I fitted a YZF swingarm to my TRX, so I could use the magnesium rims I already had. The point is, this rear rim is 6 inch wide. The original YZF rim is 5,5", the original TRXs is 5". The tyresizes are correspondig to this, so 160 on original rims for the TRX, the YZF uses 180 rear tyres. The magnesium rim runs best with a 190 tyre, because a 180 is not round enough.
Because of the weight benefits, I use the magnesium rims during track days, so i'm using 190 tyres (supercorsas or pilot powers). On the street I put the original YZF rims in with a 180 rear tyre (pilot road 2, in order to make a decent number of km's before I have to change tyres, again...).
Are you still with me? Okay. Now, I have noticed that the TRX runs wide very easily during track days. I thought it was just me, putting on the throttle to early. But I cant help thinking the bike didn't act like this this before the modifications (putting in YZF frontend and swingarm)! It really looks like I have to add more lean angle then someone that is just in front of me, riding at (more or less) the same speed on whatever bike!
Now I'm reading this book: Motorcycle Design and Technology, by Gaetano Cocco. It handles exciting stuff, but now i'm reading in chapter 4 - control of the motorcycle when cornering, after some equations:
So this complies with the feeling I already had: changing the rear rim to a light weight but wider one, maybe wasn't a very good idea... But it gets worse later on:"As a result of this, the bigger the crosssection of the tire, and equally, the greater the speed at which you enter the corner, the more you must lean the bike into the curve. "
So there, it says it all!"We hope these observations will have convinced you to be rather cautious about substituting your original tires and rims with bigger sized replacements".
Now I'm really in doubt what to do. What are the options?
- just use the magnesium rim because its cool err I meant lighter! And go slower through the corners...
- use the 5,5" YZF rim also on trackdays, like a compromise. Now I think of it, I think the 190 tyre is even worse then the 180.
- get the 5" TRX rim fitted in the YZF swingarm
- get rid of YZF swingarm and use the original one with 5" rim.
Keep in mind though that the ability to change wheels (tires) for road use and trackdays is really nice.
I would like to know your thoughts on this issue!
Edit: in case you were wondering: yes, a 6" rim with 190 tyre fits in. But it's tight. It also appeared to depend on the tyre itself, a 190 michelin pilot power is actually a tiny bit wider then a 190 pirelli supercorsa. The michelin touches the chain every now and then , the pirelly doesn't.