Weight Bias - Redux

[Silvo 1981]

Afternoon,

I'm going to attempt to gather a larger more detailed resource of data for this. I was going to collect Make, Model, Drive, Curb Weight, Weight Bias, Spring Rates, Roll Bars, Rebound and Bump. I've got a worksheet in Excel all ready to go with all the R# cars. Is there anything I've missed that you'd of used previously for these calcs that I should collect while I'm at it.

Might take me a while but I should be able to turn it round in a reasonable period I think/hope. 114 cars from the list I found, already done 2. I'll get cracking tonight in between moving house, gf's birthday (tomorrow) and looking after 9 month old insomniac son. Should be easy!

I've attached the spreadsheet as far as I've got it but I think the order needs changing to tie in with the tuning menus. I think the ARB's are before the Spring rates if memory serves me correctly.

Phil

[Blooze]

That all looks good!  There are some ratios that we care about.  Rather than try to detail them here, I am posting my worksheet for doing the same thing (great minds... ) and you can copy the formulas to your sheet, or use mine if you want.

Quite sadly, I think I can tell you what you are going to find.

• The ARB values will be inordanently low compared to production car values.  They will have a 55% ratio front to back, irreguardless of the Wb or Sb.  They are not the inverse of the Wb like they were in Forza II
• The Springs will match the Wb.
• The Dampers will have values similar to production cars and will match the Wb/Sb.  However, the Rebound to Bump will be ~50%, as opposed to ~70% in the production cars.

This whole thing is a bit strange.  For one thing, there is no way that a new Porsche and a Boss Mustang are going to use almost identical ARB configurations.  I wonder what the Hell is going on.  I may end up going over to the Daught GNet and see if I can get Greenawalt's Attention.

I am mucho bugged by this...

$

[Fit4aking]

Lets see if I can make an intellegent reply to your thoughts there Blooze.  As it pertains to Race vs production cars you've found that:

Production cars have higher sway bar values.
Race cars have lower sway bar values.

Production cars have higher damping values.
Race cars have lower damping values.

Production cars use spring bias and weight bias to set feel and it is often different than published.
Race cars use spring bias and weight bias to set feel but it is often the same as published.

What is missing here in my mind is the SWR of both production and race cars.  We've seen near 100% SWR's on production cars but race cars tend to be closer to 50%

Does this mean that perhaps there are two models here instead of just one?  Perhaps one model, the production cars is set up to run much stiffer springs, dampers and sway bars while the R class model is set to run much lower values.  Just scatter plotting at the moment but wouldn't that hint that perhaps tuning in R class would be best achieved not by using the same correlation as before but by actually trying to figure out what the ratios of spring/damper/sway actually are?

I'm going to try something on my own here with a production car and then see how it translates to higher classes and race cars.
-a static total spring value based only on the cars weight.
-weight biasing the FSR and the RSR as the only means of adjusting spring values after that is set.
-damper settings based on telemetry stiffer or softer to utilize the entire suspension travel without bottoming as best as I can without upsetting the default ratio.
-sway bar values that coincide with stabilizing traction left to right deviating from default only to try and balance over/under steer based on feel and telemetry.

Not to try and reinvent the wheel but to attempt to recreate a theory I have in my head at the moment.  I've been staring at a sheet of paper so long looking back and forth at current values and previous knowledge that I dare not quantify it at the moment without at least attempting it.  Pass or fail I've only been working on it since last night and only in theory not in application.  My mind does funny things when I can't actually play FM3.  If I'm way off base with this please delete the post or I'll move it to the speedshop.

[Blooze]

My primary befuddlement is the deal with the ARB.  I am having trouble wrapping my head around the idea that a Porsche would have the same relationship between the ARB, front to rear, as a heavier heavy nosed Muscle car.  Or a mid-engined racer.  I 'spose I need to do some research.

$

[Fit4aking]

Funny you would say that Blooze because I may be able to help out with a real world comparison.



