Where should I mount my transponder?
 

I bought a hard-wired transponder for my TT events. Where should I mount it?

The car is an '86 Carrera and all body parts on the front end are stock.

Left front wheelwell is the most popular place, mount it as far forward as your rules allow (most limit it to around 8" in front of the front axle centerline).

I mounted mine in the driver's side wheel well. I've see others mounted under the front bumper. It should be mounted pointing downward towards the track surface, and as far forward as possible. (Imagine a photo finish with yours mounted on the rear of the car.)

Location on my car.

http://forums.pelicanparts.com/uploa...1207609902.jpg

I concur, left front wheel well with clear view to the ground.

I know your car is light, but I can't believe you're holding it up with a cardboard box. :D

Its amazing what they are making cardboard out of these days.... :D

Did I say that was my car? I meant... err.... ummm... a friend of mines car... yeah that is it... a friend of mine....
http://forums.pelicanparts.com/support/smileys/wat6.gif

Best to put near the front of the car, in a relatively protected spot (like inside of a frame rail) with a good clear view of the ground...

...on the fastest car on the track. ;)

I tell my direct competitors to mount it in the rear. :D

Actually, for time trialing, which is the stated purpose in the original post, there is a very small advantage to mounting the transponder in the rear of the car rather than the front, which has to do with the additional acceleration available down a front straight (where the timing loop is usually located) by delaying the measurement for an extra car length's distance. This effect is marginal, in the fractional tenths of a second, but was documented in testing by some POC racers quite a few years ago and written up in Velocity, the club mag, IIRC.

TT

Tom, I'd like to see that article, because that doesn't make any sense to me.

I'm not familiar with time trialing, does it use one loop or two? I could believe it if it measures the time from different locations, but not if measured from the same spot. That is, unless one of the measurements is taken during an out-lap or an in-lap.

Since all parts of the car are traveling the same speed and the same distance, how can the location of the monitor change the reading.

Tom,

I understand what your theory is, but I think I can show a hole in it. I'll state it up front, this is just my thoughts, no math or scientific proof. What you would gain at the end of the lap by putting the transponder in the rear, would be offset at the beginning of the lap, as the straight would be that much marginally shorter to start with. Like Mark said, the lap time should be the same from any single point on the track for a given lap. Think about all the timing equipment you see setup at tracks, they are all over place, and I bet they are all very close to the official timing and scoring loop for the lap time.

In theory, if you could drive laps at the exact same time over and over again, you could time it from half a dozen different places and the lap charts should be identical.

I know that at some tracks you can get a better qualifying time by purposely taking a different line the turn before or after the timing loop, but that's a whole different subject.

Thanks everyone. I mounted it last night in the left front fender well. I wired it up and the green light is showing, which would seem to mean that I did something right.

Yes, that was exactly my thinking when I read the article--how could it possibly make any difference? It is definitely counter-intuitive. This was not my theory, by any means! Granted, the memory is the first thing to go, and this was a LONG time ago, but as I remember, the testing was done at Willow Springs, where the timing loop is halfway down the front straight, by simply hooking up a transponder to each end of the same car and doing the TT timing drill--an outlap to warm up and two flying laps. The difference in readings was very small, as I said, in the hundreths of a second range, but favored the rear transponder position, which they explained as due to the tiny increment of acceleration over the additional 14' or so of car length from the exit of Turn 9 down the front straight, I believe. I don't remember if the discrepancy was on the first timed lap or the second, or both, at this point. I do remember it made me scratch my head and go "huh?"

I doubt I even kept the mag or could find it again in the piles of them I have laying around here if I did, but maybe someone else remembers reading it. I think it was in a "Tech Tips" section or something like that.

It was not significant enough of a difference to keep me from mounting my transponder in the front left wheelwell, and if your sanctioning body has rules about its placement, you have no choice, anyway. Many of the people who rent battery-powered transponders for TT events tape them to the rear license plate panel, though.

TT

Tom's explanation makes sense for loops placed in the areas of the track where you are on the gas... if it were in the brake zone it would be the opposite since you are slowing down instead of speeding up. Still... the margin must be incredibly slim.

Best regards,

Michael

A "T" decal came with my transponder, but I don't recall seeing them on race cars. Does NASA, PCA, etc. require that decal be placed on the car or does everyone just toss them?

Here's another mounting location on the passenger side in front of the wheel. Front of the car is to the right.http://forums.pelicanparts.com/uploa...1230667862.jpg