woodcraft

Looking at the gear calculator,

70/11 gets you just over 50 mph at 100 rpm (in a vacuum?)

but to get up a hill, we're looking at ~ 8rpm- ouch.

At every stop sign, you have to accelerate to 10 mph before even getting to 20 rpm.

Maybe use that internal gear set up in reverse to look like 170 gear inches but actually be ride-able.

fietsbob

Motorpacing, To get above 150 mph like John Howard did , and others have since .. it has to be a Really Fast Car..

modified to push the wind aside for the paced rider, closely following..

CliffordK

I've experimented a bit with larger rings, smaller rear sprockets, and higher overall gearing.

I think my top gear I've used was about a 54:9, or about a 6:1 gearing with 700c wheels. Only slightly lower than the OP's 70:11 goal. I did have 60x9 on one bike, but never quite got up to high gear.

I don't monitor cadence, but I had calculated that I was able to hit 30 MPH at a pretty respectable 64 RPM for a short distance (54/9)

Since then I've increased my miles quite a bit, gotten stronger, and found my cadence naturally increasing (still not directly monitored, except through natural sprocket choice).

I haven't done a lot of speed tests lately, but hopefully will try it again shortly and see what it is like, now a couple of years on.

Last summer, I hit my peak downhill speed at about 54.1 MPH, spinning 53/9 at about 117 RPM. That is pretty high RPM for me to still put out some power without spinning out.

I actually had troubles with breaking spokes on my descents on that ride, and wondered if I was hitting a little higher power than I would have otherwise anticipated.

At this point it would be tough for me to achieve 50+ MPH on the level without a heck of a strong tailwind.

One thing that I found is that the effort for me to achieve 30+ MPH is pretty high, and while I could maintain 30+ for some distance off of a lead-out on a hill, doing the acceleration on the level to 30 MPH takes most of my energy, thus I can only maintain it for a short distance.



60/9 max gearing on that funny bike.

One of my deceptively not quite flat Strava segments is about 0.44 miles long, -1% average grade, and somewhat of a distorted U-Shape. I have hit my top gearing of 53/9 on that segment with a top speed of 35.6 MPH, and average speed of 31.6 MPH, and a max of about 80 RPM (calculated).

Assuming no motor-pacing, I'd encourage @tellmethetruth to build up a multi-speed bike with his gearing selection.

That Biking Green ring is mostly designed as a single sprocket up front, but one can say use the 70T as the large sprocket, and say a 54T as a small sprocket hidden inside, perhaps manually shifting.

Then say add a 11/25 cassette.

So, in the top gear, one gets a respectable 6.36:1 gearing.
In low gear, 70/25, one has 2.8:1 gearing, and should be able to get up most moderate hills.

Drop down to the 54/25, and one gets 2.16:1 gearing.

Do some experimenting with the multi-speed cassette. Perhaps try starting from zero on the 70/11, or other gears.

Then once you get your gearing ironed out, go ahead and try the single speed or fixie.

tellmethetruth

The only people qualified to have an opinion here are those who have tried at least a 60/11.
There's a lot of know-it-all's in forums like this, who turn out to know nothing in the end.

If I was 5'5", 100ibs, never touched a weight in my life. Yes, I would also think that's impossible.
I'm sure dead lifting 300kg's seems impossible to you. Yet the world record is over 500kg.

In other words, don't arrogantly say something can't be done, just because you can't do it.

tellmethetruth

Awesome reply, thanks for the great amount of info!
Rather than focusing too much on gearing itself, I'm focusing primarily on exercise. In other words, I'll build myself up to these high gears, which I'm just about there, rather than have the gears work around me.

I notice a lot of cyclists try taking shortcuts, by getting a lighter bike, getting the best equipment money can buy, etc., when rather the focus should be diet and exercise as #1 . This is perhaps why so many in the comments are pessimistic. None of them know my ultimate purpose for this build, nor my strength capacity, nor my age, potential, etc. Yet they all have their clueless opinions which are projections of their own inadequacy.

CliffordK

Again, try it with multi-speed.

Getting that rolling in high gear will be hard, as well as doing more than a couple of feet of hill climbing while at speed.

