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Old 12-22-2004, 07:40 AM   #1
RockyMtnRay
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Default RE Tundra Mods

Moderator Note: This thread is a split out of a question in a thread in the General Discussion regarding TM appearing on the cover of Trailer Life Magazine. Reason for split was these posts were divergent from the original thread subject and deserved a thread of their own. RMR.
Quote:
Originally Posted by CastleRockCamper
Rocky Mountain Ray,
Just curious with all the modifications to your Tundra, what is your mpg?
Last year (before I regeared the truck's axles from 3.91 to 4.30 in November), I was getting between 12 and 15 mpg towing (12 something going up into the mountains, 14 something (almost 15) coming back down and on level ground). Non-towing, I was getting between 19 and 21 on the highway. The regearing may drop my mileage about 1/4 mpg...but contrary to intuition it also may increase it a bit. Here's why: Before I regeared, I often had to run at about 72 - 75 mph when towing to get max torque out of the engine and avoid 3->2 downshifts on the steeper grades. With the regearing, I can achieve max torque RPM (about 3200) at 65 to 70 mph. In addition to being safer, the lower speeds will also result in substantially less aerodynamic resistance...and better gas mileage.

The lower axle ratio (high numerically) will also make towing across the mountains even easier...with the 3.91 axle I was already able to always maintain (or exceed) the speed limit on I70 over the continental divide; with the lower axle gearing I should be able to do it with few if any downshifts to 2nd gear.

The headers and muffler had little effect on the mileage; if anything they might have helped it a bit.

The Michelin tires did improve mileage about 1 mpg over the OEM BFG P-series Rugged Trails because the Michelins are a known low-rolling-resistance tire. And because they're an LT (light truck) series tire, they also have more sidewall stiffness which translates into substantially better towing stability.
Quote:
Nice addition on the Transmission gauge, did you use a Piller?
Thanks. Yes I mounted the gauge in an A-Pillar Pod and had a shop braze the sender into the transmission pan for max accuracy. It's been real nice to know just how hot the tranny is when I'm working the truck very hard. On a hot (95 degree) day, during that initial climb on I70 up to Evergreen with nearly full throttle in 2nd gear (running about 65 to 70 mph), the hottest I've seen the transmission is about 195 (still a safe temp for short term operations). Most of the time when towing it runs around 150 to 165 degrees.
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Ray

I use my TM as a base camp for hiking, kayaking, mountain biking, and climbing Colorado's 14ers


The Trailer: 2002 TM Model 2720SL ( Mods: Solar Panels (170 Watts), Dual T-105 Batteries, Electric Tongue Jack, Side AC, Programmable Thermostat, Doran TP Monitor System)

The Tow Vehicle: 2003 Toyota Tundra V8 SR5 4X4 w/Tow Package (Towing & Performance Mods: JBA Headers, Gibson Muffler, 4.30 gears, Michelin LTX M/S Tires, Prodigy Brake Controller, Transmission Temperature Gauge)


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Old 12-23-2004, 09:45 AM   #2
Larry_Loo
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Question How difficult was it to regear your transmission?

Quote:
Originally Posted by RockyMtnRay
Last year (before I regeared the truck's axles from 3.91 to 4.30 in November), I was getting between 12 and 15 mpg towing (12 something going up into the mountains, 14 something (almost 15) coming back down and on level ground). Non-towing, I was getting between 19 and 21 on the highway. The regearing may drop my mileage about 1/4 mpg...but contrary to intuition it also may increase it a bit. Here's why: Before I regeared, I often had to run at about 72 - 75 mph when towing to get max torque out of the engine and avoid 3->2 downshifts on the steeper grades. With the regearing, I can achieve max torque RPM (about 3200) at 65 to 70 mph. In addition to being safer, the lower speeds will also result in substantially less aerodynamic resistance...and better gas mileage.
Ray, I thought about regearing my F-150's transmission after we purchased our TM trailer. We purchased our truck from an individual who had won it in a drawing. It came with only 300+ miles on it and at a bargain price. Of course, it wasn't equipped with some of the options that I wanted, like power windows. Its low axle ratio and lack of a tow package never bothered me - until after we got our TM. Then I thought about having someone install higher ratio rear axle gears in it, but, never did it. I'm a dunce when it comes to vehicle engines and transmissions. Just out of curiosity, how difficult and complicated was your truck's rear axle modification?
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Old 12-24-2004, 11:12 AM   #3
RockyMtnRay
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Default Not difficult (to the owner) but kinda pricey...and worth it!

Quote:
Originally Posted by Larry_Loo
Ray, I thought about regearing my F-150's transmission after we purchased our TM trailer. We purchased our truck from an individual who had won it in a drawing. It came with only 300+ miles on it and at a bargain price. Of course, it wasn't equipped with some of the options that I wanted, like power windows. Its low axle ratio and lack of a tow package never bothered me - until after we got our TM. Then I thought about having someone install higher ratio rear axle gears in it, but, never did it. I'm a dunce when it comes to vehicle engines and transmissions. Just out of curiosity, how difficult and complicated was your truck's rear axle modification?
Just to clarify things for everyone, the regearing is not done in the transmission but rather in the differential. (Or differentials if you have 4WD). Regearing is fundamentally just replacement of the Ring & Pinion Gears with a set of R&P gears that have a different tooth ratio. For instance, on my truck, the stock axle ratio was 3.91 which Toyota achieved by using a Ring Gear with 43 teeth and a Pinion Gear with 11 teeth. I replaced that set with a R&P set that had a 4.30 ratio; I believe that was achieved by a 43 tooth Ring Gear and a 10 tooth Pinion Gear.

