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Four Wheel Steering


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#1 pierrre

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Posted 30 July 2019 - 18:05

i did a piece on four wheel steering...lets see how it survives the critque..i know some of you can destroy this



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#2 Zoe

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Posted 31 July 2019 - 15:56

Is it just me who is seeing the subtitles in a weird sort of German?



#3 Fat Boy

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Posted 31 July 2019 - 23:11

It worked fine for me.

 

The biggest thing that I can say about rear steer (having spent most of my time trying to minimize it) is that a little goes a _long_ way. I find most of the time the tuners who use it fall in love with it because it's so powerful and then fail to get the statics of the chassis correct. I could definitely see it being a great tool, but I can also see it as being an unnecessary complication.



#4 Lukin

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Posted 02 August 2019 - 04:44

It worked fine for me.

 

The biggest thing that I can say about rear steer (having spent most of my time trying to minimize it) is that a little goes a _long_ way. I find most of the time the tuners who use it fall in love with it because it's so powerful and then fail to get the statics of the chassis correct. I could definitely see it being a great tool, but I can also see it as being an unnecessary complication.

 

Hi FB! How are you mate? 

 

Have you ever (purposely) put bump steer into the rear axle (assuming front steer car)?

 

 

Also from another thread - I am with you in regard to to rebound damping. It might be from working on fat cars with crap tyres, but I had a year as a customer (we couldn't revalve) where the front rebound was fully open. I don't remember the numbers, but I think I was probably around 2:1 Compression:Rebound as a general rule. 



#5 pierrre

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Posted 02 August 2019 - 05:23

Is it just me who is seeing the subtitles in a weird sort of German?

 

youtube auto translated it so just clean up the english version and then click on auto translate for the rest of the languages...never knew subtitles can be so taxing and the best part is..just after all is translated...then realizing the original english subtitles has more mistakes from my screening incompetency. just image how the translated one would be



#6 Fat Boy

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Posted 29 August 2019 - 17:38

Hi FB! How are you mate? 

 

Have you ever (purposely) put bump steer into the rear axle (assuming front steer car)?

 

 

Also from another thread - I am with you in regard to to rebound damping. It might be from working on fat cars with crap tyres, but I had a year as a customer (we couldn't revalve) where the front rebound was fully open. I don't remember the numbers, but I think I was probably around 2:1 Compression:Rebound as a general rule. 

 

Holy ****, He lives! Good to hear from you, Lukin!

 

I don't generally put bump steer into a cars, but I do use static toe to influence the 'rotation' of the car. I have friends who do a lot of stock car work and, to them, axle steer is a hugely important. I suspect that on a live rear it's a significantly different trick than on an independent one. I know some guys use it to their advantage. It's entirely possible that my engineering approach isn't sophisticated enough to take advantage of a good tool.

 

At very low shaft speeds, I'll run higher comp:reb ratios...maybe 5:1. As shaft speeds go faster, I may get to 2:1 or lower. It's worked on fat & light cars with ****, mediocre and good tires. To this point, I haven't stumbled across anything which it doesn't work on. It might not be the best in all situations, but it seems to get me to a pretty decent place in a short period of time.



#7 Lee Nicolle

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Posted 03 September 2019 - 08:21

Bump steer, or rear steer the bane of most live axle cars. And many IFS ones as well. 

And most people do not even realise they have it. This on production based cars.



#8 Greg Locock

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Posted 03 September 2019 - 11:54

Live axle cars with watts link don't have bump steer. They have roll steer because I put it there.



#9 Fat Boy

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Posted 03 September 2019 - 23:13

Live axle cars with watts link don't have bump steer. They have roll steer because I put it there.

 

It's important to understand these are two different things.



#10 ceesvdelst

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Posted 09 September 2019 - 21:50

I would guess that as it has been used on a few rally cars, and offered no real benefits that were staggering, it might just be one of those things that is a luxury for certain manufacturers maybe?

Does anyone still use 4WS these days?



#11 gruntguru

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Posted 09 September 2019 - 22:29

Does anyone still use 4WS these days?

At least 23 models on the US market according to this. https://www.motor1.c...wheel-steering/



#12 ceesvdelst

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Posted 10 September 2019 - 17:15

Wow, I never knew that?  Is there any particular selling point for it?  Ease of parking for their often very large vehicles?

 

Don't know if it is a thing here anymore, I can only remember a few cars, Honda, Mitsubishi and maybe a few Subaru's using it in the UK?



