Dragy vs. Timeslip

[TireSmoker]

At the track last night, i got to play with my Dragy a little bit. Very cool little device.

How about 0-60 of 2.7 seconds??

[AKROVER]

That is surprisingly accurate. It seems like it is accounting for the roughly 2-foot rollout. I am quite surprised at how well that data correlates to the track position sensors. That is a really cool data set. Definitely a cool device to have.

2.7 seconds is almost exactly 1G for 0-60, depending on how the rollout is included. While tires are not purely friction in their contact with the track, friction theoretically limits us to 1G of acceleration (positive or negative) as a maximum. We get around that limit by lifting the car (4 link or ladder bar drives the tires hard into the ground while raising the car's center of gravity), which allows us to briefly exceed 1G of acceleration. We also can eventually get around that by creating downforce aerodynamically, but that can only happen once we have some air speed. That is a really good mark, though. It suggests that you have figured out how to manage the throttle on the launch to maximize the limited traction. There was little doubt that from 0 to 60 you are traction limited rather than horsepower limited, but the numbers confirm that.

[MostMint]

one drawback on the dirt drags is getting the timeslips. they don't put your car # on them so unless someone is there to pick them up they got lost. Dragy would help with that so I might be getting one soon.

[Basement Paul]

Does your Dragy allow you to set specific distances to get your times at, or are they present? Could you theoretically set it for 200' and know your time at that distance?

-BP

[TireSmoker]

Yes, I think you can set up custom distances like that.

[MostMint]

I bought a Dragy Pro and put it to work with the Caddy. Set up custom distance of 200' fairly easily.

When I put it to work on the dirt, there was a significant difference in measured time. I mounted it originally on the back on the seat. Once I see the discrepancy (about .25 second), I put the thing on the roof and that cut inaccuracy down to .15 second.

My first guess is that the roll out on dirt is creating the difference, as there is 15" between the stage beam and the red beam. Of course this means the Dragy Pro starts its 200' at a slower speed than the racing timer, which should make it slower, which means the problem is even worse.

I'll probably see if it can hitch a ride alongside someone else's Dragy just to confirm there is not some kind of calibration problem with the device.

At the end of the day, if it's consistently off I can just do the math and it will still work for me on dirt.