All,

Finally got my new wheels and tires on the car and will be doing an updated thread on the results in the coming few days. In the meantime, I wanted to finally post accurate data on the stock wheels AND the stock RE050A tires as there has never been any super accurate weight measurements (bathroom scale rough estimates don't count ). Since there were also conflicting reports in this regard it was finally time to put this issue to rest with super accurate digital scale that would measure the weights down to the one-thousandths. The results were actually not what I was expecting...

Stock 7-Spoke 19" Wheel Weight (without tire pressure sensors)

• Front 19" x 8.5" weight = 24.710 lbs
• Rear 19" x 9.5" weight = 27.560 lbs
• Total Wheel Weight (all 4) = 104.54 lbs

Stock Bridgestone Potenza RE050A Weight

• Front 235/40/19 weight (70% left) = 24.690 lbs
• Rear 275/35/19 weight (50% left) = 28.350 lbs
• Total Tire weight (all 4) = 106.08 lbs

Estimated New Tire Weight (plus 0.5 lb wear compensation factor)

• Front Tires = 25.190 lbs
• Rear Tires = 28.850 lbs

TOTAL WHEEL & TIRE WEIGHT = 210.620 lbs


When you put things in these perspectives you never really realize just how much weight is rolling around until you do the math add everything up. Keep in mind, this is not counting in the rotating mass of the brake rotors and all the other components as well, JUST wheels & Tires. Once all those other factors are included you are looking at 350 lbs+ easy for the entire rotating assemblies. Once you factory in the ENTIRE rotating mass in the drivetrain the number really skyrockets from there. The estimates I had been reading were in the 26F/28R range but were never truly accurate. Now we can all finally put this issue to rest as you will never get measurements more accurate than this


Hope this helps,
007

 

No need to estimate new tire weight. Manufacturer specs are listed on Tire Rack's website. Interestingly, the fronts are a bit heavier, and the rears are considerably heavier than your estimates: fr. 235-40-19 are listed at 26 lbs. and rear 275-35-19 at 32 lbs.

Sobering to look at the masses involved, I agree. Never really a fan of plus sizing for that reason - subjectively better looks (for some folks) but at what cost? Conversely, if you can find same size, lighter wheels that are strong enough, potential gains!

 

There are no real gains to be looked at by going lighter. people get all worked up, but the bottom line is that the weight savings on the wheels, as far as acceleration goes, is like 1.4 times the weight, as if it was sitting in the car, or 2x the weight If it all comes from the tire...... that's it... its not much. and, on a street car, the gains are very close to nothing.

 

XW: Weight gains from rotational mass is actually closer to a 4x multiple. It's the only weight worth removing actually. All the other weight from the body is minimal by comparison. The weight reduction from brake rotors / wheels / tires is fare more effective than going to sport seats or getting a lighter exhaust etc. People place so much more emphasis on those and they do virtually nothing compared to rotational mass.

Spinecho: the reason I weight them exactly is many people has actually confirmed their numbers are not that accurate and for that reason I wanted to get an exact number. Their numbers can often be off by as much as 1-1.5 pounds depending on the tire sometimes.

 

@007: completely agree that the gains from reducing unsprung weight are underappreciated. I find that although the suspension is firmer on the V12V, it feels more comfortable to me than the V8V, in that it responds more efficiently to road imperfections. A subjective observation I realize, but I suspect this is more due to reduced unsprung mass (lighter wheels, CCM brakes) than spring or shock differences.

@XW: there is more to it than a negligible increase in acceleration or braking performance. How about ride comfort and suspension performance? Minor gains in each category, but taken together, a worthwhile improvement IMO.

