Road Cycling - Frame Geometry Experiment(again)

I am doing a(nother) experiment.

I would like to ask you what is the distance(on your bike) between the tire and the seat tube(pls. see figure).

Call it reverse engineering... I'm trying to create a bike as comfy as a touring bike and still has the capability and sleek looks of a road bike...

I will build a(nother) prototype and test ride it myself.

I will share to you the specs when I have conclusive results.

Thanks

about 9mm with a 23C tyre on it

wow.... you can build your own frame???? that's really cool!!

I have a general purpose road/commuter/light touring bike. The chainstays are 42.5cm (with the axle in the middle of the horizontal dropouts). The tyre clearance to seat tube is 3cm using 28m rubber, and the bb to front dropout is 63cm. There is loads of room for toe clips, and the handling is pretty neutral, but sportier than my full-touring bike.
To take advantage of this clearance, you really should dimension the brake bridge to accept Shimano long drop calipers.

On thing I would like to do for prototyping would be to build a bike with variable head-tube angle. It wouldnt be pretty, but you could use it to explore the effect of different angles, and maybe have a front fork with horizontal dropouts for variable rake.

most builders use 41-41,5cm on the 'race' bikes.

You may want to contact some builders direct with these measurements. It can get tricky figuring it out the way you are.

The dimension you are using as an independent variable doesn't seem to make any sense. It's a by-product of the seat tube angle and chain stay length -- the latter being the true independent variable with regard to handling, i.e., shorter stays for quicker response and longer for comfort/stability/larger tire or mud guard clearance.

You can play around with different seat tube angles by incorporating seat posts that use different set-back to correct the saddle position relative to the cranks but that's about it.

Just my .02, but I think you'd be better off focusing more on the head tube angle and/or fork off-set to alter the handling. As for comfort, look to your wheelset (number of spokes, lacing pattern, rim design) and tire selection if you'd like to keep the rear chain stays short.

Regardless, it all sounds like an adventure and lots of fun. Ah, nothing like the smell of fresh brazing.

8 mm

Originally posted by livngood
You can play around with different seat tube angles by incorporating seat posts that use different set-back to correct the saddle position relative to the cranks but that's about it.

Just my .02, but I think you'd be better off focusing more on the head tube angle and/or fork off-set to alter the handling. As for comfort, look to your wheelset (number of spokes, lacing pattern, rim design) and tire selection if you'd like to keep the rear chain stays short.

Regardless, it all sounds like an adventure and lots of fun. Ah, nothing like the smell of fresh brazing. [/B]
I already did this(on my previous "experiments -- improving handling and response -- the effect? too uncomfortable)... That is why I'm trying to look in other places that people like us take for granted... (we always concentrate on top tube length, headtube angles, seat tube length, etc., but i have never seen so much variation on chainstay length on road frames)
What i'm trying to do is maintain the distance(tire to seat -- the look factor) and modify other variables(chainstay length, angles,etc.).
I'm still doing some adjustments... It will be ready for building today... Hopefully by tommorrow it will be finished..
Wish me luck.

Originally posted by deliriou5
wow.... you can build your own frame???? that's really cool!!

Yup. Its not easy though... you need to have lots of planning... And take very good care not to ruin the alignment... or else, the frame would be literally weird to ride...

I use steel... Its relatively cheap...

Originally posted by Xavier
most builders use 41-41,5cm on the 'race' bikes.

You may want to contact some builders direct with these measurements. It can get tricky figuring it out the way you are.

yes it is very tricky... but w/ CAD, it's so much easier..

Originally posted by MichaelW
On thing I would like to do for prototyping would be to build a bike with variable head-tube angle. It wouldnt be pretty, but you could use it to explore the effect of different angles, and maybe have a front fork with horizontal dropouts for variable rake. [/B]
great idea! I may want to try that sometime....

Thank you all for your replies...
I'll send the specs to you if you want. PM me if you want a copy(its free--i'm an 'amatuer')..

In the book "Touring Bikes" by Tony Oliver, he has a good treatment of bike frame geometries. The book is a bit old-fashioned but some things dont change.

dexmax: how about posting a couple of pics here on the forum. I'd like to see the frame(s) you've build.

Zack

On a Trek 5200 with 700x25 tires on the rear the gap is 3/4".

ah.... around negative 5mm :p does that help?

Originally posted by ZackJones
dexmax: how about posting a couple of pics here on the forum. I'd like to see the frame(s) you've build.

Zack

sure... but I don't have a digital camera.. I have a webcam though.. but not in the shop...

Originally posted by skdsl
ah.... around negative 5mm :p does that help?

i cannot build it like that... too difficult... almost impossible for me.

You might check out the geometry of tthe trek touring bike, the novarra touring bike (on www.rei.com ) and the cannondale toruing bike.

Originally posted by FOG
You might check out the geometry of tthe trek touring bike, the novarra touring bike (on www.rei.com ) and the cannondale toruing bike.
Thanks:D

Already finished with the frame. I'm having it painted at the moment.