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Old 12-24-2010, 01:17 PM   #31 (permalink)
Cd
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Assuming you are getting around 4 mpg, and If your current Cd is around .75, and you decrease it by 60%, ( to .30 ) you would only boost your mileage by just over one mpg at 50 mph.
At slower speeds, like this vehicle is capable of it would be even less.

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Old 12-24-2010, 02:33 PM   #32 (permalink)
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hmmm. wonder if anyone ever put a unimog into a windtunnel. Would love to see the numbers...
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Old 12-26-2010, 01:30 PM   #33 (permalink)
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My father has also one of those. It is for snow plowing puposes. Ours is quite scary to drive over 60 km/h because there is so much "loose" on the streering gear.
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Old 12-26-2010, 02:38 PM   #34 (permalink)
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Quote:
Originally Posted by Cd View Post
Assuming you are getting around 4 mpg, and If your current Cd is around .75, and you decrease it by 60%, ( to .30 ) you would only boost your mileage by just over one mpg at 50 mph.
At slower speeds, like this vehicle is capable of it would be even less.
What? Oh wait a sec. 1 mpg is a 25% increase in FE... Even then, I wonder what numbers you are using???

From Unimog links:

Quote:
Width 78.8 inch/6.57'
Height at highest point 105.5
Ground Clearance 17.5 inches/ 105.5-17.5=88 or 7.33'
Weight 7,920
FE 13 mpg
FA (?) 48.18 sq. ft , EE .19, drive train efficiency .9, #2 diesel
CRR (?) .015

Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com

Gets 13mpg @~37mph... close to 50:50 aero and rolling resistance.

I got 9.36 mpg at 50mph with .75 Cd and a 66:34 aero to rr (respective)ratio. At .30 Cd I got 15.5 mpg, a 65% improvement in mpg and a 44:56 aero to rr ratio.

I stand by the fact that aero improvements are almost always beneficial. Would adding another axle to this vehicle cut rolling resistance by a lot?
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Old 12-26-2010, 02:52 PM   #35 (permalink)
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that is a 25% improvement using your assumptions. not bad, I suspect this thing is getting closer to 6 or 8mpg while on it's way to where it is being used.
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Old 12-26-2010, 03:38 PM   #36 (permalink)
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Every little bit is gonna help...

Highway Glider (designed and patented at MIT) is "the only" product that
can actually improve your vehicle's mileage per gallon (average by about
2%-6%) at highway speeds.


Hey! Must be as good as a ScanGauge.

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Hi-yer edge-a-ma-kashun; the key to arrow-die-namical x-sell-entz.

Highway Glider

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Old 12-26-2010, 03:39 PM   #37 (permalink)
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So far it looks like adding tires will not lower rolling resistance overall. If anyone knows if this is true that would be great.
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Old 12-26-2010, 04:15 PM   #38 (permalink)
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Quote:
Originally Posted by mnmarcus View Post
So far it looks like adding tires will not lower rolling resistance overall. If anyone knows if this is true that would be great.
Different tires have dramatically different rolling and aero characteristics. Tire selection WILL have a huge impact on your fuel economy, with knobby tractor tires probably delivering the worst economy, and slick big rig tires probably being the best. YMMV, HTH.
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Old 12-26-2010, 05:45 PM   #39 (permalink)
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Different tires have dramatically different rolling and aero characteristics. Tire selection WILL have a huge impact on your fuel economy, with knobby tractor tires probably delivering the worst economy, and slick big rig tires probably being the best. YMMV, HTH.
That makes sense, but what about if his truck had an extra axle and two more wheels?

Intuitively (if they were just two more of the same type of wheels) the RR would go up 50%, but he'd get 50% more traction for braking and cornering. I don't think extra traction for acceleration would help in this case.

But if he got tires that were 25% narrower (but silmilair tread and compound) his RR would be about the same, except he'd be spreading the total trucks weight across six wheels (and bearings) for some type of RR reduction?

I'm guessing it wouldn't be worth the cost, weight and work. But anything to get the RR down seems like it would be beneifical for mpg for such a heavy vehicle. I've been searching the web-but have found no real credible info so far.
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Old 12-26-2010, 06:31 PM   #40 (permalink)
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If you've noticed some semi-trucks now have trailers with a single wide tire per axle instead of dual wheels and tires per axle, the reason for this is that for the load a single wider tire apparently has less rolling resistance, they are sticking to the trailers on this new single large tire setup because the drivers don't like how it handles as it is apparently not as stable.
having duel axles with tires inline would give some advantage on very rough roads but for road use? I don't see it.

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