Increasing gear ratios

[diesel_john]

The more a tire looks like a racing bicycle tire the better.

Keep in mind, a 4 speed manual in 4th is more efficient than a 5 spd OD manual in fifth given the the same total drive train ratio. (3 to 1 diff times 1 to 1 for the 4 spd and a 3.75 diff times 0.8 for the 5 spd.) i usually shift 1,3,5 with my 5 spd anyway. The old granny gear first, four speeds work great with about a 2.5 diff.

[Big Dave]

Check out http://greenseal.org/resources/repor...resistance.pdf

Especially the graph on page 4 and the tabulation on page 5.

The low rolling resistance 14 inch tire was the Bridgestone B381 185-70R14 (OD = 24.2 inches) Rolling resistance coefficient = 0.0062

The low rolling resistance 15 inch tire was the Mihcelin Arctic Alpine 235-75R15 (OD = 28.9 inches) Rolling resistance coefficient = 0.0081

The low rolling resistance 16 inch car tire was the Continental Conti Touring 205-55R16 (OD = 24.9 inches) Rolling resistance coefficient = 0.0083

The low rolling resistance 16 inch truck tire was the BF Goodrich Long trail T/A 245-75R16 (OD = 30.5 inches) Rolling resistance coefficient = 0.0092

The little Bridgestone 14 incher had a rolling resistance coefficient that is 33% lower than the BF Goodrich. The 14 incher had an OD that was 21% smaller than the BFG.

The 15 inch Michelin filled the middle range but the Conti was anomalous.

Yeah the data is five years old but you use what you’ve got. Rolling resistance coefficients are not something easily found.

I do agree that "bigger diameter = more rolling resistance" seems counter-intuitive but tires are generally considered the “voodoo” of vehicle dynamics.

Looks like Randy’s is short on Nissan stuff. You may have to try the Nissan Motorsports catalog.

[RH77]

Originally Posted by Big Dave

Check out http://greenseal.org/resources/repor...resistance.pdf

Also, if you have an online subscription to Consumer Reports, they are including rolling resistance with their reviews...

RH77

[DifferentPointofView]

I wish I had room under the ZJ for an overdrive unit. I hate to thinkof the driveline vibes I'd get with a shortened and steeper rear driveline...

You don't have overdrive??? I know mine has it cause there's an O/D off switch on the dash to the right of the steering column. and I also know that they come with it.

It says in the manual that the fourth gear is overdrive. But I have counted many, many times, and its definitely got 4 gears and fifth being overdrive. I count the shifts, and it shifts into o/d (5th) at 46, leaving it at about 1300 rpm.

[Frank Lee]

Originally Posted by Big Dave

Check out http://greenseal.org/resources/repor...resistance.pdf

Especially the graph on page 4 and the tabulation on page 5.

The low rolling resistance 14 inch tire was the Bridgestone B381 185-70R14 (OD = 24.2 inches) Rolling resistance coefficient = 0.0062

The low rolling resistance 15 inch tire was the Mihcelin Arctic Alpine 235-75R15 (OD = 28.9 inches) Rolling resistance coefficient = 0.0081

The low rolling resistance 16 inch car tire was the Continental Conti Touring 205-55R16 (OD = 24.9 inches) Rolling resistance coefficient = 0.0083

The low rolling resistance 16 inch truck tire was the BF Goodrich Long trail T/A 245-75R16 (OD = 30.5 inches) Rolling resistance coefficient = 0.0092

The little Bridgestone 14 incher had a rolling resistance coefficient that is 33% lower than the BF Goodrich. The 14 incher had an OD that was 21% smaller than the BFG.

The 15 inch Michelin filled the middle range but the Conti was anomalous.

Yeah the data is five years old but you use what you’ve got. Rolling resistance coefficients are not something easily found.

I do agree that "bigger diameter = more rolling resistance" seems counter-intuitive but tires are generally considered the “voodoo” of vehicle dynamics.

I can't read pdf from here but it's plain to see that your examples are not comparable tires that are merely different sizes. As sidewall and tread thickness goes up, r.r. goes up- these tires are plainly meant for different load ranges. Also the treads are likely to be quite different in design and depth. You are claiming that because a big heavy truck tire has higer r.r. than a light little passenger car tire, larger diameter leads to higher r.r.. You know the flaws with that and I shouldn't have had to point them out.

[tasdrouille]

I agree with Frank that for the data showed to be meaningful it would have to be the same tire model in different diameters.

Rolling resistance in a tire comes mainly from deformation as it rolls, and to a lesser extend tread design.

It is also interesting to note that broken in tires can lead up to 7% fuel economy for big rigs vs new tires according to a cummins fuel economy paper I read. I find this figure to be extremely high, but it just goes to show that tread wear have an impact on tire rolling resistance.

Also, rolling resistance as a whole is roughly 82% tires, 12% bearings and 6% brake friction, so smaller tires start with a disadvantage as they spin faster for a given speed.

I'll post the sources later as the pdf files are on my other laptop.

