Is 12lb total difference in weight going to affect a lot?

[Red2Liter]

Originally Posted by khcho19

So I am looking at some wheel that weights 20 lbs. This is my option 1.

My option 2 has 23 lbs, so total difference for a set of 4 would be 12 lbs.

Will 12 lbs make a difference a lot?

What's ideal wheel weight for BRZ?

[I]I sensibly waited until I had used up my OEM Michelin Primacy's before buying replacement rubber and lighter wheels. I opted for 215/45X17 Michelin Super Pilots on 14 lb. alloys from Tire Rack. I'm not convinced that going Plus one is a great option for general daily use. What you gain in increased contact patch you lose in comfort with the change in aspect ratio. The Super Pilots are far from the stickiest tire available but they are better than the OEM fitment. The combo transformed the car; the reduced unsprung weight's effect was a step in a positive direction, while the tires have more grip and are quieter and more comfortable riding than the OEM's. I suspect that the OEM's, chosen for fuel milage reasons had much stiffer sidewall construction than the Super Pilots.

[fatoni]

Originally Posted by Red2Liter

[I]I sensibly waited until I had used up my OEM Michelin Primacy's before buying replacement rubber and lighter wheels. I opted for 215/45X17 Michelin Super Pilots on 14 lb. alloys from Tire Rack. I'm not convinced that going Plus one is a great option for general daily use. What you gain in increased contact patch you lose in comfort with the change in aspect ratio. The Super Pilots are far from the stickiest tire available but they are better than the OEM fitment. The combo transformed the car; the reduced unsprung weight's effect was a step in a positive direction, while the tires have more grip and are quieter and more comfortable riding than the OEM's. I suspect that the OEM's, chosen for fuel milage reasons had much stiffer sidewall construction than the Super Pilots.

i dont think the topic was about wheel diameter and id be surprised that the pss has a softer sidewall than oem.

[rvoll]

Originally Posted by Red2Liter

[I]I sensibly waited until I had used up my OEM Michelin Primacy's before buying replacement rubber and lighter wheels. I opted for 215/45X17 Michelin Super Pilots on 14 lb. alloys from Tire Rack. I'm not convinced that going Plus one is a great option for general daily use. What you gain in increased contact patch you lose in comfort with the change in aspect ratio. The Super Pilots are far from the stickiest tire available but they are better than the OEM fitment. The combo transformed the car; the reduced unsprung weight's effect was a step in a positive direction, while the tires have more grip and are quieter and more comfortable riding than the OEM's. I suspect that the OEM's, chosen for fuel milage reasons had much stiffer sidewall construction than the Super Pilots.

I did not "sensibly" wait, and changed to PS4S when I first got the car from the dealer. The Pilot Super Sports are being discontinued so while you can get them cheap, and they are better than the Primacies, I just can't see going with them if driving fun is your goal. For a daily driver, weight does not make a big enough difference to change the wheel. In fact, the dampers were designed for the weight of stock wheels so you actually lose some of the "balance" by going very light. And I agree with @fatoni that the sidewalls of the PSS are not softer than the Primacies. At least, since I had the direct comparison on my car with the PS4S on the same wheels, the ride quality of the Primacies was indistinguishable from the new tires. That said, the car handled noticeably different with the new tires -- even at slower speeds. You get the sense with the Primacies that the rear is just following the fronts around corners showing some slight looseness while the PS4S hugged the road on all fours and made the car, and steering, feel tighter. I did not expect that much of a difference at medium/slow speeds and was pleasantly surprised. It changed the car from feeling like a "coupe" to a "sports car".

[Spuds]

Originally Posted by rvoll

In fact, the dampers were designed for the weight of stock wheels so you actually lose some of the "balance" by going very light.

I may be missing something, but I think that statement is incorrect under most circumstances.

My understanding is that dampers exert force in a direction counter to movement and proportional to the speed of that movement. Therefore a change in their behavior is only affected by the speed at which the wheel goes up and down. Considering that the vertical motion of the wheel is constrained to the ground, that speed shouldn't really be affected by the weight of the wheel.

Now we could get into tire sidewall flex when hitting a bump for example, but that gets a bit too complicated for a forum post lol. Also, you are better off with lighter wheels if a wheel gets airborne by my understanding as well.

[rvoll]

Originally Posted by Spuds

I may be missing something, but I think that statement is incorrect under most circumstances.

My understanding is that dampers exert force in a direction counter to movement and proportional to the speed of that movement. Therefore a change in their behavior is only affected by the speed at which the wheel goes up and down. Considering that the vertical motion of the wheel is constrained to the ground, that speed shouldn't really be affected by the weight of the wheel.

