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Different Spin Rates Causing Problem

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Different Spin Rates Causing Problem

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Old 07-12-18, 01:00 PM
  #51  
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Originally Posted by jethro00 View Post
I ran this by da Vinci and received the following response:
"On our tandem, the person pedaling at a slower cadence is not contributing, nor are they robbing power from the other rider. On a traditional tandem, if one person does not keep up, the other rider is pulling there(sic) legs around and being robbed of power. Todd Shusterman"
I never implied anything different from that. I feel like DaVinci agrees with my assessment actually. My post was more to inform the other poster that IPS is not limited only to hybrid tandems with the cranksets far apart and can (and is) used successfully on regular tandems.
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Old 07-12-18, 01:11 PM
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Originally Posted by Hermes View Post


We have been riding tandems beginning in 1980 and I thought it was this year that we truly clicked in a tandem race. My wife and I are both trackies and race road and track with focus on timed events such as road time trials and pursuit and team events such as team pursuit at the track.....


Thanks so much for this!

We recognized our issues quickly, and got pedal-based power meters. My wife is very much interested in contributing, and the power meters have been a very useful tool for her to see what I'm doing vs. what she's doing when we're on the tandem, and it especially has been enlightening for her to see that she really doesn't work hard on a bike (as a default). So she's really stepped up her game! She rides her single to work and back a couple of times each week during the good weather/long daylight part of the year (about 13 miles each way, with significant climbing), and she now has an objective metric to work with; it's really helped.

I'm confident that we'll figure this out in time, but the help is much-appreciated!

Mark
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Old 07-12-18, 01:48 PM
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Originally Posted by 124Spider View Post
Thanks so much for this!

We recognized our issues quickly, and got pedal-based power meters. My wife is very much interested in contributing, and the power meters have been a very useful tool for her to see what I'm doing vs. what she's doing when we're on the tandem, and it especially has been enlightening for her to see that she really doesn't work hard on a bike (as a default).
Well alrighty then. I guess we'll see, won't we. Do you mind terribly if some of us take some side action as to how long before that nice rig of yours goes on consignment? Was that mean? I mean ... dude ... you are textbook. OMG. Feel free to ignore me (if I isn't already).
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Old 07-12-18, 01:52 PM
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Originally Posted by Leisesturm View Post
Well alrighty then. I guess we'll see, won't we. Do you mind terribly if some of us take some side action as to how long before that nice rig of yours goes on consignment? Was that mean? I mean ... dude ... you are textbook. OMG. Feel free to ignore me (if I isn't already).
Kindly haunt someone else, ok?
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Old 07-12-18, 02:06 PM
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Originally Posted by Leisesturm View Post
If you are correct then millions ... no, billions of cyclists are using a crank length that is completely wrong for them and might in fact be injurious. Hmmm.
Could you even try to be more dismissive? Give it a rest. In fact, why even comment on this thread if bicycle fit is a myth? The millions, no billions, of cyclists to which you refer are not riding $5k-$15k or more tandems for recreation or competition. Pretty big difference in requirement between the cyclist on a cruiser in flip-flops riding 2 miles to the beach, and the daily commuter in casual clothes getting to work and back at a leisurely pace, versus the couple on a very expensive tandem using power meters, and performance software. And as I said in my post, if you can enjoy a hundred mile hilly tandem ride riding 20 RPM lower than you prefer on cranks 10mm shorter than ideal for you, then great. Enjoy yourself!

But just because YOU feel that way doesn't mean you should impose your preferences on someone else. And I'm not even the person in question with the issue. Barking up the wrong tree. Plus, your reply does absolutely nothing to address my analogy. I'm sure my friend would love to receive a lecture from you about how crank length is irrelevant and his injury must have been imagined.
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Old 07-12-18, 02:20 PM
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Originally Posted by LV2TNDM View Post
But just because YOU feel that way doesn't mean you should impose your preferences on someone else. And I'm not even the person in question with the issue. Barking up the wrong tree. Plus, your reply does absolutely nothing to address my analogy. I'm sure my friend would love to receive a lecture from you about how crank length is irrelevant and his injury must have been imagined.
What is his e-mail address? Better yet, just forward him the link to this thread ...
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Old 07-12-18, 02:24 PM
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Originally Posted by 124Spider View Post
Simple question: My wife is 5'4" tall, with proportional legs. She has a 175 crank on her single bike, and a 170 crank on the tandem.

