I have a 2013 g37 sedan and something I've noticed recently is whenever I'm in DS mode there are two downshifts, one at about 30mph one at 40mph, that seem rough. The 30mph downshift is really noticeable where the tachometer will jump from under 2k to about 4k rpm. I know the g's can rev match but this rough transition doesnt happen when I'm driving in D which makes me think it's a problem with the shifting logic. Anybody else experience this? Would the TSB for the transmission help?

 

I've noticed that for my '09 (don't know what TSBs have been done) it depends on how fast I decelerate. Decelerating quickly will tend to downshift with a higher rev match. Decelerating slowly tends to smooth out the transitions. At least this is what I notice when I drive in DS.

 

You're totally right. If i'm decelerating fast, say off the freeway, I'll get the 2K rpm jump. If I'm just driving around town the jump will be closer to 1.5K. However that still doesnt explain why the decelerating characteristics are so different between D and DS.

Besides this quirk though I'm lovin' my G!

 

I think it all has to do with the reason behind rev matching in order to keep you in the power band. If decelerating quickly it assumes cornering where you want to be able to get back on the throttle quickly.

 

It really depends on how abruptly and aggressively you decelerate. At 40mph, your tranny was probably at at 4th (1.41:1) or even 5th (1:1) gear and downshift rev match to 2nd (3.19:1) will cause quite a jump in rpm. 3.19/1.41 = 2.26 which explains the 2k range rpm jump.
1st is 4.92:1 so you do the math if you downshift from x to y equal z. But if you are concerned about the harshness then you might want to take to dealership to have them diagnose if your tranny is ok.

 

What he said.

Drive in DS in the twisties.

 

Thanks for the info guys. I think I just didnt have a good grasp on what rev matching was. Im planning on getting a transmission flush at 30K so I can check then but I doubt there would be much wear. I'm just going to trust the engineers did their jobs on this one.

 

To appreciate DS mode and use it as intended it helps to understand racing philosophy. In racing you want to downshift, if you were to drive a manual that is, right about when you enter a turn while still slowing down. That ensures you are in the right gear, i.e. max power band/torque when you are exiting the curve, allowing you to start accelerating as aggressively as possible, thus giving you better laps time.

That's exactly what DS mode does for you, only automatically. It downshifts when you are slowing down in an anticipation that you'll be accelerating hard any moment now.

If DS downshifted and you don't accelerate, well, it's like bringing someone close to orgasm and stopping right before it actually happens. Therefore, normal street driving is not for DS mode.

 

Wow...an edging reference lol

 

Lol, hope no one gets offended.

 

Sounds like a case of blue ***** for the trans