trail front center

[mls]

just woundering if you were to design a bike using say
a trail of 59mm you could get that trail w/a hta of 72.5*
and a rake of 46mm you could get that same trail by
using a 74* hta and a 37mm rake but the frontcenters
would be real different what effect does this make and
when would you want one over the other ? I have a colnago
w/a hta of 71.8* and my croll had 73.5* hta but the croll
had 1cm longer cs both handle fine. I am looking at something
like a waterford rs22 for my next bike and it seems like if
you used a longer fc like using longer cs you would be
designing a more comfortable bike . I think though if the
cs got longer and the fc gets longer the bikes turning would
start to slow . Can anyone shine some light on this to help
me understand it better thanks

[tch]

I have a Concours that had a shortish front-center (and longish trail). Eventually, I couldn't get over feeling that I was too far over the front wheel -- or correspondingly, that the front wheel was too much under me. I went to a fork with greater rake, thinking a lot about how much the trail would be reduced. In the end, I am much happier and the trail effect is minimal, compared to the more stretched-out feel afforded by a small increase in front center.

Note that I have not included any numbers in this description, because I have become convinced that front center is not an absolute, but dependent on a lot of factors: size of bike, intended use (real racing or relaxed touring), chain stay length, weight distribution, etc. All I can say is that at a certain point, front center can get too short and this is uncomfortable also. I would do a lot of comparison on front center dimensions for the same size bike if I were doing it again, so I could think about where I wanted it.

[Tom Kellogg]

mls:

You have introduced so many vairables, that a reasonably complete discussion would run a few pages. For example; if the two bikes were set up to fit you the same, i.e. same front centers and same trails but way different head angles, then the two bikes would need very different stem lengths. The difference in stem lengths changes the way a bike handles and your center of gravity relative to the steering axis would change and effect handling as well. It is more instructive to try to compare two theoretical bikes which only vary in one area at a time, not two or three. First, I would suggest thinking about a trail around 56mm, not 59. You may not be used to it currently, but a 56 trail will handle much more consistently. No matter what you are doing on the bike, it will always work (feel) the same. Second, try to find a frameset where the top tube length/required stem length combination is reasonable (54/9.0, 58/12.0, etc) Ending up with a 57cm top tube and an 8.0 cm stem leaves you with a bike that works like a squirelly truck no matter what the head angle is.

Just a few thoughts to confuse your weekend. Take care.

[sg8357]

Tom,

Do you vary the trail based on expected tire size ?
The 56 trail is for a 23mm tire ?

For instance a cross bike that runs 30-32mm tires do you reduce trail ?
What do you think of the French style low trail designs ?

thanks,
Scott G.

[Dave]

increases the weight on the front wheel and shortens the wheelbase. The shorter wheelbase makes the bike steer a bit quicker (for a given trail). More weight on the front might be beneficial. I like the handling of my bike better on mountain desecents with 45-46% of the weight on the front, rather than something as light as 42%.

If you've never checked the front/rear weight balance, that's a place to start. The measurement should be taken with the rider in an agressive cornering position - hands in the drops, fingers in reach of the brake levers and the upper back nearly horizontal, or as low as you'd normally ride a fast corner.

A bike with longer chainstays should improve comfort and increase the weight on the front wheel, but the longer wheelbase will slow the cornering. If you add a longer front center, it would reduce the weight on the front and lengthen the wheelbase some more. I guess you have to decide what you want. A slower but more comfortable bike or something quicker but less comfortable.

I've owned two Colnago C-40s and never thought the handling was bad, but when I moved to Colorado and started negotiating high speed corners going down mountains, I found I that the long front center that lightens the front end and the large amount of steering trail (67mm) weren't to my liking. I like a bit less trail and a shorter FC to quicken the handling. My 51cm LOOK frames seem just about ideal. They've got 72 degree HTAs and 43mm rakes, yeiding 64mm of trail, but with the short 57.1cm FC, they handle quick enough. I've owned even quicker bikes (Fondriest). The FC was about the same as my LOOK frames, but the steering trail had to be less. The bike handled great on descents, but a gusting crosswind revealed a lack of stability, I attributed to less trail.

[Fixed]

bro I don't know about you but when tom k. talks it makes sense even to a guy like me .cheers :beer:

[rpm]

TK's comments on trail are intriguing and resonate with my experience. I have a circa 1996 Ti bike with a 74 degree head angle and 40 mm fork rake (56), and a circa 2003 Ti with a 73 degree head angle and 43 mm fork rake (59).

The older one has a skinny top tube and is kind of sketchy on straight downhills, but I love how it corners, both downhill and on the flats. The newer one, with a fat top tube, is very resassuring going straight downhill, but I can't corner as well with it. I do exactly one race a year, and in the last one I found myself getting gapped in the corners with the newer bike.

