Multi variant ramps as the most significant upgrade for BMW ZF LSD besides clutch plates
March 29, 20233 min read
To understand why multiple options of ramp angles is so important upgrade of ZF LSD unit found in Alfa Romeo, BMW, Audi, Lamborghini, Ferrari, Porsche etc. you have to completely understand the concept of ramp angles in the Limited slip differential. This text explains all you need to know and it takes only5 minutes of your time.
ZF designed one of the most advanced clutch-type LSD systems of all time. If you look cross section of the LSD unit from a side, you'll find spider gears wrapped in pressure plates in the middle. Clutch plates with Belleville washers are based on each side of pressure plates. Pressure plates contains ledges (ramp angles) where cross pins come out. You can imagine that as cuts on ashtray where you rest the cigar. But if you look closely, you'll see that those ledges are not radially shaped like cross pins. They look like small triangles tangentially to central pins. The angle between this tangent (ramp angle) and Y axis is called ramp angle.
What do ramp angles do in the LSD?
Their job is to create additional pressure to clutch plates progressively increasing lock percentage. When you press the throttle, central pins tend to rotate apart from pressure plates. Like they want to get out of their ledges. The force of central pins is transferred to clutches through ramp angles by vector decomposition. In other words, part of the force on Y axis gets transferred to X axis thanks to ramp angle. And X axis force is the one putting pressure to clutches. So, the sharper ramp angle is, the greater X axis force gets by the principle of vector decomposition. The same process is happening when you release the throttle or shift in the lower gear.
The shape of ramp angles divides clutch-type diffs into 3 following categories which you must have already heard of:
2-way LSD (throttle ramp angle and coast ramp angle are the same)
1.5-way LSD (Throttle ramp angle is bigger than coast)
1-way LSD (Coast ramp angle is 0°)
Why RacingDiffs multi Variant ramps are so much better?
You see, factory pressure plates contains only 1 ramp angle combination. For example BMW uses 45°/45° rampsin their ZF unitsand that's it. So if you want your diff to be more aggressive on throttle and less aggressive on engine breaking, you need asymmetric ramp angles which aren't offered as option in factory LSD.
30/30 - drift setup (the most aggressive setup, great for drifting. 1st choice of pro-level drifters)
30/60 - mixed setup (less aggressive on down shifts, excellent for Hill climb, tarmac and gravel rally. Can also be used for drifting to get smoother transitions. The best option for less experienced drifters)
50/65 - circuit setup (The best option for any kind of grip driving as it provides smooth lockup. The 1st choice of time attack builders)
Now you see why Multi Variant ramps are so important - because you have all those combinations on 1 pressure plate. All you need to do is to switch position of cross pins to get different ramp angle setup. This way you save a lot of money too, as you don't need to buy different pressure plates. RacingDiffs Multi variant pressure plates are 3 in 1.
If you have any additional questions, or you wish some custom ramp angle design, please feel free to contact us.