Top tube downslope angle

Complete head f?&k - I'm having a frame designed; the designer has suggested a 10 degree to tube downslope, wheras I had been thinking more of a 5 degree angle.

Having googled, I can find little about the benefits or otherwise of such an extreme geometry. The designer tells me that it will make the bike stiffer (frame is being made of titanium, so this is probably advantageous). Do I just trust him and go with it, or should I stick to my guns and ask for a less extreme angle?

Aesthetically, I quite like it - same as this:

Any views on this?

i have no idea but i hate a steep slope like that moots.
just like a langser... fucking hate it.

We've done this to death in the custom frame thread.
Why are you trusting someone to build you a frame but questioning his design choices?
Looks-wise, it's fucking fine. Anti-compact geo people are cretins*.

*Thanks for my new favourite word, Object.

Yes, but the custom frame deals with aesthetics - I'm actually interested to know what the difference is to the ride between the various options. I like compact. I'm trying to determine whether or not it makes any difference to ride to go to 7 degrees or even 5 or so degrees.

Depends who the designer is, and whether you think he/she really knows their stuff, especially with regards to working with Ti.

@ Hippy/VV - you are both right; I will trust the designer. Must learn to stop over analysing!

Ask him how much stiffer, why it needs to be stiffer (to allow lighter tubes?) and so on.
If it was a real requirement of a Ti frame then there would be a lot more Ti frames like that wouldn't there?

Is that because of how it looks or how it rides?

i have no idea but i hate a steep slope like that moots.
just like a langser... fucking hate it.

We've done this to death in the custom frame thread.
Why are you trusting someone to build you a frame but questioning his design choices?
Looks-wise, it's fucking fine. Anti-compact geo people are cretins*.

*Thanks for my new favourite word, Object.

this.

Is that because of how it looks or how it rides?

it's because he has no idea what he's talking about. "like a langster" haha

my opinion is that since you're getting it custom made it's primarily a looks thing. Compact geometry is helpful for large scale manufacturers because it allows a given frame to fit a wider range of body types. Traditionally modern compact frames also have shorter bases, making the bike snappier. Obviosuly this has nothign to do with the angle of the toptube, but still is associalted with the "comapct" geometry overall. Whether or not your frame will have a shorter wheelbase is something seperate from this particular variable.

To your specific question, the smaller triangles will be stiffer in the pedaling area/BB Shell/etc. However, You will have more seatpost sticking out of the frame. If you are running ar carbon post, this will help soak up cobble stones and the like with out affecting the stiffness in the BB area. This alone is reason enough for me to go with it, but i don't think the effect will be drastic. Still a step in the right direction, by moving flex from the frame to the seatpost.

Finally, I personally love the way it looks with titanuim frames especially. Cannondales are just about the only modern frame i actually think look good with a level toptube.

Compact geometry should make the frame stiffer, as it reduces the size of the triangles* for a given bike size. It also aids standover for shorties like me. The thing to focus on here is the frame material. Most of the compact carbon frames we see will have a far shallower slope (say 7 deg for a small), often getting leveling out somewhat, as frame size increases (say 4 deg for a large). So 10 deg seems like a lot, but then its not a carbon frame, so maybe the comparision we make (being used to seeing carbon roadies) is a bad one. The Moots above is their, top of the range, all out performance frame. Moots know titanium, your designer knows titanium (I hope), so I'd trust him/her.

Aesthetically, I dont like it if the seatstay/toptube/seattube cluster is below the height of the rear wheel (not always easy in my size). This I would deem 'comedy compact'.

(*not that the main triangle is a triangle)

Thanks for the comments - all seems to make sense and is consistent with what I'm being told.

+1 on what Jersey and Smallfurry said.

The geometry I worked out for a possible XACD roadie, had a 8 degree slope. This was pretty much as high as I could go without breaking the all important seattube cluster above rear tyre rule.

ETT . . . . 535mm
HT . . . . 121mm
ST (C-C) . . . 460mm
ST (C-T) . . . 609mm
CS . . . . 403mm
BB Drop . . . 74mm
HTA . . . . 73,0º
STA . . . . 74,0º
TT Slope . . . 8,0 º
Saddle height . . . 695mm*

the other alternative is to drop the TT (but still keep it level) and slightly extend the head tube.
because you have to go oversize to get high stiffness some manufacturers use shaped tubes but the cost is very high as they have to be cold worked not thermoformed like aluminium.

are you a pie-eater? maybe that's why the builder wants to go compact? if you are a lightweight then maybe you could discuss with him about backing off the angle a bit?

the other alternative is to drop the TT (but still keep it level) and slightly extend the head tube.

Very good point. Probably worth combining the two.

Its nice to have a spacer between stem and headset for adjustment with different stems/bars. But an extended headtube is a far stiffer arrangment, than a spacer tower. I've gone with a 15mm extention in the example above, which is 10mm more than I'd expect for a frame of that size.

Ultimately, I'd trust the designer/builder though. I would'nt take my plan above to anyone more expensive than XACD, as its designed by a pleb ;)

we are having 20mm of spacers - he does not want to extend the head tube relative to the top tube as it will compromise front-end stiffness (particularly as we are not going down the integrated head tube route).

20mm of spacers isnt so much......

20mm of spacers isnt so much......

Haha that's fucked up!

Honestly who thought that was a good idea?!

that moots looks the nuts, trust the builder, remember why you chose them and not other builders to make this for you.

we are having 20mm of spacers - he does not want to extend the head tube relative to the top tube as it will compromise front-end stiffness (particularly as we are not going down the integrated head tube route).

well 20mm isn't that much.
i don't agree about an extended head tube compromising stiffness though, quite the opposite.
my cynical nature suggests the builder doesn't want to source a longer tube than the ones he has in stock :-)

i have no idea but i hate a steep slope like that moots.
just like a langser... fucking hate it.

• 1miwyon.
  
  

I hate modern road bikes because of this very thing.

Only BMX and MTB look good with a sloping top tube. FACT.

are you a pie-eater? maybe that's why the builder wants to go compact? if you are a lightweight then maybe you could discuss with him about backing off the angle a bit?

Not particularly - but it's a large frame.

my cynical nature suggests the builder doesn't want to source a longer tube than the ones he has in stock :-)

We've fiddled about with the head tube length quite a bit, as I've ummed and ahhed about the length of forks I want.

cancel the order.
save up for a better frame. carbon (parlee, crumpton) steel (vanilla, IF, Sachs, Pegoretti, Zullo)
Ti (makers who use shaped tubes to get over the low stiffness in large sizes)

do you even need custom? manufacturers/builders who offer 1cm increment sizes cover most sizes unless you are an odd size.

have you read the other custom frame thread?

cancel the order.
save up for a better frame. carbon (parlee, crumpton) steel (vanilla, IF, Sachs, Pegoretti, Zullo)
Ti (makers who use shaped tubes to get over the low stiffness in large sizes)

do you even need custom? manufacturers/builders who offer 1cm increment sizes cover most sizes unless you are an odd size.

have you read the other custom frame thread?

Who said anything about bog standard tubes?