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-   -   2021 Andy Gilmour Medium Reach Brake (https://forums.thepaceline.net/showthread.php?t=265120)

Bici-Sonora 02-16-2021 11:02 AM

Quote:

Originally Posted by 8aaron8 (Post 2882560)
I did, they measured spot on 38mm on 18mm internal rims, and with 21mm internal rims I got around 39ishmm.

Great info Aaron. Thanks for sharing. You were the first builder I know of who pulled this off. Maybe I should shoot for 38s now!

Bici-Sonora 02-16-2021 11:10 AM

Quote:

Originally Posted by hollowgram5 (Post 2882410)
It's a 60. So 595 tt and 74/72.5 on the angles.

I pulled the geo a while back from the waybackmachine but it seems to be gone from that page now. (Seems to be a Chrome issue, came up just fine in firefox...)

It's like the old Lemond/Bridgestone RB-1 geometry but with a little longer stays and more tire clearance. Thanks for adding to the discussion.

Bici-Sonora 02-16-2021 11:19 AM

Quote:

Originally Posted by lavi (Post 2882436)


It’s interesting that I’ll pick up a frame used or off the peg (looking at you Aethos) without much real fretting on geo. Order something custom...and I’m literally losing sleep thinking about it. My wife thinks I’ve lost it when she comes into a room and sees my staring blankly at the wall. She knows I’m (poorly) practicing geometry in my head. Lol

Continue the discussion please.

I totally get you. Of the peg bike: if it looks close enough, I just pull the trigger. But with a custom, you are like the CEO of a micro bike co. If it rides like sh*t, you might be the one responsible! I mean, the framebuilder is hopefully an experienced guide, but you ultimately have to sign off on the geo. sheet.

As a liberal arts major, I did everything I could to avoid math in college. But now I love fooling with bicycle geometry. If my junior high geometry teacher would have had me draw BMX frames, my whole life could be different.

Bici-Sonora 02-16-2021 12:05 PM

Sloping TT Option
 
Sorry Dan, I've begun to dabble in the dark art of the 6% sloping TT.

bicycletricycle 02-16-2021 12:46 PM

yet another thing to consider

I don't think -17 stems look good on 6 degree slope top tubes. As a general rule stems look nice when they are parallel to the top tube but this is only a rough generalization.

bicycletricycle 02-16-2021 12:49 PM

also, if it is 1" do you go threaded or threadless? each has its own...... challenges.

Bici-Sonora 02-16-2021 12:54 PM

Taking some cues from Mr. Wages and his DRB, which has the 6 degree slope:

"The main difference between a cross bike and the DRB is the height of the bottom bracket. Typically, cross bikes have a high bottom bracket (60 to 70mm of drop), so you’re not hitting your pedals on rocks and roots, and don’t have to worry about clipping a pedal in the turns. The DRB on the other hand is designed much like a Grand Tour bike from the 70’s with a lower bottom bracket, longer reach brakes, plenty of room for wider tires or fenders and longer chainstays than today’s 400mm super tight carbon bikes.

Other than the chainstays and fork being about 10-15mm longer for increased clearance, this bike has virtually the same geometry as my “go-fast” road bike. Parallel 73 degree head and seat angles, a 56cm ST c-c, 59.5cm top tube with 6 degrees of slope, and 80mm of bottom bracket drop, which really makes the bike super stable and comfy for long days."

Full article here: https://overthebarsinmilwaukee.wordp...-in-the-world/

Bici-Sonora 02-16-2021 12:58 PM

Quote:

Originally Posted by bicycletricycle (Post 2882669)
also, if it is 1" do you go threaded or threadless? each has its own...... challenges.

I've pretty much made up my mind on threadless for this one. I have plenty of threaded HS bikes, but this one is gonna be more modern I think.

You make a good observation about the TT slope and stem. I agree, the stem angle should more or less match the TT slope. Your Chapman stem does this quite well.

v531xc 02-16-2021 12:59 PM

Really loving this thread.

My data points to share:

The geo you outlined is really close to three bikes I have and very close to what I'd ideally make as a mash up of them all.

My Chapman is a little shorter in TT (585), the stack is a little taller, and the bb is a little higher (65mm drop) because of being designed around 650b, I wanted it to be more comfy/upright, and I underbike it a lot. 73.2/73.5 STA/HTA. 435 chainstays and it fits 44mm tires in 700c if I wanted without fenders.

With an 80mm bb drop, it might be more like 38mm or 40mm max.

My Bilenky is also similar about 59cm ST c-t, 575 eTT c-c. 80mm drop, 72/73.5 STA/HTA. 422mm chainstays and perfectly fits 33mm tires without fenders under midreach brakes.

My Bruce Gordon is 61 ST c-t, 59 TT, 70mm drop, 73/72 STA/HTA, 420mm stays without a chainstay bridge and fits a 43mm tire front and rear (700c).

I have a Ritchey Breakaway Road XL and if I were to get the bike you're getting, I'd emulate that and mash it up with the above three bikes to get the 80mm drop, ~430mm stays, ~600mm stack, ~410mm reach and 73/73 parallel ST/HT. Depending on the brakes and fork design, I assume it would fit 38mm tires.

On TT slope, My Chapman and Bilenky are both 6 degrees, iirc. They look good to me :-) Both are filet brazed.

