Improving Locomotive Traction

After seeing a real-life locomotive pull more than 100 plus cars before our eyes, it's hard not to be disappointed when a Z-scale locomotive has trouble pulling ten cars on level track. However, we Z-scalers have a lot more in common with our real-life counterparts than you might expect. Locomotive designers and train operators alike have had to come up with all sorts of ways get their engines to pull more freight. In the days of steam, it wasn't unheard of to sprinkle sand on the rails to increase the adhesion of the wheels. (Don't try this with Z!)

The biggest hurdle our little Z-scale locomotives must overcome is their light weight, although there are several ways to increase their tractive effort other than simply making them heavier. The following topics should help you improve the tractive effort of nearly any Z-scale locomotive.

In this article:

• Measuring Tractive Effort
• Using Multiple Locomotives
• Adding Weight
• Lightening the Load
• Additional Solutions

See also:

• Improving Locomotive Power Pickup
• Multi-Unit Locomotive Wiring

Feel free to write me if you have any additions or corrections to this page. Click on any photo to see more detail.

Measuring Tractive Effort

Tractive effort is the force that a locomotive is capable of exerting, though its coupler, to pull a train. The coefficient of static friction (and kinetic friction, if the wheels are spinning), the weight of the engine, the contact surface area of the driving wheels on the rails, and the power the locomotive can produce are all factors of the tractive effort. Likewise, curves, grades, and the weight and rolling resistance of the freight all increase an the tractive effort required to move a train.

Now, the most obvious test of tractive effort is to see how many cars a locomotive can pull on your layout. However, since the weight of cars, the number of wheels, the curvature and steepness of the track, and the dirt on the rails are all factors, this is not the most reliable and repeatable gauge.

An easier, less subjective test can be performed by simply hooking your engine up to a soft rubber band or very soft extension spring. It won't make any difference to the locomotive; all it "sees" is the force pulling on its coupler.

One end of the spring/rubber band should be fixed to a stationary object, like the track bumper in this photo, and the other end should be attached the locomotive's coupler (either a Marklin or Micro-Trains coupler should work). Move the engine until just before the spring/rubber band is extended; it should be applying no force to the locomotive (yet). Start by applying power very slowly - the engine will start to deflect the spring/rubber brand until the wheels begin to spin. Mark the position furthest from the stationary object the locomotive is able to move.

Once the wheels start spinning, you'll notice the locomotive bounce backwards somewhat. This is caused by the fact that the coefficient of static friction is higher than the coefficient of kinetic friction; in lay terms, there's more friction when there's no wheel slippage.

You can use this method to compare different locomotives, or even to test the effectiveness of the solutions on this page (or any others you've come up with).

Using Multiple Locomotives

If one locomotive can pull eight cars, two locomotives should be able to pull sixteen cars, right? Under ideal conditions, this actually turns out to be true. In fact, "double-headers" (two units), "triple-headers" (three units), and even more are commonly seen in real trains and model railroads alike for just that reason.

Here are some tips on getting the most from more than one locomotive:

• Having two Z-scale locomotives pull a train shouldn't cause a problem with power, but three or more can draw a lot of power, and as a result, your trains may run much slower. However, since Z-scale locomotives already move much faster (at full throttle) than they would in the real world, this may not be a problem for you.

• The closer the running characteristics of the two engines, the better. If one locomotive starts moving at a lower voltage than the other, for example, it will simply spin its wheels when the two units are coupled, as it most likely won't be able to move the train and a stalled engine, at least until the voltage is high enough to move both engines. The best way to test this is to put both locomotives on opposite sides of your layout (but on the same circuit), turn on the throttle, and see what happens. In addition to starting characteristics, this will help you determine relative speed; if one locomotive is faster, it will eventually catch up with the other. Hint: many locomotive chassis are interchangeable; if you have several units, you may want to mix and match shells until you have to matching units that run similarly.

• Just like with a single engine, there are times when your locomotive may momentarily lose electrical contact with the rails (see Improving Locomotive Power Pickup). If one engine stalls, the other engine most likely won't be able to get it moving again; the exception is when the train is moving, and its momentum will usually prevent stalling of a single unit. The solution is to wire the two (or more) locomotives together; in addition to improving their starting behavior, it will essentially eliminate any stalling either locomotive might exhibit if otherwise electrically isolated. See Making Your Own Wired Multi-Unit Locomotives for more information.

