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Thread: FB and speed

  1. #26
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    Quote Originally Posted by Bacciagalupe View Post
    "Excessively responsive handling." I don't own a car, so I have no idea how that term would apply there.
    How did you pick the term for bicycle handling? I've spent a lot of time studying bicycle handling, and oversteer is not a term that is used to describe it.

    Quote Originally Posted by Bacciagalupe View Post
    That may be the case, but unless you're drastically modifying the geometry, small-wheeled bikes are less stable and turn more responsively than 700c bikes.

    For example, my Swift has a wheelbase of 1010mm, which is slightly longer than my cross bike; it also has a straight fork. The Swift has excellent acceleration (with the right tires, that is ) and is better at dodging obstacles; the cross is much more stable, descends better, handles loads better, and handles bumps better.

    For general riding, it's not a big deal. For some uses, e.g. urban riding, it's a selling point. For touring, long rides, group rides, fast rides and technical descents, handling is definitely one factor among many to consider.
    Folding bicycles are a drastic change on geometry.

    Your cross bike probably has a head tube angle of 72 degrees and 45mm of fork offset. This gives it 65mm of trail and 20mm of front wheel flop:
    http://kogswell.com/geo.php?h1=690&i...2.x=14&d2.y=11

    Your Swift Folder has the same figures (72 degree HTA, 45mm of fork offset), but the wheels are only much smaller. This drops the trail to 45mm and the wheel flop to 9mm:
    http://kogswell.com/geo.php?h1=470&i...2.x=14&d2.y=11

    If you wanted to make your cyclocross bike handle like your Swift Folder you'd need to need to grossly redesign the front end. 74 degree head tube angle and 60mm of fork offset is close:
    http://kogswell.com/geo.php?h1=690&i...2.x=14&d2.y=11

    To change the Swift Folder to behave like the cyclocross frame you really should have much less fork offset. 15mm is getting you there:
    http://kogswell.com/geo.php?h1=470&i...2.x=14&d2.y=11

    That is a drastic change, removing 30mm of fork offset. The curve in the fork blades would be almost immperceptable.

    Personally I like road bikes that have around 40-45mm of fork offset like your Swift Folder. However they require wider tires to handle well. This is one of the reasons that I like the Avocet Fasgrip Freestyle on 406mm wheeled folding bikes. It is a wide tire (around 40-42mm) that has low rolling resistance and runs well at moderate pressures (I'd run it at around 50-60psi). It is probably as fast as the very narrow tires (like the Conti GP3000) that many people like to run, but greatly improves the handling of the bike.

    The other thing that helps low trail bikes is to carry the load on the front instead of the rear. Folding bikes are good for this anywhere since there is typically a lot of space between the top of the front wheel and the handlebars.

    The mistake is that folding bike manufacturers almost universally try to copy big bike head tube angles and fork offsets instead of modifying them for the small wheels. For some people (me) this works out well because we like lower trail bicycles. For the skinny/high pressure set with rear loads it is a big mistake.

    I don't think that trail and wheel flop define everything about handling. The smaller wheels make other differences too. I'd still like to see greater experimentation and study of small bike handling than what appears to be out there.

    alex

  2. #27
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    Thanks! Yes, one of my thoughts is about a folding ebike. I often have to take busses and trains to really out of the way places in rural china, then fend for myself with taxi drivers with vehicles that look old enough to have been used on the 10,000 mile march with Chairman Mao I was originally hoping to beef up a battery system on a fairly lightweight but rugged ebike to do the whole distance - without the train or bus - but after looking at the cost of batteries for such a conversion I have decided to look for plan 2, which is looking for a good folding bike that I can take with me on the train or bus. I have ridden a couple of folding bikes and was rather impressed with them but for one thing. The front ends seem way too light and squirrelly, like they are just begging to have a motor added or some other weight to give them more stability...(OK, OK I know, added a motor to a front end us a bit controversial). I have never considered anything but a 20" tire in this decision because, from my experience, the bigger the tire is the more stable the bike will be on uneven (rips, potholes, small tree branches, etc) surfaces. I am guessing that having a bike frame that is a bit on the long side might be an advantage because I will often have to travel as much as 50 miles. Longer bikes seem to be a bit more comfortable.
    Last edited by pengyou; 11-03-07 at 09:05 AM.

  3. #28
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    You're bike will be extremely heavy with your batteries and cargo. You're probably better off getting a gas scooter.

  4. #29
    Professional Fuss-Budget Bacciagalupe's Avatar
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    Quote Originally Posted by awetmore View Post
    How did you pick the term for bicycle handling? I've spent a lot of time studying bicycle handling, and oversteer is not a term that is used to describe it.
    Picked it up from someone else, no idea whom. Since the term also covers "more steering than vehicle handler intended / expected," it works for me.


