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Tire Size / Final Drive Ratio - Reality Check (More-fun-with-math!)

leety
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leety

leety

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2 minutes ago, LorenS said:

Okay, so we take (0.75/0.73) = 1.0274  Your final gear is 2.74% higher than Mike's, so instead of 68 MPH it's about 69.9 MPH.  That's with the 3.73 gears and your 19.5s. discussed above.

That 3.84 'custom gear set' would need to be 3.95 gears (1.0274*3.84) to match the MMR resulting in 66 MPH at 2k RPM.  So now you're creeping closer to 4.10s, which would put you at about 63.6 MPH at 2,000 RPM.  Be nice if you had a 7 speed, with a "five and a half" gear of about 0.85.  Then you could keep your 3.55 gears, and that gear would be like having 4.18 rear gears for uphill, and your 0.73 final gear for flat and downhill.  Or drafting semis...

 

Are you a lead-foot, 80 MPH driver with that permanent sail attached?  When one factors in drag, you may want the 4.10s for the higher speeds - which seems quite counter-intuitive.  Pushing that camper through the air will take some power!  Other folks on here would have far more experience with this type of operation than I do, hopefully they will chime in.  This might be a good question in the RV/travel trailer forum.

Good job on the math.  You get an A

 

Although I am guilty of leadfootitus, if I want to drive fast it's not going to be in this thing, I'll tell you that much.  I mostly just set it at 68-70 mph on cruize control when I'm on the highway and turn the music, really loud!  Otherwise I'm out in the dirt or on little mountain roads just creeping along trying not to tip the thing over. Snow is an optional selected adventure.  The fun thing about so cal is you could go snowboarding and surfing on the same day if you wanted to.

 

The 4.10 creates a cost issue becuase the carrier has to be changed for that leap to happen.  The 3.73 is more economical and I think will do the job just fine.  If I want more get-up-and-go, I'm going to address that with a tuner and perhaps a hybrd turbo down the road, but at this point I'm just trying not to overtax the truck by trapping the native power it has in the drive train.  I want that power to exit at the asphault or dirt, wichever the case may be. 

 

I'm far more interested in reliability and gas mileage than I am speed, that's what "performance" looks like to me on this truck.  I would like not to have to stuggle up along steep grade quite so much, esp when towing something.

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LorenS

LorenS

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11 minutes ago, leety said:

the carrier has to be changed for that leap to happen

Is that for the front or rear?  This isn't really my wheelhouse, but have looked at these enough to know there are questions I would ask an expert before I dismissed it as impossible!  I THINK you may be in luck - maybe not.  Yukon makes "thick gear" 4.11 gears to fit - I believe - the same carrier as your 3.55s.  They also make "thin gear" 3.73s to fit the 4.10 and up carrier.

Here's a link:
https://www.randysworldwide.com/product/yg-d80-411t/
Now, if you buy these and Randy sends me a 4.5% commission, don't come calling me with any complaints :nono::lol:

 

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leety

leety

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44 minutes ago, LorenS said:

Is that for the front or rear?  This isn't really my wheelhouse, but have looked at these enough to know there are questions I would ask an expert before I dismissed it as impossible!  I THINK you may be in luck - maybe not.  Yukon makes "thick gear" 4.11 gears to fit - I believe - the same carrier as your 3.55s.  They also make "thin gear" 3.73s to fit the 4.10 and up carrier.

Here's a link:
https://www.randysworldwide.com/product/yg-d80-411t/
Now, if you buy these and Randy sends me a 4.5% commission, don't come calling me with any complaints :nono::lol:

 

It’s all about Hoopers Rear Ends.  They’ve been in the greater LA area since 1976.  That’s the place to go.

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Doubletrouble

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 @leetyJust gonna take a shot at this, I'll let @LorenS do the math. If you would eventually swap to a 3:73 gear and when it's time for tires step down from the 240/70/19.5 to a 225/70/19.5 you would loose a bit over an inch in height which may make those gears work even better for you.

