43mm or 45mm for big bike?

[big D]

I need some advice. I have ordered a Ouzo Pro Criterium fork but i order a 45mm rake instead of a 43mm. What will this do the handling of my bike? My bike is a virtual 61cm frame and I think it originally came with a 43mm rake. The head angle is 73 degrees and I want a little more stability then I had originally. Need some advice so i can change the rake tomorrow.

thanks

[Peter]

You sure you got that right-a 61cm frame with a 73 degree head angle? It COULD be built with such a head angle, but most frames tend to have steeper head angles in larger sizes, presumably to keep the wheelbase in a desired spec. I don't see why that's important but I don't ride a large frame so I don't know what it feels like.

That aside, if your bike in fact has a 73 degree head angle, the 43mm fork with provide MORE stability than the 45mm, though I doubt you'll raise your eyebrows about the difference. The 73/45mm combination is considered so common because it works so well that I'm surprised you're asking for more trail.

The 2mm difference is almost not worth swapping fork choices for. Have you considered a 40mm rake fork? The 73/40mm combination would give you 60mm of trail. You only gain 2mm of trail going from the 45 to the 43mm fork. My real world experience is 5mm is the minimum difference in rake necessary to impart a perceptible difference in handling.

Reynolds makes an Ouzo Pro (though perhaps not a Criterium) in 40mm.

[musgravecycles]

43mm rake= Trail of 57.1
45mm rake= Trail of 55.1

The 43 will give you a more stable ride than a 45. If it originally had a 43 and you want more get a 40 which will give you a hair over 60 on trail. That will be better yet. I believe Reynolds makes a 40.

[musgravecycles]

Looks like Peter beat me to it while I was typing. What frame is it? Is it a custom? I just checked and Reynolds does have a Criterium in 40.

[Smiley]

Having just gone through this experiment , you also omitted the SPAN of the fork your replacing , the Ouzo is 372 mm and if your old fork was shorter, then you will RAISE the front end of your bike by just a hair that should really be like adjusting the head tube angle ( think relaxing it ) and thus making for a tad longer trail . Don't go with a longer rake if your looking for more or a slower handling front end , think the opposite as musgraves has said . The Ouzo Pro which I favored over my F1 made my front end track just right for me , keep in mind that the span of my F1 was 365 mm , so I did raise my front end . I did think to go to a 40 mm rake fork but given the span differences I chose to stay at 43 mm as advised by my hero kelly bedford .

ps: I never assume that the spans of all forks are the same , its good to check

[Kirk Pacenti]

[QUOTE=Peter]You sure you got that right-a 61cm frame with a 73 degree head angle? It COULD be built with such a head angle, but most frames tend to have steeper head angles in larger sizes, presumably to keep the wheelbase in a desired spec.[QUOTE=Peter]

Yes, this is true, it also keeps weight distribution balanced. An interesting tangent however, is that Master Builder and Designer Leonard Zinn prefers a 72* head angle for all his BIG bikes. We have talked about it from time to time and he has some interesting points.

Leonard has lots of experience racing, testing product, and building custom frames. I presume he knows what he is doing for bikes this big, he is 6'6"!
I would love to hear the jerks thoughts on this....

[jerk]

jeez---you know the jerk kirk...he doesn't really know enough about frame design to emerge from certain ancient italian archetypes. that being said he would be interested to know what mr. zinn's reasons for the slack head angle are. could you enlighten the kids here? firstly, the jerk is talking about racing bicycles with 700c wheels for bike racers...in general the jerk wants to achieve proper weight balance....the old de rosa trick is to steepen the head angle to tuck the front wheel thereby allowing for a "normal" front center and wheelbase....granted, tubing choices allow torsionally rigid bikes to be produced with extremely long top tubes now, but having ridden a few bikes that "fit" but use 61+cm top tubes the jerk has found them to handle strangely. now there are not alot of 6'6+ pro bike racers out there, but the bigger guys (axel merckx, magnus backstedt etc.) tend to use custom frames for men of their size yet they tend to have fairly normal front centers and really long stems.....now here's the other thing. the jerk is about 6'3 but his handlebars and that of many taller racers (big mig being the exception) are not really all that much higher than the regular sized guys....the reason for this is beyond the monkey arms the jerk has (and alot of taller bike racers seem to be "gifted" with) is the fact that you're going no where fast if you can't get as low as the guys you're racing with....one other point which is probably as irrelevent as all the jerk's previous points.....bikes need to handle well, all this is based upon weight balance and restricted by the design constraints of things like available tubing, components and most importantly wheel size....if the designer works around a relativly fixed range....the jerk has found that with 700c wheels seat tubes (all measurements are c-c) should be between 48-66cm....top tubes should be 50-60.5 while front centersshould really not exceed 59-62cm...this is straight coni manual stuff and nothing new but it's worked in the jerk's experience.
what do we do with the freaks then? if a morphological anomoly requires a larger top tube than this, make it up with stem length and saddle set back....all the wile making sure the balance point of rider and bike is around the bb....anyway, this stuff works and attempts by the industry over the years to step outside these design parameters have for the most part failed. at least in the pro cycling world.
jerk