Although fundamentally simple, the devil (as usual) is in the details. First, these gears have to be precisely machined together as a pair and they have to be made from extremely hardened steel. Therefore expect to pay as much as $600 per R&P set for OEM gears or as little as about $185 for aftermarket gears. Secondly, regearing always requires new Pinion shaft bearings, seals, and the use of spacers and shims which typically are bundled into an "Install Kit". Install kits typically cost around $200. And finally, there's quite a bit of skilled labor involved to not only remove/replace the so called "third member" but also to precisely (to the nearest 10000th of an inch) set the backlash and tooth contact area between the Ring & Pinion. This is a job that should only be done by an experienced differential shop. Accordingly labor will usually run about $300 to $500 for the rear axle and sometimes as much as $800 for a front differential in a 4WD that has independent front suspension (most do).

For your Ford, you should expect a total charge of around $550 to $750 for just the rear (if 2WD) or around $1100 to $1700 if it's a 4WD.

IMO, the gains are more than worth the expense, especially if you tow on hilly/mountainous roads and/or at high altitude. I'm getting a 10% change increase in usable torque across the board and more like a 15% to 20% torque increase at preferred towing speed because the engine will be into its peak torque RPM band. If your truck has something like a 3.30 or 3.5 "economy" axle ratio and you jump that up to something like a 4.10 ratio, you would experience more like a whopping 30% to 40% in usable torque because of both gear multiplication and moving the engine into its peak torque band. That's about the same as going from a small V8 to the biggest one the manufacturer sells.

Technical Note on choosing the correct axle ratio: For towing purposes, the ideal goal of regearing would be to install an axle ratio that allows the engine to turn at the RPM that provides maximum torque at the highway speed you want to tow at. If you look at the torque curve of most modern engines, it climbs quite steeply with increasing RPM until the engine is turning somewhere around 3400 to 3800 RPM and then it pretty much flattens out. You want an axle ratio that brings the engine to just about the RPM where the curve flattens when driving at your normal towing speed. In my case, the goal RPM was 3200 and the speed was about 65 mph...to reach that I needed a 10% increase in ratio to 4.30.

The major concern that people have about regearing to much lower gears (higher numeric ratio) is they will take a huge hit on gas mileage. This is mostly a false worry. According to an article I read in a recent issue of either Trailer Life or the Good Sam Club's Highways, apparently the effect on mileage is not big...typically about 1/4 to 1/3 mpg for each 10% increase in ratio. I can testify that my mileage change on the one highway trip I've taken since regearing was minimal...I got about the same 19 mpg for that combo of city/highway driving that I was getting before. And actually I might be getting a tad better mileage since the tranny doesn't have to downshift out of OD (non towing) on the hills as much.

The only real deleterious effect that I've seen so far is that there was a small, but noticeable increase in engine noise at highway speed.

The bottom line is regearing to something around a 4.10 to 4.30 ratio will make a huge, huge improvement in your truck's towing capability. It won't have much effect on fuel mileage (maybe 1 mpg) and only slightly increase cabin noise. It may help extend your transmission's life because it cuts down on downshifts under load. But it does involve a moderately to fairly hefty upfront expense.

Hope I answered your question.
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I use my TM as a base camp for hiking, kayaking, mountain biking, and climbing Colorado's 14ers


The Trailer: 2002 TM Model 2720SL ( Mods: Solar Panels (170 Watts), Dual T-105 Batteries, Electric Tongue Jack, Side AC, Programmable Thermostat, Doran TP Monitor System)

The Tow Vehicle: 2003 Toyota Tundra V8 SR5 4X4 w/Tow Package (Towing & Performance Mods: JBA Headers, Gibson Muffler, 4.30 gears, Michelin LTX M/S Tires, Prodigy Brake Controller, Transmission Temperature Gauge)


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Old 12-24-2004, 01:58 PM   #4
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Good info Ray. JOTTOMH, and from a poor-man's standpoint, could 10% smaller tires accomplish the same thing? I know you people that live in snow country don't want to be closer to the ground but some of us don't see much snow. Personally, I wouldn't mind our truck being a little lower.
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Old 12-24-2004, 03:04 PM   #5
ripp1202
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Take a look at this!!!! The Rip http://www.gearvendors.com/index.html
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Old 12-24-2004, 04:37 PM   #6
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Thumbs up Thanks, Ray.

