My highway mileage sucks. at 75 im running at 2400 with stock everything. My dually with 4:10s runs at the same rpm at 75mph. Is this right?

yep. stay under 2k and your mileage will improve...or do the 6spd converson. read more in the tranny section.

did a 300 mile trip 2 weeks ago going down 75 mph fuel 16 mpg coming back 65 mph 2000 rpm 20 mpg so go fast bad fuel mileage go slow way better

2400 @ 75 seems a bit high. Have you read the ECM with a scan tool to check if the tach is OK?
I have had to use a programmer that tunes for fuel ecomony to get decsent fuel mileage at that speed.
Would give you mileage readings, but there are too many other variables for my figures to work for you. Some variables can be: Winter or summer fuel or fuel condition/type, tire pressure, wind speed and direction, load on truck, truck raised?, plus more.
Look at the fuel mileage when running Looooong trips, such as 800 miles a day all highway for best results.

How many speeding tickets? Speedo could be off,you might be running 80

Thats pretty close to what mine reads as well. Kinda sucks cause the LB7s can run 75 at 2K.

i run closer to 80 at that rpm

I'm closer to 80 also at those rpm's. At 75 I'm usually avg 20mpg. RPM's around 2100 -2200.

yeah me too i have 265s

stay under 2k and your mileage will improve

regardless of the mph.... ^^

open loop is above 2k rpm's..meaning that's when it dumps fuel.

mines about 2100 rpms for 73-74 and getting easy 18mpg

I think the speedometer needs to be calibrated.

My highway mileage sucks. at 75 im running at 2400 with stock everything. My dually with 4:10s runs at the same rpm at 75mph. Is this right?
I ve got a power pup that gave my 05 6 to 7 more mpg city
and have seen 25 mpg+ highway on a 90 hp setting! That is 65 mph or slower!!!Again under 2000rpms! Also 4 sale:rolleyes:

I think something is off, Its hard to believe that my 4 speed dually gets better highway mileage than my duramax. I drove about 70-80 miles of all highway yesterday and burned 1/4 tank.

I ve got a power pup that gave my 05 6 to 7 more mpg city
and have seen 25 mpg+ highway on a 90 hp setting! That is 65 mph or slower!!!Again under 2000rpms! Also 4 sale:rolleyes:


Im incapable of going under 65mph:D

I ve got a power pup that gave my 05 6 to 7 more mpg city
and have seen 25 mpg+ highway on a 90 hp setting! That is 65 mph or slower!!!Again under 2000rpms! Also 4 sale:rolleyes:

Is that hand calculated?? Or the info you get off of the DIC???

Is that hand calculated?? Or the info you get off of the DIC???
BOTH I RESET TRIP & DIVIDED FUEL USED aND GOT 27.9 TO EXACT AND MY WIFE WILL ATTEST TO IT;)LUGGAGE ,2 ADULTS,3KIDS,&LAB PUP
DAYTON TO SUMMERSET KY

BOTH I RESET TRIP & DIVIDED FUEL USED aND GOT 27.9 TO EXACT AND MY WIFE WILL ATTEST TO IT;)LUGGAGE ,2 ADULTS,3KIDS,&LAB PUP
DAYTON TO SUMMERSET KY

Have you dyno'ed your truck? What kind of RWHP you think you're generating?

i ran 85 and better all the way to bowling green and got 18

i have a quad s2 on a 90hp

Have you dyno'ed your truck? What kind of RWHP you think you're generating?
Me and my son drove to BOWLING GREENE 08 New torque converter(dud)& the rest of mods except rods & pistons. 625hp range 1150trq range.:) cracked piston in aug 08 .:(KYLE HAD IT UNTIL DEC O8
ITS DETUNED AT THE PRESENT TIME:rolleyes:575-600:(NEED MORE FUEL:rolleyes:

That is 65 mph or slower!!!Again under 2000rpms! Also 4 sale:rolleyes:

I think everyone is amazed at 27mpg, but missing the key point here... he drives at the magic rpm...UNDER 2k rpm's.... remember, as it's been stated many times...above 2k is basically drinking fuel- OPEN LOOP. Good mileage can be attained if you stay below 2k rpm's OR..get the 6spd and go faster than 65 and still stay under 2k rpm's. Yes on todays highways that is a bit slow going 65, but in this economy I'd like to save every penny if I can.