 

actually, no its only 2x if the weight removed or reduced is from the tires and 1.5x if its on the rim. Ill show you the calculation if you are interested. this is its effect on HP. The unsprung weight is a entirely different situation. thats how the weight, going up and down over a bumpy surface or how the chassis reacts with quick direction changes and body roll, effect handling. it has no difference on acceleration vs how it would effect it, if the weight was in the car. lastly, where the weight is, can be a consideration, (up on the roof, or down at the floor board, as that is Center or Gravity stuff, and its looked at for handling reasons. (AM did a good job with this in the car's design).

so, again, if you shave 5lbs per wheel, that has the same effect if that 5 lbs, x 4 wheels (20lbs) x 2 (for the inertial effect) = 40lbs , has been taken out of the car. (and thats 5 lbs per wheel which is a LOT!! ) 40lbs out of the chassis, will not be noticeable by any stretch, unless you are in a race car and .5 seconds a lap might be seen.

on a dyno, this weight would have very little effect. (almost nothing) certainty not detectable by a dyno..... why, because the acceleration rates of the dyno are very slow (usually a run takes 7 seconds) accelerating 10lbs (the two rear wheels) from 800rpm to 1800rpm (basic dyno run from 3000rpm to 6000rpm in 4th gear, or 80mph to 150mph) over 7 seconds takes much less than 1hp. so you will see no difference in acceleration, especially on the street.

10lbs off the flywheel works a little different. it might be worth the effect of 20hp in 1st gear, 9hp in 2nd, 4hp in 3rd, and less 2hp in 4th. (something like this)

when you are NOT talking about a race car , all of these mods are almost insignificant. BUT, the interior changes can make the car more sporty, so that is a pretty large effect, even though the weight of the car is pretty heavy anyway and you are not changing things that much until you "Gut" the car to be a real race car. .................. (i.e. like dropping 4-500lbs by gutting it and putting in a cage. ) THEN and only then, does every little bit help.

 

on the roads we travel, and at the speeds we travel them at, its still very negligible. the suspension actually works better with the mass, so you have a less bumpy ride. But mainly, if you are not going over pot hole'd roads and driving a very tight twisty road, the effects will go unnoticed. mainly because the changes you are considering making are so very small. wheels and tires weigh 50lbs, at best. brake rotors are 15lb and at best, by taking the weight out of the hats, you might save a pound or two. the calipers are already light, being brembos, AND when you go to the larger diameter rotors the weight goes way up. the only way to get lighter brakes or unsprung weight ,is to go to CF rotors, and they are about $12k a piece, and their effects on handling could be easly debatable in some conditions.

im not trying to say that reducing unssprung weight is bad.... after all, i do build and race sports cars...... im saying that on the street, you wont be able to notice any difference. AND, no racer would ever shave 5lbs off his rotors, by using a 12' rotor vs a 14" rotor.

 

XW: I appreciate your enthusiasm on the subject and it appears you have gotten a basic primer on the subject and understand the basic fundamentals but your analysis is flawed and incorrect in a few areas. The 1.5x-2x calculation is completely off. The effects are massively more drastic than that. 4x is actually very conservative, many used to state 10x but it was proven that was highly exaggerated.

I removed 90lbs of unsprung rotating mass in my daily driver and it has such a profound effect it felt like I took a good 400+ lbs out of the car. Furthermore, my 60ft' times in the quarter mile dropped a full 2 tenths of a second, a FULL 2 tenths!! (a massive improvement). A 5300lbs SUV running low 1.9's in the 60ft is no joke. Many other similar SUVs with much more HP than mine are still running 2.1-2.2s of the same make/model.

Unsprung Rotating mass is the #1 and frankly the ONLY mass even worth considering. Lightweight batteries, race seats, lighter exhausts... all that stuff is just marketing fluff and doesn't do a damn thing in real life. Anyone that says that stuff helps is just trying to justify it in their head for spending all that money. I had the exhaust done on my previous one, absolutely no improvement was felt from the weight, only the additional 13HP past 6000rpm could be felt b/c of the X-pipe. The 35-40lbs reduction did nothing compared to the brake rotors which "only" dropped 18lbs but made a very significant improvement in acceleration by comparison. Also, having had done racing seats in many of my cars before, the different was not nearly as pronounced as rotating unsprung mass which is why I stopped doing it. Once you go down the road of seriously reducing that kind of mass, nothing else make sense or is worthwhile enough.

Now if you happening to be upgrading a part and it is lighter, great... but that shouldn't be the fundamental reason you should be doing it unless its part of the brake/wheel/tire/drivetrain rotating assembly.

