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Thread: Low-trail forks

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    Default Low-trail forks

    There has been a lot of discussion about low-trail forks for touring bikes a'la' French rando and porteur bikes. I've had bikes with low trail, notably Raleigh International, Super Course and Grand Prix, that had trail numbers below 40mm. Made them feel light, but they also had a tendency to get squirrely on high speed descents. Anyway, read Bicycle Quarterly and you'll get the whole story.

    I just gotback from 4 1/2 weeks in Italy riding the mezzogiorno I took one of my "breakaway" bikes and carried at least 50 pounds split between front and rear racks.

    The bike you can see on my website. It has 72.5 degree steering angle, 44 cm chainstays and a slightly lower bottom bracket than most road bikes. I put together a fork with Nova's heavier blade and a Pacenti Paris Brest crown, giving it about 52 mm trail. I did find that the bike tends to wander at very low speeds but was steady as a rock at higher speed. I have been crawling up those endless Italian grades, then flying down at motorcycle speeds. Whoopee!

    I am ready to think about low-trail forks now. When I get back mid-June I think I'll see what 40 degrees will do. Will I still have the high-speed stability I need for those Fast descents? One way to find out!

    I've got to say, the VO "Constructeur" front rack looks great on a show bike but it is kind of marginal for what I'm doing. It's upper attachment is a via a steel strap to a single 5mm bolt at the fork crown. It wiggles and will cAUSE YOU grief on a fast descent. My solution would be to brAZe a couple of struts to the rack and then attach them at the fork crown for a 4-point mount.

    PS the food was great and the Italians were really nice. It was cheap and fun and it didn't rain hardly at all! I'm gonna do it again next year.

    jn

    Thursday"
     

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    Default Re: Low-trail forks

    Pardon the random comment J.N. Yer such a bad @ss.
    Carry on.

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    Default Re: Low-trail forks

    I've got to say the bike worked a lot better than its rider. The 26 x 1.75" Paselas were a good tire choice and the only flat i had was a slow leak I brought with me from the US. The "Breakaway" fittings didn't loosen up and it was easy to forget they were there. The OS .8-.5-.8 tubeset was just right having just enough compliance to give my old bones a bit of a breaK, but not so much as to be squirmy under load.

    The breakaway case sailed through check-in but I had to pay for the second piece that had the panniers and all my outfit in it. And I left the cases in "baggage ritrovo" at the airport and ran up E 300 in charges there. That's as much as I was spending **per week** on food and lodging.

    Next year will be even better

    jn
     

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    Default Re: Low-trail forks

    Baggage Du Monde is my friend in Fr.
    Check out: Stow your bags | luggage storage prices & special offers for Italy

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    Default Re: Low-trail forks

    OK, I did put together a rando/stone duro touring bike with a relatively low trail number. Took it to Norway and rode from winter into summer in Telemark. Surprising results and I learned a lot. I'll post here in a few days with experiences, thoughts and recommendations

    jn
     

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    Default Re: Low-trail forks

    OK, here goes nothing!

    Low Trail Forks


    Well, I got an opportunity to build a new “Camino Duro” touring bike when Compass (now Rene Herse) came out with the 26”x2.4” “Rattrap Pass” tires. Took it to Norway and rode from late winter into summer in Telemark. Surprising results and I learned a lot. As-built with tires the steering angle measures 73. degrees using a digital protractor on the headtube. The fork rake I measured in-build in the jig at 51.4 mm. That gives me a trail number around 47 mm.

    The build was OS tubing, .8-.5-.8mm on the top tube and down tube plus a 28,6mm x .9-.6mm seat tube. Stays were 5/8”x .028” and 3/4” x .035” seatstay and chainstay respectively, aircraft grade chrome moly with bridges.

    The fork was 1” threaded with a Pacenti “Paris-Brest” crown and Nova fork blades. For racks I used a Tubus Vega in the rear and a Velo Orange “Constructeur” in the front, both modified for a 4-point mounting and both secured by 6mm cap screws on the lower mounts.

    I was building right up to the night before we left for Norway, so there wasn’t enough time to really wring out the bikem and see how it handled when fully loaded. My wife came along, also my son and brother for a bit; we used trains and buses to get around and the bike stayed in its suitcase at a friend’s place in Bǿ. They went back to the US in mid-June and I went back to Bǿ to put the bike together and start riding.

    The next morning I loaded the bike up, about 12-14 kg front and rear and took off. Soon as I got to a downhill the bike became almost uncontrollable. It was like a speed wobble on a motorcycle. I slowed way down and managed to get to the bottom of the hill, then took it VERY slow to the Bǿ bus/train station. The tires were inflated close to 30 psi. I tightened up the rack mounts, front axle and quill stem bolt while waiting for the bus to Haukeliseter where I was going to start riding. I had tightened he headset pretty well before leaving the US and it seemed OK.

    Haukeliseter is at about 1,000 meters, on the upland plateau of central south Norway, between Oslo in the east and Bergen in the west. It was early spring there and the snowmelt was still going on, also it was cloudy and raining off and on. I camped at there a couple nights, did some hiking and thought about the bike. With the load off it was its old self: light, agile steering but steady. It was still good with the rear loaded. It was the front load that was making the difference in handling. I lightened the front load a bit by moving a few items to the rear. Most of the load was beltted down in a set of very tight Black Star panniers, with the tent on the front rack and a light rucksack bungied on top if the rear rack.

    I broke camp and rode about 65 K down to Vinje. It was a long, easy descent in light but steady rain. There is no shoulder to speak of, traffic was heavy so I went as fast as I dared. Shifting my body weight to the rear really helped; every time I got forward on the bars the front end started to wobble. Needless to say I kept a strong hand on the bars.

    This was not an extreme case of low trail number. I’ve ridden Raleighs with less: and old International with less than 40 mm trail, a couple Grand Prix with low trail numbers, an early-’80s Japanese International that measured in the low 40mm range. None of them did I ride with a heavy load on the front. I know that ‘builders are claiming figures under 40mm trail for their “rando” and “porteur” bikes.

    I did get used to the wobble and rode to keep it to a minimum. I missed out on bombing some really nefarious descents. I did like the reduced tendency of the front end to wander while climbing steep.

    So what’s the deal? One difference: on the Italy bike I used Nova’s heavier fork blades (nominal 1.0mm wall) and on the Norway bike I used lighter blades, nominal wall thickness .9mm. Everything else was the same, I even took the stem, bars and headset off the Italy bike and used them on the Norway bike.

    What else could be involved? Maybe the Rat Trap Pass tires are inherently flexy in a way the contributes to wobble? I used the 1.75” Paselas on the Italy bike. I might try a tire swap.

    The other thing that might help is going over to a threadless fork with heavier blades, to cut down on torsional flex.

    In the meantime, if I get an order for a low-trail touring bike I think I’ll put a 1 1/8” threadless fork, headset, stem and bars on it.

    jn
     

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