Trail and frame sizes

[e-RICHIE]

huh huh huh huh.

i incidentally made my roadie 579. noted that that was too short, but didn't "design" by FC. I looked at standard established HTA's and Rakes and Trail ranges-and made sure i stayed "inside the lines". <cut>

Screw the lines atmo. The ranges you are referring to are likely the stepchildren of a generations long inane conversation that has been going on inside the pages of the cycling press. I have no recollection of ever having read an article in which design elements are intelligently discussed. Data point: I don't know that I would want the job or be any better at it. It's always this angle this and that trail that and all sorts of overgeneralizing about things writers have absolutely no fukcign first hand experience with. At least up until the industry was American-ized, one could find 'zines printed on the Continent in which the layouts of bicycles were detailed only in linear terms. Scan through enough of these and you'll wonder why the paradigm shifted.

Lose the protractors and stock up on tape measures and stainless steel meter sticks.

[benson]

I use more rake on smaller frames and less rake on larger frames.
No matter what size frame I make, leaning the head angle more forward not only reduces the front center, it increases the reach.
The converse is true if the head tube tilts back further.
Maybe I don't understand the question atmo.
The most critical measurement is the anxiety level; I don't let any single detail indenture me to it.

Thanks, that does answer the question.
How did you arrive at your preferred range of fork rakes?

[e-RICHIE]

Thanks, that does answer the question.
How did you arrive at your preferred range of fork rakes?

Slowly and after riding many bicycles and racing racing racing a shitload of races atmo.
It was a case of if X is good, then X+1 is better, and X+2 is better yet.
Eventually you realize that good design has limits and you work within them.
Often it's when the bicycle or the rider atop, or both, stop looking beautiful and elegant.
It's simple but not easy.

[jamaris]

The most critical measurement is the anxiety level; I don't let any single detail indenture me to it.

I need to write this down. I am hoping this took more than a couple years to figure out.

[jerk]

i have no idea what any of this is about. there's no secret to where 700c wheels need to be in relation to each other to build a proper race bike- you just need to look at what has worked for the last thirty years.

read the CONI manual and look at a de rosa geometry chart...and tweak it for modern components and road conditions. i have no fucking idea what trail any bike i've ever made has and i don't care.

[Dyon Taylor]

Thanks for this. I had previously tried to replicate my De Rosa Neo Primato in BikeCad. I didn't understand why De Rosa didn't publish the HT angle or Fork rake numbers. Now it makes sense.

[Curt Goodrich]

My take on this is slightly different. Trail matters. Front center matters too. One can arrive at a "normal" trail and an "abnormal" front center and the bike will handle suboptimal. One can arrive at a "normal" front center and an "abnormal" trail and the frame will handle suboptimal. One can choose to ignore either dimension but that doesn't mean that dimension doesn't matter. It's sort of like gravity. One can ignore it's existence and yet it still has a profound effect. I consider both trail and front center when I design a frame. I find trail useful especially when designing frames that are outside the bell curve in sizing. When I designed Too Tall's frame which had a 65cm top tube and a 13cm stem, it was helpful to me to look at the trail number because that front center was outside the norm. Still front center was part of even that design consideration.

[-HvA-]

Curt, when designing a frame outside of the bell curve like this, what FC and trail did you end up going with? I guess the FC would wall wherever it needed to accommodate for the reach (probably 74 HTA?), but did you tweak the trail from neutral in any way to compensate?

[Curt Goodrich]

Curt, when designing a frame outside of the bell curve like this, what FC and trail did you end up going with? I guess the FC would wall wherever it needed to accommodate for the reach (probably 74 HTA?), but did you tweak the trail from neutral in any way to compensate?

In this case, the front center was 666mm and the trail was 58mm with 27mm tires. Despite the long front center I put the head angle at 73 degrees because I built the frame with 80mm of bb drop. I find that a frame with 80mm of drop compared to say 70mm of drop will lean faster. To counterbalance that I don't use a head angle as steep as 74. I find it just works well. Also, I think this is an example of how all the dimensions are taken more as a whole than just on the individual basis.

[-HvA-]

In this case, the front center was 666mm and the trail was 58mm with 27mm tires. Despite the long front center I put the head angle at 73 degrees because I built the frame with 80mm of bb drop. I find that a frame with 80mm of drop compared to say 70mm of drop will lean faster. To counterbalance that I don't use a head angle as steep as 74. I find it just works well. Also, I think this is an example of how all the dimensions are taken more as a whole than just on the individual basis.

Fascinating, thanks for the info! (I'm a bit too tall myself as well ). I take it this frame has 42-43cm chainstays as well? Anything else you did to adapt to the size?

[Curt Goodrich]

Fascinating, thanks for the info! (I'm a bit too tall myself as well ). I take it this frame has 42-43cm chainstays as well? Anything else you did to adapt to the size?

The chain stays were 42.7cm. The additional length helped to keep things proportional and made room for fenders and the frame pump. The bike normally doesn't have fenders though but with the low bb and a seat angle of 72 I think the chain stay length makes sense.

[-HvA-]

Thanks for sharing Curt!

[Ross D]

Richie,how do you deal with long femur's ,short torso and limited flexability ?

[e-RICHIE]

Richie,how do you deal with long femur's ,short torso and limited flexability ?

I deal with it intuitively atmo.
Is there a rider involved?

[Luke]

At least up until the industry was American-ized, one could find 'zines printed on the Continent in which the layouts of bicycles were detailed only in linear terms.

Speaking of Magazines...is there/was there ever/does the future afford a published magazine featuring old-school paper renditions of the VS?
Is our interest group too small? Has the web swollowed 'the magazine' for good??

I've always collected Mag-pubs along my journey. (And, yes I bag each copy in a collector bag, stack them numerically...and save them forever.)
I fear that te PRINTED word has escaped us. Like e-books...not the same to me. No Kindle in my house, only stacks and shelves of classic books.

Sorry to tangent away from Rake and Trail, but anyone know more of these mysterious publications called magazines...and any knowledge of where one can find them???
(I don't read Italian)

;)

[prolix21]

I don't have anything particularly intelligent to add to this, other than the thing that has helped me understand frame geometry the most is buying a bikeCAD pro license. I wouldn't rely on the fit calculator or think it will make you an instant fit genius, but having a visual where you can screw with every single measurement and see the results in real-time is interesting to say the least

With that said, so much of our stuff at UBI was based on ST and HT angles, but after messing with the measurements for my second frame I'm starting to see why e-RICHIE says to ditch the protractor.

[Ross D]

Attachment 44043Attachment 44044

Yes Richie there is a rider involved ,my long legged sweet heart:)

I intended to build the frame around a trail of 56mm .
After reading your thoughts i did the second drawing .
Is this what you mean with the 595 front center .

Your thoughts would be greatly appreciated .

Regards
Ross D

[e-RICHIE]

Attachment 44043Attachment 44044

Yes Richie there is a rider involved ,my long legged sweet heart:)

I intended to build the frame around a trail of 56mm .
After reading your thoughts i did the second drawing .
Is this what you mean with the 595 front center .

Your thoughts would be greatly appreciated .

Regards
Ross D

No image shows up atmo (sic).

[Ross D]

Richie ,
I have attached the files again , hope this works.
Regards
Ross D

[e-RICHIE]

Got it atmo. That's a lot of numbers, 3/4 of them being ones I never look at/for or know. Is that a 69 point something head angle?
I am on Franklin County time here and going horizontal. Her saddle height is 75 something. What is the reach from the saddle nose
to the stem/handlebar center? And is the saddle nose 8 something cms behind the central movement?