Getting the ideal position

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Grldtnr
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Joined: 11 Jun 2020, 7:04pm

Getting the ideal position

Postby Grldtnr » 23 Aug 2020, 7:08pm

I am not new to recumbent's, having a 'bent trike on & off for 30 yes, but can folk advise on getting the ideal position.
I always thought the best way is to find how reclined you want to be, then put your heel on the pedal, leg outstretched, with the knee slightly flexed.
I have been used to standard length cranks, but have been reading about shorter 155 mm ones, will this make a difference?
What piqued my interest, is watching Mile Burrows riding his Windcheater on YouTube, his position was markedly different to mine, perhaps it wasn't his own machine, I ride an AZUB Tri Tris at the moment.
Incidentally ,I met Mike Burrows, and some of his machines, TOP BLOKE!

Jdsk
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Re: Getting the ideal position

Postby Jdsk » 23 Aug 2020, 7:19pm

With the heel on the pedal it's often recommended to allow full extension.

Yes, shorter cranks are often suggested on 'bents. The theory is that you don't have your body weight to add downforce, and even with a lot of back bracing that wouldn't match the weight. The practice is to try them out and see what you like...

Could you add a side-on photo of your position and a video of your leg action?

Jonathan (Windcheetah 100)

UpWrong
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Location: Portsmouth, Hampshire

Re: Getting the ideal position

Postby UpWrong » 23 Aug 2020, 9:49pm

It wasn't Mike's Speedy in the video. Straight leg with heal on pedal at furthest point is usually a good start.But be aware that it's usual to slide forward a bit during riding.

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Tigerbiten
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Re: Getting the ideal position

Postby Tigerbiten » 24 Aug 2020, 3:00pm

My understanding (but I may be wrong) is ........

The bigger the back-hip-thigh angle is then the less you use your glutes and the more you just rely on your quads for most of your power.
Hence needing a few thousand miles to fully build up your "bent legs" even if you're a cyclist.
Long term this means that the more reclined you are then the lower your maximum sustainable power output is.
Again this feeds back into the myth that "bents cannot climb well".
But once you're up to speed the gains from a lower aero resistance more that make up for the slight drop in power.

Shorter cranks lowers your mechanical advantage and makes it slightly harder to push each pedal down so you use slightly more energy per push.
Shorter cranks also ups your biomechanical advantage because your feet don't move as far each revolution so you use slightly less energy per rev.
With the correct length shorter cranks then the energy saved per rev is slightly more than the extra used per push.
If you go to short then the energy saved per rev is swamped by the extra needed per push.
You're only talking a couple watts difference, so you won't see any major speed gains but you may end a long day slightly fresher.

Luck ........... :D

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[XAP]Bob
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Re: Getting the ideal position

Postby [XAP]Bob » 24 Aug 2020, 3:07pm

Surely shorter cranks are just an adjustment to the gearing - 10% shorter cranks meaning you'll need the same force as a 10% longer gear?

There is going to be some alteration based on the distance travelled as well, but I suspect that's mostly a wash.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

Jdsk
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Re: Getting the ideal position

Postby Jdsk » 24 Aug 2020, 3:13pm

Tigerbiten wrote:Shorter cranks lowers your mechanical advantage and makes it slightly harder to push each pedal down so you use slightly more energy per push.
Shorter cranks also ups your biomechanical advantage because your feet don't move as far each revolution so you use slightly less energy per rev.
With the correct length shorter cranks then the energy saved per rev is slightly more than the extra used per push.

Is that for constant speed across the compared crank lengths? You might need to substitute force for energy in the first two lines.

Jonathan

Jdsk
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Re: Getting the ideal position

Postby Jdsk » 24 Aug 2020, 3:15pm

[XAP]Bob wrote:Surely shorter cranks are just an adjustment to the gearing - 10% shorter cranks meaning you'll need the same force as a 10% longer gear?

Some similarity but anatomical factors come into play, which doesn't happen with conventional changes in gearing.

Shirley

Grldtnr
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Joined: 11 Jun 2020, 7:04pm

Re: Getting the ideal position

Postby Grldtnr » 24 Aug 2020, 5:32pm

[vimeo][/vimeo]
Jdsk wrote:With the heel on the pedal it's often recommended to allow full extension.

Yes, shorter cranks are often suggested on 'bents. The theory is that you don't have your body weight to add downforce, and even with a lot of back bracing that wouldn't match the weight. The practice is to try them out and see what you like...

Could you add a side-on photo of your position and a video of your leg action?

Jonathan (Windcheetah 100)


No ,I am unable to film my leg action, I think my problems stem from lower gears than I am used to, I have lost a lot of my bike fitness, due to a road 'accident' many years ago, I don't ride anything near as much as I used too, I am in the 'rip&tear' pedal technique camp, tho' when riding fixed I could 'ankle', which I tried on the 'bent, there was more power, but it isn't to me a natural action.
I guess I will just have to persevere with the lower range gears, which perhaps is not a bad thing, considering the AZUB is for touring & camping.
My current set up is a single 46 tooth ring on a 9 spd Sturmey combo hub gear, I've not worked out the gear range yet , but I have a 9 tooth top end, down to something like 36 bottom end.The Sturmey gives 33% gear difference in low ,middle and high range ,which is very usefull if you should come to an unexpected stop in a high gear on the cassette,a simple click and you are in the lower range, so you can pull away

Jdsk
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Re: Getting the ideal position

Postby Jdsk » 24 Aug 2020, 5:38pm

Grldtnr wrote:I am in the 'rip&tear' pedal technique camp...

