Ascending vs Descending Curves - Stromtrooper Forum : Suzuki V-Strom Motorcycle Forums
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post #1 of 14 Old 12-01-2015, 08:17 AM Thread Starter
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Ascending vs Descending Curves

I've returned to riding after a long (40 year) hiatus. I now live in the mountains of NC in the USofA. Question: Why do I have to lean much more on ascending curves compared to descending curves?

Am blessed with some super mountain roads, very steep, very tight switchbacks. When ascending, it feels like I'm leaning well past 45 degrees to get the 650DL around the corner. This is in 2d gear at fairly low speeds (20-25mph). Going downhill, I don't have to lean that much.

Just curious, why does the bike/rider combo need that much lean going uphill?

I know that the suspension is loaded very differently in each case. Going uphill, at least 2 factors load the weight on the rear: 1. The front wheel is higher so the weight is naturally shifted to the rear. 2. The bike is using the engine to overcome gravity, so this shifts weight to the rear as well.

Going downhill, the opposite is true. The weight shift is to the front as the bike/rider are tilted forward and engine braking plus brake system are pushing the masses forward.

Does this suspension shift change the steering geometry that much? It must but I don't understand why. I have not seen this discussed anywhere in a book or online.

Any thoughts from you smart Stromtroopers?

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post #2 of 14 Old 12-01-2015, 09:33 AM
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Are you sure it's not just a perceived difference. The laws of physics and lean angles shouldn't change in up vs. down. The amount of lean is solely determined by speed but I know what you're saying. I feel less confident in downhill switchbacks. Your ground clearance might change slightly as the suspension is compressed or extended.
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post #3 of 14 Old 12-01-2015, 11:04 AM
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I suspect it is a perception difference. Gravity assists you going up and works against you going down (speed/acceleration/deceleration wise). I know I go faster around a given corner going up than I do coming down. Also, I am better (faster/more comfortable) on left hand corners than I am on right, so if I go up and down the same hill, the corners are reversed. I wouldn't think that gravity has a significant effect on the steering geometry.

A good way to tell is to have someone follow you with a GoPro and then look closely at the footage. Try to have the camera include the speedo as well if possible.

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post #4 of 14 Old 12-01-2015, 11:46 AM
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Well, braking causes the bike to go upright (watch this section of the twist of the wrist video, it's discussed in the SR of braking in a turn), so maybe the perception is very different because you are braking when going down which pushes you upright, versus accelerating going up which helps you to get deeper into the lean.

It may not be perception at all, you actually are more upright going down, but it's just because you are braking. You may also take a very different line when braking through a curve versus accelerating through a curve, so your accel's may be a tighter, or more aggressive line than your braking.
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post #5 of 14 Old 12-01-2015, 12:13 PM
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Going down hill the weight bias is towards the front, especially so if braking. So the bike turns in faster and wants to fall into the turn.

Not being on the gas doesn't allow the bike to want to come back up so you need less lean angle to make the turn.


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post #6 of 14 Old 12-01-2015, 12:55 PM
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Gravity. Imagine a plumb bob hanging from your shoulder as you lean into a turn going uphill and then downhill.
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post #7 of 14 Old 12-01-2015, 02:00 PM Thread Starter
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Thanks for the feedback.

Spec, what you wrote makes sense. Using the throttle going uphill makes the bike want to straighten up, so I have to actively force it to lean more.

I also think it may have something to do with the tire footprints. The front tire footprint going uphill must be very small.

Or, I'm just imagining stuff.

Does anyone else feel they lean more going uphill????

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post #8 of 14 Old 12-01-2015, 02:13 PM
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Post accurate perception, interpretation amiss

Quote:
Originally Posted by Stan Moore View Post
Thanks for the feedback.

Spec, what you wrote makes sense. Using the throttle going uphill makes the bike want to straighten up, so I have to actively force it to lean more.

I also think it may have something to do with the tire footprints. The front tire footprint going uphill must be very small.

Or, I'm just imagining stuff.

Does anyone else feel they lean more going uphill????
As another said, the lean is unchanged, at least with respect to the direction of gravity. What changes is this: If you are looking forward during the turn, (as we all should), you are closer to the upcoming roadway when it is uphill than when it is downhill. Also, you interpret lean relative to the surfaces you see rather than the gravity vector. The perception is a bit illusory.
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post #9 of 14 Old 12-01-2015, 05:31 PM
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Quote:
Originally Posted by Nelsonmd View Post
Well, braking causes the bike to go upright (watch this section of the twist of the wrist video, it's discussed in the SR of braking in a turn), so maybe the perception is very different because you are braking when going down which pushes you upright, versus accelerating going up which helps you to get deeper into the lean.

It may not be perception at all, you actually are more upright going down, but it's just because you are braking. You may also take a very different line when braking through a curve versus accelerating through a curve, so your accel's may be a tighter, or more aggressive line than your braking.
This would be the correct answer. Most any breaking in a corner will upright (or more) the bike irrelivent of terrain thereby changing the bikes trajectory unless additional body lean is used. Eventually a rider should learn to scrub speed before the entrance of a corner allowing them to throttle though. This is equally important when descending a roadway corner, just less throttle will be employed as with level or ascending terrain

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post #10 of 14 Old 12-01-2015, 05:46 PM
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Hmm, interesting theories. For whatever reason, the down hill right hander is my nemesis. I have to chuck the bike harder into these than anything else. Why? I believe it is due to the bike being front loaded and perception being that I am farther in than I actually am. This would be opposite to the OP as uphill the bike seems to fight falling into the corner, but downhill it wants to dive into the corner. It shouldn't be brakes as I tend to trail brake coming into sharp bends. I would like to see a video of the OP and his position in the different corners. This would make it clearer if it is perceived or actual positioning.
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