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Discussion Starter #1
The x5 4.8 is heavy. So are the wheels incl brake rotors, i.e. the unsprung rotating weight. Rim, brake rotor, tyre, all 20-30 pounds each, if not more.

I searched for some tyre weight info, and apparently runflat adds 6-8 pounds to a 255/50R19 tyre.

If I go non-runflat, I will probably notice the softer sidewalls (as reported by so many), but will the difference in wheel weight actually matter too, in real life, in any way, in such a heavy car?
 

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Nuclear engineer
02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
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Personal anecdotes, ***8220;so many***8221;, do not data make. The effect of unsprung weight and tire compliance are measured only by professionals only with huge data. Learn about diminishing returns and the Pareto Principle.
 

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The x5 4.8 is heavy. So are the wheels incl brake rotors, i.e. the unsprung rotating weight. Rim, brake rotor, tyre, all 20-30 pounds each, if not more.

I searched for some tyre weight info, and apparently runflat adds 6-8 pounds to a 255/50R19 tyre.

If I go non-runflat, I will probably notice the softer sidewalls (as reported by so many), but will the difference in wheel weight actually matter too, in real life, in any way, in such a heavy car?
When I changed my stock 18's on the E93 to Sparco Pro Corsa CSL style 18" rims and binned the RFT's, I noticed a slight but unmistakable and appreciable lightness on it's feet....
 

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Nuclear engineer
02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
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In HiFi we called ***8216;em Golden Ears that could hear the difference between high oxygen and low oxygen copper cables.
 

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Like i said, slight but unmistakable and appreciable lightness in the get-up-'n-go...Think of going running - it's much easier in trainers than it is mud-caked wellies. Same with unsprung weight on cars. Surely less mass will ADDITIONALLY give the damper less work to do, meaning the damping response occurs quicker, meaning the chassis is less unsettled for a shorter time. Just my opinion based on adding much lighter rims and tires as mentioned in post #3.
 

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Nuclear engineer
02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
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LOL. Argument by analogy is a weak argument, only slightly better than post hoc ergo propter hoc, first one must establish the parallelism from ***8220;wellies***8221; to unsprung weight.

So, if they are Golden Ears in HiFi, what might they be in personal seat-contact accelerometers?
 

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https://www.caranddriver.com/features/a15130598/upsized-wheels-tires/
What***8217;s immediately apparent from the results is that as the wheel-and-tire packages get larger and heavier, acceleration and fuel economy suffer. Neither is a huge surprise, but we measured a 10-percent drop in fuel economy and a four-percent degradation in 0-to-60-mph acceleration from the 15s to the 19s, which is worth considering should you be thinking about ***8220;going big.***8221;
 

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Lighter rims and/or tires also have less rotational mass. Accelerates easier/stops easier. . Oh and the gyroscopic effect is directly related to the inertia, which includes mass and speed in its calculation.

A good calculator is here: http://hpwizard.com/rotational-inertia.html went from 19s to 18s and that calculator showed about 20% less rotational mass, despite both sets being only about 5% different in weight.

In the future I will be going from rft to non rft is only about 5 lbs a tire but as the calculator shows, the outside mass is much more critical adding much more inertia.

Anparallelism analogy with parallelism for Doug... Compare the energy needed to spin up or show down a heavy flywheel vs a light one.
Wheels are also circular objects, or do you need me to write a paper to explain it, citing sources that you deem correct?
 
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LOL. Argument by analogy is a weak argument, only slightly better than post hoc ergo propter hoc, first one must establish the parallelism from ***8220;wellies***8221; to unsprung weight.

So, if they are Golden Ears in HiFi, what might they be in personal seat-contact accelerometers?

I have my personal seat-contact accelerometer... It works in BCls*/Min and it is incredibly accurate.


*Butt Clenches / minute - Unit of measure also equated to “holy Crap2” - Commonly used for high tension situations behind the wheel in search of measurable differences in before and after experiments


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Discussion Starter #10 (Edited)
In the future I will be going from rft to non rft is only about 5 lbs a tire but as the calculator shows, the outside mass is much more critical adding much more inertia.
Interesting. Classical mechanics basically tells us that a two piece brake rotor (with a lighter, aluminium hat at the centre) is probably on the wrong end of the Pareto Principle. Lighter tyres (outside) have a better chance of being at the right end...

On top of being cheaper and having more supple sidewalls.

Note: my current Dueler HP RFTs are listed as 44lbs, and they are due for replacement. I'm looking at Michelin Latitude sports at 33lbs according to Tyre rack specs. That is quite a difference!
 

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Yeah rotors are closer to center mass.
Two piece rotors exist for the multi piston calipers that don't slide like stock. 2+2, etc.
The rotor can move a little in the multi piece design to reduce vibration.
 

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Nuclear engineer
02/2012 X5 35d M57Y CPO 99K miles NOKIAN WR G3 12K miles
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I have my personal seat-contact accelerometer... It works in BCls*/Min and it is incredibly accurate.


*Butt Clenches / minute - Unit of measure also equated to “holy Crap2” - Commonly used for high tension situations behind the wheel in search of measurable differences in before and after experiments
Sounds like a candidate for the Supplimental Driver Restraint System, a 2” trailer-hitch ball mounted in the seat bottom. No need for DSC to pretension the seatbelts, this the driver takes care of on his own. No more “Oh *Shoot* Moments.” No more soiling one’s Kevlar longjohns.
 

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Discussion Starter #14
OP, what are you trying to win a race? You may shave off .005 off your 0-60 time ;-)


With 3 kids in the back... no. Just learning how things work and what makes sense in real world terms. I need new tyres anyway, so I could include weight as parameter too.


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Sounds like a candidate for the Supplimental Driver Restraint System, a 2” trailer-hitch ball mounted in the seat bottom. No need for DSC to pretension the seatbelts, this the driver takes care of on his own. No more “Oh *Shoot* Moments.” No more soiling one’s Kevlar longjohns.






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Butt dynos or not, look at my post and see how shaving even just 5% off a wheel can mean 20% reduced inertia to accelerate and brake.
This is why 20 inch wheels are stupid.
 

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Butt dynos or not, look at my post and see how shaving even just 5% off a wheel can mean 20% reduced inertia to accelerate and brake.
This is why 20 inch wheels are stupid.


Don’t get me wrong. I agree wholeheartedly on performance gains from this, just don’t believe these can be appreciated in everyday driving in a vehicle the size of the X5


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In HiFi we called 'em Golden Ears that could hear the difference between high oxygen and low oxygen copper cables.
And remember those "hospital grade" 120 volt power cords that cost $400 each? They were supposed to make things sound better too. I often wondered how that was possible when the 6 foot cord then was plugged into your crappy house wiring, circuit breaker box, and service line out to the utility's transformer on the pole.
 

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In HiFi we called 'em Golden Ears that could hear the difference between high oxygen and low oxygen copper cables.
False equivalence... Unsprung weight does in fact have objectively proven benefits towards certain performance metrics that can be quantified by a variety of objective measurements, as well as subjectively perceived in a tangible manner; however, High Oxygen vs Low Oxygen Copper in the realm of audio electronics has so far shown absolutely zero difference, both objectively w/ ridiculously expensive instrumentation, as well as subjectively in blind studies...

Will reducing sprung weight on an X5 show any benefit? Hard to know for sure & will depend upon differentiation between A vs B, as well as a host of other pretty narrow / unusual requirements; however, I'd guess it'd be measurable just above the noise floor for the "typical" driver on the road, where benefit is more perceived via bias rather than actual tangible difference that doesn't require direct A / B comparison in quick succession to notice / appreciate.
 
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