$.02

BOTH I RESET TRIP & DIVIDED FUEL USED aND GOT 27.9

Is that fuel used measured from the diesel pump or your DIC?

Is that fuel used measured from the diesel pump or your DIC?
Fuel used :dic

I think everyone is amazed at 27mpg, but missing the key point here... he drives at the magic rpm...UNDER 2k rpm's.... remember, as it's been stated many times...above 2k is basically drinking fuel- OPEN LOOP. Good mileage can be attained if you stay below 2k rpm's OR..get the 6spd and go faster than 65 and still stay under 2k rpm's. Yes on todays highways that is a bit slow going 65, but in this economy I'd like to save every penny if I can.

$.02
I was also amazed it doesnt make logical sense ,add hp add mpg???
The 07 wouldnt do that though?

I think something isn't right, not to say that it couldn't happen but 6-7 mpg gain on a tuner seems a little extreme.

Fuel used :dic

Unless you have verified that the DIC matches the fuel pump, your hand calcs. are duplicates of the DIC calcs.

The problem with most tunes is that no one adjusts the portion of the table that the DIC uses for fuel consumption.

I think everyone is amazed at 27mpg, but missing the key point here... he drives at the magic rpm...UNDER 2k rpm's.... remember, as it's been stated many times...above 2k is basically drinking fuel- OPEN LOOP. Good mileage can be attained if you stay below 2k rpm's OR..get the 6spd and go faster than 65 and still stay under 2k rpm's. Yes on todays highways that is a bit slow going 65, but in this economy I'd like to save every penny if I can.

$.02

What are you talking about "open loop"? You are confusing the duramax with a gasser. A diesel engine, even an electronic fuel injected diesel, doesn't trim fuel. There is no fuel trim function in there. A diesel burns the amount of fuel needed to provide the BTU's required to produce the amount of power needed to attain and sustain the speed you want. It just so happens that the engine falls off of its efficiency curve right about 2100 RPM. Get a bigger turbo, or open the vanes in your VVT and you can extend this RPM number further up. But this has NOTHING to do with "open loop" and/or fuel trim for cruising. It just isn't something that is or can be done with a diesel engine.

Unless you have verified that the DIC matches the fuel pump, your hand calcs. are duplicates of the DIC calcs.

The problem with most tunes is that no one adjusts the portion of the table that the DIC uses for fuel consumption.
I speak in laymans term
1took fuel used(gals)
2total miles driven(no i didnt measure to make sure my odometer was correct)
3 divided total miles by gallons used.PERIOD
NOT SURE WHAT YOU ARE TALKING ABOUT, ARE YOU?
AND TO ADD MY TWO CENTS WORTH BUY IT AND TRY IT OUT FOR YOURSELF!
AND TO BEAT ALL I GET 19 TO 21 WITH MY MODS NOW AT 65MPH

I am not trying to discredit but I am just really surprised to hear that. I wish my 35s gave me that. I am lucky to get 20.

You are confusing the duramax with a gasser.

not confused, just trying to explain things easier..maybe that wasn't the best method. diesel terms are completely different from gasser terms, but most people are familiar with the gasser ones. you cleared it up pretty well ;)

sorry guys..I not only do stuff for the diesel folks, but a few other automotive sites as well. sometimes I get them crossed.. LOL

I speak in laymans term
1took fuel used(gals)
2total miles driven(no i didnt measure to make sure my odometer was correct)
3 divided total miles by gallons used.PERIOD
NOT SURE WHAT YOU ARE TALKING ABOUT, ARE YOU?


As a matter of fact, yes I do.

You state you are using fuel used from the DIC and dividing total miles from this number. That is the same calc. that the DIC MPG is doing.

Most of us have experienced that once the fueling tables have been changed, the "DIC fuel used" is no longer accurate. That is why I asked if you checked this against an actual calibrated pump. I suspect that you will find the DIC and the pump doesnt match.

For the record, I allowed my father borrow my truck, his typical top speed is 50mph. His starts are more turtle vs. Jack rabbit, and the mpg for his trip was around 21.5 IIRC. The only other time I have seen someone get above 25 mpg in a DMAX, post LB7, has been when the fuel tables were altered and the person was trusting the DIC. Does this sound familiar??

