Horsepower and Torque

We’re thinking about getting a second car – Yay!

We’ve been looking rather longingly at the Mazda3 5-door. But when I look at the numbers, I get a little… confused.

Mazda 3 (2008 5-door)
Outlander (2003 AWD)
2983 lbs 3461 lbs
4.8 inches ground clearance 8.3 inches ground clearance
Fully independent 4-wheel suspension Fully independent 4-wheel suspension
2.3 liter engine 2.4 liter engine
156 hp @ 6500 RPM 142 hp @ 5000 RPM
150 ft/lb torque @ 4500 RPM 157 ft/lb torque @ 2500 RPM

Take a look for a moment at those numbers. Notice anything… odd? The Mazda has a slightly smaller engine… yet it develops more peak horsepower! How can this be?

And look at those torque numbers… the Outlander develops more torque at lower RPMs. Unfortunately I wasn’t able to find a graph of horsepower and torque curves, so we can’t compare them like that, but still, it makes you wonder.

We’ve taken the Mazda3 for a test drive – it’s definately a spunky little car with lots of “get up and go.” Moreso, I dare say, than my beloved Outlander. And yet… those torque numbers continue to befuddle me.

Horsepower vs. Torque

Horsepower and torque are confusing ideas – we all tend to think we understand them, but when you look at their definitions, you can’t help but feel a little confused. We often tend to think of more horsepower as good, because it makes the car faster, right? Well, horsepower is “work done over time.” Now try to work out in your head how being able to do “more work done over time” makes your car faster.

Same thing for torque – which few people even pay attention to. Torque is just rotational force – which gets really confusing when you realize that even if something is not rotating, it can still have torque! For example, when you try to turn a stuck bolt, you’re applying torque – even if the bolt isn’t turning.

Given that, you’d think that torque would be a very important number for cars – more turning force seems to imply that you could turn the wheels faster, right? Well, yes and no. You see, it’s not just raw turning force – you’ve got to consider that your car produces different amounts of torque at different engine speeds (RPM), and then you’ve got the gear ratio to consider (different for each gear your in, plus the gear ratio of your drive train). If you’re a casual car buyer, trying to figure all this out can give you a major migraine.

There’s got to be an easier, more objective way to measure things, right?

Power to Weight Ratios

Looking back on the Outlander vs. Mazda3 chart, I realized that it may just be the weight numbers that are throwing off my perceptions – the Outlander is quite a bit heavier, due in no small part to it’s (fantastic) all-wheel-drive system. So how can we compare?

A little bit of digging on the subject turns up the term “power to weight ratio.” Ahhhh, here’s what we’re looking for!

Mazda 3 Outlander
Torque/weight ratio 0.050 0.045
HP/weight ratio 0.052 0.041

Ah, now that’s a bit better. We’re still ignoring the final drive ratio (produced by the drive train, etc.), but this is much better for comparing power “at a glance.” And now we can see why the Mazda3 feels “zippier” – it’s power/weight ratio is a bit higher than the Outlander’s.

Of course, this reveals another anomaly – the Mazda’s HP/weight ratio is higher than it’s torque/weight ratio, while with the Outlander the opposite is true. But it’s not really much of an anomaly if you look at the rated towing capacity of the two cars – the Outlander is rated to pull (much) more than the Mazda.

So there you have it – the means to (somewhat) objectively compare horsepower and torque ratings between cars, so as to get a sense for their performance. It’s not the total picture, and of course you should still drive a car before you buy it, but perhaps this will help you narrow down your choices (as it sort of did with me).

Great Driving Roads

Recently I’ve found some absolutely wonderful driving roads here in NJ – in Morris and Union Counties, actually.

The first is a series of roads that winds their way through (and around) the Great Swamp National Wildlife Refuge. Unfortunately they are often clogged by cyclists, and of course there’s probably a lot of animals around (turtles, deer, that sort of thing). And the speed limit is rather low, but even still, they are very nice twisty roads – and they just re-paved them the other day, so they are quite smooth & well graded. A really nice drive, whether you go fast or slow.

