Short crank questions answered here

[Black Hawk Down]

On android there is an app called GearCalculator which I use quite often

I use this one:

Tables | BikeCalc

www.bikecalc.com

 

[Frito Bandito]

My Shimano 105 53/39 have 165mm crank arms and a left side 4iiii power meter. I have an 11-30t cassette and do very little climbing as most of you know. Occasionally the winds are right, and I got up into the mid 50s or even low 60s (34-39mph), but I was spinning out. Since I couldn't swap out my Shimano free hub for another hub with a SRAM XD hub to take advantage of SRAM's 10t smallest gear my only affordable option was to go with a larger chainring.

I got a good deal on a very lightly used Shimano Dura Ace 54/40t crankset that didn't have a power meter, but I was a little worried about it having 170mm crank arms. It turns out for me that the slightly longer arms didn't create any knee issues so far, and I think this might be because as a runner I had an unusually long stride.

Since I don't have a PM that also measures cadence I am not sure if I am correct that my RPMs are lower compared with the 105 cranks, but when the wind conditions are right and I am humming along at the same speeds as above I feel a lot smoother on the DA cranks. It somehow feels that I have a bit more time in the stroke to smoothly apply power to the pedals instead of having a shorter time to stomp on them.

 

[ak-tux]

Thanks. I could'nt quite figure which of the listed apps matching that name actually takes into account the crank length.

However , I found out that the good old Sheldon Brown's Bicycle Gear Caclulator has it all! .

Sheldon Brown's Bicycle Gear Calculator

A JavaScript calculator for analyzing bicycle gearing

www.sheldonbrown.com

Gain Ratios is the only system that takes crank length into account, giving a true value for the relative leverage of different gears on bicycles with different size wheels and cranks.


So using the Sheldon's caculator, if you have a 170mm Crank and a 50T chainring and make the switch to 145mm Cranks, you will have to switch to a 42T chainring if you retain the same cassette. Similarly if you have a 42T chainring with a 170mm crankset, then it will have to reduce to 36T if you make the same switch (to a 145mm crank)

 

[Black Hawk Down]

@ak-tux I wasn't sure who you were directing this answer. In my case, I have two bikes that need chain ring adjustments. On my Q45, I currently have a 40t chainring and 155 mm cranks. Using the same chain ring with 165 mm cranks, I can get up all my hills. so I need to figure out what chain ring used with 155 cranks will get me to the same gear ration as a 40t chain ring with 165 mm cranks.

On my V20, I have 165 mm cranks with a 2X chain ring 34/50. I want to try 145 cranks on this bike. So I need to figure out chain rings for 145 mm cranks.

Looking at the Sheldon app, for the Q45, These are the optimal gear ratios if I had a 165 mm crank with a 40t CR:



The app didn't have my cassette. I have a SRAM 10-52, but I had to do the comparison with a 10-50.

Here's three smaller CR's:



The best match is 38t CR, but I would rather go to lower gears than higher, so I'll probably get a 36t.

For the V20, it's more complicated as there are two CR's to figure out. It's also a Shimano 11 speed. Here's the current condition with 165 mm cranks with a 2X chain ring 34/50:




Considering the low gear (currently 34) but with a 145 mm crank:



It looks like 30t is the best match. Now for the high gear at 145t CR:



Looks like 44t is the best match, but I don't think you can get a 30/44 CR combo. You can get 30/46, and for the high gear, I want the higher chain ring anyway, for faster top end speed. 30/46 with a 145 mm crank looks like my best solution for the V20.

Thanks to everyone for their help with this. I'll report back after I tried out the changes.

Bill

 

[Always-Learnin]

Recumbent Crank Length Calculator

The Recumbent Bicycle and Human Powered Vehicle Information Center

Recumbent and Human Powered Vehicle Information Center

recumbents.com

 

[Black Hawk Down]

I found the exact crankset I need (145 mm, 46/30t) for the V20 on Croder for $372.92. Actually, there's a payment fee and delivery fee added on to bring it to $418.54. This is approximate as you actually pay in Taiwan dollars. Ouch. I'm guessing the deliver will be 6 weeks or so.

