Direct (parametric) steering

[eng622]

I read this was a relatively cheap option fitted to a number of Merc models. I'm looking to buy a 350SLK circa 2005 with it fitted as from what I read it is woth every penny. So how would I know if it is fitted?
Is it a software upgrade on the standard electric unit providing the speed sensitivity?
And all important can it be retrofitted if the car comes without it?
Owners opinions on how good it is also sought

 

[Mactech]

Parameter steering is fitted to quite a few Mercedes now. As the name implies it takes input from both the load applied to the steering wheel and the road speed to give the desired level of assistance to the steering effort.
I'm not aware that it can be retro fitted, but I think you'll will find the human brain remarkably adaptive and if you are new to the car you may not miss it.
I've had E Class with and without an after a few miles you adapt and think nothing more of it.
When electronic steering came to race cars we tried lots of different 'maps' but always came back to a direct relationship of hand wheel effort to power assistance. But then you don't try to park racecars in tight spots! (often)

 

[renault12ts]

I have it, and it is very nice, especially compared to an A Class I had on loan which didn't have it...the A Class was heavy.

 

[crockers]

I have it - so used to it I don't know it's there.....until I drive my wife's Honda which is sooooo light all the time.

 

[Diesel Benz]

It is likely standard on a 350 SLK, it is standard on a 320 CDI already on the W210 body, of course on the W211 too (and all bigger engines).

 

[st13phil]

On the SLK, Direct Steering and Parameter Steering are not one and the same.

As Mactech has accurately described, Parameter Steering provides variable power assistance according to steering input and road speed. The effect is that the steering is one-finger-light at parking speeds, but weights up nicely to give more feedback once you're on the move.

Direct Steering combines the variable power assistance of Parameter Steering with a variable ratio steering rack. The steering is quite high ratio once you have some lock applied, with only small movements of the steering wheel required to create quite a large change in roadwheel angle. Around the straight ahead position the rack is (relatively) slow so that it's not nervous to drive at speed in a straight line. The effect of Direct Steering is quite pronounced: when I swap from my wife's SLK350 which has the Direct Steering option to my C-Class which has Parameter Steering (or vice-versa) it takes a few corners to adapt to the very different steering responses.

AFAIK Direct Steering only appeared as an option on the SLK from MY08 or MY09, so early cars may or may not have Parameter Steering but only late cars may have Direct Steering.

 

[st13phil]

It is likely standard on a 350 SLK, it is standard on a 320 CDI already on the W210 body, of course on the W211 too (and all bigger engines).

Nope, Direct Steering is definitely an option on the SLK (circa £130 from memory).

 

[Diesel Benz]

Nope, Direct Steering is definitely an option on the SLK (circa £130 from memory).

I was talking about parameter steering, sorry about that.

I should have a look at the SLK option, it must be different from the variable ratio that ordinary rack-and-pinion power steering would have (at least explained for several models where the effective diameter of the drive pinion changes depending on the position of the rack being driven.

 

[Diesel Benz]

On the SLK, Direct Steering and Parameter Steering are not one and the same.

Could you provide more info about this. From the current SLK price list I could only find option code 213 which is called "Direktlenkung mit variabler Lenkkraftunterstützung". This sounds very much like the 213 option code which is "Speed sensitive power steering/vario steering" in my old data card for a W211.

If the two are separate options, they must have different options codes too.

Talking about other models, is the variable ratio only coming with power steering? This would be reasonable because one would unlikely want a faster steering gear for parking (at high angles) if the car did not have parameter steering.

If you have any WIS document numbers for reference, I'd be interested.

 

[st13phil]

Just checked the SLK & the W204 UK Pricelists and for the SLK Option Code 213 is called "Direct Steering" while on the W204 Option Code 213 is called... "Parameter Steering".

On the Mercedes-Benz UK SLK page it says this about Direct Steering

An option on the SLK-Class, Direct Steering is a speed-sensitive power steering system developed specifically for Mercedes-Benz Roadsters. And it certainly brings out the best in them.

Thanks to an ingenious spur rack, the system offers a sportier feel and generally reduces the range of steering wheel movement required – whatever the situation. On motorways it ensures good straight-line stability. On winding country roads you’ll enjoy superb touch and response. And in those tight parking spaces, it provides maximum steering assistance.

Although the option codes are the same, I can vouch for the fact that they work differently. This page on eMercedesBenz has a good description of what the Direct Steering system does about one-third the way down the page, including the statement "the system offers the same advantages as the proven speed-sensitive power steering system and even goes one step further in some cases", which reinforces the fact that it is indeed different.

Edit: Just spotted this page for the SLK on the MBUK site which says

Parameter steering (speed-sensitive power steering) is fitted as standard, with the Direct Steering system available as an option.

so that seems to nail it.

 

[Mactech]

Just checked the SLK & the W204 UK Pricelists and for the SLK Option Code 213 is called "Direct Steering" while on the W204 Option Code 213 is called... "Parameter Steering".

On the Mercedes-Benz UK SLK page it says this about Direct SteeringAlthough the option codes are the same, I can vouch for the fact that they work differently. This page on eMercedesBenz has a good description of what the Direct Steering system does about one-third the way down the page, including the statement "the system offers the same advantages as the proven speed-sensitive power steering system and even goes one step further in some cases", which reinforces the fact that it is indeed different.

Edit: Just spotted this page for the SLK on the MBUK site which saysso that seems to nail it.

Thanks for that! As I understand it the new ' Direct' steering is actually 'de-sensifies' the steering around the straight ahead position to allow more of the 'ocean liner' straight line stability for which the brand is famous, but requires less arm twirling once you are cornering. Cunning!
I've only tried this with geometry changes (mainly castor trail) and an inceased 'dead band' around the straight ahead position, but not with electronic/hydraulic mods.
I'd like to try one now!

 

[eng622]

Right, I think I understand what has been said. The Direct steer is an advancement to the Parameter system but is all refers to the latest version of the SLK. So can you clarify the position with the earlier model (circa 2005). Is there a standard steering and a parameter option? I'm sure I've read a road test that had the parameter option fitted and there were comments on how good it was on twisty roads.

 

[st13phil]

Cunning! ... I'd like to try one now!

The best bit about it is that there isn't a nasty dead band around the straight ahead wheel position and then the rapid application of steering input that you get with the electro-hydraulic systems. Instead, the effect is quite seamless with no obvious transition from the slower ratio around straight ahead to a much faster ratio as you apply more lock. As I said in an earlier post, the only time I notice it is when I swap from my W204 to Angie's SLK or vice-versa and even then it's only for the first few corners. It's definitely worth trying out

 

[st13phil]

So can you clarify the position with the earlier model (circa 2005). Is there a standard steering and a parameter option?

I'm really not sure about that one. Perhaps someone on SLK World can help out? There's a very active UK group on there, even if much of the forum is US-centric.

 

[Noodle-Pulp]

I'd like to try one now!

hmmm +1 now...

 

[eng622]

Found the road test, was in 2005. www.carpages.co.uk/mercedes_benz/slk
The car under test had the sports suspension and the 18 inch AMG wheels. The parameter speed sensitive steering is quoted as a £200 option, so sounds a bargain. Favourable comments in the main in that test. I don't want a car with wooley steering so really would like that option but how do I find out whether a potential purchase has it. If you have it on a circa 2005 one do you know the option code?