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- Feb 25, 2013
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You're 100% correct! At least as far as your second sentence, that is; not so much the rest...
The ECU sees tire slippage as a function of front/rear wheel speed variance from its hard-coded tables, and that is precisely why the tire diameter causes more TC engagement, regardless of slippage. Put a small enough tire on back and the TC will engage all the time, even puttering down the road at light throttle - nothing whatsoever to do with actual tire slippage. Ducati's TC is a pretty simple system as such systems go, which is why it can't accommodate different tire sizes, etc. The guys racing Pani's have proved numerous times that you can vastly change how it works just by changing to custom sensor rings to accommodate different diameter tires. Not sure why that should be so hard to understand, as the math's pretty simple.
The reason you see your TC light on when it's set on 5 is because Ducati made it way too sensitive. One of the first things I did when I got my Pani a year ago was turn ALL the electronic aids off and ride the thing "bare" for a while, so I could understand what I was working with sans computer interference. I'd had liter bikes with no TC at all before and knew how hard you could push without it, so I was interested to see how it worked. I picked a favorite stretch of mountain road to test on and rode it back and forth for a good while one afternoon, just to test different TC settings. Started with it on 7, which was absurdly oversensitive for dry roads, and finally got down to 3 before I could push it anywhere near as hard as I was used to (with no TC on an '08 Fireblade) and not have the system slowing the bike down way too much. Remember, any time the light is on it is slowing the bike down, for better or worse. Kept going all the way to zero, and ended up settling on using 3 for sport mode and none in race mode. I later migrated back to using 1 or 2 in race mode, just because it got to be a bit fun to just nail it off corners like a hamfisted moron, feel the rear start moving and then see the magic light come on bringing it all back in line. Fun little game for an old dirt biker like me. You can still use TC with a 190/55 S20 or similarly dimensioned rear tire, though you need to pay attention to the actual tire dimensions and not just the general size. As I noted when I first mounted mine, the center diameter of the new S20 was 5mm more than the worn OEM SP that came off. Edge diameters are what really matters for TC, but it shows the tires aren't that different in size. On that point, do note that even on stock tires, the TC will engage more as the rear tire wears, and not because it's slipping. It’s the math…
So you have to realize what the size differential does to the math and adjust the settings accordingly. However, since the system's skewed towards oversensitivity, you run out of settings pretty quick as you lose a couple of levels. If you’re running it on 5, you’ll see very similar TC engagement on 3 with a 190/55 on back (even a 190/55 Supercorsa SP). I'd like to get a custom sensor ring so I can get more range of adjustability out of the system, but I'd still want that with stock-sized tires since half the adjustment range is useless to me. Better yet, maybe one of the tuner gurus can hack the tables so we can customize TC maps. If the functionality is already there, one shouldn’t need to go to a Nemesis or the like unless they’re doing serious track time.
I'm on record here as liking the SP's a lot, and for a nice day, warm weather tire they're great. That said, there are perfectly good alternatives that have very, very nearly as much raw grip (certainly all you need for remotely sane riding on public roads), just as much “feel”, and that are better in cool or wet conditions. And of course some are a lot less expensive, which may or may not matter to a given rider.
I look at buying street tires for the Pani this way. If I were going through SP's in 1500 miles and wearing the edges out first, I'd switch to SC's or maybe Power Cups. If I were getting 5000 + out of SP’s and wearing the rear out in the middle, I'd put something harder (or at least cheaper) on there since I'd be wasting money for grip I wasn't using. But for the spirited, but sane mountain road use I put my Pani to, SP's, S20's, Q3s, and maybe the new PP3 (haven't ridden them) are all viable candidates. They all are going to last me about 2500 miles, +/-, and all of them have enough grip for my purposes. The SP’s and S20’s have a bit better feel than the Q2’s I’ve run in the past, with the Q2’s a bit closer to the SP’s in hot grip. The S20s beat both when they’re cool. Remains to be seen, but if the Q3’s are much better than the Q2’s, they will give up nothing to the SP’s.
Where did you get this info on the TC? It all makes sense, but it is fact?
Also, if you go throwing different sized tires on this bike it will throw the geometry off. This can cause a range of issues, one being what I experienced. I had very violent headshake when I installed my Power Cups at any speed over about 80, with the correct tire sizes no less. Nothing to do with the TC in my case.
I had to have my suspension setup for my weight, which cured 97% of it. If I want it all gone, I need to take some precise measurements and alter the bikes geometry for the change in tire heights. (example, adjust rear shock length, or move triples down, dependent on exact tire heights) I am worried this will be exacerbated by the 190's in some people's cases which have not had their suspension adjusted at all (I mean preload fyi).
I just think it should be known that some cases might require some work on the bike to get everything in check and fully functional.
