Other common causes for excessive lateral run out of rotors can be over-torqued wheels, run out in wheel bearings, or just cheap quality materials. The bearings have been checked and the wheels are always (re)torqued by me, by hand,with the wheel in the air to spec every time anyone removes it.
Only time will tell how this mod will work, though initial results are promising.
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| Modified air deflectors. |
The design issue I have with the rear brakes of the Q50 are:
#1. The calipers are positioned in the upper right or upper left corner of the wheel ensuring very little airflow from the under carriage.
#2. The calipers themselves are a closed design which also reduces air flow over pads. Every other sport rotor I have seen (Brembo, AP Racing, etc.) has "see-through-caliper" pad design with pins holding the pads.
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| Enclosed caliper design - bad air flow and build-up of pad material |
The Q50 does have pins for pads, but not sure why the pads sit in the little enclosed areas - definitely limiting airflow and limiting removal of used pad material which is very evident. In six months, this is the amount of pad material that has been caked on in one rear caliper. As can be seen decent pad life.
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| The amount of pad material built up in the caliper in just 6 months. |
#3. The Hybrid Sport version of the Q50 seems to use more rear brakes due to regenerative braking. Most vehicles have front bias braking since most of the inertia goes to the front when stopping. Since a percent of front braking is taken away from the front brakes due to the regenerative system, the rears appear to do more work, hence producing more heat.
#4. The Active Trace feature uses rear brakes for stabilization during high speeds, further causing more heat in the rear.
This all seems to result in is rear rotors having more lateral run-out due to heat buildup and rear pads wearing out a lot quicker than fronts.
So I took the rear under panels that are slightly in front of the rear wheel-well. Built and painted an aluminium air defector, which I then attached to the under panel and reattached. The defector is curved like a scoop (not very apparent in the picture) towards the caliper. Spaying a can of compressed air reveled the initial desired result.
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| Aluminium air defector attached to under panel tray. |
After completing the passenger side rear. Tried a little test with a handy dandy instant laser thermometer. Initially, the highest temperature of the entire brake assembly was at ~91F, which was the ambient temperature as can be seen here.
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| Left Side before Temp - 90.7F |
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| Right Side Before Temp - 91.3F |
Ran the car for 10-15 minutes, with plenty of 60 mph to 30 mph stops and pulled into a lot to re-check the temperatures on multiple spots on the rotor and caliper to get the maximum reading.
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| Left Side (No deflector) Reached a Max 228 F |
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| Right Side (With Deflector) Reached a max of 200F |
As can be seen from the pictures the right with teh air defector was about 28F cooler for the maximum recorded temp over multiple spots (200F vs 228F). If the % difference continues then it should hopefully keep the rears in a better temperature range and possibly help with more air flow out of the caliper. Time will tell, but worth the few hours and couple of bucks of aluminium.
