After countless hours of searching for information on the AHK steering assist system, I still have not obtained alot of knowledge on this rare option. I've seen that they were only avalible for the CSI's in the European market, however I see some claiming that their later model 840's and 850's came with this expensive option, considering the time and the cost of $7-8500. What all components came with the AHK option from the factory?

Also I am seeing that the DSC was taken out in order for the EDC due to AHK componets, but why? Obviously it would be alot of trouble, but could someone swap AHK components into an E31 that did not come with this option and if so, what would have to be replaced/removed?

Here's a video that I found of AHK in the works.

http://www.youtube.com/watch?v=1zX5dQkb-xQ&feature=related

AHK was offered on all German (European) models, but being so expensive, noty that many have it.
AHK is a pain in the ass. I know of one EURO CSi here that has been trying to get this thing to work properly. QUite frankly, not worth the effort, time or money.

PS. The video above shows the AHK in extreme motion (I believe it was connected to an external pump and valving to take this video - the actual unit acts less "aggresive".

I've seen that they were only avalible for the CSI's in the European market, however I see some claiming that their later model 840's and 850's came with this expensive option, considering the time and the cost of $7-8500.
Correction: AHK was introduced with and standard on the Euro 850CSI, but it was also an option for the rest of the 8 Series. However, as you found out, the price was steep so a non-CSi with AHK is rare - but they do exist. Jud (8coupe.com (http://www.8coupe.com/)) can probably give you some numbers.

Also I am seeing that the DSC was taken out in order for the EDC due to AHK componets, but why?DSC was introduced with the M73. The earlier cars including the CSi don't have DSC but ASC or ASC+T. As far as I know the M73 cannot be equipped with AHK.

Obviously it would be alot of trouble, but could someone swap AHK components into an E31 that did not come with this option and if so, what would have to be replaced/removed?
It will be a lot cheaper to buy a car with AHK than a swap...

Really? Why can't M73's get it? If 840s can have it, and they have the same (ok only some depending on year both have the) 5HP30 and diff....why can't the M73s have it??

AHK was offered on all German (European) models, but being so expensive, noty that many have it.
AHK is a pain in the ass. I know of one EURO CSi here that has been trying to get this thing to work properly. QUite frankly, not worth the effort, time or money.

PS. The video above shows the AHK in extreme motion (I believe it was connected to an external pump and valving to take this video - the actual unit acts less "aggresive".

Yeah, its in extreme motion because the car isn't in motion, I don't think you'd turn the rear wheels 90 degrees in a turn unless you were driving the Nurb :lol Neither do I think a conversion is worth the money, however worth the time. Not many of us track these cars, but on RF, someone installed the AHK and they passed M3's, miatas, etc on the track because this option gives SERIOUS grip. They describe it as if your carving the actual turn to your specifications because its so in line.

Really? Why can't M73's get it? If 840s can have it, and they have the same (ok only some depending on year both have the) 5HP30 and diff....why can't the M73s have it??

Same thing I was thinking, afterall the owners of Eurospec E31's who claimed to have AHK owned later model 8er's. With the M73 being a later model :rolleyes I'm not sure, but most of the components on the V8 are on the V12 like the diff, rotors, etc. With the CSI, DSC wasn't really needed because what was the main purpose of BMW recreating this autobahn crusier into something that was irregular compared to the "normal" E31's? PERFORMANCE which is why they recieved AHK in the first place LOL...

so what does this do?

so what does this do?

The 4 wheel steering system offers increased agility, statability, and confidence while cornering at higher speeds. Also, it can be used as parking assistance but that was not BMW's focus or reason to including this option on the CSI.

Really? Why can't M73's get it? If 840s can have it, and they have the same (ok only some depending on year both have the) 5HP30 and diff....why can't the M73s have it??
This may need some further investigation, but Jud can probably answer the question right away. I just recall that from a forum thread a long time ago at clube31.de (http://www.clube31.de/). The information in that thread may have been incorrect or I may have mixed up some facts after all those years...

