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Old 06-26-2012, 12:17 PM   #1
14TLC OP
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ABS and Dual Sport/ Knobby tires

Has anyone noticed an issue with ABS activating more often with knobby tires? The reason why I'm asking is that I noticed that the ABS activates surprisingly on more bumpy tarmac or stone pavement. Even with little braking force applied in situations where it is absolutely not necessary for the ABS to be activated. I Have the OEM Pirelli Scorpions. "Manuel" says it may be activated on loose surface. Could this be happening more with tires with less contact surface?
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Old 06-26-2012, 03:57 PM   #2
Snowy
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Knobbies will tend to skate and spin more initially than more dual sport or road tyres on the right surface.

If the surface is hard base with loose top, I've found the full knobbies lock and skate really easy. Riding with a another F800 fitted with Tourances, I found I was having ABS intervene at every corner, and he (hired bike) didn't even realise his was turned on - the way the light works). But get into loose rock and soil and there's no comparison.

I found getting the rear suspension working right was the single biggest factor in cutting down the number of times and the severity of the ABS intervening on gravel roads and forest trails.

You have to factor in that knobbies are generally designed to spin and remove dirt to get to the traction. If the surface doesn't allow this, they will skate around more than a conventional tyre because there is far less rubber in contact with the loose surface.

A lot of motoX knobbies simply don't give much drive until you spin them hard, or any braking until you lock them solid. Something that doesn't work with ABS unless you drastically change what you are doing.
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Old 06-28-2012, 12:24 AM   #3
14TLC OP
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I still haven't been off-road. Getting used to the bike. For off-road i will for sure disable the ABS. A am more concerned on bumpy tarmac, and not actually with knobby tire, but more like TKC-80 or K60 tire.
I found that it reacts more on slow speed and if you apply just a little force on the brake. The reaction is more on the front and not the rear. Still experimenting. It is my first ABS bike.
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Old 06-28-2012, 12:56 AM   #4
Snowy
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Coming from a dirt bike background I found that I had the rear ABS cutting in all the time when I first got the bike.

Every day on tar. It's like I was trying to get a feel for when it locks, but it doesn't so I just couldn't get the hang of it for some reason. I'd been riding much lighter small sports bikes for a while, as well as my dirt bikes, and I think I was used to a completely different way of braking. I know I used to get my 250 Ninja drifting under brakes really well, controlled and predictable, but for a long while I didn't trust the F800 like that.

First time I rode it on gravel roads I figured it out pretty quick. She's a big girl and the weight distribution is slightly funny, it likes more front brake than I was used to I think, in the way of brake bias.


I put a new front tyre on the other week, a Pirelli Scorpion AT, and the first thing I did was go and ride down a gravel road near home, get it up to 80, and then just mash the front brake lever into the bar. No rear brake, because I wanted to see just how well the AT bit into the gravel.

Full ABS front intervention.

Surprising stopping distance. I've never had a hang up about trusting the ABS, and it is surprising how well it works. Swerving as you're pulling up gives you an idea of the advantages of ABS on gravel. It also gives you a feel for what will go wrong in a panic stop on a slippery surface.

It's a leap of faith thing.
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Old 06-28-2012, 01:23 AM   #5
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Well, I have to learn to trust it and not caught by surprise when it reacts.
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Old 06-30-2012, 09:59 AM   #6
Bayner
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Quote:
Originally Posted by 14TLC View Post
I still haven't been off-road. Getting used to the bike. For off-road i will for sure disable the ABS. A am more concerned on bumpy tarmac, and not actually with knobby tire, but more like TKC-80 or K60 tire.
I found that it reacts more on slow speed and if you apply just a little force on the brake. The reaction is more on the front and not the rear. Still experimenting. It is my first ABS bike.
Mine does that as well (and always has). I'm sure there's something other than wheel rotation it's looking at because mine will do it with VERY little brake force applied, and I mean not enough to stop the tire if it wasn't even in contact with the ground. When you turn into a driveway with a low curb or such mine will do it most times regardless of the type of tire that's mounted. Never got a definitive answer officially or otherwise.
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Old 06-30-2012, 10:56 AM   #7
Travism
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Bayner, I get the same thing when pulling up and going over a bump. Seattle has many roads in bad need of attention and I've found that the abs will engage briefly if I'm coming to a stop and encounter a put hole or a hump in the pavement. I've learned to briefly release the brakes when going over these bits of road "personality". This would happen with the original Piirellies as well as K60s
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Old 06-30-2012, 09:22 PM   #8
Snowy
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Quote:
Originally Posted by Bayner View Post
Mine does that as well (and always has). I'm sure there's something other than wheel rotation it's looking at because mine will do it with VERY little brake force applied, and I mean not enough to stop the tire if it wasn't even in contact with the ground. When you turn into a driveway with a low curb or such mine will do it most times regardless of the type of tire that's mounted. Never got a definitive answer officially or otherwise.
Quite easily explained.

Older bikes used to use a torque reaction bar attached from the brake caliper mount to the frame. When you applied the brakes it stopped the torque reaction of the rear wheel slowing from lifting the rear tyre off the ground.

As suspension got better, they stopped using them. The Standard BMW compression damping seems to be very soft in the initial part of the stroke.

With mine on the centre stand, side stand up, and running in gear, if I tapped the rear brake the rear wheel jumped upwards dramatically.

The Ohlins shock almost eliminated this. The Ohlins with a revalve eliminated it. It is much harder to get the rear end to activate the ABS even on bad brake bumps.

So in short - it's the shocks compression valving.
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