As one of my old buddies used to say "But what do I know" :)

Mileage Calculation.
Used the gallons dispensed from the diesel pump, and the mileage from mile markers or GPS, unless you have verified your dash display.
ANY IN TOWN mileage will drop your MPG. I don't even consider the in town mileage from the DIC or in real life.
To check engine condition and/or problems I run non stop on a full tank until the low fuel warning comes on, then fill, and figure with pencil.

Back to the original question.
Do the math and you are correct about 75mph and 2400 rpm. Of course its all approx when you are using factory gauges. I get about 16 mpg max with mine at those speeds with the wind in my back. Engine loses efficiency for fuel mileage above 55. More weight and wind drag with my dually though. I was very dissapointed too. Diesel mileage is very dynamic. Too many variables. Remember, It's alot better than a gasser and it ain't some short bed family sedan :-)

Back to the original question.
Do the math and you are correct about 75mph and 2400 rpm. Of course its all approx when you are using factory gauges. I get about 16 mpg max with mine at those speeds with the wind in my back. Engine loses efficiency for fuel mileage above 55. More weight and wind drag with my dually though. I was very dissapointed too. Diesel mileage is very dynamic. Too many variables. Remember, It's alot better than a gasser and it ain't some short bed family sedan :-)

I have to agree, my previous dually 8.1L couldnt make 10 mpg unless I put the pacifier and diaper on it. When towing I got 6mpg. My diesel dually with some mods, will return a decent 17 mpg when kept under 80, and ~ 10mpg for most of my heavy towing.

Im lucky to get 13 empty at 65mph. been chasin this dog for awhile. No excess smoke, unless high idle on a -15 degree morning. I do not let this thing idle for more than 10 minutes. Treat the fuel to no end. Have a winter front. Go figure

it seems like the only time i see 65 mph and 2k rpm is when the wind is at my back. i usually seem to run closer to 2100 @ 65. i did manage 17.1 mpg according to the dic last weekend on a 200 mile round trip pulling two snowmobiles with a steady cross wind most of the way back. all mods are in my sig

I get terrible millage at 65MPH running at about 2150RPM's. I can runn 65 or 85 and still get 16.9 hand calced millage. When I bought the truck they had 245/75?16's. I recalibrated tire size with my PPE. I don't get why my millage is so poo! I'm hoping the 285's in the garage will get me some better highway millage!

If I did the math right, the following are the rpm's based on speed. Assumptions are P245 tires, 5th gear, 3.73 gear.
60 mph 1754 rpm
65 mph 1900 rpm
70 mph 2047 rpm
75 mph 2193 rpm
80 mph 2339 rpm
85 mph 2485 rpm

based on the above, you are actually going 85 mph (with the stated tires and gears) at 2500 rpm.

If I did the math right, the following are the rpm's based on speed. Assumptions are P245 tires, 5th gear, 3.73 gear.
60 mph 1754 rpm
65 mph 1900 rpm
70 mph 2047 rpm
75 mph 2193 rpm
80 mph 2339 rpm
85 mph 2485 rpm

based on the above, you are actually going 85 mph (with the stated tires and gears) at 2500 rpm.


sounds right to me! Don't forget guys, that in cold weather diesel mpg sucks!

I seem to get about the same Summer, Winter, Day light savings time. Doesn't matter.

something not right! I'm no where NEAR those numbers!

For the P285 tire guys (3.73 rear end and 5th gear)
60 mph 1620 rpm
65 mph 1755 rpm
70 mph 1890 rpm
75 mph 2025 rpm
80 mph 2160 rpm
85 mph 2295 rpm

Well the speedo may be off but I know Im not 10mph off. Im not so much complaining about mileage but why my 5 speed with 3.73's runs at the same rpm as my 4 speed with 4.10's.. Just doesnt make sense to me. Its like Im missing 5th gear.

what type of factors could cause the difference in RPM's?

Well the speedo may be off but I know Im not 10mph off. Im not so much complaining about mileage but why my 5 speed with 3.73's runs at the same rpm as my 4 speed with 4.10's.. Just doesnt make sense to me. Its like Im missing 5th gear.

