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Speedy
recumbent guru

USA
759 Posts

Posted - 07/19/2012 :  16:53:01  Show Profile  Reply with Quote
high gear ratio jumps
using the standard .5" spacing of bicycle sprockets

say the chain ring is 50T and the rear changes from 11 to 10 the effective wheel diameter change is roughly 12.25"
times that by pi sums to 38.5" more distance traveled per one crank revolution

a 100T to 11T ~ 10T will be double or 77" more distance traveled per one crank revolution ... a very large jump when a small jump is desired

to have smaller jumps in high gear requires smaller (closer) spacing between sprocket teeth i.e. a redesign of the drive system

comprehend ?


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Victor Ragusila
recumbent enthusiast

Canada
352 Posts

Posted - 07/19/2012 :  17:13:54  Show Profile  Reply with Quote
I understand why chose to make it simple 1 gear. My question was, can you train to overcome the fact that you only have 1 gear? For my untrained butt, it would lead to very low speed.

For Bluenose i will try to have a cassette with the smallest cog around 16 or 18 teeth...this way the jump is less than for a 11 tooth cog. Now, Todd likes big jumps, he doesnt feel like shifting too often, and i guess his rowing background allows for low RPM. I need to test our riders more and see what they like.

I am curious however if one can train to ride 1 gear BM rides...in which case, we might have a rather fun project in the pipeline...

Victor
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Speedbiker
human power expert

USA
2464 Posts

Posted - 07/19/2012 :  17:30:09  Show Profile  Reply with Quote
I personally would prefer to conserve my energy and oxygen in a controlled buildup. Not muscle it the whole way, only to hit my powerband at the end. And what if he is overgeared? It would seem Obree is geared to hit optimal rpm in the mid 80s. I guess it's go big or go home!
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Upright Mike
human power expert

USA
3463 Posts

Posted - 07/20/2012 :  03:41:25  Show Profile  Visit Upright Mike's Homepage  Reply with Quote
In his book, "The Flying Scotsman", Obree mentions often that his trusty old bike was his fixie. He won many 10-mile, 25-mile and 50-mile TT's on it, sometimes averaging well over 30 mph in the shorter TTs, even with hills and descents. Once I think he mentioned he put on a bigger gear and it helped him to a record, and another time I think it killed his chances of a record because of the wrong gearing. I think having a single fixed gear is an extension of his personality, whereby he sees anything else like multiple gears as a waste of energy, distracting him from being totally in focus with mind, body and machine.

I know a 100 gear inch is too large to start in (though Sam can do it). I've had that, and fell over many times. I switched to a 60 gear inch, and can now start easily. I want a higher gear this year as I felt like I was spinning too much as 95 rpm last time and causing my streamliner nose to bounce around. Fred Markham mentioned once that a lower rpm is desireable for maintaining control in a streamliner. Sam's high gear on the Varna was I think 254 gear inches, which requires about 110 rpm to go 82.8 mph.

At the Northbrook Velodrome last weekend, I pushed a monster 154 gear inch around the track on my unfaired Morciglio M1 lowracer. I averaged a race record of 30 mph while doing a low 65 to 70 rpm. That's what works for me.
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Upright Mike
human power expert

USA
3463 Posts

Posted - 07/20/2012 :  03:53:28  Show Profile  Visit Upright Mike's Homepage  Reply with Quote
Victor, in a short answer, I don't think anyone will be able to ride BM in a single gear.

After years of research, I like SRAM PG-970 9-speed cassettes, the best. These have cogs that all come apart individually, providing lots of gearing choices for a custom cassette. I've gotten tired of trying to buy higher quality stuff with cogs rivited together on custom spiders. Its SRAM's 2nd from the top-of-line cassette with fairly good quality. I've just got the following two combinations off ebay which will allow me the maximum number of individual cassette choices, for my streamliner and my lowracer
SRAM PG970 9 speed 11-34
SRAM PG970 9 speed 12-26

I'm mixing these together to create two custom cassettes combinations with lots of little closed spaced high gears and a few big gears to start out with (these combinations shift fine):
On my lowracer: 11-12-13-14-15-18-21-26-34 <--I've already used this successfully for thousands of miles, it shifts fine with a medium cage rear derailleur and a single chainring up front.
On my streamliner: 12-13-14-16-20-26-34 - only 7 speeds can fit, and I can't go smaller than a 12-tooth.

Its okay, and I think makes more sense to avoid something smaller than a 12 tooth in a streamliner. The jump is ever slightly less from a 13 to 12, than 12 to 11. And perhaps the slightly bigger cassette helps keep the chain from derailling because its got more chain wrap.

I'm sorry I didn't brink my bag of cassettes to Northbrook/kenosha this weekend. The UT team was looking for some extra cassettes!