Ray, thank you for your informative explanation about changing the gear ratio in a truck's rear axle. Now I know enough about the modification procedure to be dangerous! ;-)

My F-150, with 160,000+ miles on it, is 10 years older than your Toyota. Although it's still in good running condition, it may not be wise of me to have any extensive modification done on it. I've been thinking about a new truck for the past year - but hate to spend all that money again for something that depreciates so quickly.
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Old 12-25-2004, 06:25 AM   #7
RockyMtnRay
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Quote:
Originally Posted by fcatwo
Good info Ray. JOTTOMH, and from a poor-man's standpoint, could 10% smaller tires accomplish the same thing? I know you people that live in snow country don't want to be closer to the ground but some of us don't see much snow. Personally, I wouldn't mind our truck being a little lower.
Yes, smaller tires would do the same thing as regearing for small (~10% changes). There are a variety of tire size calculators available on the 'Net to help you determine the best size. Normally, the easiest way to do it is to reduce the aspect ratio (e.g. substitute a 50 to 60 series tire for the stock 70 series). You can also, to a degree, use a narrow tire (e.g. use a 245 tire instead of a 265 width tire). There a few considerations however:
  • Be wary of getting too narrow a tire for the rim.
  • Lower aspect ratio means less sidewall height to absorb road shock. The tire will be rougher riding and a really sharp blow (e.g. deep pothole) could actually damage the rim.
  • Reduced ground clearance.
  • Appearance. The wheel wells were designed to look right with the stock tire size. Go much smaller and the tires won't look at all right.
  • Load capacity. A smaller tire may have too little capacity.
  • For those with limited slip differentials, the spare should also be changed to the new size. Otherwise if a rear tire has a flat, to avoid destroying the clutches in the LSD a front tire would have to be moved to the rear and the spare put on the front.
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Ray

I use my TM as a base camp for hiking, kayaking, mountain biking, and climbing Colorado's 14ers


The Trailer: 2002 TM Model 2720SL ( Mods: Solar Panels (170 Watts), Dual T-105 Batteries, Electric Tongue Jack, Side AC, Programmable Thermostat, Doran TP Monitor System)

The Tow Vehicle: 2003 Toyota Tundra V8 SR5 4X4 w/Tow Package (Towing & Performance Mods: JBA Headers, Gibson Muffler, 4.30 gears, Michelin LTX M/S Tires, Prodigy Brake Controller, Transmission Temperature Gauge)


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Old 12-25-2004, 06:38 AM   #8
RockyMtnRay
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Quote:
Originally Posted by Larry_Loo
Ray, thank you for your informative explanation about changing the gear ratio in a truck's rear axle. Now I know enough about the modification procedure to be dangerous! ;-)
Most welcome.
Quote:
My F-150, with 160,000+ miles on it, is 10 years older than your Toyota. Although it's still in good running condition, it may not be wise of me to have any extensive modification done on it. I've been thinking about a new truck for the past year - but hate to spend all that money again for something that depreciates so quickly.
I regeared because I wanted a more pleasant towing experience (less downshifting on hills) and I wanted to help extend the transmission's life...and I plan to hang onto this truck for enough years to get decent amortization out of the cost of the regearing and my other mods. It's still an almost new truck (just 14 months since purchase) with low mileage (not quite 11,000 miles) so I have a long ownership expectation.

However, for you, a new(er) truck would seemingly make more economic sense than regearing the current one. Trucks have come a long way in the past couple of years in terms of both performance and driving comfort.

Buying a late model used truck avoids taking the huge depreciation hit of a new one but you also don't have any choice in what options it has (especially options like towing packages). Used trucks also tend to be more likely to have been abused/heavily used than late model used cars. But with enough searching, you very well could find a properly equipped (including axle ratio) and well taken care of used truck.
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Ray

I use my TM as a base camp for hiking, kayaking, mountain biking, and climbing Colorado's 14ers


The Trailer: 2002 TM Model 2720SL ( Mods: Solar Panels (170 Watts), Dual T-105 Batteries, Electric Tongue Jack, Side AC, Programmable Thermostat, Doran TP Monitor System)

The Tow Vehicle: 2003 Toyota Tundra V8 SR5 4X4 w/Tow Package (Towing & Performance Mods: JBA Headers, Gibson Muffler, 4.30 gears, Michelin LTX M/S Tires, Prodigy Brake Controller, Transmission Temperature Gauge)


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Old 12-25-2004, 10:07 AM   #9
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Thanks Ray. I wouldn't have thought about the spare tire until I had to put it on. You are incredibly thorough.
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Old 12-25-2004, 04:12 PM   #10
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(Continuation of my message above); Actually we haven't towed with the Tundra yet but will do so beginning next week (weather permitting) on our annual migration from Washington State to the Texas Rio Grand Valley. We will add 7000 miles or more of mostly towing by the time we return in mid March and should have a much better feel for what we have and what we need. I may actually need larger tires. I've noticed the Tundra V-8 turns 2200 at 70mph in OD while the V-6 Honda minivan we traded in turned 2000 at the same speed and was only about 300lbs lighter. We'll be towing with OD locked out so the Tundra will be very lightly challenged pulling our TM#2619 on most of the I-5 & I-10 route we'll take.

I might mention that TM's are rare in the "Valley" and we've only seen two others in several trips there. Anyone else spend time in the McAllen - Harlingen area?
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