What you guys running on diff ramp angles?
Also, just found this, which is pretty interesting.
https://racingdiffs.com/collections/...ation-ramp-set
I likely need to replace my clutch disks, but I currently have the stock ramp angles (45/45).
So far all I have played with with the BMW is replacing clutch plates and increasing initial preload.
I've been happy with that so far.
Too much lock up can promote understeer under moderate throttle.
The stock diff goes open on deceleration. The increase of lock up on deceleration can help with trailing throttle oversteer.
I used a full 1.5 way rear diff in my EVO as a throttle lift with steering input would give a bit of yaw to help it turn.
The stock 45/45 ramps on a BMW mean it's a 2-way diff that doesn't open up on decel. If it was a 90 degree ramp, then it would be open.
With a 60 degree decel ramp, it would have less lock up than a factory diff and reduce understeer.
4 clutch (and preload) changes that. I have read, lockup percentage changes linearly with # clutches.
45/45 with 2 clutches provides 25% lockup. So 45/45 with 4 clutches would provide 50% lockup. Now, go from 45 ramp to 60 deg and it gets reduced by some amount. Geometry and physics is needed. It's either sine or cosine of the angle...researching cause I kinda want to know.
Last edited by aeronaut; 02-02-2023 at 01:15 PM.
Yeah if you need ramps done, have diffsonline do it. He's a real motorsport expert doing diffs for Bimmerworld, your ramps will be properly CNC cut and then heat treated (just cutting out a notch is not enough when you have a case hardened pin riding in them).
I have 30/85 on mine and I love it but I wouldn't recommend it for someone without added rear downforce or a need for tail-happiness. It makes the car easy to steer with throttle on overrun because if I suddenly lift at turn-in, the rear will step out but with a lot of wang in the back, it's super predictable. I can also see it being amazing for auto-x or really tight tracks. Otherwise, and if you've got stock-ish aero I'd go with 30/60.
+1 for Diffsonline.
I've sourced all my diff parts from them.
It seems the diff in my E36 M3 race car has finally worn out. Got lots of inside wheel spin during my last race weekend. Did the grass/asphalt acceleration test and same result. I bought the car in 2014 and the same diff has been in there since long before I owned it.
Diffsonline seems the go-to source. I know I want a 3.73 but would appreciate feedback here on ramp angles. Diffsonline offers 45/45, 35/60 and 30/90 among their 3-clutch options. A little about the car and my usage:
1. Full race car with 700-850 lb springs, 3+deg camber, typical low ride height for race car, modest amount of aero (V2 wing and 4-inch splitter), 2950 comp weight.
2. Tires are R7 lately (225 or 245). Can't run full slicks in my class.
3. Home track has some fast sweepers (90-100 MPH) and some medium speed turns (50-80) that have a big imapct on lap times. Lately I've gotten a bit of push when accelerating out of the medium speed turns. Not sure if this had anything to do with worn diff clutches or just running slightly faster laps. Asphalt on home track is decently grippy.
Not sure if this is enough info, but what ramps angles would you guys recommend? Is it worth it to polish the gears and bearings? Whatever I get, I'd like it to last a long time in addition to performing well.
I run a 6-clutch (three per side) Drexler LSD with 50/40 ramp angles and 3.91 gearing. I couldn't be happier how it performs.
Feff
All I can add, is to spend the money now.
I'd go 4 clutch (which will change the ramp angle numbers), the diff will last longer between refreshes.
(My 3 clutch lasted 3 years of heavy use.)
Ouch. 3 years. How much did it cost to refresh?
On my list of to-do. I may just replace the clutches ("easy" DIY).
Or....re-gear/4 clutch/change ramps.
Diffsonline 30/90 full race carrier. We have a 4.44 main, and 3.91 spare. The 4.44 is like a rocket ... awesome paired with a 6 speed. The 30/90 split ramps are odd to get used to, but once you do, you'll wonder how anyone else takes a corner without it. It's like a magic slingshot.
I can see why you'd need a 6-speed to run such low gearing in the diff. I have a 5-speed and with my 3.91 I run out of RPMs before the braking zone on the main straight of my home track if I get a good run through the preceding turn. Coasting in those last 100 feet is no fun
Diffsonline only shows one option for 4-clutch: 35/60. Maybe I should just get that one, since then I won't have to decide what ramp angles to get! If the 4-clutch option lasts longer, that may be reason enough alone to go that route if it'll perform adequately for my circumstances.
I've done some brief reading and I think I understand the relationship between ramp angle and lockup proclivity, but I have zero clue as to what the practical difference is between 35/60 and 30/90 (to pick just two examples) - what circumstances/objectives would drive you to choose one over the other.
I'm not sure what sort of magic Dan builds, but we've only had to have 1 rebuild over 10 years of racing this 4.44, and I think that was just bearings? ... but I believe 30/90 means that the ramps are 30* accel and 90* decel. That means, on decel, basically 0 lockup, and on accel, very aggressive lock. Our car feels very neutral coming into a turn, then when you get on the throttle, it pull around the corner. You can get on super early, and just ride it out. Feels like the ass end wants to come around, but stay in it, and it just goes. Like I said, magic slingshot
I spoke to a fellow racer at my local track whose car is quite well optimized. He has the 4-clutch diff from diffsonline. Also spoke to Dan at diffsonline, who recommended the 4-clutch option without hesitation after asking me about the car and the characteristics of my home track.
New 3.73, 4-clutch diff from diffsonline went into the car yesterday. Can't wait to see how she does on track next month.
Bookmarks