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Low speed low side - WTF??

ThinkFast

ThinkFast

Live Long
Joined
Apr 10, 2007
Location
San RiffRaph
Moto(s)
2012 BMW R1200GS
Name
Tom
Just returned from an awesome supported and guided moto tour of southern Spain and Morocco with a group of riding friends on rental bikes, mostly BMW R1250GS’s, a couple of Honda Transalps, and a couple of BMW F-GS bikes.

On our second day out I crashed in a low speed low side on dry, clean pavement going around 20-30mph. Street tires with I’d guess at least 50% tread and a two-year-old date code.

Corner was a blind, descending, decreasing radius right hander. We’d been riding twisties all morning by the time this happened shortly before noon. The roads were clear of gravel/sand/debris, there hadn’t been any rain for awhile, and the road surface where we crashed was free of any visible contaminants/diesel/oil/antifreeze.

We’d already been through a number of similar switchbacks, so I was comfortable with my speed and line, taking a wide, late apex entry. Because the road was so narrow with no centerline and the exit not visible to me on entry, I was worried about running wide on the exit, so decided to tighten up my apex line. As I brought the bike over to the fog line the front went out without any warning at all. No tire squeal, no smoke. Just gone.
[YOUTUBE]Z0yYzskBTEM[/YOUTUBE]

I was absolutely stunned, as was my wife who was riding on the back. Having racked up tens of thousands of miles as a pillion with me, she couldn’t believe we were on the ground given the speed we were going. I got a few scrapes above my boot top from the pavement and broke or severly bruised a couple ribs in my lower back from hitting the bike after it abruptly stopped when it hit the guardrail (Note to self: let go of the bike when it’s on the ground - you can’t slow it down.:rolleyes). Wife’s foot took a hit and is a bit sore/bruised. We both managed to get back on and ride the rest of the 10 days/2400 mile tour, though. So that was good.

My take on what went wrong: the bitumen in Spain must be different than here. It gets highly polished from traffic and becomes super slippery, even when dry. So the “dollar’s worth of traction” they talk about in classes was more like $0.70 or so.

I noticed this when I was in a city and out walking on the street. Near our hotel was a really tight corner and as cars turned there you could hear their tires squealing on the shiny pavement the same way rubber-soled shoes do on shiny linoleum. Crazy.

Anyway, I’d be curious to hear from this group any thoughts/insights on this crash; or any experience with dry, clean pavement being so damn slippery.
 
I see an additional steering input right before you slid off to the side. You gotta be smooth, especially when leaned over.
 
my last street crash was sorta like this one. coming out of a tight turn leaned way over, I was on the gas to get out of the turn, lost traction, low-side, plop on the ground in an eye blink. was actually on Summit Road just north of Hwy 17, clean and dry pavement. in my case it was too much throttle.

glad to hear you were able to do the 10 days/2400 miles! :thumbup
 
Damn, glad you were able to finish the ride. My untrained eye can't see anything wrong in the video, looks like you have plenty of ground clearance left as you tighten your line and then the front just tucks. Maybe I've been lucky but I've certainly made more dramatic line changes mid corner at that speed of greater without losing traction. Only thing I can think of is maybe the front tire didn't have enough weight on it riding two up with gear, or maybe as John said, application of throttle unweighted the front and cost you that 0.70 cents?
 
ScottRNelson said:
I see an additional steering input right before you slid off to the side. You gotta be smooth, especially when leaned over.
Click to expand...

I watched several times and could not see that. I was looking to see if trailbraking was involved but could not see the brake lever.

N4teTheGreat said:
Damn, glad you were able to finish the ride. My untrained eye can't see anything wrong in the video, looks like you have plenty of ground clearance left as you tighten your line and then the front just tucks. Maybe I've been lucky but I've certainly made more dramatic line changes mid corner at that speed of greater without losing traction. Only thing I can think of is maybe the front tire didn't have enough weight on it riding two up with gear, or maybe as John said, application of throttle unweighted the front and cost you that 0.70 cents?
Click to expand...

Agree with N4te.

That is a weird one. I too am glad you and the wife were not to banged up and continued the ride. :thumbup
 
I would say your analysis is spot on - riding too fast for the slippery tarmac.
 
