Anyone want to help me design a velociraptor bike?

I know someone else just posted a thread about frame design, but mine is more specific.

Keen on putting together a bike that actually fits. The smallest 700c bikes have issues with toe overlap, and tend to be slackened at the front in an attempt to reduce this, which to me seems to fuck up the handling. Or at least perceived fun. So looking at 650c front. A bit like this;

My current road bike is as follows, want to base everything off this as the geometry aside from the fact it is a little long. Really makes me whooosh. So want the same angles. Would not dispute having BB even higher, high BB's are very agreeable for me. Low ones for some reason make bikes feel super sluggish for me.

The top tube on this is 54cm and I would like it to be 51.5 without changing headtube or other angles. (the seattube is 52) I ride this bike with bullhorns currently, because my arms are in no way long enough to hold the drops. The lowness is not an issue, it is how "forward" they are. I do want to use drops though. Even with the bullhorns it is a bit of a stretch.

I was hoping to get it done by mielec for cheapness, a bit of an experiment. With a gear hanger if they are able otherwise a fixed.

Anyone mind giving me some pointers on how to go about this? Do I need to find a fork before planning the geo? Do I need to bother accurately measuring angles of my existing frame?

In a word (or 2), compact geometry.

What you have hit upon is something that has troubled frame builders and short riders for years. For any horizontal top tube designs, you start to reach a point when you;

• can't make the seat tube any shorter because the head tube becomes non-existent,
  
• can't make the top tube any shorter because of toe overlap and the front tyre hitting the down tube.
  So you end up compromising by having steep seat angles, shallow head angles, extra fork rake and very short stems and seat posts, all of which compromise handling and make the bike look weird. Or have smaller wheels.
  
  

Compact frame designs allow a seat tube as short as is necessary with a sloping top to shorten reach without compromising frame angles or fork rake and allowing decent tyre clearance and sensible stem and seatpost length, whilst keeping 700c wheels.

Or something like that :-)

Thing is, I likes me a high saddle.

If the frame is too small like a compact, then there is so much seatpost (more than the geometry would suit) that the seat ends up further back than where it 'should' be. I could always gaston it, but I would rather not.

650x650 seems to make the back end shorter than I need, I dont need or want such a short wheelbase but like bodyweight to be balanced so there is some decent weight on the front, which is seemingly impossible on a small 700x700 bike as the headtube angles are too slack or top tubes too long. Bikes with a long back end feel fine to me, good for panniers especially. Although that is not the intended outcome for this bike.

There are always compromises to be made with bicycle design. It's your design so if you want a 650 front then go for it. You'll need a specially sized fork or a long reach brake.

tried compact drop bars?

Compact bars miss the point. A hand position well over the front wheel is optimal for handling, and I have no problems getting down low with deep drops. Arms and torso are just not long enough to deal with the typical length top tubes+a decent length stem/bar setup.

If you shorten the stem and use compact drops, in my opinion the handling is sub-optimal. Some people (including tester here I believe) say its no big deal and you just get used to it. I disagree.

Your requested dimensions are not out of reach for a 700c frame with typical angles. I have a track frame here 52 c-c top tube, 48 c-c seat and BB height of 28cm. Small cages don't strike with 25mm tires. Unless you really want a funny bike you don't have to.

48c-c equates to around 50c-t. What you have there is about the smallest size of horizontal top tubed frame you can make and still take 700c without wheel strike. Note the top tube is longer than the seat tube in this case, but a 52/52 would be pretty close to what the OP wanted.