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  #121  
Old 02-19-2021, 02:41 PM
Mark Davison Mark Davison is offline
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Looks like you have a very interesting project going here. I would like to make a few specific recommendations, based on direct experience with my Davidson Signature sport touring bicycle. They are:

1. If your primary use is credit card touring, possibly on mixed terrain, with 700C x 32mm tires inflated to 60-70psi, then you should pick a fork rake so your trail is around 53mm. This corresponds to the historically classic 73 degree head tube angle and 2 inches of rake (for example the geometry of Schwinn Paramounts up until about 1978). The current standard of 58mm of trail is perfect for 700C x 23-25 inflated to 90 - 100 psi, but with wider, softer tires there is too much net trail (geometric + pneumatic) and the bike will tend to hunt from left to right during slow climbs, and the steering will feel sluggish. The classic 53mm trail is also perfect for 700C x 35mm, carrying even lower inflation--45-50psi.

With 700C x 32, 53mm trail also supports 20 lbs of front loading in handlebar bag and panniers. You can pick your tubing for the rear triangle without worrying about being stout enough to support a rear load. A modest bike packing saddle bag will probably be fine.

2. On some trip in the future you will need to bring fenders. Set the bridges to allow for 700C x 32 with fenders, and have threaded holes in the chain and seat stays to allow mounting the rear fender without brackets. If your allowed fender clearance is 10mm then you will be guaranteeing that 700C x 35 fits without difficulty. I don't know about clearance for 700C x 38--my bike doesn't have that so I used 650B x 38 with Tektro 559 long reach sidepulls when the planned trip needs gravel capacity and fenders.

3. You may find that your chosen brakes won't open wide enough to let an inflated 32mm tire pass. This is the advantage of Paul Medium Racers and the Tektro medium reach brakes. I don't know about the VO. Old Campagnolo Record normal reach side pulls work fine too.

4. If you think you might use 38mm tires a lot, I would increase the rake so the trail is in the mid 40s. 700C x 32 and 35 will still work perfectly, but the steering with low pressure 650B x 38 will be vastly improved. In particular, you will be able to run lower pressures on the road (say 35psi) without encountering atrocious camber torque. This is the tendency for the bike to climb up out of cambered turns or ruts, and the tendency to tighten a sweeping turn unless you supply astonishingly high amounts of counter pressure--the bike wants to straighten up and just run off the road.

This is not mere speculation: my Davidson originally came with 73.5 degree head tube, 41mm rake, 59mm of trail with 700C x 28mm. I ran it for years with 700C x 25 tires inflated to 100 psi (following the received wisdom that narrow and hard tires would lower rolling resistance and get me to work on time,) commuting to work with 10lbs in rear panniers. Then I retired and had time to actually tour. I went on a fabulous credit card tour making a loop from Ashland Oregon to Crater Lake, circling the lake, and then returning via a different route. The bike was loaded lightly with 25 lbs spread front and back with panniers, a light Arkel handlebar bag and 95 psi in 700C x 28mm tires. It handled like a pig in slow climbing--darting back and forth. I could barely ride it one-handed in order to get a drink. I ditched the rear load for our day circumnavigating Crater Lake, and the handling was still off.

Then the bike got stripped off of a car rack and the forks had to be replaced. I decided to go back to a more traditional geometry and I had Bill Davidson make me a fork with 51mm of rake, giving me 50mm of trail. It now handles like a dream with 700C x 32 (with fenders) and 70C x 35 (without fenders). It handles okay with 650B x 38, but the tire inflation needs to be kept above 50psi on pavement to prevent adverse camber steer.

650B x 38 handling is much better on my other sport touring project--a 1982 Schwinn Superior. This bike came to me as a counterfeit 1978 Schwinn Paramount, with a mismatched fork (which was a Paramount fork!) whose steer tube was too short. I had Davidson make me another fork with 51mm of rake, thinking that the Superior had a specified geometry with a 73degree head angle. But it turns out, upon measurement, that the Superior has a 74.3 degree head angle, and the trail with the new fork is 45mm. Handling with 700C x 32 @ 60-65 psi is still perfectly natural, but is better than the Davidson with 650B x 38 @ 35psi.

Shimmy sometimes occurs on the Davidson if a) front and back are loaded and b) tire pressure on 650B x 38 is under 50psi. It can be avoided by only loading the front or increasing tire pressure to 55 psi.
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  #122  
Old 02-19-2021, 02:47 PM
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bicycletricycle bicycletricycle is offline
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I like the 10 more , maybe


Quote:
Originally Posted by Bici-Sonora View Post
Just curious, is anyone more keen on the 10 degree slope than the 6 degree?