Frisco said:
I would say your analysis is spot on - riding too fast for the slippery tarmac.
Click to expand...

Problem is, how was I to know the tarmac had such terrible grip?? Never would’ve occurred to me because it’s something I’ve never encountered anywhere else I’ve ridden. Nate mentioned pulling way more radical mid-corner corrections and not having any problem, that is exactly what my thought was too.

It was downhill and I was completely off the gas, so even with the bike fully loaded and heavy in the rear, I’m pretty sure the front was fully loaded and the additional steering input I made to tighten my line was too much for the tire to handle on that piece of pavement and it simply tucked.

I do agree, however, that if I hadn’t tried to adjust my line I would’ve probably made it. But only just. Crazy.
 
ScottRNelson said:
I see an additional steering input right before you slid off to the side. You gotta be smooth, especially when leaned over.
Click to expand...

I see the bars jerk inwards a tiny bit, but I'm not sure that is a steering input. It could be a steering input, a brake input, a throttle input, or just a bump causing the bike to steer itself.

@ThinkFast, which of the above do you think it was? Also, were you trail braking still, at maintenance throttle, or accelerating?

ThinkFast said:
It was downhill and I was completely off the gas, so even with the bike fully loaded and heavy in the rear, I’m pretty sure the front was fully loaded and the additional steering input I made to tighten my line was too much for the tire to handle on that piece of pavement and it simply tucked.
Click to expand...

Off the gas but no brake barely loads the front tire... like 2% loaded. Maybe 3% because it was downhill. You are correct that you need load to make steering inputs, and 3% is often not enough.
 
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ScottRNelson said:
I see an additional steering input right before you slid off to the side. You gotta be smooth, especially when leaned over.
Click to expand...

Yes, that was my thought too. On not hearing any audio in the clip so I was curious it there was throttle input at play too.

Sorry about the crash, glad you were not more seriously injured.
 
stangmx13 said:
I see the bars jerk inwards a tiny bit, but I'm not sure that is a steering input. It could be a steering input, a brake input, a throttle input, or just a bump causing the bike to steer itself.

@ThinkFast, which of the above do you think it was? Also, were you trail braking still, at maintenance throttle, or accelerating?



Off the gas but no brake barely loads the front tire... like 2% loaded. Maybe 3% because it was downhill. You are correct that you need load to make steering inputs, and 3% is often not enough.
Click to expand...

Re front tire loading, I assumed that the downhill angle of attack combined with engine braking from being off the gas (GS->big twin->engine braking) would result in pretty significant weight transfer forward, regardless of no brakes. And that would load the front tire more than the slippery pavement would allow.

I’m sure I’ve done similar turns at similar speeds and loads bunches of times over the years and never had an issue with them, thus my conclusion that the composition of their pavement is different than ours.

Thanks, all, for your comments and concern. Still sore - broken ribs suck! Will continue processing this, although tbh I’m over it. I’m putting it down to a freak occurrence due to an unusual combination of circumstances that will likely not come up again. At least, that’s the hope.
 
I think maybe I was a victim of a phenomenon researchers have dubbed “bituplaning.”

A frictional phenomenon presently observable on some new negalive textured road surfaces in dry conditions, challenges the typical understanding that the frictional properties of any given road surface in the dry are generally superior to those of the same surface in the wet.
Click to expand...

https://saferroadsconference.com/wp...Friction-and-New-Bituminous-Road-Surfaces.pdf

I also found an article about Spanish road construction and their increased use of negatively textured road surfaces to aid in water drainage. Oops.
 
ThinkFast said:
Re front tire loading, I assumed that the downhill angle of attack combined with engine braking from being off the gas (GS->big twin->engine braking) would result in pretty significant weight transfer forward, regardless of no brakes. And that would load the front tire more than the slippery pavement would allow.

I’m sure I’ve done similar turns at similar speeds and loads bunches of times over the years and never had an issue with them, thus my conclusion that the composition of their pavement is different than ours.
Click to expand...

You get more grip with more tire load. So your idea about "load the tire more than slippery pavement would allow" is not entirely valid. Almost no one crashes on street or track because they overloaded the front tire. An underloaded front tire is a much much more common issue.

