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Old 06-09-2013, 11:34 AM   #1
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Purchasing a 2005 Safari Panther with C-13 525hp

I am considering purchasing a 2005 Safari Panther with C-13 525hp with 295/80R22.5 tires which need replacing. The Alladin system shows that it is getting 5.5mpg over the life of the vehicle. ( )It has a 4.30 rear axle ratio and I believe that due to the gear ratio the motorhome runs in the wrong RPM at highway speed causing this terrible fuel mileage. The tires need replacing before I purchase the vehicle and I found a Michelin tire (295/60R22.5) that is 4" shorter with a higher load range that will give me a numerically higher rear axle ratio (575 revs per mile vs 503 revs per mile) and change the rpm sweet spot on this CAT engine and hopefully improve my fuel mileage. What are your thoughts?
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Old 06-09-2013, 11:45 AM   #2
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A shorter tire will give you MORE engine revs at any given speed.
You need a taller tire to reduce RPMs .
Also the lifetime fuel mileage, includes all idle time and user driving habits, the two biggest factors in fuel mileage.
If the owner consistently drives at speeds in excess of 60/65 MPH, and idles the engine for long periods, to warm up the engine or use the compressor to air up the tires. This contributes to poor lifetime mileage.
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Old 06-09-2013, 12:02 PM   #3
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Quote:
Originally Posted by slemnah View Post
I am considering purchasing a 2005 Safari Panther with C-13 525hp with 295/80R22.5 tires which need replacing. The Alladin system shows that it is getting 5.5mpg over the life of the vehicle. ( )It has a 4.30 rear axle ratio and I believe that due to the gear ratio the motorhome runs in the wrong RPM at highway speed causing this terrible fuel mileage. The tires need replacing before I purchase the vehicle and I found a Michelin tire (295/60R22.5) that is 4" shorter with a higher load range that will give me a numerically higher rear axle ratio (575 revs per mile vs 503 revs per mile) and change the rpm sweet spot on this CAT engine and hopefully improve my fuel mileage. What are your thoughts?
I'm skeptical of trying to engineer the hp/torque curve using tire diameter. For one thing, this 60 profile is designed for 9" wheels and the Safari has 8.25" wheels. You can put these tires on 8.25" wheels but it derates the load capacity to less than you need. The 4.30 final drive ratio should give you an rpm of between 1400-1500 at speeds of 62-65 mph. I don't think you will impact mpg in any meaningful way by trying to adjust that rpm up by an amount that this tire change would affect..

Two things will help fuel economy. Conservative driving and slowing down.
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Old 06-09-2013, 12:23 PM   #4
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I'll get in and correct myself , before someone jumps all over me.
Never trust anything to memory.
Look for the PDF file from Cat. " Understanding Coach / RV Performance "
I have it in print but I think the PDF , went south with an old computer .
3 biggest factors in fuel economy , RV.
Driver, best driver to worst a 20% difference.
Route, interstate to congested surface roads, 20 % difference.
Vehicle speed, 60 mph Vs 70 mph, 12 % difference.
Idle time is listed as a factor, 20 % idle to total run time vs 10 % , but only rated at a 1.5 % difference.
My own coach lifetime MPG shows as 6.8, yet on highway regularly gets 9+.
The PDF file used to be available on the Cat home page, but disappeared when Cat went out of the on highway engine business.
Maybe someone in the forums still has it and can get it for you.
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Old 06-09-2013, 12:33 PM   #5
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I agree with Skip. A shorter tire will increase RPM at the same speed. Also the recorded fuel mileage will be determined by how it was used. See if the seller will let you take it far a test drive to determine the mpg on that drive. That is if you are ready to do the deal and the mpg is your only concern.
We have a 2005 Safari Gazelle with the Cat C-9 400 HP and are very happy with the coach.
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Old 06-09-2013, 06:54 PM   #6
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I have a copy of the PDF from Cat. I can email it to you if you want. Iras reading about the low fuel mileage with the cat engines and it was stated that the 4:30 rear axle ratio doesn't match well with the lower peak torque rpm of the engine. Changing tire size to a shorter tire will give me a numerically higher gear ratio.
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Old 06-09-2013, 07:45 PM   #7
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I found an 06 Beaver Patriot Thunder 39' with 15000 miles and the 525 Cat. It is the sister coach to a Dynasty that I have been searching for. It was loaded, but that 525 Cat worried me. Even the dealer said it would get terrible mileage. Now if it had the Cummins ISM in it, I would be the new owner. Most think you're rich when you buy these coaches, but 6-7 mpg would be brutal.
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Old 06-12-2013, 06:14 PM   #8
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We avgerage 6.5-7MPG with our CAT 525, towing a Jeep wrangler and cruising at 60-65MPH.
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Old 06-13-2013, 01:40 PM   #9
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I looked at a Country Coach Lexa with a Cat C15 last year. The onboard system showed 4.9mpg average for it. I discussed this with a Cat representative and he said the Allison transmission is not optimum for these large engines. The dual torque converters require a large amount of power just to turn over and these engines really benefit from 12 or more gears. He also said driver technique is a large factor.

I agree with Skip. I think you need a taller tire, not shorter. The C13 makes huge off idle torque (usually called clutch release torque). Take advantage of this torque and reduce the RPM.
Having said that, I wouldn't do anything crazy. Maybe an increase to a 305 or 315/80 tire. The rest of your savings will be in driving technique.

Another possibility is to talk to the local CAT dealer and ask if they can reflash the ECM for more mileage.
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