Short cranks

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Dale08
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Short cranks

Postby Dale08 » 19 Mar 2018, 10:22pm

Thinking of trying short cranks on my ice sprint but not sure where
To go, the ones from ice aren't cheap (if they don't suit)
Thanks in advance
Gary
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[XAP]Bob
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Re: Short cranks

Postby [XAP]Bob » 19 Mar 2018, 11:20pm

I've got short cranks on my raptobike, and I really like them. I'd let you have a go, but you're a bit far away.
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.

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Dale08
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Re: Short cranks

Postby Dale08 » 19 Mar 2018, 11:34pm

Thanks bob
Not sure if I'd be safe on a rapto. Lol
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mark aldridge
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Re: Short cranks

Postby mark aldridge » 20 Mar 2018, 2:44pm

Hello Gary
Google Kiddy cranks.
Spa Cycles and SJS usually have a choice at reasonable prices.
Cheap basic solid arm cranks are easy to find and can be shortened by any competent engineer/mechanic etc.
Also scroll back through the forum and go to the BHPC website as this subject comes up frequently and there is much helpful advice.
I use short cranks on my recumbents and would not go back to long cranks.
For me a happy length is 140mm to 150mm. I have gone as low as 120mm but found the transition back to the 170mm cranks on my uprights was too uncomfortable on the odd time I used them.
The only thing I would add is just listen to your body, if you are comfortable you have the right length cranks.
Good luck.
Mark

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NUKe
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Re: Short cranks

Postby NUKe » 20 Mar 2018, 4:29pm

what size do you want ? what sort of price do you want to pay? and do you want single double or triple plenty of 155 cranks on ebay as this is BMX size probably only single s though. you could try Kevin at DTek or one of the other recumbent dealers. I use 155 on the GHopper.
Last edited by NUKe on 22 Mar 2018, 4:48pm, edited 1 time in total.
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hercule
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Re: Short cranks

Postby hercule » 20 Mar 2018, 9:23pm

Another short cranks devotee here too. I followed Sheldon Brown's advice and focussed on gain ratios. In effect this meant reducing the size of the rings by the same percentage as I was reducing the length of the cranks. In practice though this gives me the same "gain ratio" gearing as I had with conventional 170mm cranks I feel I could do with a fraction higher gearing. Were I doing it again I'd probably add about 10% to the sizes of the middle and outer rings (you can never have too low a bottom gear especially with the reduced leverage of shorter cranks).

Outcome - I spin faster, my knees ache less, I'm a bit more aero (Streamer fairing sits lower on my Trice) and there is less opportunity for wheel strike/handlebar interference on my Fuego. They felt a bit strange to start with but within a couple of miles that had gone. I'm a spinner by inclination anyway; if you tend to mash away at a low cadence they may not work for you. My average cadence went up from around 90 to around 105-110 according to my Garmin.

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Dale08
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Re: Short cranks

Postby Dale08 » 20 Mar 2018, 10:40pm

Thanks for replys and advice was looking for 155 cranks for triple,
at present have the standard truvativ cranks and 20 inch wheels
was hopping to just change the arms not the rings but I don't know which would be easier
Cheers
Gary
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Tigerbiten
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Re: Short cranks

Postby Tigerbiten » 20 Mar 2018, 11:32pm

The trouble is everything is related.
If you shrink your cranks 170 -> 155 then you have 10% less leverage through the cranks.
So you need to then shrink your smallest chainring 26 -> 24 (~10%) to keep the same feel and up your cadence by the same 10% to keep the same speed.
So unless you never use first gear then you really need to do both to get the full advantage for your knees.
Hence Sheldon Brown using the measurement of "Gain Ratio" which basically tells you how hard it is to push the pedals over by one revalution.

I also would like to try shorter cranks but Schlumpf only make 170mm kick plates for the HSD and modding the kick plates is a bit more tricky.

Luck ....... :D

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[XAP]Bob
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Re: Short cranks

Postby [XAP]Bob » 21 Mar 2018, 12:03am

I’ve done away with the kick plates on my schlumpf drive...
The buttons are reasonably ok to use, the shorter cranks possibly help there actually.
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.

brynpoeth
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Re: Short cranks

Postby brynpoeth » 21 Mar 2018, 6:00am

Crank shorteners might be a good way to try out
Where may one get some?
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NUKe
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Re: Short cranks

Postby NUKe » 21 Mar 2018, 9:29am

NUKe

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mark aldridge
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Re: Short cranks

Postby mark aldridge » 21 Mar 2018, 2:30pm

Google Highpath for crank shorteners.
These were previously made and sold by Chris Bell of Egg Ring fame and have a sound reputation.

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Dale08
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Re: Short cranks

Postby Dale08 » 21 Mar 2018, 10:40pm

This a bit more in depth than I thought,
bcd,chain lines and bottom bracket width
proper confused now !
Cheers
Gary
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mark aldridge
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Re: Short cranks

Postby mark aldridge » 22 Mar 2018, 4:01pm

Hello Gary
I think you might be overthinking the matter.
Look at your Truvative cranks. If they are solid alloy, not cut away or too fluted (ie have a narrow neck or pinch point) it would be easy to have them shortened. Then your chain line would be unaffected and your Q factor identical or slightly less (it depends on whether the crank arms are parallel or slightly angled). If they are not suitable just buy some cheap (secondhand) cranks with the same axle taper and BCD and cut them down.
I have cut down Hollowtech cranks and have had no problems despite the pedal thread only being supported at each end.
What you have to remember is that crank shortening is an ideal place to experiment. Unlike on an upright, you are looking at your cranks and will easily spot any problem as it develops. In the event of a catastrophic failure all that will happen is that you cannot pedal, a bit like coming out of of a clipless pedal. Just a minor inconvenience. It is NOT like riding an upright when a crank failure can lead to major high impact between [rude word removed] and crossbar.
If you don't get on with short cranks there is a ready resale market for them as people are after them to experiment to see if they like them.
Go for it, you won't regret it.
Mark

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Dale08
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Joined: 20 Nov 2007, 1:57pm
Location: Leigh Lancs Inbetween Liverpool & Manchester

Re: Short cranks

Postby Dale08 » 23 Mar 2018, 10:39pm

Thanks mark
Think my cranks should be ok for shortening
Will just need to get used to spinning more
Cheers Gary
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