[extragoode]

Originally Posted by DifferentPointofView

Hmmm. What RPM range do you run at 70? If you run near 2K, then you're probably doing fine. around or over 3k? we gotta work on that.

I got out on the interstate for a couple minutes yesterday, doing 70 in a 65 I was running just a touch over 3Krpm. (3050-3100). Also, I've done some research on my transmission and I'm pretty sure the only replacement that would be better would be the 6-speed nissan introduced in 2004. It looks like it would be a bolt on replacement, but I have two problems. I'm guessing this would be extremely expensive in comparison to the others. Also, it only gives me an advantage of 5% new 6th gear over old 5th gear. That doesn't really seem like it's worth it to me. The worst thing I found out is that the standard diff for this truck in the 4x4 configuration is 4.38:1! I haven't even looked for replacement diffs, because I don't think there's any way I could rationalize it to my wife even if I could manage to convince myself. Obviously, I've never done this before, but doesn't it make sense that since I'm trying to get smaller ratios, the overall size of the gears would be smaller? So couldn't I get the gears from some taller diffs, pop covers off the diffs, and replace the gears in place without changing the whole axle? I know it seems a little lego land like, but why not? It'd be a lot cheaper, possibly even if I had to have a couple gears custom made, right?

[Duffman]

Originally Posted by DifferentPointofView

You don't have overdrive??? I know mine has it cause there's an O/D off switch on the dash to the right of the steering column. and I also know that they come with it.

It says in the manual that the fourth gear is overdrive. But I have counted many, many times, and its definitely got 4 gears and fifth being overdrive. I count the shifts, and it shifts into o/d (5th) at 46, leaving it at about 1300 rpm.

Are you sure that you are not counting the torque converter locking up as a gear. I had a friend whos parents Grand Am had a 3 spd and he swore it was 4 for the same reason.

[stovie]

Originally Posted by extragoode

I got out on the interstate for a couple minutes yesterday, doing 70 in a 65 I was running just a touch over 3Krpm. (3050-3100). Also, I've done some research on my transmission and I'm pretty sure the only replacement that would be better would be the 6-speed nissan introduced in 2004. It looks like it would be a bolt on replacement, but I have two problems. I'm guessing this would be extremely expensive in comparison to the others. Also, it only gives me an advantage of 5% new 6th gear over old 5th gear. That doesn't really seem like it's worth it to me. The worst thing I found out is that the standard diff for this truck in the 4x4 configuration is 4.38:1! I haven't even looked for replacement diffs, because I don't think there's any way I could rationalize it to my wife even if I could manage to convince myself. Obviously, I've never done this before, but doesn't it make sense that since I'm trying to get smaller ratios, the overall size of the gears would be smaller? So couldn't I get the gears from some taller diffs, pop covers off the diffs, and replace the gears in place without changing the whole axle? I know it seems a little lego land like, but why not? It'd be a lot cheaper, possibly even if I had to have a couple gears custom made, right?

the benifit to having a 6 speed over a 5 speed or a 4 is that it allows your engine to stay at a lower speed when shifting, for example my jeep has a 4 speed automatic and it stays in 3 for along time(usually over 1750 to almost 2k rpm at times) before it shifts by having a 5 speed it shifts inbetween the 3 and 4 gears so the engine can stay at a lower speed and maintain better power to wheels. on the other hand it also helps for going up hills where the tranny would downshift into a gear where you can only maintain 45mph in a 65 mph zone it allows you to maintain a higher speed by adding a gear inbetween though's 2 also allowing it to downshift sooner.

[mcrews]

big dave said......As for bigger tires, I can give you one piece of advice: If you increase tire diameter, your MPG will DECREASE. Repeat DECREASE. This seems counter-intuitive but it is borne out by empirical data reported by literally hundreds of people.

MYTH MYTH MYTH MYTH MYTH MYTH


Three things cause MPG to go down as tire diameter increases.

First is that the rotational moment of inertia increases with the square of the diameter. This means you have four bigger “flywheels” you have to spin up everytime you pull away from a stop. If you were an over-the-road trucker – a creature of the superslab – this would not be very important. They get up to speed and keep rolling at the same speed for hours on end. I daresay you don’t drive that way. You do some stop-and-go. Big wheels stick it to you at every light.

Secondly rolling resistance seems to go up with tire diameter. I am screwed with my 16 inch wheels. The highest MPG cars tend to have clown-car tiny tires. Rolling resistance matters a lot at slow speeds.

Old men have very little hair on their head.
Old men get haircuts that take all the hair off.

The highest mpg cars have clown tires.........so what? THey have little engines....ergo you can't get good mileage with a big engine?????????
So go jump off a bridge????????


is that the rotational moment of inertia increases with the square of the diameter.

I really believe that WEIGHT just might play into this equation????

Fact: 255/45/18 is a larger diameter than 245/45/18. Weight is identical. I get better mpg (documented)

You tend to be in love (and thus blinded) by this idea that 'larger tire BAD'. It just is not true. It's like saying wiskey is bad. no, TOO much wiskey is bad.