Not quite Sport Touring: Sand

[doc47]

I went riding with David Beardsley Sunday before last. We met at the Tanji River Bridge at 9:30; the sun sharing sky room with cumulus banks. The point of the exercise was 1. To have a good time riding, 2. Get to know each other a bit, and 3. For me to learn some off-road riding skills, especially how to get through deep sand.

David was leery of my relatively smooth “dual sport” tires (Metzeler Tourance), which are designed for relatively firm surfaces: asphalt, gravel roads, light sand. “Let’s,” he suggested, “follow a track down here that’s reasonably well-packed. There are sections of deep stuff, but they don’t last long. Are you up for it?” I certainly was. I was also reasonably nervous about the deep stuff. Same sort of anxiety I would feel standing at the top of a steep ski slope with waist-deep powder. Not something I’m used to and afraid of consequences.

David rides a Honda XR-650; a dual-sport closer to a pure dirt machine than my BMW. It is old technology, with a bullet-proof, carbureted engine from the ‘80s, traditional tank layout, and a suspension he has tweaked a bit. He rode trials, endure and moto-cross for many years as a member of the British Army racing team. He knows his machine. He knows how to ride it. And he is essentially fearless. Not my traits at all!

With a twist of the throttle and a scatter of dirt and pebbles from his knobbies, he skidded the back end around 180 degrees and was off with me in teeth-gritting pursuit. Onto the asphalt of the coastal road, down a kilometer, then abruptly off the pavement onto a dirt road into the bush. Mourning doves and ring-necked doves exploded from the road before David’s tires. I watched him cross a deep patch of rutted sand with a sudden blast of throttle. I tried to stay in the tire tracks left by automobiles while trying to follow David’s line and emulate his throttle technique. Nonetheless, my rear tire was fishtailing and occasionally the front tire would start weaving back and forth in the sand. My heart was in my nose by now and twice I almost lost control of the front wheel. I was sitting back on the “step” of the passenger seat, trying to keep my shoulders relaxed, wondering if my death-grip on the handlebars would leave dents. I was also wondering when the seemingly inevitable dump would happen and hoping I wouldn't have any dents of my own.

The deep sand was just a bitch. I was scared every moment I was in it and was right at the edge of control. After a few kilometers I finally told David it wasn’t working for me. He agreed. He’d noticed I’d almost lost it a few times and suggested we go back and ride some packed roads to a beach side restaurant he knew and have a nice cuppa tea. So we did. We made it back to the coast road without me making a fool or a cripple of myself. After that sand the dirt road was a piece of cake. Past ladies carrying buckets or baskets on their heads, sheep wandering the road, and men driving donkey carts.

We settled down to cups of good English tea at an al fresco bar overlooking the beach. One doesn’t converse with David. One attends. He told me stories about his days with the British Army Racing Team, racing in the UK and on the Continent. Well worth listening too they were, as well. He talked about arriving, for example, at a track in the mountains in Germany. The team would get there a couple of hours early for the race and spend their time running the bikes (BSA 350 and 500 singles) and experimenting with the jetting of the carburetors and suspension setup. He had a notebook in which he’d enter the parameters for that specific track with the particular atmospheric conditions and, armed with this notebook, he could return years later to the same track and know how to jet his carb, what tires to use, etc. Sort of like the rutters kept by ancient navigators.

We talked about tires and about suspension setup. I asked him if he’d take a ride on my bike to get an impression of what needed to be done. He declined. “With those tyres I won’t like it. Get your proper tyres first,” he said. “Then I’ll ride the bike and we can start setting up the suspension.”

“In the sand,” he said, “you’ve got to use the throttle and ride fast!” He got off his chair and squatted down on the sand. “Here’s what happens when you’re riding slow.” He took the knife-edge of his hand and pushed it through the sand. I watched a bow wave of sand form and flow away from the sides of his advancing hand. “See, you’re pushing the sand out of the way. Now, hit the sand with your fist.” He punched the sand. I punched the sand. It hurt! Its behavior was different when struck than when pushed.