Would replacing the 170 on the tandem, with something shorter, perhaps help her spin faster (and perhaps help with limiting body movement when pedaling fast)?
Based on my experience both with varying crank lengths on my singles and with various crank combinations on our tandem my answer is definitely Yes to both questions. It's inherently easier to spin high RPMs when the pedals are going around in a smaller circle and therefore slower than in a larger circle (i.e. longer cranks). And if your wife is struggling to keep up a cadence that is unnaturally high for her it could certainly be resulting in extra side-to-side body movement. Switching to a 150mm crank should make your higher cadence feel more natural to her and allow her to contribute more power instead of struggling just to keep up with the current fast pedal motion.
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Old 07-12-18, 03:55 PM
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Leisesturm, I agree with you that da Vinci confirms your assessment, and also adds a factor.
So, now I have some questions for you and others about IPS versus traditional tandems.
Let's start with my da Vinci.
If captain (C) and stoker (S) pedal at different rates, then the total power = 100% of the rider spinning faster, right?
If C and S spin in sync, then is the total power 100% C + 100% S?
Do the C & S have to be perfectly in sync to combine power or just close to the same rate?

Now, let's go to a traditional tandem, like the Trek T900 we both have.
If C and stoker pedal at different rates (with C faster), then the total power = 100% C - some factor for C pulling Ss pedals + 100% S?
If C and S spin at equal rates/power, then is the total power 100% C + 100% S?

I am finding this thread educational.



Originally Posted by Leisesturm View Post
I never implied anything different from that. I feel like DaVinci agrees with my assessment actually. My post was more to inform the other poster that IPS is not limited only to hybrid tandems with the cranksets far apart and can (and is) used successfully on regular tandems.
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Old 07-12-18, 07:10 PM
  #59  
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Originally Posted by 124Spider View Post
Simple question: My wife is 5'4" tall, with proportional legs. She has a 175 crank on her single bike, and a 170 crank on the tandem.

Would replacing the 170 on the tandem, with something shorter, perhaps help her spin faster (and perhaps help with limiting body movement when pedaling fast)?
Yes and yes. Independent testing supports that.
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Old 07-12-18, 08:51 PM
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Originally Posted by jethro00 View Post
Leisesturm, I agree with you that da Vinci confirms your assessment, and also adds a factor.
So, now I have some questions for you and others about IPS versus traditional tandems.
Let's start with my da Vinci.
If captain (C) and stoker (S) pedal at different rates, then the total power = 100% of the rider spinning faster, right?
If C and S spin in sync, then is the total power 100% C + 100% S?
Do the C & S have to be perfectly in sync to combine power or just close to the same rate?
If one person slacks off so that they are pedaling at a slower rate they will immediately feel no significant resistance in the pedals. It would be the same as if you were coasting down a hill and decide to slowly turn the crank - sure you can pedal at a lower cadence, but it'll feel completely different from normal pedaling where you are pushing against a resistance force from the pedals.

When pedaling normally, i.e. each pushing against a resisting force, the two riders will always be in perfect sync.
Now, let's go to a traditional tandem, like the Trek T900 we both have.
If C and stoker pedal at different rates (with C faster), then the total power = 100% C - some factor for C pulling Ss pedals + 100% S?
If C and S spin at equal rates/power, then is the total power 100% C + 100% S?

I am finding this thread educational.
C and S can't pedal at different rates on a typical tandem since their cranks are connected by the cross-over chain between their cranks and therefore the cranks turn at exactly the same speed as long as the rings on each are the same. If one of them (say C) decides that the cadence is impossibly high and tries to actively resist the motion then I suppose you could say the total power = 100% S - 100% C, but I can almost guarantee that situation won't last long.
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Old 07-12-18, 10:33 PM
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Originally Posted by prathmann View Post
Based on my experience both with varying crank lengths on my singles and with various crank combinations on our tandem my answer is definitely Yes to both questions. It's inherently easier to spin high RPMs when the pedals are going around in a smaller circle and therefore slower than in a larger circle (i.e. longer cranks). And if your wife is struggling to keep up a cadence that is unnaturally high for her it could certainly be resulting in extra side-to-side body movement. Switching to a 150mm crank should make your higher cadence feel more natural to her and allow her to contribute more power instead of struggling just to keep up with the current fast pedal motion.
There's always an interesting tension in these sorts of discussions between fit and fitness.

