Trail Braking on the Street

Early on in my conscious riding development, I was of the mindset that you don’t use the brakes while turning in. As I started working on my track riding a few years ago, I started implementing a portion of my track riding technique into my street riding, and that included trail braking. Dave from CanyonChasers does a great video on it. While continuing my path toward ‘faster/safer,’ I’ve tried to find more ways to quantify what is happening and develop my feel for it. This is one huge element of my learning path of getting into and out of corners quickly. I might add that since implementing trail braking on the street there have been two very noticeable outcomes: 1.) my fuel mileage has gone to hell and I use front tires and brake pads at a much faster rate, 2.) I almost NEVER have pucker moments, even if I find a dirty stretch mid-corner, or a critter on the side of the road, or if a car is over the double yellow.

I’m fortunate to have several great roads only a few minutes from my home in Northern California. I know the roads well and frequent them at least a couple of times a week so there are seldom surprises. There’s one that’s a feeder for all the others and it’s a few miles of perfect pavement and I know all the nuances well so I’m comfortable riding it with enthusiasm.

In working on my trail braking, this is a great stretch for me. One of my street bikes is a BMW R1250 GS with an IMU and cornering ABS. I’m becoming much more conscious of how this bike turns once I chop the throttle and go to the brakes. Additionally, BMW has an app that records technical details including speed, lean angle, ABS, TC intervention, throttle position, and lateral and longitudinal G-force. After a nice traffic-free run up this ribbon of road, and with perfect weather, I checked in on the app and was very surprised to see a high number of ABS activations in this twisty bit I know so well. Now mind you, I do know what ABS intervention feels like but I never felt it during this stretch so I’m treating this as a great learning opportunity as this was most likely the cornering ABS doing its thing. It’s also worth noting that considering grip was good and that I’m getting ABS kicking in this much, I don’t think I want to push it any further. IMO, this is a learning experience to take advantage of technology and data review to improve my riding and my ‘feel’ for things going on that I might otherwise be oblivious to.

There’s a whole bunch of ABS engagement in this stretch. It’s all 2nd and 3rd gear stuff and I’m actively trail braking into the corners. Screenshot from the BMW Connected app.

To further back up my trail braking with this bike, I am now using front tires at nearly twice the rate of rear tires. I’m getting about 2,500-3,000 miles out of a Pirelli Scorpion Trail II front and over 4,000 miles out of the rears. I’ve tried other 80/20 and 90/10 tires and am seeing similar mileage out of them.

My last front tire on the GS shortly before replacement

For my next ride out on this stretch, I’ll try to remember to bring my AiM Solo 2 and record the ride, not for a ‘lap time’ but so that I can review the accelerometer data to get a better sense of what kind of G-force I’m experiencing in trail braking when the cornering ABS intervenes. On a race track with proper race tires, ~0.85G of trail braking G-force is the approximate theoretical maximum for most high-grade riders/racers so it will be interesting to see what kind of trail braking numbers a heavy ADV bike on street-oriented ADV tires can generate. With that data, I can then compare and adjust to the Street Triple (which is on stickier tires and is a lighter bike by more than 150lbs/68kg) and though it lacks an IMU and cornering ABS, I might be able to get a better sense of where I’m at without learning by crashing. Knowing that I’m activating cornering ABS now I know my pace is about as quick as it should be with this bike, tires, and conditions without incident, so I consider this ‘finding the limits without crashing.’

Reference: Andrew Trevitt’s section on trail braking measures

2022-03-19 Update

So I did manage to go back out with my AiM Solo 2 attached to the bike and tried to replicate the riding. In checking the BMW Connected App and importing the data from the AiM Solo 2, the amount of trail braking before the ABS registers and activates cornering ABS is less than I’d have expected, it appears to happen around 0.45 – 0.5g. Here’s a sample of the twisty bit of road where it shows in the Connected application:

GPS speed on top, braking G in the middle, trail braking (math channel) on the bottom.

Again, as mentioned before, this is with street tires (Scorpion Trail II) on a nearly 600lb bike. It might be interesting to do the same thing with the Street Triple just to see where I’m at with trail braking on that bike (lighter, stickier tires, lighter weight, more performance-oriented as a whole but no cornering ABS). Lacking cornering ABS, I’m a little apprehensive about it but interested all the same. I’ll update this page once I’ve had a chance to do the run and record the data.