- Sedan Tires & Inserts -

Words: David Jun

Tire and insert choice is probably the most important aspect of an R/C car's performance, especially in competition. Whether you're a competitive racer participating in organized racing events or a casual R/C enthusiast, the more performance you get out of your tires the more fun you'll have. With all the options available in the sedan market for the consumer, it has become somewhat difficult, not to mention confusing, looking for the right insert and tire. This segment is based on my personal experiences and is a basic guide intended to help you choose the best tire and insert for your sedan.

Let's start with tires. If you race at a local track, there is probably a popular tire that everyone already uses. Usually, that tire is popular because the most competitive drivers use it and for this reason, others have assumed it's the best choice. While this is an effective way to make your decision, keep your mind open to test other tires. In my experience competing in major events (before spec tires were implemented), the tires that most of the competitors settled on, in many cases, were not the tires favored by the track locals. A lot of this is due to the fact that conditions always change (even indoor tracks), including the same day. This is because of factors such as dust or humidity but it's mostly due to changes in temperature, even as the day progresses.

Tamiya Tires: Type B2 #53482 There are many different manufacturers that produce sedan tires and each tire was designed for a general operating temperature. Most manufacturers will not label the temperature range of their tires due to the amount of variables that can effect the overall performance. Instead, most tires are categorized by an alphanumeric code or by a simple description like soft, medium or hard. Usually, the lower the alphanumeric code, the softer the compound. Cooler temperatures typically require a softer compound as hotter temperatures generally require a harder compound. However, the track surface often has characteristics that will also effect tire choice. For example, a coarse surface will put more friction on the tire; friction creates heat and the higher the temperature the harder the compound you'll need. Yes, you can overheat a 1/10th scale sedan tire, which is why different compounds are available. In other words, just because the track temperature is low doesn't always mean you need a soft compound. Unfortunately, these cases are not as black and whites as we might like, but by taking these factors into consideration, you can better choose and test various compounds. Most tires on the market are belted with a type of cloth or glass fiber. The belting reduces tire distortion especially at high speeds and during cornering. This reduces feathering or blistering of the tire surface and extends the life of the tire.

Tamiya Tires: Type B2 #53482 With a sedan tire, you need an insert, which is as important as the tire itself. Inserts are like the air pressure in a full size car tire because both are responsible for supporting the tire. Over inflating your full size car's tires will cause them to crown, decreasing the tires surface contact to the road and reducing the tires ability to absorb bumps, both resulting in reduced performance. The difference in a 1/10th scale sedan tire is, the insert can independently effect the tire profile from the amount of support. Profile of an empty tireMeaning, a soft insert can crown the tire as much as a firm insert can. The profile of the tire is an extremely important aspect of how the tire will perform and just like a full size tire, there is an ideal range. That range is typically that of the empty tire. Manufacturers profiled the tires to maximize the surface area that would contact the track surface and generally speaking, if you alter that profile too much by using a big or tall insert, you will compromise the amount of grip the tire can generate. The key is to choose an insert that fits the tire.

Tamiya Medium Inserts #53434 Like tires, inserts are also available in various compounds as well as materials. Soft, medium and hard is for the most part, the industry standard. With that in mind, you should consider the track surface conditions before selecting a compound, because in a way, the insert and tire is indirectly a part of your car's suspension. Without going into suspension, the job of an insert is to support and maintain the tires surface area to the driving surface by resisting various loads as well as bumps. For example, a soft insert used in a high grip condition is likely to collapse causing the contact area of the tire to be reduced, which will decrease grip and stability. Higher grip levels will put more load on the tire, therefore, a harder insert will usually work better. However, a rough surface with a similar level of grip may require a medium insert. Track temperature is also a major element that will effect your insert choice.

Example of air gap on an F-1 tire A general rule applies with the operating temperature; soft is for cooler temperatures and hard is for hotter temperatures. I'll use the Reedy Race and the Roar Nationals as examples. Both of these events mandated a spec tire, so the inserts were the only variable. Towards the end of practice during both events, myself as well as most of the competitors were using a medium insert during the early part of the day when the temperature was cooler and a hard insert during the rest of the day or when the temperature was higher. There are a number of reasons for this; the hard insert during cooler temperatures was too stiff and not maximizing contact between the tire surface and the track surface. It was also not allowing the tire to reach an ideal temperature. Using the medium insert during higher temperatures cause the tire to deform and overheat. Both race events exhibited extreme changes is track temperatures during the course of the day but are both good examples of how temperatures can effect insert choice.

Left: insert w/air gap Right: insert w/ no air gap Another element of tires and inserts is air gap. Air gap is the amount of space between the tire and insert. Most tires operate best with little or no air gap but there are some tires that work much better with a certain amount of air gap, like Tamiya's F-1 rubber tires. Most tires designed to operate with an air gap are belted tires because the belting resists distortion during operation. The reason for having an air gap is similar to why drag racers under inflate their tires; the tire surface area increases, especially under acceleration. The advantage is more forward grip or 'bite.' The disadvantage is less steering response. Unlike a full size car tire, sedan tires still have an insert that supports the tire. The insert can be changed to adjust for the amount of air gap, track conditions and track temperature.

Insert w/ no air gap Insert w/air gap Once you have an understanding of the effects conditions will have on your tires and inserts, you can make educated decisions that will lead you to the best choice for each condition. As you experiment with tires and inserts, you'll find that you have to compromise and the best set-up is usually the best balance. This is what makes the R/C hobby so exciting and understanding the basics will not only help you make better choices, but also speed up your tuning process. This is very advantageous during a big event where practice is limited, keeping you one step ahead of the competition.