Frequently Asked Questions

1. Why does the Ultimate Underdrive Pulley set have three pulleys (E36 3-series) or two pulleys (E46 3-series), while others have one, two, three, or even four?

The number of pulleys and what they replace is due to the fundamental nature of an accessory pulley set vs. a replacement crank pulley.

UUC has attempted to give you the consumer as much information as possible about what the Ultimate Underdrive Pulley set includes and why it was designed that way. We can't speak for other manufacturers, but in general, you will find that other accessory sets may underdrive the alternator in a hazardous way.

A replacement alternator pulley is not included. There is a lot of speculation about the operation of the charging system in your BMW. Let's skip straight to the facts: an alternator does not constantly produce current. Like the A/C compressor, it cycles on and off as demand goes up and down. The battery buffers it from the electrical demands of the car, and it only works enough to maintain system voltage. Underdriving the alternator would have ramifications ranging from dim lights at idle, to insufficient charging ability, and potentially as far as damage to your BMW's voltage-sensitive components. It may also cause inconveniences in the operation of your aftermarket electronic devices and ICE. Additionally, the automatic voltage regulator adjusts how much the alternator is working, effectively making an underdrive pulley for the alternator worthless. For this reason, UUC has deemed that any gains made with a replacement alternator pulley will not be due to reducing its RPM.

Compared to a replacement crankshaft pulley, UUC's UUDP differs not only in philosophy, but in methodology. A smaller diameter crankshaft pulley will have the net effect of underdriving ALL your engine's accessories, even the ones you might not want to turn slower than stock. However, primary benefits from this modification are due to the decreased weight of the replacement crank shaft pulley. Such a dramatic reduction in weight is possible because aftermarket crankshaft pulleys do not incorporate a tuned harmonic damper as the OE pulley did. In the case of some replacement crankshaft pulleys, there are also replacement accessory pulleys available, but their function is primarily for appearance, as opposed to performance.

2. How difficult is the Installation?

Very easy. Unlike some cars, changing the pulleys on your BMW is a bolt-on procedure. We include step-by-step instructions with every pulley set.

3. Is it the Ultimate Underdrive Pulley set compatible with a lightweight flywheel?

Absolutely! Your engine's stock harmonic damper is unaffected by the UUDP.

5. What if I need a replacement belt?

The Ultimate Underdrive Pulley set uses a new belt that is readily available from a variety of sources including the average auto parts store (universal part number 60630). Please retain the packaging on the included replacement belt, or contact UUC Motorwerks to assist you in acquiring the correct part number from your preferred belt manufacturer.

6. Does installation of the UUDP void my new car warranty?

We at UUC Motorwerks understand that your new car warranty is very important. With that in mind, it is very important for you as a new car owner to understand exactly how your car's warranty contract works, and to understand that the majority of UUC Motorwerks products have no effect on any general warranty claims.

In a nutshell, your new car does not have a single warranty; it has many warranties, covering the various systems of your car. At no time (short of a salvaged floor car) is the entire warranty voided. Each system of the car (e.g. engine, transmission, electrical, etc.) is covered separately. The warranty impact of a replacement part is limited to the specific system affected. In fact, your right to use aftermarket parts is federally protected by the Magnuson-Moss Warranty Act (15 U.S.C. 2302(C)). If a dealer claims that a specific part has voided a portion of your warranty, it is the dealer's responsibility to prove the part was at fault.

To learn more about new car warranty issues, familiarize yourself with this information provided by SEMA, the Specialty Equipment Manufacturer's Association:

Federal Warranty Law

Unfair Warranty Denial

What to do if your warranty is denied

7. Do the Ultimate Underdrive Pulleys require any special maintenance?

No. You should of course continue to check and replace the accessory belts at the manufacturers specified intervals.

8. Will my high wattage stereo system be affected by the Ultimate Underdrive Pulleys?

No. The UUDP in no way affects alternator power output.