trail and front center....

[tch]

In several threads, people have discussed trail and front center. I am wondering if there are absolute numbers that make some sense. Specifically, I have a Concours that was designed with 55.98 front center and 6.53 trail. After much discussion with many folks (some of this forum) I changed out my fork to one with greater rake, adding about .7 cm to the front center and reducing trail to 5.83. The difference is subtle but persuasively better.

So my question: is there such a thing as ideal trail and front center? Is it a ballpark/range? If so, why would Serotta generally go for longer trail and why would I much prefer to have less? Are there builder tendencies/preferences? On another thread, there seems to be consensus that Colnagos, for instance, have more trail than some other bikes; is that a design philosophy? Any insight? Thanks.

[Ken Robb]

I'll try to find a chart that was on-line which graphically illustrated the handling continuum from quick to ultra-stable caused by varying geometry. I haven't looked for it for a couple of years so it may be gone--hope not.

[Ray]

I think front/center and trail aren't necessarily connected, except to the extent that rake and trail are one of the factors that have to be taken into account to get the desired front center measurement. But the DESIRED front center has to work with the chainstay length and the rider in question to get the right weight distribution on the bike.

That said, I never gave much thought to what the "right" trail is until I started riding a custom Spectrum last spring. The bike handles unlike any other bike I've ever ridden and in a fairly amazing way. Then I found Tom K's article on trail on his website, which I now buy into completely based on my experience on one of his frames. He has a real specfic trail target for what he considers "neutral" handling. He notes, "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". This describes the handling of my bike perfectly - something I'd never really thought about until I'd ridden this frame and read his article. The article (pretty short) is here:

http://spectrum-cycles.com/612.htm

-Ray

[sg8357]

There are two kinds of trail, geometric and pneumatic.
Short form, fatter tires have a larger contact patch that slows the steering
down. French Rando bikes with 650b (35-38mm) tires have low geometric
trail, about 3cm. But have excellent handling, not super squirrely like
you would expect from such a low geometric trail figure.

In bike design everything is deeply intertwingled.
So pick a good framebuilder and let them do their thing.

Scott G.

[Peter]

Though framebuilders certainly have more experience than I do with regard to trail and front center, that won't stop me from having an opinion!

I still can't see why some builders "build" to a particular front-center dimension as I would expect it to be a "result" of top tube, head angle, fork rake, and whatever else rather than an end in itself. Hopefully, some of the framebuilders who visit here can explain themselves.

Most of what I've read, and what experience I've had with the bikes I've owned, points to a "preferred" trail figure for road bikes between 5-6cm, with the actual range maybe a couple mm closer than that. The 6.53cm trail figure you quote seems wildly out of the range of road bikes and perhaps is more suited to mountain bikes.

I think I read on Kirk's web site that he aims for 5.9-6cm of trail, which is a pretty narrow range, but he obviously has some specific handling traits he's seeking. I once had a frame/fork repaired and spec'd a new head angle/fork rake which resulted in 50-52mm of trail; I forget. Without going into details, it handled okay but under certain conditions it most definitely did not. I had the fork modified to reduce the rake/increase the trail to 56-57mm and the difference was remarkable.

So I think there are definite practical limits to trail but some flexibility based on personal taste and riding style.

[Orin]

I still can't see why some builders "build" to a particular front-center dimension as I would expect it to be a "result" of top tube, head angle, fork rake, and whatever else rather than an end in itself. Hopefully, some of the framebuilders who visit here can explain themselves.


You missed seat tube angle, seat tube length, chainstay length and BB drop.

Seriously, they are all related if a certain weight distribution is desired...

Orin.

[Dave]

If you read the geometry charts for a large number of brands, you'll certainly see different design philosophies. Colnagos have long front-centers and more trail than most brands. Fondriests tend toward the opposite with short front-centers and less trail for quick handling.

One very common design trend is to steepen the head tube angle on larger frames, producing less trail, in an effort to counter the slower handling that inevitably occurs with the longer front-center and wheelbase on a large frame.

The bottom line is that there is no such thing as a perfect front center or trail. It SHOULD change as the frame size changes. Different brands and even different models within a brand may have different geometry depending on the intended use of the bike.

[e-RICHIE]

I still can't see why some builders "build" to a particular front-center dimension as I would expect it to be a "result" of top tube, head angle, fork rake, and whatever else rather than an end in itself. Hopefully, some of the framebuilders who visit here can explain themselves.

i build with front center in mind and never measure head angles. of course, i have a vague idea what they are, but most are chosen to complement "reach" and in conjunction with a t.t. range and decent size stem for the bicycle in question. i.e., front center is not a resultant measurement, but most often head angle is. that's all for now peter. it's 'cross season!

[Dr. Doofus]

perhaps E-Ritchie or Dave Kirk or Round will set a dead guy straight, but it seems that f-c, frame setback, and chainstay length would be where a framebuilder would start.

with the rider's measurements, first you lay out the farme setback to put the butt where it needs to be, then lay out the f-c to get proper weight over the front, then the stays to get enough weight on/under the rear. set the BB height and trail for handling characteristics....and the rest works itself out....

Sounds easy, but then again when Rodin was tellin me how he made all them little castings that Rosalind Krauss got her panties in a wad about, I thought, hey, if I was back up top, I could do that too, and make some cash for a Meivici...and then I tried it and they sucked and the forge blew up and I ended up back here trying to score with George Sand's body double and she dumped me too...

so really, no, bike design is not easy to get all the parts to work together, but yes (maybe) it all starts with frame setback, front-center, and chainstay length.....

[e-RICHIE]

snipped:
[QUOTE=Dr. Doofus]perhaps E-Ritchie or Dave Kirk or Round will set a dead guy straight, but it seems that f-c, frame setback, and chainstay length would be where a framebuilder would start.QUOTE]


this works for me.
meld "position" and fine design and vi-oh-la.
see ya'.
gotta go 'cross ride.

[sg8357]

Things that make you go hmmmm.....
Trail shmail,

http://www.benchmark.cc/ecom/janette/store/morpheus.asp

Specialized is going to jump right on this amazing idea.
To me this why beer should not be available to engineers.
scott g.

[jdoiv]

Things that make you go hmmmm.....
Trail shmail,

http://www.benchmark.cc/ecom/janette/store/morpheus.asp

Specialized is going to jump right on this amazing idea.
To me this why beer should not be available to engineers.
scott g.

Surely it wasn't beer that gave someone this idea. I think it was a crack pipe...

[Dr. Doofus]

somewhere

someone

put a morpheus

on a peg

and "loves" it

sick

bastard