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      09-07-2009, 01:28 PM   #19
M3V8Driver
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Drives: E92 M3 - DCT
Join Date: Mar 2009
Location: Pittsburgh, PA

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Quote:
Originally Posted by kmac1980 View Post
Really? so running two wheels off the track is worse than hitting a defined lip pothole in ashphalt (or worse, concrete) at 30mph in the city?
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.

Quote:
I mean I suppose heat is a factor on the track from the brakes?
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.

Quote:
I can understand i you're reffering to running into a wall or something, but i'd think the wheels would be the least of your concerns.
Yeah, ONLY after something goes wrong. The point is to avoid that if possible. Hence my concern about the complaint with the Forgestar wheels.

Quote:
I suppose on the track you get a lot more lateral forces exposed to the wheel center, as opposed to vertical forces on the street, i just didn't think they would compare, I mean even if your car pulls 1.1Gs on the skidpad, that wouldnt nearly equate to the weight of your car, plus forward momentum plowing into a pothole. I suppose it's possible though that wheel centers are much strong against their vertical forces than lateral ones?.
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.

Quote:
All I know is I have 2 friends that have bent very expensive wheels in the city, but their dedicated track setup has never experienced any issues.
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.

Quote:
Keep in mind, I was all along reffering to the wheel barrells, not the centers. I agree it would be scary to know that your wheel centers woudlnt hold up, but like I mentioned before, i havent heard of anyone that has sheared/crack the spokes on their wheel! (which the issue of "shaving" the wheel center pertains to)

I think my point as more to do with that even very expensive wheel manufacturer's products aren't immune to damage (wheel barrells), even some of the manufacturer's that are highly praised on this forum.
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.

Regards,
Dale
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