Cadence: Sure we all have a favorite cadence range. OTOH, it's not always possible. We're not a strong team but we ride in the mountains anyway. We have been down in the 50-60 cadence range on some steep roads. We were still putting down power? You betcha, we were both about 10 beats over LTHR, probably putting down more power than we could have at 85. Cadence is simply not as important as people think it is. Higher cadence contributes to endurance but not necessarily in a single ride, more a stage race concept. It's mostly what one is used to and one can get used to most anything. Before I knew better, I rode fast centuries at below 60. See:

Crank length: See the above argument. I'm a short legged 5'6". A fitter would probably suggest 160-165 cranks. I've ridden 170 cranks forever (almost) and have 175s on our tandem. I spin them both at 95 with no problem, though I prefer to climb in the mid 80's with both lengths. There is a simple fact mentioned in the above video: the higher the cadence, the larger proportion of aerobic energy is used just moving the legs. That's not so critical for well trained riders with a high VO2max, but it is critical for those "lesser" riders among us. You can't force a high leg speed on someone with limited aerobic ability and expect a lot of power in the pedals. That's a scientific fact.

Training, pedaling ability, and body movement: Everything is trainable, even VO2max to a small degree. Leg motion is very trainable, though it takes years. Body motion has little to do with crank length and everything to do with pedaling style. I watch my shadow and have no upper body motion either on my single or tandem. The object of the pedaling game is to provide a constant torque on the bottom bracket. Said torque is the sum of the torque of both cranks, so when one crank is in its weak spot, the other is in a strong spot. On the rollers, this produces the characteristic steady whhhrrr. The effect of all this is that all pedaling forces originate in the legs. They don't travel into the upper body except under extreme effort. It's fairly easy to train someone to pedal with no upper body motion at all, using a mirror for biofeedback. Besides that, good trainer drills are pedaling steadily for 15'-45' at a cadence just a hair below bouncing or 115-120, whichever comes first. Another drill is 2 minute one-legged pedaling drills - one leg, then the other, then both legs together, repeat until legs don't work anymore. Another drill mentioned above is 3 reps of 10' hill work in a big gear at 50-55 cadence with no upper body movement at all.

Besides training both captain and stoker to be able to pedal well at various cadences, when it's all said and done, in this situation the captain is just going to have to train to produce the same power while riding at a lower cadence. It's not that hard. Probably involves some stomp and sprint intervals, low cadence work, maybe some gym work. Take @Hermes at his word. it's going to take work, patience, and time. There's no mechanical fix, only training and patience. Forget the mechanical fix.
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Old 07-12-18, 11:22 PM
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Originally Posted by Carbonfiberboy View Post
... You can't force a high leg speed on someone with limited aerobic ability and expect a lot of power in the pedals. That's a scientific fact.
...
Forget the mechanical fix.
I agree with your first line above. Since you can't expect a high leg speed from the OPs stoker you should give her shorter cranks to reduce her leg speed when the OP is wanting to pedal at a higher cadence. That is a 'mechanical fix' that works for many people to adapt when they have a different preferred cadence. I don't notice much difference either when switching between 170mm and 175mm cranks, but when I ride with 165mm or shorter cranks I definitely prefer a higher cadence and correspondingly lower gears for a given riding speed. Given the large difference the OP reports between him and his stoker there should be a very substantial reduction in her crank length to get her leg speed down to an acceptable rate so she can contribute her share of the power.
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Old 07-13-18, 01:18 AM
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Originally Posted by prathmann View Post
I agree with your first line above. Since you can't expect a high leg speed from the OPs stoker you should give her shorter cranks to reduce her leg speed when the OP is wanting to pedal at a higher cadence. That is a 'mechanical fix' that works for many people to adapt when they have a different preferred cadence. I don't notice much difference either when switching between 170mm and 175mm cranks, but when I ride with 165mm or shorter cranks I definitely prefer a higher cadence and correspondingly lower gears for a given riding speed. Given the large difference the OP reports between him and his stoker there should be a very substantial reduction in her crank length to get her leg speed down to an acceptable rate so she can contribute her share of the power.
With all due respect, I am suggesting that it is because you KNOW the theory and believe it to be sound why you find shorter cranks more amenable to a higher spin rate. Your results are being influenced by your expectations. Someone less knowledgeable simply feels their feet going round and round and dang it, to them 75 rpm with a 165mm crank feels a whole lot like 75 rpm with 170mm cranks. I think 5mm works out to like 1/4". I can perceive 1/4" with my fingers readily enough. With my feet? Not so much. So would a much larger difference in crank length make a difference? Likely. How much then? Would 150mm cranks reduce the foot speed enough? Personally I doubt it. I believe one's perception of cadence has nothing to do with the persons linear foot speed around the rotation axis and everything to do with the reciprocating motions of the articulating joints of the riders legs. These motions are frequency dependent. 90rpm is 90 rpm. Period. Well that's my take on it anyway. What is less theoretical to me is the fact that a change to 150mm cranks would reduce the torque the Stoker could apply by ~25%. They are probably going to notice that more than the fact that they no longer have to move their feet as fast. I say probably because I don't really know. But I do know that cranksets cost money and changing them out costs more money if you can't do the work yourself. It's getting better but it still isn't yet the time where you can find cranks in 2mm increments at your LBS or even on Amazon. Once you get to about 160mm on the short end your options rapidly diminish. Considering all that ... I don't know ... 'standard' cranks just don't seem like such a jail sentence to this writer.
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Old 07-13-18, 09:20 AM
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Originally Posted by jethro00 View Post
Leisesturm, I agree with you that da Vinci confirms your assessment, and also adds a factor.
So, now I have some questions for you and others about IPS versus traditional tandems.
Let's start with my da Vinci.
If captain (C) and stoker (S) pedal at different rates, then the total power = 100% of the rider spinning faster, right?
If C and S spin in sync, then is the total power 100% C + 100% S?
Do the C & S have to be perfectly in sync to combine power or just close to the same rate?