[Too Tall]

Amazing Grace.....was lost but now I'm found. I'm a morphological anomoly dad :)

To a point Senor'. If we "rightsize" Coni measures for us knuckle draggers won't you end up with bikes with (gasp) custom forks? What else?

[e-RICHIE]

"...Leonard Zinn prefers a 72* head angle for all his BIG bikes. We have talked about it from time to time and he has some interesting points."



i'd be interested in reading them.

[cpg]

jeez---you know the jerk kirk...he doesn't really know enough about frame design to emerge from certain ancient italian archetypes. that being said he would be interested to know what mr. zinn's reasons for the slack head angle are. could you enlighten the kids here? firstly, the jerk is talking about racing bicycles with 700c wheels for bike racers...in general the jerk wants to achieve proper weight balance....the old de rosa trick is to steepen the head angle to tuck the front wheel thereby allowing for a "normal" front center and wheelbase....granted, tubing choices allow torsionally rigid bikes to be produced with extremely long top tubes now, but having ridden a few bikes that "fit" but use 61+cm top tubes the jerk has found them to handle strangely. now there are not alot of 6'6+ pro bike racers out there, but the bigger guys (axel merckx, magnus backstedt etc.) tend to use custom frames for men of their size yet they tend to have fairly normal front centers and really long stems.....now here's the other thing. the jerk is about 6'3 but his handlebars and that of many taller racers (big mig being the exception) are not really all that much higher than the regular sized guys....the reason for this is beyond the monkey arms the jerk has (and alot of taller bike racers seem to be "gifted" with) is the fact that you're going no where fast if you can't get as low as the guys you're racing with....one other point which is probably as irrelevent as all the jerk's previous points.....bikes need to handle well, all this is based upon weight balance and restricted by the design constraints of things like available tubing, components and most importantly wheel size....if the designer works around a relativly fixed range....the jerk has found that with 700c wheels seat tubes (all measurements are c-c) should be between 48-66cm....top tubes should be 50-60.5 while front centersshould really not exceed 59-62cm...this is straight coni manual stuff and nothing new but it's worked in the jerk's experience.
what do we do with the freaks then? if a morphological anomoly requires a larger top tube than this, make it up with stem length and saddle set back....all the wile making sure the balance point of rider and bike is around the bb....anyway, this stuff works and attempts by the industry over the years to step outside these design parameters have for the most part failed. at least in the pro cycling world.
jerk

I know you like what you like but I'd argue that the idea of increasing head angles as frame size increases has nothing to do with material limitations. Increasing the head angle won't shorten any tubes at least not enough to matter. I'm quite convinced the practice that you've described in grounded primarily in tradition. Nothing wrong with that but I don't think it's the way to make a better bike. There's nothing magical about keeping the wheelbase within 1 meter. Think weight distribution. Ignore wheelbase. Trust me.

Curt

[Kirk Pacenti]

jerk, e-R,

When LZ and I last spoke, we were discussing race bikes with 700c wheels.
Here is a link, not sure if it will be much help but it may give insight into Leonard's thinking. http://www.zinncycles.com/bikes.aspx?bike=projbig
He told me much the same that flex shimmy etc, become serious issues on BIG bikes adn geometry needs to be adjusted for it.


As for the idea that race bikes are the only ones that handle properly, I think it's just not true. Especially if you are using pro racing as the standard. Bikes should be designed for the rider using it. If the rider races Cat 5, a bike designed for Cat 1/ Pro racer is likely to do more harm than good.
I don't know many people, even racers, that would benefit from such an extreme riding position as you find in the pro ranks.

