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Old 04-13-2009, 07:52 PM   #1
Crotch Rockety
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Front / Rear Wheel Lock Up

I've had this happen twice, and I'm looking for a cause / cure. Yesterday, a friend and I were having a spirited ride through the canyons. No doubt the stock 'stones had been heated up. My friend signals a R turn. I'm in second gear, roll off the throttle, and start to slow. At about 20-25 mph, I downshift to 1st and let of the clutch. The back wheel immediately locks. I apply the front brakes gradually (I definately did not grab a handful) and the front locks up. I'm now sliding sideways (how the hell I didn't high side I'll never know) I straighten the bike out, the rear regains traction and the front stops sliding almost simultaneously. Road seemed clear and dry. Was a little cool (low 60's), but the tires should have been WELL heated from the ride. I was running 36F /38R psi.

I had this happen once before. Same type scenario, had been riding her hard, had backed the pace down, started to slow for a redlight, downshifted, locked rear (started bouncing side to side that time). Applied front, it slid too. (Only travelling in the 10-20 mph range when that front lockup occurred.) I thought it might be that there was crap on the road that time, but this last time, my friend was directly in front and had no traction issues. Are the OEM BT016's prone to skidding / getting greasy? I've noticed they don't have near the grip of the aftermarket BT016's on my SV. Are the slipper clutches on the 08/09 750's prone to lock up? Any ideas? TIA
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Old 04-13-2009, 08:02 PM   #2
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Re: Front / Rear Wheel Lock Up

I run much lower pressures when hitting the twisties. None of my buddies run the pressures you are running unless they are commuting.
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Old 04-13-2009, 08:10 PM   #3
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Re: Front / Rear Wheel Lock Up

honestly along with the pressures being to high IMO the stock tires take alot to get up to temp and even though you would think that they were warm they may not have been and the slipper clutch in my k8 at least works flawlessly it will spin up in first a little but only if i kick it down at like 65 or so going into a corner. however if the tire is cold it will spin up at 25 mph. i would try running a pressure more like 33f and 34r
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Old 04-13-2009, 08:22 PM   #4
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Re: Front / Rear Wheel Lock Up

downshifting to 1st is really rough if you don't blip the throttle, and I've locked the tire in the past also. I rarely downshift into 1st (commuter), but if I really want to be able to speed away, I blip the throttle significantly after I pull in the clutch to better match the tranny speed with the engine speed before letting out clutch in 1st, and it's still really rough. I wouldn't ever consider downshifting without blipping the throttle anymore.
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Old 04-13-2009, 08:34 PM   #5
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Re: Front / Rear Wheel Lock Up

Your bike comes with a slipper clutch

The mfrg recommended pressure for tires has been something like 38/42 psi for years

None of what your story makes any sort of sense unless you stomped on the rear brake at the same time as you let out the clutch. Dumping the clutch at 20-25mph in first will absolutely not lock up the rear wheel. I've accidentally DOWNSHIFTED from 2nd to 1st at about 80 mph and my rear didn't lock........that's what the slipper clutch is there for.

How you managed to coincide that with locking up the front also doesn't make much sense unless you were completely leaned over when hitting the brakes or were riding through a patch of gravel.




Something about this story definately does not add up.
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Old 04-13-2009, 08:43 PM   #6
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Re: Front / Rear Wheel Lock Up

...... I have to go with SPL on this one.

If you did in fact lock both wheels up, and NOT crash, and not foot stomp it, you are one of the luckiest people ever. To do it TWICE is even that much more improbable.

The rear can lock up on a downshift going that slow, but it is HIGHLY unlikely with a slipper clutch. But sometimes there is just enough pressure to chatter the rear at a low RPM low gear, but not enough to disengage the slipper.

now the front, to lock it up, you HAD to snatch the front. No other way to do it really.

It was NOT your tire pressures, I can tell you that with total confidence, unless your gage is wAYyyyyyyyyyyyy off, and you have something like 50psi, thinking you have 36 or whatever.

For the others in this thread, his pressures were fine. A street tire is not designed to run below 32 psi usually anyway.
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Old 04-13-2009, 08:44 PM   #7
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Re: Front / Rear Wheel Lock Up

Quote:
Originally Posted by surfingsk8r View Post
honestly along with the pressures being to high IMO the stock tires take alot to get up to temp and even though you would think that they were warm they may not have been and the slipper clutch in my k8 at least works flawlessly it will spin up in first a little but only if i kick it down at like 65 or so going into a corner. however if the tire is cold it will spin up at 25 mph. i would try running a pressure more like 33f and 34r
STREET tires heat up FASTER than sport tires, which heat up FASTER than race tires....... not the other way around contrary to common belief. They are designed that way. A street tire will literally melt on the track because of this.


And what do you mean by "spin up"...... spin up is a term used when on the throttle. That has absolutely ZERO to do with a slipper clutch
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Old 04-13-2009, 08:48 PM   #8
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Re: Front / Rear Wheel Lock Up

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Originally Posted by Moto_Joe View Post
......

For the others in this thread, his pressures were fine. A street tire is not designed to run below 32 psi usually anyway.
You need to clarify this as I am going to have to disagree unless we are not on the same page.

Are you saying running for example 016 or Corsa III at the track they are not designed to go below 32 psi?
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Old 04-13-2009, 08:53 PM   #9
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Re: Front / Rear Wheel Lock Up

STREET tire, not track tire. Most street tires are not designed to run below about 32psi. The carcasses are just not designed to run that way, so running much below that there really is no bennefit. You lose feel, you get a wallowy feeling, and usually overheat the tire.

