Short Crank Arms

[Ivan]

I chanced upon an eBay listing for short-crank arms and managed to pick up these! A bonus, since they were SRAM Force crank arms shortened to 150mm, so matched the rest of my groupset. I have been very curious about how short cranks would suit me as I figure (a) I would like less "flailing" of legs up on my high BB and (b) I would like the extra cockpit room they would afford, as I could move my handlebar forward.

These crankarms are a whole 20mm shorter than my previous ones. I adjusted my front-end resulting in a slightly more sloping boom. This gave me noticeably more thigh clearance to the handlebar, so I have moved the bars forward as the more I ride Silvio, the more I like straight arms. I've only done testing for fit downstairs. They feel good so far, but no proper ride yet...there was a CB thread some years ago on short crank arms. I wonder who else has them now?

With all these Silvio 2 owners waxing lyrical about their recent Vendetta experiences, my poor Silvio is getting nervous. Don't worry dear - you still look lovely...

 

[Robert Holler]

That is a nice looking set of

That is a nice looking set of cranks! Do you feel like you have lose some leverage at all?

Robert

 

[trplay]

yep felt the same way

Lol Cruz moose has been entertained by the Vendetta over exuberance also. A few of their calculations have this fat , aero bellied, cat 6 rider faster than world record holders if I just rode a Vendetta. It would be interesting to see some strava data eh?

 

[Jeremy S]

Looks nice Ivan. I too wish I

Looks nice Ivan. I too wish I had gone with shorter cranks than my 172.5's. Is it any easier for you to sit up on the bike?

I say we hold out for the Vendetta 3.0 before "upgrading", I'm sure it will leave the 2.0 in the dust.

 

[Tom Roberts]

Short Cranks


I have been using short cranks on my Vendetta for about two years. The crankset is an FSA Gossamer compact double cut down to 153.5mm. I feel like they are easier on my knees, with little effect on speed. On my next Silvio I would like to get a crankset with arms @ or around 160mm.

 

[LarryOz]

On your next SIlvio?

Are you planning on getting another Silvio or another Vendetta? (per your last post)
Do you have one of each now?

 

[Tom Roberts]

Next Silvio


I started with a Sofrider, then went to the Silvio v.1, then got a Vendetta (first production run). Within the last year the Sofrider and Silvio have been sold leaving me with only the Vendetta. I am in line to get one of the new Silvio's. I think it's wise to have an extra horse in the stable at all times.

 

[LarryOz]

Great Idea!!

Thanks Tom,
Yes, I am hooked on Cruzbike after only having and riding my Silvio 2.0 for less than 2 months.
I really want to get a Vendetta now, but the cost is making to step back and evaluate it closer. WIsh I had unlimited funds!!
I would be nice to have a Silvio to train with and a Vendetta to race with, plus you have one to ride while you are "working" on the other one.

 

[Ivan]

SILVIO: my new short crank

SILVIO: my new short crank arms made me feel really fast. I am sure I was 7% faster and felt more reclined, like down to 20 deg or so. I think I shall rename myself silVio so that no one gets any funny ideas about replacing me with a faster yellower model.

IVAN: the short crank arms were interesting during my 2 hour ride time today. Too early to say if it made me faster. I couldn't sprint any faster but cruising along did seem a little easier. Was this better aerodynamics with less flailing legs as it was only noticeable at 35-40kph or was it all this recent Vendetta talk going to my head. I was definitely spinning more and thus using different gears. While I definitely lost some leverage, it was perfectly natural to just spin up more so no penalty loss. The HUGE DIFFERENCE for me was stability. It is much easier to keep Silvio tracking straight with these short crank arms. I did some no hands riding today and I could further and straighter. So my first 2 hours says I like it!

Unfortunately had my closest call today on Silvio when 2 motorcycles and 2 cars turned in front of me at an intersection. Yikes! How they managed to miss my 800 lumen flashing front light I do not know!!

 

[ratz]

Those cranks look like the

Those cranks look like the handy work Mark over at BikeSmith, but I don't remember him doing Carbon mods for SRAM. He lives in my area I'll have to ask him the next time I see him.

This article is old but has a lot of good references in it.

http://www.slowtwitch.com/Tech/Short_Crank_Database_2862.html

 

[LarryOz]

I think I need smaller crank arms too

Wow,
I was astonished to see my knee angle was 60 degrees (or less).
Ouch! No wonder my knees hurt!!!!
I am hoping that adding the 100mm chainstay extension will open it up a little bit, but according to my calculations even that ane 150mm crank arms will not get me to the 90 degrees that I should be shooting for.
I think this will also definitely help my stability on the bicycle (less flailing too.)
Am I just a strangely sized person that I can't get the right fit?

