maddog2020 wrote: ↑Thu Dec 24, 2020 1:26 pm
Fikse FM10 18x9 with 265/35/18 Pirelli PZero Rossa's Combined weight 42.4 lbs
Fikse FM10 18x12 with 335/30/18Pirelli PZero Rossa's Combined weight 54.2 lbs
I don't remember the exact numbers but the tires weigh more than the wheels.
The overall weight vs stock really doesn't matter since I needed 18's to clear the front brakes, and needed the 12's out back for traction.
Thanks for those weights. The Fikse wheels are lighter than the average wheels of the same size, so you're as good as good can be without going fully custom. Those rear tires look massive. You must be really excited to be getting the car closer to on the road! And it looks great. Really good work there!
Vector forces from rotational inertia of the wheels/tires don't come into play when in a single plane (like when accelerating or breaking in a straight line). And their affect on steering is negligible on a four wheeled vehicle. Technically, it resists turning the wheels, including straightening them out after they are turned, but it's negligible. But, definitely a factor on two wheeled vehicles. When I first started riding motorcycles, the common rule of thumb at the time was that centripetal forces, and the related vector force affects of rotational inertia, came into play at around 6mph, give or take based on tire sizes and weights.
You mentioned before that you felt that 335's were necessary for traction reasons due to your power levels. Do you have any dyno graphs? Do you remember what gears and under what conditions you lost traction?
Since I never used a real dyno, any numbers that I have for my car are not only extrapolated from GPS or RPM readings, but also have a correction factor that is partly based on weight, CD, and frontal area, but also based on comparisons to pre-turbo power levels. In other words...there is a lot of room for error.
Combining that uncertainty with the fact that I rarely spin the tires under acceleration has sometimes caused me to doubt the power levels that I think that I have (max of ~530rwph and ~550 lb ft). However, I have some factors that contribute to not losing traction. R compound tires. 95+ degree days. And I always always always roll into the throttle. The closest that I ever come to sudden power application is the one or two times that I've started at 1,500 to 1,600 RPM with foot fully off and then just stepping all the way down to see how quickly it can go from full vacuum to any positive boost at low RPM.
So, I've become very intrigued by the torque curves on dyno graphs and comparing them to my own. And, knowing what kind of tires are being used and what attention has gone into determining the best pressure, camber and toe for them. Plus, knowing how the vehicle was driven to lose, or maintain, traction. The number of examples of those factors all being known about a car is extremely low.
Maybe it's more than you care to share, but I would love to know more about your experiences if you're willing to share. It will help to better frame my own experiences and fill in some blanks for me on the differences between NA and FI power curves on our motors.
Regardless, congratulations on your progress and I hope it all comes together smoothly for you!