Not many of us track these cars, but on RF, someone installed the AHK and they passed M3's, miatas, etc on the track because this option gives SERIOUS grip.
That's bull-shit. AHK will improve stability on the turn-in, but it will not in any way increase the cornering speed. You can perform a more aggressive turn-in without losing the rear. The car feels more nimble. It's as if the car weighs less than it actually does... which is of course impossible and once in the turn the car's weight just pulls you out of the corner as hard as a non-AHK E31.

In other words, AHK is not for going faster around corners. It's a safety mechanism, like DSC, to keep inexperienced drivers from rear-ending the car after a sudden steering maneuver.

With the CSI, DSC wasn't really needed because what was the main purpose of BMW recreating this autobahn crusier into something that was irregular compared to the "normal" E31's? PERFORMANCE which is why they recieved AHK in the first place LOL...If performance was the key point in the 850CSi development process, the car would have gotten a modern V12 with 4 overhead cams.

DSC was not available at the time of introduction. AHK was introduced and marketed as a safety mechanism. And it works great for that purpose. However, AHK was expensive, complex, prone to failures,... In the mid nineties Bosch introduced ESC (relabeled by BMW as DSC). DSC takes a different approach to increasing stability. Unlike AHK which controls only one aspect of instability during turn-in, DSC controls many aspects. And best of all, it requires almost no additional exotic hardware (like the hydraulic rear axle for AHK), thus it can be produced cheap. BMW never looked back at AHK (*)... Why should they?

Is AHK bad? No, it works great. Probably even better than DSC in correcting stability on the turn-in. But it increases the cost of a car considerably while improving only one point, where DSC improves the stability at many points.

*: AHK made a reappearance in the latest 7 Series. The main goal here is to decrease the turning circle (where the rear wheels steer in opposite direction of the front wheels). Although there's no technical reason why the E31 AHK shouldn't be capable of that, BMW decided against it. The E31 AHK offers only high speed maneuvering stability (the rear wheels steer in the same direction as the front wheels).

so what does this do?
Ever considered using the search? It's been discussed to death... 4 wheel steering? (http://forums.bimmerforums.com/forum/showpost.php?p=15276162&postcount=4)

That's bull-shit. AHK will improve stability on the turn-in, but it will not in any way increase the cornering speed. You can perform a more aggressive turn-in without losing the rear. The car feels more nimble. It's as if the car weighs less than it actually does... which is of course impossible and once in the turn the car's weight just pulls you out of the corner as hard as a non-AHK E31.

In other words, AHK is not for going faster around corners. It's a safety mechanism, like DSC, to keep inexperienced drivers from rear-ending the car after a sudden steering maneuver.

No, your speaking ignorance! Coming from the owner, I think I'd value his imput more than yours but thanks for entertaining us:

K-Bar equiped AHK E31 experiance http://forums.roadfly.com/forums/bmw/bmw-8-series-e31/forum.php?postid=4056134&page=2

No, your speaking ignorance! Coming from the owner, I think I'd value his imput more than yours but thanks for entertaining us:

K-Bar equiped AHK E31 experiance http://forums.roadfly.com/forums/bmw/bmw-8-series-e31/forum.php?postid=4056134&page=2

Be careful with what you believe from reading posts from "an owner". My experience is that alot of "owners" here really don't know what makes their car tick. Revtor is correct with the improved stability on the turn in. The laws of physics are not different for AHK and non-AHK cars.
AHK was the ultimate in stability control. If you have actually done your "homework" you will realize that the E31 already comes with a type of "passive" rear "steering" with the stock suspension set-up.
Remember, the E31 was the ultimate Autobahn cruiser, and as such was outfitted with the most modern (for the time) safety stuff.
AHK was never meant as "parking assistance" - you are think of the General Motors "Quadra-Steer" that was found on GMC and Chevy trucks. Now that was for parking and manuvering assistance.