Edited by - Upright Mike on 07/20/2012 04:06:48
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Grasshopper
recumbent guru

USA
503 Posts

Posted - 07/20/2012 :  08:55:30  Show Profile  Reply with Quote
Mike,

I took care of the U of T Team. I had an xtra cassette and gave them the cogs they were looking for.

Chris


quote:
Originally posted by Upright Mike


I'm sorry I didn't brink my bag of cassettes to Northbrook/kenosha this weekend. The UT team was looking for some extra cassettes!

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PUGZCAT
recumbent enthusiast

Canada
279 Posts

Posted - 07/22/2012 :  02:49:23  Show Profile  Reply with Quote
Obree is likely going fixed gear to smooth out the dead spots at the top and bottom of the linear drive strokes. I guess he could have used some screen door extension springs attached to the crank at the connecting rod pivots to liven up the dead spots. Sunrace manufactures Sturmey Archer 3 speed fixed hubs, that would help get things rolling off the start, but would introduce some lash in the hub internals that would feel like chain slop and add to friction losses.
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PUGZCAT
recumbent enthusiast

Canada
279 Posts

Posted - 07/22/2012 :  08:49:13  Show Profile  Reply with Quote
A mountain drive two speed bottom bracket would also work if a device could be worked out to press the crank spindle mounted gear changing button.
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PUGZCAT
recumbent enthusiast

Canada
279 Posts

Posted - 07/22/2012 :  08:57:40  Show Profile  Reply with Quote
It's bound to be an interesting week. Will Obree go faster than the other conceived and built in a vacuum British effort, Blue Yonder? !00 mph or bust, time will tell.
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Richard Myers
recumbent enthusiast

USA
196 Posts

Posted - 07/22/2012 :  10:59:52  Show Profile  Reply with Quote
Take a look at this page and you will see he is running a derailleur and has 3 gears. http://obree.com/ihpva.php

Richard Myers
Ohio
http://tinyurl.com/3445gr
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PUGZCAT
recumbent enthusiast

Canada
279 Posts

Posted - 07/23/2012 :  02:37:55  Show Profile  Reply with Quote
Not anymore.
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jdub
recumbent enthusiast

United Kingdom
182 Posts

Posted - 07/23/2012 :  14:43:18  Show Profile  Reply with Quote
I don't think it is a single gear, but you don't need many, as Sam shows us year after year. I have an SRM plot from the year he crashed. The pattern of cadence between shifts is very even. With more it would be harder to get the speed/ratio points right on the course.

JW

...got the T-shirt

Edited by - jdub on 07/23/2012 14:44:04
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Larry Lem
human power expert

South Sandwich Islands
2300 Posts

Posted - 07/23/2012 :  20:41:05  Show Profile  Reply with Quote
What resource says Graeme will be using a single-speed bike?

Larry Lem
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PUGZCAT
recumbent enthusiast

Canada
279 Posts

Posted - 07/24/2012 :  08:03:41  Show Profile  Reply with Quote
http://www.facebook.com/photo.php?fbid=10150964063947634&set=a.409805027633.187431.59088097633&type=3&theater

Read the text. 286 inch fixed single speed
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Upright Mike
human power expert

USA
3463 Posts

Posted - 07/24/2012 :  10:09:00  Show Profile  Visit Upright Mike's Homepage  Reply with Quote
I think Grame will need a big push to get started....

286 gear inch RPM to SPEED conversion

10 rpm = 8.5 mph, 13.7 kph <-ouch low rpm is hard on the knees
15 rpm = 12.8 mph, 20.5 kph
20 rpm = 17.0 mph, 27.4 kph
25 rpm = 21.3 mph, 34.2 kph
30 rpm = 25.5 mph, 41.1 kph
35 rpm = 29.8 mph, 47.9 kph
40 rpm = 34.0 mph, 54.8 kph
45 rpm = 38.3 mph, 61.6 kph
50 rpm = 42.5 mph, 68.5 kph
55 rpm = 46.8 mph, 75.3 kph
60 rpm = 51.1 mph, 82.2 kph
65 rpm = 55.3 mph, 89.0 kph
70 rpm = 59.6 mph, 95.9 kph
75 rpm = 63.8 mph, 102.7 kph
80 rpm = 68.1 mph, 109.6 kph
85 rpm = 72.3 mph, 116.4 kph
90 rpm = 76.6 mph, 123.2 kph
95 rpm = 80.8 mph, 130.1 kph
100 rpm = 85.1 mph, 136.9 kph <-he beats Sam!
105 rpm = 89.3 mph, 143.8 kph
110 rpm = 93.6 mph, 150.6 kph
115 rpm = 97.9 mph, 157.5 kph
120 rpm = 102.1 mph, 164.3 kph <-he goes 100 mph!

