Cranklength...again.

[liltommy]

I searched already and read whats been posted here already, evan read the articles by Zinn.

I want to know what length other big riders are running or your experiences with switching crank lengths.

I was on a ride last night and the guy I was riding with seemed pretty animate after watching me ride that I should switch to longer cranks. I'm on 175. If you go by the Zinns forumula, I should be on 185.

So, tall guys chime in please.

Tommy

PS. This is partially due to my pre ride last week at the sm100 course. Theres gotta be something wrong with my bike. I can't be this slow.

[mjbrox]

PS. This is partially due to my pre ride last week at the sm100 course. Theres gotta be something wrong with my bike. I can't be this slow.


I think the exact same thing, but I have come to grips with the fact that there is something wrong with me. I am 6'4" and 210 lbs, so I am trying to drop some extra weight.

I also ride with 175's, If I where to buy new cranks I would definitly get 180's, but if I recall correctly the Zinn calculator says I need 190's

[DaveG]

I searched already and read whats been posted here already, evan read the articles by Zinn.

I want to know what length other big riders are running or your experiences with switching crank lengths.

I was on a ride last night and the guy I was riding with seemed pretty animate after watching me ride that I should switch to longer cranks. I'm on 175. If you go by the Zinns forumula, I should be on 185.

So, tall guys chime in please.

Tommy

PS. This is partially due to my pre ride last week at the sm100 course. Theres gotta be something wrong with my bike. I can't be this slow.



Go with what you've been riding. If you need to change there's a lot of time after the race to experiment.

Dave

[liltommy]

Go with what you've been riding. If you need to change there's a lot of time after the race to experiment.

Dave

I don't plan on changing up that soon, this is just in general.
I thought about it before but it got dropped for some reason.

[peter6061]

I'm ~6'0 and ride 180s on my SS, 175s on my FS bikes, and 170s on my fixie and jumper. I know the formulas take into consideration all your physical factors, but there is also the leverage / spinning issue not to mention clearance. Several of my DH friends ride 170s and 165s on their big bikes.

I agree, I wouldn't change anything right before the race, but with your size, I would sure as hell think you'd be on at least 180s.

[brian_brox]

I'm 6'4" and I rode 175s until I built my new bike with 180s. I changed a lot of things other than just crank length, but I think I like the longer arms. Zinn's numbers made me think I should change, but I didn't go as large as his formula (mostly becuase it's easy to find 180s).

Clearance was a bigger issue than I expected. First ride out, I was wacking rocks left and right. I think I'll get used to it, but

I think the leverage helps in climbing, but I need to play with seatpost height because I feel like my knees come up too high on the top of the stroke.

Let me know if you want to spin them around to see if you like them

[g_barr]

Is Zinn's formula for road or mountain bikes?

From what I've seen on bike specs, most manufacturers increase the crank arm length as frame sizes increase (e.g. 165mm/S frame, 175/M, 190/L). It stands to reason that tall guys need tall cranks. I suspect the main idea is to have the pedal more properly located under the knee when the rider is seated.

The difference between 175 and 185 is 10mm or ~3/8-inch! Sure, there is a force advantage with an increased lever arm. But will a typical rider feel the difference? The number of variables affecting pedaling is big: cleat placement (on the shoe), pedaling style/efficiency (toe up/down, hammering only...), seat position, rider anatomy/fitness...

I'm interested too - what happened after switching crank arm lengths?

[smdubovsky]

From what I've seen on bike specs, most manufacturers increase the crank arm length as frame sizes increase (e.g. 165mm/S frame, 175/M, 190/L).

I think it seems to go: 170mm/S, 175mm/M-XXL. Us tall guys get shafted;) I've got a 36" inseam and switched from 175 to 180. The online calc say I should be running 190+. I chose 180 because 1) Its darn near impossible to find something longer (the 180s are already almost unobtanium) 2) BB height problems. Its only 5mm diff but I'll SWEAR that I get more pedal strikes w/ the 180s. You would think manufacturers would move the BB slowly up as the frames got larger but Noooo.... Us tall guys get shafted;)

FWIW, the cranks I used to run were such crap its hard to compare. My knee definately hurts less w/ the new cranks though - thats something Im not imagining.

[brian_brox]

Is Zinn's formula for road or mountain bikes?

From what I've seen on bike specs, most manufacturers increase the crank arm length as frame sizes increase (e.g. 165mm/S frame, 175/M, 190/L). It stands to reason that tall guys need tall cranks. I suspect the main idea is to have the pedal more properly located under the knee when the rider is seated.

The difference between 175 and 185 is 10mm or ~3/8-inch! Sure, there is a force advantage with an increased lever arm. But will a typical rider feel the difference? The number of variables affecting pedaling is big: cleat placement (on the shoe), pedaling style/efficiency (toe up/down, hammering only...), seat position, rider anatomy/fitness...

I'm interested too - what happened after switching crank arm lengths?

Big bikes usually come with 175. 190 is hard to come by - maybe only custom.

Zinn primarily makes big mountain bikes, but I think the formula would hold true for road. Remeber also that Zinn thinks you should be adjusting other parts of the bike when changing crank lenth. Bottom bracket height, seat angle and other geometries need to work well together.

10mm up and down makes a 20mm change to the circle you pedal. Trust me, you'd notice. Cleat height would not effect the size of the circle that you spin, just the height of your saddle.