Fairlight, and a few others use a 10 degree slope. It would give more seat post compliance.

Biketrike's Chapman looks great with the 6 degree--as does the Ellis DRB is this thread so that's kind of why I landed on the 6 degree.
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  #123  
Old 02-19-2021, 04:05 PM
Mark Davison Mark Davison is offline
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Davidson and Superior geometries

Here's the original geometry specifications for the Davidson sport touring bike:

Seat tube 72.5 degrees, 625mm C to C
Top tube 0 degrees, 600mm C to C
Head tube 73.5 degrees
Fork rake 41mm (original) 51mm (replacement)
BB drop 70mm
Chainstay 43mm
Front Center 614.6mm
Wheelbase 103.5
Headtube 209.8
TT, DT, ST 28.6mm diameter
HT 31.8 diameter

brake bridges set to accommodate 700C and 27" wheels with
Shimano 105SC 57mm reach brakes
Braze ons: pump peg on HT under TT, 2 water bottles, low-rider eyelets on fork, rear rack, fender eyelets on dropouts, fender bosses on bridges.

Due to an accident of nature, you can run the same Tektro 559's on both 700C and 650B with a little judicious filing at the bottom of the brake tracks. The 559's are somewhat flexible with the brake shoes all the way down, I'm going to switch to a centerpull setup with Paul Medium Racers for 700C and Mafac RAIDs for 650B.

I don't trust the Schwinn Superior published geometry. Here's a reconstruction based on actual measurements:

https://1cddaaa889ea6d02f911-be9e9c6...1835493719.png


https://www.bikecad.ca/1611835493719
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  #124  
Old 02-19-2021, 07:26 PM
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Mike V Mike V is offline
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Enjoying this post. im learning a lot. Can't wait to see the finished bike.
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  #125  
Old 02-20-2021, 02:28 PM
Bici-Sonora Bici-Sonora is offline
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Thanks for sharing your experiences and comments. I'll respond to each below:
in red:
Quote:
Originally Posted by :

1. If your primary use is credit card touring, possibly on mixed terrain, with 700C x 32mm tires inflated to 60-70psi, then you should pick a fork rake so your trail is around 53mm. This corresponds to the historically classic 73 degree head tube angle and 2 inches of rake (for example the geometry of Schwinn Paramounts up until about 1978). The current standard of 58mm of trail is perfect for 700C x 23-25 inflated to 90 - 100 psi, but with wider, softer tires there is too much net trail (geometric + pneumatic) and the bike will tend to hunt from left to right during slow climbs, and the steering will feel sluggish. The classic 53mm trail is also perfect for 700C x 35mm, carrying even lower inflation--45-50psi.

[COLOR="Red"
For this particular bike, it will be used more on the "sport" side than the "touring" side. I've done a variety of touring with very light rackless set-ups in the last few years and have found that my Ritchey with 650b x 48 (71HTA and 52mm offset) and trail of 58 it was excellent for 10 days in across Spain on paved and dirt tracks with around 10-12lbs of load. I've also toured on my MAP 650b x 42 (35 trail) and it is great with front bag and low-riders and a light load. My highest trail bike Jones 29 x 3" with 78 trail is also good loaded bikepacking style. I've owned some bikes (Jack Taylor Sports) that had that traditional 73 degree HTA and ~50mm offset and liked it quite a bit, but I never toured on that bike. In general, my experience has been that with light loads, trail numbers don't matter as much as we sometimes think. I'm certainly not discounting your comments. I do know that I dislike rear loaded bikes and avoid rear racks and panniers for that reason. Seatpacks that are lightly loaded don't seem to affect the handling in the same way.[/COLOR]

With 700C x 32, 53mm trail also supports 20 lbs of front loading in handlebar bag and panniers. You can pick your tubing for the rear triangle without worrying about being stout enough to support a rear load. A modest bike packing saddle bag will probably be fine. I agree about avoiding rear loads and don't want to have overbuilt rear stays

2. On some trip in the future you will need to bring fenders. Set the bridges to allow for 700C x 32 with fenders, and have threaded holes in the chain and seat stays to allow mounting the rear fender without brackets. If your allowed fender clearance is 10mm then you will be guaranteeing that 700C x 35 fits without difficulty. I don't know about clearance for 700C x 38--my bike doesn't have that so I used 650B x 38 with Tektro 559 long reach sidepulls when the planned trip needs gravel capacity and fenders.This will be more of a sunny day road bike. I live in a very sunny place and don't like riding in the rain. I also have my MAP with full fenders for the rare times I need to ride in the rain. On this one, I'm thinking more of a set up light a light tubed 70s stage race geo bike with room for bigger tires. However, I could add the eyelets just in case 32mm with fenders would be nice.