Be careful with what you believe from reading posts from "an owner". My experience is that alot of "owners" here really don't know what makes their car tick. Revtor is correct with the improved stability on the turn in. The laws of physics are not different for AHK and non-AHK cars.
AHK was the ultimate in stability control. If you have actually done your "homework" you will realize that the E31 already comes with a type of "passive" rear "steering" with the stock suspension set-up.
Remember, the E31 was the ultimate Autobahn cruiser, and as such was outfitted with the most modern (for the time) safety stuff.
AHK was never meant as "parking assistance" - you are think of the General Motors "Quadra-Steer" that was found on GMC and Chevy trucks. Now that was for parking and manuvering assistance.

Yes, earlier in a post, I said it increased stability in turns as well as confidence while cornering at higher speeds which makes your car faster because you have more of a feel, sort of when you get the CSI brake calipers and go out to a track, your times decrease because you have more feel and confidence knowing that you can stop later. I'd read a couple of statements from the owners who have the AHK, but that specific link dealt with the K-bars in addition to the AHK system. I know if came with some type of passive rear steering assistance components with the stock set up, however the AHK took it a step further.

Also, I wasn't thinking about the "Quadra-steer". Why would BMW have the AHK do up to 90 degree turns at the rear wheels if parking also weren't in mind:rolleyes

http://en.wikipedia.org/wiki/Steering
http://www.youtube.com/watch?v=h8MB1m9SbFY

http://www.ntpog.org/gallery/stills/3gen21.jpg

Lol...loving the Ricer comparison

Actually the prelude AWS is far more reliable 88 thru 91.

my 1993 850ci had AHK 1 of 99 none csi in the uk .
I took it to the main stealers and they showed me it operating via the diagnostics port under the bonnet.
Congratulations on acquiring the Koenig 850. Now you have a pair of Red 8’s.

Per ClubE31, attached are the build sheets for your vehicles.

I noted that CB57974 has the special 850CSi bits (see build sheet, option code 237 – AHK). As an aside, to help prop up sagging sales for the 1993-94 model year RHD M70 850i/Ci, BMW UK ordered CSi bits to be placed in 99 cars delivered to the UK, including AHK all-wheel steering. Of the 632 M70 RHD 850i/CiA’s delivered to the UK, only 99 cars were outfitted with the 850CSi bits (15.7%).

You have two special 8’s.

I invite you to visit 8Coupe.com and register you and your cars in the registry:
http://www.8coupe.com/register.htm (http://www.8coupe.com/register.htm)
(note: you can register one car per username, but use the same email address)

Regards,

Jud Spencer
E31 Registry Agent
www.8coupe.com (http://www.8coupe.com/)

No, your speaking ignorance! Coming from the owner, I think I'd value his imput more than yours but thanks for entertaining us:
I know what I speak of. Just for your information; I own a AHK equipped car and I've driven quite a few non-AHK equipped cars. What I wrote is exactly what BMW was saying back in the days. I guess they didn't know their own car? Of course you are free who to believe.

Like TxGR8White said, the "regular" 8 Series are also equipped with a steering rear axle - but passive (just as many other modern cars). The passive multi-link rear axle is of course slower in reactions and has a lesser degree of correction. Passive rear axles operate on the forces induced upon them by the weight shift on a turn-in. AHK is better in the aspect that it can react before those forces have built up. But otherwise the principle is the same. There are some technical documents floating around the web on the multi-link rear axle, describing its working.

And while the owner you refer to may have been lyrical about AHK and tracking, that's not everyone's opinion. For example, Rainer H. - who is probably not known here but he is an E31 legend in Germany - tracked the CSi in Dijon and called the AHK system "Scheiße" for driving on the edge because it made it very vague where the edge actually was.