Edited by - Upright Mike on 07/24/2012 10:13:24
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Runxner
recumbent enthusiast

USA
336 Posts

Posted - 07/26/2012 :  05:11:47  Show Profile  Reply with Quote
So this is what a tail-faired prone bike looks like.
http://www.cyclechat.net/threads/graeme-obree.104596/ http://www.legslarry.beerdrinkers.co.uk/images/pix/WHPVC2001/DaveWilliams/davwil085.jpg

Team Low-Life
Lowracer Test Pilot/Evangelist
Adelaide, Australia

Edited by - Runxner on 07/26/2012 05:12:55
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W Hilgenberg
recumbent enthusiast

USA
285 Posts

Posted - 07/26/2012 :  07:21:14  Show Profile  Reply with Quote
That looks like one hell of a fast praying mantis. . .
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jdub
recumbent enthusiast

United Kingdom
182 Posts

Posted - 07/26/2012 :  08:50:54  Show Profile  Reply with Quote
That's Tim Elsdale (following Rosemary Buhler). Graeme Obree was testing one of his bikes a while ago.

quote:
Originally posted by Runxner

So this is what a tail-faired prone bike looks like.

Team Low-Life
Lowracer Test Pilot/Evangelist
Adelaide, Australia



...got the T-shirt

Edited by - jdub on 07/27/2012 08:57:58
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Larry Lem
human power expert

South Sandwich Islands
2300 Posts

Posted - 07/26/2012 :  09:47:18  Show Profile  Reply with Quote
Jonathan,
Tell us how strong Tim is, what kind of shape he was in, and how he did in this race. Was he faster or slower than Rosemary? (Need to mention how fast Rosemary is/was in this race as well) Does Tim ride supine recumbent bikes as well and how does he do supine vs. prone?
No need to repeat the same picture.

Larry Lem

Edited by - Larry Lem on 07/26/2012 09:47:59
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jdub
recumbent enthusiast

United Kingdom
182 Posts

Posted - 07/27/2012 :  05:02:50  Show Profile  Reply with Quote
Yeah sorry about the pic. Didn't realise it was going to do that. I'd have to look up the numbers for Tim. I think it was 2001, but he won our unfaired championship one year. He had another rider who was much bigger and stronger. This machine had cranks ahead of the rear wheel. Others had the cranks behind and above. Obree's bike is probably better in that respect. Tim also made a full shell. It was known as The Coffin. Never really got it working.

quote:
Originally posted by Larry Lem

Jonathan,
Tell us how strong Tim is, what kind of shape he was in, and how he did in this race. Was he faster or slower than Rosemary? (Need to mention how fast Rosemary is/was in this race as well) Does Tim ride supine recumbent bikes as well and how does he do supine vs. prone?
No need to repeat the same picture.

Larry Lem



...got the T-shirt
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PUGZCAT
recumbent enthusiast

Canada
279 Posts

Posted - 07/29/2012 :  04:22:26  Show Profile  Reply with Quote
Obree could lace up a spare wheel with a Sturmey Archer 3 speed fixed gear hub to get easier gear ratios to get rolling and up to speed, top gear is 1:1 so losses would be minimal. What could be more British? I hope his engineering school buddies are as good as the U of T folks at designing and building fairings.
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Victor Ragusila
recumbent enthusiast

Canada
352 Posts

Posted - 07/29/2012 :  21:39:03  Show Profile  Reply with Quote
thanks! :D One thing we did learn however is that the fairing design MUST be made in the same time with the rider position. We usually iterate between the ergonomics and the aero quite a lot before the final bike is decided.

If Orbee builds a bike, and then asks students with little experience to build a fairing, i dont expect much awesomeness... they simply cannot build a good fairing unless the original rider position and bike structure were made with the fairing in mind.

Also, his front wheel is quite far forward, so the boundary layer will be tripped right away on the bottom, causing the whole bottom of the bike to be rather sub-optimal. I think EIVIE3 has the same issue, and thus looses quite a bit of aerodynamic efficiency compared with a Varna/Velox/Vortex style nose.

Victor
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Speedbiker
human power expert

USA
2464 Posts

Posted - 07/30/2012 :  05:40:57  Show Profile  Reply with Quote
Victor, if you look at the sideways streaks on the VeloX airflow test, and you also consider how fast the Eiviestretto is despite the forward wheel, it points out how much room for improvement there is on the bottom of streamliners.
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Larry Lem
human power expert

South Sandwich Islands
2300 Posts

Posted - 07/30/2012 :  07:43:38  Show Profile  Reply with Quote
All that matters is power and CdA (and a little bit of Crr). If Eiviestretto is down to 0.015 sq m, and if Eivie 3 is in the same realm, then criticizing it by comparing it to vehicles that likely have higher drag seems odd.

Larry Lem
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W Hilgenberg
recumbent enthusiast

USA
285 Posts

Posted - 07/30/2012 :  08:21:08  Show Profile  Reply with Quote
For comparisons sake, I would like to clarify that when we are talking about CdA we are talking about the A being the frontal area and not the planform area like airfoil sections are determined by correct? It's what I have been using and just seems to make sense.
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