TOPIC: Official Car calc thread.

Official Car calc thread. 5 years 3 weeks ago #345

Thought we could compile a list of gearhead (or petrolhead :topgear:) calculators. Post some useful ones below and I'll add them here.

Wheel offset calculator: kgm.tiwing.com/calcs/offsetcalc.htm
Tire size comparison: www.discounttire.com/dtcs/infoTireMath.dos
• 2008 VW GTI • No. 81 STX •
Last Edit: 5 years 3 weeks ago by Doktor Schnell.
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Official Car calc thread. 5 years 3 weeks ago #346

I made this one this morning, been thinking about it for awhile. I'd appreciate someone looking it over and making sure I didn't make any mistakes.
With this calc, you can compare cornering diameters and avg MPH to theoretically see how fast you can get around a corner (or hairpin, or skidpad)
skidpadcalc.png


In the above example, the hairpin 180° turn is 31ft in diameter, taken at an avg 20mph, and that takes 1.66 sec. I think that's correct. I think it is interesting that in B taking the turn 1 ft larger in diameter (6" farther out) at 1mph faster gets you .03 sec faster.
Download and let me know what you think.

File Attachment:

File Name: Skidpadtiming.zip
File Size: 10 KB
• 2008 VW GTI • No. 81 STX •
Last Edit: 5 years 3 weeks ago by Doktor Schnell.
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Official Car calc thread. 5 years 3 weeks ago #351

  • xilr8n
  • xilr8n's Avatar
It is more complex than that me thinks...
The real part of the time difference is the distance away from the apex cone. The rest is maxing out your traction circle. And then you could figure out if it is faster going wider with both tracks at max.
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Official Car calc thread. 5 years 3 weeks ago #352

Definitely is more complicated in reality. For one, it is assuming a perfect circle, not does not usually happen. The numbers don't tell you anything about the car, only how many sec it takes to do the perfect arc.
What it could tell you is that IF you take the inside line (30ft) as close to the apex as possible, it is slower than taking the outside line 6" away if your allowable traction circle will give you 1mph faster. Am I right?

To really use this, you would need to know your car's max speed at a given turning radius. I suppose that you could do the skidpad test. But then you'd only know your cars max speed at the one turning radius. I don't know if there is a way to extrapolate that number to a different turning radius. It probably isn't a simple linear relationship.
• 2008 VW GTI • No. 81 STX •
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Official Car calc thread. 5 years 3 weeks ago #353

Your math is correct, but is only true if your car can go 1 mph faster by taking the turn 1ft wider. To calculate the fastest turning circle for your car is far more complex. The most daunting would be calculating the potential lateral grip the car can muster. You would have to test it in a skid pad. Or, if you make the assumption that the car will generate the same grip at all radius turns, you could make 2 equations with the same unknown variable and potentially solve. Without being able to simplify the combo of weight, tire, spring rate, damping curve, camber curve, bump steer, and the rest of the suspension factors, into a number for lateral grip, the equation would get too complicated.

Some cars will be faster by taking a turn wider, but you'll need to experiment to find out.

Sorry if that was a glass half empty response.
#36 SM 1995 240sx
2005 STi - DD

"When it comes to boost, if some is good then more is better!"
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Official Car calc thread. 5 years 3 weeks ago #354

This is all useful, I think.
I don't know if it is worth trying to calculate grip, and therefore speed at a given turning radius. The variables involved are just too many, and in some cases, probably unknown--ie., what kind of weight transfer would occur at x speed and y turning radius with your 200lb friend riding along with you leaning to the right?

It might be useful to do a skidpad test on the smallest turning radius that your car can do, and then just speed up until you start pushing wider, or you oversteer and spin. As the turning radius increases, less lateral force is generated, so therefore speed can increase--everybody know that. Might be interesting to graph 3 or 4 different skidpad tests...at minimum turning radius, then +10ft larger, then +10, and +10. I have a feeling that the graph line through points would be logarithmic, since it has to approach 0 (no lateral force limiting speed) as the driving line straightens out. Am I overly simplifying?
• 2008 VW GTI • No. 81 STX •
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