The second is the roads through and around Watchung Reservation – again, some very fun and curvy roads that are just a blast to… well, blast through. Again, of course, watch out for cyclists, animals, and of course the speed limits. But most fun roads have that speed limit problem… just use your own best judgment when traversing these roads.

That’s all I have for now, but rest assured I will let you know if I find any other great driving roads (and I am always looking). If you know of any great driving roads around here, or around where you are, or even just wherever, feel free to post them in the comments.

Have fun driving!

On the Road: New York

New York drivers are much like their New Jersey neighbors, except without the strange phobia of left turns.

Actually that’s not entirely fair – as you get further away from New Jersey, New York drivers take on a style all their own.

And it’s a fast style.

Although they retain the irritating habit of slowing down for no reason, by and large you are more likely to find New York drivers doing 120% of the posted speed limit on the Interstate – if not more. They do also tend to fall into “lemming” mode and do whatever the person in front of them / around them is doing, regardless of why (which irritates me to no end), but all in all they aren’t bad drivers at all. Though I’ve never driven in New York City… but that’s really a whole different world and doesn’t count.

New York drivers are also less likely to cut you off than a driver from New Jersey, they are more likely to tailgate very, very close to you if you don’t get out of their way.

Still, as I said, not bad drivers at all (all things considered).

Next time: Connecticut!

Behind the Wheel: 2007 Suzuki Forenza

Before I even begin, let me just say I’m not really a car person anymore. I mean, they’re fine and all, but they’re just not what I would choose.

So with that out of the way, let me tell you about my recent experiences with a Suzuki Forenza. I had to rent this car to drive to Laconia, New Hampshire from New Jersey – a drive of about 6 hours (each way). So I had plenty of time to get to know the car.

First, some pros: the car’s ride is very comfortable – both the suspension and the seats themselves. I’d even say that the seats are more comfortable than in my own car, and the suspension is definitely better at soaking up bumps. At least – as long as there’s not 4 people in the car.

This leads directly into the cons: When it was just me riding, the car was nimble, maneuverable, and the suspension saved me from having a sore rear end on the highways and side-roads I traveled (this last winter in New England has not been kind to the Interstate highway system, nor to the roads in general in New Hampshire). The car turns quite nicely (as you would expect) and all in all it was a pretty quiet ride (although there was a bit of wind noise at highway speed).

BUT… when there were 4 people in the car, the suspension was seriously taxed. Bumps that I had driven over by myself and hardly noticed now thrashed the car so roughly that I was worried my passengers would hit their heads on the roof!

Of course, this is what happens when you design a suspension like that – it really can’t be helped that much, but it’s something to be aware of.

Another downside of this car is that the engine is very, very weak. Seriously. I would go to merge onto highway traffic, put the gas right down to the floor (literally) and the car would putter along at its own pace until it was happy. It wouldn’t down-shift like I expected when I stomped on the gas – and even when it did (or when I did, by manually moving the automatic shift lever), it didn’t make much difference. The car was trying very hard to stay in its “power band,” but quite honestly it just didn’t have one. Given that the engine is rated at 127 HP, I found it surprisingly sluggish for what must’ve been a very light car. I suspect that the engine and transmission were engineered more for fuel efficiency instead of power.

Speaking of which, the car did quite well on the fuel consumption scale – averaging about 33 miles per gallon at highway speeds. I was able to make the entire 350 mile trip on just under a tank of gas (about 12 gallons). So no complaints there.

The other side of the coin, however, is that the car is a bit tricky to handle on the Interstate highways. It is a light car, and it gets blown around easily from the turbulence in the wake of a big truck, and going around a bend in the highway at speed, and hitting a joint (such as from a bridge or from road work) can make the car feel like it’s just done a little jump – which is unnerving at 65 MPH!!

So in the end, a nice enough little car, and probably quite suitable if you do a lot of in-city driving, where it’s small size and lack of acceleration wouldn’t be much of a concern. But if you do any serious amount of driving on big highways, or if you need to carry more than 2 people, I’d look elsewhere. Though for such an inexpensive car, you can’t blame it. Still, I wouldn’t drive it and I’d be hesitant to recommend it to anyone else.