Help deciding on crank arm lenght

Discuss light weight issues concerning road bikes & parts.
Post Reply
apctjb
Posts: 59
Joined: Mon Oct 30, 2017 11:27 pm

by apctjb

Looking to order up crankset for new bike build and debating 172.5 vs 175 for a 50/34 crankset. I am 5-10.5" and normal proportions (inseam to torso). I have ridden both lengths and can't really notice the difference.

Any good rule of thumb or factors to consider when chosing crank arm length?

AJS914
Posts: 1753
Joined: Tue Jan 28, 2014 6:52 pm

by AJS914

The trend seems to be shorter. I started cycling on 170s, and then made my way to 175s when that was the fashion. I'd take 170s now. I'm 6 ft tall. 170s allow me to spin up hills at a higher cadence and I like to have a higher easy gear.

I think the biggest benefit for me between 170s and 175s is that I can maintain a lower position with less hip to torso angle (on the 170s).

Honestly though, the difference between 172.5 and 175 is very small - less than a 2% difference so either way you won't be noticing a huge difference.

by Weenie


Valbrona
Posts: 1482
Joined: Fri Oct 28, 2011 3:25 am
Location: United Kingdom of Great Britain and Northern Ireland

by Valbrona

The people who think they know - usually the ones that don't actually do much cycling - recommend to go short, as this opens up hip angle a little.

I have always recommend that someone serious about their cycling tries a couple of sizes to determine if a preference exists.

morganb
Posts: 439
Joined: Wed Mar 15, 2017 5:30 pm

by morganb

Valbrona wrote:The people who think they know - usually the ones that don't actually do much cycling - recommend to go short, as this opens up hip angle a little.

I have always recommend that someone serious about their cycling tries a couple of sizes to determine if a preference exists.

I have plenty of 10,000+ mile years of riding and recommend the shortest cranks that you can be comfortable on. I'm on 155mm at 5'9" and its a massive difference compared to when I was running 172.5mm. Way less knee and hip strain, smoother pedal stroke, easier to maintain high power output on flats.

Noctiluxx
Posts: 173
Joined: Tue Feb 07, 2017 7:17 pm
Location: Southern California

by Noctiluxx

Any aero testing done with the Bianchi Oltre XR4? Curious since I just picked up a new frameset.
2018 Bianchi Oltre XR4, (Celeste Matt)
2017 Giant TCR Advanced SL (Red)
2016 Specialized Allez DSW Sprint (Gold)
2016 Giant Anthem Advanced SX (FS)
2018 Trek Farley EX 9.8 Fatty (FS)
2017 Giant Toughroad (rigid 29er)

User avatar
wheelsONfire
Posts: 1757
Joined: Mon Jul 07, 2014 8:15 am
Location: NorthEU

by wheelsONfire

Go for 172.5mm.

I have tried 175mm and 170mm, i am 182cm tall and inseam of 87.3cm.
I would go 170 over 175 any day.
Bikes:

Ax Lightness Vial EVO D
Paduano Racing Fidia
Open *UP*
https://opencycle.com/showcase/the-xplo ... eelsonfire

User avatar
IrrelevantD
Posts: 151
Joined: Sun Nov 29, 2015 5:47 pm
Location: Near DFW Airport

by IrrelevantD

apctjb wrote:Looking to order up crankset for new bike build and debating 172.5 vs 175 for a 50/34 crankset. I am 5-10.5" and normal proportions (inseam to torso). I have ridden both lengths and can't really notice the difference.

Any good rule of thumb or factors to consider when chosing crank arm length?


I'm about the same height as you and I run 172.5 and have for the most part for about the last 25 years. I bought a bike that came with a 175 about 13-14 years ago and felt it was a little long. Could have been the frame had a lot of BB drop or the Q of the cranks, but I also had more pedal strikes on that bike when running those 175s than on any other bike. I know the trend is to go smaller arms and higher cadence, but I grew up cycling when it was perfectly acceptable to run a 53/39 up front, a 13-18 cassette (6-spd) and grind up hills at 60rpm.
* There is a 70% chance that what you have just read has a peppering of cynicism or sarcasm and generally should not be taken seriously.
I'll leave it up to you to figure out the other 30%. If you are in any way offended, that's on you.

srshaw
Posts: 152
Joined: Sun Apr 05, 2015 6:06 pm

by srshaw

I'm 5-10 and I would say my preference for the road is for 172.5, but seem to have acquired 170 on two of my bikes due to availability at the time. I'm not sure I really notice a difference.

I definately prefer 175 for mtb though when mashing up steep hills on a 1x.

Back in the 90s I used 175 on the road thinking it would be better to be the same all round (mtb and road), but that definately felt a bit big (although did help climb up hills on 42/23 which also was fashion of the day).

Hoing
Posts: 5
Joined: Fri Nov 17, 2017 12:09 am

by Hoing

172.5 go shorter crankset.

basurper
Posts: 43
Joined: Mon Jun 06, 2011 5:50 am

by basurper

Many people encourage you to go shortest. But the way you push the crank is not the same to the other. My height 166cm, inseam 65cm, tried 165, 170, 172.5 now settle on 170.

Sent from my SM-N950F using Tapatalk


Edit: typo

Lewn777
Posts: 150
Joined: Thu Mar 09, 2017 5:35 am

by Lewn777

I've used 170. 172.5 and 175. I feel the 175s are long and increase the angle my knees and hips have to go through so slightly increase wear and tear on the body, maybe they feel as though I'm putting out more torque, but using more energy. 170s feel a bit short and 'spinny', good for climbing but on the flat feel like I'm losing potential power. For me at 183cm tall and average leg length I feel 172.5s are spot on.

r_mutt
Posts: 331
Joined: Sat Feb 23, 2008 6:33 pm

by r_mutt

the present trend is as short as possible, so 165.

by Weenie


grover
Posts: 1108
Joined: Mon Jul 26, 2004 1:06 pm

by grover

I'm 182cm. Seat height 750mm. I started life as a mtber and stock bikes came with 175mm cranks. I bought a road bike which had 172.5mm crankarms. I liked that better. So I went shorter on my mtb too. I've been slowly trying shorter and am now on 165mm on all bikes. I prefer it. I find it easier to get over the top of the pedal stroke with less hip flexion required.

Post Reply
  • Similar Topics
    Replies
    Views
    Last post