11-17-2017, 07:47 AM | #1 |
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G01 X3 Wheel/Tire Wts & Hwy Performance
I've had trouble finding information showing how wheel size and tire combinations affect aerodynamics and rolling resistance at speed, so I was hoping we can collect data from our forum's experience. As city driving styles and conditions vary those values won't help for this question. But there should be reasonable consistency at highway speeds with cruise control if the grade is reasonably level during the sampling. So if anyone has a chance to gather the information needed in the chart below we might be able develop a better understanding. Ideally the grade should average out to be relatively level over the course of the route, and longer distances should even out elevation changes.
Last edited by Max Well; 05-27-2018 at 10:40 AM.. Reason: Updated Spreadsheet |
11-18-2017, 06:54 AM | #3 |
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Thanks, X4guy. I really hope we can get some contributions from all over as it'll be easy for me to make additions and then simply edit my opening post so we always have the most recent compilation at the beginning. With Excel I can keep the models grouped separately (30d, 30i, M40i, ...) and then subgroup based on tire sizes and then sort to speed as well. Should prove to be very interesting, and the more data contributions the more sound the analysis.
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11-18-2017, 07:01 AM | #4 | |
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Last edited by ZHPsedan; 11-18-2017 at 09:07 AM.. |
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11-18-2017, 07:09 AM | #5 | |
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I assume you expect folks to just report the numbers the car reports on the trip status vs needing to check their math by refilling gas tank and computing mileage from that--the way we had to do it before all this instrumentation. I've had some cars that seemed to come up with different numbers than I ever got. With only one fill up so far, I've not had a chance to see how accurate my M40i trip computer is, though given the advanced monitoring they have nowadays, I'd be surprised if it isn't right on. |
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11-18-2017, 08:18 AM | #6 | |
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11-18-2017, 09:08 AM | #7 | |||
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11-18-2017, 09:28 AM | #8 |
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Only thing with these early numbers is that my Ecoboost F150's mileage increased significantly after 1000 or so miles. Went from 15 MPG to 18 or so avg after break-in.
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11-18-2017, 10:00 AM | #9 | ||||
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20d and 30d due to hit the streets in a few weeks but M40i is looking like it will be delivered in the new year. My order has been in for about 6 weeks and I still don't have a build slot. |
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11-18-2017, 03:32 PM | #10 |
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A good point to consider as well, ZHPsedan - this will be very easy for me to edit at any time, so additional break-in numbers might be useful to know as well. I'm thinking I might want to add Forum Member names as another column so one could cross-reference as time goes on...
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11-18-2017, 03:33 PM | #11 | |
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11-22-2017, 08:40 AM | #12 |
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Most wheel weights added
Using the website sor provided in his 20 Nov 2017 1014AM post in thread http://x3.xbimmers.com/forums/showth...1433123&page=5 , found at https://www.etkbmw.com/bmw/EN/search...3+M40iX/USA/36 , I was able to compile almost all of the wheel (not tire) weights. There were only five missing (in yellow) so hopefully someone can find those to allow chart completion. I also added a column to now allow wheel option to be shown with the individual data sets.
I spent a fair amount of time trying to do the same for tires but it's just too difficult to find exact weights since some of the tires seem custom to BMW and there are so many of them. If some can find definite weights for specific tires just post them here and I can compile as well. So as an example, the 698M 19" total 107.6 lbs and the 699M 20" are 130.4 lbs total G01. Once the tire weights are known then maybe someone with knowledge (? skyblue2002) can share the rotational inertia figures and explain whether it would translate into a significant performance difference. |
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11-22-2017, 09:02 AM | #13 |
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It might be good enough to just come up with an average weight for the stock tire size. I know they're going to vary due to tread design, but perhaps a placeholder for now (or even calculating the highs and lows) will help determine whether the small differences between individual tire selection make any difference.
For example, looking at a variety of 245/50 R19 I see they're between 30-33 lbs. Looking at a variety of 245/45 R20 they're 28-30 lbs, and 245/40 R21are 27-30 lbs. |
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11-22-2017, 10:20 AM | #14 |
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Thanks, sor - that crossed my mind, but in seeing the fairly large spread on my worksheet (attached) even for the same tire just depending on brand, and then the error in guessing if it was close to BMW's specs, I was hoping someone with knowledge of BMW tire weights could share a definitive list. You would think that type of tire spec sheet has to be somewhere, and it would sure make this simpler and more accurate, especially if only 5-10 lbs has a significant effect at the wheel (I have no idea if it does or doesn't).
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11-22-2017, 11:33 AM | #15 | |
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Last edited by skyblue2002; 11-22-2017 at 05:38 PM.. |
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11-22-2017, 05:08 PM | #16 | |
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And I don't want to lose the forest for the trees on this, but I do think there is a need to understand some basics of what happens to the G01's performance curves when we choose certain wheel/tire sets. And I'm not referencing high-end competition track performance as one would have on the Ring, but just for understanding daily 'high' (not city) speed drives on Interstates/Autobahns. This shouldn't be a difficult question to answer but unfortunately the data sets aren't available for us to make rational decisions. Do I go for the great look of the 'x' wheel/tire or do I get the most aerodynamic profile with 'y' set? And I would suggest to those wondering why someone buys a precision performance vehicle and is discussing this - it isn't always about the fuel economy but rather most aerodynamic profile on a straight-away. End result is fuel economy, but aerodynamic efficiency is my interest. Last edited by Max Well; 11-22-2017 at 05:16 PM.. |
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11-27-2017, 08:42 AM | #18 | |
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And if anyone can find the unknown data in the yellow cells it would be appreciated. I can't find it anywhere, but it would be best to have a complete data set if possible. And although we only have a(n) N=2, already some interesting comparisons. Fascinating that the M40i has better Hwy efficiency, but only with a lot more data sets will any potential conclusions be able to be considered. Thanks again for contributing to this, ando! |
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11-27-2017, 08:54 AM | #19 |
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Here are some links about the new Bridgestone Alenza 001 tire, which was designed exclusively to meet the demands of the growing premium SUV/SAV market. Wish I could find the weight of the 21" tires...
http://www.sgcarmart.com/news/events...s.php?AID=3395 https://www.bridgestone.com.sg/ALENZA_001.html https://www.carid.com/bridgestone-ti...749825175.html https://www.redbook.com.au/news/2017...?csn_tnet=true |
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11-27-2017, 10:05 AM | #20 | ||
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11-27-2017, 11:06 AM | #21 | |
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11-27-2017, 02:33 PM | #22 |
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After seeing ando's data I went back to the spreadsheet I set up in 2014 which looked at HP needed to maintain a certain speed. Since the G01 models differ in their Cd (30i has Cd 0.29, M40i Cd 0.33), I was curious to see how they stacked up against each other and the 2nd Gen F25 X3 35i with its Cd of 0.36. At higher speeds in this sim the aerodynamic differences become really apparent - so that the G01 30i at only 248 hp has a nearly identical top speed unlimited as the F25 35i at 300 hp, around 145 mph. Kudos to BMW's Engineering and Design team for their aerodynamic accomplishments with the G01!
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