Maximum trail okay with a barbag?

[satanas]

So, currently I'm touring in Europe on a GR, but eventually this will be replaced with a custom frame. (Yes, I'm fussy.)

I get the attraction of low trail, as the bike really wants to turn, however the almost-shimmy when hitting bumps at speed aggravates me, and I'd prefer more straight line stability.

So, how much trail can one have with 42 mm tyres before things get clunky with a barbag? FWIW, I'm not likely to ever use rear panniers; fronts and a seatbag are a yes though.

Thanks,
Stephen

[Mark Bulgier]

Plenty of people have enjoyed the ride of a typical modern racing bike, say 50 to 60 mm trail, with a bar bag, so I wouldn't say low trail is a must.  My commuter is a repurposed old racing bike with a front rack, and I often bring home a heavy bag of groceries or a case of wine.  I wouldn't call the handling optimal, but it hasn't bugged me enough to bother making a low-trail fork for it.

For me the suboptimal handling of high trail with a front load crosses the line from the subliminal to the noticeable, but well short of annoying.  If I don't obsess over it, I'd say it's easy to forget about it and just get used to it.  Other people no doubt would find it intolerable.

Obviously we hope for better than "just get used to it" with a custom bike, so ideally you'd want to try some bikes with a front load and low, medium and high trail to decide for yourself before committing to the expensive custom.  For testing – most forks can have rake added or subtracted.  Fender clearance will change, so this is not ideal, and maybe best to do on a junk fork not an expensive one.  Brakes with not much up/down adjustability (such as most cantilevers) can be a problem too.  In a worst-case scenario, changing the rake a lot could mean you have to move the canti posts a little too, and a repaint.  Theoretically it also moves the front of the frame up or down, changing frame angles and BB height, but those changes are generally too small to notice.

A few folks have made adjustable-rake forks for testing to decide on what trail they like. Can be as simple as using rear long horizontal or track dropouts.  You can even leave the adjustable fork on the bike long-term, if you don't mind that it's heavier (and ugly).  I used one once but so long ago I don't remember what I decided.  I was mostly a racer then and didn't test with front loads anyway, plus that was with skinny high-pressure tires. 

I think my main take-away was how little it mattered, for a racing bike.  I could get used to the handling over a wide range of rake/trail numbers, and I've found that most other people can too.  Which makes it hard to know if the handling is optimal, or just what you're used to.  I think I settled on a high trail for racing mostly for the ease of riding no-hands while taking my jacket off, and not crashing while doing a victory salute.  ;)  

Sorry about the racing bike digression, not what you asked about.

Mark Bulgier
Seattle

[Stephen Poole]

Thanks Mark!

I've got an adjustable rake fork with long road dropouts like you describe, but for 17" or 20" wheels, I can't remember which now. Building another is an option, but I was hoping to avoid doing so if there was a consensus. In fact two may be needed, one for 700C as well...

My old Tony Oliver 700C audax frame is 73*45 mm, and that was bearable (if not ideal) with a Carradice barbag, so I agree trail isn't super crucial. I quite like 60-ish mm on road bikes, and more on small, light wheels.

Later,
Stephen

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[David Pertuz]

My primary bike is a Rawland cSogn on Hetres, which I believe has trail in the low to mid 50s with those tires. I have carried moderate front loads for years now in a boxy bar bag (first a smaller V-O, now a larger Ostrich), and I think the handling is perfectly fine. Typical loads range from the weight of the (Nitto) Rack and bag, plus a tool roll and tube, to all of that plus whatever else I need to carry that I can cram into it. I certainly would not call the handling clunky. I can feel it when I have a lot of weight up front (e.g. all of the above plus a growler of beer, which I have done) but it is not annoying. With typical loads it has become normal, and on the rare occasions that I've ridden the bike without the bag, it feels odd. I have had very little experience with low-trail handling, having only ridden an unloaded rSogn once. My other everyday bike is a One Way with trail that is lower than the cSogns, but not low. So I find low-trail handling to be a bit odd. I'd say up to the mid-50s is fine.

David

Chicago

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[Stephen Poole]

Thanks David. I think I'm inclined to agree with you regarding low trail handling...

