Unsprung weight, tire + air weight?

[evilnickwong]

I'm trying to figure out a rough approximation of my wheels weight.
Some time back, I compared the weight of my spare to my current wheel: (weighed on a normal bathroom weighing scale, not accurate, but enough to compare)

14" bottlecap, 195/60/14 tire: 14kg (30.8lbs)
16" throwing star rep, 215/50/15 tire: 18kg (39.6lbs)

Obviously an additionaly 4kg unsprung weight per corner is pretty big. I'm just wondering whether that's down to the rim or to the tire + air.

I do like these throwing star reps, but if the weight is really the cause for my 318i M40 feeling sluggish, I might consider a switch.

[E30Idea]

Your problem is the engine, not the wheels and tires.

[evilnickwong]

:D Haha indeed, but swapping the engine isn't something I will be doing anytime soon. I guess I mainly want to know if that extra 4kg/corner is substantial enough to have an effect on my handling/performance/mileage etc.

[E30Idea]

:D Haha indeed, but swapping the engine isn't something I will be doing anytime soon. I guess I mainly want to know if that extra 4kg/corner is substantial enough to have an effect on my handling/performance/mileage etc.

Its unlikley. While every pound matters, I doubt you will notice anything by purchasing a different set of wheels.

[E30Idea]

:D Haha indeed, but swapping the engine isn't something I will be doing anytime soon. I guess I mainly want to know if that extra 4kg/corner is substantial enough to have an effect on my handling/performance/mileage etc.

Well 4kg is 9lbs per wheel. That is quite a bit of weight but I doubt you will be happy with the results by only going with a lighter wheel.

[Marcos]

I beg to differ, I'm sure you would notice quite a difference in handling plus initial acceleration in a lower weight wheel/tire package. The only issue is whether you can actually go too much lower in weight at least for a reasonable amount of $.

The wheels are one of the best places to lose weight by far. A lot of people get all wrapped up in going with huge wheels and totally kill the handling.

to each his own

marcos

think 3-piece forged from HRE out of California. DOH, now that's $bling$

[Wh33lhop]

The extra weight is due to the extra metal needed for the bigger face and barrel of the wheel, and probably the mass of the tire itself (no, not the air). As you go up in wheel diameter and width, you will get heavier, as a general rule, even if your rolling radius stays the same. It is not cut-and-dry as different construction and design yields different weight as well, but that's the general gist.

10lbs per wheel is definitely big enough to notice--ricer math dictates that each pound added to rotational unsprung mass will translate to approximately 6 (some say 8) pounds added to the chassis, as not only do you have to accelerate/decelerate the mass of the wheel/tire, but you have to spin it faster or slower as well, which is significantly harder. So, you're basically adding 10*4*6 = 240lbs. That's enough to be noticeable if you try driving the car back-to-back (have a big-boned friend ride in your car and see if you notice the difference--you will). Whether that's the only issue is another story. Try switching back to bottlecaps and see how it feels then.

Honestly, though, you're going to have to get used to the car being slow if you've got an M40. :p

[evilnickwong]

Haha, yeah the M40 is pretty crap, but from this perspective, I shouldn't be making it even worse than it already is by adding unnecessary weight!

Problem I've had in looking for lighter wheels is that there aren't many options over here in Malaysia. I can get some really light Regamasters, RPF-1s or etc, but those are Jap rims and adding 20mm thick hubcentric spacers kinda adds back to the unsprung weight, so it's not really cost effective.