Now, let's go to a traditional tandem, like the Trek T900 we both have.
If C and stoker pedal at different rates (with C faster), then the total power = 100% C - some factor for C pulling Ss pedals + 100% S?
If C and S spin at equal rates/power, then is the total power 100% C + 100% S?

I am finding this thread educational.

Having four DaVinci's in the basement at the moment (but trying to reduce that to 3... check tandemclassifieds.com if you want one!) I have some experience with the DaVinci drivetrain including using various crank lengths on different bikes. On our new road tandem we tried 160mm rear cranks - not for cadence reasons but for fit reasons. At 5'00" my wife has short legs and the difference between 165mm and 160mm was very apparent to her. It reduces the amount her leg has to bend at the top when the saddle height is set correctly for the leg extension at the bottom. The shorter the legs, the more a small change in the diameter of the circle being pedaled matters. I'm sure a 5mm change would not make nearly as big a difference to me with much longer legs and 175mm cranks.

But as for the spin and power. With a few exceptions already noted (Counterpoint, etc) the riders can't spin at different rates on a traditional tandem and can't deliver power to the drivetrain at different rates on a DaVinci. So on most tandems either the stoker is able to put power down at the current cadence (contributing), just able to keep up with the motion but not able to put any power down (neutral), or actually being pulled along by the captain (negative input). But in all cases the riders are turning the same cadence.

On a DaVinci only the third scenario changes. You can have the stoker providing power (contributing), just able to spin but not putting any power in (neutral), or not able to keep up (still neutral, but the phase of the pedals will constantly change and you'll hear the left freewheel clicking). I'm a bit surprised how rare it is for one of us to pull the pedals even a single click ahead. When it does happen it usually means we're spinning above 100 rpm and one of us is tired.

