front-center

[hypnos]

This forum has been a great resource for learning about bicycle geometry and fit. Can you folks help me out with the measurement and implications of front-center? I understand the obvious implications with regard to weight distribution and TCO. How is proper front-center calculated for a particular rider?

Thanks,
Jeff

[hypnos]

Anyone?

[dirtdigger88]

I have been waiting too- :confused:

Jason

[Black Bart]

Try Don Ferris' website, www.anvilbikes.com - click on "Frame & Geometry Variables" - he has a simple (possibly too simple for your purposes) discussion of front center and its implications.

[hypnos]

Black Bart,

Thanks for the link. I'm still wondering how the appropriate front-center distance is determined for a given rider. Is there some formula based on body measurements? Inquiring minds want to know. :)

Jeff

[Ray]

I'm still wondering how the appropriate front-center distance is determined for a given rider. Is there some formula based on body measurements? Inquiring minds want to know. :)

I'm the last person who should be responding here, but that's never stopped me before, so...

I can't imagine there's a single correct front center measurement for a given rider. It seems to me that the whole point is to have appropriate weight distribution, which means the front center needs to be determined along with chainstay length and worked out with the appropriate head angle, rake, etc to achieve the handling the rider wants. If a given rider orders two bikes, one with racing characteristics and the other with more sport touring/rando characteristics, the front centers would likely be different, as would the chainstay lengths, as would the steering geometry.

But I could be completely wrong yet again.

-Ray

[Grant McLean]

I'd be as bold to say that "front-center" is the most important geometry dimension, period. Obviously fit is about the relationship between many factors, but the reality is, in the handleing department, the front center is the one thing that cannot be changed once you own the frame.

Raise or lower the bars, slide the seat around all you like, the front center is there where it is for good or bad. In the real world, how much does chainstay length really change... not much. When I look at a stock production frame, the first thing I look at is front-center. If it's not in the range, forget about it. Personally, I like about as long a front-center as I can find. I'd go up a size or two to get there. This is overly simplified. I'm constantly surprised at a few brands who have very short front centers, and I very much dislike the way they ride.
With the bunch of bikes I own and haven ridden, they all fit the same, with the seat height, set back, reach, and bar drop is identical. The major differences left being front-center and bb height. It's an interesting experiment.


Grant

[cpg]

Front center is a meaningless dimension unless all the other fit and geometry dimensions are known. Ray Sachs got it right. There's no one right front center. This doesn't mean front center isn't important but it's just part of the mix.

Curt

[e-RICHIE]

Front center is a meaningless dimension unless all the other fit and geometry dimensions are known. Ray Sachs got it right. There's no one right front center. This doesn't mean front center isn't important but it's just part of the mix.

Curt

"Ray Sachs got it right."
it must be something to do with the killer initials.

cpg-issimo is on the mark (not that there's anything wrong
with that...); all measurements are part of the whole, but
not the courtney love type. it's the same rationale as with
the fork rake issue thread across the hall. everything's connected.
hey - thanks for reading.

[sg8357]

Front center is a meaningless dimension unless all the other fit and geometry dimensions are known. Ray Sachs got it right. There's no one right front center. This doesn't mean front center isn't important but it's just part of the mix.

Curt

Curt what order do you figure out the geometry in ?
I look at factory bikes usually you see 3 different head angles and
one fork rake and one chainstay length. So the front center proportion
is going to vary. What is an acceptable range on front center, before the handling goes wonky ? Is there a magic range for like a race bike vs a
rando bike ? Do fat tire bikes use a different geometry ?
(insert gradute seminar here :) )

Scott G.
2005.2 Chris Kvale

[hypnos]

I'm still confused. :confused:

[cs124]

I'm still confused. :confused:

no one here is going to give you a magic number you can trust for at least one of these reasons...

they don't know either

they don't want to divulge the hard earned secrets of their 20+ years of frame building

there really is no magic number because bike frame design is dependent on many factors, all of them related and interdependent

just get Kelly B to build you a bike, it will ride nice

sorry i couldn't be more helpful

[e-RICHIE]

there really is no magic number because bike frame design is dependent on many factors, all of them related and interdependent





bingo

[David Kirk]

Thank you.

Dave

[e-RICHIE]

Thank you.

Dave



bingo-issimo

[David Kirk]

dude - you have the biggest font ever. You must get more tail than Dean Martin.........or was that Jerry Lewis........remember he's loved in france.

Dave

[weisan]

There is no magic formula, no spread sheet that sets front center. The designer needs to look at all the numbers in context and use thier experience to set the right front center.

Things like seat angle, head angle, top tube length, fork rake, chainstay length, etc. all factor in.

I hesistated to post this answer as I realize it sounds like a cop out answer. The problem is that it's not simple.

Dave


OVer heRe...Dude-Dave-Pal!

[David Kirk]

There is no magic formula, no spread sheet that sets front center. The designer needs to look at all the numbers in context and use thier experience to set the right front center.

Things like seat angle, head angle, top tube length, fork rake, chainstay length, etc. all factor in.

I hesistated to post this answer as I realize it sounds like a cop out answer. The problem is that it's not simple.

Dave

[Grant McLean]

Dave Kirk wroteth: "There is no magic formula, no spread sheet that sets front center. The designer needs to look at all the numbers in context and use thier experience to set the right front center."

Geeze, you wouldn't happen to be a designer would you? You are right that there is no magic involved, that's for sure. Just some basic facts, like short front centers suck and long ones are da bomb. Ever seen an E-Richie frame with a short front center? (or less than 50mm of rake?)

What this discussion should be about is why forks don't have MORE rake than 43-45mm. That's where the practical geometry problem is. If you want to build a frame without a short F-C, and there is a stock carbon fork, you have very limited abilty to adjust the head tube without more rake options. If given the choice between different frames, I would be to ride the one longest top tube, shallowest headtube, most rake in the bunch, and therefore the longest F-C.

my $0.02

Grant