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Wheels | Tires | Spacers | Hub -- Sponsored by The Tire Rack Specific topics relating to wheels and tires. |
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05-24-2018, 04:33 PM | #113 |
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[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.
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05-24-2018, 07:03 PM | #114 | |
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Drive upgrades. Don't buy them.
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05-24-2018, 10:11 PM | #115 | |
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05-24-2018, 11:14 PM | #116 | |
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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. |
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05-25-2018, 01:09 AM | #117 | |
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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. |
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05-25-2018, 01:49 AM | #118 |
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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 |
05-25-2018, 02:12 AM | #119 |
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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 ...
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05-25-2018, 02:29 AM | #120 | |
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05-25-2018, 08:20 AM | #121 |
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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? Last edited by churchx; 05-25-2018 at 08:42 AM. |
05-25-2018, 08:30 AM | #122 | ||
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Damping is directly related to the speed of the relative motion. Mass is only indirectly involved in damping force.
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[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. Quote:
Last edited by ZDan; 05-25-2018 at 10:18 AM. |
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05-25-2018, 09:53 AM | #123 | |
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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. |
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05-25-2018, 01:12 PM | #124 | |
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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. |
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05-25-2018, 01:57 PM | #125 | |
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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. |
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05-25-2018, 02:14 PM | #126 |
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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.
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