If you are comparing a gas job to a diesel there is a difference in the gearing in the transmission itself. Just because you have 5 speeds in a transmission, doesn't necessarily mean that its going to be different. In this case, the gas job has more of a broad power/torque band. lets just say 2000 rpm to 4000 rpm. Where a diesel has a smaller window of opportunity. Mine pulls good from 1200 rpm to about 22-2300 rpm before you feel it drop off. So therefore you have that extra gear to shift quicker.

there is my $.02

hes running 275/60-16's(28.9) diameter is about 1.5inches under 245/75-16's(30.45). he's cranking out those miles, but not traveling them. correct your speedo before making calculations. actual tire diameter depends on air pressure/side wall deflection. best to get gps and verify.

For the P285 tire guys (3.73 rear end and 5th gear)
60 mph 1620 rpm
65 mph 1755 rpm
70 mph 1890 rpm
75 mph 2025 rpm
80 mph 2160 rpm
85 mph 2295 rpm

Mine is not like that. at 70 mph I'm at 2000 -2100 RPM. I have recalibrated my speedo with the Predator as it was confirmed with a GPS. One thing that I do notice is that since I added my 06-07 towing mirrors, my RPM at 70 has gone up a little.

I say again..... don't trust your dash gauges.
Use some other means to verified and/or correct your speedometer, and odometer distance shown compared to actual known distance from GPS or other outside source. Tire wear will change distance and speed shown by about 5-6%! The longer the testing period, the more accurate you could get the distance/speed.
Also, on short runs...less than 500 miles, your calculations will be off.
Then use the real mileage over the actual gallons pumped to calculated MPG.
Don't even bother looking at the DIC or speedo for this info.

While your checking things out, use a "TechII" or similar to verify/correct the tach, and check what gear your in. Also is the converter locking?

Doing the verification for stock or modified will help you know whats going on.

If you are comparing a gas job to a diesel there is a difference in the gearing in the transmission itself. Just because you have 5 speeds in a transmission, doesn't necessarily mean that its going to be different. In this case, the gas job has more of a broad power/torque band. lets just say 2000 rpm to 4000 rpm. Where a diesel has a smaller window of opportunity. Mine pulls good from 1200 rpm to about 22-2300 rpm before you feel it drop off. So therefore you have that extra gear to shift quicker.

there is my $.02


They are both diesel. I know there is gonna be a difference but there is absolutely no reason these two trucks should run at the same rpm. I didnt think about the gps, I will check this weekend. If gps confirms speed is there something else to look at?

The F350 likely has larger tires than the 2500HD if they are both stock. May make up the difference in the gear sets of the two. The F350 may have a taller overdrive than the Ally.
Is the GM running 2400 RPM at 60 or 1900 at 60 MPH? Run in fourth or fifth? Both engines like top gear.
5% or more variation on the dash gauges is not a lot. 5% on each added could be out 10% total. Or the tach might be lazy of the F350, and the speedo read a bit higher than your actual going. The Chev maybe the oposite. My tach is out about 75 RPM at 2000 RPM according to the OBDII scanner. Speedo happens to be out only 2 MPH at 60 according to the GPS. They all seem to have some problems.
If I am force to ride in my friends F350 the top gear engine speed is about the same as the 2500HD for a given ground speed. When the F350 drops a gear the 6.0L goes to a lot higher RPM than the short throw Ally.

My highway mileage sucks. at 75 im running at 2400 with stock everything. My dually with 4:10s runs at the same rpm at 75mph. Is this right?

An 05 dually should have 3.73 gears. Grab a handheld gps and check your speedo.

An 05 dually should have 3.73 gears. Grab a handheld gps and check your speedo.

A gasser dually had an option to have 4:10's (I believe I saw it said the dually was a gasser in the thread)

Correct me if im wrong.

~John

My highway mileage sucks. at 75 im running at 2400 with stock everything. My dually with 4:10s runs at the same rpm at 75mph. Is this right?

My 03 with stock 245s runs 2400rpms at 75mph. When I switched to 285s it ran 2000 at 70MPH and that was a corrected spedo using bully dog. It still runs at 2000rpms/70mph with 285s using EFI live to correct the spedo. The best mpg I have ever gotten with either programmer was 21mpg and that was driving 70mph.

My 03 with stock 245s runs 2400rpms at 75mph. When I switched to 285s it ran 2000 at 70MPH and that was a corrected spedo using bully dog. It still runs at 2000rpms/70mph with 285s using EFI live to correct the spedo. The best mpg I have ever gotten with either programmer was 21mpg and that was driving 70mph.

