2023-05-15 – Used vs Fresh Tire

I was recently at Sonoma Raceway with my Daytona 765 over two separate events. The first event (May 11, 2023) I used a fairly worn SC2 rear tire–it had ~100 A group miles at Thunderhill East from October 2022. During my riding with it I wasn’t looking for it but the amber traction control (TC) light flickered a good amount, particularly during corner exits. It wasn’t enough TC that I felt like it was impeding my acceleration but I was cognizant of it.

I returned to Sonoma 4 days later (May 15), this time with fresh tires (the rear was from late 2022 and unused and the front was a 2023 manufacture date) and was able to go faster. I certainly felt more confident but the TC light on the dash didn’t catch my attention–again, I’m not consciously looking for it but I do tend to notice it sometimes as I’m picking the bike up accelerating out of some corners.

Since I have fairly comprehensive data on the Daytona, including TC engagement, I thought it would be fun to check it out graphically. To qualify this data, this is on a 2020 Triumph Daytona 765 in the default settings in ‘Track’ mode. This mode has the least intrusive TC and ABS and the most aggressive throttle map available on the bike. The bike does not have an IMU so TC is simply looking for speed differences between the front and rear wheels.

Sonoma, same bike, lap times less than 1/10th of a second of each other. Blue is well-used SC2, Red is SC2 with ~25 miles. The vertical lines represent TC intervention.

Just to check things a little more, I added my throttle graph. I wanted to make sure nothing was too off (red T8 entrance there was traffic, otherwise the laps are quite similar for what I wanted to look at). For the 2nd day I was very consciously working on not rolling out of the throttle before braking (instead snapping it shut), which I’m pleased to see in a couple of areas.

Same data as the first image, this time adding hand throttle position. As before, the vertical lines represent TC intervention.

The run up to T2 and the run to T3 are both exceptionally bumpy if you’re using a good amount of throttle you’ll definitely trigger TC so I’m not really looking at that. Where I notice the real differences are things like the exits of turns 6, 7, and 9 and some TC engagement on red’s laps near peak speeds.

What does this demonstrate? The data indicates that TC was engaging on hard throttle exits with the worn tire (blue). Seeing how the fresh tire was showing TC engagement near peak speeds in some areas, that was most likely the wheelie control (WC) aspect of TC engagement, however the blue lap, even with similar throttle wasn’t showing it which might indicate that the tire was spinning enough that there wasn’t adequate grip to wheelie the bike but not enough slip to trigger the TC.

To drill into this to validate the theory, I can pull up suspension travel. At this particular point where red had TC engagement with minimal lean angle, I see the front wheel has very little weight on it, only 4.3mm of travel used on the front so it was barely on the ground and unloaded enough that it was spinning a little slower than the rear.

The front suspension is unloaded enough to allow some wheel speed differential, the 2nd graph in this set also shows lean angle.
In Red, I see that the rear wheel is showing a speed of 8 mph higher than the front, which is enough of a differential that it triggers the TC; lean angle is the 2nd graph here as well.

In Summary:
1.) While I did occasionally notice the TC light flickering, it appears that the fresh rear tire allowed more drive out of corners. I don’t think the rear tire was worn enough to trigger enough TC to impede acceleration but maybe a little.
2.) I was surprised to see that the fresh rear tire gripped enough that it was starting to lift the front enough to trigger the TC while upright.
3.) Probably the most significant aspect of the fresh vs used tire was my own confidence. The used tire, since it had a full day at Thunderhill East, showed a visible amount of wear on the left drive section of the tire. It was hard to not notice it. By the end of the 2nd day on that tire, the left turns felt off while on the side of the tire and I lacked confidence to hold lean angle.

So much of riding a bike quickly is about confidence, whether it’s based on subjective or objective data. I enjoy riding my Ninja 400 at a good pace on Q3+ tires, even well-worn tires. On that second Sonoma day I did a few sessions on the 400 and the front tire is very tired and worn–enough that I had some slip on maintenance throttle in T6 but it didn’t cause me to panic. I just knew I wasn’t going to try carrying more speed than what I was already. I’d try to find time in other areas (crack the throttle open slightly sooner, carry throttle longer and push my braking markers a little, etc.

For future reference if needed, blue is 2023-05-11 11:01 AM session, full lap #3, red is 2023-05-15, 10:42 AM session, full lap #5.