AkumaNoZeta Posted October 31, 2009 Share Posted October 31, 2009 Why is wheel track measured at the center of the tires? I was thinking it could be because that's where most of the weight on the tire is, but that may or not may be true based on tire pressure and camber. I have a feeling that track should be measured by the outermost edge of the tread. I've been thinking about this while playing with the Lateral Load Transfer equation in Tune To Win by Carroll Smith. Quote Link to comment Share on other sites More sharing options...
tube80z Posted November 1, 2009 Share Posted November 1, 2009 I think you'll find in this day and age most things are measured the way they are because of convention. SAE has a standard set of definitions that are commonly used in the automotive world so people understand what each other are talking about. Cary Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted November 2, 2009 Share Posted November 2, 2009 Tires are not solid, correct? They shift laterally under load (obviously less with stiff, low profile stuff), but technically, that's the center of the contact patch and the center around which the tire might 'sway'. That'd make sense as the measurement point. As an aside, I have even heard of factory Mitsu Evo wheels flexing laterally enough (on the spokes) to rub the calipers with slicks and whatnot in roadrace settings. Quote Link to comment Share on other sites More sharing options...
AkumaNoZeta Posted November 2, 2009 Author Share Posted November 2, 2009 I guess I just don't like it because with the idea of the track being measured at the tire's center than track width would decrease with wider tires keeping the outsides in the same spot. The SAE standard code thing is the only way it makes sense to me. Quote Link to comment Share on other sites More sharing options...
Valmont Posted November 2, 2009 Share Posted November 2, 2009 Could it be because the center of the tire is (because of centrifugal force) the only "guaranteed" point of contact with the ground? Val Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted November 2, 2009 Share Posted November 2, 2009 I guess I just don't like it because with the idea of the track being measured at the tire's center than track width would decrease with wider tires keeping the outsides in the same spot. The SAE standard code thing is the only way it makes sense to me. Well, whoever said you wouldn't need to recalculate track for different wheels, anyways? Track isn't the only thing to bear in mind, too. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 2, 2009 Share Posted November 2, 2009 I think Smith's equation is a generalization. You'll get an idea of weight transfer from it, but just thinking of the related issues I can come up with several things it doesn't account for, like cg height changing under different conditions, weight changing under different conditions, and of course the g loading changing. Track width on a Z changes too as the suspension compresses, so that too could change. Use the formula as an estimate not a concrete answer. Quote Link to comment Share on other sites More sharing options...
AkumaNoZeta Posted November 2, 2009 Author Share Posted November 2, 2009 I was just playing with it to do a 5.0 vs. EJ25 type thing. I assumed 19" CoG for the 5.0 and 15" for the EJ25. I also did it in 2 ways, first I did it assuming the vehicle was 2400lbs with 45/55 weight distribution and then I did it with differing factors. For the 5.0 I changed it to 2500lbs with 45/55 and the EJ25 with 2300lbs and 40/60. It kept me occupied for a little bit at least, supports my reason for wanting an EJ to. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 2, 2009 Share Posted November 2, 2009 Your estimated cg heights sound high to me. That's the problem with estimating I guess. It might be nice to see if anyone had a known cg height. Some corner weight scales do that calculation, so maybe someone here already has it. I seem to remember 260DET saying that the ZX had a cg height that was the same as the output shaft of the transmission for some reason, and the straight 6 should have a higher cg than a V8. It's tough to extrapolate that out, but 19" just sounds really high... Quote Link to comment Share on other sites More sharing options...
AkumaNoZeta Posted November 2, 2009 Author Share Posted November 2, 2009 19" is what I heard for a LS1 Camaro that got corner scaled so I used that as a base and used the 4" difference as an estimate of how much lower the EJ sits. With the way I think I rather do the work with the higher CG heights so that whenever I get to the swap and it's actually lower I would be more satisfied, instead of shooting for a lower number and it actually becomes higher. Quote Link to comment Share on other sites More sharing options...
WizardBlack Posted November 3, 2009 Share Posted November 3, 2009 EJ's are retarded light. I had an EJ25 shortblock sitting on a pallet for some time. When I needed to move it, I could lift it with one arm as long as I can get a good handhold on it. Quote Link to comment Share on other sites More sharing options...
260DET Posted November 4, 2009 Share Posted November 4, 2009 Your estimated cg heights sound high to me. That's the problem with estimating I guess. It might be nice to see if anyone had a known cg height. Some corner weight scales do that calculation, so maybe someone here already has it. I seem to remember 260DET saying that the ZX had a cg height that was the same as the output shaft of the transmission for some reason............... At top of the gearbox where the gear lever fits in, according to Nissan's info book on the 280ZX. I guess that would be fairly representative of any similar car ie straight six motor, RWD. Quote Link to comment Share on other sites More sharing options...
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