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 Head angle -FWD low racer

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nigel schroder Posted - 02/12/2010 : 12:41:26
What is the best head angle for a FWD low racer?
I want to be able to race on the road at speeds between 35-60kph.
20" front wheel(driven) and 26" back.
I was also thinking about using pistol grip handle bars will this work on a FWD.
Cheers Nigel
25   L A T E S T    R E P L I E S    (Newest First)
mhelander Posted - 06/26/2012 : 05:52:06
quote:
Originally posted by sean costin

Last year I was coached in sprinting on a upright by a national caliber sprinter. He taught me that wiggling the bike from side to side is inefficient and the best sprinters work hard on keeping from doing this. You should try to keep the bike as straight as possible when sprinting.


This is my understanding also. Applies to sprinting, TT riding in general and going fast in uphills. My riding gets little wobbly in uphills when done enough hard ones during the ride. Sign of better stay below anaerobic level and utilize more momentum when approaching following hills...

Cheers,
-Mika

MetaPhysic 700c @ 2011, M5 CrMo Lowracer @ 2010
sean costin Posted - 06/26/2012 : 05:08:51
Last year I was coached in sprinting on a upright by a national caliber sprinter. He taught me that wiggling the bike from side to side is inefficient and the best sprinters work hard on keeping from doing this. You should try to keep the bike as straight as possible when sprinting.

Here is a video of the best sprinters in the world. They get a little wiggly out of the saddle, but I think that is just a balancing thing. Otherwise. very straight.

http://www.youtube.com/watch?v=Y-t8lFpLlaA
JerseyJim Posted - 06/25/2012 : 16:01:25
quote:
Originally posted by Dana Barlow

"pedal steer" as force "A"=power in put at 90* to head tube ,can be then comepaired to "0" pedal steer on same in-line with head tube[not posible but to get point across],so as your power line =[hip to foot line] comes off of 90* to head tube were it is max. bad,like as exsample 30* off you get 1/3 less pedal steer for same power in put.

Dose that help any one with some under standing of just "pedal steer" when pedals are ahead of head tube.? This explans why you get less when lowering the BB. but if BB moves with the fork it is even higher force going into steering from extra arm you added to power input[= less control]and you wast lots of power trying to counter leg power with your arms. Making that very poor design work.
We actuly also get some other types of dinamic balance force from pedaling that also is a interplay with steering, from the out of balance from side to side of leg/foot load efecting steering.
I designed a way to counter most of that efect back in the 80's that I called "Barlow Spinners"
But that is another story compleatly.
Most of these designs I'm seeing are just bad,but we humans can learn to ride nearly anything and after a time can even think we're doing good with a design that should of been junked.
But then there's fun of making it work kind of anyway,even though it's not good engineering at all.


Dana
Team Strange
"Strange One","Too Strange","Strange Try"
Miami Fla.



I know this is an old thread, and as they say, I have no dog in this hunt: MBB, Fixed BB or otherwise, however I have to ask this question regarding this post;

If as stated, the greater the head angle to the pedals, the more the wasted energy, why would an upright bicycle racer rock the bike from left to right when sprinting? By now, with over 100+ years of bicycle racing, some coach somewhere should have come up with a technique that uses less energy and works better to generate maximum power. Presumably that technique would be to keep everything in line while pedaling.

While I agree that there is some wasted energy I'm not convinced that the level of inefficiency is that great, or greater than standard sprinting technique on an upright.

Perhaps some energy is wasted with the arms countering the pedaling motion in a MBB design, however there must be some energy from the arms that increase the leverage on the pedals in the same way sprinters gain leverage (presumably) from pulling on the handlebars.

Anyway, as I said MBB or not, I don't really care. There's advantages and disadvantages to every design, and while I do believe that some designs are dangerous (rear wheel steering) I don't understand this analysis and conclusion that the MBB design is inherently inferior due to the power transfer dynamics as described. In light of the sprinting techniques of upright racers, I don't see much difference.


nigel schroder Posted - 09/03/2010 : 21:46:40
quote:
Originally posted by tom porter

I tried to send you an e mail on the 31st with a couple of pics. Did you recieve it? Let me know if there are problems on this site.

