rim size

[Howard]

Assuming the same tread depth and compound, larger tires (diameter-wise) last longer. I would assume that larger tires tend to be made with a "gripper" and hence shorter-lasting compound, though.

 

[imported_Truenofan]

actually pacman, even if its on the inside of the rim, its still more mass/weight that the engine has to spin, so its going to be slower no matter what if the rim is heavier.

 

[Howard]

Originally posted by: Truenofan
actually pacman, even if its on the inside of the rim, its still more mass/weight that the engine has to spin, so its going to be slower no matter what if the rim is heavier.

uh, i was on crack there, let me try taht again

The closer the mass is to the rotating axis, the lower the moment of inertia. The lower the MOI, the easier it is to accelerate angularly. Even if there may be an added mass penalty, if the MOI decreases the acceleration of the car may well increase.

 

[imported_Truenofan]

um....more weight hurts no matter where it is, srung or unsprung, doesnt matter. more weight slows accel/decel and handling. kinda the reason they make racing cars super light and have light weight rims.

 

[TheSlamma]

Pick up an alloy wheel then pick up a tire. Then remember this phrase "unsprung mass"

 

[Apex]

Originally posted by: Howard

Originally posted by: Truenofan
actually pacman, even if its on the inside of the rim, its still more mass/weight that the engine has to spin, so its going to be slower no matter what if the rim is heavier.

uh, i was on crack there, let me try taht again

The closer the mass is to the rotating axis, the lower the moment of inertia. The lower the MOI, the easier it is to accelerate angularly. Even if there may be an added mass penalty, if the MOI decreases the acceleration of the car may well increase.

This is very true.

That's why people who race on Dymags love them so much. Though they're not that much lighter than many competition wheels, the weight is carried closer to the center (with their carbon fiber hoops being relatively light compared with their magnesium spokes).

 

[jagec]

Originally posted by: Truenofan
um....more weight hurts no matter where it is, srung or unsprung, doesnt matter. more weight slows accel/decel and handling. kinda the reason they make racing cars super light and have light weight rims.

So you're telling me that if I gave someone 50 lbs of lead that they had to put in their car somewhere as a handicap...they'd have no preference on where it went?

Personally, I'd want that weight as low and as centrally located as possible, in order for it to be sprung mass (yes, it does make a difference), not have any angular inertia component (yes, it does make a difference...look up the principle of the flywheel), and not add any polar moment of inertia or raise the CG (again, it makes a difference, although these last two matter for handling, not acceleration).

More proof it's different: Remember those little cars that you used to have as a kid, where you'd slide them across the floor to spin up a flywheel, and then let go and they'd keep going for quite a while? It was pretty hard to push (read: accelerate) those cars compared to a Matchbox car of the same weight, right? The ONLY difference was the angular inertia of the flywheel.

 

[imported_Truenofan]

im saying that weight in general hurts a vehicle in every way or form, placing it in specific spots may hurt more and others may hurt less, yes he's right on where the most weight on a rim will hurt, but the weight will hurt none the less. and i didnt play with those. yes i understand the point your making in your second paragraph and i agree completely. having the weight on the outside of the rim will hurt more than the inside, but its still leaving an impact. and i was right on the point i made that Howard tried to prove me wrong, the engine is STILL spinning that weight up to speed the car up, thats the point I'm attempting to make but some aren't understanding. the engine is still having to deal with the additional weight.

http://www.mazda6tech.com/inde...k=view&id=16&Itemid=50]http://www.mazda6tech.com/index.php?option=com_content&task=view&id=16&Itemid=50
http://en.wikipedia.org/wiki/Unsprung_weight]http://en.wikipedia.org/wiki/Unsprung_weight
going by those, if you have those nice heavy 40lbs rims that weigh even more with tires, you would also have to increase your spring rate to deal with the weight traveling upwards. lower unsprung weight, is better, and lower weigh overall, is the best option. lightweight ftw.

http://www.sportcompactcarweb....ring/light_wheels.html]http://www.sportcompactcarweb.com/tech/0506scc_handling_cornering/light_wheels.html

edit: called a ballast as well, they use it in some European racing when the winner keeps winning and they need to slow him down so the rest of the cars can compete. usualy put it in the rear if the car is front heavy to balance it out if needed.