New 4.88:1 gearing for a V8 Toyota 4Runner. An ARB Air Locker was also added.
Question and backgrounder
Our 2001 Ford 7.3L Power Stroke Diesel engine has been modified, mostly for better efficiency, with new injectors, fuel and oil pump upgrades, intake and exhaust mods, and a tuner. Exhaust gas temperature (EGT) is not currently a problem. The truck has a 6-speed manual transmission, with an aftermarket South Bend Clutch. We have a Four Wheel Campers popup slide-in, and sometimes tow a trailer through mountainous terrain. The truck runs great, we’re just trying to add a bit more power while remaining practical. Would you upgrade the turbo or change from the original 3.73:1 gears to a lower 4.10:1 ratio?
Answer and questions
Do you know how much power/torque you are making? What is the gross weight of your 2001 Ford Super Duty and Four Wheel Camper loaded for most trips? How much weight and wind load does your trailer add?
Sounds like a turbo could complement your previous mods if you are needing more air, but if the fuel is burning well and completely it might be unnecessary. How many miles on your current turbo? Turbo lifespan may be a consideration?
Lower gearing multiplies torque. I’m a fan of lower gearing in general, particularly on gasoline-powered rigs, but moving from 3.73:1 to 4.10:1 gears is not a huge change for the cost of the surgery. Only you can determine if the added performance will be worthwhile. You will likely lose some fuel economy with lower gears.
Original 4.10:1 gears in a Dana 60 front differential, on a 7.3L Ford Power Stroke Diesel.
If overall gearing is too low—as was the case with my ’96 F-350 with factory 4.10:1 gears, only 33” tires, and a 0.77:1 top cog—then overdrive may be required to maintain comfortable highway rpm when transmission sympathy would dictate using direct. However, that may not be a concern with your setup.
Is the top ratio of your ZF-S6 tranny 0.72:1? If so, that’s rather tall for a manual gearbox, and you probably have plenty of overdrive combined with 35” tall tires, depending on your highway speeds. Spending some time in 5th/direct at higher road speeds with your current gearing, as well as playing with some online gearing calculators, should be informative.
Do you currently downshift out of overdrive when climbing big hills? If so, is direct/5th enough for most grades unless the road requires lower speeds? Don’t be overly hesitant to grab a lower gear and spin the engine a little faster (while keeping an eye on the gauges), which reduces the load on the tranny and clutch. You might have all the lower gearing you need at your fingertips with your transmission’s underdrive gears. Unless you are wanting to avoid downshifting, are using all the power you already have, and/or would like to accelerate more quickly.
Gas vs. Diesel
It’s worth noting that making more torque and power with a turbodiesel engine is generally much easier, less expensive, and less invasive than with gasoline-powered platforms. Lower gearing for gas trucks can provide a very satisfying boost in felt torque and acceleration compared to similar money spent on engine modifications. I’ve chosen to add lower, 4.88:1 gears to three gas engine rigs, one Jeep and two Toyotas, but have yet to re-gear a diesel truck.
Copyright James Langan/RoadTraveler All Rights Reserved
Factor 55’s FlatLink MultiMount (winch line shackle mount) was added to the Warn 16.5 ti-S winch, housed inside the aluminum Buckstop front bumper, on our 2017 Ram/Cummins Hallmark Camper project truck.
The folks at Dick Cepek/Mickey Thompson introduced a new hybrid truck tire just before the SEMA Show, the TrailCountry EXP. I love the appearance of this new tread, less aggressive than the Dick Cepek Fun Country I wrote about here Fun Country review, but with deeper tread and more void than the much more conservative Trail Country (no EXP) 5-rib design. I love hybrid light-truck tires, and have tested several of the EXP’s competitors.
Cooper Discoverer SRX is a M+S rated SUV/CUV tire.
Our 2005 Lexus RX 330 was one of the cleanest and best maintained used vehicles we ever purchased. For the first 11 years of life it logged just 52,000 miles, and it was religiously dealer-maintained.
Still, it needed a few things, new brakes were one and new rubber another. The tires had more than legal tread—though that’s not saying much, as legal is only 2/32” most places during the dry months—but certainly not as deep as we prefer for all-weather traction. Tires are expensive, so we postponed getting replacements for over a year. We stretched the worn Michelins through the first winter, but before Jack Frost arrived again we wanted new rubber on the car.
Gone! Legal or not, 4/32” is ridiculously low tread depth.
Waiting was good, because at the 2017 SEMA Show, Cooper Tires announced 30 new sizes in their Discoverer SRX SUV/CUV line, originally introduced in 2014. One of the new sizes was exactly what we needed for the RX 330, a 235/55R18.
We needed a new, matching spare.
The Discoverer SRX is an all-season design that blends innovative technology with advanced engineering to deliver long tread life, a quiet and excellent ride, with improved efficiency for a wide range of applications. Our size has a 65,000-mile treadwear warranty. Key features include:
•3D Micro-Gauge™ sipes maximize tread contact with the road surface to
grip the road better
•Optimized five-rib tread pattern evenly distributes the load across the tire’s
contact patch leading to improved treadwear, responsiveness and handling
•Traction grooves facilitate the expulsion of water away from the tread surface
effectively reducing the potential of hydroplane while increasing grip
•Winter edge feature creates a higher snow-grip area in the tread to provide
•Stabiledge™ helps stabilize the tread elements during driving conditions,
enhancing steering precision
•Wear Square™ treadlife indicator gives consumers a convenient way to gauge
the amount of wear on the tread of the tire, showing when it is time for replacements
Cooper’s consumer-friendly Wear Square treadwear indicator in the center of this photo. All four sides showing indicate full, or 100% tread. Sides of the square are worn away in 25% intervals.