Tom Porter

O---o



No I didn't get it.

Try this (nigelmelanie at gmail dot com)

cheers
tom porter Posted - 09/03/2010 : 21:05:07
I tried to send you an e mail on the 31st with a couple of pics. Did you recieve it? Let me know if there are problems on this site.

Tom Porter

O---o
tom porter Posted - 08/31/2010 : 11:03:05
I'll try to send some phots to you Nigel ASAP. The bike Warren posted has frame angles that are too severe in my experience. The small tubes don't help either. The small brace from the headtube will help some but this joint at that steep angle will move side to side and fail, I did a frame like this and got about 10 weeks of riding and it failed, might be a picture of the fix on my peojects page. The weather here is getting a bit more comfortable I'll try to make a sketch for a design in the next couple of days to send. I see you are wondering also about tubing, I would think someone in NZ would be able to supply you. 4130 is really the way to go.

O---o
warren Posted - 08/31/2010 : 06:07:11
Probably something like this:


-Warren.
nigel schroder Posted - 08/31/2010 : 01:34:01
Hi Tom
I tried to send you a Email but it wouldn't work.Could you please send me one through my "User Profile"

This is what was in the Email:

I'm about to make a start on the low racer this weekend.

It will be a 406 fwd twist chain with a 700c rear wheel.

You posted on the "forum" (The best way I think would be a single chainring with a 3 x 8 hub on the wheel using two pulleys, if I was going to attempt this again I would use this.)

Can you please draw me a simple sketch of this.Also what were the refinements to the design you were talking about.
Any help would be great

Thanks Nigel Schroder

cheers Nigel

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
tom porter Posted - 08/27/2010 : 16:50:19
Hi Nigel, If you look at the photos on my project page for Tom Ries, you may get an idea of what the rough layout was. Can't find the frame, must have chucked somewhere along the line. Probably be better if you e mail me about particulars, I see Warren hasn't updated it yet. It's tomrec@att.net and then I'll have yours. Will be happy to help you out, I always intended to refine some design elements over the years but of course I got sidetracked.

O---o
nigel schroder Posted - 08/19/2010 : 19:08:20
quote:
Originally posted by tom porter

The best way I think would be a single chainring with a 3 x 8 hub on the wheel using two pulleys, if I was going to attempt this again I would use this.

O---o



Hi Tom
can you please draw me a simple sketch of this set-up

cheers
tom porter Posted - 08/17/2010 : 13:04:55
Hello Nigel, been banging about looking for some pieces found some and I think I have some other still around. Later in the week I'll have more time and I'll post further info then.

O---o
nigel schroder Posted - 08/16/2010 : 22:55:39
quote:
Originally posted by tom porter

Hi Nigel,

This bike was built in 2003 so the only pictures are the ones posted. The front derailleue had the cage shorted and mounted almost upside down. The intermediate drive is a Shimano 8 speed cassette body with pawls removed, this is a pretty common thing. Gearing is vitually unlimited. The single chainring was mounted on a sliding boom for tensioning. If your interested in building something on the order of this let me know, meanwhile I think most of the bits are stashed somewhere nad I'll have look around. I probably can come up with some refinements of the design if your'e interested.

Tom Porter

O---o




Hi Tom

I'm back in the land of computers.
Have you had a look for the parts? And I would love to here about any refinements that you have come up with.I think this design will work very well for me ,because as you say the gearing is unlimited. It will be very easy to change the gearing when I add a fairing.

cheers Nigel

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
tom porter Posted - 08/02/2010 : 10:47:16
Hi Nigel,

This bike was built in 2003 so the only pictures are the ones posted. The front derailleue had the cage shorted and mounted almost upside down. The intermediate drive is a Shimano 8 speed cassette body with pawls removed, this is a pretty common thing. Gearing is vitually unlimited. The single chainring was mounted on a sliding boom for tensioning. If your interested in building something on the order of this let me know, meanwhile I think most of the bits are stashed somewhere nad I'll have look around. I probably can come up with some refinements of the design if your'e interested.

