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A close look at the F104X1 - Part #2 By: David Jun

Welcome to part 2 of the F104X1 product article. This portion focuses on adjustments/settings and everything featured in this article is TCS legal for 2012. If you haven't seen part one, it can be found here and provides an overview of the F104X1 chassis and features.

There are two things that must always be considered when setting and tuning any car; Balance and Compromise. In other words, when you make a change to one end of the car, it can affect the other end. This is why you must compromise to get balanced handling so keep this in mind when making changes and adjustments to your car.

Tires -

Although there are both foam and rubber tires available for the F104X1, this article covers rubber tires (Foam tires were covered in the original F104 Pro article here). The choices are simple with two compounds to choose from front and rear.

The hard compounds offer the longest life but will have less overall traction. However, in very high track temperatures, the hard compound may have more consistent traction. For most asphalt surfaces, the best tire combination is usually soft compounds front and rear. At the Tamiya track in Aliso Viejo, this is what is used most of the time.

Inserts are just as important as the tire compound, especially in the soft tires. Inserts control the compliance of the tire as well as the overall contact patch on the track surface. Typically, a harder insert works better in high traction conditions and soft inserts usually are better in low traction condition. However, the stiffness of the tire must be considered when making your insert choice. For example, using an excessively soft insert in the soft rear tire can reduce grip because the carcass of the tire is already very soft. This can cause the tire to collapse during cornering, resulting in less traction, overheating and more wear on the tire.

Front

54198 - Hard Front Tire: Reduce front sensitivity and/or grip, high track temperatures. Running with no insert can work well in this tire to enhance traction due to its firm construction. This can be an "in-between" setting if you don't quite need the grip of the soft tire.

51399 - Soft Front Tire: High front traction and steering, low track temperatures. Trimming the corners of the insert is a common adjustment to allow a little more flex in the tire which improves steering. This tire can also be run with no insert in some conditions for maximum grip and steering.

Rear

51400 - Hard Rear Tire: Long wear, high track temperatures. This tire usually works best with no insert due to its hard construction.

54199 - Soft Rear Tire: High grip, low track temperatures. This tire should always be used with an insert due to its very soft construction.

The front tires usually work best when "scrubbed in". This means they work best after they are run for a few laps. This eliminates the "twitchy" feel and provides more consistent lap times. The rear tires are best when new.

Chassis & Suspension -

Front

The primary areas of adjustment on the front of the F104X1 are:

*Springs -* Three spring rates are included with the F104X1 ranging from soft, medium and hard. Choosing the spring rate should be based on several things such as amount of traction, track surface and how the back of the car is handling. High traction conditions may require a stiffer spring due to more weight transfer and a low traction condition may need a softer spring to allow more weight transfer to the tires. A bumpy surface may need softer springs to better absorb the bumps where a smooth surface could benefit from a stiff spring. Because everything you change will influence other areas of the car, a stiff front spring will transfer more weight to the back of the car than and a soft spring. For the Tamiya track, I found the gold spring (medium) to work for most conditions. With the gold springs, there is naturally about 2mm of sag. This is the amount the chassis naturally settles from its own weight. This should not be eliminated with shims because it provides the suspension with up travel and reduces chatter.
*Ride height -* Ride height can be adjusted via spacers above and below the steering knuckles. Besides the overall ground clearance this adjustment makes, this also will vary the rake of the chassis. For example, having the front lower than the rear will reduce caster. It will also lower the roll center of the front of the car in relation to the rear. This can make the front of the car more responsive.
*Camber -* Camber changes on the F104 platform is performed by moving the front pivot of the suspension arms in or out. This is achieved with Aluminum Upper Suspension Mount (Standard on the F104X1). Because only the front of the arm is moving in or out, caster is reduced then adding camber and increased when decreasing camber. Take this into consideration when making changes.
*Ackerman and Toe -* Ackerman and toe are the two most sensitive adjustments on the front of the F104X1. There is a myriad of ackerman and bump steer possibilities that are dependent of the servo position, the servo horn and the ball end location on the steering knuckle. I personally like to achieve a linear feel with steering response and this was best achieved with a Kimbrough Servo Saver and spaced as illustrated in the F104 Pro article. The toe setting also effects ackerman so the adjustment will vary depending on the amount of ackeman the car has. With my ackerman setting, toe out reduced initial steering and improved stability.

