# Routed Track-Power Rail Height



## Sir Slotsalot (Jan 23, 2010)

Just starting to research routed track construction. Any one know what the official standard (universally accepted) power rail height is for HO routed track? More definitively, what should the distance be between the pavement and the top of the rail. Does this rail height dimension remain the same for all scales of routed track? Lastly, is there a book of "standards" available for routed track building?


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## SwamperGene (Dec 1, 2003)

A lot of builders shoot for the .013 - .015 range, which is a very acceptable height for most chassis designs. If you start going too far above or below it will require people to do major setup changes if they race on other tracks. I've seen as low as .009 and as high as .020, at those extremes people end up mangling shoes trying to get the geometry right. :freak:

It's never a given but most tracks I've raced on have been in the .011 - .015 range, this would include Bucks, Max's, 21st Century, Bowman, WizTracks, Tyco, Tomy, and others. While most brands tend to be fairly consistent, you will find deviations even on the same track. Some guys hone them for more consistency but even then temperature fluctuations can easily create variations throughout a given course. To say a track has .015 rails is usually the result of an average of a handful of measurements taken at various points, at least when I'm the guy measuring .

Brad Bowman sells a book, I've never seen it but it seems most guys consider it to be the track building bible.


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## Sir Slotsalot (Jan 23, 2010)

Thanks for the info. Know what you mean about the inconsistency. I run Tomy plastic right now and see variations in rail height from one track to the next. Either their mfg. specs are loose or QC took the day off when they made my track. Track straightness is pretty bad as well.


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## AfxToo (Aug 29, 2003)

SwamperGene is correct about rail heights for different track types. There is no standard. 

There are three main factors we care about with rails: height, cross sectional area, and material. The track builder must select these three factors when building a track. The rail material is straightforward, some metals simply have more magnetic downforce than others. The rail material establishes *how well* the magnetic lines of flux from the magnets influence the magnetic properties of the rail. The rail height and rail cross section establish *how many* magnetic lines of flux from the magnets influence the magnetic properties of the rail. Magnetic interaction is all about lines of flux, or specifically, flux density - how many lines of magnetic flux you have in a given area.

The main reason we care about rail height is because it directly affects the magnetic downforce available for the car to use. The closer the rail is to the car's magnets, the more lines of flux from the car's magnets cut the rails, thus the more downforce. In fact, the magnetic flux density from the magnets is very non-linear from a distance perspective. The flux is heavily concentrated very close to the face of the magnets and drops off exponentially with distance. In simple terms this means you want to be able to get the magnets very close to the rails. Instead of raising the rails, can't you just simply adjust the car to tune it to a desired downforce? Within the limitations of the car's chassis geometry the answer is absolutely YES. With non-adjustable magnets the primary way to make this downforce adjustment is to vary the ride height of the car with different size and compound wheels/tires. 

However, racers tend to buy a lot of different size and compound tires within a fairly narrow range of tire heights. Tire heights are selected based on experience on the tracks the racers use. Being able to tune the right amount of downforce into the car depends on having the right wheel/tire setup in your pit box. If the rails on a specific track, especially a one of a kind custom, are radically different than what the racers expect, you can run into a situation where you can't get a good setup. I have run, or tried to run, on tracks that had very high downforce rails, to the point where even with my tallest and hardest tires I could not get it to work without fear of burning up the car. You may ask, why not swap out the traction magnets? Well, when you are paying $40 for a pair of magnets you don't buy spare pairs, much less weaker pairs to use just in case you encounter a mega rail scenario. In a national race you would do whatever it takes to make it work, but for club racing, taking a pass may be better than risking a $50-$60 arm.

The other dimensional variable is rail cross section. The more cross sectional area that the rails expose to the magnets, the more lines of flux cut through the rails, and the more downforce. For example, if you use the same rail material used on a Tomy track, set the rail height around the median of what Tomy has, but have a wider rail, the downforce will be greater than the Tomy track. 

So what do you do? The safest bet is to emulate one of the well known tracks and try to get material, height, and width as close to the known entity as you can. If you are using an unusual material, say tie wire or welding wire, try to find someone with a race proven application of that material and learn from them. I'm sure there are some mathematical ways to come up with the right combination, but I don't know what they are and I suspect they would involve finite element analysis and a sophisticated modeling program. Something like a force gauge, a reverse magnet marshal of sorts, could be constructed through trial and error. Getting some solid advice from someone who has been own the same path may be your best bet, or you can pick a reference model and copy it.


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## Hornet (Dec 1, 2005)

Don't forget to factor in your paint thickness if you're going to be painting the track after laying the rail,a couple coats of paint are usually good for a coupl'a thous in rail height changes.:thumbsup:


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## Sir Slotsalot (Jan 23, 2010)

Yes, AFXToo and Hornet, I agree with you on all points. I have not decided on rail material either. I have access to round wire for free. I like the idea of a "rounded" or "eliptical" contact surface as it will be less wear on the pick up shoe. However, it will a pose a narrower contact area. Now considering what you mentioned about magnet behavior, wire is now another variable to deal with. Since its free, it won't cost or cause harm in experimenting I suppose. The bottom line is, I want to build something that works for most cars configured in the "usual" way making it a pleasant experience for guest racers.


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## AfxToo (Aug 29, 2003)

Sir, you should try to contact Kevin Shaw at Full Tilt Speedway. He specializes in custom track designs with rounded rails. These tracks have some distinct advantages. He might be able to give you some pointers to help get you headed in the right direction. Worth a try.

http://www.fulltiltspeedways.com/


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