Rear Wheel Dancing!

auldblue said:

Wake up

Thanks for that, any more info on the subject?

J

Click to expand...

What sort of info?
The date was 1989 or 1990. The bike was a Honda XBR, the method of recording braking effort was a pragmatic one which didn't rely on any sophisticated stuff. One of my jobs used to entail the accurate and repeated reading of stopwatches. So I made a little stopwatch holder to attach the watch to the top of the tank. Then I headed out to a quiet piece of well surfaced (granite chips) road, nice and straight, no potholes etc etc. So the procedure was to make sure there was no traffic around, accelerate up to a predetermined speed, start the watch, observe that all was clear, when a set time had elapsed (3,5 or 10 seconds, I can't remember) check the speed , check the watch, hit the brakes (or brake, depending on the test). Note the time that everything stopped, write it down. This required a lot of effort, as it was done at speeds of 60, 80, 100kph, 5 times at each speed, using both brakes. Then to confirm/refute the 75%/25% brake effectiveness split, tests were completed using front brake only, and rear brake only.
The Australian Design Rules stipulate a minimum deceleration of -6.85m/s2, the tests showed a maximum deceleration of -8.17m/s2 with an average deceleration of -7.72m/s2
As a result of all this, the front disc was effectively worn below Honda's minimum disc thickness. I don't remember the details but I calculated the front suspension geometry whilst undergoing heavy braking. It's A LOT different from that at static laden condition, and different in the increasingly unstable condition, thanks to the wonders of telescopic forks.
As a result of all this I ended up designing a system that was based on that designed by Fior.
cheers
wakeup

Tires condition and pressures a huge factor.

Chill when I got the flat tracker ride the peg and brake were rather low mounted and shift up by ankle level so after hitting as much power band
in 2nd as could stand I intended to snick 3rd but hit brake instead, ugh.
So ya might have tapped brake too which is whole another thread than it self applying or you actually loosing traction or just a isolastic wiggle. Now I'm confused on whether your bragging or complaining. Either way I enjoyed putting myself in your seat having a blast. Keep at it till repeatable to make sense of.

wakeup said:

auldblue said:

Wake up

Thanks for that, any more info on the subject?

J

Click to expand...

What sort of info?
The date was 1989 or 1990. The bike was a Honda XBR, the method of recording braking effort was a pragmatic one which didn't rely on any sophisticated stuff. One of my jobs used to entail the accurate and repeated reading of stopwatches. So I made a little stopwatch holder to attach the watch to the top of the tank. Then I headed out to a quiet piece of well surfaced (granite chips) road, nice and straight, no potholes etc etc. So the procedure was to make sure there was no traffic around, accelerate up to a predetermined speed, start the watch, observe that all was clear, when a set time had elapsed (3,5 or 10 seconds, I can't remember) check the speed , check the watch, hit the brakes (or brake, depending on the test). Note the time that everything stopped, write it down. This required a lot of effort, as it was done at speeds of 60, 80, 100kph, 5 times at each speed, using both brakes. Then to confirm/refute the 75%/25% brake effectiveness split, tests were completed using front brake only, and rear brake only.
The Australian Design Rules stipulate a minimum deceleration of -6.85m/s2, the tests showed a maximum deceleration of -8.17m/s2 with an average deceleration of -7.72m/s2
As a result of all this, the front disc was effectively worn below Honda's minimum disc thickness. I don't remember the details but I calculated the front suspension geometry whilst undergoing heavy braking. It's A LOT different from that at static laden condition, and different in the increasingly unstable condition, thanks to the wonders of telescopic forks.
As a result of all this I ended up designing a system that was based on that designed by Fior.
cheers
wakeup

Click to expand...

Ok Phil I'm not going to take the bait, but it's not up to your usual standard of offensiveness !

