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52T vs 70T (pic)

Old 03-17-19, 07:55 PM
  #26  
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The Bonneville bike that made the news last year used the mid drive from a Da Vinci tandem to achieve the needed ratio
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Old 03-17-19, 07:59 PM
  #27  
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This thread...cant say it delivers quite yet, but it's shaping up to!
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Old 03-17-19, 08:05 PM
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With a Schlumpf High Speed , 2.5 X overdrive internally geared crankset

you could do a 70t equivalent with a 28t actual chainring...
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Old 03-17-19, 08:06 PM
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Originally Posted by tellmethetruth
Your "reality" is clearly not everyone else's reality. Aka, your inadequacy only reflects on others via all-knowing over confident narcissism... "It's physically impossible". What a bold statement from someone who can't push 38-11 up a mild gradient.
You didn't mention anything regarding my bet? What are you hesitant about? Aren't you confident in your super modest knowledge of cycling and gearing?
I know you're not addressing me, but this post was convenient to use.
I'm guessing it's going to be fully faired for some kind of record attempt. Two weeks is going to be a long time.
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Old 03-17-19, 08:17 PM
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Originally Posted by fietsbob
With a Schlumpf High Speed , 2.5 X overdrive internally geared crankset

you could do a 70t equivalent with a 28t actual chainring...
Please explain the mechanics of how a 28t will be the equivalent of a 70t chainring, and how this schlumf is superior to a 70t in terms of hitting high speeds. I've never heard of schlumf, must be new.
Thanks!

--edit after some quick research, apparently you lose up to 5% efficiency. And considering it's over 800$, you could find a 70t chainring for less than 100$. Only benefit is the ability to hit a lower gear. Cool but not for me.

Last edited by tellmethetruth; 03-17-19 at 08:27 PM.
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Old 03-17-19, 08:29 PM
  #31  
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That thing is surprisingly cheap on eBay.
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Old 03-17-19, 08:31 PM
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Originally Posted by GrainBrain


That thing is surprisingly cheap on eBay.
There's a few other companies that sell a similar price range.
Either way you can get one CNC'd for even cheaper if you know the right people.
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Old 03-17-19, 08:57 PM
  #33  
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Obviously he's rebuilding a Honda Gold Wing....
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Old 03-17-19, 09:05 PM
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Originally Posted by BirdsBikeBinocs
Obviously he's rebuilding a Honda Gold Wing....
The 500 honda gold wing owners will understand your reference.
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Old 03-17-19, 10:03 PM
  #35  
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Old 03-17-19, 10:36 PM
  #36  
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On a tandem, I’ve wanted more than 54X11. But that riding partner is no longer around.
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Old 03-18-19, 07:08 AM
  #37  
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Originally Posted by mstateglfr
This thread...cant say it delivers quite yet, but it's shaping up to!
Haven't had a good digression...like talking about aviation gas and antique aircraft, yet....need a good one. Maybe a want ad needs to go up?

Perhaps this is a job for Craigslist Casual Encounters?
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Old 03-18-19, 07:22 AM
  #38  
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That 70T would be a little high for a lowracer with a 20" drive wheel but not outrageous. Good for someone who doesn't like spinning, or maybe just doesn't like using an 11T cog in back.

Schlumpf speed drive? Internally-geared bottom bracket with a +2.5x multiplier. 28 Teeth becomes 70 Teeth in Overdrive.
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Old 03-18-19, 07:22 AM
  #39  
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104-teeth
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Old 03-18-19, 07:36 AM
  #40  
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Originally Posted by BlazingPedals
That 70T would be a little high for a lowracer with a 20" drive wheel but not outrageous. Good for someone who doesn't like spinning, or maybe just doesn't like using an 11T cog in back.
The OP has never made any sort of indication that this is about a recumbent, just that he's going to do 50mph on flat ground. Even if it does turn out to be something not diamond-framed, we're looking at a sustained effort of ~120rpm @ 1,300-1,400W. Unless it's fully faired, in which case who cares. Fully faired can go really fast without a pie-plate in the front.
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Old 03-18-19, 08:02 AM
  #41  
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I find it interesting to try different things. I'll be curious how this turns out. No harm in trying.
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Old 03-18-19, 08:37 AM
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I mean, it exists for a reason to be sold. I can't criticize what it would be used for if I don't even know, that's silly.

People use 60T front rings on normal TT bikes in flatter courses. Avoiding using the 11t or 12t can save watts worth paying attention to. And since two in the front is worth one in the back, going from 50t/11 to a 13 for efficiency would mean needing a 54t in front. Downwind or downhill you'd use it.

I'd assume for speed records you wouldn't want a ludicrous cadence as it might hurt the stability of the rig.
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Old 03-18-19, 08:38 AM
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Originally Posted by tellmethetruth
And so what will you say when you see me hitting 50 mph? Let's make a bet. If I hit 50 mph on a flat, you have to delete your account.
Flat ground, road bike, 70/11 single-speed conversion, non-fared, unassisted and not motor-paced? Lol. Subbed.
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Old 03-18-19, 08:41 AM
  #44  
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Originally Posted by DrIsotope
The OP has never made any sort of indication that this is about a recumbent, just that he's going to do 50mph on flat ground. Even if it does turn out to be something not diamond-framed, we're looking at a sustained effort of ~120rpm @ 1,300-1,400W. Unless it's fully faired, in which case who cares. Fully faired can go really fast without a pie-plate in the front.

The world record for fully-faired upright on level ground with no outside assist is 51.28 mph on a Moulton AM 7. That record is about 33 years old. Jim Glover did that with a full cowl and 82x10 gearing.

Godspeed OP!
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Old 03-18-19, 08:50 AM
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Originally Posted by burnthesheep
And since two in the front is worth one in the back, going from 50t/11 to a 13 for efficiency would mean needing a 54t in front.
That's not the way ratios work. The difference between 11 and 13 is roughly 18%. The difference between 50 and 4 is roughly 8%. You'd need a 59t paired with a 13t for the gear ratio to be the same as the 50/11
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Old 03-18-19, 08:57 AM
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Originally Posted by WhyFi
That's not the way ratios work. The difference between 11 and 13 is roughly 18%. The difference between 50 and 4 is roughly 8%. You'd need a 59t paired with a 13t for the gear ratio to be the same as the 50/11
Oops. You’re right.

Just trying to show a reason people see huge front rings.
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Old 03-18-19, 09:02 AM
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Originally Posted by tellmethetruth
And so what will you say when you see me hitting 50 mph? Let's make a bet. If I hit 50 mph on a flat, you have to delete your account.
You have to define the bet. Upright bike? Fairing? Drafting behind a motorized vehicle?

If you're upright, without fairing, and entirely unassisted, you're going to hit a brick wall of wind well below 50 mph, I don't care how fit you are. The evidence for that is simple--no one on earth has ever done it.

Even with fairing, the 30+ year old world record is only 51.28 mph, upright and unassisted. And that was done with a much bigger gear ratio than you're using.
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Old 03-18-19, 09:13 AM
  #48  
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Let's ride Pikes Peak!!
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Old 03-18-19, 09:20 AM
  #49  
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Originally Posted by badger1
... and your point is?
Apparently his point is showing us that a 70 is bigger than a 52. But I knew that already.
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Old 03-18-19, 09:24 AM
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Originally Posted by Reynolds
Apparently his point is showing us that a 70 is bigger than a 52. But I knew that already.
I know. I was just fishing for the sub-text, but that is now clear.
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