On tubing, I agree on going OS with a bike like this. My Bilenky is OS but has a 6-4-6 top tube. I really like the flex, but its very different from the other bikes which are stiffer. the Chapman being OOS and OS and the BG being a mix of stuff.

A 1" fork would be great, as you'll get all the flex characteristics you might want. But if you want swappability with something like a Whisky mid reach fork, then you'll need to find some flexy blades to go with the 1.125" steerer. I've really liked the stuff that Richard Sachs has for the standard fork blades. And I hear good things about what Rene Herse has to offer, too.

bicycletricycle 02-16-2021 01:05 PM

custom steel threadless stem painted to match I hope.

Quote:

Originally Posted by Bici-Sonora (Post 2882677)
I've pretty much made up my mind on threadless for this one. I have plenty of threaded HS bikes, but this one is gonna be more modern I think.

You make a good observation about the TT slope and stem. I agree, the stem angle should more or less match the TT slope. Your Chapman stem does this quite well.


Bici-Sonora 02-16-2021 01:46 PM

Sloping TT iteration:
https://uploads.tapatalk-cdn.com/202...b821bb3c08.jpg


Sent from my iPhone using Tapatalk

Bici-Sonora 02-16-2021 01:56 PM

Quote:

Originally Posted by bicycletricycle (Post 2882682)
custom steel threadless stem painted to match I hope.

This is the problem with 1" threadless-I love a good custom color matched custom stem-but the cost and time (after you are sure you have the length/angle perfect) is a pain. I want a 31.8 clamp so that limits options further. I could use a painted Deda Superlegero/shim like Dan did on the Kirk.

If I go 1 1/8" there are plentiful good looking options off the shelf. I would just have to get as light a steerer as possible and light blades. Plus, options for a *gasp* carbon fork should I ever lose my mind.

Bici-Sonora 02-16-2021 02:23 PM

...and the 3 degree top tube slope version:
https://uploads.tapatalk-cdn.com/202...2d67e47b95.jpg


Sent from my iPhone using Tapatalk

Clean39T 02-16-2021 02:26 PM

Quote:

Originally Posted by Bici-Sonora (Post 2882733)
This is the problem with 1" threadless-I love a good custom color matched custom stem-but the cost and time (after you are sure you have the length/angle perfect) is a pain. I want a 31.8 clamp so that limits options further. I could use a painted Deda Superlegero/shim like Dan did on the Kirk.

If I go 1 1/8" there are plentiful good looking options off the shelf. I would just have to get as light a steerer as possible and light blades. Plus, options for a *gasp* carbon fork should I ever lose my mind.

The Deda is -8 deg, so if you plan to use that, you could bring the TT to a more reasonable -4 deg and still be a in a good spot. I say more reasonable because with longer headtubes, sloping TTs can start to look pretty ungainly. You should of course choose based on function - I'm just a sucker for form, as is well documented.

bicycletricycle 02-16-2021 02:34 PM

This whole project is already going downhill.
painted aluminum stems?
carbon forks?
1.125" steerers?

Oversize bars always ruin (edit: not really ruin) these bikes, not because of the bars but because they ruin the proportions of the rest of the bike. Bigger bars = bigger stem = bigger steerer tube = funny looking little fork blades in comparison to the huge head tube.

My Tournesol and on my first Chapman both have 1.125" steerer tubes and regular fork blades and I think the fork blades look out of proportion with the headtube so on my blue chapman I used these really big Sachs fork blades to help smooth the transition some. They don't ride as nice but they do feel a little more "precise" I guess. I do like a lot of the modern bar shapes but I also love RH parallel bars and nitto noddles. The long flat ramps behind the hoods are so comfortable.

I would just run rene herse parallel bars (On the my tournesol right now, 25.4mm clamp which is annoying, nitto has some options) and keep the front all smaller dimensioned.

I think a lot of this is just annoying nit picking, oh well.

OOS lugged chapman with normal blades-
https://live.staticflickr.com/1960/4...c2a1c4ea_c.jpgIMG_6516 by bicycletricycle666, on Flickr

OOS Tournesol with normal legs-
https://live.staticflickr.com/65535/...801e2823_c.jpgUntitled by bicycletricycle666, on Flickr

OOS tubes with oversize RS fork kit-
https://live.staticflickr.com/65535/...a707cced_c.jpgUntitled by bicycletricycle666, on Flickr

cool ellis, look OOS with normal legs-
https://live.staticflickr.com/65535/...54682c64_c.jpgellis by bicycletricycle666, on Flickr

english, small tubes, NACA profile fork legs I think -
https://live.staticflickr.com/65535/...a21eb4aa_c.jpgenglish by bicycletricycle666, on Flickr

Quote:

Originally Posted by Bici-Sonora (Post 2882733)
This is the problem with 1" threadless-I love a good custom color matched custom stem-but the cost and time (after you are sure you have the length/angle perfect) is a pain. I want a 31.8 clamp so that limits options further. I could use a painted Deda Superlegero/shim like Dan did on the Kirk.

If I go 1 1/8" there are plentiful good looking options off the shelf. I would just have to get as light a steerer as possible and light blades. Plus, options for a *gasp* carbon fork should I ever lose my mind.



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