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Old 03-21-14, 07:33 AM   #1
dbg
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"Plowing" through loose gravel

I plan to experiment on this myself but am wondering if others have real experience.

On my light touring setups (road bike geometry, with approx 55 - 60mm of front fork trail) I have experienced an effect in loose gravel I refer to as "plowing" --where I attempt to turn the front fork to adjust balance or correct path and the bike seems to just plow straight ahead.

My theory is that high trail is a significant contributor to this effect --and that low trail will make gravel grinding noticeably easier. Anybody with very low trail (less than 40mm) experience "plowing" in loose gravel?
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Old 03-21-14, 07:58 AM   #2
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In my experience, shifting weight rearward, MTB-style, solves the problem for a lot less money.

Between my three bikes--all drop bars with variations on a theme of road geometry--I have high-trial, neutral, and low-trail covered. The low-trail bike plows just as much, but its natural tendency to pop upright by itself masks the condition. Yes, it pops upright and stops plowing, but it follows a straight line when it does so rather than completing the turn.

Standing on the pedals and shifting my weight off the back of the saddle (pulling back and up every so slightly on the bars) allows the front wheel to float up out of plowing and complete the turn. I get a lot of practice with this technique commuting through the winter. Even a studded snow tire will plow in loose and slippery conditions.

Loaded rear panniers also relieves the condition without my having to move myself around.

Of course, the other, less desirable solution is to simply slow down. But who wants that?

EDIT: Now, what makes the low-trail nice in the rough stuff is exactly its tendency to stay upright and moving straight ahead. It's not pushed around off line nearly so easily as my other bikes. This is especially pronounced on the cobbles, particularly on cobbled descents where my low-trail bike lets me go faster becasue it holds its line so much better. It's exactly the reason why Eddy Merckx preferred a low-trail bike in the classics.

So for a gravel grinder, I think low-trail is the way to go, even if it doesn't, by itself, solve the plowing problem. My neutral-handling Litespeed is my second choice on dirt and gravel.

The high-trail Portland rates a distant third, even though I switch to 34mm cyclocross tires in the dirt and gravel. The benefits of high-trail come at faster speeds than I usually ride off pavement. In the snow at low speeds, high-trail works against it, I think, because of how light the steering becomes at low speed. But it's my only bike that fits studded snows.

Last edited by tsl; 03-21-14 at 08:11 AM. Reason: i before e
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Old 03-21-14, 08:43 AM   #3
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Definitely following this thread, thanks for making it OP. Great info for my gravel grinder build in progress.
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Old 03-21-14, 08:58 AM   #4
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Paging @BluesDawg.
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Old 03-21-14, 08:45 PM   #5
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Paging @BluesDawg.
I have never ridden a low trail bike (AFAIK). I usually try to limit steering input and shift up and pedal harder through sand or loose gravel.

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Old 03-22-14, 11:00 AM   #6
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My Cyclocross bike with a 66mm trail is neutral: allowing both tires to drift when exceeding traction on loose-over-firm gravel (aka ball-bearings). I notice that the front will push (to use a NASCAR term) at the beginning of the turn but that the tail will also drift as the turn continues. I try to "stay the course" or gently increase the turn radius when this happens, since changing positions or correcting the steering abruptly can lead to a fall.
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Old 03-22-14, 12:22 PM   #7
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small wheel bike , & low trail .. but you got farm roads graveled out there they are logging roads

and at the top of hills, here .. corners in gravel develop berms to their outsides .

I've seen towns in NL where they use interlocking fired brick pavers on packed sand,
and the pavers berm up too .



DIY science time .. learn by testing ..

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Old 03-22-14, 02:35 PM   #8
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My Cyclocross bike with a 66mm trail is neutral, allowing both tires to drift when exceeding traction on loose-over-firm gravel (aka ball-bearings). I notice that the front will push (to use a NASCAR term) at the beginning of the turn but that the tail will also drift as the turn continues. I try to "stay the course" or gently increase the turn radius when this happens, since changing positions or correcting the steering abruptly can lead to a fall.
I don't think the automotive use of "neutral" handling is the same as with bicycles. And 66mm seems to be fairly high rather than neutral.

My go-to reference is Trail and Its Effects at Spectrum Cycles. Quoting:
Quote:
As a general rule when dealing with 700-C wheels, a trail of about 56mm will give a frame set "neutral" handling. My use of the term "neutral" here refers to two things. First, neutral handling means that a frame set will respond to steering input in the same manner no matter what speed the bicycle is traveling. Second, while cornering, a neutral handling bike will have neither a tendency to climb out of a turn nor have a tendency to dive into the turn, it will simply hold the line that the rider sets up unless further rider input is applied.
My high-trail bike is my cyclocross-based Trek Portland. I think designers choose high-trail for CX bikes for the light steering feel at the lower speeds of cyclocross.