WhyFi

You offered to make a wager with @DrIsotope, but you neglected to say what your end of the bet would be. What exactly are you offering up? And can you confirm that the task to be accomplished is: 50mph on flat ground, unassisted (no tail wind, no motor pacing, no push start, etc) with a road bike, without fairings, converted to a 70/11 single speed?

BlazingPedals

I had a 52/42/30 and a SRAM 3x7 on my first recumbent. Overdrive in the 52T was equivalent to a 72 tooth chainring. On the back I had an 11-28 cassette. With a 24-inch drive wheel, the combination gave me a gear range of 17 to 144 inches.

52T and overdrive was my favorite gear range, although I spent most of my time in the middle of the cassette, not the 11T. Still, I had a few powered downhills at 50+ mph.

I ultimately decided that I could make do with a more-normal gear range, and converted it to 3x9.

tellmethetruth

He ignored my offer 3 times...why would I bother with it any further? Unless you're asking to get in on the bet

WhyFi

Sure. Confirm the goal, the terms, the timeline and what's on the line.

DrIsotope

For the first point, this isn't Vegas. My account is mine to do with as I please, and yours is yours to troll to your heart's content.

The OP has still never stated what kind of bike it's going on or what it will be used for. A recumbent? A faired recumbent? If that's the case, a 70T isn't that odd, just pairing it with an 11T cog is. There's no real reason to make a 70-11 other than to say, "Look what I made."

Then that claim of 50mph on the flats-- assuming that you're talking about a traditional diamond-framed bike, in non-assisted conditions, (no drafting, no motor-pacing) on flat ground... is just physically impossible.

At this point, the OP can't move the goalposts, because they're not even on the field yet.

Maelochs

@Telmethetruth needs to go away and come back in three weeks with his Strava data from his rides. Otherwise it will be endless, pointless bickering until then.

WhyFi

Nah. There's Strava-doping, too. There needs to be corresponding GPS and video evidence if there's going to be something in the line.

Reynolds 

70/11 50mph on a regular road bike, flat ground, no wind, no wind shielding, is more like dead lifting 1,000kg. Sure I can't do it, nor you, nor any human.

JanMM

woodcraft

Drivetrain-vu:

https://www.bikeforums.net/road-cycl...same-time.html

CliffordK

A fun app is "Bike Calculator". There are a few different ones, but they are all similar.

Bike Calculator

Ok, so for some sample data:
220 lb rider (100 kilos)
20 lb bicycle
tubular wheels
Aerobars
70 degrees F
500 ft
0 grade
0 headwind

20 MPH --> 143 Watts (1.43 watts / kilo)
25 MPH --> 252 Watts (2.52 watts / kilo)
30 MPH --> 408 Watts (4.08 watts / kilo)
35 MPH --> 623 Watts (6.23 watts / kilo)
40 MPH --> 905 Watts (9.05 watts / kilo)
45 MPH --> 1265 Watts (12.65 watts / kilo)
50 MPH --> 1711 Watts (17.11 watts / kilo)

Now, let's try the same with the same parameters, Clinchers/Drops.
20 MPH --> 183 Watts (1.83 watts / kilo)
25 MPH --> 322 Watts (3.22 watts / kilo)
30 MPH --> 523 Watts (5.23 watts / kilo)
35 MPH --> 799 Watts (7.99 watts / kilo)
40 MPH --> 1162 Watts (11.62 watts / kilo)
45 MPH --> 1625 Watts (16.25 watts / kilo)
50 MPH --> 2200 Watts (22.00 watts / kilo)

WHEW!!!

Note the huge power differences when comparing speed with aerobars/tubulars vs drops/clinchers.

Ok, here's an often quoted chart to give one an idea of power for riding a bike.

https://cyclingtips.com/2017/06/just...road-cyclists/



Ok, looking at the chart...

A trained amateur should be able to get 30 to 35 MPH for up to a minute or so.

One gets up to Cat 1 and Pro levels to maintain that for 5 minutes.

The Pros should be able to put out the power to maintain 50 MPH for about 5 seconds, but they would struggle with putting out the power to accelerate from say 20 MPH to 50 MPH in open air which likely would take longer than the 5 seconds.

This, of course, is independent of gearing.

Now, you get into power/cadence/force.

https://bicycles.stackexchange.com/q...indoor-trainer
Ok, let's solve the equation for force.

