This is a great question and answer to a recent Tech email. Question: I run a 94 Mustang in several of the budget endurance race series. I am looking at a torque biasing diff for the rear axle. I have narrowed it down to the T2R or the Truetrac. Please tell me what is better about the T2R that you sell vs. the Truetrac and which bias ratio would work best. I have read some things on various forums discussing the T2R and it wearing out. Has there been issues with the T2R wearing and losing its ability to perform? If so, what is the lifespan that I can expect from the T2R in terms of hours in our type of roadracing. The car is a 94 Mustang 5.0 with stock suspension arms and subframe, urethane bushings, 250 HP, 3:27 RP, 17X9 wheels w/255/40-17 BFG Rivals. Answer: The T2R has a TBR of 4 to 4.25:1. The TrueTrac has a TBR of 3.5:1. Neither of them have clutches. A higher TBR is needed if the car is used in situations where the lateral weight transfer is very high. If the car has 500lbs static on each rear tire and in a corner it transfers 300lbs to the outside tire, then the dynamic loads are 200lbs and 800lbs. In this case the differential needs to send 20% of the torque to the inside tire and 80% to the outside tire. The differential therefore needs to have a TBR of at least 4:1. If the TBR were only 3.5:1, then the differential would send 22% torque to the inside tire and 78% torque to the outside tire. Since 22% torque on the inside tire is more than 20%, the inside tire is going to start spinning. The driver will need to reduce the throttle position until the inside tire has 20% torque going to it. This will make the torque at the outside tire 76%. The result is that the car will accelerate with only 96% (20% + 76%) of the torque that the first differential could deliver to the pair of tires. If the car is never going to transfer this much weight from side to side, then the TBR of the differential can be lower with no downside. The greatest lateral weight transfer will occur in a slow speed corner with an autox tire such as a Hoosier A6 tire. The BFG Rival tire is a very high grip street tire. In a road race situation, I dont think it would require the TBR of a T2R. The TrueTrac TBR of 3.5:1 is probably high enough. We have never worn out a T2R in our racecar or in any of our Mustangs. We cant really give an accurate count on the number of hours, but they have probably seen more testing than most of our customers car ever will.
Posted on: Thu, 07 Aug 2014 15:37:39 +0000
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