The latter is a problem with all these stability systems (AHK, DSC and whatever is out there): They give a false feeling of control over the car. The car is rock stable (*) until the edge because it supresses all warnings of instability. Once the electronics can no longer compensate, it's back up to you to correct the instability, but that's usually at a point when it's way too late... The primary goal of all these systems is to make the car safer for inexperienced drivers in emergency situations. Not to make it faster or a better track toy. The systems may boost the confidence of the driver, but I'm not sure that's is a good thing. That's not what they have been designed for.
*: Rock stable may not be the best word to describe it. An experienced driver will feel the stability control working, but the system masks what the car is doing, making it very difficult to anticipate when the system goes beyond its degree of correction.

Does that make drifting and controlling the car beyond the edge impossible? Not at all! If you deliberately push the car into oversteer, the car controls very well and behaves predictable. Flicking it in a turn to get in a drift requires a bit more effort because of AHK, but inducing a drift by applying throttle is just as easy as in a car without AHK - AHK has no effect here. But in both cases you expect it to oversteer and anticipate for it. It's completely different when the stability control gives up and leaves it to you when you don't expect it.

Will the 850CSi put a miserable performance down on the track? Not at all! But saying you beat M3's, WRX's, and Esprits says more about the other drivers than the 850CSi's performance. A two ton heavy battle cruiser can never match the cornering speed of a lighter car unless the CSi had really, really, really wide tires in comparison to the rest of the pack, the track contained mainly long straights and only a few low speed bends, or more likely... the other drivers didn't push their cars.

Please, also note that neither Paul, nor Greg K mention AHK as reason for the success that day (but rather the choice of tires, brakes, K-bars,... and of course his instructor). So what makes you think it's because of AHK he was quicker?

Also, I wasn't thinking about the "Quadra-steer". Why would BMW have the AHK do up to 90 degree turns at the rear wheels if parking also weren't in mind:rolleyes
Most four-wheel steering applications have the rear wheels turn only a few degrees. That's enough to make the turning radius a lot smaller. The extent to which AHK can turn the rear wheels is plenty for a parking assist system. In fact some of the early articles about the 8 Series mention AHK (by then still not introduced) as a parking assist system (and high speed maneuvering stability control). So it seems BMW did have parking assistance in mind, but for some reason they decided to drop it. The most heard explanation is safety issues, but if the Japanese could do it I don't see why BMW shouldn't...

PS: You should not always blindly believe what someone writes or says (that also goes for what I write of course). I'm not saying everyone is a liar or misinformed, but just like TxGR8White writes, many people don't know what some systems in their car actually do. A nice example of this is the well known review (http://forums.bimmerforums.com/forum/showpost.php?p=14594796&postcount=18) of the dakar yellow 850CSi (owned by Peter Rice of the UK E31 community). At a certain moment, the reviewer describes the EML switch as "sport and comfort settings for the suspension and throttle control". Perhaps he was misinformed, but there is no EDC suspension control on the CSi (EDC was not even available as an option). But later in the review he switches from K (comfort) to S (sport) while driving and claims "all the dampers become firmer ... so it unleashes a whole new echelon of performance and handling". The point here is that even thinking the switch affects the suspension makes you feel it (or at least think you feel it), while in reality there is not even a link between the switch and the suspension! And that's someone who reviews cars for a living. You'd expect he'd know when the handling changes...

Very nice Revtor, a nice read of real world information.... thanks.

I know what I speak of. Just for your information; I own a AHK equipped car and I've driven quite a few non-AHK equipped cars. What I wrote is exactly what BMW was saying back in the days. I guess they didn't know their own car? Of course you are free who to believe.

Like TxGR8White said, the "regular" 8 Series are also equipped with a steering rear axle - but passive (just as many other modern cars). The passive multi-link rear axle is of course slower in reactions and has a lesser degree of correction. Passive rear axles operate on the forces induced upon them by the weight shift on a turn-in. AHK is better in the aspect that it can react before those forces have built up. But otherwise the principle is the same. There are some technical documents floating around the web on the multi-link rear axle, describing its working.

