more fuel than an engine spinning slower. Think a bicycle in a really high gear...you have to pedal harder and you're not going fast. Click the gears down and you are going faster, with less effort.
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  #19  
Old 11-01-2008
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thanks for the advice.
well i went to the ranger station link and heres what i came up with



Ratio Hi Ratio: 3.81
New Ratio: 4.18
Lo Ratio: 4.56

i have the 4.0 ohv auto. so what gear should i put in it for 33s? i was about to buy 4.10 but should i?
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  #20  
Old 11-01-2008
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Quote:
Originally Posted by bryan240sx View Post
Everything that's already been said is true...plus remember poorer fuel economy. On stock tires with 4.10, I'm running about 3,000 rpm at 70 mph in a 4.0 liter OHC.

An engine spinning faster will nearly always require more fuel than an engine spinning slower. Think a bicycle in a really high gear...you have to pedal harder and you're not going fast. Click the gears down and you are going faster, with less effort.
Yes and no.

If the engine is having to work harder, it will be wasting more fuel. Better to be at 3,000 RPM and 1/3rd throttle than 2,000 RPM and over half throttle.

Using the same analogy, if you are on a high geared race bike, but you just want to cruise at 10-11mph, the highest gear will likely tire you out because you will be standing up and pumping to keep up speed.

a good example of this is the Wankle engine in the Mazda RX series. Those engines are "notorious" for being unreliable in inefficient. This bad rep came about because that engine wants to be up in the high RPM range. If you are doing 40mph you shouldnt be in top gear. The engine is nowhere near its efficiency band or its powerband at lower RPMs and extra fuel is being put into the engine causing carbon buildup and ruining the seals and obviously, wasting fuel. If drivers would drop down a gear or two at those speeds they wouldnt have these "issues." The engine did fantastic in the 24hr lemans race where the engine is running at high RPMs all of the time with great efficiency to the point that they banned the wankle from competition.

The same goes for small, high reving 4cyls such as those in the S2000 and Toyota's ecotech engines. My parents both drive scions for their daily driver. The engine rarely goes below 3,000 RPM while cruising at any speed.

Last edited by CBFranger; 11-01-2008 at 02:49 PM.
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Old 11-03-2008
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good thread, bookmarked
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Old 11-03-2008
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Quote:
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good thread, bookmarked
X2 thx all for the info
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  #23  
Old 11-03-2008
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STICKY this thread. Tons of useful info.
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  #24  
Old 11-03-2008
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Originally Posted by CBFranger View Post
Yes and no.

If the engine is having to work harder, it will be wasting more fuel. Better to be at 3,000 RPM and 1/3rd throttle than 2,000 RPM and over half throttle.

Holy crap this is news to me!! Forgive me for maybe sounding dumb but I always thought fuel mileage was directly related to the engines RPM's.

Everyday I drive my truck I try to keep my RPM's under 3000 thinking I am saving money but sometimes to do that I am in a higher gear than I know I should be for the speed I am going and yes I am over half throttle to maintain the speed. Due to the fact my gear ratio is not right for my tires.

So you are saying I am better off driving at higher RPM's with the throttle closed more? Will I actually get better MPG this way than the way I have been driving?

Man if this is true I learned something today....
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Old 11-04-2008
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sticky this people!! That first thread reply....was probably my biggest reply ever!!


*installing 4.88's as i type!!*
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