What does that mean, please?

Jonathan

PS: Is there a missing Vimeo link?

Grldtnr
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Re: Getting the ideal position

Postby Grldtnr » 24 Aug 2020, 6:08pm

Jdsk wrote:
Grldtnr wrote:I am in the 'rip&tear' pedal technique camp...

What does that mean, please?

Jonathan

PS: Is there a missing Vimeo link?


Basically it means a gear masher, someone who can push high gears rather than spin a low one, much like sprinters use, I could spin high gears fairly easy, but not low ones.
Ankling is something fixie' riders get used to,you flex the ankle,having to turn the pedals all the time promotes flexability

Jdsk
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Re: Getting the ideal position

Postby Jdsk » 24 Aug 2020, 6:13pm

Thanks

Jonathan

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n0ct0
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Re: Getting the ideal position

Postby n0ct0 » 24 Aug 2020, 7:53pm

Is yours a 26” or 20” rear wheel? I’ve a spreadsheet that I use for my IGH bikes that calculates top speed in each gear for a given cadence. I could plug some numbers into it for you.

Grldtnr
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Re: Getting the ideal position

Postby Grldtnr » 25 Aug 2020, 6:23am

n0ct0 wrote:Is yours a 26” or 20” rear wheel? I’ve a spreadsheet that I use for my IGH bikes that calculates top speed in each gear for a given cadence. I could plug some numbers into it for you.

Mine ,is a 26".
Speed isn't the issue, it's a touring / camping setup, what I would like to do is find a comfortable gear range for Cross country riding, I was doing a short tour around Suffolk, and really suffered in places, maybe it's a lack of laid back miles in the Legs, but it came with standard block,on my road bike, I have a step and half block, with 46/36/ 28 on the front, I have a good mix of ratios, which serves me well, but Upwrongs ride different to 'bents.

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Tigerbiten
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Re: Getting the ideal position

Postby Tigerbiten » 25 Aug 2020, 10:23am

Grldtnr wrote:but Upwrongs ride different to 'bents.

I agree with that.
A lower max power plus not being able to get out of the saddle means you fatigue more quickly when hill climbing on a bent.
My solution is gear right down whilst slowing my cadence down a touch and also dropping my power a little as well.
I drop my cadence to lower end of my cadence power band.
That way I'm not wasting energy trying to spin my legs super fast.
I've tried it and it's not worth it when hill climbing.
without any cooling from airspeed below 5 mph, I'll quickly overheat at max power.
So I drop the power before I do.
Over the years I've found what my maximum sustainable output is.
That's why my trikes geared right down to 9.6", two turns of the pedals for one turn of the 20" front wheel.
I may only be going at just over 2 mph but I can climb 20% hills reasonably easily even with a full camping load.
25% hills still hurt ...... :(

One thing to think about is reducing the size of the inner chainring.
Measure the gap between the chain and the bottom of the front derailleur.
The chain moves down 2 mm per tooth reduction.
So if you've a 12mm/0.5" gap you could fit a 24 tooth granny ring.
This will basically give you another gear down.

Luck ......... :D

Lodge
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Location: Staffordshire Moorlands

Re: Getting the ideal position

Postby Lodge » 25 Aug 2020, 10:23am

It took me some time to find my ideal position on my ICE Sprint. The starting point was straight leg to heel on the pedal at bottom-dead-centre. Then I played around and shortened a bit as it turned out I'm more comfortable and can go longer without aches and pains if I keep my legs slightly more bent. I noticed that when I push really hard I tend to move back on the seat as the foam pad compresses and my shoulders brace into the back so it probably ends up at the original heel on pedal straight leg at BDC position when mashing.

That said I rarely mash but spin with an average cadence in the high 80's to low 90's. I have 165 mm cranks. I've tried 170 mm but they were too long, and 155 mm were too short. I run a gear range of 18.7 to 98.2 gear inches (Rohloff).

Interestingly, my wife's Kettwiesel Kross runs 14.4 to 75.9 gear inches - but that's much more for off road usage and needs the low gears for climbing.

On my mountain bike and on our tandem I run conventional 170 mm cranks and use lower cadence (low 80's). I've put the 155 mm cranks on my Brompton (I didn't want to lose them having paid out) and find I can spin happily at 95-105 rpm for hours. Short cranks are useful on the Brompton as the bottom bracket is low and the pedals otherwise easily catch the ground if I'm not careful round corners (how do I know?).

Bottom line - short cranks tend to go with higher cadence but lower torque. Since power is torque times rpm it can balance out. Just like short stroke high revving internal combustion engines versus long stroke sloggers. It all depends upon where the optimum lies for your personal motor i.e. your legs. Experiment and find out!