And while the owner you refer to may have been lyrical about AHK and tracking, that's not everyone's opinion. For example, Rainer H. - who is probably not known here but he is an E31 legend in Germany - tracked the CSi in Dijon and called the AHK system "Scheiße" for driving on the edge because it made it very vague where the edge actually was.

The latter is a problem with all these stability systems (AHK, DSC and whatever is out there): They give a false feeling of control over the car. The car is rock stable (*) until the edge because it supresses all warnings of instability. Once the electronics can no longer compensate, it's back up to you to correct the instability, but that's usually at a point when it's way too late... The primary goal of all these systems is to make the car safer for inexperienced drivers in emergency situations. Not to make it faster or a better track toy. The systems may boost the confidence of the driver, but I'm not sure that's is a good thing. That's not what they have been designed for.
*: Rock stable may not be the best word to describe it. An experienced driver will feel the stability control working, but the system masks what the car is doing, making it very difficult to anticipate when the system goes beyond its degree of correction.

Does that make drifting and controlling the car beyond the edge impossible? Not at all! If you deliberately push the car into oversteer, the car controls very well and behaves predictable. Flicking it in a turn to get in a drift requires a bit more effort because of AHK, but inducing a drift by applying throttle is just as easy as in a car without AHK - AHK has no effect here. But in both cases you expect it to oversteer and anticipate for it. It's completely different when the stability control gives up and leaves it to you when you don't expect it.

Will the 850CSi put a miserable performance down on the track? Not at all! But saying you beat M3's, WRX's, and Esprits says more about the other drivers than the 850CSi's performance. A two ton heavy battle cruiser can never match the cornering speed of a lighter car unless the CSi had really, really, really wide tires in comparison to the rest of the pack, the track contained mainly long straights and only a few low speed bends, or more likely... the other drivers didn't push their cars.

Please, also note that neither Paul, nor Greg K mention AHK as reason for the success that day (but rather the choice of tires, brakes, K-bars,... and of course his instructor). So what makes you think it's because of AHK he was quicker?


Most four-wheel steering applications have the rear wheels turn only a few degrees. That's enough to make the turning radius a lot smaller. The extent to which AHK can turn the rear wheels is plenty for a parking assist system. In fact some of the early articles about the 8 Series mention AHK (by then still not introduced) as a parking assist system (and high speed maneuvering stability control). So it seems BMW did have parking assistance in mind, but for some reason they decided to drop it. The most heard explanation is safety issues, but if the Japanese could do it I don't see why BMW shouldn't...

PS: You should not always blindly believe what someone writes or says (that also goes for what I write of course). I'm not saying everyone is a liar or misinformed, but just like TxGR8White writes, many people don't know what some systems in their car actually do. A nice example of this is the well known review (http://forums.bimmerforums.com/forum/showpost.php?p=14594796&postcount=18) of the dakar yellow 850CSi (owned by Peter Rice of the UK E31 community). At a certain moment, the reviewer describes the EML switch as "sport and comfort settings for the suspension and throttle control". Perhaps he was misinformed, but there is no EDC suspension control on the CSi (EDC was not even available as an option). But later in the review he switches from K (comfort) to S (sport) while driving and claims "all the dampers become firmer ... so it unleashes a whole new echelon of performance and handling". The point here is that even thinking the switch affects the suspension makes you feel it (or at least think you feel it), while in reality there is not even a link between the switch and the suspension! And that's someone who reviews cars for a living. You'd expect he'd know when the handling changes...

