Educate me on Low Trail Fork Measurements

[Tom Norton]

So today I thought I would try to determine the trail of some of my bikes. I read how to go about it but what I cannot seem to find is what measurement = low trail.
Would appreciate your assistance!

[William Lindsay]

"Low trail" is in the ~30mm range.  The lowest I see is in the high 20s.  The borderline between "low trail" and "mid trail" and "high trail" is a matter of opinion, but for typical roadish bikes, higher trail would be in the high 50s low 60s.  I guess I would call the upper end of 'low trail' somewhere in the high 30s low 40s.  I'm not an expert on this topic, but I am a numbers/math person. 

Bill Lindsay
El Cerrito, CA

[Steve Palincsar]

Let me add a modifier to Bill's excellent summary:  "...~30mm range for 650B bicycles."  That might be assumed given the list; but it's worth noting that for bicycles with 700x32C, the low-trail range is more like ~39-45mm.   (I'm not a numbers/math person, but I do own two low trail 700x32C bicycles.)

-- 
Steve Palincsar
Alexandria, Virginia 
USA

[Scott Stulken]

During the Technical Trials, bikes needed to have 20-50mm of trail.  I think people generally shoot for the middle of that range when spec'ing "low-trail" bikes these days.

- Scott

[Reed Kennedy]

Following on regarding wheel size and low trail, I currently have three low trail bikes:

MAP, 700c x 32mm tires, 31mm trail

Velo Routier, 650b x 42mm tires, 30mm trail

Fitz, 650b x 48mm tires, 30mm trail

I’ve found the MAP extremely well behaved. I have not noticed any drawbacks of combining 700c x 32mm wheels / tires with 30mm trail. 

I don’t expect to purchase another 700c bike, as the MAP is basically perfect. But if I did I would hesitate to go with 30mm trail again. 

Strangely, the most shimmy-prone if the three is the Velo Routier, which also has the stoutest tubing and most compact frame. 

Reed

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[Tom Norton]

Thanks for this info! It has helped me out.
My Miyata 610 which I converted to 700c measures 40mm. I am going to put a set of 650b wheels on it and redo the measurements and see what happens.

[mitch....@gmail.com]

On Sunday, October 8, 2017 at 5:57:22 PM UTC-6, Reed Kennedy wrote:

Following on regarding wheel size and low trail, I currently have three low trail bikes:

MAP, 700c x 32mm tires, 31mm trail

Velo Routier, 650b x 42mm tires, 30mm trail

Fitz, 650b x 48mm tires, 30mm trail

I’ve found the MAP extremely well behaved. I have not noticed any drawbacks of combining 700c x 32mm wheels / tires with 30mm trail. 

It's not that you necessarily get drawbacks of combining 700Cx32mm with 30mm trail, but that with narrower tires you start getting the advantages of low trail at about 45mm like Steve says. 

To the original question, and with the understanding that tire width affects how low trail works, this is my take:

Low trail = 30-45mm. (Down to 20mm when you count older designs that used it.) 30mm trail the sweet spot Jan Heine writes about in his blog series a few years ago. He says 30mm is where you get the precise handling he likes with low trail. I have a couple 30mm trail 650B bikes and agree with him. In my experience you get the front-loading-friendly ability of low trail starting about 45mm. Low trail is also known for being less reactive to weight shifts (due to low flop) which is noticeable to me once I start paying attention to it. Most noticeable in slow cycling situations (like steady steep climbing) where the bike does not wander due to stray weight shifts. You can turn to took over your shoulder without having to correct for the weight shift as much like you would with mid-trail. "Pneumatic trail" of fatter tires, especially at lower pressures effectively adds trail, and is one reason trail handling is affected by tire width. I have a vintage race bike with 42-45mm trail that has every good handling characteristic I like (with tires from 23 to 32mm), and I can't think of any reason I'd want anything but low trail (for road riding, and this is despite the fact I really like mid-trail handling too). This is true for me whether it's a 30mm trail bike on BSPs or a 45mm trail bike on skinny race tires. 

High trail = 65mm and up. With high trail you get lots of castor and the directional stability it gives you, especially with speed. That directional stability is why front loading works fine with high trail most of the time. But the flop is why high trail is less good for front loading at low speeds. That can be coped with fine but it's not surprising that people may prefer low trail for front loading. There's plenty to say about high trail handling characteristics but the original question was about low trail. 

Mid-trail = 50-60mm. Mid-trail merits the separate category, to me, because it feels completely different from low and high trail. Whereas high trail has a lot of stability (repentance to direction change) due to castor effect, and whereas low trail is comparatively un-reactive to weight shifts (due to low flop), mid-trail is neither. It reacts even more readily to weight shifts than high trail but doesn't develop the high directional stability that high trail does. In other words, a mid-trail bike is always ready to turn. That can feel twitchy to some but it's worth noting that the mid-trail figure of 56mm is the most widely used trail across sport/race bikes today and has been since the late 70s. A lot of people swear by this "responsive" feel. I really like mid-trail handling and it took me some back to back comparisons with my low trail bikes to discover that I was doing some weight shift compensating during slow climbing on my mid-trail bikes to realize how little attention was required for this on my low trail bikes. Mid-trail bike handling is really tied to narrow tires and I personally have little interest in mid-trail for tires wider than 32mm. "Pneumatic trail" of fatter tires makes mid-trail bikes handle like high trail bikes in my experience. 