“If you hit the sand hard with your tire you don’t give it a chance to flow away,” he said. “It acts like a solid.”

It hit me suddenly, the analogy with boating physics. Sand, like water, is a fluid when pushed slowly. It is solid when it’s hit fast.

The motorcycle tire moving slowly through sand is like a boat with a displacement hull. The sand parts and flows along the sides. Speed isn’t going to happen. Once you start moving faster a different physics goes into play. The tires become planing hulls. They ride up on top of the sand and, as in a boat, the captain has to keep the power on or the hull/tires settle back down, become displacement hulls and the sand becomes a fluid again. Ride fast enough to turn the sand to a solid and things become more predictable.

“It’s the transition that’s tricky,” he said. “It’s while you’re getting from riding slow to where you’re up to speed that’ll get you in trouble.” He was, of course, right, but I found that giving it power, just like in street riding, settles the back end down (just like a boat "squatting"), lightens the front wheel, and gets you through.

So, how is changing direction accomplished? A boat, planing at high speed and trying to change direction will drift sideways unless prevented by some lateral force. In the case of the boat it is the keel or skeg or centerboard. In the case of my motorcycle it is the meager side ridges on the tire treads. On David’s bike it was the sides of the knobs on his tires. On mine, I had very little of this lateral resistance and I tended to drift out. Some of that drift could be countered.

There are various techniques for turning but the one David explained to me and the one I used was contrary to all my street training. You stay upright and lean the bike under you. Weight on the outside peg forces the tire straight down into the sand. With the bike leaned over and weight pushing down the centrifugal force of the tire pushes sand to the outside of the turn and, at speed, this wall of displaced sand becomes an instant berm, pushing back against the tire. Force and counterforce. Pure Third-Law Newton.

We finished our tea and David proposed we ride the beach back home. Fine with me. I’m up for a nice, leisurely ride to settle my still-frazzled nerves. We mushed through the deep stuff and got out to the firm sand at water’s edge. There were gulls and fairy terns overhead, broken shell and cuttlebone in the sand and David set off like he had a hot date waiting at home. (Perhaps he did!) 60, 70, 80, 90 kilometers per hour. I kept trying to relax my shoulders and grip and gradually it worked. I experimented with leaning the bike, sensing the counter-push of the sand against the tires.

David would get well ahead of me and then noodle off into the deep sand up the beach, wasting time until I caught up. He did this twice and then I figured, “Sod it!”, turned up the wick and raced him all the way to Brufut Village. I kept thinking of the book A Twist of the Wrist, II, and the constant admonishment to fight one’s normal survival instinct to back off the throttle. Crank it on! Apply power. Power is what settles the machine; what gets you through.

We parted in Brufut, both with many things to do with the rest of our day. It has been nine days since that ride and my confidence in the sand has leaped exponentially. Thanks for the great mentoring, David.

 

[Francois_Dumas]

Great story Doc, and interesting too. The analogy with speed boats is great and makes sense. Never thought of that :-)

[roadscholar]

That's the best explanation I've ever seen for riding sand, thanks Doc. I've had to learn how because it's nearly the only off-road surface we have here in Florida (when its dry). Once you do it you realize going fast is far better than going slow, the bike tracks much more predictably. Never heard anyone explain it in terms of physics though, fascinating. I think of it as motorcycling's leap of faith (making the transition), your brain has to make your hand twist the throttle, something it doesn't want to do, but once you cross the threshold, all is good, usually. We have some very long, flat stretches of dirt roads with about a four inch layer of loose sand on top. When you go very fast on them the bike seems to raise itself onto the very top almost like a hydrofoil and becomes completely controllable. I've often thought of it as skiing in powder also, a good analogy.

