(This article first appeared in the November 2008 issue of SportsCar magazine)

By Philip Royle

Stopwatches. According to the GCR, these are an acceptable alternative to the use of electronic timers for logging racecar lap times at SCCA Club Racing events. Quoting 5.10.2.D.2 of the GCR: “The stopwatches should time to the nearest 1/100th of a second. The minimum acceptable resolution for a stopwatch is 1/10th of a second. Timers will record the cumulative time of passage for their assigned car(s), then compute and record the individual lap time.”

While the GCR may still consider stopwatches acceptable, virtually all SCCA Club races utilize electronic transponders mounted to the racecars for their timing needs. When the racecar passes over a track-mounted loop, the transponder reports to Timing and Scoring and lap times are automatically generated. Best of all, the transponder system is generally recorded to 1/1000th of a second – far more accurate and consistent than any stopwatch.

Born from requests from the regions, the SCCA placed transponder guidelines in the GCR in 2001, thus standardizing transponder usage across the Club and naming AMB as the transponder company of choice. During the early days of transponders, however, SCCA regions wanting to utilize transponders for their timing needs had to purchase fleets of the transponders and rent them to racers for the weekend, as few racers owned their own transponders.

As time progressed, racers began purchasing their own transponders, permanently mounting them in their racecars (a movement aided in part by AMB launching its race tracking Web site, MyLaps.com). Racers owning their own transponders helped alleviate some of the drain on the regions, as the regions no longer had to maintain a slew of rental transponders. However, racers were left with the task of figuring out which transponder would best fit their needs – and then there was the problem of mounting it.

What’s right for you

AMB sells two Club Racing transponders: the TranX260 rechargeable and the TranX260 direct powered transponder. The rechargeable unit is the one most regions rent to racers. The rechargeable units can operate for up to five days on a single charge and offer the benefit of not having any external wires to worry about – 30 seconds and a couple zip-ties is all that’s needed to mount this transponder.

The other option is the direct powered transponder, which must be wired into the car’s power supply. “Generally speaking, the direct power transponder is a huge advantage in that it’s on, it works and you never have to think about it for years,” explains Bill Skibbe, sales and support engineer for AMB. “The advantage of a rechargeable unit would be for someone who wants to use [the transponder] on several cars at different occasions. This way he doesn’t have to have multiple transponders.”

While the rechargeable unit does have its advantages, most SCCA Club Racers would probably benefit from the direct powered transponder, as it is very much a “set it and forget it” item – there’s nothing worse than having to rent a transponder because you forgot to charge yours.

Tricks to the trade

“The way the transponder works is that it generates a magnetic field,” says Skibbe. “Any kind of iron or magnetic metal around [the transponder] would distort the field and weaken it.” To keep the transponder’s signal strong, you want to make sure the transponder is not mounted above carbon fiber or metal, and make sure the correct side points to the track.

“Mounting it above fiberglass or Kevlar is ok,” says Skibbe. “Generally, [mounting the transponder above] plastic is no problem – the bracket is plastic. Part of the reason for the bracket being plastic is to insulate it from the metal it’s going to be attached to.”

According to Skibbe, the normal mounting location for a transponder is at the front of the car, either in the fender or behind the front valance but away from flying debris. “It’s [usually] easiest to get power to the transponder from a location up front.”

The ideal minimum mounting height for the transponder is one foot off the track, with a maximum height of two feet. “We’ve seen installations from guys in formula cars who believe they get a better transponder reading by getting it as close to the track as possible,” says Skibbe, “but what that does is reduce the amount of contact time the transponder has with the loop. Between one to two feet gives you the most identifying hits and the best definition of the signal in order for the decoder to process the data and give you an accurate time.”

If you purchased or rented a rechargeable transponder, there is no wiring; a direct powered transponder requires 10-30v DC power and a ground. It’s recommended you tap into a fused wire that is powered when the ignition is turned on.

Spend a few minutes in the paddock and you’ll undoubtedly find someone that has wired their direct powered transponder into a switch so they can turn the transponder off while the car is on.

“Originally, a lot of guys mistakenly thought a transponder would drain the battery if it were on all the time,” says Skibbe, “but the power draw from the transponder is so small that you can’t possibly see the affects throughout the day. Having the ability to turn the transponder on and off within the car is really unnecessary and leads to forgetting to turn it on.” Skibbe also notes that a switch can also introduce a point of failure.

The only catch is pricing. The AMB TranX260 rechargeable unit costs $420, with the direct powered unit coming in at $380. Considering many regions rent transponders for $50-$60 a weekend, it only takes seven weekends for a transponder to pay for itself – and by the SCCA picking a transponder standard, racers can safely purchase one of these transponders with the knowledge that it will work at almost every SCCA Club Racing event anywhere in the country.

Real world installation

We chose to install the TranX260 direct powered transponder in one of our Club Racing project cars, as we liked the idea of never having to remember to charge the unit. We opted to mount the transponder at the front of the car just in front of the radiator support near the factory horn mount. A metal bracket was fabricated, the transponder was bolted to the bracket and the bracket was attached to the car via an existing hole that was already threaded.

The AMB direct powered transponder comes with several feet of wiring you can trim to fit your needs. We tapped into a12v power line that’s live when the ignition is on, and we grounded the black wire. If you need to add wire, make sure to use a sufficiently thick gauge. When the transponder is powered, a green LED illuminates on the front of the transponder.

Once we’d found the ideal mounting location, installation took 15 minutes. With our mounting location, the bottom of the transponder sits 18 inches off the ground – perfectly located between the acceptable height of one to two feet. The transponder also has no metal below it, allowing for a clean signal.

Prior to this, we’d been renting a TranX260 rechargeable transponder from our SCCA region for $60 a weekend. Using the same transponder number now means we can utilize one of AMB’s online features: MyLaps.com.

MyLaps allows racers to view lap charts and information about their races online. Once you’re registered, you can view a variety of charts packed with information about your race weekend. While MyLaps is no replacement for data acquisition (and keep in mind, the race results printed on MyLaps are not official results), the information is very useful and it makes for easy tracking of your racing history.

AMB, http://www.amb-it.com