clutch tuning tips

Tuning a clutch to match the engine, track and driving style consists of two fundamental changes one does to the clutch, outside of swapping the entire clutch assembly for a different type or brand.

One can change the engagement point (RPM) of the clutch and or change the characteristics (transition phase) of the engagement. Changing the RPM at which the clutch engages involves either changing the mass of the shoes or changing the stiffness of the retaining spring. On the other hand, modifying the transition phase involves changing either the material of the shoes and/or the form of the contact area with the bell.

Traditionally tuning thus involves the tedious process of removing the engine, partially or completely disassembling the clutch, modifying it, reassembly followed by testing of the results. Unfortunately their is no 'Golden-Rule' except experience that would simply the process of tuning. This is probably why so many buggy drivers are using poorly tuned clutches. in the wake of these disadvantages some of the newer clutches simplify the process. The revolutionary new (available since DEC 2003) RMV Speed II clutch even allows tuning of the clutch without removing the engine from the buggy!! Until more such clutches become available we will have to resort to the tedious way.

Changing the characteristics of engagement usually involves changing the material of the clutch shoes. Here a list of commonly used materials for clutch-shoes and their properties based on the authors experience. Please note that not all types of shoes are available for all clutch brands

Picture	Material	Characteristics
	Carbon Composite	These are the most common type of Shoes/Material used in buggy clutches. There quite a few variations in the compounds of different manufacturers. Most carbon-composite shoes exhibit a more or less linear transition phase and fairly smooth engagement. Disadvantages: wear quit quickly.
	Hardened Aluminum	Aluminum shoes have become quite popular in recent years. They characteristically have a long transition phase with low-grip followed by a fairly quick peak to full engagement. The clutch will seem to engage later but harder. Disadvantages: maintenance intensive because of burs that occur on the edges.
	Teflon with or without fiberglass reinforcement.	Teflon shoes are similar to aluminum but don't bite as hard on engagement. An excellent recommendation for circuits with a slippery surface. They are quite heat-resistant and are known to last well.
no pic	Epoxy	Epoxy shoes have a very long and smooth transition. With these shoes the clutch seems to engage later, and they provide excellent control on slippery or dusty tracks. Disadvantages: are prone to break.

Almost all clutches engage too early for most racing motors. When the clutch engages too early, the engine is not yet producing enough power and seems to bog. This leads improper tuning of the engines carburator which in return leads to overheating and dreaded flameouts. Tuning a clutch thus involves adjusting the engagement point to a higher RPM (later engagement)

There are several ways to have a clutch engage later. We can either reduce the mass of the shoes, reducing the centrifugal force with which they push outwards, or we can stiffen the retaining spring. Another way would be to change the the contact area between the shoes and the bell giving us more slippage and later engagement. That involves changing the shape of the shoe. A fourth method involves changing the shape of the retaining spring of swinging clutches, reducing the leverage of the shoe against the spring.

Picture	Method	Comment
	Drilled shoes	This method involves drilling a 2-3mm hole in the trailing edge of the shoe. it makes the shoe Lighter reducing the centrifugal force. It retains the original shape and transitional characteristics of the shoe. This method works for swinging and for sliding clutches. Disadvantages: cannot be reversed. If you drilled too much you will need to buy new shoes.
	Trimming the Shoes	Here you take a sharp knife and remove a tiny amount of the trailing edge of each shoe as shown in the red circle. We recommend to first remove only 1/2 to 1 mm at a time. This method not only reduces the mass of the shoe, it also reduces the contact patch with the bell. Disadvantages: cannot be reversed. Some people report excessive heat development and premature wear of the shoes.
	Cut Spring	only works for swinging-clutches witch scissor styled springs. Cut the spring at the marked spot. This reduces the leverage the shoe has, effectively making the spring seem harder. The method has the advantage of not changing the shape or stability of the shoe. It can be done in increments until the right tension is achieved. Disadvantages: cannot be reversed.
	Changing Springs	Some clutch manufacturers offer different strengths of spring for their clutches. Buying thicker springs causes the clutch to engage later. The nice part about it is that if you are unhappy with the result you can reverse the process. Disadvantages: it's a tedious process changing springs.