S130 Suspension Tech

[JMortensen]

I'm not a suspension guru either, but I think I have a pretty decent handle on this subject: dynamic toe change is bumpsteer. Do you prefer bump steer in the front? I know John Coffey talked about running different spacers left and right on some tracks to get better dynamic toe out of one side for tracks that had a lot more right turns than lefts, etc, but for the most part the consensus amongst racers is that less bumpsteer is better, and if you want to change direction of the wheels, you do that by inputs on the steering wheel. There are some pretty sophisticated link setups out there that feature dynamic toe changes, but the idea for me is that I don't want the toe changing without any input from the driver. 

 

What's a bigger sin IMO is using huge squishy bushings that allow toe change. Either way, bumpsteer on either end essentially causes hysteresis: the toe changes due to compression or droop of the suspension, which forces a change in the traction at the contact patch (can't steer the tire around without changing its available traction), the changing toe has an effect on g forces which causes the body to bob back and forth, which changes the compression of the shock, which adds more toe change, wash, rinse, repeat. I had my Z in a pretty bad part of the bumpsteer curve in the front end for a while and I would go through a sweeper and experience this firsthand. The car would roll, steering angle would change to keep the car pointed in a straight line, then it would come back, steering changed again, then it would roll more, etc. One of the most noticeable improvements I found after minimizing bumpsteer in the front was that I wasn't constanty sawing at the wheel on sweepers to keep the car moving in a consistent arc. The more bumpy the turn, the worse the effect. A car with less bumpsteer on either end of the car should tend to be more stable, and I think you can show this tendency in semi-trailing arm setups by watching older 911s spin at track days. I used to go to Porsche HPDEs when I was working for a Porsche shop 20 years ago, and I saw that phenomenon in person more than a few times, exacerbated by the rear weight bias no doubt. 

 

Don't get me wrong, as you've said so many times, there are plenty of fast race cars with semi-trailing suspensions, and having dynamic toe change doesn't mean a car can't be fast, but reversing the logic that dynamic toe on a fast car proves that dynamic toe is good or desirable (especially as you see in the case of STA's) doesn't work IMO. 

[260DET]

The term 'bump steer' has by itself negative connotations and I think that we all agree that for the front bump steer = bad. And let's not forget that bump steer includes both toe in and out changes, having a front suspension change dynamically between toe in and out is simply to be avoided and that usually is what bump steer involves. 

 

But the rear is different, for a start we as drivers have no direct input there so any dynamic changes need to be predictable and for a purpose, just like when as some makers have done a car is fitted with a rear steer device. Also dialing in roll/bump steer at the rear is a common solution used by makers to ensure that a car will not oversteer at the limits. So what I have in mind, using dynamic toe in, is no different to what is commonly done by makers. In effect roll toe in induces a form of rear steer, the outside loaded rear tyre by toeing in helps the rear of the car point in the direction of exit.

 

My new project is a Z31 but for S30's I'm sure that rear toe is not understood by most given their habit of spinning out 

 

However one of the S30 guns here is obviously aware of what rear toe in can do, he runs 5mm rear static toe in each wheel. I'm not here to convince anyone I'm right, whatever that is, I'm trying to run through the theory and it's application to make sure that something is not missed so all comment is great. 

Edited January 13, 2017 by 260DET

[260DET]

To clarify what I advocate as far as rear dynamic toe in is concerned, firstly we are talking about only a small amount, maybe a mm or two in total, secondly it should be coordinated with the rest of the suspension design characteristics such as dynamic camber gain, all strictly controlled by the amount of roll which is allowed by considering roll centre placement, springs, anti roll bar and so on. Obviously different suspension types will dictate what they can and can't do, at present I'm considering the race Bluebird trailing arm with two lateral link type which, other than being a bit heavy, looks promising for the Z31.