Hobot
After 14 days bouncing around on the Tasman Sea, I went for the Wednesday club run ( one out as usual), the road is well frequented by Bikes of all ages, size and style( also a good road for beginners), plus the Ferrari club. Really a fun road, I've been riding the road with YDS 250, SR 500, Harley FXRS, Ducati Mike Hailwood Replica ,Beesas, AJS, and my Nortons since the early Sixties. Love the road, it is where I go to clear my head, more info tyres 300 miles from new, Dunlop TTs, the wheel bearings and the iso's don't wobble. I'm starting to think I might put the Corbin seat back on to set me back a bit.

Thanks for all the suggestions.
Peter

Chili said:

Hobot
After 14 days bouncing around on the Tasman Sea, I went for the Wednesday club run ( one out as usual), the road is well frequented by Bikes of all ages, size and style( also a good road for beginners), plus the Ferrari club. Really a fun road, I've been riding the road with YDS 250, SR 500, Harley FXRS, Ducati Mike Hailwood Replica ,Beesas, AJS, and my Nortons since the early Sixties. Love the road, it is where I go to clear my head, more info tyres 300 miles from new, Dunlop TTs, the wheel bearings and the iso's don't wobble. I'm starting to think I might put the Corbin seat back on to set me back a bit.

Thanks for all the suggestions.
Peter

Click to expand...

Isolastics may not wobble, still doesn't mean they are set correctly.....

Were you running TT100s of the same sizes before?

I like Chris's suggestion to also stay off the back brake and maybe adjust it slacker.....

auldblue said:

Ok Phil I'm not going to take the bait, but it's not up to your usual standard of offensiveness !

Click to expand...

To quote Manuel "....que??...."

I'm not a Phil, I'm a wakeup, what has caused offence now??
cheers, I think
wakeup

SteveA
Yes, the same TTs, In fact the only change was the flat bars,and after each work spell, and before a run, I check all the running gear as I'm a bit anal like that!
Peter

SteveA said:

Chili said:

Hobot
After 14 days bouncing around on the Tasman Sea, I went for the Wednesday club run ( one out as usual), the road is well frequented by Bikes of all ages, size and style( also a good road for beginners), plus the Ferrari club. Really a fun road, I've been riding the road with YDS 250, SR 500, Harley FXRS, Ducati Mike Hailwood Replica ,Beesas, AJS, and my Nortons since the early Sixties. Love the road, it is where I go to clear my head, more info tyres 300 miles from new, Dunlop TTs, the wheel bearings and the iso's don't wobble. I'm starting to think I might put the Corbin seat back on to set me back a bit.

Thanks for all the suggestions.
Peter

Click to expand...

Isolastics may not wobble, still doesn't mean they are set correctly.....

Were you running TT100s of the same sizes before?



I like Chris's suggestion to also stay off the back brake and maybe adjust it slacker.....

Click to expand...

SteveA

You are a supreme diplomat.

Chilli

I don't think it's your left foot that is at fault, I think it is your right wrist!
Your riding like a maniac!

J

Auldblue
The bike is a Mk111 so it's right foot and right wrist, no not a maniac just trying to stay young!!!
Peter

Hot Chilli I'm grinning on the well practiced route you and other blow off steam on. Still confused if your sense of dance was only a instant jerk or had some oscillation to it and if traction lost d/t over leaned over powered or by brake onset or just hidden sand right then. I am firmly fully in camp that steering at speed with power increasing or on loose stuff needs as much mass on rear as possible or rear tends to let go too soon and unpredicable. There is a threshold on my linked and unlinked Cdo and SV and Ninja that I learned I'd better slide my ass back or front will grip more than rear - which aims us into an outward low side till it hi sides, but with most mass on rear front can let go but rear still angled right and hooked to carry us on around. That level sets my limits per bike to ride it like ordinary racers, to go faster takes rather more power/speed to get into predicable flat tractor slides but no way to just creep up on that extra level as you know yo'll crash if not going fast/harsh enough to have some ballistic momentum or one tire or the other may hook up too soon and launch to the moon. I do not think I can control slide an un-tamed Cdo or pavement as it gets so upset with just a little rear or front skip out at such slow speeds compared to my modern I hope to never find out. I work up till its too scary for me and then know I'd better not press to full fun level on un-tamed isolastics. Generally this is as fast as any sane modern pilot will hang turns any way so generally can keep up with anyone having normal level thrill ride but know deep down in my heart they are all corner cripples needing extra skill not to crash on a mere joy ride. Btw I did soak in your time at sea with unending roughness, whew.

