First off I do not want this to come off as a flame. I know that when the new guy in the house says something it can come off the wrong way, even more so when its asking for a call to arms of sorts.
I have looked at length at the FAQs and done a ton of searchs and while I have found some pearls here and there I have not exatly run across a mother load of super detailed info on what makes the 240 special and how we need to go about bringing the best out of the car. Much of the information seems to be product based which is good in some ways but I guess I don't want to know just what works, but WHY a product works.
To these ends I want to offer an example of a post at a board that I have spent a great deal of time at over the last few years. I feel its a good example of internet knowledge share at its highest level and worthy of reading for just about anyone into cars and suspensions as it helps set a base from which others can build.
What I hope to gain from this post is that we may form a group that will put some effort into digging deeper into the 240 and its chassis. I have emailed and put a call into one of the principals of the linked post who has since left internet forums to take a job with a three lettered german auto company who is rather well known for cars that handle. He is reading up on the 240 and tells me that he's going to try to get a spin in one soon to see what all the fuss is over. I hope to take some of what he shares with me (if he can and will due to his new position and agreements to no longer freelance) and bring it back here to help expand understanding and push the envelope as it were.
In the end I will be using my own car to apply many of the thoughts here as I did with my Golf and see just how theory translates into practice. If others do the same we will all be MUCH stronger as a result.
Hope this strikes the right cord... enjoy the read.
http://forums.tdiclub.com/showthread.php?t=133342
Modified by DanS at 12:35 PM 8/16/2006
Lets raise the bar.
Re: Lets raise the bar. (DanS)
I don't really see the need for a compilation like that.
There are basics that everybody understands, and this is the basis on which people tune suspension. Everything from there is trial and error to make parts work together.
We already have a sticky here that goes over said basics.zerothread/11638
Things like the results of increasing sway bar stiffness, spring stiffness, etc, are all discussed in that thread.
Understeering is inherently stable? Huh? When a car is understeering you have absolutely no control.
1.)More gas will just cause further plowing.2.)Braking will slow you down and eventually allow you to have front end grip again3.)Steering will have no effect on angle or actually turning the car.4.)When a car is understeering, you cannot accelerate, and you cannot increase turning angle without slowing down.
Next, a few notes about oversteer:1.) when oversteering you can still use the steering wheel to manipulate the car2.) you can also steer the car with the rear end by giving more or less throttle3.) Oftentimes the best racing line involves oversteering to setup angle and approach for the next corner4.) You can maintain speed or increase speed when oversteering
Any condition during oversteer will cause you to spin?
This just isn't true. It is even possible to maintain a large degree of slip angle through an entire turn while maintaining a proper line (Drifting). You only spin if you introduce too much angle or too much throttle or both when oversteering.
Note: I haven't read through much of that thread you posted except for the first post. Despite my obvious complaints about the post I quoted, there is a lot of VERY good information in that thread. The diagrams and animations and graphs on page 3 are good examples of useful stuff.
Modified by naed240sx at 10:22 AM 8/16/2006
There are basics that everybody understands, and this is the basis on which people tune suspension. Everything from there is trial and error to make parts work together.
We already have a sticky here that goes over said basics.zerothread/11638
Things like the results of increasing sway bar stiffness, spring stiffness, etc, are all discussed in that thread.
I don't even know what to say about this. This is obviously written by a driver of a fwd car, and not a sports car enthusiast, or somebody who understands proper handling for fast driving.referenced thread wrote:Think about the implicatons of the above for a moment!: if a car is set up to be truly Oversteering, then any sideforce -- any gust of wind, pothole, slope, crazed gerbil, etc. -- will cause the car to spiral into a spin, unless of course the driver intervenes in a timely fashion by turning the steering wheel in the right direction. Conversely, an Understeering car is inherently stable: when you shove it to one side, it turns away from the shove and then tries to straighten out, without ever wanting to spin. This Understeering situation is inherently much, much safer, and thus it should come as no surprise that essentially all passenger cars are designed to understeer: if they were not, then high-speed driving would be a continuous white-knuckle struggle to avoid spinning off the road -- even if the road is dead-arrow straight.