Tom Porter

O---o
nigel schroder Posted - 08/01/2010 : 19:49:43
quote:
Originally posted by tom porter

I've built several FWD's with a small tire (349,406,451). Tried every possible way except one. Big chainring 72T/52T double with a 451, was OK with a 42 - 120 inch gear range, used two pulleys, shifting wasn't very crisp though. Intermediate drive on the other two, 349 had triple crankset with normal chainrings and about 6 speeds on the intermediate on a 8 speed cassette body, single speed freewheel on wheel hub. Finally the 406 had a single chainring with 3 speeds on the intermediate drive shifted with a modified front derailleur ond a 9 speed cassette on the wheel, thes both shifted crisply. Only issue is clearance for the knee on the right side. Seemed to be OK for others who rode these bikes. The best way I think would be a single chainring with a 3 x 8 hub on the wheel using two pulleys, if I was going to attempt this again I would use this.

O---o



Hi Tom

can you please add some close up pic's of this Fwd of yours
(http://www.recumbents.com/wisil/porter/images2004/porterFWDDualSusp9.jpg)

And what are the size's of all the cogs?
and what did you have to do to modify your front derailleur?

cheers Nigel
(ps: I'm away on holiday for a couple of weeks, so look forward to seeing something when I get back, no rush)

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
tom porter Posted - 07/31/2010 : 18:03:15
I've built several FWD's with a small tire (349,406,451). Tried every possible way except one. Big chainring 72T/52T double with a 451, was OK with a 42 - 120 inch gear range, used two pulleys, shifting wasn't very crisp though. Intermediate drive on the other two, 349 had triple crankset with normal chainrings and about 6 speeds on the intermediate on a 8 speed cassette body, single speed freewheel on wheel hub. Finally the 406 had a single chainring with 3 speeds on the intermediate drive shifted with a modified front derailleur ond a 9 speed cassette on the wheel, thes both shifted crisply. Only issue is clearance for the knee on the right side. Seemed to be OK for others who rode these bikes. The best way I think would be a single chainring with a 3 x 8 hub on the wheel using two pulleys, if I was going to attempt this again I would use this.

O---o
nigel schroder Posted - 07/31/2010 : 15:57:08
When I start the rebuild I still want to keep it FWD,so there are two options that I'm thinking about.

Option 1 --- Big front chainrings and idler's

Option 2 --- Small (standard) chainrings and a step up/mid drive.

The front wheel is a 406

I want to be able to race on the road at speeds between 35-60kph and maybe add a full fairing at a later date.

What are the pro's and con's of the two options?
and what do you think will work best?

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
25hz Posted - 07/29/2010 : 04:26:19
MBBs do weird **** when they wipe out. Not being a physicist or an engineer, the main reason I can come up with, from repairing post-wipeout damage, is because the CoG moves left and right of centre.

When you steer, especially in extreme control, or over control moments, as your legs are moving left and right of centreline, this obviously also moves the CoG, and that amount of movement with the forces present in a wipe-out, might be what is causing rear wheels and frames and forks to twist like they do. If the CoG is lined up with centreline and the wheels, pushing sidways on the CoG makes the bikes rotate in an arc with the pivot being the contact patch of the tires, and the bike goes over. With the MBBs, turning displaces the CoG to the side of centreline and the contact patches, so now, lateral force on the CoG adds lateral force to the contact patch before the CoG can be raised a little more than normal to still rotate up and over to the side. That spike in loading, during a wipeout, might be what is causing the twisting that happens.

With a more normal 2 wheel bent, even during a wipeout, the only thing that's moving left and right of centre, is the relatively low mass arms and handlebars/tiller.
nigel schroder Posted - 07/28/2010 : 12:33:22
quote:
Originally posted by alevand


Flexing of the rear fork may have something to do with it too.

C:
Tony Levand



I used the rear fork like this trying to get a little suspension in the back end.

After the crash the back wheel still spins straight and round but the axle has been bent. Do you think this was caused by the fork flexing side to side before the crash?

I have seen other people use forks like this has anyone else ever had problems with this type of flexing?

When I rebuild the bike do you think that I need to reinforce the back end? or do I need to start all over again?