Interesting. My friends LB7 will run 75 at 2K with 285s. Speedo corrected with Bullydog.

I double checked my math and even found a few calculators online. The numbers I posted are correct. Make sure that you are not driving around in tow/haul mode and double check the speedo corrections.

Ok just checked against gps and if anything im going slower than speedo but they were pretty close the whole time(1-2mph) My dually is a 99 f350 diesel(4.10's) my 2005 is the duramax(srw)
Maybe when I get my 33's things will get better but it still seems too high

Interesting. My friends LB7 will run 75 at 2K with 285s. Speedo corrected with Bullydog.

This is strange? mine runs about 2200 at 75. My neighbor is a trafic cop maybe I can get him to use his radar to check my speed. It he does i will post the results.

This is strange? mine runs about 2200 at 75. My neighbor is a trafic cop maybe I can get him to use his radar to check my speed. It he does i will post the results.

Yeah it's weird the way he can run 5 mph faster then I at 2 grand. The only difference we have in trucks is the programmers(he has a bullydog and I have the Predator) and his is an LB7 and mine an LLY. Next weekend I have to take a little trip. I'm going to see if I can't borrow a friend of mines Garmin GPS thingy just to double check it.

wbens what year is the LLY, late 06 should have 6speed. are the tires same manufacturer and trade name, some mfgr's will make 265/75-16 but tread, sidewall stiffness, load rating and operating air pressure will give about 1 inch diameter difference. i wonder if his transmission is shifting up or if converter is slipping or not locking up, should set code if too much slippage. from what i've seen gm speedo will usually read 2-3mph faster. 75mph is about 21-2200rpm on mine.

For the P285 tire guys (3.73 rear end and 5th gear)
60 mph 1620 rpm
65 mph 1755 rpm
70 mph 1890 rpm
75 mph 2025 rpm
80 mph 2160 rpm
85 mph 2295 rpm


I did mine tonight. @

55mph 1800rpm
60mph 2000rpm
65mph 2150rpm


05 245's with PPE re claced to 30.25" and 3.73 gears along with below mods.

wbens what year is the LLY, late 06 should have 6speed. are the tires same manufacturer and trade name, some mfgr's will make 265/75-16 but tread, sidewall stiffness, load rating and operating air pressure will give about 1 inch diameter difference. i wonder if his transmission is shifting up or if converter is slipping or not locking up, should set code if too much slippage. from what i've seen gm speedo will usually read 2-3mph faster. 75mph is about 21-2200rpm on mine.

Mine is an 04.5, he is driving an 03. I have Cooper Discover S/Ts on my truck and he has WideTrack Baja M/Ts on his. Both are 285/75/16s. Right now mine are on the stock PYO for Winter and he is running on some 16x8 Mottos. In the Summer I have some 16x8 Pro Comps. Either way we get the same results.

Ok I went out and checked my RPMs at different speeds.

55-1650
60-1750
65-1900
70-2100

So is what you guys are saying is that with bigger tires (285 from 245) the rpm's will go down thus giving better mileage. When it would seem that with bigger tires you would get less mpg's.

So is what you guys are saying is that with bigger tires (285 from 245) the rpm's will go down thus giving better mileage. When it would seem that with bigger tires you would get less mpg's.

to a certain point you get better mpgs, then aero dynamics and tire contact patch take over. not to mention agressive tread.

Ok I went out and checked my RPMs at different speeds.

55-1650
60-1750
65-1900
70-2100
Close to what P245 tires calculate out to. For P245 tires I am using 30.58 inches as the diameter (8.0 circumferance). For P285 tires I am using 32.96 inches as the diameter (8.63 circumference). There may be some diameter variation from tire model depending on the manufacturer in addition to some minor errors in the speedo calulations. We have enough specific information posted in this thread to figure this out, just don't have all of the pieces put together.

Close to what P245 tires calculate out to. For P245 tires I am using 30.58 inches as the diameter (8.0 circumferance). For P285 tires I am using 32.96 inches as the diameter (8.63 circumference). There may be some diameter variation from tire model depending on the manufacturer in addition to some minor errors in the speedo calulations. We have enough specific information posted in this thread to figure this out, just don't have all of the pieces put together.