Understeering is inherently stable? Huh? When a car is understeering you have absolutely no control.
1.)More gas will just cause further plowing.2.)Braking will slow you down and eventually allow you to have front end grip again3.)Steering will have no effect on angle or actually turning the car.4.)When a car is understeering, you cannot accelerate, and you cannot increase turning angle without slowing down.
Next, a few notes about oversteer:1.) when oversteering you can still use the steering wheel to manipulate the car2.) you can also steer the car with the rear end by giving more or less throttle3.) Oftentimes the best racing line involves oversteering to setup angle and approach for the next corner4.) You can maintain speed or increase speed when oversteering
Any condition during oversteer will cause you to spin?
This just isn't true. It is even possible to maintain a large degree of slip angle through an entire turn while maintaining a proper line (Drifting). You only spin if you introduce too much angle or too much throttle or both when oversteering.
Note: I haven't read through much of that thread you posted except for the first post. Despite my obvious complaints about the post I quoted, there is a lot of VERY good information in that thread. The diagrams and animations and graphs on page 3 are good examples of useful stuff.
Modified by naed240sx at 10:22 AM 8/16/2006
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Q45tech
- Moderator
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- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Re: Lets raise the bar. (naed240sx)
Understeering is the steering wheel angle vs the tire angle corrected for steering ratio.
If a car understeers you must turn the steering wheel a few degrees more than a neutral steering condition........over steer the opposite a few degrees less than the tire angle.
A Q45 has 15:1 with 2.6 turns and the tire max angle is ~~36 degrees so 1.3 turns = 36deg so 1.3 x360= ~470 deg of steering in 1.3 turns so it takes it takes 13 degrees of steering wheel movement to move the tires 1.0 degree.
Under/over steering is defined as so many steering wheel degrees [extra or less] required at a certain G load usually at 0.5G and again at limit [~~0.8-0.9G].
A good car might require 10 extra degrees and a mediocre one 20-45 extra degrees of steering wheel at the same G load.
Understeering is primarily caused because the front tires are too weak to handle the static plus weight shift caused in turning.
Engineers always design in understeer for safety primarily with weak front tires and too large a front sway bar...........the fix a much higher load index front tire and a weaker front sway bar...........adding a rear sway bar or stiffening it just reduces rear traction adding load to rear tires.
When you increase the front tires load carrying ability about half the percentage gain goes directly to handling improvements.
A stronger front tire will operate at REDUCED SLIP ANGLES compared to oem tire thus reducing the understeer.............adding psi to front tire is similiar but not as effective as a stronger tire at the same psi.
Weigh each front tire load [say 1168 vs 1521 load index] you will see that 77%-85% of max load is used up sitting still] not much left for turning.
http://www.auto-ware.com/setup/undr_mid ... 54...9.pdf
Change the above link from Lec1.pdf thru Lec18.pdf to see all class notesand get a real education on vehicle dynamics
If a car understeers you must turn the steering wheel a few degrees more than a neutral steering condition........over steer the opposite a few degrees less than the tire angle.
A Q45 has 15:1 with 2.6 turns and the tire max angle is ~~36 degrees so 1.3 turns = 36deg so 1.3 x360= ~470 deg of steering in 1.3 turns so it takes it takes 13 degrees of steering wheel movement to move the tires 1.0 degree.
Under/over steering is defined as so many steering wheel degrees [extra or less] required at a certain G load usually at 0.5G and again at limit [~~0.8-0.9G].
A good car might require 10 extra degrees and a mediocre one 20-45 extra degrees of steering wheel at the same G load.
Understeering is primarily caused because the front tires are too weak to handle the static plus weight shift caused in turning.
Engineers always design in understeer for safety primarily with weak front tires and too large a front sway bar...........the fix a much higher load index front tire and a weaker front sway bar...........adding a rear sway bar or stiffening it just reduces rear traction adding load to rear tires.
When you increase the front tires load carrying ability about half the percentage gain goes directly to handling improvements.
