wheel flex?

[ljs96076]

Hello all, I am new to this forum seeking an answer that is being debated by non-engineer-types. I searched the subject but had no success and am not familiar with this sites navigation so sorry if I have missed an easy route to find an answer.

Basically what I am trying to find out is this...
does the wheel on a car actually flex under cornering forces? Every wheel has its designed offset, but is it possible for an offset to be altered during cornering loads and then return to its designed position once cornering forces are no longer applied?

I have been saying that this does not happen on quality engineered/designed wheels. It seems to me that the spokes would crack either at the hub or at the rim of the wheel if such force was applied that could actually push the center of a wheel inwards. This isnt even considering the far less amount of force I am thinking it would take for the tire to be torn from the wheel itself in a corner, much less the tire simply losing grip mid-corner.

Am I wrong here? Does a wheel actually "flex" inward and outward during cornering? This topic came up when considering wheels with spokes that only cleared calipers by 1 or 2 millimeters, and someone thought that the wheel could flex during cornering loads and actually lose that clearance. It is my belief that this is impossible on properly designed wheels.

Does anyone know the truth on this matter?
Thanks in advance
LJ

 

[NormPeterson]

My 3500# front engine/RWD car has somewhere between 1/32" and 1/16" static clearance between the inner flanges of the front wheels and the outer tierod ends (front steer arrangement). Wheels are 15 x 8.5" one-piece cast aluminum Cragars with wide spokes of channel section, tires have been various summer performance makes/models. I have experienced no rubbing under any conditions yet encountered, including 3 seasons of autocross over several different lots. Whether the use of DOT "R" compound or grippier tires would bring on any rubbing is unknown.

On the other hand, I have caused wheel covers on steel wheels retained by the OE spring clip mechanisms to fly off from cornering-induced distortion only (generic all-season tires).

Norm

 

[NickE]

ljs96076- have you ever spoked up a bicycle wheel? Then you would understand the kind of flex that Greg and I are talking about. Thats why I mentioned hoops in my post above, if you push at any one side of a hoop the whole thing reacts.


nick

 

[GregLocock]

Quick estimate - an alloy rim designed for the same kerb impact type load will be as heavy, but 2.5 times as stiff, as the equivalent steel rim. in a 16 or 17 inch

Incidentally, how stiff do you think wheel bearings are, in this context? and the spindle? and the stub axle? and the wheel studs?



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[RvL04]

Here are some interesting pictures mildly related to this discussion:

http://www.michelinmedia.com/naias_2005/html/tech_tweel_gallery.htm

best,

Ron

 

[ljs96076]

I'm not really sure Greg, to be honest, but I thought it was a safe "educated" assumption that tire grip would be exceeded long before enough force could be exerted to break the bearings or flex the halfshaft. Am I wrong to assume the tires' grip would be the weakest link in the chain of a sportscar equipped with high-performance / race tires on cast/forged alloy wheels?
I hope you guys dont seriously believe I expect any of you to actually acquire test data for me, I simply hoped this would be a a good spot on the net to catch an automotive engineer with experience in wheel design, and toss the topic to the mind of someone obviously more "in-the-know" than myself.


Very interesting those pics of the "Tweel" were.....I dont care how fuddy duddy I look X-number of years from now for shrugging off the inherent benefits of them, I will not put those things on my car! lol

 

[GregLocock]

You are confusing stiffness with strength. The flexure of the wheel is just one of a series of compliances betwen the car's body and the tire.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.