Custom Bike Phase II - Geometry Wars
 

I started my order with Pelizzoli (Ciocc) for a Corsa GP.
I sent my measurements, design ideas, and deposit. I also sent Cervelo's geometry, my intended use (aggressive, racing, etc)

Normally i'm between a 56 (Cervelo S2, 110mm stem) and a 58 (Felt AR, 100mm stem) in bike sizing.

Pelizzoli sketched the following for my bike's geometry. It looks like hell, but from a guy who's been doing it for so long, i didnt really expect CAD. One note, i'll be supplying my own fork.
http://i.imgur.com/3OcGl.png

This is my Cervelo S2 geometry:
http://i.imgur.com/uIGMR.png

My question is:
How different would this be from what i'm used to?
Could/should i ask him to 'tighten up' the geometry to make it more aggressive?

its good. no.

i was concerned that the wheelbase was much longer than my S2.

For comparison, here's the numbers on my new Kirk Frameworks JKS series (Dave's 'Race' bike).

https://lh6.googleusercontent.com/-C...BikeDesign.jpg

My top tube is shorter, which accounts for some of the front-center length difference, other than that, looks pretty close. I think you'll like it. Trust the man who has seen your numbers and your requests over a bike built to fit a wide range of riders.

Oh, and why are you supplying your own fork? Wanting to go carbon I guess? Have you told the builder the trail of the fork so he can take that into account for the build (I'd hope so, but just checking)

The front center seems long, which isn't bad by itself, but if your top tube is only 1 cm longer but your front center is 8 cm longer... it implies an extremely shallow head tube angle or a very high fork rake (or both). One or the other won't determine stability/agility (both together will determine stability/agility).

I'd check and make sure the head tube angle and fork rake are semi-standard (since they'll both need to be semi-standard to work properly). Although unusual designs work it's harder to get forks that don't have, say, a 43-45mm rake for example.

If you run shorter stems (100-110mm) you may want to think about getting a slightly shorter top tube to get more weight on the front wheel. I suppose I lean towards one side of the spectrum but I prefer a 120mm stem (with normal bars, which means 130mm or more with a compact drop bar) in order to get good weight on the front tire.

As far as long wheelbase, my two custom frames, with very very short seat tubes (40 cm, compact style, so about 50 cm for a traditional shape frame), have over 100 cm wheelbases. This is due to the 56.5 cm top tube lengths (and 73 head tube angle with 43mm rake fork).

get a matching fork, silly.

that front center is 61.5.

Not having him make a matching fork is a huge mistake IMHO as is trying to influence what he does with the geometry. Guaranteed he knows WAY more about this than you or anyone in this thread.

yea, no ish he knows more than me.

i just don't want a steel fork. I'll tell them that i plan to use a fork with a 43mm rake and see if that changes anything.

It's like if botto and feitsbob had a love child!

if that's true (looks like it is - my grandfather writes his 1s like that) then it's really not that far off from my current bike. I was reading it as 67.5.
I will email them that I plan to use a 43mm rake fork and want to use a 120mm stem.

For what it is worth, I am 6'0" with long femurs and can ride typically most size 56cm or 58cm frames (generally 120mm stem on 56cm frames), and here is the geometry I went with on my custom bikes:

http://2.bp.blogspot.com/-XKJV0TCt2y.../CustomGeo.jpg

I prefer a somewhat upright position, hence the long head tube (so I can run the stem with minimal spacers).

Me too. My bad.

It's 61.5, no doubt. Compare the 1 to the 7 on the top tube.

So i emailed them and told them id want to use a 120mm stem and a 43mm rake fork. I got an email back from them today:

So that's pretty cool.

facepalm to non custom fork.

getting a carbon fork.

I looked into a custom frame through an Italian supplier. They only talked about front center, nothing about head tube angle and rake.

I couldn't get my head wrapped around that, since I had a variety of poor handling stock bikes. I had an idea of what I liked from each one but couldn't express it in front-center (still can't). To me front-center was and is a result of the 3 sides of the bike - seat tube angle, top tube length, head tube angle + fork rake. Going the other way I can't quickly tell what happens when front center goes out, say, 1 cm.

Ultimately, even though the custom cost was nil, I decided against getting a frame through them. For one thing they said that a 55-56 cm top tube was ridiculous.

they think:
1) front center and rear center: very slightly variable, a balanced weight distribution that classically works and scales a small amount for rider size
2) head tube angle: highly variable, to adjust for your the reach
3) rake: highly variable, to correct the trail
4) top tube length: whatever connects the dots

you think:
1) rake and head tube angle and trail and rear center: almost locked, 43ish and 73ish and 57ish and 400ish, or whatever
2) top tube length: highly variable, to adjust for a persons reach
3) front center: whatever ends up happening

youll end up with the same contact points, head tube length, and trail but different front centers, head tube angle, rake, and top tube length.

Pardon me, but I need to clean brains off the desk. My head just exploded.

Makes me wonder if paying closer attention to my geometry might make me more comfortable and faster. Until now, I have just relied on cool schwag :D

or often, front center then top tube then a head tube that connects with a rake that corrects. basically, they key more in on the front and rear balance of the two axles and of the two contact points and have the fabrication capability, especially with forks!, to make it work.

Is this steel right??? 100% racing machine right?

Well if you want something aggressive I would go 73.5 in the back and 74 degrees in the front. Stays made to fit only 23 mm tubulars in there (short dropouts), why? the chainstays will be shorter, climbing and sprinting will be nasty nice, very snappy.

74 degrees in the front, the bike will turn in a dime and cut curves big time, and if the fit is right the complain i'll get about the woobble of death it wont be present ever. And since pelizzolli bikes rock big time you wont suffer of this ever, his forks are like 35 mm rake so it will hava a nice handling.

Shorter rear end will bring a shorter wheelbase, there u have it, the bike will handle super nice. Hope you can handle the bike, some guys can't really handle snappy guys because their handling bikes abilities just SUCKS!

Good luck with the bike, please post pictures when you get it ;)