# HP to maintain speed **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [April 8, 2008, 9:26pm UTC](https://community.cartalk.com/t/hp-to-maintain-speed/12707 "2008-04-08T21:26:34Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Beadsandbeads](https://avatars.discourse-cdn.com/v4/letter/b/c57346/32.png) [@Beadsandbeads](https://community.cartalk.com/u/Beadsandbeads)\ **Post date:** [April 8, 2008, 9:26pm UTC](https://community.cartalk.com/t/hp-to-maintain-speed/12707/1 "2008-04-08T21:26:34Z")
Does anyone have an approximate figure for how much power it takes to maintain a modern sedan at cruising speed, say 65 mph? ---
**Author:** ![velocityboy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/velocityboy/32/541_2.png) [@velocityboy](https://community.cartalk.com/u/velocityboy)\ **Post date:** [April 8, 2008, 11:28pm UTC](https://community.cartalk.com/t/hp-to-maintain-speed/12707/2 "2008-04-08T23:28:12Z")
I suspect you’ll get a lot of replies philosophizing about gear ratios, tire size, weight, wind, etc… Personally, I have no clue, but a quick google search pulled up this: [http://www.insightcentral.net/community/viewtopic.php?f=4&p=66139](http://www.insightcentral.net/community/viewtopic.php?f=4&p=66139) It all seems to revolve around the Honda Insight, but there also seems to be some good math formulas concerning your question that I suspect are applicable to most any vehicle. ---
**Author:** ![researcher](https://avatars.discourse-cdn.com/v4/letter/r/edb3f5/32.png) [@researcher](https://community.cartalk.com/u/researcher)\ **Post date:** [April 8, 2008, 11:50pm UTC](https://community.cartalk.com/t/hp-to-maintain-speed/12707/3 "2008-04-08T23:50:42Z")
As I remember from some rough calculations, I figured about 40 to 60 horsepower. A lot has to do with the frontal area of the car; its shape; how high it sits above the road; and devices available to keep the air passing through the engine and under the car to a minimum. I will respond later with the formula for translating MPG into average horsepower. ---
**Author:** ![Caddyman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/caddyman/32/23_2.png) [@Caddyman](https://community.cartalk.com/u/Caddyman)\ **Post date:** [April 8, 2008, 11:54pm UTC](https://community.cartalk.com/t/hp-to-maintain-speed/12707/4 "2008-04-08T23:54:11Z")
Depending on the vehicle, 17 to 25 hp will maintain 65mph, flat and level, no wind. ---
**Author:** ![Craig58](https://avatars.discourse-cdn.com/v4/letter/c/3da27b/32.png) [@Craig58](https://community.cartalk.com/u/Craig58)\ **Post date:** [April 9, 2008, 12:03am UTC](https://community.cartalk.com/t/hp-to-maintain-speed/12707/5 "2008-04-09T00:03:44Z")
That sound about right, it takes surprisingly little power to cruise at a constant speed on level ground. I have a 240D (my wife’s car) that weighs about 3500 pounds and is about as aerodynamic as a brick; the car has a total of about 70 HP and will very easily cruise at 65 mph (at about half throttle). A newer, more aerodynamic car would require much less power. ---
**Author:** ![Beadsandbeads](https://avatars.discourse-cdn.com/v4/letter/b/c57346/32.png) [@Beadsandbeads](https://community.cartalk.com/u/Beadsandbeads)\ **Post date:** [April 9, 2008, 12:14am UTC](https://community.cartalk.com/t/hp-to-maintain-speed/12707/6 "2008-04-09T00:14:42Z")
Thanks, those are the kind of answers I was looking for. I probably did not use good search terms for Google. I was guessing 20-30 hp with no real basis beyond the throttle position. The reason I asked is because I had a short discussion with a colleague about natural gas consumption in a whole-house generator. I said that if the gas was compressed, you could store enough natural gas to power it for quite a while since CNG cars will run for quite a few miles. He tried to tell me the generator takes a lot more power to run the generator than to cruise in an auto. I differed, but I need a little more info. 16 KW gen should take less than 25 hp to run = I win. Before anyone chimes in, I know that CNG cars have a more limited range than gasoline power. I am willing to accept other criticism of my assumptions and reasoning. ---
**Author:** ![Craig58](https://avatars.discourse-cdn.com/v4/letter/c/3da27b/32.png) [@Craig58](https://community.cartalk.com/u/Craig58)\ **Post date:** [April 9, 2008, 12:22am UTC](https://community.cartalk.com/t/hp-to-maintain-speed/12707/7 "2008-04-09T00:22:53Z")
Yup, 16 kW is about 21.5 HP, considering loses it still should be less than 25 HP; you win.