    Quote Originally Posted by awetmore
    Folding bicycles are a drastic change on geometry.
    Ya think?

    Trail is important, but handling is affected by multiple aspects of a bike's geometry: wheelbase, BB height and position, seat tube angle. Taller handleposts may be another factor as well. (Oddly enough I haven't noticed any major changes in 20" handling based on tire changes, only acceleration, max speed and comfort.)

    In addition, change one specific aspect of bike geometry, and 2 other things change, yes? What other effects will reducing fork offset have on the bike? Would it slow down handling and potentially deteriorate handling at slow speeds?

    I expect there are mechanical reasons why folding bike manufacturers don't use forks with lower offsets. I assume if you sat down with a folding-bike frame maker who has spent time experimenting with different forks, they could tell you what their research turned up. Maybe some of the Wal-Mart folding bikes skipped on the R&D, but there's no doubt that Bike Friday and even Dahon has done some R&D on this. I have zero doubt that if Dahon could make a 20" bike that steered the same as a 26" or 700c bike, it'd be a part of their lineup.


    At any rate, unless you're going to go out and pick up a custom fork, the vast majority of folding bikes will have [insert term of choice to indicate less stable handling] than a 700c bike designed/marketed for that exact same purpose.

  5. #30
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    Yes, but I have never seen a folding gas scooter I think 2 sets of some kind of Lithium batts at about 12 pounds each with a 30 pound set up will get me where I need to go.

  6. #31
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    Oversteer has a very specific meaning as defined by The Society of Automotive Engineers. Specifically, that the sum of the rear tire slip angles are greater than the sum of the front tire slip angles. The slip anlges that are experienced by a bicycle are pretty stinkin' small. The ultimate result of oversteer on a motorcycle can be a high-side crash while low-sides are more often understeer. Good motorcycle racers are not worried about oversteer, but intentionally understeering a bike is dicey business at best.

    Probably a better term to use is for what you are describing is steering response...in this case, very quick steering response.

    A lot of geometry work has been done on 20" tires, specifically on BMX bikes. What are the head angles / trail numbers of your average BMX'er? They're very stable, that's for sure. I'd guess a slack angle and a lot of trail.

  7. #32
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    Quote Originally Posted by pengyou View Post
    Yes, but I have never seen a folding gas scooter



    http://www.goped.com/Products/

    Last edited by spambait11; 11-03-07 at 09:55 PM.

  8. #33
    Professional Fuss-Budget Bacciagalupe's Avatar
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    American Heritage Dictionary: "To turn more sharply than the operator would expect. Used of vehicles, especially automobiles." ( http://www.bartleby.com/61/44/O0194450.html )

    Merriam-Webster: "the tendency of an automobile to steer into a sharper turn than the driver intends sometimes with a thrusting of the rear to the outside; also : the action or an instance of oversteer" ( http://www.merriam-webster.com/dictionary/oversteer )


  9. #34
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    I bet you look up sexual terms in the dictionary and giggle at them, too, huh? My point is that the term you were using wasn't particularly helpful in explain the phenomena that you were describing. As a person that uses understeer and oversteer on a daily basis (along with many other terms describing limit handling characterstics), I was trying to help you out.

  10. #35
    Car free since 1995 pm124's Avatar
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    Quote Originally Posted by pengyou View Post
    Yes, but I have never seen a folding gas scooter I think 2 sets of some kind of Lithium batts at about 12 pounds each with a 30 pound set up will get me where I need to go.
    I've seen some of the great masses of electric folding bikes in China. But I've never seen a high quality electric folding bike there. I know that some higher end folders are sold there, but I haven't seen any. If you are on rutted roads, you'll be better off with bigger wheels.

  11. #36
    Car free since 1995 pm124's Avatar
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    Quote Originally Posted by Fat Boy View Post
    Ya, but he likes his kool-aid and has been repeating this same basic message on every thread that's even remotely related. I think he's going to enter an A-bike in the TDF next year and clean up.
    You are a real charmer. I'm sure you have lots of friends off line, too.

  12. #37
    The Legitimiser Sammyboy's Avatar
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    Quote Originally Posted by Fat Boy View Post
    Actually, in car terms it's the other way around. The rear sliding towards the outside of the corner and the front continuing on the path that they were pointed until the car spins. Regardless, I'm a bit confused by the term as well when attributed to a bicycle. Perhaps he just meant that the steering response was quicker.
    This is exactly right. Oversteer means the back end steps out, meaning the car is pointed more round the corner than you intend, or has oversteered. At the extreme end, it means a spin. Understeer means the wheels can't turn the car enough and it ploughs on, rather than going where you point it, or understeers. At the extreme end, this means ploughing off the outside of the bend.