[russell_bynum]

. I think of it as motorcycling's leap of faith (making the transition), your brain has to make your hand twist the throttle, something it doesn't want to do, but once you cross the threshold, all is good, usually.

 

Yup.

 

Tires make a big difference, though. I just put new tires on my DRZ to replace the old worn out ones that were on there before. The difference was like night and day. Seriously. I thought I'd forgotten how to ride because every time I'd hit a sand wash (out west we've got lots of deep talcum powder sand) I'd wind up with the bike doing war dance and me just holding on hoping I hit something soft when I came off. With new tires, everything was back to normal.

 

But...though I think that better tires make it easier and allow you to go slower while still being somewhat in control, you're definitely right...there's a threshold that you have to cross. It's hard because logically you know it will be better if you just open the throttle, throw your weight back, and steer with your feet. But then there's that part of your brain that says "yeah...but then you're going that much faster when you crash."

 

 

I really enjoy the sand on my DRZ (with newish tires)....just blazing down the washes wide open in 4th or 5th with the bars dancing around is a hoot.

 

Now...if I could just figure out how to ride in mud....

[roadscholar]

Tires are the big variable and I've never put enough emphasis on them. When I put TKCs on it makes things a lot more fun, but many times I just leave the 607s or Tourances on the big bikes because there's a good deal of back and forth on pavement. If its real soft you have to stop and let the pressures down to 20 or so, which helps considerably.

 

Mud? Your guess is as good as mine, I try to avoid big stretches of it, too much work for an old guy. I remember completely submerging a Husky 250 once where they used to run The Alligator Enduro in Daytona, it was the last time I tried that.

 

 

 

 

[Huzband]

Mud's easier than sand. More fun, too.

[russell_bynum]

Mud's easier than sand. More fun, too.

 

Not for me. I can handle sand, but every time I get in mud I find myself going backwards at 30mph...without my motorcycle.

[doc47]

Mud's easier than sand. More fun, too.

 

Only if you're wrestling a woman!

[Huzband]

I suppose it has a lot to do with what conditions you grow up riding in. Not much sand in N. Al., but plenty of mud, especially in the winter months.

 

I can show you how to ride in mud, but I don't think I can describe it here.

[AviP]

“In the sand,” he said, “you’ve got to use the throttle and ride fast!” He got off his chair and squatted down on the sand.

The motorcycle tire moving slowly through sand is like a boat with a displacement hull. The sand parts and flows along the sides. Speed isn’t going to happen. Once you start moving faster a different physics goes into play. The tires become planing hulls. They ride up on top of the sand and, as in a boat, the captain has to keep the power on or the hull/tires settle back down, become displacement hulls and the sand becomes a fluid again. Ride fast enough to turn the sand to a solid and things become more predictable.

Very well said Doc. I experienced deep gravel (not sand) in Newfoundland and it scared the bejesus out of me. But I plodded on steadily increasing my speed, building confidence, working the turns without getting off the throttle. About 30 minutes later, I was doing a confident and exhilarating 100 mph and steering with throttle. Oh yeah, it was on the RT.

[Huzband]

The motorcycle tire moving slowly through sand is like a boat with a displacement hull. The sand parts and flows along the sides. Speed isn’t going to happen. Once you start moving faster a different physics goes into play. The tires become planing hulls. They ride up on top of the sand and, as in a boat, the captain has to keep the power on or the hull/tires settle back down, become displacement hulls and the sand becomes a fluid again. Ride fast enough to turn the sand to a solid and things become more predictable.

 

I get it. The GS was actually a boat.

 

Now I get Whips anchor jokes.

[outpost22]

Good show Doc. You also must realize that in addition to him being an accomplished rider, the bike he is riding handles much better off road than yours. He also has a 21" front wheel as opposed to your 19" wheel which helps a LOT in sand in addition to his bike weighing a lot less.

Sand techniques of "riding fast" is the ticket right up until the point you have to slow down. Then things can get interesting, especially if you're loaded with touring bags.