#13 kikiturbo2

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Posted 10 September 2019 - 18:12

I would guess that as it has been used on a few rally cars, and offered no real benefits that were staggering, it might just be one of those things that is a luxury for certain manufacturers maybe?

Does anyone still use 4WS these days?

 

Ferrari and Porsche use it to great effect to virtually shorten the wheelbase of their ever growing cars and make them nimble again... The Porsche system works brilliantly on 991.2 cars (and 991.1 Turbo)

Renault also uses it but I am not really fond of the way it is claibrated.. bit artificial



#14 ceesvdelst

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Posted 10 September 2019 - 22:00

Oh okay, thankyou I had no idea that it was still used, always seemed a bit of a gimmick.

 

Amazed Porsche use it, must have been tested to death and must presumably have give solid results. And Ferrari too, wonder who used it first and then the other just copied lol!



#15 Fat Boy

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Posted 17 September 2019 - 04:25

Oh okay, thankyou I had no idea that it was still used, always seemed a bit of a gimmick.

 

Amazed Porsche use it, must have been tested to death and must presumably have give solid results. And Ferrari too, wonder who used it first and then the other just copied lol!

 

A customer has a Porsche GT2 street car at a local 'country club' track which he has slicks on and uses as a 'play' car. I had a couple laps in it and can tell you the Porsche definitely has rear steering and it works _really_ well. It's a tick unnerving to feel, but it does an amazing job and adjusting car balance without inducing any negatives. Having said that, the Porsche GT3 and GT Cup have standard rigid toe-links.



#16 RDV

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Posted 17 September 2019 - 10:26

It worked fine for me.

 

The biggest thing that I can say about rear steer (having spent most of my time trying to minimize it) is that a little goes a _long_ way. I find most of the time the tuners who use it fall in love with it because it's so powerful and then fail to get the statics of the chassis correct. I could definitely see it being a great tool, but I can also see it as being an unnecessary complication.

Hmm, quick run past forum after a long time (Back in Yurp now so less jetlag posting in early hours, plus had forgotten login to forum), see the usual suspects still posting.

 

Roll steer can be quite useful when built in and adjustable to driver(or car...) needs, even today. 

 

The most extreme case was a Andros trophy case, where it was essential for going into corners. Process was to flick into hairpins, rear wheels steering opposite to ft via a cardioid shaped cam, go into hairpin backwards at full throttle to exit better. 

 

If you run some Porsches look into the Weissach axle geom. Also assimetric rubber bushes that alter toe w/ power. 



#17 kikiturbo2

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Posted 18 September 2019 - 22:54

A customer has a Porsche GT2 street car at a local 'country club' track which he has slicks on and uses as a 'play' car. I had a couple laps in it and can tell you the Porsche definitely has rear steering and it works _really_ well. It's a tick unnerving to feel, but it does an amazing job and adjusting car balance without inducing any negatives. Having said that, the Porsche GT3 and GT Cup have standard rigid toe-links.

 

street legal 991 gt3 has active rear steer too.. race cars probably have rigid rears.. but yes, porsche's system works sensationally... I first tried it in a 991.1 turbo S and that transformed the car.. helped save the longer wheelbase 991 platform that is a bit numb on slower roads without active rear steer..



#18 kikiturbo2

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Posted 18 September 2019 - 22:56

Oh okay, thankyou I had no idea that it was still used, always seemed a bit of a gimmick.

 

Amazed Porsche use it, must have been tested to death and must presumably have give solid results. And Ferrari too, wonder who used it first and then the other just copied lol!

 

well, honda used it long time ago, as well as Nissan on R32 GTR... the only reason it was disconnected on race cars was because the engineers building the race car for australian touring car championship had too much on their plate allready (with 4wd for start)



#19 Fat Boy

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Posted 18 September 2019 - 23:41

Hmm, quick run past forum after a long time (Back in Yurp now so less jetlag posting in early hours, plus had forgotten login to forum), see the usual suspects still posting.

 

Roll steer can be quite useful when built in and adjustable to driver(or car...) needs, even today. 

 

The most extreme case was a Andros trophy case, where it was essential for going into corners. Process was to flick into hairpins, rear wheels steering opposite to ft via a cardioid shaped cam, go into hairpin backwards at full throttle to exit better. 

 

If you run some Porsches look into the Weissach axle geom. Also assimetric rubber bushes that alter toe w/ power. 

 

The Master returns! Good to have you back!

