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An interesting tweak could be to make tire diameter and section width user-definable for race tires that are really different sizes than their nominal equivalents, like Codrus' hoosiers for example, that are a full 20mm wider than a quoted 245 at the same overall diameter.
As long as the reference tire diameter cell matches off with what you want, you can fake in whatever width/ratio numbers you want to get to your actual known diameter. That reference diameter cell is what the calculations reference for the math part of things.
Your curve doesn't really seem all that bad at glance. Your torque dips off hard the last 250rpm, so you aren't gaining time by revving out to that speed unless it means you are saving a shift prior to a braking zone, but the main meat of the graphs from 55mph+ look pretty strong. short shifting 4th and 5th may be a slight benefit if the track layout allows.
Ok sure, ill retract the "desperation" from my comment, but in our region (Norcal ST4) I think you really need to optimize everything to be competitive. Is it a bad graph, yeah not really, but if I can smooth out the overlap I can use all the gears to whittle down lap time/keep up with the podium guys.
Here's my dyno sheet for context. Its a torque monster in the mid range, but I think I need to put the squaretop back in to let really breathe up top, as you can see it ***** the bed after 6500.
Yeah, hence why it needs to go back on the dyno. Ill need to play some tricks to optimize for st4 hp avg, so it wont look like that, but I have a few ideas.
Always nice seeing articles from HPA that reinforce exactly what I stated in the OP. This is good for a nice little read if you still have questions on how to interpret tractive force graphs.
Good evening, Padlock.
I downloaded your spreadsheet and I'm very impressed with it. I added some elements to it to see how everything relates. However, I added a line of the max traction force at the two rear axles(=(weight in kg)( % of weight at rear)(g)(u of static friction)(0.224809 lbf/Newtons). Somehow, according to the chart, first and second gear produce forces that break traction which doesn't happen in real life. Am I doing something wrong with my calculations, how would you add this max tire traction line? I added a picture for reference. Thank you.
Good evening, Padlock.
I downloaded your spreadsheet and I'm very impressed with it. I added some elements to it to see how everything relates. However, I added a line of the max traction force at the two rear axles(=(weight in kg)( % of weight at rear)(g)(u of static friction)(0.224809 lbf/Newtons). Somehow, according to the chart, first and second gear produce forces that break traction which doesn't happen in real life. Am I doing something wrong with my calculations, how would you add this max tire traction line? I added a picture for reference. Thank you.
Well your maximum traction line is a perfectly level straight line/threshold which doesn’t seem to account for weight transfer, which would probably be most pronounced in the lower gears. So in those lower gears with weight transferring to the rear under heavy acceleration, you’ve got more weight on the rear tires and thus a higher static breakaway force.
Good evening, Padlock.
How would you add this max tire traction line? I added a picture for reference. Thank you.
I think a key miss that you have is assuming the normal force is a constant (it isn't). As a vehicle accelerates, it transfers weight to the rear end, which provides more traction than you'd calculate in the static condition. How much gets transferred depends on the chassis/suspension setup. Aero on the vehicle will also influence this as speeds get higher. coefficient of friction will also vary depending on road surface, road/ambient temperature, tire compound, tire contact patch, etc.
Completely modeling a traction curve would be fairly involved, but testing it is as easy as a test drive. If you want to get really involved, plotting traction circles with G-force data logs is the best way to understand the grip you have available. I have an example shown here. Lots of examples online to research into if you are curious.
Originally Posted by wombat57
wow - don't know how I missed this - Padlock - this is good stuff. I'm going to play with the ZF8 ratios. Thanks for putting it together!
I was playing with data today on a laptop that doesn't have Excel, so of course I went on a tangent and used AI to generate a static HTML file that does this work, plus some extras.
Claude offered to add a traction limit line, which takes into account the vehicle weight and the stickiness of the tire. It even grabbed some data for some tires. It turned out to be useless to me, but maybe someone will find value.
It also added a slider for drivetrain loss. I didn't think to remove that and it's not really bothering me.
Oh boy! I exploded a few heads a couple of weeks ago when I said that a heavier car can sometimes have better 1/4 mile times and 60 to 0 times, because weight. This is in reference to the new hyper ZR1X (or whatever) 1,250hp Corvette. It's HEAVY, but when you have weight like that and yuge amounts of torque, the weight gives you more traction (lbs per square inch).
I'm lazy....anyone want to compare how a 1,000lb ZR1X with 1,250hp would compete against a 4,500lb ZR1X, same horsepower and same contact patch?
Oh boy! I exploded a few heads a couple of weeks ago when I said that a heavier car can sometimes have better 1/4 mile times and 60 to 0 times, because weight. This is in reference to the new hyper ZR1X (or whatever) 1,250hp Corvette. It's HEAVY, but when you have weight like that and yuge amounts of torque, the weight gives you more traction (lbs per square inch).
The theoretical traction that tire will deliver is the coefficient of friction of the compound times the vertical force pushing it into the road, meaning that while it's true you get more traction by adding weight, the amount you gain is balanced out by the increased weight that you're trying to move. In reality tires are not perfectly linear here and you actually gain a little bit less traction than the weight you add, so heavier means less traction per pound.
The place where power to weight doesn't tell the whole story is top speed. That's much more about drag than about weight, and while it's true that heavier cars are usually bigger (and thus have more drag) it's not proportional. So two cars with the same power/weight will likely be very similar in the first half of a quarter mile (small advantage to the lighter one), but the heavy one will likely recover an advantage in the second half.
0-60 times are all about the launch and the gearing choices. Using a speed as a target instead of a distance makes it disporportionately sensitive to small changes at the beginning.
0-60 times are all about suspension, gearing, tire selection, and utilizing weight transfer as far as I'm concerned.. drag race classes wouldn't have minimum weight limits if weight truly helped (F=ma is a rather hard physics formula to break as it turns out). The key is having appropriate suspension to load the tires as the car accelerates. A properly setup 4-link straight axle will typically manage this extremely well for a drag car, but then that same rear end setup will suck for road course work. Getting an IRS car that behaves better during road course work is going to struggle more on launching and driving the tires into the ground. Yay design compromises!
The whole reason the C8 corvette (2.9s 0-60 base model) went to mid engine was to improve weight transfer during acceleration as the C7 (3.7s 0-60 base model) reached the limits of what was possible for what GM could offer in a production car. The C6 Z06 and C6 ZR1 were both early signs to GM that they were reaching limitations on weight transfer with the front engine / rear drive architecture as they were struggling with making the ZR1 report a faster time without better tires. GM has a neat video out there that interviews the engineering team and explains that which I can't seem to find now.
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