F[N] = P[W] * 60,000 / { l[mm] * w[rpm] * 2 * pi **
Force [lbs] = F[N] / 4.44822 = P[W] * 60,000 / { l[mm] * w[rpm] * 2 * pi * 4.44822**



Ok, so let's try some numbers.
Watts = 1000
Crank Length = 175 mm
Cadence = 100 RPM

Force [lbs] = 1000W * 60,000 / { 175mm * 100 RPM * 2 * pi * 4.448**

Ok, so I think that comes up to about 123 lbs force on the pedals, for 100 RPM.

Hmmm, not too bad, actually, considering all. But, I presume that is for a full stroke. So, if one averages 50% max force for the full stroke, then the max force would be about double that or 256 lbs force.

Now, this was all based on a 220 pound person, so the force is about 10% more than the person's entire weight, and has to be made up by pulling up on the opposite pedal and the bars.

Now, one can play around with the numbers.

Double the watts to 2000W at 100 RPM, and the max force would get up to about 500 lbs.

Likewise halve the cadence and the power requirement doubles.

If you can squat 1000 lbs, then can you apply 500 lbs to the pedals? Well, not exactly.

You can take your body weight (220 lbs in this example). You have to apply more force than the body weight, so pulling up with the opposite leg by a substantial amount, giving more downward force.

So, you need to increase the downward force by > than your weight by 280 lbs. So, pull up say 100 lbs, increasing the downward force of the one leg by an equal amount (100 lbs), and still needing to pull up on the bars by 80 lbs.

And, of course, repeat that on each side a couple of times a second.

To counteract these maximum amounts of force, and body weight, riders increase the cadence. So, going from 100 RPM to 200 RPM means that all the calculated forces get dropped in half, and suddenly is hard, but not necessarily impossible.

Still, applying a substantial amount of your body weight at a very high cadence is difficult, and takes a lot of training and practice.

Now, the strong/heavier riders can likely spin at a somewhat slower cadence than the super light riders, compensating for the slower cadence with greater force. But, that only works to an extent.

aclinjury

OP, goddamn it ignore the old geezers. Post a video when you make your run. Even if you can't hit 50 mph, I still wanna see you turn that 70T ring.
I respect people who try and fail, not a bunch of armchairs.

tellmethetruth

For sure man. Definitely not going to stop because some randos online said it's impossible.

CliffordK

That thread was started and closed before I joined.

But, yes, my testing indicates that 60/9 is a tough combination.

Hopping up one sprocket, and 60/10 is equivalent to 6:1, which is equivalent to 54/9, which is somewhat possible on the level, but is still a tough gear to spin.

In part the issue has to do with the force on the legs at the various cadences. And, at a slow cadence, one ends up with more force than one's own weight. Which then one compensates with pulling up with the arms and opposite leg. But, that is still sub-optimal, with severe limits of the amount of additional force that can be generated. Perhaps standing, one also makes sharper high/low force transitions than a "round stroke", meaning even more force is required.

The final issue with standing is that with high power/speed, one needs to optimize one's wind profile, and standing up may capture more wind than one wishes, and thus be counter-productive.

woodcraft

That's good, since I'm not qualified to give an opinion.

I have a single speed with 42/18, & have experienced that 'sub-optimal' thing going up 15% hills. Character-building, but my knees use a different term.

CliffordK

I'm a "Masher", but the more I ride, the better the knees seem to get.

Now, Mashing does strain the back, but doesn't seem to be making it worse either.

I do believe, however, that my cadence is slowly naturally increasing as my mileage increases.

I believe in "use it or lose it".

livedarklions

I absolutely want to see you try it, and I expect you will go very fast, but you do understand that 50 mph on an upright, unassisted, level would beat the world record by several mph, right?

If you really can do it, figure out how to get clocked officially, because no one will take your word on it.

I notice you continue to refuse to specify whether the bike is faired or recumbent. At this point, I don't think that's an accident.

clengman

...or on rollers?

robnol

only a clown with a serious small man syndrome would ride with a huge chainring...its gotta be a down hill aid to go faster he thinks he will do 50 on the flats....maybe with a hurricane force tailwind .....if he can do 50 why isn't he a pro biker now or is his small chainring holding him back