 

I know you're not strictly a Euro guy, but I find Euro guys spend a lot of time with this type of thing. For me, I'd rather bump steer to zero and work with other variables. I believe that it can be used to produce good results, but I also believe that most people (myself included) could do more harm inducing this type of variable than by eliminating it as one.

 

Like I said, I'm all about using toe to steer the car (including asymmetrical rear), but I've seen competitors really screw themselves up by using it incorrectly. Engineers tend to want to introduce as many tuning screws as we can find, but, anymore, I try to eliminate them.



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#20 Fat Boy

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Posted 18 September 2019 - 23:42

street legal 991 gt3 has active rear steer too.. race cars probably have rigid rears.. but yes, porsche's system works sensationally... I first tried it in a 991.1 turbo S and that transformed the car.. helped save the longer wheelbase 991 platform that is a bit numb on slower roads without active rear steer..

 

100% correct. It makes a relatively large car (it sucks that I'm describing a "911" this way) act like it has a much shorter wheelbase.



#21 kikiturbo2

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Posted 19 September 2019 - 06:37

Yeah, but the 911 has really grown in the last generation.. :D

It is really evident when you drive the 997 gen vs first 991.1 without rear steer vs. 991.2 with rear steer.. Different cars alltogeather on slower stuff.

 

RWS is real interesting and is something that Prodrive was developing as a way of giving different driving character to FWD cars that would use the same platform but tune the character by changing the way rear steer worked.

 

I have tried the Renault system on new Laguna and Megane RS, as it gives the car some additional agility but just feels artificial after the Porsche system..



#22 Greg Locock

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Posted 19 September 2019 - 12:03

At some point somebody will develop active toe adjustment, effectively a ballscrew in each tie rod. I think that'll be very interesting. 



#23 Fat Boy

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Posted 19 September 2019 - 16:28

Yeah, but the 911 has really grown in the last generation.. :D

It is really evident when you drive the 997 gen vs first 991.1 without rear steer vs. 991.2 with rear steer.. Different cars alltogeather on slower stuff.

 

It's pretty damned apparent when trying to engineer them as well. The 997.2 was probably the best Cup car Porsche ever produced. The 991.1 wasn't nearly as good. The 991.2 has more power and better chassis characteristics, but it's still not as fun of a car.

 

All these 'Challenge' or 'Cup' racecars are really getting out of control. The Ferrari and Lambo have entirely too much power and then all sorts of driver aids so rich guys have at least a fighting chance of keeping the damn things out of the fence (which they still routinely accomplish). Now Porsche wants to enter the arms race by throwing all sorts of power at their Cup car. It's entirely unwarranted and unnecessary. The vast majority of these cars are for gentlemen drivers and the last thing they need is an edgy car with tons of HP.



#24 Bikr7549

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Posted 19 September 2019 - 16:53

At some point somebody will develop active toe adjustment, effectively a ballscrew in each tie rod. I think that'll be very interesting.


Agree, and that will be a fun change. One of the Carrol Smith books discusses toe changes he made to get the inside front tire to work better and this would assist that without any detrimental alignment issues in other places on the track. Would this be a legal setup under current racing regs (of any nature)?

#25 Fat Boy

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Posted 20 September 2019 - 15:31

Agree, and that will be a fun change. One of the Carrol Smith books discusses toe changes he made to get the inside front tire to work better and this would assist that without any detrimental alignment issues in other places on the track. Would this be a legal setup under current racing regs (of any nature)?

 

Not really. Maybe off-road?



#26 RDV

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Posted 20 September 2019 - 18:07

The Master returns! Good to have you back!

 

I know you're not strictly a Euro guy, but I find Euro guys spend a lot of time with this type of thing. For me, I'd rather bump steer to zero and work with other variables. I believe that it can be used to produce good results, but I also believe that most people (myself included) could do more harm inducing this type of variable than by eliminating it as one.

 

Like I said, I'm all about using toe to steer the car (including asymmetrical rear), but I've seen competitors really screw themselves up by using it incorrectly. Engineers tend to want to introduce as many tuning screws as we can find, but, anymore, I try to eliminate them.

From english school, zero rear bumpsteer guy too. It is something to use for that extra little bit of control & driver aid, but you need to know your car & geometry very well to use it effectively. Hmm, I would add also knowing your driver well too, they are strange people.....Another variable in the mix already full of variables..

Remember also static bumpsteer done on a setup patch not necessarily what you will get under load on the track. A run on a K&C rig can be quite disturbing.