• Some Marklin locomotives, such as the 8871 ICE set or the 8832 Union Pacific F7 ABA set come with two units wired together. However, the way they're wired ends up decreasing the effectiveness of this design; see Improving Marklin Multi-Unit Wiring for a solution.

• Many Marklin steam locomotives don't have front couplers, making it impossible to place two of them in tandem. The solution is either to use two different locomotives (as long as one of them has couplers front and rear), one modern diesel locomotive behind the steamer (sometimes seen today on railfan excursions), or even adding a front coupler (such as the Micro-Trains #905) to a steam engine.

Adding Weight

There are no two ways about it - heavier locomotives can pull more cars. Given the small size of Z-scale locomotives, however, it's often very difficult to make them heavy enough.

The little motors (both the three and five-pole varieties) installed in Marklin units are easily capable of moving heavier engines. However, Marklin continues to make their engines too light; the average weight of a Marklin F7 diesel is about 0.75 oz (21 g). Some Marklin models are heavier, though - the Marklin 88861 pictured here weighs about 1.5 oz (43 g) without its tender, thanks to its cast metal shell.

At 2.25 oz (64 g), the heavier Micro-Trains F7s are designed to pull a lot of cars; their light-weight cars make things even better. The heaviest engines I've tested, though, have been the all-brass locomotives by American Z Lines; weighing in at 2.75 oz (78 g) (for the C44-9W and PA-1), they're terrific pullers.

Luckily, it may be possible to add weight to the locomotives you've already got. The biggest hurdle, though, is the limited space in our little Z-scale engines. The solution is density - the denser the material, the less space it needs to make a difference.

• Lead is an inexpensive way to add weight to your models, as is available in a variety of forms. Most hobby shops will sell lead in self-adhesive 1/4-oz (7 g) segments (as shown in the photo), typically used for model airplanes and larger scale trains; although the small segments will still be way too large for most Z-scale engines, lead is very soft, and can easily be carved with an X-acto knife. You can also get small lead shot (as small as 1mm in diameter) from a gun/ammo supply store, and fix with a little glue. Scenic Meadows Supplies (1730 Scenic Meadows Drive, Imperial, MO 63052-1564, 3l4-464-3507) makes soft lead sheets that can be shaped, cut, and glued into place; a package of three 1/64" thick sheets (2oz each) sells for about $3.50. Lastly, A-line (P.O.Box 7916, La Verne, CA 91750) makes moldable lead putty (part #13010), available in some hobby shops and sporting goods stores (about $2.50/oz). (Thanks to Greg Elmassian for suggesting lead shot, and Greg Elmassian and Terry Sutfin for suggesting lead putty.)

• Tungsten is about 1.7 times as dense as lead, which means you'll be able to fit 70% more weight in the same space (or fit the same weight in about 60% of the space). Tungsten is available as a fine powder, and when mixed with a little lightly-thinned white glue, can be fit into just about any space. Commonly used to add weight to golf clubs, tungsten powder can be purchased from some golf supply stores, such as Golfsmith (get item #9466). At about $17.00 per 8-oz (227 g) jar, it's not cheap, but a little does go a long way. (Thanks to Bill Kronenberger for suggesting tungsten powder.)

• Silly Putty, a material you probably wouldn't expect to be in this list, can actually be a pretty good choice in certain circumstances. Although it's not nearly as dense as lead, it's very easy (and safe) to work with, can be fit into any space without glue (example), won't cause an electrical short, and can be easily removed. Technically, Silly Putty is a liquid, meaning that it will (eventually) deform to fit the shape of its container. However, if used in small quantities, it seems that its adhesive strength is strong enough to hold it in place. The Silly Putty in this photo has been in place for about four months, but I certainly can't guarantee that it will work in all situations. The main reason I use Silly Putty is for measuring space for other weights; see below.
  

Note that both lead and tungsten conduct electricity (and tungsten is ignitable), so you'll want to make sure to electrically insulate any weight you add, especially if it's near the motor or circuit board.

The next step is to find space in your locomotive for the weight, and you'll find some engines to be more accommodating than others. For example, this photo shows two Marklin 8860 locomotives, one with its shell removed. Here, you can see the amount of wasted space between the top of the chassis and the ceiling of the shell, especially at the rear.

Steam engines will provide more of a challenge because of the nearly non-existent amount of free space. However, the portion of the chassis that fits inside of the boiler (in the shell) likely has some free space where a little tungsten powder can be tucked.

