C. of G.
07-19-07 | 07:13 PM
#1
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C. of G.
I'm converting a ten speed road bike with drop bars into an upright sitting bike.
It's going to have a Nitto North Road handle bars and super long stem. With the
old drop bar, the c.g. is probably right between the two wheels. With the new
North Road bars, the c.g. is probably be a lot closer to the rear wheel. That puts
a lot of weigh on the rear wheel, and the front wheel will be very light. Do you
think my new upright setup will have negative impact on the handling of the bike?
In automobiles, the weight is mostly on the front wheels. I think that's suppose
to make the car stable. A rear heavy car would be unstable. I'm just think this
principle would apply to bicycle also.
It's going to have a Nitto North Road handle bars and super long stem. With the
old drop bar, the c.g. is probably right between the two wheels. With the new
North Road bars, the c.g. is probably be a lot closer to the rear wheel. That puts
a lot of weigh on the rear wheel, and the front wheel will be very light. Do you
think my new upright setup will have negative impact on the handling of the bike?
In automobiles, the weight is mostly on the front wheels. I think that's suppose
to make the car stable. A rear heavy car would be unstable. I'm just think this
principle would apply to bicycle also.
07-19-07 | 07:20 PM
#2
Senior Member
Joined: Jul 2007
Posts: 194
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It depends what you are doing with the bike.
With my mountain bike, it has a super short rear triangle and a raked out front end. This is awesome for downhill rides and putting the power down to the wheel in the back. Steering is a little slow, but that is due to the length of the fork, and not the weight being over the rear wheel...
The downside is that on steep climbs, unless I move myself forward, the front end loses grip and in really steep climbs actually wants to come up...On a road bike however, I dont think this would be a huge issue...mountain climbs tend to be a little steeper in some spots than road climbs.
With my mountain bike, it has a super short rear triangle and a raked out front end. This is awesome for downhill rides and putting the power down to the wheel in the back. Steering is a little slow, but that is due to the length of the fork, and not the weight being over the rear wheel...
The downside is that on steep climbs, unless I move myself forward, the front end loses grip and in really steep climbs actually wants to come up...On a road bike however, I dont think this would be a huge issue...mountain climbs tend to be a little steeper in some spots than road climbs.
07-19-07 | 07:26 PM
#3
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Just for commuting on mostly flat roads, but in heavy traffic that requires a lot of filtering and evasive maneuvering.
I notice cruiser bikes have very long wheelbase, so that eventhough you're sitting upright, the c.g. is still at the center of the bike, i.e., weight is evenly distributed on both wheels.
I notice cruiser bikes have very long wheelbase, so that eventhough you're sitting upright, the c.g. is still at the center of the bike, i.e., weight is evenly distributed on both wheels.
07-19-07 | 07:30 PM
#4
Senior Member
Joined: Jul 2005
Posts: 2,308
Likes: 16
I did a road bike conversion like this with a super tall stem so that I sat bolt upright.
The first thing I can recommend if you do this is a sprung saddle. You get a lot more road shock up your spine when you sit upright like that. My back hurt after the first five-mile ride (though this was pretty extreme--I used a tall stem and a stem extender, wanting to see how tall and upright I could get).
I never had a problem with popping the unwanted wheelie. However, when I first rode it after setting it up, the handling felt very strange (like a long wheelbase recumbent, if you've ever ridden one). The steering was super light, very touchy. It really surprised me when I first climbed on. However, I got used to it pretty quickly (like, after one mile).
I saw a thread once where somebody posted a photo of a "conversion" like you are describing, and he ridiculed it, saying that it was a waste of what the frame was designed for--which amounted to, essentially, a lower and more forward CoG, plus the greater relative power resulting from the tucked position.
But life is not all about looking at the top of your front wheel.
The first thing I can recommend if you do this is a sprung saddle. You get a lot more road shock up your spine when you sit upright like that. My back hurt after the first five-mile ride (though this was pretty extreme--I used a tall stem and a stem extender, wanting to see how tall and upright I could get).
I never had a problem with popping the unwanted wheelie. However, when I first rode it after setting it up, the handling felt very strange (like a long wheelbase recumbent, if you've ever ridden one). The steering was super light, very touchy. It really surprised me when I first climbed on. However, I got used to it pretty quickly (like, after one mile).
I saw a thread once where somebody posted a photo of a "conversion" like you are describing, and he ridiculed it, saying that it was a waste of what the frame was designed for--which amounted to, essentially, a lower and more forward CoG, plus the greater relative power resulting from the tucked position.
But life is not all about looking at the top of your front wheel.
07-19-07 | 07:56 PM
#5
Senior Member
Joined: Jul 2005
Posts: 2,308
Likes: 16
The difference between one of these and a rear-weighted road bike will be the steering geometry, as japollner implies. Those recumbents will probably have a lot more trail, making them more stable at speed. Road bikes will have less trail, making the steering quicker at speed, for better maneuverability.
The difference on your bike will also be the tiller in the steering (the distance between the steering pivot point (i.e., the center of the steerer tube) and the lever axis (i.e., the line between your hands--I just made up the term "lever axis"). On a road bike with drop bars, the tiller is typically quite small. This, combined with narrow bars, gives you less leverage--maybe this, combined with the weight on the front wheel, slows down the steering feel to a tolerable level. On a long-wheelbase recumbent, and on an upright-riding bike, the lever axis is often farther away from the steering pivot, giving more leverage, or tiller. This makes your steering output/input ratio smaller, but also more powerful. This can make the steering squirrellyer, or more squirrelly.
Maybe MnHPVguy will comment. He rides both bents and upright-riding English three-speeds, plus he's a frigging bike design genius. He could tell you anything you might need to know about your prospective change. Though, I bet you've already gotten an earful/eyeful from me.
07-19-07 | 08:01 PM
#6
While drop bars do place more weight on your hands and thereby the front wheel, 50/50 is not likely. Even the "new" short top tube long stem (135mm) set ups.
If you placed a pair of bathroom scales under the wheels and got on the bike you would be surprised how little is on the front wheel. With drop bars more like 70/30, a bit more if you are in the "hooks". I have seen 80/20 too, a bathroom scale set up is not perfect but does give you a data set.
Upright bars will place more weight on the rear, depending on the stem length used and where the saddle is positioned, I have seen it moved forward 1cm to happy effect. A wider saddle, or even a sprung one will reduce the shock loading, typically as the back is more upright, the compression loading on the discs increases dramatically, might look at mtb. straight or minimal angle back, say 3 degrees, it will get you higher than hands on the hoods, but could still get your torso leaned forward a bit to avoid compression. Done this for a few guys who no longer had the neck flexibility to use drop bars, and worked well for them. Your mileage may vary....
If you placed a pair of bathroom scales under the wheels and got on the bike you would be surprised how little is on the front wheel. With drop bars more like 70/30, a bit more if you are in the "hooks". I have seen 80/20 too, a bathroom scale set up is not perfect but does give you a data set.
Upright bars will place more weight on the rear, depending on the stem length used and where the saddle is positioned, I have seen it moved forward 1cm to happy effect. A wider saddle, or even a sprung one will reduce the shock loading, typically as the back is more upright, the compression loading on the discs increases dramatically, might look at mtb. straight or minimal angle back, say 3 degrees, it will get you higher than hands on the hoods, but could still get your torso leaned forward a bit to avoid compression. Done this for a few guys who no longer had the neck flexibility to use drop bars, and worked well for them. Your mileage may vary....