Ivan, how did you come across those 150mm cranks. Where they specially shortened somehow. The smallest cranks I can see on any SRAM crank arm is 162.5mm. What is your measured leg angle when your pedal stroke is the closest? Thanks!

I have SRAM FORCE 22 170mm now.
If anyone see a compatible set of 150mm cranks, please forward me the information!
Thanks,
Larry

 

[LarryOz]

I think I need smaller crank arms too

..

 

[Rick Youngblood]

Hey Larry, hard to tell by

Hey Larry, hard to tell by the photo. What is your xseam and how tall are you?

I have legs of a 5'10" guy. That was my original height before my spine compressed made me about 5'8". My xseam is roughly 42".

I installed the 100mm extension a couple of days ago. The extension won't open it up more, what will happen is the handlebars will rotate downward into your belly area. The BB/pedals will sort of rotate up and back towards you.

In order for me to get clearance for the top of my thighs on the pedal back stroke I moved the handlebars closer to me, thus my arms are a little more bent now. My thigh still touches some, but I can't go back any further.

I'm using 165mm crank arms. I've tried 175mm, 172.5mm, 170mm, 155mm, and 145mm, and settled on 165mm. With short arms you give up leverage and you swill pin a higher cadence. I like the leverage for hills, that's where you will miss the leverage.

Make sure your boom is adjusted to work for you. Generally if boom is in too far in, the top of the knees may ache, out too far back of knees may ache.

For me, it takes trial and error on anew bike with lots of small adjustments to get it right. So you may need to experiment some.

The bike smith is a good source for short cranks: http://bikesmithdesign.com/Short_Cranks/shorten.html

 

[Tom Roberts]

Short Cranks


Bike Smith is where I got my short cranks.

http://bikesmithdesign.com/Short_Cranks/shorten.html

 

[defjack]

short cranks

I have 155 105s on my Silvio V1 and 158 Sram Apax on my Silvio V2.1>Bikesmith did them both.Im happy with them. Jack

 

[LarryOz]

stats

I am 5'7'' (or a touch under at the start of the day!)
X-seam is 40.5"

Thanks everyone for the feedback.
I am hopefully installing my chainstay extension (thanks in advance to BentAero for the help) tonight and will be able to experiment with the boom and body position also.
It sure would be nice to have a full set (140 - 165mm ) of cranks to just try out! dream on!

Bob also said he thought I was sitting too far back in the seat (but not in right place), so maybe everything will work out and get me a better position!
I will let you know how it goes and hopefully post a photo of the new setup.

 

[ratz]

Too far back and boom too short

Incase anyone is looking at those picture and figuring out the ergos. It looks like that the boom is too short, (perhaps too far back after it's lengthened) AND your are touch too far back on the seat. I be curious how far back other sit; we definitely are sitting to the front of the seat. If you only scooted forward the knee bend problem would actually get worse. If you get the boom longer the feet will move out and down which fixes that knee angle. The extension will then elevate the feet for the aero you seeking. Just adding the extension won't solve it; as those feet need to move forward horizontally to fix the knee bend. It was riding the quest that taught us that we always start with the booms too short.

Mrs Ratz is 5'7" also with long legs fitting her was a challenge as it was easy to miss the optimal position in a number of ways. Her boom appears to be set longer than your picture; thus her crank is farther forward and lower that what you have pictured. Boom length 33", and from the slider clamp to the handlebar clamp is 13"(short arms), neither her nor I break 90 degrees at the knee when we pedal. We are however using 165mm cranks. I'm guessing gary can get you all situated; this really one of those you have putter with until it's right or have someone fit you on the bike that has done it before.

 

[Rick Youngblood]

Yeah, looking at the close

Yeah, looking at the close up, right knee looks a little too bent, at least it would be for me, which would cause my knees to ache. As far as where Larry is on the seat, I can't comment. I do like the Angle Tech rear seat pod however, looks like lots of room too.

 

[Ashtabula]

Adjustable Crank Arms

Though pricey, you can always try http://www.powercranks.com/OrderPowerCranks.html. Here are a couple of photos from their website...

 

[Jeremy S]

Larry, from your photo a

Larry, from your photo a chainstay extension doesn't look workable, to me -- I'll be interested to hear what happens with that! Seems like lengthening the boom and shortening the cranks are the things to try.

As for the position in the seat, I used to have some discomfort in my lower back if I scooted all the way back in the seat, so I would sit forward a bit. But, on my last couple of rides I found it perfectly comfortable to sit all the way back in the seat. I'm not sure it matters much, except that it does affect the pedal/handlebar/headrest adjustments.