The XDN2 is a horrible tire. Line Energy D has a Rolling resistance if only 89. XDN2 has a RR of 119. Much higher on the XDN2. If your gonna go with singles, the Xone Line Energy D is the best tire. He staying on the highway and rarely driving in snow. There is no reason to spec the tire for anything but fuel economy. The line energy D is only available in 445/50R22.5. If he can spec the truck anyway he wants, why not spec it for the lowest RR tire on the market. the line energy d is 517 rev;s/mile.
Engine RPM x 60 / (Axle Ratio x Tire Revolutions per Mile x Transmission Ratio) = Top Road Speed (MPH)
With my suggestion of line energy d and 2.64, you will hit 68 at 1547 rpm in 11th gear. you can either leave it in 11th and be kinda high on rpm or bump up to 12th and loose the benefit of direct, but maintain that speed at only 1207 rpm. The benefit of this setup is you can easily go 65 or less in 11th and save fuel. You also can use the higher rpm on hills in 11th. You also can go up to 80 easily if you ever want to. (keep in mind tires are rated for 75.) At 75 mph your rpm would be only 1331. Your motor wont be screaming to go fast. In 5 -10 years as speed limits go up, your truck will be ready.
Now, Ngr's suggestion is using the 455/55R22.5 xdn 2 and running in top gear all the time with 3.36 rear. That at a rotation per mile of 491. Admidiantly, not as bad as i originally thought after i did the math. You need 1459 rpm in top gear to achieve 68. (my spec needs 1547 or 1207 depending on gear) If you want to get the benefit of direct you need to slow to 55 mph. (my spec allows direct up to 66ish) So clearly you have a much higher cruise rpm and don't get the benefit of direct unless you really slow down. You also will be at pretty high rpm to go 70 or 75 if you have to. To go 75 you will be at a woping 1609 rpms. The truck specked as NGR suggest basically cant go or sustain 75 mph if you have a hot load. If you attempted it, your motor would be gulping fuel and wont be able to afford to keep your right foot down.
His spec isn't bad, but its a traditional way to spec. A better way is designing the truck to take advantage of direct when you can. Having a higher 11th gear lets you actually use 11th more. Also my spec allows the truck not to have a heart attack if you ever need to go 75ish. With future tires, the truck could do 80 without any trouble. His spec would literally blow at that speed. It sound to me like you want a truck you can burn rubber in. A 3.36 with XDN2 does not allow you to go above your norm cruise easily. With my spec you can cruise at low rpm in top gear and when you hit a hill drop to 11th for more power without sacrificing much speed. if you have a slow day you can drive 65-66 in 11th and benifit from direct all day. Runnign his spec you will take a 1-2/10ths mpg hit do to the tire as well. if you were flatbed deliving to muddy job sites, i might not recommend the X1LED, but ur reefer or van.
NGR, i used the formula above to determine road speed. That comes directly from Easton. Please do not take my opinions personally, it just feel the math still shows th op would be better off with the specs I proposed.
FYI to mods, im not trying to start an argument here, simply trying to show the math on both sets of specs.
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Volvo is doing weird things lately, speccing high 2 (2.79 thereabouts) with overdrive transmissions depending on application. They want the new D13s cruising around 1200 rpms for max efficiency, some even closer to 1100 rpm.
I will say this : the new Volvos are getting incredible MPG. My dad with his 2000 volvo has been the fuel mileage king at my company of 200 trucks for 5+ years. He hauls light and does well, and has averaged over 8 USMPG for entire quarters. The new Volvos are doing just as good if not better than he is.
@Ritcher. I spec my trucks based on real world experience and what works best. I run reefer from east Canada to Cali for the last 12 years driving Volvo trucks only. What I suggested would work best in any situation to the OP, if he decided to go north, south, east or west. My last 780 had 7-7.5mpg at 65mph loaded and up to 9mpg if empty or lightly loaded with XDN2 22.5 rubber. Wind resistance with Aliarc you're saying... How about $5000 minimum of repairs plus your downtime after meeting a small "Bambi" in the after hours on your way. Specing the light D13 motor and I-Shift will leave him with room to add a 300lb. moose guard and still be OK on his steers when loaded. You complicate things too much in your specs. I would finally suggest to the OP if he is all about saving fuel is to go with Volvo XE13 package overdrive. That will give him 455HP and 1550-1750lb. Eco torque with 2.69 rear end, and put him in around 1200RPM @ 68 MPH. When he'll hit the hill it'll downshift to 11th. and pull. With that saying, still if I would spec the truck to travel over mountains I would go with my previous recommendations.
I don;t think the Op is all about mpg. I was trying to spec him a performance truck that also got decent mpg. Im trying to find him a spec that wont sacrifice power and hill climb but still can get a decent bottom line.
Ok so I complicate my specs? Let me make it simpler. Can we agree an rpm range of 1100-1500 is ideal with lower rpm getting best mpg...and higher rpm more hill pulling power?
Option 1: If under 65 cruise in 11th for better mpg, @ 68 go into 12th and cruise @ 1207 rpm. Hit a hill and drop to 11th without loosing much speed
2.64 rear w/ X1LED:
11th (direct) 48mph-66mph
12th (overdrive) 62mph-84mph (as fast as you ever should go lol)
Option2: (NGR) Stay in 12th all the time. Higher RPM to cruse at 68 . Gain start ability from dead stop, loose high top speed and low rpm cruise. This set up would be good trying to pull 80,000 up a hill from a dead stop, or off road like in mud and such. Once moving and above 1200 rpm the ratio wont help.
3.36 rear w/ XDN2:
11th (direct) 40mph-55mph
12th (overdrive) 51mph-70mph
Option 3: (NGR second choice) Similar to the first option. This comes down to the difference in tire more then anything.
2.69 rear w/ XDN2:
11th (direct) 50mph-68mph
12th (overdrive) 65mph-87mph (as fast as you ever should go lol)
Ritcher I will tell you one more thing. I spec the truck based on everyday traveling speeds or per state speed limits. Us Canadians when crossing to US, we face the states mostly with 55MPH limits, followed by states with 60MPH, 65, 70 and 75 (some times 80MPH for a short burst down south), then back to 55MPH in Cali. So the average between east Canada and Cali is 65MPH. In my experience Volvos ain't Pete's or KW's and at speeds above 70-75MPH starting to feel unsettled on the road, simply because of the design characteristics of the Volvo trucks. The best speed for Volvo truck is between 65 and 70MPH, exactly what OP is requested. You seem like trying to spec a Formula 1 car with 80+ MPH ground speeds. Get real, your economical specs won't matter in a heavy truck If you're flying at 75+ MPH. You will burn fuel and tires along with it due to the wind resistance no matter what at your speeds, period! I will leave this pointless discussion with you trying to push you spec's around and let the OP make his choice. To the OP, if you need more help from me do not hesitate to PM me.
NRG and Richter while having different focuses when specing a truck, obviously are both very knowledgeable in doing it. You both have provided great advice to the OP, and others less experienced in this important task.
Thanks to you both!
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