Last post on Mar 24, 2008 at 9:20 AM
You are in the Sedans
What is this discussion about?
Acura RL, Audi A6, BMW 5 Series, Cadillac STS, Cadillac CTS, Infiniti M35, Infiniti M45, Lexus GS 300, Lexus IS 350, Sedan
#98 of 102 Re: But.... [unlimitedjoe]
Jan 08, 2008 (3:23 am)
because audi racing would beg to differ, they are banned from most events.
I can concede that a highly sophisticated, lightweight race car version of AWD might be an advantage on some tracks. Just like a thumb activated SMG gearbox has an advantage in keeping both hands on the wheel as you try to negotiate 3 g hairpin turns. But I still prefer a three pedal manual in a sports car that is "only" capable of 1.0 g's. Race car analogies have their limitations. Otherwise, Goodyear would be trying to sell racing slicks to AWD sedan buyers gullible enough to think that because Shumacher uses them, they must be right for the street.
I don't know the full story of Audi and why, at least by your posts, they seem to be beating their head against the rules of Formula One or whatever circuit(s) you are referring to. There are tons of rules about what you can and can't do that all of the automakers have to comply with. And, if you recall, its been 20 years since the AWD Porsche 959 was introduced and obliterated everybody in a few racing contests, including Audi, I believe.
My issue with Audi is similar to my issue with Acura. They both clearly have some extraordinary engineering talent from their racing division. But that talent hasn't made its way into street production cars to the extent I would like. Rather than applaud Audi for having a race car that doesn't compy with the rules, perhaps you and others should encourage Audi to take some of that technology into the showrooms. There is no reason, IMO, that a two seat "sports car" should weigh 650 lbs more than my old 1995 Nissan Maxima, AWD notwithstanding. For my part, I'll try to encourage Acura to do something with their engineering prowess other than just the Honda S2000. Like a RWD TL or a flagship RL that actually performs like a flagship and not a gussied up Accord, SH-AWD notwithstanding.
So many problems to fix and so little time.
#99 of 102 Re: But.... [habitat1]
Jan 08, 2008 (7:26 pm)
was basically replying to wwest on his superior comment, so if you care to surf the web on audi racing and there history, be my guest, maybe youll come to a different conclusion on superiority then me.
sorry that the R8 & RS4 dosent cut it for you, and personaly i appreciate the great bang for the buck on the S2000, but not into convertables, but my wife is, has TT quattro.
getting back to great bangs for the buck, for me i feel the GT-R (and to show you i do have an appreciation to rwd) the Z06 are dynamite bangs for a buck, especialy comparing it to the GT2, which is a 100k more.( out of my league.)
but to each his own.
oh yea, my cars all have three pedals
as for me, not to many problems to fix, just to little time to have fun with.
#100 of 102 Re: But.... [unlimitedjoe]
Jan 10, 2008 (9:33 am)
Again, my ideal AWD design would be one that distributes engine torque as a function of roadbed traction capability. Heavier in the front, fine, more torque to the front appropreate to weight biasing.
But just as soon a lateral forces begin to build I want engine traction, leading or lagging, removed from the front in order to dedicate front tire traction to directional control. Apportioning engine torque to the front inverse to lateral forces would be perfectly fine, IMMHO.
It appears to me that the 4runner AWD mode does exactly that, and maybe the Acura SH-AWD system.
#101 of 102 Re: But.... [wwest]
Mar 23, 2008 (4:50 pm)
You are totally right in your appreciations, because the awd mode of the 4runner is a torsen certen differential, just like quattro of audi. The main characteristic of this diff is that it`s internal friction an oposition to un-locking, when cornering, make it change the torque split from an initial 50:50 (or 40:60), to a more rear biased distribution, up to 25:75(the more you turn, more power and retention is taken away from the front wheels and send to the rear). This is caused by the high speed of the front diff in corners due to the need of the front wheels to move faster, because they have to make a longer path than rear wheels. The torsen absorbs this higher front diff spee, but offers a great resistance to un-lock, so the internal friction tries constantly to acelerate the rear wheels sending more power to the rear diff. That`s why an RS4 under a very wet track with low traction tends to oversteer under heavy aceleration.
This behavior of the torsen is purely mechanical.
The SH AWD system is a very complex system, wich uses a multi-plate clutch to engage the rear diff(just like like haldex, in this case with a 70-30 torque split on normal), but unlike haldex and other Front biased AWD systems, between the multiplate clutch and the rear diff, there is a planetary gear set, that absorbs the speed diference between front and rear diff, but tries to acellerate the rear wheels.
The only thing that doesn`t make sense about the SH-AWD is how can split torque up to 30:70 if there is no center differential and the front diff is always fully connected to the transmission. in theory when the clutch is fully locked no more than fifty percent of the torque can go to the rear wheels
#102 of 102 Re: But.... [nisis]
Mar 24, 2008 (9:20 am)
Only the sedan has the planetary gearset in series with the rear driveline. The SUVs have a fixed overdrive ratio to the rear driveline. It is this overdrive ratio, variable in the case of the sedan, that allows for more than 50% being apportioned to the rear.
Basically with the rear left and right clutch paks locked the rear wheels turn ~5-15% faster that the front wheels. Not something that can be done on a constant basis but certainly quite viable for adverse/slippery roadbed conditions, applied only to the outside rear wheel when turning, or even brief periods of hard acceleration.