rx8thunder

I weighed my OEM rim & tire tonight and it's 46.5 lbs.

When I compare that result to this measured weight shown shown in this thread re: the popular Enkei Rpf1 18x9.5 with Falken tires and I only see a 1.7 lb advantage.

I do realize that the rim and tires are wider and that will in itself help performance, but the lightness advantage going this route seems to be overblown IMHO or what am I missing?

I also saw some one say that unsprung weight reduction is worth 10 times that of sprung weight from a performance advantage POV (i.e. reduction of 10lbs in unsprung weight equates to 100 pound reduction in sprung weight). Any validity to this argument and what is it based upon?

LionZoo

You're forgetting tire weight. A wider tire is needed for the 9.5" width and the extra width is heavier.

rx8thunder

^ yeah I mention the width difference in my post.

But most people go wider when they go with after market rims, don't they?

BigRed

that is just an approximation, i assume. when rotating an object there is something called rotational inertia. rotational inertia determines "how easy it is to spin something," in easy terms. the larger the mass, the larger the moment of inertia. I dont know much about this topic specifically relating to wheels, but I'd assume each manufacturer tests the wheel for the moment of inertia instead of calculating it because of curves of spokes, etc. there are different equations for stuff like disks, hoops, and spheres that are easy equations, but wheels are just complicated.
in a short answer, i'm sure you can approximate it to be the 10 lb thing, although it wont be entirely accurate.

my head hurts

chancejat

iTrader: (2)

if you dont like them then give them to me....ill pay for shipping...lol

rx8thunder

^ <lol> I haven't ordered anything as yet...

kersh4w

iTrader: (3)

not 10 times, more like 4 times.

if you are so concerned about weight, get the stock rim size, 18x8.

or get 15x7. each rim is 9lbs.

Spin9k

It's really tough losing that 5lbs, esp. if you get good tires with stiff sidewalls that tend to be heavier than limp noodle everyday tires. Falkens are definitely not light, and neither are what I use.

But below is an example of a wheel/tire solution that does get closer. The wheels look similar, and they are, but they're 17"s not 18"s, and they're 9" wide not 9.5". So the wheels alone loose 2 more pounds. The tire is variable weight of course. But the combo shown weighs in at 4.5lbs less than the OEM setup you quote while being better in every way, (except tire wear!), and 18 lbs less total all around. If you used a 235 or 245 series normal street tire, it could likely weigh a bit less & reach or exceed the 'loose 5lb' goal, plus ride a heck of a lot smoother than 35 series Falkens. BTW I think Falkens are great, so I'm not knocking them, just comparing them to something else.

My combo is an Enkie 17"x9" 15.6lbs + a Nitto NT-01 255/40/17 26.4lbs (including a bit of lead wheel weight) = 42lbs light and far, far cheaper, like to the tune of $132 per corner in my case or a nifty $528/set savings over your Falken Enkei example.

By the way the 18x9.5 and Falken combo, (aside from looking great!) is slower accelerating than stock and with only somewhat better grip, plus worse gas mileage and harder ride due to the 35 series. Some things are better (and cheaper) executed in moderation.

robrecht

The stock Potenzas weigh 27 lbs and the stock Dunlop SP Sport 8090s weigh 25 lbs. Lighter tires I have found (in this same stock size) are:

21 lbs:
Pirelli PZero Rosso: Only the 91Y, not the 95W

23 lbs:
Yokohama ADVAN Sport
Hankook Ventus S1 evo
Continental ContiSportContact 2 or 3s
Toyo T1R

24 lbs:
Michelin Pilot Sport & PS2s

Some people have reported here that there are two different manufacturers of our wheels also: LM= U-Mold or H= Hitachi. Most people seem to say the stock wheels are around 22.5 lbs but tpyror said his wheels weighed in at 18.5 lbs. Hard to believe there's such a difference but, if so, it would be really nice to confirm this.

My favorite wheel is the Volk Racing CE28N (6.5 lbs 14" on my Miata!). I've seen differing weights for the 18" stock size (width and offset matters). IIRC, GR8RX says his 18x8.5s weigh 13.7 lbs and someone else had some Volk TE37 Magnesium wheels, which supposedly weigh only 12.9 lbs.

As you may have guessed by now, I love light wheels, but don't expect dramatic differences in acceleration--the difference in braking distance is more noticable. The greatest benefit in my experience is road holding on rough surfaces and actually the ride is noticably more comfortable on bumpy roads. It's a subtle difference but delightful and definitely missed if you go back to a heavier set-up.

rx8thunder

Curious with how you came up with 4 times.

Would I go with 17's? Maybe but I really don't like the look as much... would really need to think about that one some more

Robreht/Spin9k:

Thanks fpor your thoughts. After thinking about this some more, I am seriously thinking about rims that are 7.5 to 8 inches wide, with rubber that is no wider than OEM.

robrecht

Here's a very nice compilation of articles and threads that discusses this issue:

https://www.rx8club.com/series-i-wheels-tires-brakes-suspension-55/effects-wheel-size-weight-performance-51865/

It's nowhere near 10x, probably more like 3x to 4x, but wheels are also at the far corners of a car so that makes a bigger difference as well when you're considering overall handling. You also have to consider that rotational weight is more important as you consider whether the weight savings is closer or farther away from the hub so there's no exact number, but a savings in tire weight at the outside circumferernce of the wheels should not be overlooked.

imput1234

iTrader: (6)

Spin9K: do you have a pic of your car with the 17" RPF1's.

