Why is 6th gear so low (2006 Sport)

Well that is just the way it goes. My 2003 LS turns 2,800 RPM at 60 MPH. (in 6th gear) That is 400 RPM less that my '91 turned at the same speed in 5th gear You may just need to chalk it up to "Sport". :-) Oh. and you are not going to wear that engine out much faster just because of that. You will however, burn more gas over the life of the car!

Bruce Bing '03 LS

Since an engine's efficiency is highest at about its peak torque RPM, lower gearing will only take it further away from 5000 RPM and *less* efficient.

A properly designed engine isn't going to be experiencing undue wear operating at less than half its redline RPM.

So you wouldn't have to downshift for hills on the highway. If you wanted a freeway cruiser or gas miser, you bought the wrong car.

Small Engine=High RPM, Large Engine = Low RPM So a Corvette loafs along at 60 mph with a low RPM, and an MX-5 at 3000RPM or so. MX-5s are tuned for preformance, not gas mileage. (Sports car, not Econo Car, remember?) Now if you have some spare change, the rear axle ratio can be changed to 3.6 with a resulting improvement in gas mileage. And the 6th gear use will seem like the car has less power than it does now. Or perhaps a larger tire size?

highway because in 6th gear,

Then why buy a Miata? I consider 3,000 to be low revs in a Miata.

Tom

A Corvette is naturally a low-revving, lazy engine, assuming they're still using the traditional American crossplane V8. These have a huge inertial mass, although they're perfectly balanced. A Ferrari V8 will rev much higher, but that's a flatplane V8 - poorer balance, but no need for big counterweights.

because in 6th gear,

We didn't get a MX5 Sport because the ratios are so close. We find the 5 speed quite enough changes. We live near London and enjoy visiting a daughter and taking in the scenic roads and the beautiful scenery in Scotland. Snag is it is a 400 mile drive up motorways to get there and in the UK most people cruise at over 80mph. Our other car is a Mazda 3 Sport which also has low ratios. With Mazda you get the zoom zoom but pay for it in fuel and noise if you are covering long distances at speed. At least with the coupé it is a lot quieter doing the high speed bits to get to the nice top down bits. Is there still a 50mph limit in most states in the US? In the UK it is

70mph but not very strongly enforced.

Usually 75mph on the interstates but if you do cruise at 75mph you'll be blocking traffic and really irritating everyone who is going 85-

95mph.

The Invisible Man wrote in news:46160007$0$78517 $ snipped-for-privacy@reader.news.newnet.co.uk:

Depends on the area/state and even time. Illinois is 65 (average speed of traffic: 75-80), Missouri is 70 (average speed of traffic: 70-75), Texas is

75 during the day and 65 at night (what's up with that??)..

Usually around cities the limit drops to 55 or 60.

-Scott

Maybe where you live. Here in the midwest it ranges from 55-70 depending on where you are.

It may be less efficent at 5000 RPM, but it would get better mileage at far lower RPM.

It may make the most power/gallon at 5000, but it is making much more power (and using more gas) than it needs to cruise on the highway.

Where would he find a 3.6 rear axle?

I'm sorry, but you can't know that for sure.

It gets the most power out of however much gasoline is being burned at

5000, hence at any other engine speed it will burn more gas for the same power.

So, provided road speed is kept constant, how is it that it could be more efficient at a lower RPM. There is one factor, but do you understand what it is?

Everything I've ever read about getting high mileage from gasoline IC engines says that. You want to run at as low an RPM as possible (which if you've an appropriately sized engine means you're runing at very nearly wide-open throttle).

because in 6th gear,

Because it's not an economy gear like on some cars, it's simply a little longer than the fifth in order to maximize acceleration.

Kind regards Bruno

PS. I did 300 miles in my NB at around 100 mph average today and at times I did wonder if I should have worn ear plugs. A high speed trip on the free way is not what the MX-5 does best :-)

I think that the FACT that cars get better MPG at lower PRM is pretty well established. Sorry if reality conflicts with your understanding of theory.

Perhaps, but the point is it doesn't need 5000 RPM worth of power.

Sorry, but I'm not going to play 20 questions. If you want to back up your theory that cars get the best MPG at 5000 RPM, then do it.

Cars get better MPG at lower *speeds* which unsurprisingly correspond precisely with lower RPM.

Sorry, but at any reasonable RPM it doesn't need as much power at highway speeds as can be made at that RPM.

So you admit you don't understand the subject...

Fine with me.

Here's a thought experiment:

Forget about "highway speeds" - let's take any vehicle traveling at 30 mph. Let's say we can go 30 mph in first gear at 6000 rpm, 2nd gear at 4000 rpm,

3rd gear at 2000 rpm. Which gear would you think would get you the better gas mileage? If Mazda made 6th gear a higher ratio, it would likely get better gas mileage, but would lose torque. It would then essentially be an overdrive. But because they want to keep the ratios close to each other to improve torque in higher gears for a sportier feel, they set the 6th gear ratio lower than an overdrive. However, I do not feel that the slight increase in RPM will have any effect ont engine wear. If it is running within its optimum rpm/torque range, it would likely minimize engine wear.

In my 2001 LS, the six speed is the same way. I feel it would get better mileage if 6th was more like an overdrive, but I still average 30 mpg in daily driving and don't have to downshift on hills or headwinds like you do with overdrive. If I had my way, I would have gotten a 5 speed - I just don't see the need for a 6 speed in a car this light.

Either change the ring and pinion, or get an Australian model differential.