Gearing Tech Thread
02-01-2016, 01:56 PM
#1
Senior Member
Thread Starter
Gearing Tech Thread
***Mods please sticky***
There are two major things to consider when contemplating a re-gear due to larger tires:
1) Size - when running 'back to stock' calculations (what diff gearing with what increased tire size will equal stock final ratio) all you are accounting for is mechanical advantage due to a change in size. If you also choose a heavy tire, you will still feel a sluggishness due to an increase in rotational mass AND rolling resistance (more aggressive tread pattern)
2) Weight - You might need to jump up two sizes if you go up in size AND weight - also don't discount the impact of rolling resistance, IE going to a more aggressive tread pattern vs. stock.
Example: in the 09-14 year group, 4.10:1 is the right gear for 35's IF you stick with a lighter tire and a less aggressive tread (an example would the be Raptor 34.5" BFG A/T). If you also pick a heavy tire, say 10+lbs heavier per corner, and more aggressive tread you'll more than likely need 4.56:1 to have the same snappiness as with the stock tires.
gearing calculator:
http://www.crawlpedia.com/gear_ratio_calculator.htm
^^^ this only accounts for size, the weight / rolling resistance thing is up to you to decide. EDIT - the flaw with these calculators is that they use factory gearing as part of the equation - if you started under-geared, you'll end up under-geared using this methodology.
Side bar: size does not always equal size... there are tires labeled 35s that are actually 34.5", 37s that are 36.5", etc... when performing your calculations, do your research and use the actual size vs. advertised size. Some are much smaller than advertised some are only a half or 1/4in some are right on.
Tip: Lots of manufacturers don't advertise tire weights. If you add a tire to their shopping cart then calculate shipping, it will show you the shipping weight - there is some fudge factoring there because of packaging but you'll at least have a ball park number - best to allow for 1-3lbs for packaging - more if you are buying a tire/wheel combo because there will be more 'stuff' used to protect the wheel in transit.
I have relatively heavy / aggressive 37s, I'm running 4.88s. At 80mph I'm at like ~2,200ish rpms. I'm getting 14+ avg in a Raptor.
Does getting a tune negate the need for gears - No.
From the factory your vehicle was given a certain final drive ratio, that ratio is based on the OD gear in the trans, the tire size and the diff gearing.
Yes, you can add 90hp/120tq with a tune to your EcoBoost and it will absolutely feel like it doesn't need to be re-geared because it has so much more power than it did before. This doesn't alter the fact that the transmission is geared to move (x) size tires with (y) diff gear ratio and adding hp/tq only increases the stress on the transmission because you have reduced the mechanical advantage the trans had over the wheels/tires (in relation to vehicle movement) from the factory. Same for the 5.0, the 3.5n/a, 2.7TT, the 6.2, etc... IMO, you need to recoup mechanical equilibrium to ensure you don't incur excess wear and tear on your transmission. Is this a marginal increase? Unknown, but it is an increase.
Have lots of folks just tuned (eco/5.0/6.2) and not changed their gearing, yep. Lots of folks run lift blocks and leveling pucks too... You have to decide what you can afford and how far you are willing to go WRT modifications. I'm not trying to steer you one way or another, just give you the facts.
Without mucking up this post, yes, you could change the gearing in your transmission and leave the diffs alone - this is not the typical method but it is one method (adding overdrive or under-drive as an add-on and or changing the actual trans gearing).
There have been numerous posts regarding larger tires / re-gearing and lost MPGs. MPGs are a function of how easily your engine can move the vehicle AND how heavy your foot is (and aerodynamics, rolling resistance, etc...).
All things being equal, adding larger tires will negatively impact your MPGs (as will increased rotational mass and rolling resistance). By adding larger tires you have already taken a hit, when you install the appropriate gearing you can recover some of that loss but not all - that's the price of looking good.
Real world example:
The SDHQ Eco-Raptor gets over 16 MPGs (driving like an idiot) running 4.88:1 gears with heavy 37s. I'm almost certain I remember Serena, the original owner, saying she could get 18 out of it driving normally on the highway (Raptor Forum post).
SCAB with 5.5" bed - was 6klbs factory, at least 6.5klbs now with the added bumpers, larger tires, etc...
Since wheels are part of this overall equation:
You can offset some if not all of the weight increase from the tires by choosing lighter wheels. Choose light enough wheels with light enough tires and you might even make up for some of the rolling resistance.
Hope this helps.
There are two major things to consider when contemplating a re-gear due to larger tires:
1) Size - when running 'back to stock' calculations (what diff gearing with what increased tire size will equal stock final ratio) all you are accounting for is mechanical advantage due to a change in size. If you also choose a heavy tire, you will still feel a sluggishness due to an increase in rotational mass AND rolling resistance (more aggressive tread pattern)
2) Weight - You might need to jump up two sizes if you go up in size AND weight - also don't discount the impact of rolling resistance, IE going to a more aggressive tread pattern vs. stock.