Also, your statements regarding the flywheel indicate you do not fully understand all the factors of inertia throughout the drivetrain. The SAME EXACT principle that applies to the flywheel, ALSO applies to the wheels and tires. The "moment of inertia" is at its absolute highest when they are in a steady state at rest (aka 0MPH 1st gear). It is for this reason why upgrading rotating unsprung mass has the largest effect on 60ft times at the drag strip b/c this is where the moment of inertia is at its highest and the engine HP/TQ is at its lowest. Minimizing that amount of energy required to overcome that inertia makes the engines job much easier getting out of lower rpms and into the engines sweet spot in the powerband. Lowering wheel/tire/brake weight is the exact same thing as the flywheel. The only difference its its being done after the gearing multiplication of the differentials... that's the ONLY difference. If anything, for that reason it has an even LARGER effect than a lightweight flywheel does in many ways. More important, Wheels/tires/brakes ALSO help with braking, ride quality, handling, where as flywheel does none of these things. For that reason it is the #1 place to start to improve the overall characteristics of the car (and coincidentally usually the last people most place start looking). Although the gains in 4th gear may only be 8-12hp/tq at most depending on the car (mitsubishi guys have documented gains of up to 12hp for lighter rotating assemblies on loading dynos), you must realize that in the lower gears (1st-3rd) the effect is far more pronounced, just like a flywheel.

The inverse is also true of braking from very high speeds. The rotating mass inertia is so high that it makes the brakes jobs much harder. For that reason reducing the rotating mass drastically improves the braking performance simply by making the brakes jobs a lot easier. there is much less mass it has to stop, especially at larger diameters b/c Inertia = Mass x Radius^2. For that reason, the radius of the mass is literally "exponentially" more important than the mass itself. With that said, all rotating mass is important when compared to all other forms of mass reduction which do very little by comparison. There is a reason why Formula 1 spends millions of dollars to make all the suspension arms out of carbon and brakes out of carbon and wheels out of magnesium... every ounce they save makes a difference.

One more impact also not discussed is Fuel efficiency. The less rotating mass the less energy is wasted on getting everything up to speed. with significant mass reduction you can see improvements of up to 2-2.5mpg just by making significant upgrades. Granted most manufacturers don't do this b/c it is incredibly cost prohibitive and at the end of the day they have bottom lines and need to make money to stay in business so they leave these remaining inefficiencies for the aftermarket to address.

Your statements on adding weight to improve ride quality is 100% false. This goes directly against decades worth of technological improvements and the laws of physics themselves. Ride in a car with heavy wheels & tires vs a light one and the light one will do a MUCH better job of following the contours of the road and absorb road imperfections. One of the main reason our stock Bridgestone RE050As ride so damn terrible is they are one of the heaviest tires for their given size. After having switched to Michelin Pilot Super Sports (which are on avg 2-3lbs lighter per tire) I now realize just how much of our cars poor handling characteristics are due to the stock wheel/tire/brake setup. There is simply WAY too much weight moving around.

Brakes: There are plenty of ways to massively reduce the weight of your brake rotors without going to Carbon Rotors. You can get the Brembo 2-piece rotors which save 9lbs PER ROTOR. That's 36lbs for the car roughly. That is certainly no joke and it makes the car behave completely differently at a tiny fraction of the cost of a full carbon brake setup (overkill for our applications). In conjunction with a good wheel/tire setup you can see some very healthy improvement in ride quality as well as acceleration & braking performance.

I appreciate your enthusiasm and you were 50% of the way there on many of your statements, but you didn't quite have the full picture of all the forces at work. You were definitely getting onto the right track but some of your information was incorrect or simply old forum myths handed down over the years. This is by no means a knock on you, we are merely having an intellectual debate on a very important topic that no nearly enough people are aware of. Having had to learn a lot of these myths were false the hard way I can tell you everything above should point you in the right direction.

 

You may have misunderstood my comments about handling, but the acceleration factors are actually true. I tried to save you a lot of the calculations with the flywheel, and it is not the same, because the flywheel weight is not going through the gear ratios (it doesnt know what gear you are in) this is why, the effect of 7 lbs off a 9" flywheel is like
200lbs in first
71 in 2nd
31 in 3rd,
16 in 4th
and 10lbs in 5th for most situations.

the equation is (for the flywheel ) is V= w x R/gear x final drive so, M = I x (gear x final/2)^2

where "gear" is the gear ratio and "final" is the final drive ratio

KE (rotation) = 1/2Iw^2 = 1/2M(wxR)^2 (linear)
For the mass on the tires and wheels, its becomes M = I/R^2


so, for a 25" diameter set up, the weight in the car vs it on the wheel and tire is 2x, NOT 10x or 4x or anything close to that. In fact, if you use radians per second for the velocity component above, you get the right answer, if you use RPM, the error you quoted is the source, in most cases.



