6 axle vs 4 axle locos

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RickVS

Member
I have a couple 4 axle n scale locos that are having a difficult time getting up a grade. Would I be better served by getting a 6 axle loco? Are all 6 axles powered or just 4? Is the additional weight of the larger loco going to make a big difference? Thanks.
 

Selector

Well-Known Member
Generally, the more weight on the tires driving the locomotive means more traction. With two extra axles, each weighing about four tons, plus another traction motor on each, the six axle locomotive is going to have more traction because it will bear down on the rails with the weight of another ten tons or so....figures pulled out of my butt.
 

montanan

Whiskey Merchant
I would say no. As mentioned weight is what is important. I am in HO scale and at my club we have a two and a half percent grade as well as my home layout. I had an Atlas RS-1, DCC of course and I was lucky to get it to pull 8 or 9 cars up the grade. My home layout is DC only and my Atlas RS units can pull 14 to 16 cars up the sane grade.

DCClocomotives are at a big disadvantage because the weight inside the shell has to be reduced to allow for the electronics. I finally got an F-7 A-B-A consist and can now pull more than 50 cars up the grade because of the wider shell allowing for more weight.
 

bnsf971

Gomez Addams
Staff member
Most six axle locomotives will pull better because they have more mass. They weigh more, but that weight is spread over more axles, so the weight per wheel is less. There's just more of them. Originally, 6 axle locomotives were intended to be used on lighter rail because of the lower weight per axle.
 

DakotaLove39

Always Improvising
I have a couple 4 axle n scale locos that are having a difficult time getting up a grade. Would I be better served by getting a 6 axle loco? Are all 6 axles powered or just 4? Is the additional weight of the larger loco going to make a big difference? Thanks.
Are you running them together or separate? You might need to have more locos either way.
 

RickVS

Member
Are you running them together or separate? You might need to have more locos either way.
Right now I have two GP40 4 axle locos running together. The previous poster suggested the longer 6 axles are heavier which would mean yes to my question, however he/she also made the point that the weight per axle is less, and if there are only 4 powered axles maybe it really wouldn't help. So still not sure if I should replace one of the GP40s with an AC6000.
 

bnsf971

Gomez Addams
Staff member
Right now I have two GP40 4 axle locos running together. The previous poster suggested the longer 6 axles are heavier which would mean yes to my question, however he/she also made the point that the weight per axle is less, and if there are only 4 powered axles maybe it really wouldn't help. So still not sure if I should replace one of the GP40s with an AC6000.
An N scale AC6000CW is 6 axle drive, and is about the largest diesel currently on the rails. I'm guessing you're talking about the BLI version, and not a brass model. The only diesel that would have more mass would be either a Gas Turbine pair or a Kato E unit.
 

RickVS

Member
I'm new to this so don't have all the jargon. Not sure what BLI means or what brass refers to. I'm just looking on eBay for the largest and heaviest locos that I thought might pull more and came across the AC6000CW. Broadway Limited for instance sells a CSX (the brand I've settled on) engine for about $100-$150. I'm not really interested in DCC at this point. When you say 6 axle drive, are you saying that all 6 axles are powered? If so, then I would think with the additional weight it would pull more up a grade. If I get the AC6000CW then I would probably return one of the GP40s and I just want to make sure that I would net a gain in terms of more grade pulling power.
 

santafewillie

Well-Known Member
BLI is Broadway Limited Imports. Brass refers to a locomotive body made from brass instead a body made from plastic. 6 axle drive does mean that all six axles are powered. While I am not an N scaler, I think that an AC6000CW will weigh much more than a GP40. You would be hard pressed to squeeze much more weight into any N scale locomotive. While it's your railroad and you can do what you wish, prototypical operations would most likely not have a GP40 (introduced 1965) paired up with an AC6000CW (introduced 1995).
 

RickVS

Member
Oh, okay. I guess I could just go with two AC6000CWs. It's only money, right? :) Unfortunately I don't have $300 at the moment. The other thing I am finding is that my RR is really susceptible to start and stop operation. It seems that the tracks and wheels get dirty really quickly. I didn't realize there would be this much maintenance. Sometimes my train stutters even with things being clean. I was hoping that with two locos that if one hit a dirty patch the other loco would pull or push it a bit so it wouldn't be an issue. I'm finding however that one loco can't pull the train by itself so this doesn't work like I was hoping. That's the other reason I was thinking of going with two stronger locos so that maybe I could leave my training going slow in the background without it stopping while also not having to clean the tracks as often as I am. I'm curious how often other people clean their tracks.
 
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dave1905

Active Member
The question nobody has asked that I can see is how steep is the grade and how long of a train are you trying to run? I have operated on several N scale layouts with long grades and helices and 4 axle diesels seem to do fine with a reasonable train on the grades. It could be you have too steep of a grade to get good performance. Also if the grade is steep and you get a longer engine, that makes the transitions at the top and bottom of the grade more important, too sharp and a longer engine will uncouple or the ends will drag on the track at the bottom and the engine will high center at the top.
 

