Bizzare gear change lag/bogging down

  • Thread starter FussyFez
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FussyFez

FussyFez

1,460
United Kingdom
England
Hi guys.

I've posted this here as it may well be an issue concerning GT as a whole, rather than just in the circumstances I am about to describe.

I am experiencing a bizarre bogging issue when changing from second to third, using manual on my DFGT. I don't think it's an issue with my wheel.

Whilst drifting with my freshly built V8 M3, I change up from second to third mid drift, full throttle, and rather than slipping almost instantly into 3rd like it would any other gear, it delays a split second, causing me to grip up and get spat out of the drift.

When I first built it, I took it out offline for a shakedown and was very happy with it. Moved online and started experiencing this gear change lag. It was not present offline.

I have the triple plate clutch installed for fast gear changes mid drift, and all my other cars are fine. The change from 1st to 2nd is fine, as is 3rd to 4th all the way up to 6th, it's only 2nd to 3rd.


Another drifter in the room seemed to be having the same issue with his long term 350Z and he was getting rather frustrated as it's normally his best car. We agreed somthing fishy must be going on.


I'll try and get a video if it does it again when I get on next.


Any similar experiences or thoughts?


Obviously TC off all aids off except abs 1.


Edited to add, I'm a reasonably experienced drifter, I'm 99% sure it's not a technique issue, and is some sort of bug.
 
Stock fully customisable gearbox. Just set to 155mph, with no other adjustments.

Once the gearchange is complete, it behaves fine. Its the actual gear change that takes too long, causing the traction gain. Almost as if the change from 2nd to 3rd is acting like I have the stock clutch installed. A lethargic shift compared to the other gears.

I'm just getting on now, so if it does it, I'll grab a video.
 
FussyFez
Stock fully customisable gearbox. Just set to 155mph, with no other adjustments.

Once the gearchange is complete, it behaves fine. Its the actual gear change that takes too long, causing the traction gain. Almost as if the change from 2nd to 3rd is acting like I have the stock clutch installed. A lethargic shift compared to the other gears.

I'm just getting on now, so if it does it, I'll grab a video.
Click to expand...

Just narrow the second gear and you'll be fine.
 
FussyFez
Stock fully customisable gearbox. Just set to 155mph, with no other adjustments.

Once the gearchange is complete, it behaves fine. Its the actual gear change that takes too long, causing the traction gain. Almost as if the change from 2nd to 3rd is acting like I have the stock clutch installed. A lethargic shift compared to the other gears.

I'm just getting on now, so if it does it, I'll grab a video.
Click to expand...

I did a couple of tests with the M3 and I found that the shift time is depending on how close the ratios are.

Here are the data from three shifting tests with the stock customizable gearbox, measured in the number of frames (@ 60 fps) required for each shift (from the throttle is cut to when the throttle is back at 100%):

gearframes2.png

From 1st to 2nd took 12 to 13 frames.
2nd to 3rd took 9 frames.
3rd to 4th took 5 to 6 frames.
4th to 5th took 4 frames.
5th to 6th took 3 frames (only did that shift once though).

With the stock ratios, the ratios gets closer the further up you go, and that is what makes the shifting take less time. You're waiting for the engine rpm to drop, and with widely spaced gears the rpm needs to drop more than with closely spaced gears.

Here is a test I did with the gearbox setup to constant space (each gear is exactly 1/1.3 of the previous gear), in this chart I also marked the time required for the throttle to go from 100% to idle ("off")and from idle to 100% ("on").

gearframes1.png


The longer time required for the shift from 1st to 2nd is most likely caused by a hiccup of the physics engine. In the 3rd frame of every shift there is a small throttle blip (3.7%) and looking at the MoTeC data it seems like the physics engine applied the engine force for that blip in two frames instead of one.

The time for 2nd to 3rd gear is just one frame longer than the other shifts, so it falls within the margin of error.

So to fix your problem, try making the 2nd gear slightly taller or 3rd gear slightly shorter and the shifting time should drop.
 
eran0004
I did a couple of tests with the M3 and I found that the shift time is depending on how close the ratios are.

Here are the data from three shifting tests with the stock customizable gearbox, measured in the number of frames (@ 60 fps) required for each shift (from the throttle is cut to when the throttle is back at 100%):

View attachment 421857
From 1st to 2nd took 12 to 13 frames.
2nd to 3rd took 9 frames.
3rd to 4th took 5 to 6 frames.
4th to 5th took 4 frames.
5th to 6th took 3 frames (only did that shift once though).

With the stock ratios, the ratios gets closer the further up you go, and that is what makes the shifting take less time. You're waiting for the engine rpm to drop, and with widely spaced gears the rpm needs to drop more than with closely spaced gears.

Here is a test I did with the gearbox setup to constant space (each gear is exactly 1/1.3 of the previous gear), in this chart I also marked the time required for the throttle to go from 100% to idle ("off")and from idle to 100% ("on").

View attachment 421856

The longer time required for the shift from 1st to 2nd is most likely caused by a hiccup of the physics engine. In the 3rd frame of every shift there is a small throttle blip (3.7%) and looking at the MoTeC data it seems like the physics engine applied the engine force for that blip in two frames instead of one.

The time for 2nd to 3rd gear is just one frame longer than the other shifts, so it falls within the margin of error.

So to fix your problem, try making the 2nd gear slightly taller or 3rd gear slightly shorter and the shifting time should drop.
Click to expand...
Thankyou very much @eran0004, that's some excellent research and findings.

I'll have a fiddle with the gearbox and report back.

I tend to just set the top speed to a suitable speed for the track, I rarely ever play with the individual ratios, but it looks like I shall have to if I want to solve the issue.

Thanks again, I couldn't have hoped for a better response. :cheers::gtpflag:
 

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