So, I'm wondering if it would be worth it to try a fork with a 45 mm rake on my newer bike. Do you folks think this is a "princess on a pea" idea that's totally in my imagination, or do you think it might give me the quicker cornering that I'd like?

[mls]

thanks tom for your response its great to have someone w/your
knowledge adding to this forum. I see other builders like serotta,
kirk shooting for 59mm trail and then builders like you shoot for 56mm
trail then you have waterford building their race bikes [r22] at 56mm
trail and then their century bikes w/60mm what gives would falling
somewhere in between for a non racer be ok

[tch]

I said I thought numbers were individual, but just for comparison, here are mine. I used to have a 54 cm Concours with a 72* HTA, 43 mm rake fork, 6.53 trail, and 55.98 cm front center. I went to 49 mm rake fork, which made my front center 56.5 and brought the trail to 5.9. If I could further lengthen fork rake and get to trail number of 5.6, and correspondingly lengthen my front center, I'd do it.

[yeehawfactor]

coupla questions:
what is front-center?
what exactly is trail? the difference in a horizontal plane between the front hub and the ht?
how does adjusting trail differ from adjusting hta?

[divve]

coupla questions:
what is front-center?
what exactly is trail? the difference in a horizontal plane between the front hub and the ht?
how does adjusting trail differ from adjusting hta?

Play around with it here:
http://www.kreuzotter.de/english/elenk.htm

(Use 67cm for an average wheel size.)

[mls]

In my 2nd reply i guess i got off my point if tom says
56mm of trail fine but a hta of 74.5* w/35.3mm of rake
gives you 56mm trail and so does 71.5* hta w 52.9mm
rake but the fc could be 4.5 cm difference so if a builder
uses 56mm trail how does he come up w/the hta and the
rake to give him that 56mm ?? I guess it would come down
to fc ? Do you know what i am saying ? Tom help us please

[e-RICHIE]

I guess it would come down
to fc ? Do you know what i am saying?.



i hear ya'.
it's a gestalt thing.
don't overanalyze it!
e-RICHIE©™®

[amg]

I forget, for a 700c wheel, what is the actual diameter?

Thanks,

Antonio

[Dr. Doofus]

coupla questions:
what is front-center?
what exactly is trail? the difference in a horizontal plane between the front hub and the ht?
how does adjusting trail differ from adjusting hta?

dang it, patrick, how long have you been working in bike shops?

google search both...given that your co-workers, and my ex-co-workers, dis the doof, doof will let you find this on your own so you can edumacate yer pals at Sport!

[yeehawfactor]

dang it, patrick, how long have you been working in bike shops?

google search both...given that your co-workers, and my ex-co-workers, dis the doof, doof will let you find this on your own so you can edumacate yer pals at Sport!
thanks, i think. when you look at hours worked, i'm really more of a boone bike employee. but altleast ilan agrees that design and fit are more important than material.

-patrick

p.s.-the six13 is a turd

[Dr. Doofus]

thanks, i think. when you look at hours worked, i'm really more of a boone bike employee. but altleast ilan agrees that design and fit are more important than material.

-patrick

p.s.-the six13 is a turd


but do the guys get why the CSi got e-bayed for peanuts -- on account of its 62.5cm f-c...and that the gunnar isn't as well made, but in the end is a better bike?

ain't drinkin that haterade...just hope that the bike in question was a learning experience....

[yeehawfactor]

but do the guys get why the CSi got e-bayed for peanuts -- on account of its 62.5cm f-c...and that the gunnar isn't as well made, but in the end is a better bike?

ain't drinkin that haterade...just hope that the bike in question was a learning experience....
such discussion is lost on me until i am enlightened to f-c.

[Dr. Doofus]

patrick --

its the distance from the BB to the fork tips.

its just one variable in the handling equation, but as a very general rule, a longer f-c means less weight over the front wheel, or, it means having to move the rider forward on the bike to get the weight distribution right...or it just means a really long front end, which translates into a long "turning radius."

for my personal dumbass preference, doofus, I who am, likes a bike with a 57.5-58.5 f-c, and 53-55mm of trail (assuming the bb is in the 7cm of drop range, and a 73 sta)...sharp, but not nervous...

doof loves ilan and would work there again if ilan would have him

[e-RICHIE]

such discussion is lost on me until i am enlightened to f-c.


