Date: Tue, 23 Nov 2004 08:45:21 -0500
From: "John Clay" <jmedlockclay(AT)nettally.com>
Subject: [Frame] RE: Touring frame advice
I'm glad to have provided some food for thought.
>*Perhaps I haven't ridden a slack HT bike with proper trail but most of them
>seem to require some work getting in and out of turns. My 1st frame is a 74
>deg, 43mm rake (700x23) it almost predicts the turn before I enter it. Then
>again most rigid mtbs with slicks and the typical 71 deg handle quite well.
>I'm thinking maybe 72.
Anything reasonable can perform nicely. If 72+559+1.9+rake with fenders
doesn't cause toe overlap it would be just dandy. A very nice compromise.
I use 70 because I have a soft spot for it (and it's what I have) but my
latest road is 72+622 with 45mm rake or thereabouts if I remember
correctly. It handles very nicely on the road. BTW - I use fenders for
touring. They make the journey much nicer if it gets nasty.
I really would encourage you to do whatever it takes to eliminate overlap
on a tourer. Not sure if I mentioned this to you before but touring is
different than typical recreational riding. The rider workload is higher:
everything is unfamiliar, the bike is loaded like a pig, you're tired,
wet, cold - grinding up a steep gravel road in your 16" gear doing
everything you possibly can to stay moving and upright while wondering if
you're in the right place, steering corrections are huge, gross and adhoc
- the last thing you need is to have to time them with your pedal stroke.
And then you'll do it again, and again. You don't need to fall and the car
isn't back at the trailhead. Whatever frontend geometry/wheel choice it
takes to eliminate overlap is where I'd be. You can easily adapt if it's
less than your otherwise ideal design.
Your comments about FC are well taken. I have legs
>of someone 6'2" but a torso of someone 5'8" so bike fit has always been a
>little tricky. I run 175 cranks but prefer a 56cm or shorter TT. This is
>one reason I'm going 559.
559 makes all kinds of sense.
>*You're right on the BB drop. I'm going with 52 since 58 would make it too
>low with anything lower than 1.5s.
The red bike has something like 30mm drop, or was it 25? Less than I'd
design but the up side is that I rarely worry about catching anything in
the pedals. Not saying you should use 30 just giving some additional
>*The SS mounting kind of goes back to whether I want a full tourer or a mix
>of other design elements.
If you really think you'll tour I'd suggest no, or very few compromises.
You can build another!
FWIW I did do a FEA on a 18" c-c mtb frame with
>the SS at 15". I modeled a 28.6/0.9 SG ST with 400lbs on the saddle at full
>extension. This gave ~11mm deflection (mostly back but some down) at the
>saddle and ~50 ksi total stress which occurred right below the SS where
>seatpost ended. The geometry of this design is not as extreme and I think
>would result in less stress, even reducing to 0.8 wall thickness. BUT, this
>does not take into account buckling and a buckled ST would put a rather
>quick end to a tour. I know Don Walker does this on track frames with a 0.6
>ST (I think) without problems. Perhaps I should save this for another
>project and just use a sus saddle.
Interesting. I had not considered that mode of loading the ST. My gut
reaction is that I'd still use a conventional seat cluster arrangement and
a long enough seat post to lessen stress on the ST where the post ends
BUT: I've done no professional structural analysis and I've never analyzed
bicycle frame loads. That is most interesting. How long was the seat post
insertion? Do you know of ST failures due to seatpost loads?
>*Yea, my 2nd frame is a mtb with a sus fork. I went with 31.7x28.6x28.6 and
>it rides real nice but a bit wobbly at times. My next suspended mtb will
>have a 35 DT but I may keep the 28.6 TT
>*A 28.6 steerer might be good and I wouldn't have to buy a 1" cutter for the
>HT. Plus the steerers are generally longer, True temp give 40mm more on the
>*Yea I think my bar height has risen a few mm every year. For touring I'd
>like something level with the saddle. I tried to get a "north road" bar
>from harris but the nitto stock is depleted and yet to be replenished.
Try everything well in advance of departure so you can make changes. I use
the sprung Brooks B17 - and I'm not a retro grouch, not usually. I tried
it as a last ditch attempt to get something that didn't hurt. I'd tried
everything else. Money back guarantee from Wallingford and I had nothing
to lose. It has made all the difference. Were it not for that saddle I'd
be back on recumbents. That's where I get much of my ride compliance.
>*I checked out your pics, looks like some beautiful riding.
As little touring as I've done and I can say that that kind of riding just
knocks my socks off. There is nothing in the world that compares.
I didn't know
>who was who though and which was you bike. One caption read "john's jamis".
I'm on the red bike (the one that you won't see having the tire repaired).
~'85 Jamis fillet brazed Dakar. Heavy, durable, powercam rear brake, Troy
Courtney fork. Hanging from Joe's in Tallahassee for a long time. Nobody
wanted it. I love it. It's the one bike I'll keep forever, even when I
replace it with a tourer of my own construction.
While you're collecting parts you might look for a set of cranks with a
58mm inner bolt circle. I'm a huge proponent of a 20x34 low gear. The
crank on the Dakar has 20/32(or 34)/44 and for touring and it's sweet.
Thought about a 46 but I'd only spin it out down hills. No sense there,
for me. This arrangement gives 3 useful ranges with enough overlap so you
don't have to thrash the front der back and forth if on the edge of a range.
Lots of brazeons, with reinforcing diamonds where applicable.
I'll include fork crown shoulder bottle bosses so I can attach a low front
bag/map case support like on the old rando bikes. My bar bag is pretty
high - no huge problem but lowering it can't hurt and I might not have to
use reading glasses to focus on the map.
I'd be interested to see what you ultimately cook up.
touring frame advice