 Biggest drawback to the big wheels is the rotating mass. I don't know what that tire combo weighs compared to a stock wheel/tire but I would guess they would be heavier. They do look good though. Just my $.02

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NIsaacs

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More-fun-with-math, humm, Loren, gonna need some help here...

 

But, I think the difference between 3.55 and 3.73 gears is about 5% or about 100 rpm or about 3.5 mph @70. $1500 for a 5% bump in performance?

 

The oem power of the HO is 245/505...add 5%...that gives a new rating of 257/530. My guess is the butt dyno wont feel it.

 

The Edge EZ adds 65/180...so now the oem power jumps up to 310/685, you will feel that:thumb1:

 

The EZ also claims a mileage increase of 1-2 mpg.

 

When your 245's wear out you can drop to 225's that is about 3.5%

 

How many miles per year do you drive the truck? Unless you are running a huge tire, like 37's" a gear change is the last thing I would do, then 4.10's make sense. 

 

If it ain't broke don't fix it. Now, with that said....65/180 additional power increase will make a fun ride out of that 3500 truck!

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leety

leety

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1 hour ago, NIsaacs said:

 

Appears to be legal.

 

https://edgeproducts.com/shop/2001-2002-dodge-24-v-ez-5-9l

The edge is definitely legal.  The truck had an old on on it when I got it but it was contributing to al full-time coal plume so I deleted it.  Most of the plume is gone.  That wasn’t the only contributor.

 

I have a BHAF which is not legal.  For that I keep an original air box handy so I can swap it in every 2 years for smog.  A girls gota do what a girls gota do.

2 hours ago, LorenS said:

One possible problem with a tuner is California emissions, unless it has a CARB certificate (Gale Banks may have one?). Gears surely wouldn't come in to play.

That’s not difficult to get around.

 

Tuners are easy enough to temporarily remove every 2 years for smog.

 

I do that with my BHAF

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LorenS

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My dad had an Edge EZ on his 01' dually with 6/speed and loved it, even tipping the scales at 35k pounds on a trip to the dump.  He drove slow (65 MPH usually) and would regularly get well over 20 MPG, hand calculated.  I think his record round-trip to our cabin +100 miles away was upper 20's.  It was cool, almost foggy weather.  Enough the air felt saturated, but the pavement was dry.  He didn't run any gauges, though, so who knows what EGTs would get to be when he refused to downshift and just rode the torque curve all the way down...  Otherwise stock truck besides coolers on the tranny.

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leety

leety

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27 minutes ago, Royal Squire said:

Could go with a quad and tune out smoke. Still way cheaper than gears 

The quad is something on my short list of considerations.  It'll do everything the Edge EZ does and much much more.  The quad is not legal in CA but smog happens every 2 years so I just have to swap out a couple items to pass smog.  Not biggy.

 

I wanted to get as much smoke gone as I could with the orriginal equiptment.  I don't like to solve problems with a bandaid, I'd rather get at the phisical root of the problem and then introduce the the quad on to take it beyond the limitations of the hardware. By correting the issues with the OEM bits first I have gotten most of the smoke to go away.  I think my final drive ratio is the last bit of OEM adjustment I need to consider.  I believe I have covered all the other contributers to my coal plum at this point.

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leety

leety

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On 10/12/2020 at 8:12 PM, Royal Squire said:

You should probably make sure gears haven’t been changed previously 

So armed with the beautiful math of @Mopar1973Man and @LorenS coupled with the best question on the post I attempted to take this picture. Yes it’s blurry but this my actual realty in terms of speed per rpm.  So is it possible that a gear change happened by a PO?

 

How can I figure this out?

 

B5DD5C13-CE6E-4A90-8A2B-2D84907B2F28.jpeg

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leety

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1 hour ago, Mopar1973Man said:

3.73 would be just about right for most people with slide in camper or tow a lot. For me its all the steep mountain roads. 

Yep it’s very steep twisty mountain roads for me.  And a bit of towing.

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