Before you add weight to any locomotive, try jamming some Silly Putty in there first. It won't harm your locomotive, it doesn't conduct electricity (and won't cause a short), and when you put the shell on the chassis, it will push the Silly Putty around. This way, you can determine exactly how much space you have to play with. Watch out for lights, windows, and pantograph contacts in electric locomotives; use an X-acto knife to trim away any excess.

You may wish to test any of these methods on the inside of a lowly boxcar first; you won't be risking your locomotive shell or mechanism, but it's the same plastic, and should allow you to more accurately predict the results. Note that any weights fixed with white glue can be loosened with a small amount of water and a large amount of patience.

Lightening the Load

Naturally, a locomotive can pull more cars if those cars weigh less. Cars are typically weighted carefully at the factory; too light, and they'll derail easily - too heavy, and no engine will be able to pull them. However, depending on your rolling stock and your layout, you may be able to lighten some of your cars.

Marklin 50-foot boxcars (American) and Micro-Trains 50-foot boxcars both weigh the same; about 1/3 oz (9.5 g). However, only Marklin cars have removable weights; Micro-Trains units get their weight from their metal chassis. Marklin passenger cars all have removable weights, but tank cars and gondolas (both Marklin and Micro-Trains) do not.

In this photo, you'll see that the metal weights are held to the plastic frame with two plastic "welds" (plastic pins melted against the metal). To remove the weight, simply trim the plastic welds with an X-acto knife, and pull them off - reattach by remelting the plastic with a soldering iron, or by using a small dab of glue.

The weights in PennZee hoppers are metal rods fixed to the inside of the chassis with glue. To remove them, pop out the coal loads (details here), and cut away the glue with an X-acto knife.

After removing the weights, the cars will be lightened by about 25%-40%, which means you'll be able to pull 20%-50% more of them with the same motive power. Watch them around tight curves and especially across turnouts, but in many cases, the lighter weight won't cause a problem; if it does, try placing the heavier cars closer to the front of the train. Naturally, some experimentation is encouraged.

NMRA Standards The National Model Railroad Association's recommended car weight guide is a great resource for calculating the optimal weight of most types of cars. (See also the NMRA RP-20.1 Car Weight standard.) Although they don't specifically mention Z scale (no surprise there), you can extrapolate by multiplying the recommended N scale weights by roughly 40%. (That's Z/N cubed, or (160/220)3 = 0.384) So, according to NMRA standards, a Z scale car should weigh 0.20 oz plus 0.06 oz per inch (or 5.70 g plus 0.70 g per centimeter), which is just about what most Z-scale cars weigh out of the box.

Additional Solutions

Here are some additional tips that will help you get more tractive effort out of your Z-scale locomotives:

• Grease, oil, and dirt are all slippery substances, and dirty track will mean more spinning wheels. Wheels stick to clean track better than dirty track, not to mention the fact that they'll pick up electricity better. See Cleaning Z-scale Track for details.

• Likewise, dirt on the wheels will reduce adhesion - see Cleaning Locomotive Wheels for an effective solution.

• Traction tires are sometimes used in larger scales (such as Marklin HO), but the cost of reduced power pickup is often too high for their use in Z-scale. However, if you take steps to improve the power pickup of a locomotive, either by adding electrical contacts to cars or tenders, or by wiring multiple locomotives together, you might be able to get away with it. Keep in mind, though, that tires can wear out fast, are very hard to find in the right size, and won't do that much without the weight to back it up. Schmidt Modelleisenbahn provides a service that installs traction tires on the drivers of steam locomotives and adds extra power-pickups to tenders. I've also thought of using small rubber bands (such as those used by Orthodontists), but have never tried them.

• Bullfrog Snot (yes, that's actually the name of the product) is basically green slime you "paint" onto a pair of your locomotive's driving wheels, like this. Since it's a liquid, it'll work with any size wheel, and can be easily reapplied if it runs out. Here are installation instructions (courtesy of Zscale Monster Trains), Frequently Asked Questions, and some Testimonials.

• If you're typically having trouble on steep grades, keep in mind that real-world train engineers often face the same problem. If you're still designing your layout, try to avoid any grade steeper than 2.5% (although this can be difficult in confined spaces). "Helper locomotives," inserted in the middle of a train, are not unusual in some mountain passes, although they might cause derailments with the lighter-weight Z rolling stock.

• Take a look at Tractive Effort Tests (by George Schreyer). Although it deals with a much larger scale, the principles can still be applied to Z.

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