A stronger front tire will operate at REDUCED SLIP ANGLES compared to oem tire thus reducing the understeer.............adding psi to front tire is similiar but not as effective as a stronger tire at the same psi.
Weigh each front tire load [say 1168 vs 1521 load index] you will see that 77%-85% of max load is used up sitting still] not much left for turning.
http://www.auto-ware.com/setup/undr_mid ... 54...9.pdf
Change the above link from Lec1.pdf thru Lec18.pdf to see all class notesand get a real education on vehicle dynamics
-
Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Re: Lets raise the bar. (Q45tech)
From the above chart you see at 5 degrees the tire generates 425 pounds and at 10 degrees it is NOT DOUBLE. If the tire was linear you would expect 850 pounds instead you see 725 pounds...............this difference is roughly the undesteer factor of that specific tire under that load.
Using a stronger tire raises the linerarity of the graph thus reducing understeer.
If the rear tires [lower load] are linear and the front tires higher load are not linear = understeer .........as you increase the front slip angle [by speed or turning angle] the understeer get worse until the rear tires start getting non linear or you run off the road.
It is really hard to persuade non engineers or non trained that the front tires should be stronger than the rear tires because manufacturers continue their safety designs with big wide rear tires to protect operators from wet/rain oversteer when the accelerate too much for conditions.
Also consider that under braking the front tires see almost double the static load............luckily most stops take less than 3 seconds.
Using a stronger tire raises the linerarity of the graph thus reducing understeer.
If the rear tires [lower load] are linear and the front tires higher load are not linear = understeer .........as you increase the front slip angle [by speed or turning angle] the understeer get worse until the rear tires start getting non linear or you run off the road.
It is really hard to persuade non engineers or non trained that the front tires should be stronger than the rear tires because manufacturers continue their safety designs with big wide rear tires to protect operators from wet/rain oversteer when the accelerate too much for conditions.
Also consider that under braking the front tires see almost double the static load............luckily most stops take less than 3 seconds.
Re: Lets raise the bar. (naed240sx)
What I think he is trying to point out is that understeer is by its nature the car trying to stay going forward and not turning. Oversteer by its nature is much more unstable but by its instability much happier to change direction. An example of this would be that some modern fighter jets can not fly without computer control. They are simply unstable otherwise and while they will turn like stink they would spin wildly out of control without constand intervention by avionics. OEM trys to dumb down cars to keep from killing folks and thats good. I like the fact that my wife drives a big porky understeering Passat Wagon that will live through a bomb blast but I want to drive a car that is much more likely to spin like a top if I don't mind my physics.naed240sx wrote:Understeering is inherently stable? Huh? When a car is understeering you have absolutely no control.
The fact that everything posted there is in relation to a car that I love but sadly has cr@p suspension is of note but as you go on to point out, my man and his animations give you the very best of what there is to be had in the understanding of the inner working of chassis and control. THAT is what I want to bring out for the 240 in particular and maybe a few other platforms as well seeing as the same rules of dynamics apply.
Q45tech. Way to come up huge and go yard. I looked at all of those, every last one and must say that my head hurt after the first two. No seriously... my head hurt. I did not start doing math as I would have had to take off shoes but the power of numbers was evident and makes me giddy with anticipation of what we could get done with some work.
One of the first things I plan to do with my car is get it up on a rack and take LOTS of pics. I will measure everything and try to get a friend to model everything and do some animation for us as things go through their arcs. Of course it will be based on S14 cause thats what I'll be rocking and I'm greedy and all but hey.
I also think I'm going to make a few calls and send a few emails to some folks at Aftershocks, Koni and DMS and see what they are thinking about for the Nissan S chassis.
I do think its interesting how you mention the amount of work that you point out that the front tires do. No question at all this is the case but to a degree the thing I like most about the S13/14 to this point is the rear end. The VWs have such poor rears that a real live independant rear is just a god send. I also think that having the drive axles in the back opens a whole new world for the front in that we have the option (if we wish) to do a whole new subframe and go ape with front attachment points. We are limited only by geometry and wallet thickness and while I'm not exactly made of money I like having options.