  13. #38
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    Quote Originally Posted by Fat Boy View Post
    I bet you look up sexual terms in the dictionary and giggle at them, too, huh? My point is that the term you were using wasn't particularly helpful in explain the phenomena that you were describing. As a person that uses understeer and oversteer on a daily basis (along with many other terms describing limit handling characterstics), I was trying to help you out.
    Why so aggressive and unpleasant?

    This is a forum for civil people. You could just say, 'That's not the way I see it - here's my view,' and say what you want to add to the discussion. We actually don't usually get uncivil remarks here, and speaking for myself, I don't think we want them.
    “Get a bicycle. You will not regret it, if you live." - Mark Twain

  14. #39
    Car free since 1995 pm124's Avatar
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    Quote Originally Posted by EvilV View Post
    Why so aggressive and unpleasant?

    This is a forum for civil people. You could just say, 'That's not the way I see it - here's my view,' and say what you want to add to the discussion. We actually don't usually get uncivil remarks here, and speaking for myself, I don't think we want them.
    I'll second that.

    Speaking of over-performing, perfectly steering small wheeled bikes, how is the Moulton?

  15. #40
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    Quote Originally Posted by pm124 View Post
    I'll second that.

    Speaking of over-performing, perfectly steering small wheeled bikes, how is the Moulton?
    I've got it layed up indoors now the weather has turned nasty. I take it out on sunny afternoons but I'm damned if I'll ride it on wet cold days or worse still if there's salt on the roads which there will be soon. Being a rather classy machine the cold dark garage is out of the question - you don't put up aristocracy in a stable do you.

    Meanwhile the little Merc is still earning her keep. That little beauty is as good as ever. She sleeps in the hallway near a radiator. My family are patient with these eccentricities.

    Noticing your 'car free' slogan - I had to pay £250 yesterday to get the cam belt on my diesel car changed. Given that at Top Dead Centre the space in the combustion chamber is about 2mm, I didn't fancy the cost of a new engine (£4,500) if the cam belt broke and the heavyweight diesel pistons walloped valves sticking down into the cylinders. They reckon its a total write off issue for the engine.
    Last edited by EvilV; 11-09-07 at 06:02 AM.
    “Get a bicycle. You will not regret it, if you live." - Mark Twain

  16. #41
    Car free since 1995 pm124's Avatar
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    Quote Originally Posted by EvilV View Post
    I've got it layed up indoors now the weather has turned nasty. I take it out on sunny afternoons but I'm damned if I'll ride it on wet cold days or worse still if there's salt on the roads which there will be soon. Being a rather classy machine the cold dark garage is out of the question - you don't put up aristocracy in a stable do you.

    Meanwhile the little Merc is still earning her keep. That little beauty is as good as ever. She sleeps in the hallway near a radiator. My family are patient with these eccentricities.

    Noticing your 'car free' slogan - I had to pay £250 yesterday to get the cam belt on my diesel car changed. Given that at Top Dead Centre the space in the combustion chamber is about 2mm, I didn't fancy the cost of a new engine (£4,500) if the cam belt broke and the heavyweight diesel pistons walloped valves sticking down into the cylinders. They reckon its a total write off issue for the engine.
    Sorry to hear that. I assume your family won't put up with being piled up on the Merc for routine outings.

  17. #42
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    Quote Originally Posted by Sammyboy View Post
    This is exactly right. Oversteer means the back end steps out, meaning the car is pointed more round the corner than you intend, or has oversteered. At the extreme end, it means a spin. Understeer means the wheels can't turn the car enough and it ploughs on, rather than going where you point it, or understeers. At the extreme end, this means ploughing off the outside of the bend.
    Yeah, but it seems that (as the definitions provided by Bac imply) that the back end stepping out is caused by trying to turn too sharp. In other words, if the steering were less responsive then the same input at the steering control (wheel or handlebars) would result in a wider turn which would eliminate the phenomenon of the back wheel sliding out. On the other hand, for the same input, more responsive steering implies a sharper turn which would worsen the sliding.

    So, all else being equal, they go hand in hand and are, thus, appropriately referred to by the same term.

    Quote Originally Posted by EvilV View Post
    Why so aggressive and unpleasant?

    This is a forum for civil people. You could just say, 'That's not the way I see it - here's my view,' and say what you want to add to the discussion. We actually don't usually get uncivil remarks here, and speaking for myself, I don't think we want them.
    Thanks EvilV. People like you are what makes "Folding Bikes" the most civil and pleasant subforum on BF. (seriously, the rest of BF is a jungle compared to this place)

  18. #43
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    Well I just think we come here to help each other find out stuff and to encourage enthusiasm. I've seen the way it goes on some of the forums and it isn't terribly encouraging of the exchange of ideas. There are people here who must spend countless ideas sharing their skill and experience. I think the fact that people behave in a decent ordinary way here helps make that continue.
    “Get a bicycle. You will not regret it, if you live." - Mark Twain

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