 

I was reading Fred Puhn's book, again, the other day and was struck by how conservative some of his comments are in 2017. Like on front caster and yes rear toe in. He would shake his head at using 10mm total toe in at the rear on a S30 Datsun but it works, I suggest by its effect on the outside tyres slip angle when turning in to get the back come around into the corner and joint the rest of the car. Not on corner entry cock itself up at the rear diagonally and then proceed to lose rear grip totally like so many standard modified type S30's do 

[JMortensen]

But the rear is different, for a start we as drivers have no direct input there so any dynamic changes need to be predictable and for a purpose, just like when as some makers have done a car is fitted with a rear steer device. Also dialing in roll/bump steer at the rear is a common solution used by makers to ensure that a car will not oversteer at the limits. So what I have in mind, using dynamic toe in, is no different to what is commonly done by makers. In effect roll toe in induces a form of rear steer, the outside loaded rear tyre by toeing in helps the rear of the car point in the direction of exit...

 

To clarify what I advocate as far as rear dynamic toe in is concerned, firstly we are talking about only a small amount, maybe a mm or two in total, secondly it should be coordinated with the rest of the suspension design characteristics such as dynamic camber gain, all strictly controlled by the amount of roll which is allowed by considering roll centre placement, springs, anti roll bar and so on. Obviously different suspension types will dictate what they can and can't do, at present I'm considering the race Bluebird trailing arm with two lateral link type which, other than being a bit heavy, looks promising for the Z31.

First, a rear steer device. If you go look, you'll find that Super HICAS delete kits are pretty popular in the racing scene. So yes, they may be there as either a techno sales gimmick or as a way to reduce the turning circle, etc, but they aren't very popular among racers. Even if you subscribe to the idea that they get deleted because of weight, that still means that the weight associated with it, which is maybe 30 lbs isn't worth it, in a race car that might get down to 2500 or so. 

 

Secondly, I agree completely that the amount of toe change is the key here. If an out of the box 280ZX had a mm or two toe change over its full range, I certainly wouldn't be complaining about it. But I think it's quite a bit more than that. FWIW, lots of people here, including me, have suggested pretty heavy toe in on the rear of the S30. I think if you look you'll see that I always recommended about 5mm (3/16") total toe in, which isn't a small amount. For what it's worth, I once got a "bad zero" on the alignment rack at the shop I worked at 20 years ago and set the toe at something more than 1/2" total toe in, and I wore the brand new rear tires on my car out in about a week. I did do really well at an autox at that time though...

 

As a static setting, toe in provides the stabilizing effect of the outside tire driving inwards, but the toe angle doesn't change mid-corner with bumps on the track. If you could get a mm or two of toe through the whole range, the effect would be very muted and my complaints about STA rear suspension evaporate, but STA suspension isn't normally anywhere near that good out of the box, and the big squishy bushings aren't helping anything either. 

[260DET]

Yes, I'm aware of the HICAS deletion thing for racing, what I was getting at was that some manufacturers were sufficiently convinced that some dynamic toe was a good thing that they incorporated it into their sports production models. But once you go racing all suspension aspects are up for evaluation. I know bugger all about modern sports car suspension but they are so good out of the box that I'm sure that there are dynamic suspension factors at work, they have moved on from merely tweaking static settings like caster. As an example, the Honda rear suspension I posted about on Ozdat, clever.

[turbogrill]

I'm the one that asked about them and the owner made some shortly after telling me they were the first set he sold. So you got a test set for free!? ...well, at least you were the one to make sure they didn't break.

 

Are yours red or silver? I got a silver set and everyone else that I have seen buy their tension rods had red.

I got them as well. Great product. A buddy of ours broke two of the stock ones on a bumpy race track. Not sure if he had poly bushings or not but the T3 tension rods are a must if you are serious about racing.

 

Also give you caster alignment.

 

 

However I would just get the LCA kit from T3. The MSA camber adjusters are not the best.