Now we could get into tire sidewall flex when hitting a bump for example, but that gets a bit too complicated for a forum post lol. Also, you are better off with lighter wheels if a wheel gets airborne by my understanding as well.

Force equals mass times acceleration. Under your proposal, mass plays no role in the movement. That contradicts the laws of physics. Damping force is directly related to the mass being moved. Let's take an extreme case. Take a damper and place one pound (the mass) of force on it. It will barely move. If you had a damper designed for one pound of force, you'd bottom out on the slightest bump almost as if you had no damping force whatsoever. Sidewall flex is, indeed, part of the equation. But the lower profile tires you have (and the tires are lower profile on our car), the less sidewall flex you have so it is a minimal part of damping. Now if you had a monster truck with low pressure tires, this would obviously be different.

The designer of the twins always talks about balance. Dampers, springs, and other parts of the suspension are designed for a particular car, for a particular purpose, at a particular weight. Deviation of a well balanced car generally leads to poorer overall performance. Now if you change the performance goal of the car, then you are aiming for a different balance. Track cars do not have a comfortable ride. But track cars do generally have adjustable dampers so you can achieve the balance you desire.

[churchx]

rvoll: let's not talk about artificially too extreme examples. Dampening/spring rates are more made to match/support weight of whole car (which doesn't change that much vs wheel weight) not wheel/tire weight and to provide wished dampening/rebounding, characteristics/curves with specific tire grip level. +OEM (probably, if "designer of the twins always talks about balance") struts and springs are not just about best possible track driving balance, but also with targets of cheap price, long life, comfort. Sometimes those other compromises (especially price) might be that bad, that higher quality track suspension might feel even more comfortable then oem ones, that are supposed to be more comfort oriented.

Much grippier tires (which most on track will use anyway) will throw off "balance" much more then lighter wheels will. But due less mass/inertia with same dampening/springs shocks will be able to move wheel much quicker following road imperfections, resulting in better wheel contact & thus grip with road more of a time. Regarding comfort change from lighter wheel it has both pros & cons though. Better absorbing large road defects, but dampening worse small vibrations on better roads. Link

[nikitopo]

Originally Posted by rvoll

Track cars do not have a comfortable ride. But track cars do generally have adjustable dampers so you can achieve the balance you desire.

Beware your audience. Most here will claim that smoothness/comfort means that you are faster. Engine-wise, suspension-wise and so on. They are not aware that a track car doesn't focus on NVH minimization ...

[rvoll]

Originally Posted by churchx

rvoll: let's not talk about artificially too extreme examples. Dampening/spring rates are more made to match/support weight of whole car (which doesn't change that much vs wheel weight) not wheel/tire weight and to provide wished dampening/rebounding, characteristics/curves with specific tire grip level. +OEM (probably, if "designer of the twins always talks about balance") struts and springs are not just about best possible track driving balance, but also with targets of cheap price, long life, comfort. Sometimes those other compromises (especially price) might be that bad, that higher quality track suspension might feel even more comfortable then oem ones, that are supposed to be more comfort oriented.

Much grippier tires (which most on track will use anyway) will throw off "balance" much more then lighter wheels will. But due less mass/inertia with same dampening/springs shocks will be able to move wheel much quicker following road imperfections, resulting in better wheel contact & thus grip with road more of a time. Regarding comfort change from lighter wheel it has both pros & cons though. Better absorbing large road defects, but dampening worse small vibrations on better roads. Link

Basically agree with everything you've said. However, damping is designed for BOTH total weight and wheel/tire weight. Lighter wheels may push against the ground faster, but depending on road undulations, that could also lead to excessive movement on uneven pavement and the resultant loss of traction. As said before, it is a matter of balance. As a daily driver, some level of comfort may be desired. I'm not sure there is a precise answer because each of us has our preferences. But over the years, putting on hundreds of different tire/wheel combos on a number of cars, I've generally found that deviating from the manufacturer's design does decrease the balance of the car. Again, if your purpose is track, then you don't necessarily want the balance of the car's design. For a street car, I've always regretted putting on lighter wheels/tires. And I've almost never found a better ride with alternative/higher priced suspension parts because they are designed for performance and not comfort. It is theoretically possible, but have you looked for springs with lower spring weights than OEM? Or dampers with less damping?

