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To regear or not


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#11 rando

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Posted 11 December 2018 - 11:58 PM

Interesting. What RPM's do you like at level freeway cruising speeds? Must be over 3200ish.

 

On flat highway at 65-75 somewhere between 1800 - 2200rpm in 6th/5th.  The gearing is tall in 6th, but the auto downshifts quickly for hills.    Heading up a steep hill on the highway (the passes on I-70 for instance), you will quickly drop down to 3rd/4th and be at 5000 rpm, but it will hold 65 no problem.    The 3rd gen Tacoma has about 20% more power than the 2nd gen (and better fuel efficiency to boot), but that power is at a higher rpm.   I don't think regearing is going to buy you much.

 

Also an intake and exhaust will primarily just make it uncomfortable (loud) to drive at high rpm without any real gain in power.


Edited by rando, 12 December 2018 - 12:05 AM.

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#12 So Cal Adventurer

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Posted 12 December 2018 - 12:04 AM

Frstnflt,

 

You actually answered your own question.

 

As you surmised, installing higher numerical diff gears would give you some extra pull in first gear with your manual transmission. Beyond that, all it's going to mean practically is that in each gear the engine will be turning slightly (depending on how drastic you go) higher rpm. So you might wind up in a situation where you might be doing, say, 70mph in 6th gear at 3,000 rpm, where with your stock gearing you'd be doing the same speed at the same rpm in 5th gear. But so what? The engine doesn't care what gear you're in. 

 

Furthermore, both your fifth and sixth gears, IIRC, are overdrive gears, and thus slightly weaker than the 1:1 or "underdrive" gears. Pulling a load up a hill the transmission is better off in the lower gear. The simple fact is, as was mentioned, these engines produce their highest torque (not to mention horsepower) at absurdly high rpm, and you need to keep the engine up in that region to get the best power.

 

Also, remember that a higher numerical ring and pinion is weaker than a lower one. It's been argued ad nauseam how much this affects durability and reliability, but the indisputable fact is that a 4.56 r&p is weaker than a 4.11 r&p, and a 4.88 or 5.29 are weaker yet.

 

If you plan to install taller tires the equation shifts a bit, and re-gearing will compensate somewhat for the added diameter. But you'll still be weakening your diff, and compounding that stress with the added rotational inertia and mass of the larger tires.

 

Best Explanation of gearing i've read in a log time, and spot on!

 

Is this the Jonathan Hansen that gave me a copy of his Outdoor Photography book (which i still proudly have) when i met him in AZ with Scott Brady 10+ year ago???

 

Big tall bald ugly Kevin (that raced the baja 1000 in an 80 series) and was copartner in Baja Overland before it became a buzzword.


Edited by So Cal Adventurer, 12 December 2018 - 12:05 AM.

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#13 cwdtmmrs

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Posted 12 December 2018 - 02:32 AM

On flat highway at 65-75 somewhere between 1800 - 2200rpm in 6th/5th.  The gearing is tall in 6th, but the auto downshifts quickly for hills.    Heading up a steep hill on the highway (the passes on I-70 for instance), you will quickly drop down to 3rd/4th and be at 5000 rpm, but it will hold 65 no problem.    The 3rd gen Tacoma has about 20% more power than the 2nd gen (and better fuel efficiency to boot), but that power is at a higher rpm.   I don't think regearing is going to buy you much.

 

Also an intake and exhaust will primarily just make it uncomfortable (loud) to drive at high rpm without any real gain in power.

 

Wow. I'm suprised that engine can produce enough power at those RPM's to sustain 70MPH with that weight.


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#14 rando

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Posted 12 December 2018 - 03:50 AM

The weight isn't much of a factor on the flats as you are not accelerating or pushing the weight up hill.   I think wind resistance is the primary issue on the flats - not that the Cd is all that good with the double thickness cab over. 


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#15 Zoomad

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Posted 12 December 2018 - 05:05 AM

Keep this in mind if the plan is to go larger with the tires and regear.  One kind of negates the other.   The larger diameter tire acts like a an OD gear slowing the engine speed for the same road speed with the same gearing.  

 

Playing around with an online gear calculator to see where you would need to be to maintain stock like feel with larger tires.  

 

 

https://www.crawlped...calculators.htm

 

The ring and pinion calculator is a good way to see what you have, input the new tire size you want to run and it will suggest the ratio to compensate for the increase in tire size.  Meaning it's going to behave like stock, but not really add too much extra torque over what is compensating for the larger tires.   I'd suggest if you want more power (at the expense of highway cruise RPM) to take what the caluclator says for larger tires and step up to the next higher numerical ratio available.  If it say recommends 4.10's, go to 4.56's, or if it recommends 4.56's, jump to 4.88's.   

 

Like others have indicated the higher numerical ratios do have some strength issues as the pinion gear looses teeth at the numerical ratio increases.  But, sticking with good quality gears and professional setup should keep things lasting.  