[e-RICHIE]

i think the only measurement that we'll see on pro's bicycles
that isn't very telling is the drop from the saddle to the 'bars.
the saddle heights are "normal", and so are the reaches, but
the drop is not something to mimic if you are not a full time
athlete racing 110 days a year. you simply won't have the
upper body strength and flexibilty to assimilate this.

reach is one thing; drop is another.
biker beware.

[e-RICHIE]

"When LZ and I last spoke, we were discussing race bikes with 700c wheels.
Here is a link, not sure if it will be much help but it may give insight into Leonard's thinking. http://www.zinncycles.com/bikes.aspx?bike=projbig
He told me much the same that flex shimmy etc, become serious issues on BIG bikes adn geometry needs to be adjusted for it."


could not find any 72 degree h.a. chat there...

[jerk]

I know you like what you like but I'd argue that the idea of increasing head angles as frame size increases has nothing to do with material limitations. Increasing the head angle won't shorten any tubes at least not enough to matter. I'm quite convinced the practice that you've described in grounded primarily in tradition. Nothing wrong with that but I don't think it's the way to make a better bike. There's nothing magical about keeping the wheelbase within 1 meter. Think weight distribution. Ignore wheelbase. Trust me.

Curt

ok, the jerk trusts you. but wouldn't achieving proper weight distribution necesitate keeping the front center/wheelbase within certain parameters? a steep head angle doesn't shorten any tubes noticibly but it would help bring the front wheel a little closer to where it's supposed to be for proper balance.
jerk
(hey you build frames, the jerk just rides them.)

[Kirk Pacenti]

could not find any 72 degree h.a. chat there...[/b]


There used to be geometry charts there, that was a while ago. Maybe potential customers were scared off by the slack angles and he pulled it? ( I don't know)
All the chat we had was the real kind, verbally over the telephone. ;)

[Too Tall]

(below snipped from the honorable Titan Zinn's Website)
"The oversized tubing minimizes weight while maximizing stiffness and increasing the resonant frequency of the frame (thus reducing shimmy). "

He didn't mention 72 but he did say resonant :) I'm kidding! OMG where is your sense of humor????

Could it be so he can use std. rake forks????

[Orin]

As for the idea that race bikes are the only ones that handle properly, I think it's just not true. Especially if you are using pro racing as the standard. Bikes should be designed for the rider using it. If the rider races Cat 5, a bike designed for Cat 1/ Pro racer is likely to do more harm than good.
I don't know many people, even racers, that would benefit from such an extreme riding position as you find in the pro ranks.

Depends on what kind of racing the Cat 1/Pro bike is meant for I'd think. Sure, a fast handling crit bike wouldn't be good, but a bike meant for a long stage race?

The carbon fiber Treks are popular with some local randonneurs and that's not even racing. My early '80s Koga-Miyata Full Pro frame (Capri-Sonne rode the same frames in '81 or so - see Peter Winnen's bike in the Cycle Sport climbers issue) is the best handling most stable bike I have.

Orin.

[cpg]

ok, the jerk trusts you. but wouldn't achieving proper weight distribution necesitate keeping the front center/wheelbase within certain parameters? a steep head angle doesn't shorten any tubes noticibly but it would help bring the front wheel a little closer to where it's supposed to be for proper balance.
jerk
(hey you build frames, the jerk just rides them.)

In my opinion, No. I don't believe there's a magical wheelbase. What matters, to me anyway, is where the rider is located between the two wheels after the rider's contact points are resolved. The Italian methodology seems to reverse that order of things. Does that make sense?

Curt

[e-RICHIE]

it's a "stew" of choices that all work in unsion;
the steeper head angle "also" allows the upper
body to be placed further out without adding
mm's to the top tube or stem.

[Darrell]

it's a "stew" of choices that all work in unsion;
the steeper head angle "also" allows the upper
body to be placed further out without adding
mm's to the top tube or stem.