Is your speedo off by a lot?



Thanks.

Spin9k

Not yet, just got the tires mounted on the new RFP1s a couple days ago. I'll have pics on Thursday when I go to the track and put them on for the first time. The speedo will definitely be off. From this site http://www.rims-n-tires.com/info_specs.jsp using OEM and these tire/wheels comparison...

"When speedometer reads 60mph (96.6km/h) actual speed will be 57.9mph (93.2km/h): 3.5% slower."

...but that's OK I'll have better acceleration thru the gears and I'll be .45" closer to the ground. This is all on purpose of course, if I wanted to approximate stock diameter I'd get 245/45/17s which are only 1% short. Here's a pic of what that looks like on my car with some other 17"x9" wheels (I have lots of wheels!)

rx8thunder

Not sure what you mean by 91Y vs 95W

Would this be a good partner with the enkei RP-F1 18x7.5?

Together, they would only weight 38 lbs, a reduction of 8.5 lbs per corner (34lbs overall)

pdxhak

iTrader: (2)

Bigger and wider does not always equal more weight!

Bridgestone RE40 225/45/18 weigh 28lbs.

BFGoodrich KDW2 255/35/19 weigh 26lbs.

My 19x8.5 wheels also weigh 2lbs less than OE wheels so overall I saved 4lbs per.

rx8thunder

Here's another 2 potential options:

17" option: Toyo PROXES T1-S (225/45ZR17 94WRD) 20.9 lbs + enkei RP-F1 17 x 7.5 15.4lbs = 36.3 lbs (10.2 lb reduction vs OEM)

18" option: Toyo PROXES T1-S (225/40ZR18 92WRD) 22lbs + enkei RP-F1 18 x 7.5 17 lbs =39 lbs (7.5 lb reduction vs OEM)

Thoughts?

imput1234

iTrader: (6)

I'm tempted getting 17" know of all the advantages. But am worried about how they will look/speedo being off. but in your pic the 17s look good

rx8thunder

^ I know what you mean, I'm tempted as well. The thing that is causing me to hesitate is looks. My goal is aggressive though, I would like to lose 10 lbs on each corner.

I always thought that if I'm going to bother changing the rims and tires, the change has to SIGNIFICANT enough to matter so that I'm not "pissing into the wind", especially if the rims I choose are not just for looks per se (best looking rims are heavier than I'm looking for).

That's why I have in my head, it should be a 10 lb reduction on all corners or nothing. I have nothing to back this up ofcourse, but it seems like if I hit that goal, it SHOULD make a difference. Sort of a "go big or go home" mentality.

I will be using as a daily driver but also occassionally going to the track. I'm really looking for a more nimble 8, one that feels lighter and more agile, in everyday driving. As you can see by my sig, I've done opther things to improve performance already (not all of them implemented yet)

Here area few options below to getting their (Of note: Current OEM rims are 21.5lbs and tires are 25lbs)

1. Spend the big $'s on Buddy Club rims and get lighter tires than OEM.
A. 18x9 (6.75 lb reduction) + tire that is 21.7 lbs or less
B. 17X8 (8.1 lb reduction) + tire that is 23 lbs or less

2. Spend less $'s on enkei RP-F1
C. 17X8 (6 lb reduction) + tire that is 21 lbs or less

Thoughts? Potential light tires to check out? Thanks.

robrecht

95W = 25 lbs
91Y = 21 lbs

This explains speed and load ratings.

Don't rush your decision, nor put too much emphasis on tire weight. Tires are consumables and there's always better tires coming out every year. You won't want to be locked into a particular tire just on account of its weight. Whereas wheel weight is all that matters WRT performance.

Razz1

mu ha ha... that's what i thought.

Bathroom scales are off.

My stock setup is 48.5 lbs. MKW 18x7.5 and Kumho 225's

Enkeis were not weighed but I went with light tires and expect to be 42 lbs.

Keef

you guys drive light 4 seater torque less vehicles... Go Speedline Magnesium wheels, there 17x7.5 so the max tire width you could get would be 235, you pay 205 bucks for a 9 lb wheel. Okay, stock is 22, no matter what you say after this post I couldn't care. 9 lb's is insane. Unless you had too much torque, I don't see why not....

Spin9k

Little delay... but here you go.... hot laps on track...with 17x9s

LionZoo

Wheel stiffness is also a big issue that affects performance. It's just less talked about since it's not very easy to quantify, unlike wheel weight.

LionZoo

How's the steering response and feedback with 17s compared to 18s?

Spin9k

A difficult question. I've never had the same tires on the 18s as the 17s. I now use 40 series 255s r-comps on 17s, my other combo was also 17s, same r-comps but 245 45 series, IOW 2.6lbs heavier and 10mm narrower and slightly higher profile so differences are hard to pick out from behind the wheel. Plus these r-comps are new full 6/32nds tread, the others are now slicks, so still loads of fun.


On 18s I've only had RT-615s and Goodyear F1 DS-G3s. Good as both are as street/casual track tires, neither can hold a candle to the r-comps under track conditions and when pushing it to 9/10 and beyond.

Bottom line, I'm just thinking about being the best I can be with what I've got in my hands at the moment. And they are all so damn good and very very sticky, speaking of the r-comps only, to the point it's me not daring to plumb their limits, not the other way around. I have to study my track logging data a bit to see any emperical differences in g-forces, etc. I was able to extract.