Mission impossible: modding a Unimog - Page 4 - Fuel Economy, Hypermiling, EcoModding News and Forum

Cd · 12-24-2010, 01:17 PM

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.

bandit86 · 12-24-2010, 02:33 PM

hmmm. wonder if anyone ever put a unimog into a windtunnel. Would love to see the numbers...

Vekke · 12-26-2010, 01:30 PM

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.

mnmarcus · 12-26-2010, 02:38 PM

Quote:

Originally Posted by Cd

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?

bestclimb · 12-26-2010, 02:52 PM

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.

Rokeby · 12-26-2010, 03:38 PM

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.

(Click to enlarge.)

Click image for larger version

Name: Hiway Glider.jpg
Views: 43
Size: 88.9 KB
ID: 7574

An aerodynamic license plate cover

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

Highway Glider

mnmarcus · 12-26-2010, 03:39 PM

So far it looks like adding tires will not lower rolling resistance overall. If anyone knows if this is true that would be great.

RobertSmalls · 12-26-2010, 04:15 PM

Quote:

Originally Posted by mnmarcus

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.

mnmarcus · 12-26-2010, 05:45 PM

Quote:

Originally Posted by RobertSmalls

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.

Ryland · 12-26-2010, 06:31 PM

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.