Engine braking is not that effective for loading the front tire. Think about how much your fork springs compress when engine braking compared to using the front brake. Even dragging the front brakes (ie 5-10% braking) compresses the front end more, loading the front tire more. It's all vector math.

I'm sure the pavement is different than ours and it contributed to your crash. It looks slippery even through Youtube's crap bitrate :laughing. But you may not be optimizing your cornering skills. And that applies to all corners.

This crash seems to be caused by an underloaded front tire, whatever caused that bar twitch, and pavement with less grip than expected. Fix or remove any one of those issues and you probably would have stayed upright. That's true of almost all crashes - it's never just one thing that went wrong.
 
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stangmx13 said:
You get more grip with more tire load. So your idea about "load the tire more than slippery pavement would allow" is not entirely valid. Almost no one crashes on street or track because they overloaded the front tire. An underloaded front tire is a much much more common issue.

Engine braking is not that effective for loading the front tire. Think about how much your fork springs compress when engine braking compared to using the front brake. Even dragging the front brakes (ie 5-10% braking) compresses the front end more, loading the front tire more. It's all vector math.

I'm sure the pavement is different than ours and it contributed to your crash. It looks slippery even through Youtube's crap bitrate :laughing. But you may not be optimizing your cornering skills. And that applies to all corners.

This crash seems to be caused by an underloaded front tire, whatever caused that bar twitch, and pavement with less grip than expected. Fix or remove any one of those issues and you probably would have stayed upright. That's true of almost all crashes - it's never just one thing that went wrong.
Click to expand...

Huh. Interesting. That makes sense, too.

What’s surprising to me is that it happened at all in the dry, and not going that fast. I’ve low sided on the track before due to too much speed for the corner, so that would be an example of what you’re talking about I think. But the street environment is so different - or at least it is the way I ride it. I damn nearly drag my pegs on my GS in the dry running a big block knobby front which has nowhere near the contact patch of a road tire, but still hangs on because I’m nowhere near the limit of traction at the speeds I go through a given corner.

Re never just one thing - that would seem to be the case here - a perfect storm of bad inputs on my part meeting up with bad conditions. At least when I crashed on the track I could go back and dissect it and figure out why. This one is a bit unnerving that way because I just don’t believe it would’ve happened on the roads I’m used to riding on.

Thanks for your input - really helpful.
 
Sorry to read this Tom, but glad it was low speed and everyone's all good.

I'm with Robert, but also noting the weight bias towards the rear with the wife/ boxes and pretty decent acceleration into the corner. Thinking the same thing: unloaded front tire + lean angle = small contact patch and high bar leverage pushes overwhelms whatever contact patch exists. Combine that with the road surface you talked about and that's all she wrote.

The weight bias + throttle is where I'm at. Other than that, the trip looks well worth doing!
 
Thanks. Yeah, I think that’s about it. As always, smooth=good in the corners. Set it and forget it.
 
Yeah, the "loading == traction" becomes absolutely obvious the first minute in a rally car in the dirt. Without weight on the front, steering doesn't do jack -- the wheels are turned, and you plow on ahead. Rotation begins with weight transfer forward.

And take the glorious videos of tourist spin-outs on the Nurburgring. They start to get sideways, panic brake, and spin into the barriers. In hitting the brake, they're inducing the most effective rotation -- the front (pivot) is biting hard, the rear is unweighted, there's already yaw.. goners.
 
I see problems with the lane positioning. You entered that turn very wide; would've been very difficult to deal with an oncoming vehicle cutting the corner. When you tightened the line, you ended up early apexing by the time you crashed. The whole event seems to indicate excessive entry speed and tightening the line made it worse. (I would hug the inside fog line the whole time in blind turns like that.)

The litmus test: Were you riding faster than everyone else in the group? Did anyone else crash in that corner? If no one else crashed there, then it's likely something you did, rather than a random event.
 
I do always worry about slippery pavement. Spent quite a bit of time on wet roads where moss was growing on the shoulders yesterday and just assumed things were slick as snot. There's also a section of road on TAM (Pantoll road) where the sap from overhanging trees has made the pavement shiny and slick enough to cause a handfull of bicycle crashed (or so those who crash have said). Never had a problem on my moto but the appearance of that pavement always slowed me down a bit. Negative textured roads sound worse that chip seal, and I hate fresh chip seal.
 
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