My observation of how these different handling traits work first hand, plus observing varying preferences of list members on this and other lists that obsess about trail, suggests to me that trail preference is highly influenced by habituation. What you've ridden a long time is what you prefer. In my case I've had both low trail and mid-trail race bikes from my teen years and that's what I learned bike handling on. It doesn't surprise me that I really like both and find both super easy to ride. No surprise that I really don't like high trail handling on pavement because I never had a high trail road bike, but I do really like high trail on a mountain bike because almost all mtbs have high trail including my own 1981 mtb. Also track bikes tend to have high trail, including all the ones I've ridden/raced. They feel fine to me on the track but I'm not crazy about their paved road handling when I ride my track bikes on roads (with a front brake installed). Another thing that tells me trail preference has a lot to do with habituation is that counter-steering became habitual for me when I was riding motorcycles daily. Motorcycles are designed with way high trail and mostly require counter-steering to initiate a turn on pavement, one of the first things they teach you in safety class. I'd long been aware of counter steering before this but it's just seldom necessary or useful with mid-trail or low-trail bicycles. But I personally experience that counter-steering is required for initiating turns on pavement with high trail bicycles. It's a subtle maneuver but if you don't know it, it can be frustrating if your high trail bike feels like it's "on rails" as you approach a turn on paved roads and feels reluctant turn. My theory is that people who are habituated to paved road riding on high trail bicycles counter steer a lot, perhaps intuitively and without having to think about it, and this accounts for why some people love high trail handling on pavement and others don't. Since low trail was mostly out of the N.American market for a long time, not many people had a chance to habituate to it. It's interesting to compare responses to people who try low trail, some finding it a revelation that makes everything better, and others disliking it right away and never warming up to it. Some of this must depend on the specific low trail bike they're trying. 

--Mitch 

[mitch....@gmail.com]

Arg. Should have read: "stability (resistance to direction change)"  Agreeing on descriptive terms like "stability" is hard enough without complicating it with religion. 

--Mitch

[Randall Daniels]

Thanks for the informative post. Does front-loaded high-trail offer any advantages or is it just another option?

I've been playing around with front-loading a gravel bike with 80mm trail (700x35 tires) and it's been...interesting. It's definitely workable and fun to ride but has some quirks to learn. As spring project planning time approaches I'm wondering if low trail offers anything I'm not getting? Really the only thing I don't like about the high trail is how much it gets blown around by cross-winds and how the steering falls apart on slow (<10 mph) gravel downhills - feels very disconcerting.

[mitch....@gmail.com]

On Monday, October 9, 2017 at 9:17:19 AM UTC-6, Randall Daniels wrote:

Thanks for the informative post. Does front-loaded high-trail offer any advantages or is it just another option?

I've been playing around with front-loading a gravel bike with 80mm trail (700x35 tires) and it's been...interesting. It's definitely workable and fun to ride but has some quirks to learn. As spring project planning time approaches I'm wondering if low trail offers anything I'm not getting? Really the only thing I don't like about the high trail is how much it gets blown around by cross-winds and how the steering falls apart on slow (<10 mph) gravel downhills - feels very disconcerting.

My experience with high trail front loading is just like yours, fine at speed in a straight line (where high trail excels) but flop is noticeable at low speeds, and you feel cross winds more. I only mention it because since low trail works so well for front-loading, and mid-trail tends to be noticeably poor at it, sometimes people forget that high trail's stability makes front loading an option. The advantage you ask about would be just if 1) you have a good reason to use high trail such as a gravel bike you like, and 2) you prefer front loading, so why not try it. All my high-trail gravel riding has been on rigid mountain bikes--I haven't ridden one of the new generation high trail gravel bikes based on road bikes. My road bike-on-gravel-at-speed riding has all been done on low trail bikes (works fine) and I personally don't know if mainstream gravel road bikes are high trail for traditional design-inertia reasons, or if high trail has advantages at speed on gravel I would like too. Maybe they allow stability at higher speed on gravel. Others here will know a lot more about this than I do, and I'm interested. 