 

The little KLR 250 in the picture didn't have near the "plowing" effect my bike had on this sand in Mexico.

 

[doc47]

It does make me wonder why BMW insists on odd-sized tires. I could be wrong here but it seems most off-road bikes have 21" front and 18" rear. Of course, the Dakar has a 21" front, but still has the 17" rear for which there are far fewer choices of tires.

[outpost22]

Doc,

It's all about seat height and suspension. A 21" front wheel will raise your ride height and the rear set-up has to match it. Just look at a Dakar (21" front wheel) next to our standard F650GS. The seat is probably 2" higher on the Dakar. This can be "tippy" in slow going, but a boon on the off road stuff at speed. Conversely, the cornering on the standard GS with 19" wheel and 17" rear will corner on pavement better. It's all about trade-offs.

No matter what anyone says, the F650GS is no "sand machine" compared to real off road capable bikes. My old KTM's never would flinch in sand whereas this bike tucks it's tail (or nose as the case may be)

[bimmers]

No one mentioned SNOW.

That is of course depending on the temperature ie consistency of the snow. In real cold it is fluffy like sand and in wet it is close to mud, sometimes a blend.

 

Speed is key I guess in most cases where the surface is soft, you try to stay as high as possible and with loose arms..if you can.

 

I was disappointed in the F650GS being so heavy and cannot imagine the 1200GS in same conditions.

 

 

h

[Endobob]

“In the sand,” he said, “you’ve got to use the throttle and ride fast!”

 

Very well said Doc. I experienced deep gravel (not sand) in Newfoundland and it scared the bejesus out of me. But I plodded on steadily increasing my speed, building confidence, working the turns without getting off the throttle. About 30 minutes later, I was doing a confident and exhilarating 100 mph and steering with throttle. Oh yeah, it was on the RT.

 

I understand and often have used speed to keep going through sand, mud, and snow, however, I can not image running at 100 mph in deep gravel!

[doc47]

“In the sand,” he said, “you’ve got to use the throttle and ride fast!”

 

Very well said Doc. I experienced deep gravel (not sand) in Newfoundland and it scared the bejesus out of me. But I plodded on steadily increasing my speed, building confidence, working the turns without getting off the throttle. About 30 minutes later, I was doing a confident and exhilarating 100 mph and steering with throttle. Oh yeah, it was on the RT.

 

I understand and often have used speed to keep going through sand, mud, and snow, however, I can not image running at 100 mph in deep gravel!

 

+1. 100 is jest a bit quicker than I think I'd like to go on anything unpaved.

 

As for snow? Check out Paul Mondor.com for a man who really knows snow. Paul used to be active on this board but got busy on his own. He's a kick and a great storyteller.

 

Tire sizes: you are right. Motorcycles, like anything else that's designed, have to be trade-offs. If you want something you have to give up something else. The F650 isn't the best at anything but it will do a lot of things pretty well. I like the bike more and more all the time.

[Lineareagle]

One doesn’t converse with David. One attends.

 

I really enjoy 'attending' when the person I am attending knows what they are talking about. David, is surely one of those.

 

The truly sad thing about riding sand or gravel is that timidity or hesitancy result in nastiness, and although going faster presents the feeling of control in fact you are on the edge of no control until you have many hours in the stuff and a few spills along the way. DAMHIK

 

It is however a skill every rider should work on but I would suggest to most that starting out on a 250 is much more realistic than taking the 700 pounder into the fray.

 

The other thing is as all analogies the boat one will only take you so far. Because if completely true then the smoother the tire the better, in sand, of course that is not the case you do want the blocks to grab chunks of material to maintain the line and resist the slip. You do not want them to go off seeking their own path.

Woe to the person that hits a cross rut while planing through the sand, on any tire! Or hits a tub of sand on a packed road!

 

At any rate your and Dave's description makes me want to ride the dirt again in the new year.

Thanks for the re-up.