What do you mean by the rear wheel 'dancing'?

If you mean it is bouncing up and down in a pretty much uncontrolled manner, this can be a sign of having no, or inadequate, damping in the rear shocks. If you have your shocks on the firmest setting, this could go a long way to hiding the problem, especially under slower conditions.

When braking, weight is transferred forward, now you've added to this with your flat bars, all this could be allowing the lack of damping to show itself.

Adjust your shocks to the minimum pre tension, then (bike off the stand) press down on the rear end and let go, you should be able to see if the shocks are damping (slowing down how it springs back up).

Wheels being way out of balance could also cause, or exacerbate the situation.

Eddie
Adjusted the shocks yesterday, will try today, thanks. ( dancing ie., squirrelly)
Hobot
You talk a lot of sense, the corner was a 35 kph("advised") left hander going down hill, good tar, and offset to the right for water run off. Again this discussion has given me a lot too think about, THANKS.

Peter

J

AMEND to stupidity of using rear brake to slow but when going rather slowly any way or if so loose slick steep surface front can't hold to slow by itself. I have nil respect for those that find applying brake and throttle at same time especially in any leaned condition unless for stunting antics. I've had this explained to me by the hot shots years ago that visit here and a few articles so had to practice it to find it ain't for me. The dogs that got SuVee last fall had me feathering both brakes for dozens of yards slowing down THE Gravel trying not to lock but maybe subconscious extra toe curl as one dog cut across a few yards in front - rear snatched us down so fast at ~15 mph by then didn't know what happened till I looked back up hill to see the rear slid marks but not front. Anywho fun for me to know of others taking their chances on a Commando any style they can.

Hobot
I agree, but that was the advised speed, nobody but cage drivers and beginners would do it, all by my self no Mr Plod, just me feeling immortal, other than that corner I had a top day, I realised afterwards that I had got my adrenalin up and just relaxed into the ride and enjoyed it, tho I think with all the information given, I've been able to set the bike up BETTER!
Thanks again.
Peter

Alright Chilli its soul food for me to know of other immature Cdo pilots going against the prim&proper safety advice but I know as I age and reflect back on life its these hi points of adrenalin spikes and handling saves that float to the top. Cheap/simple enough to make ya own breast link and buy a top link for another level of stable security that can still induce hinging at rather higher speeds and frequency over rougher surfaces or wind gusts > so beware until getting the main handling transformer the very rare rump link fitted to see why I consider all other cycles as corner cripples and feel sorry for those that think I'm full of it. Even with the links I had to set iso gaps down pretty close to normal or hinge would still onset [though still cornering beyond what heated fatso tires can hold near edges] and if much tighter than .01" vibes noticed. My late friend Gerry Bristow an UK expat in Italy had a cresting turn he'd worked up to catch air sideways in delight as place to test his swash plate head steady in his last few years over age 70. That my friends is Phase Four handing delights. Aneurism popped at family BBQ in UK after a days delight riding with his brother. He'd had to stop riding d/t knee failing but I healed him long distance with against the grain neck re-growing protcol and got to meet him in INOA Ohio rally where he told me he'd not been able to travel other wise. Also mentioned shopping at a ski resort town prior to the rally his knee stopped him short - for a time- till he thought what would hobot do, so stretched his neck and knee eased right up and he finished his whirlwind America tour just fine w/o gimp. Said I saved him surgical money & recovery time to spend on real life. What a lucky man was he.