 

One thing not really discussed (I'm surprised too) is the aero drag from these campers.    I noticed it big time with mine.  I'm running a 5.3 Vortec in my K5 with a FWC and it made a huge difference in mileage and power.  Pre-camper the 5.3 pushed my K5 around Colorado with 4.10 gears and 35" tall tires without too much issue.  I was averaging 15-16 MPG on the highway too.  I put the camper on and I noticed aero drag requiring more throttle to overcome the wind.  Throw an uphill grade and it got worse.  My tire size was great for keeping my cruise RPM lower even with the 4.1's, but the RPM was low enough I was almost 1000 RPM or better below peak torque.   It caused sooner downshifts to maintain speed and keep the RPM closer to peak torque.  

 

I've felt the drag when driving into the wind to be so much I had to downshift to 3rd and leave it there until the winds calmed.  What this means is if you do plan on re-gearing, use a gear calculator and go the next gear up from the target to gain a little torque on top of the tire size change.  

 

I could use to move to 4.56's in mine to compensate, but I'm going to install a 7.4L big block to overcome the lack of low end torque from my 5.3.   The peak torque is lower and comes in sooner so it will limit my need to spin the engine to the moon to build the torque needed to get the truck/camper rolling down the road.  Granted swapping engines isn't a realistic idea on a late model Toyota, but bump in gearing will help a lot.  You will continue to rev the engine too the moon though.  


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#16 JHanson

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Posted 12 December 2018 - 08:56 PM

Best Explanation of gearing i've read in a log time, and spot on!

 

Is this the Jonathan Hansen that gave me a copy of his Outdoor Photography book (which i still proudly have) when i met him in AZ with Scott Brady 10+ year ago???

 

Big tall bald ugly Kevin (that raced the baja 1000 in an 80 series) and was copartner in Baja Overland before it became a buzzword.

 

Wow, that would be me, although I don't recall you being ugly!

 

Technique aside, that book is about as outdated as can be these days. I believe I discussed something called "film."


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#17 knoxswift

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Posted 12 December 2018 - 10:23 PM

Late to the discussion but I can add that this is one of the best Gear Ratio calculators out there on-line:

 

http://www.grimmjeeper.com/gears.html

 

If they don't have your trans you can enter your own numbers.

 

This calculator was dead on perfect for when I did my re-gear in a 2nd Gen Tacoma. (Tacoma with 33' tires, Manual Tras and an Eagle FWC).

 

My 2c re-gear if changing tires and go slightly higher on the RPMs when doing so from stock. Also quite frankly Toyota should of had a 4.10 option in these newer trucks (Stock tire size)  but I think EPA/MPG is why they don't have more aggressive gearing...


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#18 Zoomad

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Posted 13 December 2018 - 05:33 AM

Most truck manufacturers have moved away from deep gearing in the axles in favor for higher gear count transmissions.  6-speeds are the norm when 4-speeds used to be for automatic transmissions.   Now the 8-speed is getting more common and 10-speeds are right behind them.  GM (what I'm used too) dropped 4.10's in half tons many years ago and made 3.73's the normal when you wanted a "towing" gear ratio.  With the 6 and 8 speed transmissions now, GM has dropped to 3.42's as the deepest gearset you can get in a 1/2 ton truck.  

 

Why?   Normally the 6, 8 and 10 speed gearboxes are coming with deeper gearing in 1st, 2nd and 3rd.   By combining deep 1st gear ratios and a mild axle ratio like 3.42's they still are getting a similar ratio to the older stuff with a lower numerical first gear and higher numerical axle gear.  The bonus is better gear splits that keep the high revving engines working in the right RPM range for optimum torque.  Then once the truck is up to speed, the lower numerical axle ratio allows for an even lower cruise RPM to sip fuel.  

 

It's not uncommon to see the new GM 1/2 tons with a 6 or 8 speed transmission cruising at 65 mph with the engine RPM below 2,000.  The downside is the need to make multiple gear downshifts when the need for more power is required.  6 to 4 downshifts are the norm and if you aren't ready for it kind of surprising when the engine goes from 1700 rpm to 5000 rpm as quick as you can snap your fingers.   


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#19 cwdtmmrs

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Posted 13 December 2018 - 07:26 AM

Late to the discussion but I can add that this is one of the best Gear Ratio calculators out there on-line:

 

http://www.grimmjeeper.com/gears.html

 

If they don't have your trans you can enter your own numbers.

 

This calculator was dead on perfect for when I did my re-gear in a 2nd Gen Tacoma. (Tacoma with 33' tires, Manual Tras and an Eagle FWC).

 

Wow that is quite a chart! In the old days before computers we just used:  MPH X GEAR RATIO  X 336 = RPM

                                                                                                                       TIRE DIAMETER

                                                      


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#20 ntsqd

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Posted 13 December 2018 - 02:21 PM

As an aside, I've never understood why over-drives. Why not make top gear 1:1 with deeper 1st gears and taller axle ratios? End up in the same place, but now top gear doesn't have the parasitic losses of extra bearings & gears under load.

 

CVT's are really what it will come down to. Infernal Combustion Engines run the best when they are tuned for one RPM. As soon as you ask them for a power range or band efficiency and economy of operation decrease. The wider that band, the less efficient the engine is within that band. To say nothing of when operated out of that band.


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Thom

Where does that road go?




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