Cooper Tires StablilEdge performance.
Our Lexus RX 330 was a replacement for my wife’s 2013 Volkswagen Jetta Sportwagen TDI with a 6-speed manual transmission. Unfortunately, the TDI was bought-back by Volkswagen as part of their diesel-emission-cheating debacle. The little diesel VW was fun to drive and very economical. The RX is a nice, luxurious SUV, but does not drive or perform like the TDI, and fun is not an accurate descriptor. The Lexus has a soft, marshmallow-like suspension compared to other vehicles we have owned. It is neither a modern sedan nor heavy-duty truck, but the masses must love them as we see them everywhere. My wife says it is her soccer-mom or grandma car. We like the RX 330 fine; it’s just a very different ride for us.
Replacing worn tires with new can dramatically improve the safety and performance of your vehicle.
Acknowledging and understanding how different the VW and Lexus platforms are, we both still thought that the RX drove poorly compared to the TDI. The alignment was checked by a trusted, journeyman expert. All was well. If anything needed attention in the near future it would likely be the independent-rear-suspension (IRS), where the camber was just within specification. The front was fine, and there was no need for adjustment. However, the Lexus had a distinct tendency to drift right or left, often requiring constant steering input to keep the car tracking forward, even on relatively straight and level roads.
Cooper Tires Fix A Problem
My extensive experience with light-truck rubber has shown that changing treads sometimes involves compromises. Some designs have a tendency to pull one direction or another on some chassis, or exhibit other unpleasant traits, and mechanical adjustments may be needed to return drivability to acceptable levels. It’s almost impossible to know how a particular pattern will work on a vehicle until you try them. Boy were we in for a surprise….
Mounting the Cooper Discover SRX to the Lexus produced no drivability quirks. Quite the opposite, the Cooper Tires were a dramatic improvement. The Discoverer SRX made the RX 330 drive much better, the wandering was gone, and constant correction was no longer necessary to go straight. The old, worn rubber was the problem. Our little SUV had been transformed!
Still loving the Cooper Discoverer SRX after several thousand miles.
After returning from my test drive I downplayed the improvement to my wife, simply telling her the new tires were “fine,” not wanting to color her first impression when she drove her car. After her first-drive on the SRX Coopers, she was also extremely impressed, telling me that her little wagon drove much better. It actually made her like the car more.
Great All-Around Design
The SRX were mounted in late November 2017. Our winter was moderate in the Northern Sierra Nevada, but there was plenty of on-highway snow, ice, rain, and grit. After every slippery commute I solicited comments from my wife. She’d enthusiastically reply with how much safer and better her all-wheel-drive SUV drove, and didn’t slip, with the Cooper Discoverer SRX tires. The tread design and siping works. Our only minor critique is that the SRX sometimes follow rain grooves on concrete freeways. This is not unusual for a ribbed all-season. It has more to do with the roadway than the tires.
3D Micro-Gauge sipes and a silica-infused compound for wet traction.
It’s important to have a good, matching spare, particularly for an all-wheel-drive vehicle. The original, 10-year-old spare was still tucked under the Lexus, so a fifth, matching SRX filled that need. Sticking with the stock, 235/55R18 size meant there were no challenges fitting the spare, the speedometer remained accurate, and the traction control and ABS systems remained happy.
The SRX are wearing evenly and similarly on both the front and rear axles. They received their first rotation slightly late, after 6,700 miles had been covered.
As this is written, we’ve logged 8,800 miles over 10 months, with the tread measuring about 9/32”, down from the original depth of 11/32”, for an impressive 4,400 miles per 1/32” of rubber.
11/32” of depth in this size.
As autumn and winter weather approach, we have the utmost confidence that these Cooper Discoverer SRX tires will take us anywhere we want to drive the little crossover SUV.
Gorilla Automotive Wheel Nuts and Locks
This car had factory Lexus/Toyota wheel locks. Sufficient, but not the brand or style that I prefer because the key-to-lock engagement is shallow.
Gorilla’s lock-to-key engagement depth is the best we’ve seen and used.
For several years I have been using Gorilla Automotive locks on all my four-wheel-drives, so I inquired what might be available to fit the factory wheels. The standard, light truck wheel nuts and locks fit the original aluminum wheels perfectly, and were pretty much the only choice. That’s what I ordered. There was an optional bonus I was surprised and happy to learn.
It was possible to order the wheel locks to accept the same key I was already using on my two late-model Dodge Ram 2500 pickups. Wow, awesome! I still ordered a few extra keys; we don’t like to be without them, one for my toolbox and a couple in the car. Having most of my vehicles in my garage using the same wheel key is fantastically convenient for routine maintenance.
Wheel nut torque is an often overlooked maintenance task, but we check ours often.
Copyright James Langan/RoadTraveler All Rights Reserved
Flatbed camper truck suspension tinkering and changes are not risk free, and I like to say that often “modifications lead to modifications.” Followup mods might be desirable upgrades, or unwelcome consequences.
Application specifics matter. Assuming that standard tweaks which work well on the typical unloaded/lightly-loaded truck are also good for a much heavier outfit, are often naïve.