Yamaha TRX850 Enthusiasts Forum

Last Tuesday I competed in the 4H endurance race on Assen, with a Yamaha TRX only team: 4 TRX's were used.
A lot of firsts for me; never been on track within competition before, first time crashing on track

Sadly there are no action pics, but here 's me waiting for the transponder from Huberts bike.

Hubert is the guy from http://www.bergwerkstatt.de (Killerwhale mentioned him on this forum before).
He is a very nice guy and he is fast too. His interesting bike was only his spare, the 118 bps version was still in his garage after a crash.

Although I improved my personal best to 2:02, I'm not really happy with the wear pattern on the rear:



Any hints on this? I'm familiar with https://lifeatlean.com/motorcycle-tyre-wear-guide/ but that doesn't quite answer my problem I guess.

that sounds like like an awesome things to do!

re the tyre wear, its not too bad, I would you had a bit too much pressure in your rear tyre for the conditions. I had the same problem on the last track day and the more I reduced the pressure the more it cleaned up. you have the correct 'wet sand' pattern on the more upright part of the tyre, and like me you can see where you you become confident to open the throttle at a certain lean angle.

the other thing that might have caused that is track temp, if the track temp is really cold then I also get that tearing.

basically you have to be a magician to know whats going on

Let me guess Robert, low side exiting a corner????

cobbadiggabuddyblooo wrote:Let me guess Robert, low side exiting a corner????

Almost right.
It happened during a practice session in the morning. Low side entering the corner after start/finish.
It started raining, so I suppose that is the main cause. It happened just seconds after I told myself to slow down because of the rain...
Sliding on the ground while looking at your bike laying on its side... Horrible!! And it feels like you're sliding for like an hour or so.
I tried to get up too soon (too much speed left) like a real pro!
Some easy parts took all the damage: slide protector and foot peg (both half gone!), exhaust (original Suzuki so easy to replace but it still works well).
And the oilpump cover was completely worn out so oil was leaking. Fairing remained free of damage.
When I entered our pitbox, first thing I heard was that a new oilpump cover was on its way.
During lunch the bike was fixed so I could take part in the 4h race in the afternoon!

Still feel a bit sorry for my Yamaha leather suit (which is already some years old but I still like it very much), boots and gloves took it all very well. Proved to myself once again how important good clothing is! My helmet is brandnew and did not touch the ground.

Crashing in the morning and beating my own laptime in the afternoon, looks like I 'm getting there.

coxylaad wrote:that sounds like like an awesome things to do!

It is! It's also hard work though, really different compared to a 'normal' trackday, where you can chill between the sessions.
Now it is besides riding, doing stuff on the bike, on yourself (eating / drinking), helping your teammates etc. etc.

re the tyre wear, its not too bad, I would you had a bit too much pressure in your rear tyre for the conditions.
8<

Pressure was as low as 1,6 bar cold, 1,9/2,0 warm.

basically you have to be a magician to know whats going on

That would be handy

Sounds like you guys had a ball.
Glad to hear it was an easy fix for you and not too much damage.
How did the Marchesini wheels feel???
I noticed something on the facebook page about this with videos attached when I reactivated my profile for 5 minutes earlier today.

How can I forget to mention the Marchesini's! They are great; quick and easy steering.
Very happy with 'm!

Pressure was as low as 1,6 bar cold, 1,9/2,0 warm.

I ended up up with 25psi hot (1.6bar)
it looks to my untrained eye like cold tear where the carcass isnt flexing enough to generate enough heat, and the rubber touching the track gets so hot at the contact patch compared to the rest of the carcass it tears away at the surface.

Some genius suggested to me to solve the problem I just need to ride harder to generate more heat...because I wasnt already riding as hard as I could...

If it's not pressure related, ( I was running dunlops last trackday and running 1.2 bar cold in the rear.)
Ambient winter temps of around mid 20's on the day.
I'm going to gamble on a geometry and squat issue. Right where your laying down the power out of the corner. It's soaking up the power in the rear suspension instead of the tyre carcass.
Check your swing arm angle as you need 12* and over to find some anti squat especially with the torque your bike puts out Robert.

coxylaad wrote:

Pressure was as low as 1,6 bar cold, 1,9/2,0 warm.

I ended up up with 25psi hot (1.6bar)
it looks to my untrained eye like cold tear where the carcass isnt flexing enough to generate enough heat, and the rubber touching the track gets so hot at the contact patch compared to the rest of the carcass it tears away at the surface.

Some genius suggested to me to solve the problem I just need to ride harder to generate more heat...because I wasnt already riding as hard as I could...

1.6bar with hot tires seems quite extreme!
I even use tire warmers nowadays. But that doesn't have to be a guarantee for not having cold tear.

cobbadiggabuddyblooo wrote:Yep and I'm going to gamble on a geometry and squat issue. Right where your laying down the power out of the corner. It's soaking up the power in the rear suspension instead of the tyre carcass.
Check your swing arm angle as you need 12* and over to find some anti squat especially with the torque your bike puts out Robert.

Thanks for the hint Cobba (also saw your PM). I will check the angle.
There are YZF750 dogbones fitted now if I remember correctly.

Do you still have the revalved yzf750 sp shock fitted???

The tears don't look deep enough for a cold tear so it may be a hot tear, usually caused by under inflation, although your pressures at 1,6 bar say otherwise.

It's like a thin tear line don't you think???
That's why I'm thinking more on a geometry related tear.
Right when your tapping on the gas and not squashing the carcass enough to generate the heat spread throughout the carcass and that squash is being soaked up in a little too much squat so it's generating too much heat in that smaller contact patch.
The suspension setting as such like comp/rebound look pretty good with no edge patterns on the grooves or spring rate related wavey patterns on the tear.

Just a note, the tyre pressures I ran are with a 180 not a 160 rear so they will differ due to construction differences.

cobbadiggabuddyblooo wrote:Do you still have the revalved yzf750 sp shock fitted???

No, this is the new OVER bike: WP springs in front and WP shock rear.
This WP shock feels stiffer than the ohlins so I prefer the WP for track use.
The ohlins did well and gave good tire wear on track (after a lot of adjusting), but it feels quite soft. So I like that to use on the road bike.
Could swap them for investigation... but no trackdays planned yet.

cobbadiggabuddyblooo wrote:It's like a thin tear line don't you think???
That's why I'm thinking more on a geometry related tear.
Right when your tapping on the gas and not squashing the carcass enough to generate the heat spread throughout the carcass and that squash is being soaked up in a little too much squat so it's generating too much heat in that smaller contact patch.
The suspension setting as such like comp/rebound look pretty good with no edge patterns on the grooves or spring rate related wavey patterns on the tear.

Just a note, the tyre pressures I ran are with a 180 not a 160 rear so they will differ due to construction differences.

Agreed it's a tear line but I don't think it's a cold tear, they tend to be deeper

i thought hot tear was deeper?

its a feckin mystery!