Tom F&L GoR
Enthusiast
Deceleration Rate Measurements: OEM vs. 40mm Rear Brake Calipers (Negative \"G\'s\")
Lots of folks have asked about performance measurements of the larger rear brake calipers – I finally have some. This customer car is a stock 1994 with 2-year old Michelin Pilot Sports, OEM Brembo brake pads front and rear, and about 28,000 miles on the odometer. Tests were conducted with driver and passenger on a little used, well shaded public road (so road surface temperature change is minimal) in both directions (to account for wind and slope.) Other than different rear calipers and about 2 hours time, there was no other difference with the car before and after these tests.
Because it was a public road, the measurements I paid attention to were only the deceleration rates, not how many feet between 60 MPH and stop. I didn’t want to mark the road, measure distances or be locked into exact positions. (“No, officer, I’m not going fast, I’m measuring how I slow!”) As you’ll see, using “G” forces still gives a reasonable picture.
The question of “yeah, but how hard were you trying?” can be answered looking at the sudden upward slope in any figure. At this point one of the front tires was finally locking up, slipping, resulting in a poorer vehicle deceleration rate. As the data shows, I am not very good at braking, but by being a poor example, it shows where the room for improvement lies.
This chart shows three of the cleaner runs (stops?) with the OEM brake caliper. It was reasonably easy to sustain 0.80 G’s deceleration, with good feel it looks like one could drop to 0.85 G’s, but touching 0.90 G’s braking results in a tire locking up. Since it wasn’t my car, any time a tire locked I would back way off the brake, and as a result there would be a slight upward spike due to slippage followed by a large upward spike due to release of pedal.
The second chart shows three of the cleaner (!!) events with the 40mm rear caliper installed. Yes, I ****, and now you all know, too. Deceleration of about 1.0 G’s is sustainable, around 1.1 G’s a front tire locks up.
The following chart averaged the three before and three after runs together. With all stops included, it would say the rear caliper change improves braking from 0.8 G’s to 1.0 G’s, with better results possible with a different driver. Certainly stickier tires will also improve the results.
All runs were with the proportioning valve still in place, as per customer request. Most runs I did not come to a complete stop. Feel free to dispute the absolute level of the results, you can tell me that it should have been 0.7 for OEM brakes and 0.9 for the 40mm rears, results will vary with tires, brake pads, and road surface, etc. Bigger images are in my picture gallery (sorry the axis labels turned out so small.) But as far as documenting relative performance, it’s an obvious, measurable, noticeable difference in braking. If you’re near Chuck Tator’s let me know and perhaps we can suction cup this accelerometer to your windshield and try it again.
Questions, comments, or better explanations, please let me know.
Lots of folks have asked about performance measurements of the larger rear brake calipers – I finally have some. This customer car is a stock 1994 with 2-year old Michelin Pilot Sports, OEM Brembo brake pads front and rear, and about 28,000 miles on the odometer. Tests were conducted with driver and passenger on a little used, well shaded public road (so road surface temperature change is minimal) in both directions (to account for wind and slope.) Other than different rear calipers and about 2 hours time, there was no other difference with the car before and after these tests.
Because it was a public road, the measurements I paid attention to were only the deceleration rates, not how many feet between 60 MPH and stop. I didn’t want to mark the road, measure distances or be locked into exact positions. (“No, officer, I’m not going fast, I’m measuring how I slow!”) As you’ll see, using “G” forces still gives a reasonable picture.
The question of “yeah, but how hard were you trying?” can be answered looking at the sudden upward slope in any figure. At this point one of the front tires was finally locking up, slipping, resulting in a poorer vehicle deceleration rate. As the data shows, I am not very good at braking, but by being a poor example, it shows where the room for improvement lies.
This chart shows three of the cleaner runs (stops?) with the OEM brake caliper. It was reasonably easy to sustain 0.80 G’s deceleration, with good feel it looks like one could drop to 0.85 G’s, but touching 0.90 G’s braking results in a tire locking up. Since it wasn’t my car, any time a tire locked I would back way off the brake, and as a result there would be a slight upward spike due to slippage followed by a large upward spike due to release of pedal.
The second chart shows three of the cleaner (!!) events with the 40mm rear caliper installed. Yes, I ****, and now you all know, too. Deceleration of about 1.0 G’s is sustainable, around 1.1 G’s a front tire locks up.
The following chart averaged the three before and three after runs together. With all stops included, it would say the rear caliper change improves braking from 0.8 G’s to 1.0 G’s, with better results possible with a different driver. Certainly stickier tires will also improve the results.
All runs were with the proportioning valve still in place, as per customer request. Most runs I did not come to a complete stop. Feel free to dispute the absolute level of the results, you can tell me that it should have been 0.7 for OEM brakes and 0.9 for the 40mm rears, results will vary with tires, brake pads, and road surface, etc. Bigger images are in my picture gallery (sorry the axis labels turned out so small.) But as far as documenting relative performance, it’s an obvious, measurable, noticeable difference in braking. If you’re near Chuck Tator’s let me know and perhaps we can suction cup this accelerometer to your windshield and try it again.
Questions, comments, or better explanations, please let me know.