FWIW, I've had good results front-loading a mid-trail bike by using a rack that keeps the bag as low and as close to the head tube/steering axis as possible. With light weight around 5 lbs (typical non-commuting day-ride load for me) it was almost perfectly fine and I could ride no-handed almost as easily as usual. At 10 lbs in the bag (GB 25) it began to be noticeable that I had to control flop more but was still manageable up to 14 lbs. I wouldn't want to ride all day that way because I had to keep my hands on the bar. But it was not nearly as reactive as mid-trail usually is with a front load further out over the wheel. This is not to recommend mid-trail for front loading but just to say that as you experiment you learn the principles involved and what the limits are. Fun experiment but it was mainly because I had a favorite mid-trail planing bike I rode all the time but then I found I prefer to ride with a front bag all the time, so I put the two together. Result worked fine for two years of riding but it only led me to order a 30mm trail custom. In the two years since taking delivery of that custom I haven't ridden that mid-trail bike once. I think I miss it but apparently not ;-)

--Mitch 

[satanas]

It would be really useful if people would specify *exactly* what they're thinking of when they say "front loading." Do they mean a trad style bar bag (i.e., GB), front panniers, a bikepacking roll bag, cargo cages, a combo of some of these or something else?

Also, 80mm trail on any vaguely normal production gravel bike seems rather unlikely; somewhere between 60-70mm would be much more common. What are the actual head angle, fork offset and front tyre radius numbers?

FWIW, my experience is that 60-70mm trail is fine, including with front panniers, though it always helps if these are as light as possible, and located as close to the steering axis as can be achieved.

Bar bags are more of a vexed issue (for me) and my experience has been that these *do not* improve handling, irrespective of trail or attachment method, though some are worse than others. I'll probably use a Revelate Egress pocket on the next bike, with minimal contents like passport, wallet and small camera; that shouldn't impact handling or require geometry changes to compensate. YMMV.

Later,
Stephen

[Randall Daniels]

2016 medium Diamondback Haanjo Comp - HA is 70 degrees, fork rake 45mm and 700x35 tires. I will admit I did not verify any of these measurements myself and used the yojimg.net to get the trail number. For some reason the medium diamondback gravel bikes are all much higher trail than a lot of other bikes in the same category.

I'm using a front rack with a variety of containers, sometimes a lunchbox, sometimes a smaller tupperware container. Usually 1-8 pounds of misc items mounted as low and as close to the headtube as possible. I've actually been thinking about ditching the rack and going with something like the Ornot/Rickshaw handlebar bag but I really like the flexibility a front rack gives for unexpected road finds and occasional small grocery items.

[Mark Guglielmana]

It's fairly difficult to measure trail directly and accurately. It's easier to measure rake, head tube angle, and tire size then calculate it empirically. I do this a lot when I'm doing 650b conversions. My main tool is http://yojimg.net/bike/web_tools/trailcalc.php. I have a jig to measure rake accurately:

But I'm an anal engineer, you can get by with a framers angle and site down it, it'll be pretty close. 

To measure the head tube angle, many people believe that they can just measure off of a horizontal top tube. This assumes the top tube is truly horiziontal. A better approach is to put your bike on a flat (not necessarily level) surface, then use a digital angle finder which has been zero'ed off of the flat surface. 

And, yes, that's a pretty slack head tube angle on that 71 Raleigh International.

[Stephen Poole]

On 14 Oct 2017 3:17 am, "Mark Guglielmana" <mark.gug...@gmail.com> wrote:

But I'm an anal engineer, you can get by with a framers angle and site down it, it'll be pretty close.

^ So, is an "anal engineer" the same as a proctologist, or perhaps something to do with alien probes?  ;-)

BTW, there are (free) digital angle finder mobile phone apps; there's no need to buy a special tool.

Later,

Stephen

[Brad]

And that bike is good for gravel because ?      It sounds like a 90's mountain bike with 700c tires.   Lots of flop.

[Brad]

A poor man's way to meaure rake is as follows:
Get a piece of paper.
Put the head tube down on the paper and draw a circle around the head tube.
Now flip the fork and sight the circle through the head tube and while siting the circle
use a pencil to mark the front and back of the dropout tangs.
Then using a ruler mark a line halfway between the marks - or may be two lines one for the front  and one for the back.
Then find the center of the circle you drew around the head tube.
Measure a line perpindicular to the line of the axle to the center of your circle.
Not close enough for precise engineering, but close enough for a rough calculation with Jim G's calculator.   It leaves out the challenges of sloping legs on the fork itself or older crowns without flat surfaces.

[Steve Palincsar]

and did he mean "sight down it"?

On 10/13/2017 05:59 PM, Stephen Poole wrote:

On 14 Oct 2017 3:17 am, "Mark Guglielmana" <mark.gug...@gmail.com> wrote:

But I'm an anal engineer, you can get by with a framers angle and site down it, it'll be pretty close.

^ So, is an "anal engineer" the same as a proctologist, or perhaps something to do with alien probes?  ;-)

Who do you think designs those colonoscopes?

BTW, there are (free) digital angle finder mobile phone apps; there's no need to buy a special tool.

Later,

Stephen

-- 
Steve Palincsar
Alexandria, Virginia 
USA
"Who's being anal now?"

[Tom Norton]

After the replies I decided to redo the measurements.
I made a jig that would hold a straight edge along the centerline of the headtube & fork.
After doing this my trail measured 52mm.
Thanks for keeping me on track!