Lou's Tuning Tips....

So there are a tone of resources out there for tuning reference, so I'm not going to write a tuning guide. I'd only be regurgitating what many, many, many, many (name that movie) have done before and will do again... Not gonna dewit.... With the Porsche pack, May DLC and June DLC (50 cars) not covered in SMTC, I'm actually now tuning with no tools other than the Xtreme Skills calculation to get a good spring rate and Slave Munky's TC if I need to get a good base trans tune on some cars... Otherwise it's just tune, test, repeat.... And I'm getting some really GREAT results...

I posted this in another thread where a question about brake bias/balance was asked. I realized that while there are a ton of tuning guides, there's not much around brake tuning... Over time I developed my own way to set the brakes up, and it works (for me) 95% of the time.... Slave Munky's FMTC moves the bias WAY TOO much in either direction, so I developed my own method...

Here's what you do:

1. Once you've finished installing all parts, take the front weight % of the car and subtract 50 from it. (yes you will get a negative number if the fr weight % is below 50. That's good)
   
2. Divide result in half (divide by 2)
   
3. Add that number to 50 and you have your starting brake balance (yes you will add a negative number)
   
4. see the examples below

Example 1:

Front weight bias = 43%
Diff from 50 = -7 / 2 = -3.5
Remove 3% to 4% brake bias (basically set it to 47% or 46%)... You are moving more brakes to the rear of the car...

Example 2:

Front weight bias = 62% (obviously a FWD car )
Diff from 50 = 12 / 2 = 6
Add 6% to the brake bias (basically set it to 56%)... You are adding brake bias to the front of the car....

I will be updating my Xtreme Skills calculator to also provide a starting Brake Bias %....

Cheers!

Good post Lou, very simple and makes perfect sense!

Hmmm... my head's telling me this doesn't quite work, maybe it's my inexperience and you could clear it up for me?

Under heavy braking, weight shifts forward, and therefore off the back. If you put your best brakes at the back, surely you lose potential? Like I said maybe I'm missing something? What I mean is, standing still it makes sense, but during decelleration the weight from a 45-55 car becomes more like a 55-45 depending on springs?

HotDog... It all depends on where the center of mass is of the car.... If 55% of the car's weight is in the rear, having more brakes upfront will tend to cause the ass to want to whip around the nose... If the car has 55% of it's weight up front, too much rear brake will cause frequent rear locks. the weight does shift forward, but not in the same way it would in your daily driver. The lower the center of gravity is, and the stiffer the suspension is, will cause more of a parallel to the road surface shift in weight as opposed to more of a "nose dive" in a street car.

Too much brake up front will cause you to slide the front end at corner entry and too much rear will cause the rear end to slide and whip with the slightest deviation from a straight line... What you want is the brakes to work together front and rear... There is a maximum amount of adhesion the front tires will be able to handle before they begin to understeer and ultimately lock-up... Tuning the brakes to the weight distribution is a must, but you want to find that sweet spot where the front and rear brakes lock up at the same time under full brake pressure. If you use ABS in game, this does not matter as much, but it will still prevent ABS from kicking as soon.

While some like to match the weight distribution % in the braking balance, I've found that meeting halfway is much better set-up.

Ah ok, thanks =D
I don't tend to touch break balance so much, mostly due to the fact I never lock the wheels any way. Maybe I could break harder and make up some more time....

FM4 and Tires: What I've Found to be true!
This came from another thread here on the U2SC forums, but it goes well with this thread as well!

beefsupreme42 wrote:I have a couple questions I was hoping you would be able to answer for me. On VVV Worm's tuning guide, it says more ARB=Higher tire temperatures and more spring=more tire temperature. does that mean that the springs are a multiplication factor of the heat created by the ARBs? also are there other ways of lowering the tire temperatures other than softening the ARBs and raising the tire PSI?

So... the tire temps associated with the ARB's is simple... the stiffer the ARB, the more the car will slide hence raising temps.... Same thing with spring..

Now... As far as tire temps go, I'm glad you asked... yes there is, but it's not 100%.... Tire aspect ratio plays a part in temps and it has to do with the volume of air in the tire. The more volume of air inside the tire, the more consistent the temps will be....

Example: A tire size or 305/55-R15 will have much lower temps than the same car with 305/35-R19's..... Why? The 55 series tires have the same tread width but much taller side/walls...

What do the 55 and 35 numbers mean? Those numbers represent the height of the tire's side wall in % of the overall tread width.... So.... For the sizes mentioned above, 305mm tread width (the tread width is in mm btw) with a 55 series sie wall = a 168mm high sidewall. the 35 series tire has a 107mm high sidewall...