Now, this is some great information Revtor:buttrock

I have to commend you on this. The articles I read on the AHK were from owners who have tracked the car. It's not as if I read one thread and said, "this is so awsome, I bet it's faster than M3's around the track." I read about 4 which described the AHK's abilities to give confidence and assistance, as you said, to drivers. I took it into account because of the similar descriptions of the handling aspects from the cars. But, as you said, the other drivers of the M3, etc could have been inexperianced. Either way, no arguing, just taking in information:cool

And while the owner you refer to may have been lyrical about AHK and tracking, that's not everyone's opinion. For example, Rainer H. - who is probably not known here but he is an E31 legend in Germany - tracked the CSi in Dijon and called the AHK system "Scheiße" for driving on the edge because it made it very vague where the edge actually was.

As long as living legend Rainer doesn´t posses it it´s "Sch..." - but be sure that if he had it it was heaven on earth! :stickoutt

The spoon of wisdom that he´s got wasn´t half as big as he claims or have you ever heard of the racedriver Rainer_H? :nono

No question that he knows a lot about the 8, but he´s a storyteller too!

As long as living legend Rainer doesn´t posses it it´s "Sch..." - but be sure that if he had it it was heaven on earth! :stickoutt
The spoon of wisdom that he´s got wasn´t half as big as he claims or have you ever heard of the racedriver Rainer_H? :nono
No question that he knows a lot about the 8, but he´s a storyteller too!Haha, certainly truth in that! :D. But then again, which professional (or even amateur) race driver does race an E31 on a regular base? Only idiots would choose an old and nearly two tons heavy GT for competition racing (I don't consider a few hours of fun at a track day racing), or they would modify the car to such extent it only shares the looks of the E31 (like Toni Nieminen). Face it, the E31 - even the 850CSi - was never meant for racing. It's an Autobahn cruiser, and a damn fine one. The 850CSi may have sports car manners, but it's no match for cars like the M3.

Personally I think AHK is a great system, but you should relativize it and not give it mythical proportions... It can certainly save the day in emergency situations - that's what it was designed for. AHK is special in the aspect it makes the car feel less heavy and more nimble during agressive maneuvers, but even though it may seem so it cannot defy the laws of physics. The car still weighs just as much as with AHK disabled. And simply put, weight and grip are what limits the cornering speed. AHK may help to keep the car stable on the turn-in (which is of course an important factor when cornering), but it won't increase the speed through the turn.


New post but automerged by the forum


For those who are interested in how the 850CSi handles in comparison with a few other cars, here's an excerpt from an article in the August 1996 edition of "Auto Motor und Sport" (a well known German car magazine). I've translated the table headers so it's understandable to non-German readers:

http://tweakers.net/ext/f/XMWcOqMbbT2D9GL4UFqFw6kh/full.png

I wish there would have been more direct competitors to the 850CSi in the test (like the Porsche 928) and a more diverse field of sports cars (including BMW M series), but the test clearly highlights where AHK excels at.

The tests where sudden weight transfers occur are the 850CSi's playground. The car performs very well in the short 36 meter slalom, but puts down an amazing performance in the high speed moose test (http://en.wikipedia.org/wiki/Moose_test) - beating the over 500 kg less heavy Porsches and Ferrari. This is AHK at work! This is what makes the 850CSi feel so nimble despite the huge weight.

The cornering speed at the 205 meter skidpad shows an average performance. Considering all cars that beat the 850CSi are at least 500 kg less heavy, it still looks like an impressive achievement. But, it must be noted that the 850CSi had much, much wider tires than the Citroën Xantia and Fiat Coupé. Wider tires mean more grip and thus a higher cornering speed. The only car with comparable tire sizes which performs less good is the Mercedes 600S, but it weighs 200 kg more than the CSi and that's clearly visible in its performance. The reason the 850CSi can't put itself on the top of the table here is simple. AHK slows down weight transfers that occur when maneuvering, but once in the turn the center of gravity remains stable. In other words, AHK has no effect once in the turn and thus it cannot increase the cornering speed. Only the wider tires and perhaps a better suspension make it up.

Thanks to Reinhard from 8er.org (http://www.8er.org/) for pointing me at this article. I had almost forgotten it existed!