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      09-07-2009, 05:11 PM   #20

Drives: '11 535xi, (former '08 M3)
Join Date: Jan 2006
Location: toronto

iTrader: (1)

Well said, I agree with you on all points...

However, have you seen (first hand) wheel centers fail catastrophically? That seems like a gross error of design/engineering that should be caught by a regulating body.. (DOT? who regulates manufacturers of wheels?)

Originally Posted by M3V8Driver View Post
Well, actually, yes. If I run a wheel off the track, it's going to be upon exiting a turn, in other words, under high speed and duress... much more so than cruising over a bump or pothole at 30mph. Thre are ruts and bumps off the sides of most tracks. It's just natural where pavement meets soil. But that's neither here nor there, because safety isn't as much of an issue. If a wheel bends, you might lose air, which isn't as serious as a wheel hub shattering.

Yes, that is another factor that backs up my point about the track-worthiness of a wheel. Wheels are subjected much, much more to stress (lateral and longitutenal), vibration, and heat when tracked.

Yeah, ONLY after something goes wrong. The point is to avoid that if possible. Hence my concern about the complaint with the Forgestar wheels.

Not all of the wheight of your car is going to be on one wheel at one time. If you know what corner balancing is, then you know there is only a percentage of weight at each corner (sitting still on scales). For the sake of simplicity, let's say an E92 M3 weighs 4000 pounds with driver and fluids topped off. Let's say the car is perfectly balanced with 1000 pounds at each corner, and each mph add a pound of force. If you roll over a speed bump on the street going 20mph, you're talking about 1020 pounds per wheel. If the speed bump is sharp enough, that will likely be enough to bend a weak wheel rim, but do nothing to the hub, because the rim absorbed the blunt of the force when it bent.

Now suppose I'm taking a corner at 1.1g (like you described above) and 90mph. That's 1090x1.1 = 1199 pounds of force on each outside wheel, and at an angle that more stressful to the hub. Now say I put a wheel off and hit a bump while doing so. Imagine the blunt force the wheel is subject to at that moment, going 90mph, pulling 1.1g, then hitting a bump. If the hub can't take it, it's game over. if the rim bends and the tire loses air, there's a good chance I'll be able save it and limp it back to the pits.

You're sort of backing me up here, because I am trying to emphasize the importance of wheel integrity for track use. Your two friends are out a pair of wheels, and perhaps some time and trouble of resolving the matter, but their cars didn't get mangled, nor did they get injured.

It was crimsone90 who wrote "There are some issues with the Forgestar wheels. They machine too much from the hub and end up weakening the wheel." Let's see what he and/or others have to say in response.