So...... With the same section width of 305mm, but taller sidewalls, the 305/55-19 tires have more volume at the same PSI. That means it takes more energy and time to heat the tires. It also means that the 35 series tires require less time and energy + you can run higher tire pressures.

Why is it not 100%? Well... If you have not increased the Rim size on a car, then there is no way to reduce it to bring temps down. On the flip side, if you are having issues with getting tires up to the proper temps, try increasing the rim size in 1" increments to see if it makes a difference...

Rule of thumb? If you are dropping tire pressure below 28 PSI, try increasing the Rim size to see if that will bring more heat to the tires. Go the other way if you have too much heat (if you can).

Here is a GREAT read on what tire sizes mean and then some. It's what I used when I first started tuning as well.... http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=46


Let me break down the tire information as well...

Example: 305/55-15

• 305 = The total section width of the tire from the widest point on each side. This does not indicate contact patch, but the width between the sidewall "bulges" or widest points.
  
• 55 = the height of the tire sidewall in % of the section width. In this example the sidewall height is 55% of the section width of 305mm. That equals 167.75mm.
  
• 15 = Rim diameter in Inches (yeah inches)

What will increasing the rim size do in FM4?
Good question.... In FM4 it actually effects two things. Tire Temps and Final Drive ratio.

• Tire Temps: I think I explained that in pretty good detail above. In a nutshel, increasing the rim size in FM4 ONLY effects sidewall height. This means the overall diameter and width of the tire remain about the same. This , in turn, means a reduction of air volume in the tire. This then effects how the tire handles heat.
  
• Final Drive Ratio: I actually stumbled on to this one while tuning in FM4. I set a tune in FMTC and then changes a few bits including rim size, then updated FMTC. To my surprise, the final drive and top speed changed. So I did some research, but I didn't really find any useful information other than this. increasing the rim size, also increased the unsprung weight of the car (car weight not supported by the suspension). With more wheel weight, it takes more force to turn the wheel. This is turn requires slightly different gearing. If you change the rim size either way, head back to the FMTC (if you use it) and recalculate the gearing.

I need to try your brake bias calculation, I have a few cars that are unpredictable under heavy braking. Thanks for sharing!

OK... It's been a while since I posted in this thread. There is something that I've been testing and tracking over the last month or so, and I wanted to share with you guys...

I've asked the question several times in various forums and to our resident Tuning expert Frank.... "Does changing the rim size have any effect on the car? Does it help or does it hurt?"... The answer I receive is usually the same. "It all depends on the car!"

Here is what I've found..... It all depends on the car and you cannot trust the PI + or - from the change.... WTF does that mean?

First:
Older cars have smaller diameter rims.
.......Why? Because tire technology was not as good.
.......But does that mean I should increase the rim size? Not really....!
.......What should I do? Tune and test the car using the STOCK rim size (not stock rims but the stock size)..
.......Really? Why? You want to test the handling and tire heat with the stock rims to check handling and optimal heat.
.......So what am I looking for? If you cannot get heat in the tires even though you've dropped to 27/28 PSI, it's time to bump rim size up in 1" increments both F & R and test again!
.......How does changing the rim size help with temps? It lowers the volume of air in the tire. Lower Volume = easier to heat.
.......Doesn't bigger rims = better handling? Not always. Increasing the rim size might actually make a car very loose and prone to wheel spin!
.......Anything else? YES!

If you change the rim size, you will need to adjust the final drive and individual gear ratios to get optimal acceleration.

As you increase the rim size, you increase weight (unsprung), which in turn reduces handling.

Ultimately BE CAREFUL when dealing with Rims and tires... It's not always the best move increasing rim size and tire width... Make changes in small increments and test....

Tire wall height changes in accordance with rim size, some obvious things you notice especially on older cars with those tall tire walls are tire wall flex, which is what makes it easier to predict when its on the limit of tire grip unlike low profile tires where the limit would be found much more like an immediate loss of grip - "peaky"

Fear740 wrote:Tire wall height changes in accordance with rim size, some obvious things you notice especially on older cars with those tall tire walls are tire wall flex, which is what makes it easier to predict when its on the limit of tire grip unlike low profile tires where the limit would be found much more like an immediate loss of grip - "peaky"

Exactly!! Especially when using racing tires, which reflects real life. Most real life racing tires are actually 40 and 50 series tires. Why? Racing tires have much stiffer sidewalls as ell as squarer shoulders...