I think as a group we get too caught up on unsprung weight at times. This magazine has done back to back testing on larger/small/lighter/heavier wheels and tires several times over the years, and at times the results have been counterintuitive. At times the heavier wheel/tire combo (while trying to normalize for other factors) has proven faster. What that means to me is that in the real world of amateurs having fun at autocross and track days, the difference in unsprung/rotating mass isn't as large an issue as we all (want to) think it will be. This isn't F1. To me, wheel failures on lower priced wheels isn't a condemnation of any particular wheel, it's more like a commendation for cheap steel track wheels. There are probably hundreds of thousands of oval racers out there abusing wheels on dirt and asphalt far beyond what we as a collective will do at an autocross or track day without issue, or if there are issues cracks in steel are often easier to spot and way cheaper to replace. If I get back into track work, I'll save money and carry a few extra lb's. If you are one of those chasing National championships, well then all bets are off. Time for $1,200 a corner real forged wheels. YMMV
Dead_Sled said:
You don't have to exceed the yield strength of a material to fail under high cycle fatigue.
Aluminum does not have an infinite life like ferrous metals. Given enough cycles, an aluminum component WILL fail under cyclic loading.
1500 track miles is going to be alot more than 5x10^8 cycles.
I would bet the stress induced by a wheel revolution is so small that it is near-infinite.
I imagine the stress induced from ND levels of acceleration is not terribly high either.
The stress from 1+ G cornering is significantly higher, as is hitting the curbing. The number of cycles here is probably a lot lower
In reply to Adrian_Thompson :
i had to read that sentence a few times because condemnation and commendation look really similar
Adrian_Thompson said:
I think as a group we get too caught up on unsprung weight at times. This magazine has done back to back testing on larger/small/lighter/heavier wheels and tires several times over the years, and at times the results have been counterintuitive. At times the heavier wheel/tire combo (while trying to normalize for other factors) has proven faster.
I thought in that test the heavier wheels ended up with more rubber on the road? Which would certainly negate a few extra pounds.
ProDarwin said:
I would bet the stress induced by a wheel revolution is so small that it is near-infinite.
I imagine the stress induced from ND levels of acceleration is not terribly high either.
The stress from 1+ G cornering is significantly higher, as is hitting the curbing. The number of cycles here is probably a lot lower
many interesting points here.
what part of the wheel carries the vertical load? the part between the contact patch and the hub. so that part of the wheel is in compression once per wheel revolution. and when that part of the wheel is at 12 o'clock, it's carrying zero vertical load (well, technically that part of the wheel is in tension), so it is true that every spoke is cyclically loaded in compression/tension with approximately the corner weight of the vehicle once per every revolution of that wheel.
and what is a G? it's just an easy way to talk about forces without units of force. we arrive at G by dividing applied force by normal force. so when looking at one individual wheel on a car, the wheel is cyclically loaded in compression by the normal force due to the corner weight on that wheel, ie 1G vertical. and that's just in a straight line. Now throw that car into a corner and lets say the tires and the suspension are good enough to generate 1G lateral, now that wheel is loaded with more than the original corner weight vertically, because it's the outside wheel in the turn and there's lateral weight transfer because the CG is above ground and the track width is not infinite. PLUS the lateral force.
About body damage - here's my experience. Rear drive flange failed and I drove over my own wheel in Turn 9 at Laguna Seca. Took out the muffler, banged up the trunk floor and uglified the rear bumper. I have skid plates all over the bottom of the car, so they did their job and protected the important bits. I would have lost the diff otherwise. Also, had I hit the gravel the wrong way a roll was very possible.
You forgot to embed video:
In reply to GameboyRMH :
I'm putting that one down as damn lucky to stay shinny side up!!!
I was lucky that the wheel came off at the apex, which gave me the maximum amount of time to scrub off some speed on the asphalt before we got dirty. I was thinking about the cage as we went through that, though...
AngryCorvair said:
ProDarwin said:
I would bet the stress induced by a wheel revolution is so small that it is near-infinite.
I imagine the stress induced from ND levels of acceleration is not terribly high either.
The stress from 1+ G cornering is significantly higher, as is hitting the curbing. The number of cycles here is probably a lot lower
many interesting points here.
what part of the wheel carries the vertical load? the part between the contact patch and the hub. so that part of the wheel is in compression once per wheel revolution. and when that part of the wheel is at 12 o'clock, it's carrying zero vertical load (well, technically that part of the wheel is in tension), so it is true that every spoke is cyclically loaded in compression/tension with approximately the corner weight of the vehicle once per every revolution of that wheel.
and what is a G? it's just an easy way to talk about forces without units of force. we arrive at G by dividing applied force by normal force. so when looking at one individual wheel on a car, the wheel is cyclically loaded in compression by the normal force due to the corner weight on that wheel, ie 1G vertical. and that's just in a straight line. Now throw that car into a corner and lets say the tires and the suspension are good enough to generate 1G lateral, now that wheel is loaded with more than the original corner weight vertically, because it's the outside wheel in the turn and there's lateral weight transfer because the CG is above ground and the track width is not infinite. PLUS the lateral force.
The cycling compressive loading due to rotation would almost never cause a failure in the spokes. The bending load from the lateral force has to be huge. Think about the moment from the hub to the tire. This load grows as tires get stickier and wheels/tires get larger in diameter.
It makes sense to talk about it in terms of cornering force. Pretty easy to convert to force. Lets say you have a 2000lb car with a 60% front TLLTD that corners at 1.2G. The lateral load generated at the front wheel is 1440lb. Now if you have a 25" tire and a hub say 5" in diameter you have a 10" moment arm that you are applying your 1440lb load on the end of. Now bump a curb and that 1.2g becomes 2g...