I love the DaVinci drivetrain, but i don't think it does any more to solve this issue than a traditional drivetrain set out of phase. It is easier to experiment with different out-of-phase options, but on the other hand it is probably pretty tricky to reliably get the exact same out-of-phase position of the cranks. I suppose it is something the team could learn with practice, but if you prefer to be out of phase all the time a regular drivetrain (or a locked-down DaVinci) would work better.
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Old 07-13-18, 11:34 AM
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Originally Posted by prathmann View Post
I agree with your first line above. Since you can't expect a high leg speed from the OPs stoker you should give her shorter cranks to reduce her leg speed when the OP is wanting to pedal at a higher cadence. That is a 'mechanical fix' that works for many people to adapt when they have a different preferred cadence. I don't notice much difference either when switching between 170mm and 175mm cranks, but when I ride with 165mm or shorter cranks I definitely prefer a higher cadence and correspondingly lower gears for a given riding speed. Given the large difference the OP reports between him and his stoker there should be a very substantial reduction in her crank length to get her leg speed down to an acceptable rate so she can contribute her share of the power.
Going from 170mm to 165mm decreases leg speed at the same cadence by 3%. However, it also decreases crank torque by the same 3% at the same pedal force. I don't see how she comes out on it in terms of power. After a period of adaption during which the stoker's power might well be lower, the captain's cadence might go up by 3%, but I don't see a power advantage there, either. High cadence was popularized by EPO using cyclists with artificially high VO2max which allowed them to pedal fast while still producing power. Now it's become a fad. I've ridden with LD cyclists who pedal 95 on the flat in a paceline while my HR is like 108 and I'm pedaling 75-80 at low effort. They're just wasting energy looking cool.

The fact that generations of cyclists of various sizes have "made do" with the same stock 170 cranks with no complaints rather argues for adaptation being the important thing rather than a particular mechanics.

For a much more extensive, better reasoned, and more experienced discussion of crank length vs. leg length vs. power, etc. than I can give, see Steve Hoggs: https://www.stevehoggbikefitting.com...gth-which-one/
Warning: the good stuff is near the bottom of this long article, so read all the way down and the comments.
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Old 07-13-18, 01:09 PM
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Originally Posted by Carbonfiberboy View Post
Going from 170mm to 165mm decreases leg speed at the same cadence by 3%. However, it also decreases crank torque by the same 3% at the same pedal force. I don't see how she comes out on it in terms of power.
Recent Study-- pedal speed / crank length
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Old 07-13-18, 01:16 PM
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OK but that's the idea need a lot more moving parts in the drive train

to actually have the stoker pedalling at a different cadence...


probably have to get the frame fabricated around that.

counterpoint was a stoker recumbent in front captain steering in a diamond upright in back

those likely had a countershaft and that input rate different from the final drive..






....

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Old 07-13-18, 02:36 PM
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Originally Posted by surak View Post
Nice. I also like that kind of conclusion.
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Old 07-13-18, 03:55 PM
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One point of confusion on the da Vinci drivetrain- the riders (if pedaling normally) are both pedaling at exactly the same cadence, but not necessarily in sync in the sense that both have the right foot up at the same time- so it can look funny if you're not use to seeing it. I've run across a number of people who confused independent coasting with independent shifting, tho.

Always reminds me of this:
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Old 07-13-18, 07:57 PM
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We get funny looks on our da Vinci when we reach the turn around point of our ride on the river levee. I take a break and stand on my pedals (without pedaling) for a bit while the stoker pedals.

[QUOTE=StephenH;20446100]One point of confusion on the da Vinci drivetrain- the riders (if pedaling normally) are both pedaling at exactly the same cadence, but not necessarily in sync in the sense that both have the right foot up at the same time- so it can look funny if you're not use to seeing it.
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Old 07-14-18, 08:29 PM
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You know, another possibility- put the shifters on the stoker's handlebars and brakes on the captain's handlebars.
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Old 08-12-18, 05:16 PM
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As is the case with many of you, my stoker has a significantly lower cadence than I do. It is especailly an issue when we are climbing - either we are spinning way too fast for her to feel like she is contributing or we are in a higher gear and I feel like I’m struggling. Over the years it has been a better adjustment for us to spin a cadence maybe a tad faster than she is comfortable with and for me to do the majority of the adapting.
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Old 08-12-18, 06:43 PM
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As long as this has been resuscitated, I'll bring you all up to date on our progress.

We're doing fine. For anything at 2% grade or less, there's really no problem. We're still working on steep hills; when we find ourselves on a double-digit incline, where I have to give it my all, it can be tough for us.

But we're getting there!
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Old 08-12-18, 07:08 PM
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@WrenchSpinnr , thanks for confirming that my theory is the way to go. That's pretty much what we do now. I have to bear it in mind. Glad you've made progress, @124Spider .
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Old 08-13-18, 11:25 AM
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Lower cadence, longer cranks, faster cadence, shorter?
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