As soon as I pulled in the Porsche I realized what it was parked next to.  I'll  measure the stock sway bars on each car and post the diameters and I believe D^4 is how you determine stiffness.  I'll double check my chassis book to be sure.  At least then you'll have the actual sway bar bias between a modern RR car and a heavy nosed FR muscle classic.

[fndrbndr]

Gee, I wonder what it's like to win the lottery and drive exotic sportscars for a living....(closes eyes)

Damn.  It was worth a shot.  lol

[Blooze]

Damn!  How's about that for handy??  Very cool Fit!

$

[Fit4aking]

I did some math with the values but don't have the time to do a write up at the moment. Here are the values though.

Porsche 2003 Carrera (base)
Ft 23mm
Rr 19mm

Ford 1965 Mustang Fastback
Ft 18mm
Rr 0mm as in not there.

Here's my reference material for thickness vs stiffness:
http://books.google.com/books?id=rY2ujnNrhf0C&pg=PA15&lpg=PA15&dq=determining+roll+bar+stiffness&source=bl&ots=HeNBgbsU7v&sig=mqSSxi34Uhuk6HBxHcQDLYL7sMk&hl=en&ei=_KrxSt3UJoedlQeh5bChCw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CBkQ6AEwAzgK#v=onepage&q=&f=false

[larryCR]

You also have to consider mounting point geometries. Put a long arm on a stiff bar and you get the equivalent of a thinner bar with a shorter arm. Thickness alone doesn't tell the stiffness tale.

[Fit4aking]

I hear what your saying larry but in Forza there is only one value, stiffness.  I doubt very seriously that you could go through and completely spec out a real life car and have any success in the virtual world.  I would love it if that were the case but I doubt it.

All I was trying to accomplish was a rough estimation of the sway bias on a real car vs the way its modeled in game strictly as a comparison, not as a way of determining a setting. 

Oddly enough it looks like the split front to rear on the P-car is roughly 70%-30%.  At least that's what I took from the equations.

Ft 23^4 = 279841
Rr 19^4 = 130321
Total sway = 410162

Front percentage of total = 68.2
Rear percentage of total = 31.7

It may make sense to think of the sway adjustment as exponential instead of linear but I don't know if that's the case. I don't have the an unlocked version of the Tonka Toy to check and I don't even want to go near Feuers numbers!!  Scary stuff in there I'm sure. 

Again just scatterplotting right now, well more like throwing paint at the wall and seeing if anything sticks.

[Blooze]

Hmmm, so then it isn't out of line to consider that a Porsche and a Mustang would have similar similar settings as far as stiffness is concerned... i.e., biased toward the front.

My brain wants think that the stiffness should align itself with the weight bias of the car. 

Thanks for checking that, Fit

  $

[fndrbndr]

Actually, you can plug in RL values and get a pretty good car in-game.  Bimmer and I have build Targa-based miatas with some success, and I know he looks up ARB numbers online for his tunes frequently.

[bimmerlovere39]

I consider 1.00 FMU (Forza Motorsport Unit  ) to be 1mm of Diameter IRL.  I used the same conversion in V2 and V3, and so far, it has held true. 

As for the biasing, real life cars are set up to understeer (which is the biggest disadvantage of running what I consider real life bars in-game, unless you do a lot of throttle rotation - which I do). 

[larryCR]

I hear what your saying larry but in Forza there is only one value, stiffness.  I doubt very seriously that you could go through and completely spec out a real life car and have any success in the virtual world.  I would love it if that were the case but I doubt it.

Fit: There is only one value of stiffness in RL too. What I was trying to say is that it is a combination of the twist resistance of the bar and the mounting points on the chassis and suspension. This article says it better than I ever can:
http://en.wikipedia.org/wiki/Sway_bar

So measuring the bar thickness is not enough. You also need to measure the length of that last lever arm that connects to the suspension. With these two measurements you should be able to get a good measure of the relative front/rear ARB stiffness on those two RL cars.

[fndrbndr]

Hm....the RL values I use tend to be specs for track cars and such.  I use less throttle rotation, too.  Interesting.