 

When we got our first Porsche 917 in the shop, bumpsteered it zero-zero, then went out on test. It handled like **** & destroyed a set of tyres in five laps. Quick call to Prof Helmut Flegl, Porsches 917 project lead, detailing problem brought the answer that the bump-steer was built in to compensate for chassi deflection under load, making it zero on track (Not surprising, look up Porsche 917 chassi pics....). So Porsche has that in the company DNA, you can see where the Weisach axle concept came from. On the 956, 962 & the Interserie (same as CanAm) 917/30 we actually had toe out on rear , only way to make it turn in into corner when running spool-diffs. 24" wide tyres & spool gives understeer that can only be described as terminal.

 

Incidentally in all the cars I have run, only had two cars that had zero bumpsteer at front with lock, a Ralt F3 & a historic Lotus 33. All others zero in straight ahead, but as soon as lock is applied the three bar compatibility goes off. Try it with lock, you might be surprised & could sort out unusual handling, or at least you can see where it comes from. 

 

If I have a shunt & little time to rebuild car before use, I concentrate on rr bumpsteer, drivers can feel it well, front has to be very wrong for them to complain, so can be temporarily ignored.

 

By the way, will pop up from time to time now I have found my login, but any questions can be addressed to twitter @RDV69 , easy to contact as is on phone. Has some nice photos of planes, racing cars, the occasional tech article & the monthly rant on Racecar Engineering. 



#27 Bloggsworth

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Posted 20 September 2019 - 20:30

First car I drove wit 4 wheel steering was an Austin 7 Ruby - 1/4 elliptic rear springs...



#28 Greg Locock

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Posted 21 September 2019 - 06:30

The truth is that virtually every car ever built has rear compliance steer. You'll notice on watts link cars that the bushes in the watts (if it is behind the axle) are kept very stiff, this helps to give understeer. I'm not a huge fan of rear roll steer - it was why the 1990s Falcon suffered from two stage cornering, you'd go into a corner, and then somewhat later have to feed in more (I think it was)  SWA to maintain the curve, as the car rolled. That was sorted in 95 by a change to the rear arm geometry.



#29 Bloggsworth

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Posted 21 September 2019 - 07:54

The truth is that virtually every car ever built has rear compliance steer. You'll notice on watts link cars that the bushes in the watts (if it is behind the axle) are kept very stiff, this helps to give understeer. I'm not a huge fan of rear roll steer - it was why the 1990s Falcon suffered from two stage cornering, you'd go into a corner, and then somewhat later have to feed in more (I think it was)  SWA to maintain the curve, as the car rolled. That was sorted in 95 by a change to the rear arm geometry.

 

It was extreme in the 7, making it difficult to drve in a straight line. You could turn a corner by getting a heavy passenger to slide from one side of the back seat to the other.



#30 Greg Locock

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Posted 21 September 2019 - 12:06

I can believe that. One of my more standard questions with production cars is... if I fill the fuel tank it changes response X by this much... is this a real thing?



#31 Fat Boy

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Posted 24 September 2019 - 17:54

I can believe that. One of my more standard questions with production cars is... if I fill the fuel tank it changes response X by this much... is this a real thing?

 

God, I find myself asking that question for damn-near everything. Here's something that we don't often discuss. We try to do things in a scientific manner, but that's damned difficult to really test in a scientific manner.

 

During any given session, I'll get 1-2 changes I can make to the car. Tire life, track conditions, traffic, fuel load, driver, etc all make it difficult to discern what change produced which effect. The best we can do is attempt to follow the driver comments and logged data to make questionable guesses for the next run. Maybe F1, LMP1 or NASCAR teams have a better handle on what is actually happening, but most of us get by on thumb-nail generalities & track savvy.



#32 RDV

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Posted 27 September 2019 - 10:59

RCE-SetupScreenshot%202017-03-21%2018.48https://www.dropbox.com/s/y6ds1ttp388qj92/RCE-SetupScreenshot%202017-03-21%2018.48.47.png?dl=0RCE-SetupScreenshot%202017-03-21%2018.48

God, I find myself asking that question for damn-near everything. Here's something that we don't often discuss. We try to do things in a scientific manner, but that's damned difficult to really test in a scientific manner.

 

During any given session, I'll get 1-2 changes I can make to the car. Tire life, track conditions, traffic, fuel load, driver, etc all make it difficult to discern what change produced which effect. The best we can do is attempt to follow the driver comments and logged data to make questionable guesses for the next run. Maybe F1, LMP1 or NASCAR teams have a better handle on what is actually happening, but most of us get by on thumb-nail generalities & track savvy.

 

Nah, all of them same...