3. You may find that your chosen brakes won't open wide enough to let an inflated 32mm tire pass. This is the advantage of Paul Medium Racers and the Tektro medium reach brakes. I don't know about the VO. Old Campagnolo Record normal reach side pulls work fine too.

4. If you think you might use 38mm tires a lot, I would increase the rake so the trail is in the mid 40s. 700C x 32 and 35 will still work perfectly, but the steering with low pressure 650B x 38 will be vastly improved. In particular, you will be able to run lower pressures on the road (say 35psi) without encountering atrocious camber torque. This is the tendency for the bike to climb up out of cambered turns or ruts, and the tendency to tighten a sweeping turn unless you supply astonishingly high amounts of counter pressure--the bike wants to straighten up and just run off the road.I'm only going to run 700c wheels on this bike--most likely 35mm tires max. I also don't want that low of trail on this one. I ride a Rivendell Quickbeam (72.5 HTA and 45mm offset) regularly with 700 x 42 (65mm trail tires run tubeless at ~40psi) and find it's geo is really great for me, even with 10-15 lbs. of groceries in the front basket (did that this morning)

This is not mere speculation: my Davidson originally came with 73.5 degree head tube, 41mm rake, 59mm of trail with 700C x 28mm. I ran it for years with 700C x 25 tires inflated to 100 psi (following the received wisdom that narrow and hard tires would lower rolling resistance and get me to work on time,) commuting to work with 10lbs in rear panniers. Then I retired and had time to actually tour. I went on a fabulous credit card tour making a loop from Ashland Oregon to Crater Lake, circling the lake, and then returning via a different route. The bike was loaded lightly with 25 lbs spread front and back with panniers, a light Arkel handlebar bag and 95 psi in 700C x 28mm tires. It handled like a pig in slow climbing--darting back and forth. I could barely ride it one-handed in order to get a drink. I ditched the rear load for our day circumnavigating Crater Lake, and the handling was still off.IYou Davidson does sound like it had pretty racy geo. for touring. I haven't run more that 70psi in a tire for years, and can' t imagine touring on that psi! I did Crater Lake this last summer on my MAP with the road was still closed to cars. What a blast--cold enough that I had to add and remove layers on each decent and climb

Then the bike got stripped off of a car rack and the forks had to be replaced. I decided to go back to a more traditional geometry and I had Bill Davidson make me a fork with 51mm of rake, giving me 50mm of trail. It now handles like a dream with 700C x 32 (with fenders) and 70C x 35 (without fenders). It handles okay with 650B x 38, but the tire inflation needs to be kept above 50psi on pavement to prevent adverse camber steer.

650B x 38 handling is much better on my other sport touring project--a 1982 Schwinn Superior. This bike came to me as a counterfeit 1978 Schwinn Paramount, with a mismatched fork (which was a Paramount fork!) whose steer tube was too short. I had Davidson make me another fork with 51mm of rake, thinking that the Superior had a specified geometry with a 73degree head angle. But it turns out, upon measurement, that the Superior has a 74.3 degree head angle, and the trail with the new fork is 45mm. Handling with 700C x 32 @ 60-65 psi is still perfectly natural, but is better than the Davidson with 650B x 38 @ 35psi.

Shimmy sometimes occurs on the Davidson if a) front and back are loaded and b) tire pressure on 650B x 38 is under 50psi. It can be avoided by only loading the front or increasing tire pressure to 55 psi.
One reason I don't want low trail on this bike is I find I like the stability of a mid-to-high trail bike if I'm not riding with a front load. In general, I'm trail agnostic--bit I've been able to get all my low trail bikes to shimmy in certain situations. It's usually not a big deal, but it limits riding no-handed. I really liked the 58mm trail on Clean39T's Kirk that I rode the last six months.

Last edited by Bici-Sonora; 02-20-2021 at 02:40 PM.
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  #126  
Old 02-20-2021, 02:47 PM
Bici-Sonora Bici-Sonora is offline
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I'm thinking more about PL member Slups Riccorsa All Road lately. Also thinking more about level top tubes. Maybe the middle ground (~6 degree slope) is dumb. Maybe the TT should be level or >10 degrees and not somewhere in between.

