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CV Joints Explode when Excessive Torque is Applied Off Road Rock Racing

It may seem a silly question, but why on earth would anyone direct drive huge 40" (or larger) tyres via a low gear ratio transfer case all via a 1.50" (38mm)  or 1.75" (44mm) axle? When 4WD vehicles had 30" and 31" Tyres in the 80's and 90's, enthusiests would often break axles and CV joints if we tried to fit bigger engines, larger tyres and/or wheels.

 

Over the years, Off Road Racing and ULTRA 4 Rock Racing, and Rock Bouncing Vehicles have increased their tyre size signifiantly and 37", 39", 40", 44" tyres are quite common at events every weekend.

 

When you think about the task competitors are asking a direct driven axle and CV joint to perform, you would be insane to direct drive a large off road tyre.

 

 

Lets take a look at some vehicles that were designed from day one to drive "large" off road tyres in the dirt, not built from car parts that were "increased" in size.

You should note that none of the vehicles shown above drives the wheels directly via an axle. Off Road Vehicles have a small gearbox at each driven wheel which increases the axle torque between 200% and 1000%. An axle that is driven into a 2:1 gearbox can drive a wheel twice as large as an axle that drives a wheel directly.

 

Off Road Race and Rock Racing vehicles have evolved  alot over the years, but the basic designs are all build aroud OEM direct axles and Drivetrain systems that started their life on Passenger Vehicles. Most off road "Race Components" you see on buggies and trucks are typically "Larger" versions of what you can purchase from your local Auto Spares Shop every day.

 

So lets put things in perspective. If a medium sized pickup truck, Jeep, or 4WD that has a 1.25" Axle, designed to drive 33" tyres is modified for competition with a big horsepower engine, a special low range Transfer Case and Low Range diff ratios, the Axle could easily experience 500% to 2000% more torque/load than driving on the highway and occassionally seeing a weekend of 4 Wheeling.

 

  • Modified Engine

    • 200% -300% Torque

  • Special Low Range Transfer Case

    • 200-400% Torque

  • High Ratio Differentials

    • 150% Torque

 

Updating mid sized truck diffs and CV Joints with 35, 40 or even 44 Spline Axles does not realy fix the problem. Off Road Competitors apply 5 to 20 times the torque to his axles than the manufacturer intended. Have a look at all the exploded and broken compoenents below, many of which were broken whilst they were used at competition events less than 10 miles in duration. Imagine if a tractor or harvester broke drivetrain parts every 10 or even 100 miles of use?

 

Off Road Enthusiests and Competitors have started to "expect" to regularly break drivetrain components and keep buying bigger and bigger versions of the same part, INSTEAD of looking at the root cause of the problem and an effective solution.

Broken 40 Spline Gun Drilled Axle Off Road Rock Racing ULTRA 4 Racing
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A stock H1 Hummer may appear to have very small CV joints and half shafts compared to today's hand built off road competition vehicles, but the axle torque is multiplied by 200% (actually 191% but lets round things up) at the portal hub. The H1 Hummer was designed from initial concept to drive 37" tyres by engineers that knew the benefits of Portal Hub Drive Systems.

 

Although a STOCK OEM Hummer Axle is only 28mm (1.125") in diameter, the Portal Hub DOUBLES the torque that the axle provides and HALVES the torque applied to the Axle so you can imagine a 56mm (2.25") diameter 66 spline axle driving the large 37" tyres. 

 

If a 2.25" axle sounds strong, that is only comparing a STOCK, small H1 Hummer axle with a typical axle. Now imagine a Purpose Built, 35 Spline 1.500" Heavy Duty Chrome Moly Axle and Series 21 CV race joint MULTIPLIED by 200% at the Portal Hub.

 

A 35 Spline axle driving via a portal hub would be like driving your truck with a 3.00" 70 Spline Axle and having 10.0" diameter CV joints with 2.00" CV Balls !!! (Who could break that?)

 

Running 2", 2.5" or even a 3.0" (As above), 8" or 12" CV Joints in a vehicle is totally rediculous, but this is where the competitors are heading. Everyone is making bigger and bigger axles and CV joints. Competiors that were at one time happy with Dana 44 Diffs and 33" tyres are now using expensive 10" Hand Made Diffs and 40 or 44 spline axles, but I think any engineer would agree, these are only badaids to the root cause of the problem. When will this madness end?

Benefit 1
Increased Ground Clearance

 

Unimog, VW Kombi, Kamaz, Hummer and most Military Vehicles all benefit from the aditional ground clearance provided by Portal Axles (Hubs). The wheel hub (Output) is typically 100-150mm (4-6") below the centre of the Diff providing much more ground clearance.

 

Benefit 2
Fewer Drivetrain Failures
 

As stated, a 2:1 gearbox places 50% less load on the Axles and CV Joints, so just imagine a 35 Spline 1.5" Axle running through a 2:1 portal hub equates to a 70 Spline 3.0" and you get the idea of the bebefits of a Portal Hub Drive System.

 

Imagine a Series 21 CV Joint multiplied by 200%. That would be a 10.5" (260mm) Diameter CV joint with massive 2.0" (50mm Balls)

 

ULTRA4 OFF ROAD TIRE INFLATION
Benefit 3
CTIS (Central Tyre Inflation System)

 

An airline cannot be run through a CV Joint, but when the CV joint sits above the wheel spindle, Central Tyre Inflation becomes a reality. Being able to deflate and inflate your tyres whilst moving provides many benefits in Off Road Situations and Competition Use

 

 

 

 

 

 

 

Benefit 4
Improved Braking Force

 

The gearbox multiplies the braking force applied at the disc by the gearbox ratio. For example, a 12" rotor connected to a 2:1 portal hub is similar to running a 24" (600mm) Disc Rotor on your vehicle.

 

Benefit 5
Brakes protected from Dirt and Debris

 

Brakes that are mounted up inside the chassis are protected from the effects of mud, dirt and debris.

Inboard Brakes apply 200% Braking Force via Portal Hubs
Benefit 6
Smaller Diffs | Smaller Axles | Less Weight

 

Running Portal Hubs allows competitors to use much smaller Diffs, Tailshafts, Axles and CV Joints which results in a much lighter drivetrain and of course a much faster vehicle with better suspension and handling

 

Have a look at the size of the little diffs in a H1 Hummer, but remember to multipy the size by 200% when you look at the torque handling ability of drivetrain

Proformance Portal Hubs
 

Portal Hubs are not for everyone, but maybe they are just what you need? If you are a serious competitor and getting sick of breaking drivetrain components and the DNF that follows, then talk to our Imagineers about our Portal Hub Systems.

 

Our Portal Hubs are specifically designed for Off Road Motorsport are made to be light weight yet ultra reliable and are suitable for engines up to 1000HP and tyres up to 44".

 

For more information about Proformance Portal Hubs for ULTRA4 Racing and Rock Bouncing, click the portal hub image or click here.

Download our Capability Statement - Click Here

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