Later,
Stephen (who spends way more time going in a straight line than cornering)

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[David Banzer]

My experience echoes David P. I've hung on to an '84 Schwinn Voyageur and used it primarily for a few years as a commuter with a large rando bag carrying substantial loads - dense stuff overfilling bag. It handles perfectly with a front load and feels funny to me now without any front load as I've rebuilt it temporarily with just a rear rack. I was surprised to look up the specs after riding it for a long time and find out that the trail was in the 50s, could've sworn it was lower.
David
Chicago

[David Banzer]

My last comment was not 650b specific, I now see. FWIW my experiences are the same on 650b bikes as well.
David
Chicago

[rcnute]

Mark, just for that we need a victory salute photo.  Then or now acceptable.

Ryan

[Mike Schiller]

just for the alternate point of view... I got rid of all my mid trail bikes because for me, the handling is so much better overall with a well designed low trail bike.  While I believe most of us can adjust to the way a mid trail bike rides with a front load I enjoy cycling too much to have just OK handling.   I especially like how they handle sweeping turns and dodging road dangers as the bike is much easier to steer. Even riding singletrack is better as the low trail bikes are easier to maneuver at slow speeds as well.  There is no way I would go back.

I've found a trail of about 38-44 mm optimal for all around riding, even without a front load in answer to your question. I have a custom touring, a Rando and  a monstercross bike all designed and built with low trail.

~mike

Carlsbad Ca.

[Stephen Poole]

So Mike, are you saying your "low trail" touring/rando bikes have 38-44 mm trail? I was thinking of shooting for something like that, so confirmation would be very helpful. :-)

The 30 mm or so on the GR is less stable than I'd like...

Thanks,
Stephen

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[Ken Freeman]

Jan did an article about how for different wheel sizes the characteristics of handling changed with trail.  Certainly he had 30 mm trail at the "very low trail" extreme for 650b, so maybe Soma took it a step too far.  My Terraferma 650b with 35 mm trail handles nicely as Mike describes with no load, and I've never taken it out yet with a front load.  My Woodrup 700c has about 40 mm trail and was nicer than a high-trail bike on a long ride with moderate front load (Berthoud less than full).  The ranges are not the same for all wheel sizes, for example my 700c Trek 610 with its custom fork has 36 mm trail and is a very very easy-steering without load, though not stability-challenged.  I think it is at the low end of what's good for 700c.

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Ken Freeman
Ann Arbor, MI USA

[Ken Freeman]

What Mike has described agrees with what Jan described as the handling with low trail.

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[Brad]

The trail number is a stand in for the flop of the front end.  Low trail = low flop.  If you will be riding at slower speeds some of the time this matters a lot with a front load near the handlebars.  
One reason it matters is that high flop requires you to lift the bike out of the flop with your arms when correcting or over steering.  That is not an issue at higher speed.
It can be a big issue when you are climbing or when you are tired or slow dean to deal with complicated bumpy roads.
It matters when you get really tired, much less so when you are zipping along and full of vim and vigo(u)r.

Low trail changes the way you steer.  Less leaning and more fine tuning of the track.  My experience is that I can steer around a certain pot hole at the corner of my street with my low  train bikes
where with high trail bikes I had to take a wide arc farther out in the lane. 

So at the end of the day trail may not matter to you, or at the end of the day being completely pooped out on a cobble street climbing it may matter a lot.

[Mark Bulgier]

'Brad' wrote:

The trail number is a stand in for the flop of the front end.  Low trail = low flop. 

Isn't that a slight oversimplification there?  Though maybe justified in this case.  But I think it is possible for a high-trail geometry to have less flop than a low-trail, if the high trail bike has a sufficiently steep head angle (HA for short).  That is, steeper than the low-trail bike we're comparing it to, by enough to more than compensate for the tendency of the high trail to make for high flop.