That is with 285/75/16s. I have my pred set at 285/70/16 to get the speedo to read correctly. I'm going to try to recheck it this weekend if I can borrow my friend s GPS. I can't see how it would change over the winter but I'll try to find out.

I think my rpms are a little lower than yours Will, but thats because I run 35s. at 70 i run close to 2k. At 75mph i run about 2000 or so. at 80 I run a little

So your saying bigger tires?:clap::D

I think the message here is, match the rpms as close to factory settings, so with bigger tires the only way to really do that is to regear. But with 35s or smaller, unless you tow it is not that necessary, but for towing you need more low end power.

I get about the same rpms as mentioned in the thread topic. I'm running 265/75/16 and a ZF-6. So when it says 75 I'm assuming it's really around 78 or so with a slightly larger tire than stock. There's tools on the internet that make it really easy to calculate how much your speedo is off by comparing stock tire size to chosen tire size.

With that being said, I get 19mpg daily driving with what would be considered city driving. DIC says 20-20.5, my calculations say 19mpg. I normally don't drive more than 60mph. I usually take off in 2nd, switch to 4th, then 6th. Engine is stock, no tune, only thing different is a straight through exhaust. No muffler, no cat, just a very straight pipe. Was like that when I bought it.

Ok here me out here, this may be a stupid question but..
Tow haul mode keeps you out of Overdrive, Correct? So if im cruising at 75mph and hit tow haul I should drop a gear and my rpms should shoot way up. Well when I hit tow/haul nothing changes at all. Does this sound right? Like I said before it feels like im not getting to fifth gear.

and at 70 mph im at like 2250 rpm.

Ok here me out here, this may be a stupid question but..
Tow haul mode keeps you out of Overdrive, Correct? So if im cruising at 75mph and hit tow haul I should drop a gear and my rpms should shoot way up. Well when I hit tow/haul nothing changes at all. Does this sound right? Like I said before it feels like im not getting to fifth gear.

No. You have to hold the tow haul button to lock out over drive. A light will appear on the dash.

I checked my speedometer with a GPS tonight. Guess mine is off a touch. 65 on my speedometer is 68 on the GPS.

http://www.allisontransmission.com/service/faq/index.jsp?CategoryID=11

and read what the trany maker says about T/H, overdrive inhibit, and etc.

So what size should I program in the Predator to get my speedometer set correctly? It reads a couple mph slow compared to a GPS.

So what size should I program in the Predator to get my speedometer set correctly? It reads a couple mph slow compared to a GPS.
Using the same calculations from previous posts try entering in the tire as a 285/70/16 should get you really close. I show your actual tire/wheel diameter as 31.86 inches which translates into a 7.93 inch sidewall. Convert to metric gets me to 199.84 mm. A 285/70 tire should have a 199.5 mm side wall so this is less than a 1/2 mm differeence.

Using the same calculations from previous posts try entering in the tire as a 285/70/16 should get you really close. I show your actual tire/wheel diameter as 31.86 inches which translates into a 7.93 inch sidewall. Convert to metric gets me to 199.84 mm. A 285/70 tire should have a 199.5 mm side wall so this is less than a 1/2 mm differeence.

Well I went and double checked it after posting that. Apparently that is how I currently have it set up. Maybe I should try 285/65/16s.

Well I went and double checked it after posting that. Apparently that is how I currently have it set up. Maybe I should try 285/65/16s.
That should get you very close...65.4 MPH when the GPS shows 65 MPH, and the engine turning 1900 RPM.

I had the chance to take out an 01 LB7 with P245 Michelin Tires and the RPM/MPH figures that I had calculated were spot on. I think that those that don't match have errors in their speedo correction software (most likely), have inaccurately sized tires (next most likely), or are not locked down in 5th gear (least likely).

with 265s im at 2K going 80...

Im right on 2k rpm at 69-70 with 3.73 gears with 4.10s 2500 rpm sounds right at 70 or a little above.

Not to argue with the group, but a while back, I built a spread sheet to see what size tires I wanted to run. All of this was to keep the drive train at the same or close to the same numbers as stock without changing the gearing. Attached is a shot of the numbers. First line is stock, last line is with the 305 - 55 - r20's.

Thats pretty close to what mine reads as well. Kinda sucks cause the LB7s can run 75 at 2K.
Not mine, its more like 2200 around 70.

Checked mine today. 67 mph=2000 rpm.