- 20 to use a digital caliper -

A good set of calipers are a must-have for any serious hobbyist. It seems that everything is going digital these days, so why stop at servos, escs, and radios? Tools, and more specifically calipers, are where it's at. Digital calipers allow us to save time by reading big flashy LCD readouts instead of complicated analog numbers, making it possible for us to ogle the trophy girl that much longer (dial calipers will work well too, they just don't usually offer both metric and standard readouts in one tool). Here are 20 things that you can measure with your digital calipers that will make you faster while ripping up the track with your machine.

Words: Jeff Eveleigh

Issue 135 (February 2007)

Keeping the left side of your car matched to the right side of your car with regards to turnbuckle length is important. Instead of trying to eyeball the center of each ball cup when measuring with your calipers, try getting your dimensions from the base of one ball cup to the base of the other to ensure you are comparing your left to right turnbuckles much more accurately.

Measuring droop with digital calipers is as simple as propping your chassis up onto level blocks with your wheels removed and measuring the axle height from the bottom up to any flat surface such as a setup board. Unless you do some math to include the size of your rims and tires you can only use this method to ensure that the axle height on the left of your chassis is the same as on the right; however, this is an amazingly accurate way of keeping your droop levels equal from one side of your chassis to the other.

Shocks are the single most important tuning aid on your vehicle, and it is super important that they are the same length from one side of your car to the other. You can use your calipers to compare a few dimensions when working with your shocks. Measure from the base of the shock body to the base of the plastic ball cup, and also compare the overall length of the shocks to be sure they are equal in size from left to right. A quick turn or two of the lower shock ball joint should match up any discrepancies between the two shocks.

Shims are a perfect place to stop with your digital calipers. Thin shims are used in areas where proper spacing is vital to performance, such as in the diffs on a 1/8 scale buggy, truggy, or monster truck or to eliminate excess play out of axles, hingepins, or clutches. It is always useful to know the thickness of various shims so you can use the correct ones in the correct place—not to mention the valuable dimensions you can get regarding inner and outer diameters so you know you are using the correct shim for the job.

Most manufacturers color code their shock springs so they can be easily identified with regards to coil thickness, but if you are unsure of how two springs are matched, you can use your calipers to verify they are made from the same diameter of wire. It is also a wise idea to match the overall length of springs so you can run a matched pair from left to right on your car. Manufacturers try their best to package shock springs in exact pairs, but there are times when one spring can be a slightly different in length as compared to its twin brother.

Whether you are calculating rollout or simply wanting to match up tire diameters from race to race, digital calipers are the best tool to use. With tires in one hand and calipers in the other you can also determine sidewall height, tire width, or even wear rates from race to race. All of this information is vital when trying to find the perfect tire setup. It will also help you maintain consistency from race to race once you do find the ultimate package.

This one is pretty obvious, and also shows the major advantage of a digital caliper over a dial caliper—the fact that you have access to both metric and imperial dimensions. This is handy when you are unsure of the origin of the bearing you are measuring. If you're trying to match a given shaft diameter to a bearing, calipers are the perfect tool. You may need to know bearing dimensions so you can hit up the local hobby shop for some replacements.

You can jam socket wrenches, hex keys, or any other random objects into your shocks to try to measure spring preload, but nothing will be as accurate as a set of digital calipers. Assuming that your shock springs are exactly the correct length (which they should be if you're reading this article in order), you can easily set your preload from left to right and ensure your vital shock dimensions are accurate and your car is sitting flat.

Whether you are checking droop, tweak, or balance it is always beneficial to know the exact center of your chassis. Using your calipers you can measure the overall width of the front and rear of your chassis, divide the number by two, set the calipers to that number, and scribe an accurate center point into your carbon fiber, aluminum, or molded chassis to help you with many other setup issues that require a reliable chassis centerline.

This one is simple yet useful. The thickness of a sway bar is directly proportional to the stiffness of that sway bar, so use your calipers to quickly reference what diameter of sway bar you are running and what other options you have sitting in your parts box. This comes in handy when you are trying to lock your chassis to the racing surface.

The thickness of a clutch spring determines its stiffness, so being able to measure wire diameter is a very useful clutch tuning aid. Remember that a thinner clutch spring will cause your clutch to engage earlier, making your car easier to drive on low traction surfaces—but at the expense of your snappy feel. A thicker clutch spring will make your clutch engage more into the power band of your engine, giving you explosive power out of a turn to clear that huge set of doubles.

One of the main advantages to knowing your commutator diameter is to determine how much life you have left in your motor. At some point your comm becomes too small to cut any more material away. In many handout stock motor classes, a smaller comm diameter will produce faster motors—so there may be a buzz around the track on what size commutator produces the highest output. You can use your calipers to measure this. Finally, some drivers like to use break-in tools to pre-break-in their brushes, and since these break-in tools are available in different sizes, it is important to know what your commutator diameter is so you can use the correct tool diameter.

The title pretty much explains how useful digital calipers are in this situation. You won't have to wonder if you're using the correct size screw the next time your instructions ask you to bolt up your bulkhead with a 4mm x 12mm flat head screw.

Most commonly used when drilling pistons, but also useful in other drill bit dimensional instances...digital calipers will ensure you are always boring holes with the correct sized drill bit.

Not everyone owns a fancy setup system to accurately establish toe, camber, and width settings on their pillow ball car. Using the center marking you made on your chassis earlier, you can accurately match the left and right side of your chassis by measuring and comparing key points from chassis center to hubs, outside of wheels, or even the gap between your suspension arm and hub. Nothing beats a setup system, but digital calipers will definitely beat an eyeball setup any day!

Digital calipers aren't only useful when you wrap the jaws around something to get a dimension. The beam of your caliper is a reliable straight edge that you can slap against the bottom of your chassis to determine if it is still straight after front-siding the wall at the end of the straightaway.

You can get some valuable information on the wear characteristics of different brush compounds, motor spring rates, gearing, and timing settings by measuring the length of your motor brush between battery packs. Be careful not to take a chunk out of the face of your motor brush when you close the caliper jaws around them to get your numbers. The tip of the claws are sharp, and could easily damage the delicate motor brush.

The old "slap some solder through the glow plug hole and turn your engine over to squish the solder" trick is only useful if you have a good set of calipers around to measure the squished solder when you are trying to determine your head clearance. Even after you've determined your head clearance, it is useful to have digital calipers around so you can measure the thickness of the head shims you want to either add or remove from your engine.

Measuring the thickness of your brake disks will give you info about the wear patterns of your brakes. You can also use digital calipers to set the gap between your brake pads to ensure they are evenly spaced across the entire face of the brake disk.

The gap between your clutch shoe and bell on your Centax Clutch is extremely important. Setting this gap too big will offer huge amounts of bottom end power, but can cause slippage that can melt your clutch. Digital calipers allow you to set this gap with incredible accuracy. Calipers are also useful to measure the diameter of the spring coil when choosing a spring rate to install within your clutch.

As you can see, digital calipers are an asset to have on hand when wrenching on your machine. The list of uses obviously goes way beyond the 20 we just stated here, but these are the ones you'll use on a day to day basis while at the track or at your work bench to ensure your chassis is built straight and balanced, and all of the vital dimensions are in check to make you faster on the track.