Archive for March, 2008

Horsepower, torque, and gears

One way to understand horsepower and torque in your rig is that horsepower is how fast you can get up a grade and torque is what gear will be needed to do it. Both engine parameters are proportional to the engine speed from near idle up to where the engine is having too much trouble thrashing its pistons and such things.

Your engine will only go so slow and only so fast and it has a speed where it is at its most efficient. Engineers design vehicles so that the most efficient engine speed is used most, such as for cruising down the road but have to consider how the vehicle gets to that speed and how it can handle road conditions such as grades. Horsepower ratings are one of those things that get a lot of people going so there are all kinds of rules and regulations and arguing. There is some difference about what an engine will actually produce and what actually gets to the road. That is because there are losses between the engine and the tire and there are other things in the car that need engine power like lights, air conditioners, and other equipment.

The fact to keep in mind is that the range in horsepower (hp) for engines used on the road is rather small. Big 18 wheelers running 40 tons down the road may have a 500 hp engine while a small car in the next lane will have 100 hp for its 1 ton. Most tow vehicles have engines in the 200 to 400 horsepower range. That big rig is probably using the engine nearer its power maximums and that shows by its 6 miles per gallon fuel use. The small car isn’t taking all that much power from its smaller engine so it might get 40 miles per gallon. The lesson is that the power of the engine itself isn’t all that important compared to other things.

Most of the RV engines idle at about 700 RPM and cruise at about 2000 RPM. They may redline somewhere near 5000 RPM but you generally don’t want to run them above 4000, if that. Matching this engine speed to road speed is what gears and and torque is all about. The gears include those in your transmission and rear differential and also tire size. These are chosen to keep your engine in the optimum RPM ranges for normal travels. The transmission allows changing gear ratios so you can match the torque on the road to engine power in order to accelerate or climb hills. The gears act like a lever that can adapt the force and distance from the engine to a force needed to move the vehicle over a distance.

If you have a big and heavy rig it is like moving a big rock with a crow bar. The fulcrum or leverage point is close to the rock. You move your end of the bar a couple of feet and only move the rock a couple of inches. This is a lot of leverage and is the same idea as deep gears in a vehicle. That is why big rigs have lots of gears. A smaller vehicle doesn’t need the leverage so a change in its engine speed will be a fairly large change in road speed and it doesn’t need all the gears.
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See also:

Figuring how tire size influences distance traveled per rotation – Tire size calculator – the 235/85r16 for an E350 van (235 mm wide and .86 times that high in a 16 inch inside diameter) have about a 31.7″diameter or 99.7 inch circumference. A 235/75 has a circumference of 93.9 inches

Tire Size Vs. Gear Ratio – A Formula – rpm = mph x gear ratio x 336 / tire diameter

Truck engine performance questions answered at the Caterpillar On Highway engine FAQ

Torque vs Horsepower

Torque and power are inescapably linked by the fact that horsepower equals torque (in ft-pounds) times RPM divided by 5250, so people who talk as if they are independent are full of it. If you have a given torque curve for an engine, you have the horsepower curve also. Knowing how these two numbers work with each other lets you can poke through some of the BS you might read.

Torque and Horsepower by Gerald Luiz at Hummer at Off-Road.com – one of a number of ‘technical’ articles that can help you understand your vehicle.

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Best rebate credit cards for gas purchasing

Bankaholic has a list of Best Gas Credit Cards. If you spend a lot on fuel and maintenance for your RV, you might want to consider this technique for reducing costs.

Gas credit cards are a great way to save energy and money at the fuel pump. Gas rebate cards usually pay 3% to 5% cashback rewards on gas, depending on the bank that issues the card. Your cash back savings are added up until you obtain about $50 credits. At that point, you can request a check from your credit card company for a rebate.

A 5% rebate on fuel means that $3.00/gallon is really costing you only $2.85. For those class A’s with 100 gallon tank paying $3.50 for diesel, that means more than $27 on a tank of fuel. — might be something to consider if you can handle a credit card properly. That means paying off the entire balance every month and using it much like a debit card.

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What are these people thinking?

Chuck is one of those guys who helps manage public lands near Bridgeport. Every winter he encounters some of the more clueless, a group that you do not want to join. Bodie is a nice place to visit but you should make that visit when the road is open. Like many remote areas, especially in the Great Basin area, you can easily get lost or stuck and without any means to communicate – even when conditions are good. Here are some of Chuck’s stories from this year:

“We dragged two guys back to HWY 395 who went around the road closure signs and made it up the snow covered road about 6 miles until they broke through the hard crust and got high centered and stuck. If we had not come by with our snowcat I imagine they would have spent a pretty cold night out on the Bodie Road cursing themselves for not calling ahead about road conditions or for ignoring the signs.