Rear

The primary adjustments on the rear end of the F104X1 chassis consists of:

*Differential -* The differential setting can affect steering and corner speed. It is ideal to have as free rotation of the differential with no slipping while driving. This allows maximum acceleration as well as a consistent handling car. A differential that is too tight can cause corner speed and steering to be reduced.
*T-Bar plate -* The T-Bar plate is an adjustment that affects compliance of the rear suspension over bumps and cornering roll. The T-Bar itself can be changed with three options to choose from; Black, soft and High-traction. Included with the F104X1 is the high traction T-Bar which is the softest of the three with Black being the stiffest. The tension of the T-Bar is set with the adjustment screw. The best setting will vary depending on the amount of traction as well as the track surface. Typically, tighter will reduce rear traction/increase steering response and looser will increase rear traction/reduce steering response. A good way to set a base-line starting point is to back off the screw so there is no compression of the o-ring. Then slowly tighten the screw just until you can feel the resistance from the o-ring starting to compress. Then back off the screw half a turn. Making adjustments from here should be no more than a quarter turn at a time.
*Ride height -* Overall ride height is adjusted by changing the rear shaft spacers. Like the front, making the rear higher or lower than the front changes the rake of the chassis. This is an adjustment that can fine tune the handling balance of the car.
*Chassis posts -* The chassis post control flex. Using all 4 included posts would be the most rigid setting. The more rigid the chassis, the more responsive it will be.
*Shock and roll damper -* Included in the F104X1 are three rates of shock springs. Where the front springs control the bump compliance and roll of the car, the shock spring only controls bump compliance so tuning this area should reflect this aspect. It should also be considered that the T-Bar is also a spring. Roll damping is controlled by the Roll Damper and this is tuned with grease or oil. I prefer silicone differential fluid because it's easy to find and there are more steps in viscosity available. 10,000 weight is a good starting point. The Roll Damper should be treated just like a shock in the way it controls the rate of weight transfer. The T-Bar selection and tension setting on the o-ring acts as the spring rate for roll movement. The tighter the o-ring setting, the heavier the roll dampening should generally be.

Weight -

Most of the time, it's ideal to minimize the weight of a car for the best performance. However, there exceptions such as low traction conditions where there just isn't enough weight transfer regardless of the chassis and suspension settings. This is the type of condition the F104X1 is designed for and adding ballast can improve the traction and stability of the car. However, placement of this ballast is equally as important because you want to add as little as possible. I found that the air box is a good place to add ballast because placement here basically raises the CG (Center of gravity) of the chassis which more effectively transfers the added weight to the tires during cornering. Considerably more weight would need to be added for an equivalent effect if placed low on the chassis and this tends to negatively affect tire wear, acceleration and cornering. For the Tamiya track, adding 20 - 30 grams in the airbox is a good starting point.

The steel axle and counter weight is standard on the F104X1 and provides more rear traction than using the carbon axle without the counter weight. Having said that, I preferred the light weight carbon axle (54162) and clamp type wheel hub 84196 (54240 blue) option here because it gave the car more steering and corner speed. The weight added to the airbox provided ample stability and cornering traction so this was a good compromise.

Conclusion -

The F104X1 is a very stable and easy to drive on low grip conditions. Only a few additional Hop-Ups are necessary. Because conditions as well as personal driving preferences vary, it's important to make changes to suit you and your car. This article is an aid to explain the general setting options of the F104X1 so that you can get the most from your car. Included is my base-line set-up for the Tamiya America track.

List of additional Hop-Ups used: