modulating front end

[Racer-unk]

When I brake whether hard and then end of the straight or a normal stop in the neighborhood the front end modulates....when I lift the front end ans spin the wheel I dont detect any run out on the discs. Even with brake slightly applied it feels smooth. I cant remember, but do think this started when I installed the emulator....any similar experiences like this? I intend to change master to a radial unit to see if this makes a difference.

[Snod Blatter]

I haven't noticed any difference with emulators, it juddered before and it juddered afterwards! Loose steering head bearings can make it feel a lot worse but at least slightly warped discs definitely seems to be a feature of these bikes..

[cobbadiggabuddyblooo]

Clean all the buttons on the discs where they attach to the carrier. Std they are semi floating and will be tight but the buttons should still turn. Spray some cleaning agent around the button then place a bolt through the button and tighten a nut on the outer side so you can use the bolt to spin the button to work out any brake dust.
Fully floating discs are different and the disc will freely spin and rock side to side on the button. Plus the button isn’t like a rivet but is held by a clip.

[Racer-unk]

Its a strange feeling.
No juddering, nor a thud usually associated with loose head bearings, but a rhythmic smooth up and down of the front end at low speeds.
It does occur when braking hard at the end of the straight, but it does not affect me really, other than damping my confidence slightly.
Maybe if resolved, I will have a lot more confidence turning the bike in???? I am currently slower than last year..... , and there must be a reason for it....

It feels crappy on the neighborhood roads. as a rule i have not ridden a road bike for 15 years, so currently I am only used to ridding flat out....
I can't ride my bike in town on bumpy roads with that long first gear and the stiff suspension. Yet, i love that long gear on the track.....

.....to get back to the issue..... it almost seems as the YSS PD valve opens a bit and then the forks rebound and it opens a bit and the process repeats itself....???
I will however clean the buttons first, test, then fit the radial master cylinder, which I am certain wont fix this problem......and then remove valves and tighten the spring a turn or two.

[Tarwetijger]

Two things come to mind.
- not perfectly round shaped front tyre. I've the suspicion this is the case on my SZR at the moment.
- the brake discs do not have the same roughness all round, if you understand what I mean. I've had it with cheap discs from Ebay (China), they looked good and from proper quality. But the friction was not consistent, so brake force was also modulating. This was fixed by a specialist, a company who treats brake discs (surface treatment).

(Not the easiest stuff to translate, I hope you understand).

[Racer-unk]

Thanks Tarwetjiger

I will remove wheel and clean discs with scotch guard pad (as read on one of Cobb's posts). They are still original and in good condition.
front tyre still looks lovely evenly worn and seems fine.

(Ons kan ook in Flaams gesels).....met so bietjie gesukkel....

[cobbadiggabuddyblooo]

While you have the wheel off just check for balance. Maybe you lost some weights ???

[ac@39]

Tyre not being round - very similar experience - too much wear on one side so basically it was lopsided

[Tarwetijger]

8<
(Ons kan ook in Flaams gesels).....met so bietjie gesukkel....

Prachtige taal! Maar ik weet niet of ik alle woorden zou begrijpen...

Tyre not being round - very similar experience - too much wear on one side so basically it was lopsided

Exactly, easy fix though.

[Racer-unk]

turned rebound adjuster 2 positions faster and i turned the spring bolt stiffer on the emulator. Better under braking and modulation sensation is basically gone. However.......I still dont have any sense of confidence to tip the bike fast and hard into a turn with the standard forks. Acceleration in sweeps are fine.
Vowed not to return to the track until I have better forks.

[Tarwetijger]

turned rebound adjuster 2 positions faster and i turned the spring bolt stiffer on the emulator. Better under braking and modulation sensation is basically gone. However.......I still dont have any sense of confidence to tip the bike fast and hard into a turn with the standard forks. Acceleration in sweeps are fine.
Vowed not to return to the track until I have better forks.

Do you still have the original springs? Other springs are a no-brainer modification. Some use emulators (?) to properly adjust the damping.
FZR-R forks are used by several people, if I remember correctly, from the most recent model years, those are fully adjustable.

[Racer-unk]

Front springs was the first thing i changed. My problem is that you rob Peter to pay Paul when you do any changes. Stiff enough seeing it only travels 90mm in front under harsh braking, but soon as I speed up rebound i loose slow corner stability.
Lets face it, standard forks are no good for racing purposes

[cobbadiggabuddyblooo]

You found the boundaries of the std forks... so the second or 2 you picked up under heavy braking you lost 2x as much through the slower corners..
It’s that happy medium and why corner speed is suited to the trx.
Look at gearing too...
If you keep the gearing tall looking for hi top end speed and late braking you’ll loose out with instability and slower exit speeds unless on a really fast circuit like PHILLIP Is.
Mine is screaming it’s head off in top gear at 220kph with 16/41 but works well for me because 210-215 is max speed for me down the straight anyhow. But boy it gets there fast with plenty of drive out of corners in 2nd and 3rd are only momentary engagements before I find 4th so 160-180kph is there before you know it.
I have 2 rear sprocket carriers. 1 set up with a 41 tooth and the 2nd with a 40 tooth so and 16 plus 17 tooth sprocket gives me a good compliment of choices in gearing with the 4 combinations available giving me the variety to suit my needs with small incremental changes.
But again it’s always a compromise and why I personally would have closer ratio gears made so 1st is a touch lower than the std 2nd gear because no curcuit around me I use 1st gear anyhow unless rolling through the pits.
At the end of the day it’s still only a trx...
16/41 and 16/40 are what I run 95% of the time and 17/41 was ran when I first built the motor and It was still pulling at 230kph when I’d run out of road.
Personally I just don’t want to go there any more.

Plan your attack if your looking at a later model USD front end.
Fork extensions are another option if the front is too low or machine a new stepped top yoke to give you the height back. But again clip on position is the compromise and why fork extensions are a good option.

[Tarwetijger]

I really like the feel of my UPSD forks from a YZF750R - '96 so it's fully adjustable.
My track bike currently has original forks (albeit with WP springs), because the Marchesini wheel (light weight!) fits straight in.
The light wheel in the YZF750R forks would be an ideal combination, but that would take a little project on itself because the discs are spaced differently and I would need a special made front axle. Maybe, some day. But, with all this consideration, I realised I know a guy who's at least 4 seconds faster than me on Assen - with a totally original TRX.

[PrfctChaos]

All balls racing has a usefull fork conversion tool on their website: (Only checks bearing diameter combinations, not steering axle length!)
https://www.allballsracing.com/index.php/forkconversion

I used a set of their bearings and put a 2006 GSXR750 front end on, very easy (Now she doesn't mind late braking). The USD fork possibilities are endless.