For example, taking it to the extreme to make it clear: if the HA is 90° and the bike is not leaning, then there is zero drop as you turn the fork (steer).  I'm less clear on what happens when the frame is leaned, as it pretty much has to be when turning at some nonzero speed.  Unless the rider is doing gymnastics to lean his body while keeping the frame upright – which is possible to do, but people don't actually do that very much in real life (except on racing trikes)

Since in real life, the steering angle and lean angle vary with speed, the full formula is very complex, too tough for me*. So I'm all in favor of useful simplifications.  For example let's say for a given head angle.  If the HA is kept the same, then the statement "Low trail = low flop" is valid – I think.  Keeping the HA the same is a fair assumption if the frame is built already and we're just deciding on how much rake to put on the fork.

But it's good to keep in mind when designing the frame too, that we can mitigate the effect of flop by steepening the HA. This may partly explain why racing bikes with high trail also often have a steep HA.  Not that most framebuilders think about flop, but they experiment and keep designs that feel right.  Same reason as why bikes with skinny tires usually have more trail.  Not that the designers think about pneumatic trail (or have even heard of it), but just that it works in their experience.

* For anyone who wants to delve into the governing equations, or at least get an idea of how complicated it it really is, check out this article by John Olsen and Jim Papadopoulos:  "Bicycle Dynamics – The Meaning Behind The Math", in the December 1988 edition of Bike Tech magazine.  As far as I can tell, this is still considered scientifically valid, as far as it goes. (The authors clearly state that their work is incomplete – the article is not meant to be a complete explanation of all the factors and phenomena, so the article should not be considered a failure.  It's an overview).  If there are any more thorough, correct or better-explained papers out there, or if this one is considered garbage due to mistakes caught in later critical reviews, please let me know.  Not that I need to study the latest papers – I really don't – but just so I don't keep recommending the 1988 Olsen-Papadopoulos article as a good one for other people to read.

Mark Bulgier
Seattle

[Alex Wetmore]

​I was involved in two VBQ articles where we experimented with different trail numbers.  Both of these were a very long time ago: 2006/2007.  

The first was the Kogswell P/R prototype test (I think this is in Vol 4 No 3) where we had bikes with 25mm, 40mm, and 50mm of trail.  I preferred the 40mm bike because it handled the best for me across a wide range of loads.  If I remember correctly Jan preferred the 25mm bike because it handled the best with a light front load (1-2kg, matching a handlebar bag load).

A few months later (Vol 5 No 3) we did another test with loads from 20lbs to 50lbs (the 50lb load was Alistair Spence's groceries) and most (maybe all?) of us agreed that we preferred the 40mm fork with loads in that range.  Alistair had raked his Rivendell's forks to <30mm range and started making new forks with slightly more trail after this test.

I've personally built a lot of bikes with trail numbers in the 38-40mm range and really like that.  I found that this provides the best combination of riding well unloaded, with very heavy front loads, and with anything in between.  It feels strange to have one universally good trail number, but it has worked for me across rando, touring, commuter/porteur, and cargo (cycle-truck) bikes.  I think my most rando-esqe bike has more like 35mm trail, and the Travel Gifford that was used to test the Rat Trap Pass tires might also benefit from a little lower trail (since the high volume tires have more pneumatic trail).

30mm trail does work really well for the specific use of carrying a light load on the front.  I find that makes it the front end feel too light and twitchy when there is no front load (where 40mm feels fine), and is also a little harder to control with very heavy front loads.

All trail numbers referenced here are for "normal" head tube angles of 72-73 degrees and "normal" rim diameters of 559mm to 622mm with wider (at least 30mm) tires.

Tires and load really do matter, I remember having a 45mm trail Trek (early 80s model, 73 degree HTA with 55mm of offset) and finding the front end really light and ultimately crashing on it.  I was riding that bike with 23mm tires pumped to 120mm (so almost no "pneumatic trail") and carrying a rear pannier that probably weighed 20lbs.  That is the worst possible condition for a lowish trail bike, and seeing how most touring bikes were outfit in the early 80s makes it clear why Trek pretty quickly changed from building lower trail touring bikes to very high trail touring bikes between 1983 and 1984.

alex

---

From: 65...@googlegroups.com <65...@googlegroups.com> on behalf of Ken Freeman <kenfre...@gmail.com>
Sent: Thursday, April 9, 2015 4:08 AM
To: Stephen Poole
Cc: Mike Schiller; 650b
Subject: Re: [650B] Re: Maximum trail okay with a barbag?