One of the first things I plan to do with my car is get it up on a rack and take LOTS of pics. I will measure everything and try to get a friend to model everything and do some animation for us as things go through their arcs. Of course it will be based on S14 cause thats what I'll be rocking and I'm greedy and all but hey.
I also think I'm going to make a few calls and send a few emails to some folks at Aftershocks, Koni and DMS and see what they are thinking about for the Nissan S chassis.
I do think its interesting how you mention the amount of work that you point out that the front tires do. No question at all this is the case but to a degree the thing I like most about the S13/14 to this point is the rear end. The VWs have such poor rears that a real live independant rear is just a god send. I also think that having the drive axles in the back opens a whole new world for the front in that we have the option (if we wish) to do a whole new subframe and go ape with front attachment points. We are limited only by geometry and wallet thickness and while I'm not exactly made of money I like having options.
Re: (DanS)
Dennis>*
Writing a compilation like that takes a lot of effort and time, but could be done.
The things overlooked in the above graph is that that chart dones't keep increaing, it peaks and rolls off. Also, different tires generate different cornering forces at various slip angles.
I had a thread regarding slip angle and it's relationship to under/oversteer a while back to help some drifters realise exactly what was going on during a drift
There are a few major factors in how a car handles:-Tires-How well the car keeps the tire in "optimal contact" with the road surface-Weight (inertia)
Pretty much everything else is derived from there. CHasis bracing and tuneable suspension can assist in keeping the tire in optimal contact with the road.
Lighter wheels can reduce unsprung weight making the suspension function more ooptimaly and resond better and a stickier tire will generate more force at given slip angles.
Reducing weight will reduce the inertia weight the tire has to overcome with it's cornering force, increasing the overall speed and lateral acceleration through a turn...
If yo look at the stickies, there's a lot of info, but unfortunately since I wrote and compiled them I've entered grad school and been working 60 hours a week..not good. But I digress....
The fundamnetal drawback to the 240 as I see it lies in the camber gain (or lack thereof) on the mcpherson front strut deisgn in comparison to the very nice multi-link rear. Although this design means it understeers (because under bound the rear tire gains more negative camber relative to the front and thus are able to generate more cornering frce and the tire tries to roll over) mildly, this nets a margin of safety and predictability to the car, since the rear is also subject to driveline torque.
The second isue is one of chassis rigidity, since the car requires signifigant bracing to reduce chassis flex and allow the sspension to work more optimaly.
More alter If I can dig up this damned thread...
Hopefully that helps a bit
-Chet
Writing a compilation like that takes a lot of effort and time, but could be done.
The things overlooked in the above graph is that that chart dones't keep increaing, it peaks and rolls off. Also, different tires generate different cornering forces at various slip angles.
I had a thread regarding slip angle and it's relationship to under/oversteer a while back to help some drifters realise exactly what was going on during a drift
There are a few major factors in how a car handles:-Tires-How well the car keeps the tire in "optimal contact" with the road surface-Weight (inertia)
Pretty much everything else is derived from there. CHasis bracing and tuneable suspension can assist in keeping the tire in optimal contact with the road.
Lighter wheels can reduce unsprung weight making the suspension function more ooptimaly and resond better and a stickier tire will generate more force at given slip angles.
Reducing weight will reduce the inertia weight the tire has to overcome with it's cornering force, increasing the overall speed and lateral acceleration through a turn...
If yo look at the stickies, there's a lot of info, but unfortunately since I wrote and compiled them I've entered grad school and been working 60 hours a week..not good. But I digress....
The fundamnetal drawback to the 240 as I see it lies in the camber gain (or lack thereof) on the mcpherson front strut deisgn in comparison to the very nice multi-link rear. Although this design means it understeers (because under bound the rear tire gains more negative camber relative to the front and thus are able to generate more cornering frce and the tire tries to roll over) mildly, this nets a margin of safety and predictability to the car, since the rear is also subject to driveline torque.
The second isue is one of chassis rigidity, since the car requires signifigant bracing to reduce chassis flex and allow the sspension to work more optimaly.
More alter If I can dig up this damned thread...
Hopefully that helps a bit
-Chet