Nate Tempest

So, I've had the 997.1tt for a few months now, and just recently installed the DSC box. Stock suspension otherwise. We have a couple of those 'speed humps' (not speed bumps, but the larger ones) right near our house, so I go over them frequently. Pre-upgrade I found that with PASM in normal mode, I'd get a noticeable oscillation when the rear-end went over the bump. With the suspension set to stiff, no oscillation. Now, that's not too surpising - the weight is in the back, and the springs are stiff. So when the shocks are turned down, it's slightly underdamped - not enough to notice in most circumstances, but it is when going over a big hump.

Now, one thing that's surprised me since installing the DSC box is that I now get a bit of that underdamped response even with the PASM light turned on. It's perhaps slightly less than in normal mode, but the difference is much, much less pronounced now, to the point where I'm not even certain it's there. That's actually the case all around - where the firmer mode was bone-rattling before, it's much more compliant now. And overall it seems like an improvement. But this speed bump thing is making me wonder if it's not sacrificing something for that improved ride, or if it's maybe not operating as it should.

So, long story short: can anyone with a DSC box confirm that they get a *bit* of bounce when going over large speed bumps? like.. down-up-down-up-good, as opposed to the critically-damped response of down-up-good. If that makes sense... Actually, for that matter, have others noticed it with the stock controller, when PASM is in normal/compliant mode, going over large speed bumps?

atcbi5

Sounds like you either like it or it's a trade off ? Did I misunderstand? I am on the fence in the TPC DSC module.

Nate Tempest

In general I like it. I haven't had a chance to do much spirited driving since installing it, so I can't really comment in any detail. It certainly makes the sport pasm mode more driveable. I just want to confirm with someone that this slight underdamped response on large speed bumps is normal, since I didn't get that with the stiffer setting on the stock controller. I mean, it makes sense - stiff springs with lots of weight need stiff shock absorbers to avoid that underdamped bounce. My hope was that the DSC could react fast enough to turn up the damping as you go over a large bump like that, giving best of both worlds. It may be doing so to some extent, but not perfectly. (Either that or my rear shocks are dying, but that seems unlikely since I didn't get any bounce with the stock controller when set to stiff.)

All that said, it may well be a good tradeoff. The stock stiff mode was very harsh, to the point where it could likely unsettle the car if a bump was hit at speed. I just want to make sure it's as expected.

DSC Sport

Here's why you're still experiencing oscillation. The DSC controller alters your shocks damping rate based on a variety of inputs - g-force, speed, brake pressure, throttle position being most important...speed bumps are not one. I'm assuming based on the description that you're hitting this speed bump at very low speeds, without loading g-force into the car, and you're probably not deep on the brake when you hit the speed bump. So the suspension is at its softest for that given mode when you're riding over this speed bump.

If you were going 60mph and hit a decent-sized bump, then the suspension would be firmer because you're going 60mph. Now there are ways to add in damper for scenarios like the speed bump, but I wouldn't really recommend it, as you're not looking for performance at speed bump speeds.

However, you may want to bump up the default rate in Normal or Sport mode (whichever you'd be using most for the commute that has these speed bumps) just to stiffen up your damping when there is little to no load on the vehicle.

Also just to note: The technology of the 9x1 vehicles does allow us to start tuning for scenarios such as this. Because they are equipped with ride height sensors, we can use that data to determine shock piston velocity and tune by velocity. So using our software on a newer car, we could actually go in to your Normal setting and add in low speed damper by compression/rebound like you would a more traditional shock with adjustment *****.

Nate Tempest

Awesome, thanks for the detailed response! That explains it perfectly. Guess I need to start nailing speed bumps at 60mph...

Now, I do find that the default (low-speed) rate in both normal and sport modes feels pretty close. Even up to ~30mph I don't feel a big difference in ride quality on bumpy roads. Which, I mean, is good - you obviously don't want a harsh ride just to feel how tough your shocks are. But I expect I could stand to bump up the sport level a bit without any negative effect.

I haven't tried playing with your tuning software yet.. could you give me the quick version of how to do that? (IE a link to the instructions and just tell me which value to edit, or similar?)

TT Surgeon

Nate, that's a programmable version, I had it set super compliant in non sport mode bc the roads around here are ****. I had Tom at tpc set it up for me, I think you can easily tighten it up a bit if desired, I just wasn't computer literate enough to deal with it.....

Nate Tempest

Oh, I didn't realize you'd tweaked the settings. Is it possible to set it back to defaults without having to manually undo the changes? Or do you have a record of exactly what was changed?

TT Surgeon

No, when I bought it I asked tom to do it, ck with him it's apparently easy to do.

DSC Sport

You can take a look at our Software User Manual, but admittedly it needs some work. If you just want to bump up the default rate in the tuning software, go to the g-table and adjust the Default Rate. If it's 10, bump it up to 15. If it's 15, try 20, etc.