Handling of low trail bikes?
05-10-10, 05:49 PM
#26
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The adjustable rake fork is going to be close to Road Fan's description. (And believe me, I'm always happy to hear more ideas!)
The only difference is that instead of a horizontal slot, there will simply be multiple locations for the axle, cut into steel plates that extend forward from the ends of the fork blades. This is not my original idea, BTW, as I saw essentially the same thing more than 20 years ago.
The only difference is that instead of a horizontal slot, there will simply be multiple locations for the axle, cut into steel plates that extend forward from the ends of the fork blades. This is not my original idea, BTW, as I saw essentially the same thing more than 20 years ago.
05-10-10, 09:22 PM
#27
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The next step is under way. I have a front rack installed on the Woodrup and a headset decaleur installed. It holds the bag so that its loaded CG is at least an inch behind the front axle. The handlebar mount was somewhat in front of the axle.
How does it ride? I loaded the bag with a lock/cable, my tool pouch, gloves, candy bars, a pump, my wallet, and a tube. It weighed about 7#. The steering was surprisingly easy, with just a little more friction due to tire loading. It was a little slow to change line, but could be no-handed. I need to test that more. This is with 28 mm tires, 70 psi in the front and 85 psi rear.
I'm early in my season, so I'm climbing pretty slow. The front wheel saws back and forth when I climb at 6 mph, but less than it did with the bar bag. The bike can be ridden no hand at 8 mph and above, and it gets almost normal feeling above that speed.
Next steps, besides more riding, are to add a bottom securing strap to hold teh bottom still, and to adjust the decaleur position to hold the bag straight up but still focus its weight on the rack. Another step is to investigate installing a much smaller, much lighter TA rack. Aside from the weight, it moves the bag down nearly another cm and back by nearly two cm. This will further reduce the fork moment of inertia when loaded, at least with the 8# I'm using.
Andrey used a big bottle of car wash, which has two potential problems; the sheer weight and the liquid sloshing. I think solid stationary loads are much more realistic. It's looking to me like the improvement in handling is due to the reduction of the fork moment of inertia. Lowering the bag, moving it closer to teh steering axis, and stabilizing it are all important.
Andrey, I expect that your bike will be pretty good on that fleche.
How does it ride? I loaded the bag with a lock/cable, my tool pouch, gloves, candy bars, a pump, my wallet, and a tube. It weighed about 7#. The steering was surprisingly easy, with just a little more friction due to tire loading. It was a little slow to change line, but could be no-handed. I need to test that more. This is with 28 mm tires, 70 psi in the front and 85 psi rear.
I'm early in my season, so I'm climbing pretty slow. The front wheel saws back and forth when I climb at 6 mph, but less than it did with the bar bag. The bike can be ridden no hand at 8 mph and above, and it gets almost normal feeling above that speed.
Next steps, besides more riding, are to add a bottom securing strap to hold teh bottom still, and to adjust the decaleur position to hold the bag straight up but still focus its weight on the rack. Another step is to investigate installing a much smaller, much lighter TA rack. Aside from the weight, it moves the bag down nearly another cm and back by nearly two cm. This will further reduce the fork moment of inertia when loaded, at least with the 8# I'm using.
Andrey used a big bottle of car wash, which has two potential problems; the sheer weight and the liquid sloshing. I think solid stationary loads are much more realistic. It's looking to me like the improvement in handling is due to the reduction of the fork moment of inertia. Lowering the bag, moving it closer to teh steering axis, and stabilizing it are all important.
Andrey, I expect that your bike will be pretty good on that fleche.
Last edited by Road Fan; 05-11-10 at 07:32 AM.
05-17-10, 07:49 PM
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I am happy to report that the bike did very well on the fleche. I did not have the front bag overloaded , but there was a Nitto rack, Lumotec CYO headlight mounted on the rack, Acorn bag with 6 power bars, 6 gels, 4 AA battery pack with Dinnotte light, a pack of Noon tablets, sunscreen lotion, tube of Assos butt cream, 3 pairs of gloves, head gear, glass case with extra lenses, tissue ,maps and a brevet card.
With the old fork even with the small load like the handling of the bike would feel heavy and would refuse to turn at speed. I have a vibration riding with no hands though. The front end starts shaking and I had to keep at least one hand on the bars for the vibration to stop . It does not bother me that much, because almost never I ride with no hands. I will try to load the front bag with more stuff to see if the vibration will go away, but I do not think it will.
I am happy to report that I could decent at 40-45 mph at night safely now, no under-steer issues like with the 60 mm trail and it is more important than vibration.
I read that people have vibration problems with low trail bikes and as far as I know nobody had it resolved. I thought I would not have the issue because my trail is still a reasonable 50 mm and nor 20, 30 or 40 mm. But I guess it is a know issue for the bike manufactures and that is why they have all the bikes at around 60 mm trails nowadays.
With the old fork even with the small load like the handling of the bike would feel heavy and would refuse to turn at speed. I have a vibration riding with no hands though. The front end starts shaking and I had to keep at least one hand on the bars for the vibration to stop . It does not bother me that much, because almost never I ride with no hands. I will try to load the front bag with more stuff to see if the vibration will go away, but I do not think it will.
I am happy to report that I could decent at 40-45 mph at night safely now, no under-steer issues like with the 60 mm trail and it is more important than vibration.
I read that people have vibration problems with low trail bikes and as far as I know nobody had it resolved. I thought I would not have the issue because my trail is still a reasonable 50 mm and nor 20, 30 or 40 mm. But I guess it is a know issue for the bike manufactures and that is why they have all the bikes at around 60 mm trails nowadays.
05-18-10, 07:29 AM
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The vibration is what most riders call "shimmy." I'm getting a little of it on my Woodrup. Some riders, including Jan Heine, think it is mitigated by using a needle bearing headset rather than ball bearing. They have a little extra drag and are much more tolerant of being adjusted slightly tight, but still steer well. Ball bearing headsets might wear out sooner if they are over tightened.
The classic needle bearing design, the Stronglight A9, is not easy to find, and some people have reported that when they get their part home it turns out to be ball bearing.
The classic needle bearing design, the Stronglight A9, is not easy to find, and some people have reported that when they get their part home it turns out to be ball bearing.
05-18-10, 08:50 AM
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I installed a new Velo Orange ball bearing headset with new fork. I had it adjusted very loose and very tight and shimmy was still there both times. I do not think it is the headset or type of bearing that cause the vibration(at least in my case), but I do not know what it is( probably the nature of a low trail front end).
05-18-10, 07:53 PM
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I am a firm believer in needle bearing headsets. I have been using them for more than 20 years and believed they could stabilize a bike before Jan wrote of his opinion. (I was very glad to see some independent confirmation!) And of course they last essentially forever, too.
But as Andrey has pointed out, they are not a panacea. The low trail bikes are indeed less stable, in my experience. If alignment is not perfect - or if a wheel is slightly out, or the gods not smiling, or... - then shimmy may result.
But as Andrey has pointed out, they are not a panacea. The low trail bikes are indeed less stable, in my experience. If alignment is not perfect - or if a wheel is slightly out, or the gods not smiling, or... - then shimmy may result.
05-18-10, 10:58 PM
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High trail produces slower response, and lower trail produces faster response. The stability margin of the bike is reduced with low trail. On many single-track vehicles, steering dampers have been used to damp shimmy but not affect geometry. Many motorcycles have had them over the years. Needle headsets, as has been said, have more drag than ball. Part of that is because as cylindrical bearings, they slip and roll at teh same time. That frictional drag IS steering damping. That's why I think needle bearing is worth a try.
