T-Nut Power

Gaining horsepower by utilizing parts that reduce resistance has never been more important. In all actuality, these resistance reductions don’t really gain horsepower – they just use up less of the available power that you have. Efficiency is vital and anything you can do to add to your coast down horsepower will make for faster lap times. With any race car, any improvement in coast down horsepower is going to be a benefit. The benefit is magnified if you have a motor rule that limits horsepower or run a crate motor.

Just what is “coast down horsepower?” If you have a safe hill nearby you can measure your coast down losses by letting your car roll down the same hill with the engine off. Literally – you just mark the starting point and let the car coast down a safe hill and see how far it rolls until the gravitational energy of the hill is expended – you then mark your end point. Your car will coast until gravity slows your car to a stop. You might have trouble finding a safe hill, but if you do you can get a bench mark and return to the hill to measure your coast down gain – you can track the extra roll in feet every time you find a resistance reduction. Aerodynamic savings and mechanical rolling resistance gains can come from a variety of creative sources.

The Billet 5 X 5 Hub is shown with the rotor flange and the T-Nuts (Gold) installed to "float" the rotor. The T-Nuts fit solidly in channels for firm braking, but can move slightly left and right adapting to changes that occur due to heat expansion.

Anytime you have found a reduction in resistance – you can go to your favorite safe (safety is first, second and last) hill and let the car roll. If you have recorded your start and stop points you can visually see if you have found resistance savings that allow the car to roll further down the same hill keeping variables as close as possible. Gravity and the same starting line is all you need. Make sure you use the same tire widths and air pressure. Even stagger needs to be maintained to keep your coast down measurements relative.

This rotor flange and cast hub can be bolted solidly or T-Nuts can be added at anytime as the rotor flange accepts both direct mounting of a floating set up. 

 A great way to make your car coast further is to use a floating rotor set up. Floating your rotor with T-Nuts gains 6 to 8 coast down horsepower. T-Nuts reduce resistance and improve braking force. T-Nuts promote even pad wear and make your brake system more efficient. Even wear and rotor that adapts to movement and creates better pad contact under braking. The same action frees up the rotor allowing the car to roll freely with less drag between the rotor and the pads.

T-Nuts allow for side to side movement of the rotor to reduce pad drag and reduce heat transfer from the rotor into your shocks. T-Nuts fit solidly in rectangular channels controlling rotational force for rock solid braking. The Left to Right movement of the T-Nuts compensates for heat expansion and negates the effect of slight caliper misalignment. 

 Floating allows the rotors to move laterally, but maintains solid stopping power in rotation. The T-Nuts fit in tight tolerance channels providing a solid connection to apply stopping force from the caliper, through the rotor and ultimately to the tire contact patch. The same T-Nuts allow the rotor to move slightly left and/or right. The movement reduces drag friction on the pads. The floating action cancels out any slight misalignment in the caliper mounting and washes out friction from rotor warping to some degree. The T-Nuts allow the rotor to run true through the center of the pads in a parallel fashion.

As an added benefit, the aluminum rotor flange dissipates heat allowing your braking system to run cooler. The T-Nuts are floating so the indirect contact with the rotor flange transfers less heat from the caliper and insulates that same heat from transferring into the hub. Reduced heat transfer helps your parts to perform and last longer.

This rotor flange can be bolted solidly or can be used with T-Nuts for a floating rotor set up. The bolt on rotor flange helps to dissipate brake heat. Used in conjunction with T-Nuts, heat transfer created at the rotor is reduced due to the T-Nuts "floating" in the rotor flange which interrupts the heat path for superior performance.

NASCAR teams often use the “coast down” hill test and let gravity be the constant that allows for solid repeat testing. Cup teams also use chassis dyno’s so they can measure the horsepower that actually makes it to the ground. My sources tell me that they have witnessed floating rotors add 6 to 8 horsepower on the chassis dyno as compared to running solid rotors.  Making 6 horsepower or so due to brake efficiently is a nice gain and you get the added benefit of parts that last longer due to lower operating temperatures.  

The HP gain is due to the floating rotors finding center through out the heat expansion range so rotor rubbing on the pads when your foot is off the pedal results in less friction. The T-nut set up and rotor flange allows for a bit of movement that absorbs rotor warping and isolates the rotor from the hub resulting in less brake pad drag. You get the horsepower gain and the brakes run cooler due to less pad and rotor contact. Drivers report smoother braking with reduced pulsing adding to the efficiency of the braking system.

Additional coast down gain can be found by adding low friction hub seals. Low friction seals pick up a few more horsepower. The low friction seals do come at a higher cost, but if you use hubs with a seal retainer system you can re-use those expensive seals again and again. Standard hubs require seals to be a onetime use item so low friction seals need to be considered alongside the budget available to your team.

Low Friction Seals reduce rolling resistance, but can cost about 4 times as much as standard seals. The low friction seals increase Coast Down Horse Power and is a good idea if you budget can afford the added expense. Using hubs with a Seal Retainer System allows you to re-use expensive seals over and over again helping to offset the added expense. 

Coast down horsepower is a phrase that should be ingrained in the minds of race teams. Any idea that makes your car coast downhill with less effort should be considered. T-Nuts are a mechanical example, but low friction bearing seals and hub friction are other areas of great gain. Aerodynamic changes can result in benefits as well.

Several past tech articles that can be found in the JOES Knowledge Center touch on other areas where rolling resistance can be reduced via mechanical or aerodynamic improvements. The goal is to keep your team thinking of every advantage to get efficient application available energy resulting in increased speed. More speed involves pushing on ingenuity. Ingenuity builds exponential momentum that will push new ideas down the hill of continuous improvement.

Go Forward – Move Ahead

Jeff Butcher

01/29/13