SPIRIT Modular Crankset / Road, MTB and Birdy

SPIRIT is the modular crankset that allows you to select the crank arms, axles, spiders, and chainrings separately, combine easily as well as fully customized.

www.crodercycling.com

I'm going for it. I don't want to wait any longer. I bought the 36t chainring for my Q45 on Wolftooth for $79.95.

Direct Mount Chainrings for SRAM 8-Bolt Gravel / Road Cranks

SDM® chainrings replace your existing spider and chainring with one clean looking, lightweight, and stiff piece of machined billet. The ring is attached via 8 bolts on the backside of the spider near the spindle. Wolf Tooth’s patented Drop-Stop® wide/narrow tooth profile for the ultimate chain...

www.wolftoothcomponents.com

 

[ccf]

They have a 46/30 even.

How do they get down to 30t with 110 BCD?

 

[Black Hawk Down]

How do they get down to 30t with 110 BCD?

Here's your choices:

 

[DavidCH]

Thanks. I could'nt quite figure which of the listed apps matching that name actually takes into account the crank length.

However , I found out that the good old Sheldon Brown's Bicycle Gear Caclulator has it all! .

Sheldon Brown's Bicycle Gear Calculator

A JavaScript calculator for analyzing bicycle gearing

www.sheldonbrown.com

Gain Ratios is the only system that takes crank length into account, giving a true value for the relative leverage of different gears on bicycles with different size wheels and cranks.
View attachment 17358

So using the Sheldon's caculator, if you have a 170mm Crank and a 50T chainring and make the switch to 145mm Cranks, you will have to switch to a 42T chainring if you retain the same cassette. Similarly if you have a 42T chainring with a 170mm crankset, then it will have to reduce to 36T if you make the same switch (to a 145mm crank)

View attachment 17357

That's very interesting as GearCalculator doesn't even give you the option of 145 cranks!


I also suffer terribly with yo yo weight. In the winter I gain a few kilos and I have to do zone 2 for a couple of months before my body calibrates to known and loved gear ratios in order to get up long climbs.

Does Sheldon deal with semi inteligent linear interpolation with riders weight as it should be a factor?

 

[McWheels]

Sheldon's website does not care about your weight, it's a mechanical advantage calculator. I found it most helpful when I was working out what chanring to get for a Sturmey-Archer 8-sp IGH on 700c wheels. Small was the answer.

 

[DavidCH]

Well , if you are bike packing I would suggest a smaller chainring.

 

[Jim Parker]

Regarding BB wrenches for the Croder BBs, your local bike shop should have the correct wrench. If you like to do your own installation here are specific recommendations for affordable wrenches that are compatible:

This one works for the T47 BB (V20c):
ZTTO Special BB Wrench Aluminum Alloy BB Tool For BB T47 BB386*30 BB386*24 BSA30 ITA30 Bottom Brackets Frame Shell Crank


These two (below) will work for the Croder BSA BB (T50, S40, Q45, V20):
ZRACE 4 in 1 Bottom Bracket Wrench Tool , Compatible with SRAM DUB, SHIMANO BSA / FC-25 / FC-24, CNC AL7075 DUB-BSA TOOLS


ZTTO Bicycle Bottom Bracket Tool DUB BBR60 MT800 BB TL-fc24 fc25 Remove Lockring Implement BB93 MTB Mega BSA30 BB386 Install Cup


You can order these online. I used Aliexpress.com.

Jim

 

[Black Hawk Down]

Hi @Jim Parker ,
I bought the SPIRIT Modular Crankset directly from Croder as I needed a 2X system on my V20. I have a Shimano Ultegra component group with a compatible BB. I didn't consider the BB for the new Croder set. Do I need to buy one, or will the Shimano compatible BB work? If I have to buy one for the V20, looking at BSA BB for road bikes, this is on the website:


I assume that would work for the 2016 V20?