[tube80z]

Yes, I'm aware of the HICAS deletion thing for racing, what I was getting at was that some manufacturers were sufficiently convinced that some dynamic toe was a good thing that they incorporated it into their sports production models. But once you go racing all suspension aspects are up for evaluation. I know bugger all about modern sports car suspension but they are so good out of the box that I'm sure that there are dynamic suspension factors at work, they have moved on from merely tweaking static settings like caster. As an example, the Honda rear suspension I posted about on Ozdat, clever.

 

I think the big difference is really stability and control.  In a street car you want to have a limit behavior that is benign.  This gives the driver confidence in their ability to take the car to the edge and still be able to bring it back in one piece most of the time.  But often those tricks end up slowing down the ability of the car to provide good feedback when transitioning quickly for a more experienced driver.  I once heard an explanation that  you have a triangle (or radar diagram) where you have grip, stability, and control.  If you want a really stable car then you generally have to give up grip or control and vice versa.  

[260DET]

I think the big difference is really stability and control.  In a street car you want to have a limit behavior that is benign.  This gives the driver confidence in their ability to take the car to the edge and still be able to bring it back in one piece most of the time.  But often those tricks end up slowing down the ability of the car to provide good feedback when transitioning quickly for a more experienced driver.  I once heard an explanation that  you have a triangle (or radar diagram) where you have grip, stability, and control.  If you want a really stable car then you generally have to give up grip or control and vice versa.  

 Yes, your triangle of behaviour and the grip apportioining pie, similar visuals.

 

Of course final understeer is a good and common example of a manufacturer designing in handling behaviour for safety reasons but It seems to me that where sports type cars are involved they are designing in other characteristics that just make the car faster where the driver is keen enough to push it, this is the difference between a S30 and any modern sports car. The grip some modern sports cars display is just sensational, often ignored because power is an obvious factor in lap times and one most commentators seem to concentrate on.

 

This is more for Jon but I came across some good comment on the racing use of HICAS by a former Nissan engineer. Apparently Nissan did race using tweaked HICAS, the standard version being too slow to react and not sufficiently aggressive for racing. Just shows how we can get a wrong impression, apparently the tweaking is beyond the capabilities of most although the electronics to do so are available.

Edited February 3, 2017 by 260DET

[260DET]

Looking for info to help the suspension design process for the project car and ran across the cut paste para below, part of a Honda blurb about their five link suspension. Note their comment about dynamic toe in when cornering.

 

Toe-in Characteristics
Under Cornering
The upper, lower and control arms are arranged to be true to the wheel longitudinal axis, which, coupled with a straight arm design, ensures high stiffness against lateral force. The wheel center to control arm span is longer than the one between the wheel center and the lower arm, allowing a greater displacement of the lower arm bushing to increase toe-in under cornering. This translates into improved handling characteristics and traceability.

[tube80z]

For a racing car you don't want any compliance.  Those often lead to weird limit behaviors.

 

If you're looking for advice there's some good info in the online tech section here, http://www.ronsutton-racetechnology.com/pages.item.29/Tuning-Support.html

[260DET]

For a racing car you don't want any compliance.  Those often lead to weird limit behaviors.

 

If you're looking for advice there's some good info in the online tech section here, http://www.ronsutton-racetechnology.com/pages.item.29/Tuning-Support.html

 

The problem with compliance is that the amateur racer has difficulty in measuring and evaluating it. As I keep saying, the good modern sports type cars in stock form handle like something most S30 drivers can only dream of, as mentioned, Honda for one use compliance to improve handling. But all is not lost for us old schoolers, if our suspension allows, we can work at using dynamic suspension changes to improve handling eg toe in. If you don't accept that known and managed dynamic rear toe in could help then you are truly old school

 

EDIT It's a pity that that Ron Sutton has little experience with rear independent suspension and is reluctant to advise on it, accordingly I would disregard anything he says about rear suspension. It's a pity because he seems very helpful and certainly seems to know the solid back axle stuff.

Edited February 18, 2017 by 260DET