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
LongJohn Posted - 07/28/2010 : 08:15:53
Tony,

I don't see how these speed-wobbles are related to what Nigel experienced.
I think what Nigel experienced was an overcompensation of a steering action induced by ??? (fill in the blanks).
This could have simple be related to the steering geometry.

What we do know, is that steering of a bike is very complex. Several universities have spend there share of time researching it.
Also the Lord of the Chainrings has done his share.
Stability of a MBB bike is something totally different from that. Which implicates that you would have to depend on "previously succesfull geometry".

If there is a deviation in geometry you might get stability issues.

I don't expect this is related to frame stability...

Thomas
alevand Posted - 07/28/2010 : 04:45:29
Speed wobble is mysterious. Yes, frame torsional stiffness is key, I think. Instead of using the tear drop down tube and two bottom tubes, a single larger diameter tube would have many times the torsional stiffness without a weight penalty, since it scales as diameter to the forth power for round tubes and width to the cube times height for non-round sections. Flexing of the rear fork may have something to do with it too. Speed wobble is a resonance that occurs at a specific speed and not just on MBB bikes, the Mango crashed at Battle Mountain. Rear steering is not an answer for a high speed bike!

Mango crash:
http://www.youtube.com/watch?v=i5Dapy1xUq0

A dramatic motorcycle crash:
http://www.youtube.com/watch?v=RmtoOmq3ppw

skate board crash:
http://www.youtube.com/watch?v=yRuBDAIkhZU


But watching this video, the very skillful rider recovers. I may have to rethink the torsional stiffness theory.

http://www.youtube.com/watch?v=HtjQ4SK4GXk

These are all interesting and entertaining:

http://www.youtube.com/results?search_query=speed wobble&aq=f

C:
Tony Levand
25hz Posted - 07/28/2010 : 03:58:43
You could always make the front end like the MBB, but make it rear steered like the one dude on the Python list did. his seemed very stable according to his videos. The problem with speed wobbles on a MBB, if/when you get them, is it's just not the front wheel going crazy, it's the whole front end AND your legs. The way it starts to thrash your body makes it hard to recover. I had a large number of high speed wipeouts, but they were all low sides in less threatening ground areas.
nigel schroder Posted - 07/27/2010 : 21:31:37
quote:
Originally posted by Larry Lem

I still love the simplicity of the drivetrain. No power-robbing pulleys and a short chain. Maybe I'll try some experiments after Battle Mountain.

Larry Lem



I think if I was going to do this design again ,I would use duel 26" wheels and make it a mid-racer.

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx
Larry Lem Posted - 07/27/2010 : 21:12:01
I still love the simplicity of the drivetrain. No power-robbing pulleys and a short chain. Maybe I'll try some experiments after Battle Mountain.

Larry Lem
OpusthePoet Posted - 07/27/2010 : 20:55:39
There are two kinds of speed wobble. One is called "shimmy" and is a higher-frequency shaking caused by elastic interactions in the frame and is almost impossible to predict or control once it gets started. The other is lower in frequency but higher in amplitude and is cause by steering geometry of the bike. This one is usually called a "tank slapper" and can get violent enough to throw the rider off the machine. The problem with trying to fight a "tank slapper" is you only have a fraction of a second to use muscles to damp it out before it throws you off, and the things that make a bike fun to ride are the same things that make a "tank slapper" possible. The two things that work together to prevent tank slappers are lots of trail, combined with lots of friction in the steering. Conversely, having steering with little trail and very low friction steering makes for a nimble feeling bike.

One factor known to help prevent "shimmy" is a very stiff frame from side to side.

Opus

My gas is up to $.99 a burrito, $5.99 for premium and I'm only getting 20 miles to the regular burrito.
nigel schroder Posted - 07/27/2010 : 00:35:35
quote:
Originally posted by LongJohn



Like I said; leave it for a couple weeks and reconsider. It will take some time getting used to.

Cheers,

Thomas



Hi Thomas
The bike was very ridable and I got the hang of it a lot quicker than my first RWD low racer. But it was just to unpredictable.I do still love the design ,so I will give it some thought ,but it is so bent now
that it needs to be cut which ever way I go

"It never gets easier, you just go faster."- Greg LeMond

"Don't buy upgrades; ride up grades." - Eddy Merckx

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