 

[Mike Schiller]

Yes Stephen,  My two 650B bikes, a touring bike, built with 8/5/8 OS tubes and the Rando, built with 8/5/8 std both have a trail of 38 mm.  Both have front bags on most of the time.

 The 700C Monstercross, built with 9/6/9 std tubing has a trail of 44 mm with 40 mm knobbies. Lately though, I've been running 47 mm 29er tires and the trail is a bit higher.  This bike gets ridden without a front load most of the time.  But it does great with a front bag too.

I weigh about 195lbs BTW.

~mike

[Stephen Poole]

Jan wrote something about testing three forks with one of the Cogswell frames, IIRC with 30/40/50 mm trail. 50 he liked with a rear load, 40 for either/both, 30 for front only. ISTR 40 mm was said to be the more versatile option.

In any case, I really hate anything even vaguely resembling shimmy, so will likely aim for ~40 mm trail, or perhaps a bit more. I've had two bikes in the past with shimmy issues, and one which IMO was insufficiently stable (AM), and would much rather work a bit more to turn than have to pay attention to *not* turn.

Later,
Stephen

[satanas]

Thanks again everyone - you've all been really helpful! I will try to digest the article Alex referenced, but am not all that fond of equations, so may not get very far.

Maybe Jack Taylor was right way back when - he is said to have preferred 38 mm trail.

I really wish there was a way to turn off auto-quoting of everything in Android. (Sigh)

Later,
Stephen

[Brad]

You can use JimG's trail calculator to play with the numbers. http://yojimg.net/bike/web_tools/trailcalc.php
I would agree that you can get a low flop result with a steeper head angle.
You would probably have to make the top tube longer to make the wheels fit and you might have toe clip overlap.
You wont get as much spring effect from a less raked fork.

[Brad]

An additional useful bit of math would be to calculate the lever moment and the movement at the handlebar which results from wheel flop.
Putting loads toward the front creates some really significant lever moments, toward the center much less so.
Low rider panniers centered had little effect on ride as a recall the results of Jan & company's testing which follows.

[Dave Feldman]

This is part rack and decaleur design and part bike frame front end geometry, but look at bikes that carry big front bags and notice how the front axle is--at its farthest forward--at least centered under the bag.  To me and my own front bag experiences on a few bikes (none 650b yet, however) getting the axle under the front load is a big deal.  The worst experience I ever had with a front bag was a situation consisting of 1. Bag high up on a springy steel mount, 2.Italian racing frame; 74 degree head angle and 43mm fork offset--lots of trail 3. Bag mount set it about 2" forward of the handlebar.  In all the fork rake/trail/head angle/ talk, placement of the weight seems to take a back seat and I believe it's really important.  I'd like to hear/read the opinions of other people with a lot of bike work and riding experience about this, it's just a fixation of my own.

On Wednesday, April 8, 2015 at 7:46:51 AM UTC-7, satanas wrote:

[Fred Blasdel]

On Wed, Apr 8, 2015 at 2:14 PM, Dave Feldman <feldm...@gmail.com> wrote:

This is part rack and decaleur design and part bike frame front end geometry, but look at bikes that carry big front bags and notice how the front axle is--at its farthest forward--at least centered under the bag.  To me and my own front bag experiences on a few bikes (none 650b yet, however) getting the axle under the front load is a big deal.  The worst experience I ever had with a front bag was a situation consisting of 1. Bag high up on a springy steel mount, 2.Italian racing frame; 74 degree head angle and 43mm fork offset--lots of trail 3. Bag mount set it about 2" forward of the handlebar.  In all the fork rake/trail/head angle/ talk, placement of the weight seems to take a back seat and I believe it's really important.  I'd like to hear/read the opinions of other people with a lot of bike work and riding experience about this, it's just a fixation of my own.

I spent a couple years of grocery getting on my old Kogswell P/R experimenting with this

Fore / Aft load placement changes the inertial feel in low speed handling, but it's pretty small and about the steering axis not the axle. It's easier to tell the difference in balance over the whole wheelbase going up and down curbs, that's where the front axle comes into play.

