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DIY Ford F-150 Gear Swap

Posted June 18, 2010 12:01 AM by motorztv

In this episode, Motorz TV shows you how to upgrade the gears on a 2005 Ford F-150. There are many reasons to do a gear swap, but in our case it's been needed since the F-150 was lifted 6″ and 35″ tires were added. You see, when you lift a heavy truck like this and add on the extra weight of huge wheels and tires, the truck isn't as quick off the line. It loses low-end torque because there's much more mass for the engine to push forward.

That's where new gears come in handy. In our case we went from a stock 3.55 gear ratio to 4.56, which means there are more teeth in the ring gear. As a result, the gears spin faster which helps when you punch the pedal from a stop. As for the install, there's too much to document here, so just watch the video!

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#1

Re: DIY Ford F-150 Gear Swap

06/19/2010 10:21 PM

You lost me with this macho man,

"You see, when you lift a heavy truck like this and add on the extra weight of huge wheels and tires, the truck isn't as quick off the line. It loses low-end torque because there's much more mass for the engine to push forward."

The oversized tires' diameter is the real reason you need to change the gear ratio. Not added weight. The added weight is not enough to require a gear change. You don't change gears when you haul four fat guys around, do you?

So much for your "expert" help. You are wrong!

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#2
In reply to #1

Re: DIY Ford F-150 Gear Swap

06/20/2010 4:19 AM

Or to put it another way..if you didn't mess with the darned thing in the first place...but hey ya gotta get out the house somehow.
Del

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#3
In reply to #2

Re: DIY Ford F-150 Gear Swap

06/20/2010 10:28 PM

Well,

I'm just in a mood.

Add to that the fact that I did a swap just like the one here with oversized tires and lift and I never considered a gear change. Didn't need to. OK, so I had 373 gears to begin with. But the point is, weight isn't the issue. Tire diameter is.

Cheers

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Anonymous Poster
#4
In reply to #3

Re: DIY Ford F-150 Gear Swap

06/21/2010 5:12 AM

After watching the video, I must agree with your tire diameter, but disagree with a couple of your other comments.

1.) Who is their right mind would put 4 fat guys in a regular cab truck. Unless it is not illegal in your state to haul talking ballast in the back, if so.. scrap No.1

2.) There is an extremely large difference in weight between a regular factory wheel/tire and a 35" mud bog tire. After doing a search to find the actual documented weight for these tires I was able to find a link.

Q. "How much does a 35-inches-when-mounted-and-upright LT315/70R17 BFGoodrich All-Terrain KO tire and SVT rim actually weigh?"

Answer 970 lbs... each.

Links at http://jalopnik.com/5378268/an-svt-raptor-tire-weighs-how-much and at www.edmunds.com

Q. "How much does a 35" tire weigh?"

A. The average 35" tire weighs 880 lbs unmounted.

Link http://superbowl.kgb.com/

Either way.. that is four really big guys.

3.) The 6" lift kit also adds additional displacement. The average clearance for a reg size cab truck is 8.8". When lifting a vehicle an additional 2/3 (approximately) of the original clearance the force against the truck has changed.

stress= F/A

acceleration = force/mass

force

Force with displacement equation is

Ideal acceleration is achieved between a 10:1(rabbit speed) to 16:1(turtle speed) weight/hp ratio.

So, bottom line t x 4 - ( t_o x 4) = additional weight, an additional 3600 lbs in weight adds to mass, 6" additional height adds to the displacement.

4.) The blog is titled "DIY ...Gear Swap", not "Reasons for... Gear Swap"

I guess he just didn't want to confuse the issue with the physics involved.

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#6
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Re: DIY Ford F-150 Gear Swap

06/21/2010 10:27 AM

I sincerely doubt that big tires and wheels add almost 4,000# to the weight of the truck.

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#7
In reply to #4

Re: DIY Ford F-150 Gear Swap

07/15/2010 10:58 AM

Well, I checked a few things out...

Your #1: This 4 door truck would handle 4 big guys

Your #2: The image from jalopnik.com shows the tire on a Taylor #7004 scale, which reports to 1/10 of a pound. It reads 97.0 pounds, not 970 pounds. lynlynch's skepticism is well placed: do not believe everything you read on the 'net.

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#8
In reply to #7

Re: DIY Ford F-150 Gear Swap

07/15/2010 11:31 AM

I may have not thought that through completely... The Taylor 7004 reads pounds OR Kg, selectable. My American mind jumps to pounds, but that might not be correct. Either way, a lot less than 970 pounds.

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#5

Re: DIY Ford F-150 Gear Swap

06/21/2010 8:26 AM

The tires and wheels weigh about 50lbs ea more than typical wheels and tires. Consideration should be given to better brakes and lower gearing because of the added wheel/tire diameter. There are many considerations when jacking up a truck and maintaining road safety. I did the gear change, added bigger brakes and modified the steering and suspension for around $16,000 on a Ford F-150 4 wheel drive. Gas mileage went from 16.5mpg to 12.4mpg. It will also become less sweet to tow things and it is like climbing the monkey bars at the playground to get in and out of it.

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