[churchx]

And i - never regretted upgrade to lighter wheels, i may had regretted only how much it costs , but not in my case, as wheel upgrades came in way of wheels bought used for 1/4th of price. I suspect, that some of your regrets may have been not because of you feeling car behaving worse vs to your liking, that you may have changed several things during those times (eg. different tires, or other upgrades, or wheel size (eg. width or offset, changing feel not by weight, but due different scrub radius), not single variable of reducing weight with rest staying same. Or that you got dissapointed, that improvement was too slight for it's high cost.

And subjectively i felt improvement on street in performance / comfort / handling feel. Change was subtle but it could be felt and it was overall positive. Of course, if OE wheels had been much heavier (not the case. Twins wheels are far from being VERY heavy OE wheel), difference would be more drastic. If you wish to experimentate with feel change and want to make difference bigger, you can borrow some 17" steelies and try to switch between those (and even OE wheels).


As for aiming to keep balance "as engineers intended to" .. it's fine wish .. just that imho lighter wheels are wrong subject to aim that wish to. As i already wrote, in post before, something like different, much grippier tires will impact balance, and with going to grippy tires worth eg. stiffening suspension/spring rates/reducing slack in bushings or car will roll too much, due higher cornering speeds ride on bottomed out dampers more often, squishiness & play within stock soft bushings will get more pronounced and so on. But with only lighter wheels if you feel that it may throw off "balance" of sorts, it's not so. Dampening/rebound/spring rates are more for car, not for unsprung mass (which is relatively small portion of whole car/vs sprung mass, so lighter wheels will reduce little enough both unsprung mass and even more so total mass for that to never be and issue. If eg. some coilover maker wrote, that their dampers can be used with spring rates different by +25% .. will car mass change by 1% really "trow off balance"? Heck, even damper manufacturing variances probably are much bigger then that, or dampening changes from wear by mileage).


Only problems with lighter wheels (rest being same) are not related with suspension balance, but 1) with budget, as the lightest (eg. top manufacturer monoforged wheels) cost too much, and the price/performancy is bad for eg. forged wheels set costing $3-4K new (if it wouldn't be so, all cars as OEM wheels had forged very lightest ones, but due costs those come as OE only on expensive upmarket sport cars) 2) sometimes wheels are too overlightened and might get compromised rigidity/strength of wheel, and might be too easy to get damaged/bent (eg. heard that about kosei K4R, which are cheap, weight same as forged wheels but are cast .. and seen posts that they often can be bent). Take it as given, that lighter wheels, rest being same, will always improve performance, grip, handling, and partially comfort if they are strong enough and if one can afford to overpay a lot for slight change. Expensive car makers can afford, track teams aiming for any slightest gain no matter the costs can afford, for cheap cars - OE wheels are heavy cast or even steelies only to get within budget, not "because of balance". BUT! if car owner upgrades wheels anyway for looks/personalisation reasons .. why not aim to get lighter ones too?

[ZDan]

Originally Posted by rvoll

Damping force is directly related to the mass being moved.

Damping is directly related to the speed of the relative motion. Mass is only indirectly involved in damping force.

Let's take an extreme case. Take a damper and place one pound (the mass) of force on it. It will barely move. If you had a damper designed for one pound of force, you'd bottom out on the slightest bump almost as if you had no damping force whatsoever.

That's not correct.
[edit]Sorry, I misread what you wrote. *IF* you designed a damper to have next to no damping force you would bottom out more easily as it would have no resistance. But that has nothing to do with how you would design a damper for reduced unsprung weight! If the dampers were designed specifically for lighter-weight wheels, they might have a little less compression damping and might have a little more rebound damping.
But for an unsprung mass difference of only 5% (for 3 lb. lighter-weight wheels), most likely there wouldn't be any difference[/edit]

Again, the damping force is related to the velocity of the motion. A lighter-weight unsprung assembly will be shoved upward at about the same speed when you hit a bump and so will see the same damping force. The good news is that a lighter-weight wheel/tire is more likely to stay in contact with the road after hitting said bump as the spring and damper forces are larger relative to the unsprung mass, i.e. they can do a better job of holding the tire on the road. Also, going over a pothole, the lighter-weight unsprung mass will follow the road better while a heavier unsprung mass will be more likely to lose contact with the road and then crash into the pothole.

Reduced unsprung mass is always going to be better for ride and for handling, even if the dampers were designed for heavier wheels.

The designer of the twins always talks about balance. Dampers, springs, and other parts of the suspension are designed for a particular car, for a particular purpose, at a particular weight. Deviation of a well balanced car generally leads to poorer overall performance. Now if you change the performance goal of the car, then you are aiming for a different balance.

