what factors affect how well a car coasts?

[dlb]

i've been driving both my all trac and my wife's '92 civic hatchback and found that the civic coasts about twice as far as my all trac. that seems really odd to me because the all trac is so much heavier, and more weight seems like it should mean more momentum once moving but i realize there must be other factors at play. i don't imagine aerodynamics can make that much of a difference at low speeds like 60 km/h (40 mph) but it's possible. dragging brakes would obv play a huge role. what 4wd vs 2wd? it seems like it could play a significant role since the momentum of the car would be partially used to rotate more heavy parts, like the intermediate and propeller shafts. just curious about this and wonder what you guys might think.

[keith]

AWD and 4WD both have much higher driveline friction than FWD. That is why they don't get the same gas mileage.

[splatterdog]

Driveline friction,tires,alignment,tailwind and plenty of others. The awd can add a lot. This can be exaggerated by tire mismatch and/or underinflation.
I've pushed most cars made in the last 20 years getting it to the bay or just positioning for the hoist. You just never know which ones will roll easy. BTW, the T4 beats most of them. Some small cars push harder than a full size truck. Some cars and trucks I just can't/won't push!

Do both cars have the same type trans? I would expect an auto would have more drag than a manual on a coast. How is the awd modulated on the alltrac? I thought it had an electronic controlled clutch. Maybe it's being overapplied? Are the tires of similar design? Some roll better than others.

Does one have a double gasket?

[dlb]

Does one have a double gasket?

too soon, SD, too soon!

nah, it's not too soon. the civic is doing fine and still raking in amazing mileage, thank heavens. i will run out and buy another if it does die. i did an oil change on our new-to-us f350 and you can bet your nuts i checked for the gasket and a clean mounting block surface. lesson learned, oh boy.

i drove my friend's manual t4 a while back and found it coasted just slightly better than my all trac but nowhere near as well as the civics. the f350 surprised me by coasting better than both the t4 and all trac but i suppose it's just so heavy that it's momentum works for it gets going.

off topic but the first tank of gas in the f350 was 7.5 mpg. that was all city and moving many loads of hay but apparently it doesn't get much better. even on the highway, they're only rated at 12 mpg. sure doesn't help me see the appeal of driving a massive truck.

[ARCHINSTL]

This is admittedly a bit anecdotal, but - back in 2010, I had occasion to drive Goldie with the rear driveshaft removed while waiting for the reman to arrive. I drove her for a little over 200 miles and decided to do a fill-up to check the MPG. It had improved by almost 3 MPG. And of course, the rear diff and axles were still turning.
Now, I didn't notice any "road difference" save an absence of the noise of the old driveshaft.
Pushing her on my gravel/rock driveway/parking area is something I try to avoid...
Tom M.

[Petros]

Consider all of the rotating parts in the rear drive train, plus the extra weight. You have the three u-joints with 4 bearing each, the rear output shaft and transfer case, the diff bearings and all of these use 90 wt gear oil in both the trans and the diff housing, and the driveshaft center bearing. EAch one by itself is not that bad, but all together it will add up. The drive train up to the main output shaft of the transfer case is rotating even when not in 4wd. Aero makes a differernce at about about 30 to 40 mph, but below it is very small.

[irowiki]

off topic but the first tank of gas in the f350 was 7.5 mpg. that was all city and moving many loads of hay but apparently it doesn't get much better. even on the highway, they're only rated at 12 mpg. sure doesn't help me see the appeal of driving a massive truck.

Yes but you couldn't be hauling the hay in a Tercel!

[Mark]

Hey! I haul hay in my Tercel...of course they're just 1/2 bales. -And only one at a time.

[Petros]

I saw a really shabby gold Tercel4wd in our local town once, I did not get a chance to say hi, or find out what part of town they were from, but they had three bales of hay on the roof, and at least two inside, perhaps three. looked remarkably stable.

Of course some people even carry their live stock in their Tercel4wd;

[danzo]

Been awhile since I've seen a camel-toed T4. Also that's the best use of a Pontiac I've seen recently.