RickVS

Member
Good thoughts. The train is 18 cars long and goes up 48" of track to a height of 2". I did have an issue with the 2 axle engine not being firmly on the track at the high point of the grade, but I lowered the top piers and it fixed the problem. It's a 2.1 % grade.
 
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GeeTee

Well-Known Member
Oh, okay. I guess I could just go with two AC6000CWs. It's only money, right? :) Unfortunately I don't have $300 at the moment. The other thing I am finding is that my RR is really susceptible to start and stop operation. It seems that the tracks and wheels get dirty really quickly. I didn't realize there would be this much maintenance. Sometimes my train stutters even with things being clean. I was hoping that with two locos that if one hit a dirty patch the other loco would pull or push it a bit so it wouldn't be an issue. I'm finding however that one loco can't pull the train by itself so this doesn't work like I was hoping. That's the other reason I was thinking of going with two stronger locos so that maybe I could leave my training going slow in the background without it stopping while also not having to clean the tracks as often as I am. I'm curious how often other people clean their tracks.

The number of wheels on the model is somewhat irrelevant , draw bar pull is determined by locomotive weight and the coefficient of friction between the wheel and the rails (around .2) , the one thing you do get with 6 axle is more consistent traction , and 6 axle locomotives tend to be heavier . I have known people who were somewhat disappointed when their Blu Box SD40s didn't pull significantly than their Blu Box GP38s , and the 38s tracked better because of the shorter wheelbase. The SDs had a little more pull but their dummys were heavier so the net effect was a wash.

On the prototype ,things are a little different .Things like sand , active traction control , traction motor heat build up, weight distibution and other factors , come into play , that make 6 axle more desirable ( 4 axle are for the most part gone ).

From a modeling perspective , 4 axle is more forgiving of track issues.

Bottom line is if you want to pull more cars , you either
(a)lighten the cars
(b) use a heavier locomotive ( either purchase or add weight)
(c) reduce the grade 2% is usually about the max (2" for every 100")
or (d) all of the above.



If your having trouble with stalling you might want to start another thread , we need to know things like type of track , locomotive type ,pics help. Several issues can cause stalling.
 

KB02

Well-Known Member
Bottom line is if you want to pull more cars , you either
(a)lighten the cars
(b) use a heavier locomotive ( either purchase or add weight)
(c) reduce the grade 2% is usually about the max (2" for every 100")
or (d) all of the above.
When all is said and done, all locomotives, whether prototype or model, work on a concept of tractive effort: The greater the weight of the loco bearing down on the rails, the more weight it can pull. While I am certainly not saying to not buy a new loco (heck, if you can swing it, get two! They're fun to have! ;) ), but you might find a simple solution to your problem by simply adding weight to the locos you already have. If you lightly press your finger on top of your 4 axles and they pull just fine, the weight may be all you need.
 

RickVS

Member
Thanks. It does seem if the rails and loco wheels are pristine, my two GP40 locos can pull my train up my grade. What seems to stop things are the smallest amount of accumulating dirt. If one loco loses electrical contact, then the other loco isn't powerful enough to pull the train and the stalled loco until the stalled loco regains electrical contact, so the train just stalls. It doesn't spin it's wheels (which may indicate the need for more weight), it just doesn't run. So I thought that if I had two heavier, more powerful locos, then maybe each would be able to pull the train and the other stalled loco over the dirt and resume operation without my being involved. Ideally, I'd like this train to just very slowly crawl along my layout in the background while I do other things. Instead I'm finding that it needs a lot of hands on TLC because things get dirty so quickly.
 

GeeTee

Well-Known Member
Thanks. It does seem if the rails and loco wheels are pristine, my two GP40 locos can pull my train up my grade. What seems to stop things are the smallest amount of accumulating dirt. If one loco loses electrical contact, then the other loco isn't powerful enough to pull the train and the stalled loco until the stalled loco regains electrical contact, so the train just stalls. It doesn't spin it's wheels (which may indicate the need for more weight), it just doesn't run. So I thought that if I had two heavier, more powerful locos, then maybe each would be able to pull the train and the other stalled loco over the dirt and resume operation without my being involved. Ideally, I'd like this train to just very slowly crawl along my layout in the background while I do other things. Instead I'm finding that it needs a lot of hands on TLC because things get dirty so quickly.
Most locomotive have worm reduction drives, if it stalls the wheels are basiclly locked . Not sure but there may be more to it than just loss of electrical conductivity.
 

RickVS

Member
The problem resolves itself if I clean the wheels but it seems that I have to clean them every day. I wasn’t anticipating this much maintenance. Not an issue if the train is moving at a decent clip but my desire is for a steady really slow speed.
 




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