Now, if you got .2 seconds from a 90lb reduction , that can be due to all sorts of advantages, part of which is pure acceleration capability that would be like you dropped more than 2x if you are talking huge wheels and tires. my example were standard sized tires and wheels up to about 18" rims with the appropriate tires for street cars. yes, it could be quite a bit higher on a truck, and thats what you are taking about, NOT our AM v8s.

but even if it was on our cars, 90lbs, acting like 180 lbs, could easily give a .2 second advantage, but grip and technique especially at the start, is what its all about. Now, if you are talking about your 5300lb SUV, i would venture to guess that your tires might be at 30" diameter which could get you in the 4x the weight as if in the car range.

Now as far as lightening the car vs the wheels and tires. what i say is true. its about 2x as if it is in the car. dynos CANT measure this becuase they accelerate too slow (usually, in 4th gear) dynos measure the rate of change of kinetic energy and 5lbs per wheel and tire (10lbs over all) over 7 seconds takes less than 1hp. you can calculate this yourself, using the same equations that are BUILT into the dyno. what i mean by this, is that if a dyno does read more than 1hp gain, you can rule out that it was due to the tires and wheels, its that CLEAR of a fact.

Now, handling, YES, i totally agree . lighter wheels and tires do make a car perform better , handling wise. however, large inertia can resist lock up under max braking. just like heavy flywheels are easier to let the clutch out with. pure performance does go to the lighter stuff , i agree.

unsprung weight for handling is a big yes too, but no one here pushes the car hard enough on the street to notice 5lbs of change of a tire or a brake rotor.
Ive raced long enough to know, and have done much more of the significant testing to experience the "real " differences. I was constantly jumping back and forth between 30lb tires and 25lb tires, with no difference than the grip that the real race tire had vs the street tires WCGT had us race with. (nothing measurable) acceleration wise, again, that 20lbs total was like having 40lbs in the car missing. not huge, not measurable on the dyno, but certainly worth .25 seconds a lap. handling-wise, if you are on a smooth track, there would not be much diff. but, on a bumpy track, you bet. also, quick transitions would be helped too. differences in tire manufacturer or style is more of a tire composition or air pressure setting , than a tire weight. so many factors in handling with tires, weight is just a very small factor. (sidewall stiffness, rubber grade, tread design, size ratios, and durameter, just to name a few)

as far as your own "butt dyno", loosing 18lbs of rotor weigh should have equaled your 40lbs of car interior weight, physics-wise. again, its easy to calculate. if you felt more, it was just a feeling. do the calculations yourself for 9lbs per rotor on a 7" radius, what the effect is power wise on a dyno that spins it up from 900rpm to 1800rpm. (your car going from 80mph to 150mph). its going to be much less than 1hp, and maybe around 15hp in 1st gear. no where near the gains of the real 12hp, overall, you got for the exhaust system. dont take my word for it, just calculate it out. Its very simple and thats what i love about physics... its absolute.

all the weight of the drivetrain that isnt used to stablize vibration can be remove and its gain can be calculated pretty easily. its simple.. its a rate of change of Kinetic energy..... this is HP by definition. that weigh has more of an effect reving the engine in neutral, or accelerating in 1st vs 5th gear.
we are not talking dragsters here, but if we were, yes, every little bit of weight would help. in street cars that are not racing, and occasionally brought to the track....... nah, you cant get enough weight out of the drivetrain to make a HP difference. However, i do like lighter flywheel and clutch systems , as they rev quicker and make it easier to shift more precisely. keep in mind, when the entire car is on the road, the engine is driving the weight of the car, drive line, and wheels and tires, all stuck together!! Its all one big mass, some spinning some fixed. 5-20lbs of spinning weight on a tire, is only a small fraction of the the 3600lb car. and it has the relevance of the equation above for a 25" diameter tire. about 2x the weight, if it was sitting in the car.