the f-c is the measurement from the front axle to
the bb spindle. it has to taken in metric. 'cannot
recall why. you wonder why it's an arcane issue
and difficult to articulate? consider that gestalt
word i used earlier. in f-c, what is above the fork
is as critical as what is below. the same steering
column that telescopes the hub axle to a certain
point also holds the h'bars a certain distance from
the saddle assembly. hence, it's little use describing
f-c (and all the similar ways one can achieve similar
trail measurements with head angle/rake combos),
without considering the rider's reach measurements
up there above the top tube line. by the way, who
misses Climb90210? i surely do.
e-RICHIE©™®

ps

arrange disorder

:cool: :cool: :cool:
;) ;) ;)
:D :D :D

[Dr. Doofus]

what e-ritchie said

a 58 cm bike with 52mm of trail and a 57.5 f-c with a 120 stem and say 7cm of saddle setback, with a seat height of 79 cm and maybe 9 cm of drop would put a rider who is properly sized for that 58 cm bike in a very good handling position...what's above that tight f-c is arranged so as not to be in disorder

now, that same 58 cm bike with 52mm of trail and a 57.5 f-c set up with a 100 +16 stem, 4.5cm of saddle setback, a seat height of 77.5 cm and 2cm of drop to accomodate a five-six dude with no flexibility would be a danger to the poor slob riding it, and all in his path....

[Brian Smith]

what e-ritchie said

a 58 cm bike with 52mm of trail and a 57.5 f-c with a 120 stem and say 7cm of saddle setback, with a seat height of 79 cm and maybe 9 cm of drop would

Whoa, ya lost me.
Is this an Actual Bike (tm) or thought experiment?
Who the heck has used 9cm drop with 700c roadwheels?

[Dr. Doofus]

was thinking saddle-to-bar drop, brassman...of how a rider might be positioned on a bike that size...trying to further for patrick the point that f-c needs to be taken in context of what's on top -- namely, the rider

9cm of BB drop?


yyyiiiikkkeees!

[yeehawfactor]

the f-c is the measurement from the front axle to
the bb spindle. it has to taken in metric. 'cannot
recall why. you wonder why it's an arcane issue
and difficult to articulate? consider that gestalt
word i used earlier. in f-c, what is above the fork
is as critical as what is below. the same steering
column that telescopes the hub axle to a certain
point also holds the h'bars a certain distance from
the saddle assembly. hence, it's little use describing
f-c (and all the similar ways one can achieve similar
trail measurements with head angle/rake combos),
without considering the rider's reach measurements
up there above the top tube line. by the way, who
misses Climb90210? i surely do.
e-RICHIE©™®
ah, ok. so f-c is of little use unless you also evaluate hta and bar reach. i can't just say xx.x mm of f-c is right for me unless cockpit length is considered.

thanks for splainin richie and doof. well, thanks to richie anyway :cool:

[jerk]

listen to e-richie or at least read what he said. one has to view it as a totality. unfortunatly most of the people who truly "get it" are dead now, or may as well be.

jerk

[e-RICHIE]

am i the only one here with a heart.
doesn't anyone else miss Climb90210?
hey - thanks for reading.
e-RICHIE©™®

[Dr. Doofus]

overall, doof misses climb-0

wisfully,

time for the james gang

[93legendti]

am i the only one here with a heart.
doesn't anyone else miss Climb90210?
hey - thanks for reading.
e-RICHIE©™®

Yes, we miss him...what happened to him?

[jerk]

am i the only one here with a heart.
doesn't anyone else miss Climb90210?
hey - thanks for reading.
e-RICHIE©™®


th jerk has it on good authority that climbo90210 will be back in the hizous byh the end of the week.....he's back in the land of the free at least....so there's hope. the jerk missed him too.

jerk

[e-RICHIE]

i asked steven hawkings and he said
he shared a few drinks and an arm
wrestling match with Climb90210 here:
http://imagine.gsfc.nasa.gov/Images/news/BH_med.jpg

[manet]

!

http://www.totaltravel.co.uk/images/british-beer-guide/bowler-hat-man-drinking.jpg

[e-RICHIE]

!

http://www.totaltravel.co.uk/images/british-beer-guide/bowler-hat-man-drinking.jpg


ted and joey said it best...
http://www.webfitz.com/lyrics/index.php?option=com_webfitzlyrics&Itemid=27&func=fullview&lyricsid=4322

[manet]

ted and joey said it best...
http://www.webfitz.com/lyrics/index.php?option=com_webfitzlyrics&Itemid=27&func=fullview&lyricsid=4322

and so they (climbO + steveO) are, training hard for
the next granite state leg press fest:

http://homepage.mac.com/amclaughlin1/.cv/amclaughlin1/Sites/.Pictures/new%20tender%20miss%20web/7%20drunk%20and%20wheelchair.jpg-thumb_273_195.jpg

[Len J]

th jerk has it on good authority that climbo90210 will be back in the hizous byh the end of the week.....he's back in the land of the free at least....so there's hope. the jerk missed him too.

jerk


I thought he was out of the country........

Len