Example: in the 09-14 year group, 4.10:1 is the right gear for 35's IF you stick with a lighter tire and a less aggressive tread (an example would the be Raptor 34.5" BFG A/T). If you also pick a heavy tire, say 10+lbs heavier per corner, and more aggressive tread you'll more than likely need 4.56:1 to have the same snappiness as with the stock tires.
gearing calculator:
http://www.crawlpedia.com/gear_ratio_calculator.htm
^^^ this only accounts for size, the weight / rolling resistance thing is up to you to decide. EDIT - the flaw with these calculators is that they use factory gearing as part of the equation - if you started under-geared, you'll end up under-geared using this methodology.
Side bar: size does not always equal size... there are tires labeled 35s that are actually 34.5", 37s that are 36.5", etc... when performing your calculations, do your research and use the actual size vs. advertised size. Some are much smaller than advertised some are only a half or 1/4in some are right on.
Tip: Lots of manufacturers don't advertise tire weights. If you add a tire to their shopping cart then calculate shipping, it will show you the shipping weight - there is some fudge factoring there because of packaging but you'll at least have a ball park number - best to allow for 1-3lbs for packaging - more if you are buying a tire/wheel combo because there will be more 'stuff' used to protect the wheel in transit.
I have relatively heavy / aggressive 37s, I'm running 4.88s. At 80mph I'm at like ~2,200ish rpms. I'm getting 14+ avg in a Raptor.
Does getting a tune negate the need for gears - No.
From the factory your vehicle was given a certain final drive ratio, that ratio is based on the OD gear in the trans, the tire size and the diff gearing.
Yes, you can add 90hp/120tq with a tune to your EcoBoost and it will absolutely feel like it doesn't need to be re-geared because it has so much more power than it did before. This doesn't alter the fact that the transmission is geared to move (x) size tires with (y) diff gear ratio and adding hp/tq only increases the stress on the transmission because you have reduced the mechanical advantage the trans had over the wheels/tires (in relation to vehicle movement) from the factory. Same for the 5.0, the 3.5n/a, 2.7TT, the 6.2, etc... IMO, you need to recoup mechanical equilibrium to ensure you don't incur excess wear and tear on your transmission. Is this a marginal increase? Unknown, but it is an increase.
Have lots of folks just tuned (eco/5.0/6.2) and not changed their gearing, yep. Lots of folks run lift blocks and leveling pucks too... You have to decide what you can afford and how far you are willing to go WRT modifications. I'm not trying to steer you one way or another, just give you the facts.
Without mucking up this post, yes, you could change the gearing in your transmission and leave the diffs alone - this is not the typical method but it is one method (adding overdrive or under-drive as an add-on and or changing the actual trans gearing).
There have been numerous posts regarding larger tires / re-gearing and lost MPGs. MPGs are a function of how easily your engine can move the vehicle AND how heavy your foot is (and aerodynamics, rolling resistance, etc...).
All things being equal, adding larger tires will negatively impact your MPGs (as will increased rotational mass and rolling resistance). By adding larger tires you have already taken a hit, when you install the appropriate gearing you can recover some of that loss but not all - that's the price of looking good.
Real world example:
The SDHQ Eco-Raptor gets over 16 MPGs (driving like an idiot) running 4.88:1 gears with heavy 37s. I'm almost certain I remember Serena, the original owner, saying she could get 18 out of it driving normally on the highway (Raptor Forum post).
SCAB with 5.5" bed - was 6klbs factory, at least 6.5klbs now with the added bumpers, larger tires, etc...
Since wheels are part of this overall equation:
You can offset some if not all of the weight increase from the tires by choosing lighter wheels. Choose light enough wheels with light enough tires and you might even make up for some of the rolling resistance.
Hope this helps.
Last edited by WarSurfer; 11-01-2018 at 08:21 AM. Reason: calculator explanation
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05-28-2016, 02:42 PM
#2
Threads like these are extremely helpful for folks like me who don't really know much.
I have a 2012 4x4 SCrew with 3.55 gears. I recently added a 2" level and 35x12.50 Nitto Trail Grapplers on 18" Rockstar II's. Just like with my 2004 (same setup), I immediately noticed a more sluggish truck and my MPG's instantly dropped.
I am definitely considering 4.10's now.
I have a 2012 4x4 SCrew with 3.55 gears. I recently added a 2" level and 35x12.50 Nitto Trail Grapplers on 18" Rockstar II's. Just like with my 2004 (same setup), I immediately noticed a more sluggish truck and my MPG's instantly dropped.
I am definitely considering 4.10's now.
05-28-2016, 08:33 PM
#3
Senior Member
I have an '07 with a 4.2 V6. A month ago I got 4.56s and a traction lock diff so I could run 35x12.50r17 BFG KO2's with a Boss Ultimate kit. It's tuned with an SCT X4 and has a K&N CAI. My last 3 tanks my overall MPG's have been 15.5, 15.3, and 15.4. Seems like the same MPG as before running on 3.55s with 31.5" KO2's. Really happy with the setup and I'd do it all over again. (Truck has 74,000 miles)
05-28-2016, 10:05 PM
#4
Senior Member
This would be an EXCELLENT sticky. There are a lot of misconceptions and mis-information floating around concerning gearing. WarSurfer's post sums it up pretty thouroughly.
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06-20-2016, 11:19 AM
#9