For the record, automotively, what we call "trail" is referred to as "caster", and is a front wheel alignment matter. While felt in handling, other factors influence oversteering, understeering and neutral handling.

Last edited by tsl; 03-22-14 at 02:45 PM.
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Old 03-22-14, 02:53 PM   #9
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I don't think the automotive use of "neutral" handling is the same as with bicycles. And 66mm seems to be fairly high rather than neutral.

My go-to reference is Trail and Its Effects at Spectrum Cycles. Quoting:
The term "neutral" is used in a normal way to describe handling. Neutral is commonly used to describe behavior without bias. In this use, the bike has no bias towards the front tire, in the way PO stated. I'm not using it to describe the amount of trail.
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Last edited by Barrettscv; 03-22-14 at 03:07 PM.
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Old 03-22-14, 03:23 PM   #10
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The term "neutral" is used in a normal way to describe handling. Neutral is commonly used to describe behavior without bias. In this use, the bike has no bias towards the front tire, as the PO stated. I'm not using it to describe the amount of trail. Are you incorrectly using one term in one sentence to have implied meaning in another?
Putting it more clearly, when we speak of neutral handling in automobiles, we're referring to the interaction between steering and vehicle yaw angle. With bicycles, we're referring how steering interacts with vehicle lean angle. Most cyclists don't yaw their bikes in turns, but we all lean them.

It was mistake to introduce the comparison of bike trail angles with car caster angles. Where I was heading was that car caster angles don't directly affect yaw angles, whereas bike trail angles directly effect lean angles, or rather how we achieve, hold, then straighten from them. While what I was meaning to differentiate was automotive use of neutral (yaw) vs. cycling usage of neutral (lean).

Back to the OP, the differing amount of trail in my bikes don't seem to greatly affect how the bike plows, pushes, or understeers (choose your term) in loose stuff, whereas weight transfer does, and to a significant degree in my experience. Trail does effect how my bikes track over bumpy surfaces.
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Old 03-22-14, 03:39 PM   #11
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Putting it more clearly, when we speak of neutral handling in automobiles, we're referring to the interaction between steering and vehicle yaw angle. With bicycles, we're referring how steering interacts with vehicle lean angle. Most cyclists don't yaw their bikes in turns, but we all lean them.

It was mistake to introduce the comparison of bike trail angles with car caster angles. Where I was heading was that car caster angles don't directly affect yaw angles, whereas bike trail angles directly effect lean angles, or rather how we achieve, hold, then straighten from them. While what I was meaning to differentiate was automotive use of neutral (yaw) vs. cycling usage of neutral (lean).

Back to the OP, the differing amount of trail in my bikes don't seem to greatly affect how the bike plows, pushes, or understeers (choose your term) in loose stuff, whereas weight transfer does, and to a significant degree in my experience. Trail does effect how my bikes track over bumpy surfaces.
Both the automobile and the bicycle can be tuned to handle. On a bike: wheelbase, bottom bracket drop, trail, and other factors produce a variety of outcomes. The automobile designer must consider weight distribution, wheel camber, anti-roll bars, springs and other factors. It would be a mistake to discount one specification just to make a rhetorical statement.
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Last edited by Barrettscv; 03-29-14 at 03:09 AM.
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Old 03-22-14, 08:35 PM   #12
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Thought about this thread today as my wife and I ran into a pile of gravel on an off camber turn. Neither of us went down but she had quite a scare when her front wheel did a little skid. I made more noise than anything else, but it did give an exciting few seconds.
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Old 03-28-14, 09:16 PM   #13
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Both the automobile and the bicycle can be tuned to handle. On a bike: wheelbase, bottom bracket drop, trail, and other factors produce a variety of outcomes. The automobile designer must consider weight distribution, wheel camber, anti-roll bars, springs and other factors. It would be a mistake doesn't discount one specification just to make a rhetorical statement.
This is true-ish, but changing those factors on a bike takes money and effort. At least for conditions around here (more sand than gravel), I cope by using larger tires, shifting my weight to the rear and avoiding sudden inputs. And at 69, I'm not too proud to get off and walk when necessary.
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Old 03-29-14, 07:31 AM   #14
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Both the automobile and the bicycle can be tuned to handle...
Agree, but the process and characteristics are a lot different. A big difference is that a bicycle or motorcycle needs to balance, leans into a turn and preferably does not fall over. A car doesn't and can't fall over.
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