There are some "crossover" trackday tires that are starting to go lower to about 30, but that is not a "street" tire by what I meant as they are usually rated at like 80%track, 20% street


Now my race tires (which are DOT legal, so I guess loosely are "street" tires ) I start with about 21psi in the rear.
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Old 04-13-2009, 08:58 PM   #10
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Re: Front / Rear Wheel Lock Up

I see what you are saying. Yes I agree it does depend on the tires you are running.

Tires like the Corsa III, PP2CT and Power 1 are more of a track/street tire and can benefit from below 32 psi pressure at the track.

I will not comment to DOT race rubber a that will really confuse the masses.
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Old 04-13-2009, 09:08 PM   #11
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Re: Front / Rear Wheel Lock Up

PP2ct I disagree, I wouldnt run it below 32 either...... Power1, and CorsaIII are like I said really 75-80% or so a track tire.

People USE them on the street...... but that does not make them ideal on the street really
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Old 04-13-2009, 09:10 PM   #12
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Re: Front / Rear Wheel Lock Up

The OEM BT016 are just fine for the street as they worked so damn well at the track.

It's not the tire, it's your riding (in)ability.
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Old 04-13-2009, 09:11 PM   #13
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Re: Front / Rear Wheel Lock Up

Quote:
Originally Posted by Moto_Joe View Post
PP2ct I disagree, I wouldnt run it below 32 either...... Power1, and CorsaIII are like I said really 75-80% or so a track tire.

People USE them on the street...... but that does not make them ideal on the street really
I run my PP2CTs at 29/29 at the track for the last 2 years and have never had an issue.
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Old 04-13-2009, 09:13 PM   #14
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Re: Front / Rear Wheel Lock Up

I think we are saying the same thing in a round about way.

Plus tire pressure is like vagina what is loose to some is tight to others.
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Old 04-13-2009, 09:19 PM   #15
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Re: Front / Rear Wheel Lock Up

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Originally Posted by Tyg View Post
I run my PP2CTs at 29/29 at the track for the last 2 years and have never had an issue.

It wont cause you "issues" but IMO you are not gaining anything either. The tire that low will feel a bit more loose usually (wallowy even) and might grow too much when it reaches its hot pressure.

And as RRaider eluded to Tire pressures are soooooooooo touchy. Basically as long as you are only getting 5ish PSI growth, you are probably fine regardless of where you start out

This post was mainly about street riding..... and the fact the tires had zero to do with what happened to this guy, whatever that might have been
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Old 04-13-2009, 09:36 PM   #16
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Re: Front / Rear Wheel Lock Up

moto joe im not saying thats they warm up faster than track tires im saying that they warm up slower than most other street tires or at least thats what i experienced with my stock bt016's i had the stock bt015's on my kawi and found that they became warmer faster and would have grip earlier than the 016 but not as much grip if that makes sence. granted im no professional but this is what i have observed.
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Old 04-13-2009, 09:40 PM   #17
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Re: Front / Rear Wheel Lock Up

Quote:
Originally Posted by Moto_Joe View Post
And what do you mean by "spin up"...... spin up is a term used when on the throttle. That has absolutely ZERO to do with a slipper clutch
what i mean by spin up is when you would downshift to a low gear putting it at high rpms the wheel has to spin up to catch the speed of the engine it actually does make sense and i know what your talking about as well i guess im using the wrong term but it sure as hell is not locking up when down shifting as its spinning faster than the front wheel when this happens.
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Old 04-13-2009, 09:42 PM   #18
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Re: Front / Rear Wheel Lock Up

Quote:
Originally Posted by SPL170db View Post
Your bike comes with a slipper clutch

The mfrg recommended pressure for tires has been something like 38/42 psi for years

None of what your story makes any sort of sense unless you stomped on the rear brake at the same time as you let out the clutch. Dumping the clutch at 20-25mph in first will absolutely not lock up the rear wheel. I've accidentally DOWNSHIFTED from 2nd to 1st at about 80 mph and my rear didn't lock........that's what the slipper clutch is there for.

How you managed to coincide that with locking up the front also doesn't make much sense unless you were completely leaned over when hitting the brakes or were riding through a patch of gravel.




Something about this story definately does not add up.
If it did, I wouldn't have posted. I've played with the tire pressure. I started at the 38/42. Those pressures put the 'stone in Bridgestone.

I finally compromised at 36/38, but will try lower again.

I didn't touch the rear brake. I didn't grab the front brake. Sorry, it didn't happen. Both times I was traveling straight and upright.

Basically, I wanted to see if anyone else had this issue. Apparently not.
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Old 04-13-2009, 09:47 PM   #19
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Re: Front / Rear Wheel Lock Up

No one is saying you are not telling the truth but this is a very strange issue but than again stranger shit has occurred before.

Can you have you buddy video tape this occurring?

Can you make it do this anytime by downshifting in to first or is it intermittent?
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Old 04-13-2009, 09:49 PM   #20
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Re: Front / Rear Wheel Lock Up

i've downshifted from 3rd to 1st on accident before because of bumps in the road and the rear tire didn't break loose that bad because of the slipper clutch, so i don't know how you're breaking traction going from 2nd to 1st.

as far as the front is concerned, sounds like you're just grabbing too much brake. you shouldn't grab the brake, you should squeeze it. it's not an on/off switch, the best way to use it is to start with as little pressure as possible and then start to squeeze harder until you're at the desired level of braking. if you squeeze too hard too fast, before weight is transferred to your front tire, you can easily lock up the front.
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