I am looking at economy cars in the compact and midsize classes and am seeing different horsepower ratings
Cars like Scion xa, Honda Fit, Toyota Yaris are around 105-115 hp
Toyota Corolla, Toyota Matrix, Honda Civic around 125-140 hp
Toyota Camry, Honda Accord 160-180 hp
some of these weigh more
is there a standard formula for horse power to curb weight a car should have?
I’m not interested in drag racing or bragging rights but also want to be able to climb San Francisco’s hills and accelerate onto expressways.
It’s not all horsepower and weight ratios. The torque and powerband should be considered since this is what will give you the pulling power.
I won’t go into a dissertation on that but a net search explaining it should be very easy to find.
Cant think of any small cars offered that I would considered underpowered.
All cars for sale in the US have adequate power. If you like shifting gears you can quickly merge onto freeways and race up Lombard St. in SF with even the smallest compact. By comparison, the original beetle imported into the US had 24 HP and a top speed of 68mph! The beetle weighed a little less than the smallest Toypota Yaris. Provided you don’t want to pull a trailer, all small cars have enough power and torque for normal US driving.
Are you concerned about the price?
First consider what size class meets your needs. You listed subcompacts, compacts and midsize cars. Do you need a car that can seat 5 people? Are your cargo needs such that you need a larger car? Is the ability to fit into a small parking spot on SF streets near the top of your list? Give us a bit more information about what you want, and maybe we can help you organize your list so that you can make an informed decision. If it were me, I’d buy the 4-cyl. Accord from your list. But that’s me. You are the one buying the car and we need to meet your needs.
Docnick is exactly right. They don’t sell anything in this country that’s underpowered by world or historic standards. Most full-size cars in the 60’s had horsepower ratings in the range of what many economy cars have these days.
Of course, horsepower isn’t really the best measurement for how a car is actually going to drive. In my opinion torque is more important, which along with good gearing can make a pretty low-horsepower car drive just fine. Horsepower became the popular measure simply because the term appeals to marketing departments.
So the power is alright. Get the one without the large roof pillars that block your forward view. The Yaris kind of blocks your view. The thing about San Francisco is that you don’t want to hit anything or anybody. Your insurance will be high enough there. If you don’t absolutely need a car, don’t get one.
Horsepower costs money. How fast do you want to go? Horsepower is what gives you top speed. Torque is what pulls you up a hill or produces the initial acceleration.
Divide the curb weight by the advertised horsepower. 10 to 12 pounds per horsepower produces a VERY fast, expensive, burns lots of gas car. 13 to 18 produces an fairly quick vehicle. 20 to 25, this is econo-car range, acceptable but on the slow side. Good mileage however. Over 25 pounds per horsepower and you might be wishing for a little more…But you will get outstanding fuel mileage…
My 4000 pound Lincoln has about 280 HP/285 ft. lbs. of torque and it can be felt bogging on steep hills so why would anyone think a small displacement, square or oversquare 4- banger with a narrow power band is not going to fall off on a 7 or 8% grade.
Do the math on that weight to HP ratio and keep the torque part of things in mind.
I drove an overloaded Hyundai Accent with a 1.5L 90hp I-4 across Canada, including the Rockies and west coast mountains. It made it to the Pacific and back with no problem. Unless you’re planning on hauling boats around or racing, the power really isn’t that important - unless you think it is. But in any case, every car made today for sale in North America has enough power.
This brings up a good point. It really depends on the transmission and how smart it is, driver (manual) or electronics in an automatic.
I went up a 9% grade highway(I-91VT) at a high elevation(1800 ft) for New England, I never felt my Subaru WRX with 2.0L(227HP/230ft-lbs torque/3200 lbs) with a manual tranny lose any power in top gear at 75MPH and actually had plenty of acceleration left.
At the steep grade(9%) a tiny Yaris that passed me earlier fell back way behind in my mirror.
OK, I’ll over-simplify this a bit and say torque is what makes you accelerate, horsepower is what keeps you going once you are up to speed. It doesn’t take much horsepower to just keep going at 70MPH, but it takes some real torque to get up to 70 in a hurry. So, for the hills of SF and fast freeway onramps, torque is what you want. Look for the most torque per horsepower in whatever class of car you are looking for. Then test drive some to make sure you get a real feel for it.
A hybrid is just about made for SF. Electric motors have maximum torque at lower speeds, and with all those hills the regenerative braking would keep the batteries topped up pretty well. Not that I’m a hybrid fan or anything, just saying that’s a good environment for them.
OK, time to be the science geek for a moment. Torque and power are very interrelated, they are not separate things. If you multiply torque by speed (rpm) you get power. When folks talk about high torque engines, they are simply saying that the engine is capable of producing reasonable amounts of torque at relatively low rpm, which may not translate into a high peak power.
Think of it like this, if an engine could produce a constant amount of torque at any rpm, the power curve would be a straight line sloping up with rpm. If an engine produces more torque at low rpm (i.e., a diesel) the power curve will level off at a fairly low rpm. If an engine produces maximum torque at a higher rpm, the power curve will have a relatively “sharp” peak at a high rpm (i.e., a narrow power band).
It’s really meaningless to talk about torque and power as two different things, they are just two different measurements of the same parameters.
I agree that they’re interrelated. The example cited by Andrew about the Yaris is a good example of a narrow power band and low torque numbers. The spec on the Yaris is 103 ft. lbs. at 4200 RPM so there’s not going to be a lot of grunt with that one at all. One can imagine what the torque number is at say at 2 or 3000 RPM since many people are not going to normally driving in the 4200 or above RPM range.
I’ve got some dyno sheets around here somewhere for my modified Merkur and those are pretty neat. It hits maximum torque at 1800 RPM, the torque line remains flat, and torque does not even start to fall off at all until about 4800 RPM. Even then it’s a gradual drop. Nice.
Push the accelerator pedal down at just about any speed and in an Energizer bunny sort of way, it just pulls and pulls and pulls without letup.
Wow. You’ve asked 5 different people and gotten 10 different answers. Impressive.
Ignore the horsepower ratings. Test drive the cars. Buy the one you like that goes up the hills in a manner that you’re happy with.
You need no other information.
Well put!
When most people talk about torque what they’re really talking about is the shape of the torque vs speed curve. If the torque were a flat line vs speed (like it essentially is with an electric motor) gear selection would be the great equalizer. But IC engines have low torque at low speeds then torque rises with speed and reaches a plateau or a narrow peak or something in between. The shape of that curve affects drivability and gear ratios can only help so much.
I agree completely, you can talk about power in terms of the shape of the torque curve, or you can talk about torque in terms of the shape of the power curve. If you give me one curve, I can draw the other without any additional test data.
The shape of that curve affects drivability and gear ratios can only help so much
Well, that got my attention. The way I read this, I have to disagree. Gearing is everything (all else being equal). As an example, a wide ratio 3sp may require a 1000rpm band between gears whereas a close ratio 6 sp might only require 500rpm. That keeps the engine in the power band the whole time. An oversimplified example but hopefully the point is clear. So I’m not sure what you meant by that. Clarify?