FYI, @Robert Holler

Thanks,
Bill

 

[Jim Parker]

Hi @Jim Parker ,
I bought the SPIRIT Modular Crankset directly from Croder as I needed a 2X system on my V20. I have a Shimano Ultegra component group with a compatible BB. I didn't consider the BB for the new Croder set. Do I need to buy one, or will the Shimano compatible BB work? If I have to buy one for the V20, looking at BSA BB for road bikes, this is on the website:

View attachment 17388
I assume that would work for the 2016 V20?

FYI, @Robert Holler

Thanks,
Bill

Hi Bill, I am pretty sure that you will need the Croder BB, but I would check with Croder. We sell the Spirit modular crankset with the Croder BB to make sure everything is compatible. You can absolutely use our crankset for a 2x system. Just order an 8-bolt spider and the rings that you want from all the various online shops. Sorry if I didn't make that clear in my original post.

 

[Black Hawk Down]

Hi Bill, I am pretty sure that you will need the Croder BB, but I would check with Croder. We sell the Spirit modular crankset with the Croder BB to make sure everything is compatible. You can absolutely use our crankset for a 2x system. Just order an 8-bolt spider and the rings that you want from all the various online shops. Sorry if I didn't make that clear in my original post.

If I ordered it from Cruzbike, I figured I'd have to throw away the ring that comes with the kit. It may have been the better option, but it's too late now. I will go ahead and order the Croder BB.

 

[Randyc3]

Looking at a new drivetrain with a Classfied Wheel for the V20c. Will consider shortening the cranks some(currently @162.5mm). Not sure I would go all the way down to 145mm, but sure my knees would be benefit with some reduction. Perhaps when I gain a better understanding of the gear inch, torque(actual physical effort), speed relationships and how it is going to affect my climbing I will have a plan. Keep the posts coming!

 

[DavidCH]

Looking at a new drivetrain with a Classfied Wheel for the V20c. Will consider shortening the cranks some(currently @162.5mm). Not sure I would go all the way down to 145mm, but sure my knees would be benefit with some reduction. Perhaps when I gain a better understanding of the gear inch, torque(actual physical effort), speed relationships and how it is going to affect my climbing I will have a plan. Keep the posts coming!

I am 63 and my knees are delicate, probably because I am flatfooted, I know for sure that from 165mm to 155mm there was a drastic improvement. If I want to , I can cycle every day. Its a no brainer. I don't fancy double knee replacements at 70 so I think it's an aero update that you will have to do. I thought buying new cranks was expensive so I got some sram rival cranks 2nd hand and found a engineer that would cut them down to 155mm.

Revelation time, my cranks are 150mm LOL.

From 2017... i looked it up for you.

Subject: Re: Shortened crank


Hello David,


The Rival range is solid, but it does have rather deep fluting at the back. I can shorten to 150 from 172.5 but the resulting pedal hole is thinner than ideal. If you are happy to have them done at your risk then send them by all means.

We shape the ends on a CNC milling machine to suit the new hole.

Best Regards
Patrick

Patrick McLoughlin
Director, Highpath Engineering Limited
www.highpath.co.uk
admin@highpath.co.uk
07557 305867

 

[Robertas]

53/39 have 165mm crank arms and a lef

Here's your choices:

View attachment 17376

Yes, it no so cheap. I done some modification and now have both 175mm and 145mm at the same time. It took 2h nice time in my garage and here it is. What do you think, will it be so strong as my feet force during uphill's, will test soon.

 

[kizarmynot]

Yes, it no so cheap. I done some modification and now have both 175mm and 145mm at the same time. It took 2h nice time in my garage and here it is. What do you think, will it be so strong as my feet force during uphill's, will test soon.

Very interested to hear the results of your test. I have a crank from an older bike that would be a good candidate for a test.

 

[Black Hawk Down]

Yes, it no so cheap. I done some modification and now have both 175mm and 145mm at the same time. It took 2h nice time in my garage and here it is. What do you think, will it be so strong as my feet force during uphill's, will test soon.

I am very happy with my 145 mm cranks. Worth the investment.