Konstantin

speed -> squat but HP -> cube with increased speed. just in case anyone wants to caculate the nececary force to slow down the car during the shifting

Konstantin
now we are realy of topic

Bill S.

When you press the clutch pedal, the car's velocity looks like an upside-down U, not an upside down V. That is, the car first goes from increasing velocity, to steady velocity, and then to decreasing velocity. It doesn't go from increasing to decreasing velocity instantly with no steady velocity in the middle. Now, if you happen to shift very fast, you'll shift when the velocity is steady rather than decreasing. Many people shift when the velocity is decreasing, which implies negative acceleration, or negative Gs.

If you're really fast, you'll complete the shift right at the start of the upside-down U. Then you'll see positive acceleration, or positive Gs during the shift time.

You can actually calculate the shape of the "upside-down U", but that's probably not a real practical exercise.

Jean

Richard Chamberlain has kindly offered me to post one of his runs at the Donington (sp) track.. I will leave to him the comments about the chart shown, but essentially he highlighted the drop in Gs to slightly below zero during his shifts in this sample.

I would keep in mind two things (among other) impacting the drop in Gs into negative territory,, first is his aero drag, whjoever has seen Richard's car will know what I am talking about, and the second is his monster rolling resistence as well with those tires..

Thanks for the data Richard! We are a lucky bunch with both of you guys, not the sort of data that is accessible to most of us..

935racer

Thanks for posting the graphs. The scales are completely wrong for the post but the traces show a G incursion of -0.08 for the first gearchange (actually into 4th) and -0.15 for the second change (into 5th). Linear acceleration before the gearchanges is around 0.4 G (positive). The gearchange period is about 0.3 seconds as measured from the time taken to close the throttle back to 100% throttle. The throttle does not fully close due to a number of reasons. The main reason is that my dump valves do not waste the pressure fast enough and the pressure in the plenums holds the throttles open. This can be seen on a number of my races by an increase in revs as I depress the clutch. The dump valves are too small and are not close enough to the plenums to do their job correctly so its another task for the winter!
The point of the traces is to try and show that when the drive is removed from the car it slows down. My car is very draggy but this does not matter. It just helps to show what is happening to everyones car even if my case is a little extreme. The principle stays the same.
Thats all folks!!
Richard.

John Welch

Great thread!

It reminds of me of two things. One is the "acceleration" one experiences when leaving a track and encountering wet grass.

The other is, how can the expansion of the universe be accelerating if the force (Big Bang) is no longer acting on it...

Oh yeah, one more thing, is it possible that the ground wasn't level during the shifts? Perhaps a little gravity might be involved...