“We also gave a lift to two cross country skiers just the other day who had “dilly-dallied” around at Bodie until it had gotten pretty late and then tried to cross country ski out the 13 miles after dark with only one flashlight between them.

“I have been stranded on that road several times in the dark by myself over the years and I can well imagine what these guys were thinking.

“We pull out or rescue about 10 or 12 vehicles a year. The Sheriff’s department just pulled a guy out that was about 8 miles in, in a two wheel drive Suburban. I have no idea what these folks are thinking. They go by the road closed signs, the parking area for us that has a number of 4 wheel drive trucks parked there, sometimes a snocat parked there, and usually a big berm of snow put at the beginning of the unplowed area, then they tell you “Oh I didn’t know I couldn’t make it to Bodie”. DUH!!!!! ”

Sometimes, these circumstances creep up on you and you don’t notice until it’s too late. That is why an experienced Nevada tourist trying to find the SNU rally at Unionville might get worried – heading up the canyon when it gets narrower and narrower and the road rougher and rougher. Is that rally site still ahead or did I miss it? If I go too far, how will I be able to get back to where I can turn around or will I get stuck on a grade or in sand? These aren’t “don’t worry, be happy” circumstances.

Plan ahead, be prepared, take note of conditions, take appropriate precautions, and ask folks like Chuck first if you don’t know for sure what you might find in exploring the remote areas of the American West.

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Fulltimin-it planning – medical expense estimation

How much do I need to go full timing in my RV?

One of the issues that many seriously considering the full timing lifestyle worry about is the costs involved. The day to day living costs are the easiest to calculate as you have a good history of those for extrapolation. Health costs are one of the more difficult costs to estimate. Business Week recently reported a finding that a retired couple at age 65 needs to have $225,000 in savings to pay for “Medicare premium payments, co-payments, and deductibles, as well as out-of-pocket prescription drug expenses.”

If you amortize that over a 20 year life expectancy at 5%, it comes to nearly $1500/month for health expense for a couple. Compare that to a 80+ something retiree with $1122 withheld from social security payments and $2500 for a pension health care plan annually. That’s about $300 per month. Add $400 per month for long term care insurance and then $200 per month for prescriptions and then add in dental and some other costs for a total of about $1000 per month.And that is just for one, not a couple.

A related consideration is what you will do when fulltimin-it in your RV requires a bit more than you can handle. That is why long term care insurance is attractive. It is also why plans need to be considered for parkin-it and being able to enjoy what you can when you can.

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DST and the semi-annual to-do list

Consumer’s Reports has a good reminder in Tip of the Day: Prepare for daylight-saving time on March 9. As a twice a year occurrence, DST clock changes provide a good reminder for other things that need to be done or checked on an semi-annual basis. Some like backup battery changes in alarms are fairly common recommendations. The suggestion to check storage areas for hazardous materials is a bit less common.

Take a look at the Consumer’s Reports list and expand it for your RV springtime getting ready for checkout routine. What do you need to check to make sure your rig survived the winter and is ready for spring?

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SNU March 2008 Newsletter

Dear SNU folks

The March 2008 Newsletter has been posted

* Note: Links to photo galleries and additional information mentioned in articles in this newsletter can be found there, too.

The newsletter features include:
* March rally at Pyramid Lake
* President’s Ramblin’s
* El Charro review
* Larry’s visit to Jackson Center
* Chinese New Year Airstream Style

>>March 27 – 30 Rally at Pelican Point
Pyramid Lake will be the site for the first SNU rally of 2008. The rally will be held at Pelican Point about three miles past the town of Sutcliffe. -> BEFORE < - you get to the rally site, be sure and stop at the station near the entrance to the reservation when coming up from Reno on route 445 or at the Sutcliffe Marina near the RV park on the north side of Sutcliffe and pay your camping fees ($10 per night). We plan a good old American hamburger/hot dog/polish sausage BBQ on Saturday for lunch. Bring firewood for all day campfires. If you can't make it for the entire time come on out for a visit anytime during the weekend. > Check the Zephyrs weblog to find out what else is new on the website


SNU HQ

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