If I follow you correctly, then for example a two degree angle change will give approx 4mm extra true horizontal reach. I am unsure why and how one would let the head angle be decided by the desired horizontal reach dimension, by staying within constraints of a fixed dimension TT and stem constraints that is within the "Stew of Choices".
But you are correct, it will give a greater reach, but then the bars are lower by about 4mm as well. So when the bars are lifted to the same vertical measurement as one started with, then the true horizontal reach is reduced due stem moving towards the saddle due to the head angle and thus reach is closer to 2mm.
Not contradicting thoughts, just digesting here.
You have got to love CAD! {when your maths is as bad as mine}

[e-RICHIE]

"If I follow you correctly, then for example a two degree angle change will give approx 4mm extra true horizontal reach."

i would never consider a 2 degree change for the
frame-in-question in order to acheive a "reach" fit.
a few minutes is all i'm ever considering.

"I am unsure why and how one would let the head angle be decided by the desired horizontal reach dimension, by staying within constraints of a fixed dimension TT and stem constraints that is within the "Stew of Choices"."

for me, head angle is always part of the "reach" equation.
it's part "reach", part "steering".

"But you are correct, it will give a greater reach, but then the bars are lower by about 4mm as well. So when the bars are lifted to the same vertical measurement as one started with, then the true horizontal reach is reduced due stem moving towards the saddle due to the head angle and thus reach is closer to 2mm."

why would the bars be lowered?
they'd simply periscope out further by
dint of the more inclined head angle.

[jerk]

yeah what e-richie said.
jerk

[e-RICHIE]

yeah what jerk said.
e-RICHIE

[Too Tall]

You guys get a room already :rolleyes:

[Darrell]

i would never consider a 2 degree change for the
frame-in-question in order to acheive a "reach" fit.
a few minutes is all i'm ever considering.[/B]

if 1 degree makes 2mm dimension change to position then Crikey one minute of a degree will make .033mm,


for me, head angle is always part of the "reach" equation.
it's part "reach", part "steering".
Agreed, that is all logical.

why would the bars be lowered?
they'd simply periscope out further by
dint of the more inclined head angle.
When you change the head angle you are rotating the stem with it. That alters the vertical and horizontal placement of the bars, then if you raise or lower the bars to obtain desired bar height then the reach, horizontal will be changed, reduced if the stem is raised, my example of two degree head angle change will only result in 2mm horizontal increase if the bars are at the same height
You got to love CAD. Next best thing to a lathe!
All this is "Spliting a frogs pubic hair", but fun." ;)
but I have got to go and work on my nuclear accellerator down stairs, some far off dusty dry country in the middle east has ordered one. That way I will not have a two year waiting list :cool:

[e-RICHIE]

well i increase a head angle by a few minutes to
increase a "reach" thingy; i would normally respect
the 'bars vertical placement upon assembly, regardless
of the CAD.

[Darrell]

I need some advice. I have ordered a Ouzo Pro Criterium fork but i order a 45mm rake instead of a 43mm. What will this do the handling of my bike? My bike is a virtual 61cm frame and I think it originally came with a 43mm rake. The head angle is 73 degrees and I want a little more stability then I had originally. Need some advice so i can change the rake tomorrow.

thanks

What you may think your getting maybe not what what you have.
Something to consider.
I have found Reynolds forks can have + - 2mm varation in fork off set {rake} to what is quoted. I spoke to Reynolds and they said +-1mm is the tolerance.
Many carbon fork makers cannot hold the tolerance they state.
I cannot believe any one can tell the differance of 2mm of off set and also the fork length may be different and this will affect head angles etc.
Cheers from a never believe till I measure Dazza :cool:

[Darrell]

well i increase a head angle by a few minutes to
increase a "reach" thingy; i would normally respect
the 'bars vertical placement upon assembly, regardless
of the CAD.

Then 2* head angle change and with the bars at speced height will then result in 2mm reach alteration. So I still cannot see how head angle factors in considering stem and TT length.
I got to go and split a few atoms down stairs. Too much to do.
And also read more about SolidWorks 3D parametric modeling rather than net time, so I can use space shuttle tubing to go faster in the crosswinds while monitoring my hamatecrits while listening to Jean Michael Jarre Oxygen part 1 to 13.
Ciao Bella :cool:

[Grant McLean]

Dazza wrote: I cannot believe any one can tell the differance of 2mm of off set and also the fork length may be different and this will affect head angles etc.


Dazza,

Really? I think _anyone_ can tell the difference. It's night and day!

cheers,

Grant