mc3456

Tom, quick advice requested. I have a 991.2 C4S Cab with V3 installed. After getting it, I installed some lighter than OEM forged HREs. The fronts were each 4lbs lighter and the rears were each 6lbs lighter than stock wheels. With the lighter wheels, the ride seemed much more compliant, but on occasion, a bit too soft. Having recently sold the HREs and gone back to OEM wheels, I notice the ride is much firmer. Is that just increased suspension responsiveness from the much lighter wheels? Is the DSC automatically compensating for the change in unsprung weight? I never added a Mini-USB capable when installing my DSC module but now rethinking that as maybe I need to play around with different maps. I’d kind of lime something in between what the car felt like with the HREs and OEM wheels, as I will be getting another set of HREs in the Spring.

AdamSanta85

You should to Zero out the ride height with a laptop when you install the unit to get best performance. I would try that first.

I never noticed any suspension weirdness going between different weight wheels (Stock vs HRE).

https://rennlist.com/forums/991/1161...n-and-dsc.html

mc3456

Why would you need to zero out height if you don’t lower the car? I bought it directly from DSC Sport and it was supposed to be plug and play. The only thing I changed was the wheels, which I assumed with less unsprung weight would allow the PASM to react quicker/more efficiently if having to damp less weight/momentum. Am I wrong?

tosha

This is no longer applicable to V3. It uses relative ride height values to compute piston velocity, so this is a moot point.

The documentation is out of date.

tosha

Were the tires and psi different than on other wheels? The tires are part of the suspension and have a damping effect. I believe they’re often modeled as additional spring rate, which is a function of tire wall construction and psi.

Around town mapping is challenging partly because tire pressure doesn’t go up very much during slow driving. Once on the highway, the additional 4+ psi has noticeable effect on comfort. Depending on where in the “sweet spot” range you are, more psi can actually add stability and remove the bouncing you probably observed.

AdamSanta85

Ah thanks. I have a V2.

Tom@TPC Racing

The difference in the ride quality that you feel is likely not from the weight of wheels. Typically the ride quality feel for street use has more to do with the diameter of the wheels, the tire size, the tire compound, and tire pressure than the weight/material of the wheel. Examples: Changing from 20" wheel to 19" wheel the ride will feel softer. Changing from Michelin Cup2 to 4S the ride will feel softer. Dropping the tires pressure 2 psi the ride will feel softer. This is because the tires/wheels is part of the car's "spring rate".

DSC adjust the damping force commands to the driver's input in real time. It will also adjust to the tire's grip in real time via g-force. But it does not adjust to the ride quality of changing tires/wheels, the user would have to do that if one particular tire/wheel combo feels 3% softer than another combo...

Tom@TPC Racing

...also, age hardened old tires will ride stiffer.

mc3456

Same exact tires swapped over to different rims, same air pressure on same size wheels, just heavier wheels vs lighter wheels.

My question has more to do with how the DSC Sport actually works. Isn’t it supposed to adjust damping rates dynamically vs the OEM’s “static” damping rate, no? If so, shouldn’t a lighter wheel create less momentum/force going over a bump, hence the suspension not needing to firm up the damping rate as much to accomplish the same thing? Shouldn’t that alone provide a more supple/compliant ride if the damping doesn’t need to act as aggressively to control the rebound of the heavier wheel going over a bump? All I can say is that going to the lighter forged HREs, saving 6lbs/rear wheel & 4lbs/front wheel, dramatically changed the ride on the car. I noticed it when the HREs were first put on, and then felt the opposite effect when the heavier cast OEM wheels were remounted. Again, same exact set of tires and same air pressure.

Tom@TPC Racing

DSC adjusts to g-force changes and to other inputs on the car's computer network. It does not adjust to the weight of the wheels, unless the weight of wheels causes a detectable change in the travel velocity of the suspension, which they likely do not.
Sorry I have no explanation for you as to why the same set of tires on different wheels changes the ride quality. If anything, I would have guessed that the forged wheels would ride stiffer due to less flex.
I'm off to racing.

MidEngineRules

^^ the combined tire and wheel weight makes a 4 and 6 lb difference much less of an overall affect (under 10%). Exactly where the weight differs matters too. It certainly isn’t at the outer diameter as the same tires account for that. Could be the cast rim is stiffer than the aftermarket’s rim, which is probably thinner as it’s rolled. Surely not the case here but I’ve yet to hear a person who bought marginally lighter wheels not believe they can feel the difference. I’m betting the aftermarket rim has some comparative flex to it.

koala

That GT3 Tour file is fantastic! Just gave it a try on my 991.1 S today. Firmer, sharper, even gear changes feel more solid.

AdamSanta85

Agreed. Thank you very much for all your help Tom. I ran my 991.1S with B16's and DSC/GT3 Touring file at the track this past weekend. I was passing a couple GT-R's all day once we got into the twisty sections... and that was on Pirelli P Zero...

mc3456

The rims together are 20lbs+ lighter, so 6 lbs+ lighter per rear rim and 4 lbs+ lighter per front rim. That is not insignificant. Forged rims are much stronger than cast rims, not more “flexible”. In a golf analogy, forged golf clubs feel much better than cast clubs, as they do not transfer harsh vibrations into your hands. Anyway, still questioning why people would state that a lighter, stronger rim would not allow the suspension to be more efficient/responsive at adjusting damping of bumps, especially if the DSC Sport is purportedly measuring and adjusting damping in real time.

mc3456

Are your HREs P101SCs or R101s? They slightly look different than the P101s that I had before selling them.