Also, I may abandon the breakaway feature (I already have a rough and tumble breakaway bike) and probably don't need two. This one might be stripped down pure 35mm all-road elegance.

If you need a reminder about what that might look like, here is Slups again: https://forums.thepaceline.net/showthread.php?t=248722

He also was kind enough to send me the geometry, which is pretty close to what I'm aiming for.

Last edited by Bici-Sonora; 02-20-2021 at 02:51 PM.
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  #127  
Old 02-20-2021, 04:10 PM
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bicycletricycle bicycletricycle is offline
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I do like the look of a level top tube, classy.

Especially with custom matching stems, really ties the room together.
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  #128  
Old 02-20-2021, 04:23 PM
hollowgram5 hollowgram5 is offline
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Quote:
Originally Posted by Bici-Sonora View Post
I'm thinking more about PL member Slups Riccorsa All Road lately. Also thinking more about level top tubes. Maybe the middle ground (~6 degree slope) is dumb. Maybe the TT should be level or >10 degrees and not somewhere in between.

Also, I may abandon the breakaway feature (I already have a rough and tumble breakaway bike) and probably don't need two. This one might be stripped down pure 35mm all-road elegance.

If you need a reminder about what that might look like, here is Slups again: https://forums.thepaceline.net/showthread.php?t=248722

He also was kind enough to send me the geometry, which is pretty close to what I'm aiming for.
This is definitely one of my favorites on here. I'm curious how the geo differs from some of the others (and my Cielo).
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  #129  
Old 02-20-2021, 04:47 PM
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bicycletricycle bicycletricycle is offline
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level tt, 10mm headtube extension, 80deg stem

bici sonora V.1 level tt assembly by bicycletricycle666, on Flickr

same but also 73 head angle and 440mm stays and tighter bend fork
bici sonora V.1 level tt assembly 73-440 by bicycletricycle666, on Flickr

same as above but 1.5 slope
bici sonora V.1 level tt assembly 1.5deg by bicycletricycle666, on Flickr
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Last edited by bicycletricycle; 02-20-2021 at 05:07 PM.
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  #130  
Old 02-20-2021, 09:36 PM
Mark Davison Mark Davison is offline
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A sport touring bike with 35mm tires

The red Davidson as a fenderless 35mm vintage bike.

https://www.flickr.com/gp/8277723@N06/012m02

The brake bridges on the Davidson were set to take 27” x 1 1/4” wheels under fenders, using Shimano 105 57mm reach double pivot sidepull brakes.
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  #131  
Old 02-20-2021, 09:42 PM
Mark Davison Mark Davison is offline
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Picture of red Davidson with 700C x 35

E3C67F19-CC22-452F-B5D5-6E1B2E9C560F.jpg
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  #132  
Old 02-20-2021, 09:53 PM
Mark Davison Mark Davison is offline
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1972 Schwinn Paramount with 700 x 35C

The 1972 has a classic early 70s stage racing geometry with 73 degree head and seat tubes. Brake bridges were set to accomodate 27 x 1 1/4” wheels with fenders, for winter training, using Weinmann 610 front and Weinmann 750 rear. 700C x 35 fits with no fenders.
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  #133  
Old 02-20-2021, 10:11 PM
Mark Davison Mark Davison is offline
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1982 Schwinn Superior

Part of the short run of Schwinn Superiors from 1980 to 1983 built up out of excess Paramount tubing and lugs, but with a sporty late 70s stage racing geometry—410mm chainstays, 73 degree seat tube, 74 degree head tube.
Built to take 700C x 28mm and fenders under normal reach Campagnolo record brakes. Clearance for 650B x 38mm and fenders was created by dimpling the chain stays and installing a new fork with a Sachs Newvex crown. 650B version uses Rene Herse centerpulls. 700C x 32 also fits, using Campagnolo Record normal reach sidepulls.
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  #134  
Old 02-20-2021, 10:26 PM
Mark Davison Mark Davison is offline
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1972 Schwinn Paramount dressed for the winter

27 x 1 1/4” clinchers under fenders and new toe clip covers for the winter.
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  #135  
Old 02-21-2021, 02:41 AM
Mark Davison Mark Davison is offline
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another 70s stage racing bike—1972 Bottecchia Professional

I road this at Eroica CA. No published geometry: I’ll have to measure it. Similar brake setup to the 1972 Paramount. Clearance for 27 x 1 1/4” wheels with fenders. Supports 700C or tubulars with the brake blocks all the way down. Universal centerpulls.
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