Load height makes a huge difference, even from small changes, in all handling scenarios. When you were using a rackless handlebar bag this is what you were feeling.

Left / Right load placement is obviously a big deal too, especially when you have a bunch of small heavy things to balance out.

[Brian Rowe]

I had a similar experience when I set up my '81 Bianchi Limited 650B conversion for a front bag. With a ~3 pound U-Lock strapped to the rack, the handling was just fine. With a similar amount of weight in a handlebar bag on the rack and secured with a decauler, the handling was terrible, in fact so bad that I only tried that setup for one ride. The bag put the weight higher and more forwards ( I do recall the center of the bag was beyond the front axle) and that must have made the difference.

[David Pertuz]

I have noticed this, too. When I switched from a smaller Velo Orange bag to a larger (in both height and depth) Ostrich bag on my Rawland and started carrying my seat/wheel cable in the front pocket, I could feel the difference in turn-in feel immediately.

David

Chicago

--

[Jaswkah]

while we're on the topic of trail and measuring trail, i'm still not sure of the difference between "mechanical trail" and just "trail." on the http://yojimg.net trail calculation page there doesn't seem to be much difference than a few mm between the two designations. i read -- and tried to understand -- the definitions on wikipedia but couldn't really see the difference here, either. can anyone shed some light on this?

thanks.

jason

[Mark Bulgier]

Trail is measured along the ground, from where the steering axis hits the ground back to the center of the tire contact patch.

Mechanical trail is the lever arm by which the contact patch applies twist on the steering axis.  It's measured from the center of the tire contact patch as with "trail", but not along the ground, but up to where it makes a 90° angle with the steering axis, which is shorter than the measurement along the ground.  See the attached drawing which will help I think.

Mark Bulgier
Seattle

[anal...@gmail.com]

hi mark

thanks very much for your explanation and
diagram. i now understand the difference between
the two trails but i'm still not clear which one
is more important to pay attention to when
designing a frame. which do you use?

jason

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[Mark Bulgier]

'Jaswkah' wrote:

> i'm still not clear which one ["mechanical trail" or just "trail"]

> is more important to pay attention to when
> designing a frame. which do you use?

Regular trail measured along the ground is all I've ever heard of anyone using, other than a few scientists trying to work out the equations for bike handling.  If you know either of them and the head tube angle, then you can calculate the other, which to my mind means they're practically interchangeable.  Certainly within the narrow range of headtube angles in use.

My advice is to forget you ever heard of mechanical trail unless you just happen to love that kinda shinola.   For me, it's not a concept that deserves much "mind share", a limited resource.

Mark Bulgier
Seattle

[Andrew]

Mark, Fork rake is measured as the shortest distance between a line through the centre of the steerer and the centre of the hub. It is always at 90 degrees to the steering axis as viewed from the side of the bike, and not parallel to the ground as shown in the diagram you attached. If it was measured as per the attached diagram, a fork would have a different rake depending on the head tube angle if the frame it was in.

Andrew

[Jim Bronson]

The flop at low speeds on my Rivendell custom when using a Topeak handlebar mounted bag was terrible.  That was in the early days of my randonneuring adventure and I tried it on a 1000K (another bad idea).  It didn't take me long to reject that configuration.  Honestly though once underway, above 5mph or so it seemed fine.  I didn't have any problems with it climbing the big passes on that 1000K.  It was only when starting at stopping.

I have a friend who runs a Giles Berthoud handlebar bag on his Rivendell custom with a cantilever mounted rack and he's always swearing it works way better when you mount the bag with a lower center of gravity.  Maybe I'll try it sometime.

On Wed, Apr 8, 2015 at 1:44 PM, Mark Bulgier <bulg...@gmail.com> wrote:

Plenty of people have enjoyed the ride of a typical modern racing bike, say 50 to 60 mm trail, with a bar bag, so I wouldn't say low trail is a must.  My commuter is a repurposed old racing bike with a front rack, and I often bring home a heavy bag of groceries or a case of wine.  I wouldn't call the handling optimal, but it hasn't bugged me enough to bother making a low-trail fork for it.