edit: as a side note to address your comment about the rotating weight on the flywheel vs wheels.... its very different. its why I can say that 7lbs ligher flywheel can be worth 200lbs in the car in 1st and only 10lbs in 5th. HP to weight ratio wise, with a 10:1 car (weight to HP), that's like 20hp in 1st and 1hp in 5th gear. the reason it doesn't apply to the wheels and tires, is gearing. in 1st gear, that weight is spinning 1/5th as fast due to 1st gear being a big reduction as compared to 5th gear. remember, rate of change of kenetic energy, so it should be relatively constant at the wheels and tires due to gearing. 1st gear acceleration is faster, but in a much slower 1/5 as fast speed range. 5th gear is much slower acceleration, at a higher speed (5 x faster) range. this why we can calculate what the weight on the wheels and tires equivilance, if it was sitting in the car. If you do a rolling dyno, like on a dynojet 248e, its why the power output of the car wont change at the rear wheels, even If you run it in 3rd, 4th or 5th. ( the small differences in the lower gears are usually gearing efficiency losses which is usually around 5hp per gear difference)

 

Did you go through the calculations to verify my " rotating weight" effect - equivalence?


Good discussion by the way. I always like these, as it does dispel a lot of "myths" and "feelings" that some have propagated over the years about car performance and mods. It also forces the folks, making the claims to check our work and do the research so that we get better at explaining it, and make sure we are correct.

 

Just a thought but would 18 inch wheels, with tyres to match the rolling radius of 19 inch alloys, reduce the weight of the wheels?

Interesting to note that the new Mclaren 650s 19 inch alloy wheels are based on a design to minimise weight by using the lease amount of metal (with added benefit of improving brake cooling):

 

another misconception actually, rubber is heavier than aluminum, but in actuality its a pretty even trade off. you might get a 1lb lighter wheel and exchange that for a 1lb heavier tire in the same radius area.

 

Acceleration in gears 1st - 3rd are by far the most important are they not?? . Lol.

I don't know how many people go WOT in 4th on the street, you are well into triple digits at that point. Yes obviously as gears get higher the effect is less, but for around the street it makes the most difference as the first 3 gears are the ones most of us have the most fun in which is why IMO they are the most important ones to focus on.

Vergis, XW is actually right that rubber does in fact weight more than aluminum based on volume, with that said its important not to neglect the wheel weight as well. They are ALL important. By carefully planning your modding plan you can find an all encompassing solution like I did trying to save as much weight as humanly possible with every component you replace. Remember, I removed 8 pounds while massively increasing the widths of my wheel & tire combo without event touching the brakes yet. A full 2-piece Brembo brake kit will save roughly another 36lbs!! However, that weight reduction does come at a smaller radius so it's impact is slightly less, but the mass reduction is far greater so it will still make a noticeable improvement in handling, braking, steering response and feedback. Bumps will be much softer still allowing you to then compensate by going with a more aggressive spring setup with no negative ride quality compared to stock.

My main purpose of this thread was to illustrate the point how important it is to plan ahead when doing mods and not just doing it haphazardly (which most tend to do). Depending on how long I keep the car I will probably end up doing rotors as well for a maximum effect.

Wi regards to rotating mass, the same is true for crank pulleys and lightweight flywheels, they always have the greatest impact in 1st - 3rd gears (the most relevant for city driving). But I am getting ahead of myself ... In due time.

 

Just to throw in another thought.

How many of us have filled the tank and noticed the car feeling sluggish straight after? Yet that is maybe 60 pounds of additional weight added in 5 minutes. It was when I realised that my personal butt dyno didn't notice a 60 pound difference, that I stopped thinking about spending a few thousand on weight saving changes.

On the track its all measurable, but on the road what really matters is how much extra pleasure you get out of any changes you make to the car, and apart from the satisfaction of knowing you've made a difference, I'm not convinced that the car will feel any different with the weight reductions being discussed here.

 

With body weight you are 100% correct, that's why I don't waste a dime on body weight reduction, it honestly does next to nothing. Rotating Unsprung mass though is a completely different world compared to body mass. Apples vs. oranges. Once you try it you will be hooked. Wheels/tires/brake rotors are the first things I usually modify on cars now to maximize performance because they literally affect everything (handling, ride quality, grip, steering response, acceleration, braking, on and on).