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      03-19-2013, 01:03 AM   #61
esquire
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Drives: 2011.5 Dakar Yellow M3 Coupe
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Quote:
Originally Posted by VCMperformance View Post
The differential and its torque twist witch is cause by the rubber mounts it hangs on is a big cause of wheel hop the differential will twist more then you think. Most times wheel hop happens is launching the car and the tires are grabbing for traction. Each little slip of traction the torque twisted differential will unload and the rubber bushing will spring the differential back to a neutral position. The regain of traction will load the differential twisting it down again starting a pendulum affect that will make the suspension load and unload wheel hop happens. There is many other causes for wheel hop but on IRS rear ends this is the main one. The differential brace he is reviewing will help keep the diff from loading and unloading helping with wheel hop.

I do believe it happens on the m3 in varying degrees many times the driver will not feel it. Other times BAM BAM BAM BAM. HP levels, tires, age and state of rubber bushings all play into wheel hop. Take a stock hp m3 with some big sticky rear tires and do some good launches probably get some mean hop like being on a sticky drag strip starting line. I say stock hp m3 for the reason of not having the compete power of over whelming the tires. The feeling of the car becoming more planted and stable could be from lsd differential being able to work more efficient in a turn due to it not waiting for the bushing to react to on and off throttle inputs. Just my two cents....
Quote:
Originally Posted by swamp2 View Post
A few comments.
  • If the product can/does eliminate wheel hop it could be a great product. I have had wheel hop on multiple occasions and it does feel like the rear end of the car is falling apart.
  • Pics are terrible and the link to the non M system doesn't help as the systems appear very different.
  • I do not at all buy these overly optimistic (imaginary) reports of all sort of benefits and improvements in feel, more solid, less bounce (sure less wheel hop, maybe).
  • There shouldn't really be any more benefits for a DCT over the 6MT.
  • It simply can not improve any flaws/shortcommings you have found with the DCT. This is in your head OP, sorry.
  • Quotes from the designer of the system need some serious improvement. It sounds like bable/techno babble without really getting to any sort of engineering/technical explanation of the product and what it is actually doing. Too bad VCMperformance had to fill in for the vendor with a reasonable good/simple explanation of what this product actually does.
Quote:
Originally Posted by Malek View Post
The design philosophy behind this product is pretty simple. They are adding a 4th mounting point to the differential it seems instead of the 2 front and 1 rear bushing mounting design the car already has.

As far as NVH, this kit is replacing the 3 factory bushings and it's adding another mounting point that might be solidly mounted to the sub frame. If that is the case, NVH will definitely increase.

Will this help a DCT more than a manual? No. In fact it should help a manual a lot more. Ever seen how harsh a 6MT power shift is?

Sadly, there is no technical specifications on this product and going by how something "feels" is not the best method of testing the efficacy of this bracing kit. No pictures, no drawings... these things would help.

I am with swamp2 on this.

VCM, Swamp, Malek - can either of you elaborate on how this product differs from a solid rear subframe (such as that discussed in THIS thread)? Is one a more thorough solution? Does one offer benefits that the other doesn't? Does one create negative effects that the other doesn't? Difficulty of install? It's a newb question, I know. But I'm contemplating a solution along these lines and am trying to understand the fundamental difference, to see which solution is (1) more thorough and (2) applies best to me)


Quote:
Originally Posted by defivfab View Post
Ok, I'm here to answer a multitude of questions in regards to what this is, why it works and whatever else you'd like to throw my way. We'll start with the factory differential mounting strategy-for whatever reasons, bmw opted to utilize a 3 point mounting system on this car.Any understanding of torsional loading will quickly unveil the faults of the design, perhaps it isn't as apparent on factory or lightly modified cars,but when a supercharger or added displacement,etc falls into the mix, the weakness of this design becomes apparent-especially with the dsc off. I was approached by a local s/c M3 owner preceding the OP's install do devise an M variant after the success of the N54 version. Balancing between effectiveness and low nvh was not immediate, I ended up having to utilize the solid forward diff mounts (same as an N54 car) which are billet aluminum. Originally,the brace was solid mount to the subframe, but excessive nvh became apparent, so the design was altered. Two brands of polyurethane were used before deciding to have a softer formulation made via Energy suspension, which is now in use. The way it works is rather simple, it essentially mounts to the differential via 4 of the cover screws and then affixes to the subframe via a custom insert nut and sleeve system in the drain holes located just inside of the rear subframe to body mounts. It does it's job by restricting the differential from rotational movement under load. Wheel hop is created by a reactive effect of a multitude of areas. the first being the tires as the fight for grip-all this rotational loading is applied back to the differential-which is receiving steady power in via the propeller shaft. The resulted reaction is a push-pull effect which is where the 3-point system shows it's weakness. The passenger side will then bounce up and down creating a tramping effect, which transfers back to the wheels and the suspension will amplify this motion via the springs. that's how wheel hop works, and why it's prevalent to some with higher output and more aggresive driving styles. It's interesting to note that these effects can be tamed slightly via stiffer suspensions/ coil-overs on some cars, alignment plays a role-but none of those solutions solve the core of the issue, they're simply band-aid approaches. If you drive your car in a way that hop doesn't present itself then obviously this product isn't for you, I'm not here to argue why every M3 needs one, because they don't. Those of you who do experience these issues are whom the product was intended for,plain and simple. Results so far have been very positive, I understand we live in a suspicious and proof thirsty world(I'm probably worse in regards to skepticism than most of you, so I can understand)
As far as shift feel goes, the same benefits apply to DCT or MT6 cars. Restriction of unwanted movement results in tighter upshifts and stability regardless of transmission type. As far as track testing is concerned, It's winter here in PA so that's currently impossible although proper before/after documentation will come in the spring.If there's any specific data anyone would like to see, feel free to ask.
The brace shown in the OP's pic is one of 3 variants, it is the "plate" style. Next in line is the 4130 chromoly tubular version, which is lighter obviously. I'm currently working on a limited run of Titanium braces which will be a numbered production run. These are all currently made to order, I will post pictures of the other versions as they are made, which will be within the next week or so. Any other questions you may have, feel free to ask me via post/PM. I will inquire into vendor fees before discussing sales here.
Thanks Rick@Defiv Fabrication.
Rick,

Maybe you can also comment on my above questions in regards to the difference between this solution and a Solid rear subframe. Would appreciate your input.

In addition to those questions, I noticed you discussed suspension as one of the contributing factors to creating the wheel hop. You mentioned that the suspension "amplifi[es] this motion via the springs." Do you find that that stiffer suspension (such as KW clubsports) minimize this motion/effect? If so, does this product still offer a worthwhile/noticeable improvement in wheel hop for a car that is equipped with a stiffer suspension.

I'm also curious to know (1) the weights of each of these units using each of the differing materials you mentioned (including Titanium) and (2) the prices for each of the differing materials (again including Titainum). If you're not comfortable mentioning price here in the open forums, feel free to PM me with pricing information.

Thanks to all. And sorry for the inexperienced question.


- esquire
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