For me the suboptimal handling of high trail with a front load crosses the line from the subliminal to the noticeable, but well short of annoying.  If I don't obsess over it, I'd say it's easy to forget about it and just get used to it.  Other people no doubt would find it intolerable.

Obviously we hope for better than "just get used to it" with a custom bike, so ideally you'd want to try some bikes with a front load and low, medium and high trail to decide for yourself before committing to the expensive custom.  For testing – most forks can have rake added or subtracted.  Fender clearance will change, so this is not ideal, and maybe best to do on a junk fork not an expensive one.  Brakes with not much up/down adjustability (such as most cantilevers) can be a problem too.  In a worst-case scenario, changing the rake a lot could mean you have to move the canti posts a little too, and a repaint.  Theoretically it also moves the front of the frame up or down, changing frame angles and BB height, but those changes are generally too small to notice.

A few folks have made adjustable-rake forks for testing to decide on what trail they like. Can be as simple as using rear long horizontal or track dropouts.  You can even leave the adjustable fork on the bike long-term, if you don't mind that it's heavier (and ugly).  I used one once but so long ago I don't remember what I decided.  I was mostly a racer then and didn't test with front loads anyway, plus that was with skinny high-pressure tires. 

I think my main take-away was how little it mattered, for a racing bike.  I could get used to the handling over a wide range of rake/trail numbers, and I've found that most other people can too.  Which makes it hard to know if the handling is optimal, or just what you're used to.  I think I settled on a high trail for racing mostly for the ease of riding no-hands while taking my jacket off, and not crashing while doing a victory salute.  ;)  

Sorry about the racing bike digression, not what you asked about.

Mark Bulgier
Seattle

On Wednesday, April 8, 2015 at 7:46:51 AM UTC-7, satanas wrote:

So, currently I'm touring in Europe on a GR, but eventually this will be replaced with a custom frame. (Yes, I'm fussy.)

I get the attraction of low trail, as the bike really wants to turn, however the almost-shimmy when hitting bumps at speed aggravates me, and I'd prefer more straight line stability.

So, how much trail can one have with 42 mm tyres before things get clunky with a barbag? FWIW, I'm not likely to ever use rear panniers; fronts and a seatbag are a yes though.

Thanks,
Stephen

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Keep the metal side up and the rubber side down!

[Mark Bulgier]

"Andrew" wrote:

Mark, Fork rake is measured as the shortest distance between a line through the centre of the steerer and the centre of the hub. It is always at 90 degrees to the steering axis as viewed from the side of the bike, and not parallel to the ground as shown in the diagram you attached.  If it was measured as per the attached diagram, a fork would have a different rake depending on the head tube angle if the frame it was in.

Yes, quite true, bad drawing.  Sorry about that, it's not my drawing, just something snagged from Google image search.  I only checked it for mechanical trail since that was what the question was about, didn't look at the other call-outs.  That's what I get for stealing someone else's drawing!

Mark Bulgier
Seattle

[Stephen Poole]

So, my impression is that the closer  to the steering axis the weight is, the better, i.e., the further back the bag is, and also bag depth front to rear and packing can be problems if the result is weight too far forward.

Does that agree with others' impressions?

Later,
Stephen

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[Michael Arciero]

Have resisted the rack/decaleur setup on my 650b (Stag). Was not looking forward to sorting all that out. Have been using Ortlieb bar bag, (which has worked pretty darn well, though I could use a little more space) and always  have been curious about the effect of the height. On the one hand, the moment that the load makes about the steering axis is independent of height, so height would not seem to affect steering feel/ wheel flop-type affect. On the other hand, with a rack and bag, it is possible for the bottom part of the bag would be closer to the steering axis, which would affect steering less than a  load at greater height. There is also the side-to-side motion, in which case the "moment arm" is distance from ground to the bar bag, etc. It seems that some here find the effect dramatic. At any rate, I am likely going to take that plunge with rack/decaleur and find out.  

Mike

[satanas]

Hopefully have a GB decaleur on the way, and am hoping this will stabilise the top of the bag adequately. We'll see...

Later,
Stephen