Axle ratios

[Swadian]

I believe you have confused me with Mr. Wang, but indeed, we are not towing. We will talk to a professional mechanic about putting in 3.73, 3.58, or 3.21.

[eagle19952]

I believe you have confused me with Mr. Wang, but indeed, we are not towing. We will talk to a professional mechanic about putting in 3.73, 3.58, or 3.21.

define professional 

[kyle4501]

I'd like to save fuel at both 75 and 80.

Sounds mutually exclusive to me since the best way to improve fuel mileage is to reduce the power required. The relationship between speed vs required power is not linear.

If a gear change does improve fuel mileage, its gonna take a LOT of miles to save enough to pay for the change.

Just sayin . . . . .

BTW, I can roll at 80 in mine, but 65 to 70 is much easier on me physically.
YMMV

[Swadian]

define professional 

Someone who knows more about motorcoaches that you do.

[kyle4501]

Someone who knows more about motorcoaches that you do.

Good luck with that ! 

Hope you get better than my mom, when she asked if the car was fixed, the old mechanic said -- " It will be fine as long as nobody complains "


Sadly, I have found that my needs are so unique & specific that most mechanics can't relate or have different definitions for success than I do. So, I have to either fix it myself, or do without. 

[buswarrior]

This is an engineering/design issue, a professional mechanic's training is to replace broken parts.

The mess a busnut gets into at the hands of "professional mechanics" is a major reason these Boards exist.

Re-design is NOT what they were trained to do.

You need a driveline engineer and/or those belt and suspender types who shoulda been an engineer...

happy coaching!
buswarrior

[Iceni John]

I'm wondering what the stopping distance is for a bus full of people and baggage doing 80 MPH?   I think one would need rather more than the recommended 3 seconds of space behind the vehicle ahead.   I've been in buses doing 80 or more (I still distinctly remember being in an old AEC Reliance coming down a long straight grade at almost 100 MPH), and while it's a thrill it hardly inspires confidence in the MO of the operating company!   There's good reason that all the better buses in Mexico are strictly limited to 95 KMH (just under 60 MPH), and they all have TPMS and reinflation systems.   A front blowout at 80 MPH on a heavily-loaded bus would not be pretty  -  hot road surface is a significant contributor to tire failure rates.   Look what happened to the ACF Brills that used to run across Texas at 80 MPH  -  tire blowouts had very nasty consequences for them.

John

[TomC]

Axle ratios are very important to commercial vehicles that travel over 120,000mi a year. Just squeezing 1/10 of a mile per gallon more can mean an extra $700 in the pocket of the owner.
With our driving, it isn't that important. You must weigh the difference between changing the rear axle ratio, and the fuel savings.
I wanted to change the rear ratio on my truck from 3.55 to 2.7, but the cost was too much. Besides, I usually drive around 60, which with my gearing is 1690rpm. At 2100, I have a top cruise speed of just shy of 75. For bursts of speed, I can rev to 2300 for a top speed of 81, which is more than fast enough. Good Luck, TomC

[eagle19952]

i guess you missed my cryptic point there are plenty here whose advice is worthy. beyond that, taking the words and running them past the horse would serve you better.
you might should ask for a list of horses.
i'll start.
Allison.
Freightliner
MCI
Prevost

all have knowledge of what gears move what weight relative to wishful thinking.

[lostagain]

Many companies have their vehicle speed governed, to save fuel, and for safety. Two that I have worked for: Swift at 60 mph. With 40 000 tractors (now that they have merged with Knight), that is a big saving in fuel cost. And Transportation Charter Services of Orange CA, with 20 buses also out of Calgary serving western Canada, at 68 mph.

JC

[daddysgirl]

I found this old sheet from Allison.
I took a photo of the Gear ratio information, just in case it isn't totally irrelevant.

Never mind. Moment of idiocy even given this topic is not a strong suit. Apologies.

[Oonrahnjay]

I found this old sheet from Allison.  I took a photo of the Gear ratio information, just in case it isn't totally irrelevant.

Never mind. Moment of idiocy even given this topic is not a strong suit. Apologies.

      Actually ... in my (fairly worthless) opinion, this info is actually pretty valuable to have.  Not everyone will need it or use it even if they do, but I think that it needs to be out there.

     (Back to the long-time discussion of how much "forums" maybe used as reference in the future and how much , if any, we need to assure that info here is correct and useful.)

[Dreadnought]

This is an engineering/design issue, a professional mechanic's training is to replace broken parts.

The mess a busnut gets into at the hands of "professional mechanics" is a major reason these Boards exist.

Re-design is NOT what they were trained to do.

You need a driveline engineer and/or those belt and suspender types who shoulda been an engineer...

happy coaching!
buswarrior

Well said!

And people often confuse the two (especially in the UK and its infuriating).

[brmax]

Professional mechanic! kindly here retired, licensed, certified, government tested.
I worked directly under Engineers my whole career, specifically on their assigned fleets thereby myself being "the responsible one". Please dont forget the certifications required for the pay/"carrots".
When the million dollar projects shuts down, guess who is the gettr done person! And who is called. There are caculations needed and that my freinds is where engineers shine. I as the professional mechanic have to have the ability to understand the "parts" you mention yet easily rely of my talents to produce the product or machinery. Let me help you to understand my talents can move your project forward. Or you can call me in a month to ask for assistance in the same. Btdt

Please take this respectfully,
yet be clear of the understanding what a "Real professional mechanic is"
Or quit dam callin 

Im Floyd and off my soapbox

[Dreadnought]

In engineering- this is how efficient gearing is worked out:

You look at the vehicle- specifically the engine-speed-load map and see where the vehicle will 'sit' during the typical vehicles duty cycle. The slide below shows a truck with a 13 litre engine. The star on the engine- speed load map shows where it would 'sit' at 60 mph and 1100 rpm. This particular 13 litre engine is most efficient between 1000 and 1100 rpm. However 'where it sits' will change depending on cross winds and road gradients and other road loads so these need to be factored in.



For a bus the duty cycle is different compared to a HD Truck:




You will notice that the typical duty cycle for a bus is quite different to a line haul HD truck- both are still predominantly high load but the bus application is more scattered where as the line haul is focused or concentrated more along that 'central band'.

This is some calculations I did- comparing my MC5 duty-cycle-loading vs my Jaguar XJR (first pic is my bus and second is my Jag). I had to make some assumptions for frontal area and drag coefficient for the bus). I put both vehicles through the well known US FTP 75 Federal cycle.





You will notice that the XJR or almost any automotive application is relatively low load and engine speed- its running less than half its load capability. The bus, like the earlier plot is scattered all over the speed load map and predominantly high load. This is why cooling is critical on a commercial vehicle.

And finally- one needs to match the road load vehicle duty cycle to the engine characteristics.

This last plot shows an assortment of truck engine BSFC or engine fuel efficiency curves along the full load lug curve. The 8v71 is in there , against a Cummins engine, a Maxxforce 13 and a DT466 . The 8v71 more efficient point is higher up in the rev range for a HD engine. You need to rev the engine to get it to be efficient. This is predominantly due to the way the blower and scavenging is set up. It makes things complicated. I don't think the 8v92 is quite as 'peaky' as this.




I hope this helps