Every design is a compromise of many factors. OEM wheels are generally designed to be stiff and strong and durable so people don't complain about bent wheels after hitting a pothole or curb. There is a cost in terms of ride and handling performance, but it isn't that huge. Aftermarket wheels can be a lot lighter-weight, and this is good for both handling and ride quality. But they're more likely to get bent when you hit something hard.

[Spuds]

Originally Posted by ZDan

Damping is directly related to the speed of the relative motion. Mass is only indirectly involved in damping force.

That's not correct. Again, the damping force is related to the velocity of the motion. A lighter-weight unsprung assembly will be shoved upward at about the same speed when you hit a bump and so will see the same damping force. The good news is that a lighter-weight wheel/tire is more likely to stay in contact with the road after hitting said bump as the spring and damper forces are larger relative to the unsprung mass, i.e. they can do a better job of holding the tire on the road. Also, going over a pothole, the lighter-weight unsprung mass will follow the road better while a heavier unsprung mass will be more likely to lose contact with the road and then crash into the pothole.

Reduced unsprung mass is always going to be better for ride and for handling, even if the dampers were designed for heavier wheels.


Every design is a compromise of many factors. OEM wheels are generally designed to be stiff and strong and durable so people don't complain about bent wheels after hitting a pothole or curb. There is a cost in terms of ride and handling performance, but it isn't that huge. Aftermarket wheels can be a lot lighter-weight, and this is good for both handling and ride quality. But they're more likely to get bent when you hit something hard.

Everything Zdan said above is correct. The car is the "mass" side of the vibration model, not the wheel. The wheel is the "fixed" side.

The model changes a bit if the wheel is in the air, so I can address that since we seem to be diving in to math and dynamics. Assuming both the lighter and heavier wheels hit the same bump and travel upwards at the same speed, the spring/damper combo will arrest the motion of the lighter wheel first, since it has less mass. So the lighter wheel is lower to the ground and the upward motion has been stopped earlier in time. Since its closer to the ground the downward stroke takes less time for the lighter wheel. I haven't run through the equations, but the damper should actually slow the heavier wheel more over both strokes further increasing time off the ground.

All this has nothing to do with balance and more to do with extreme bump performance/ride. On a somewhat smooth surface, the light wheel or a heavy wheel does not affect suspension travel at all.

[ermax]

Originally Posted by Spuds

Everything Zdan said above is correct. The car is the "mass" side of the vibration model, not the wheel. The wheel is the "fixed" side.

I'm not sure where ZDan said the wheel is fixed and that only the sprung weight is a factor.

IMO lighter wheels would need less dampening. The more mass the more inertia. Once the wheel hits a bump and changes direction it's going to continue in that direction longer and farther before the spring can push it back down therefore it seems you would need more dampening to control this motion. Surely this has been debated somewhere else.

[Spuds]

Originally Posted by ermax

I'm not sure where ZDan said the wheel is fixed and that only the sprung weight is a factor.

IMO lighter wheels would need less dampening. The more mass the more inertia. Once the wheel hits a bump and changes direction it's going to continue in that direction longer and farther before the spring can push it back down therefore it seems you would need more dampening to control this motion. Surely this has been debated somewhere else.

Only if the bump is sharp enough to get the wheel airborne. Idk about you, but my wheels remain on the ground most of the time except the occasional big frost heave. Suspension is intended to separate the main weight of the car from the ground specifically to prevent the wheels from getting airborne.

The car is the counterweight that the spring acts on. The wheel has a hard restriction to the ground except in cases when it is airborne. On modern suspensions, that simply does not happen often. Think about it a bit. If you still don't believe me, give me real spring and damping rates with wheel and car weights and I'll do the math at some point this weekend to prove it.

Sprung weight is what needs to be controlled by damping. If you've ever seen an underdamped car rolling around you'd know what I mean. The car is rolling around, the wheels remain on the ground.

[ermax]

Originally Posted by Spuds

Sprung weight is what needs to be controlled by damping. If you've ever seen an underdamped car rolling around you'd know what I mean. The car is rolling around, the wheels remain on the ground.

Well obviously the sprung weight needs to be controlled. But that is slow movement. The wheels also need controlling and would be high speed. I can assure you our wheels DO NOT stay on the ground 100% of the time. I'm not talking about rally style jumps. I'm talking about very high rates of movement up and down where the tires unload reducing grip. All I'm saying is the potential for this to happen would be higher with more unsprung mass and IMO would require more damping.