Heads up, YZF750 swinger, rear-sets and footbrake...

[HansJ]

This is almost embarissing to tell, but here we go...

I've only done 8 trackdays on 4 different occasions this year. The third one was on a really bumpy track. It was more than a year ago since i was there, and i thought it had become a lot worse. I was almost thrown out of the seat in a high-speed right-hander, no matter which line i tried. Then on the next trackday i had some serious issues with braking after the looong straight, the rear was skidding around and didn't ffel so planted as i recalled. While i changed the front cog (16/41 is not optimal for +200 straights...), i noticed something really strange:

That's how the setup look from the side.




This is how it looks from above, see what i am getting at?



And, tadaa, this is the the "after" picture.



I had managed to press the footbrake main cylinder in below the swing! The swing was completely stuck under the protruding banjo protector, and i had to use brute force to get it away. The last pic shows that it had been going on for a while, since the side of the swing has been damaged as well. I have in the picture filled the damage with some colour, to see if it would be starting scratching the swing again. I have also used the Dremel and cut away the sharp corners on the protruding part of the pump, so that it wouldn't get stuck again.

It all explains why i had the impression the bike was going wide in the corner-exits, the odd tyre-wear, and the skidding rear while braking from high-speed... Guess my application as a test-driver for Öhlins will have to be withdrawn now... Pity i only got one session to try it all out, and it was partly ruined by the new gear ratio, i had to implement a completely new gear-changing strategy as well. But for what it was worth, the bike felt a lot more compliant. It also stood much better with the side-stand down, before i had noticed that the bike was standing unusual up-right, but i was unsure if it used to be like that (last time riding was in beginning of June, and this was September.

So, lesson learned, ride more often, and if one thinks somethng is weird, investigate just to be safe. (Funniest thing was that i had some free advice on suspension at the event before this one, and the bloke (an English bloke) told me to pre-load the fork a bit more, after i told him i thought the bike was running wide on exits. In a way he was right, but none of us saw the swinger "pre-load" being the problem. After all, it was some odd 3 cms of pre-load , and that was the measure at the swing, not back at the wheel...)

[alextrx850]

Hi Hans, so the brembo brake cylinder assembly was fouling the movement travel of the upper swing arm reinforcement..? because you have the further back rearsets..?
If so, did you have much suspension travel ..if any ?

[HansJ]

Hi Hans, so the brembo brake cylinder assembly was fouling the movement travel of the upper swing arm reinforcement..? because you have the further back rearsets..?
If so, did you have much suspension travel ..if any ?

Correct, at first probably only fouling, but ultimately the swinger bracing was stuck on top of the brake cylinder. That meant that i had a lowered rear, almost no suspension travel (at least on the last track session which hada much smoother track-surface). I have semi-race Poweer Pure B's, and a fairly low pressure at the rear, 1.7. The rear tyre probably covered up the lack of suspension travel, but this also meant excessive wear. And in any case, the geometry was way out of line, with the rear of the bike sitting a couple of cm's too deep... Not to mension thelack of negative travel/rebound, which meant that the rear was in the air while braking hard.

[alextrx850]

Hans, those coerce rear sets must set the foot position to the rear a way..ive the YZF rear with the TRX sets and measured about five inches for the rear master to foul the rear swing at all....
Looks like the rear swinger is still useable anyway and you stayed upright.....your rear hoop shows how hot they become if used hard on low pressure...learn and then move on.

[cobbadiggabuddyblooo]

stick to a std swingarm..problem solved if you can get that to flex with 90 odd horses no need for the extra weight. Discussions with the dunlop rep here where interesting on the std rim and tyres with a 180 slick fitting no problem ...I'm already running a 170 with no dramas on my trackdays and I'll try a 180 next time

[Killerwhale]

Hans, those coerce rear sets must set the foot position to the rear a way..ive the YZF rear with the TRX sets and measured about five inches for the rear master to foul the rear swing at all....
Looks like the rear swinger is still useable anyway and you stayed upright.....your rear hoop shows how hot they become if used hard on low pressure...learn and then move on.

Those are the "Max forum master" standard ones

[Killerwhale]

stick to a std swingarm..problem solved if you can get that to flex with 90 odd horses no need for the extra weight. Discussions with the dunlop rep here where interesting on the std rim and tyres with a 180 slick fitting no problem ...I'm already running a 170 with no dramas on my trackdays and I'll try a 180 next time

Dunlop recommend 170 for the TRX, and there are a interesting thread online about that a 190 dunlop actually is much better on a 5,5"...will try that next time.
And dude, you don´t put a YZF swinger on because you are scared of flex....you do it so the rear doesn´t look similar to the bicycle

ps. SE dude tried the 180 but that was compressed to much on the 5"...just saying before you buy...

[HansJ]

The wear was quite "impressive", especially considering that the air temperature was well below 15 C, and basically no sun at all... The rear tyre was under some stress!

The swinger came with the bike, i do actually agree, the standard swing is lighter and sturdy enough. There's always a bling factor, but for serious track purpose, i'd actually want the std swing instead.

Re tyre sizes, 180s are easier to find, both used and new. That's the main reason for me for having a 5.5" rim. I know two guys that used to run 180 Pirelli slicks and intermediate on the standard rims, and they were both really fast on the track, and had no issues with . With that said, not all combos will work. I guess it's a question of brand/type, even if it says 180 it is often differing.

[cobbadiggabuddyblooo]

compression on the tyre may not be so much of an issue as such here with air temps averages in the hi 20's and to the mid 30's and only as low as 32/30psi (2.2bar) in the rear. (1.7 bar is only 25psi) The 170 has a rounder profile than the 180 so to gather the same contact patch it will be an interesting comparision with tyre pressures no doubt,..
the air temp has so much to play with in set ups on these bikes as I learn with jetting being so much higher in your colder climates also