I have a short friend who switched from 170 to 165 on her road bike and it made a world of difference for reducing knee pain. I'm not a bike fitting pro, but one of the issues is that there are certain angles that you don't want your knee to be at when you are applying force. The crank arm length is one of the variables that impacts this.

[Dirt]

Hey Tommy.

I'm replying using my phone since I'm waiting for my wife to finish shopping. I didn't read all the other replies, so please excuse me if I repeat that they said.

Crank length is a trade off and is really subjective.

175s will give a little easier spinning, be easier on your knees and have fewer pedal strikes.
185s for me give more cranking power, but make you whack your pedals all the time unless you have a frame with a taller BB. That affects how the bike rides in a bad way in my view. I'd be worried that 185s would tweak your knee by making your leg apply power deeper in its bend. Think of the difference between doing full squats with your femur parallel to the ground VS. not bending so deeply.
180s are somewhere in between.

Pete

[Dirt]

Hey guys.

I ment Leonard Zinn years ago when a team I was riding for used his frames as team bikes. They were extraordinary. This was back when he only made road bikes and they were all steel.

Zinn is a very smart man. He's very good at taking the theory of how things work (relationship between a rider's dimensions to the size of particular components) and how they actually work and writing it down in a way that makes sense to you and me.

He's also a good salesman. He has developed his business around the ability to provide bikes that fit the proportions of those at the extremeties of the bell curve.

His talk about crank lengths is one of the areas that I tend to disagree with him. There are many things about which he is 100% correct with his calculations of crank lengths. There is one thing that doesn't factor into his calculations very well. That is ground clearance.... or the ability to minimize pedal strikes.

Put 190mm cranks on your bike and you'll be really suprised at how many times you smack those pedals on rocks and logs. I noticed a difference going from 175s to 180s. The benefit of the 180s was enough that I don't mind having a few more pedal strikes. I had a set of 186mm Bullseye Cranks and I found that I didn't ride as well with those because I was wacking pedals all the time.

There are some frames that have been designed to work well with long cranks. I've got a Grove Innovations Hardcore that has a 13.5" BB height. It is a rigid single speed (though it is suspension corrected and has a derailleur hanger welded to the bottom of the track dropouts). It was designed as an east coast, back woods bike that gave better clearance for rocks, logs etc.

When I bought the frame, I got a set of 195mm Grove cranks to go with it. The combination was AWESOME. I really felt like the cranks fit my pedal stroke well. I loved the added cranking power up the hills since that was my first ever single speed (circa 1990).

The bike was not without its flaws though. Having the BB so high made it so the bike didn't corner as well as my race bike. It had a much higher center of gravity. It was awesome for bashing around in the woods, but WOW did it suck on tight twisty singletrack at speed. My ABM (aluminum hardtail that I still ride as my commuting bike) kicked butt on it under those conditions.

I was on a ride last night and the guy I was riding with seemed pretty animate after watching me ride that I should switch to longer cranks.
In my opinion, that makes no sense. I can look at you standing there and make a guess that you might want to try some 180s, but unless you (meaning 6'4" Tommy) are riding 165mm cranks, a person can't tell much about the correct crank length by watching them ride... at least not with any certainty. That's kind of like telling a person's nationality by their shoe size. "Size 11.5? You must be a shifty Bulgarian!" (No offense to any Bulgarians intended... shifty or not. That little tidbit was put in there for Jabberwocky and Squirrel Girl's entertainment.)

As usual, I've prattled on way too long. And I didn't even get to talk about my other bike with insanely long cranks. Anyone remember the IRD Stoker? Damn I loved that bike... at least until I moved to Virginia and discovered that a bike with 205mm cranks kinda sucked when you had to deal with logs.

Take care. Y'all can wake up now. I'm done typing.

Pete

PS: Can you tell I'm not typing on my phone anymore?

[Dirt]

One more thing. At our age, I'd suggest not changing crank length by more than 5mm at a time. You need to know how your knees, ankles and hips are going to adjust to the change before you go crazy.

Pete

[saxman]

Tommy, I don't know much about Zinn's formula, but I can tell you that I am 5' 6" and I use 175mm cranks. Granted, a good chunk of that 5'6" is leg as I have a 32 inch inseam, but I would think that someone 6'4" should be using a larger crank than someone who is 5'6".

When I first bought my Trek, it came with 170mm cranks, and it drove me absolutely nuts as I was used to riding 175s on the Klein hardtail. Once I switched the cranks to 175, the bike felt a whole lot better.

[liltommy]

I'm going to see if I can borrow some first, I've got a few possible sources where I can get my hands on something to try.

Just real quickly I looked at a few of bigger online retailers. I didn't see anything other than 175s. I get the feeling if I want do want to go bigger there not going to be cheap or easy to get.

I'll update when/if I get to test drive.

Thanks all.

[Dirt]

180s are easily available through your LBS (They'll have to order them) or places like Speedgoat.

185s and longer are not as easy to find. Profile makes a Chromoly crank in their BMX style. They are great, but a little heavier than most are used to.

There is another place that makes custom cranks up to 200mm. I'll see if I can find the link at home.

Cranks longer than 180s are a bit pricey.

Pete

[smdubovsky]

180s are easily available through your LBS (They'll have to order them) or places like Speedgoat.

Are there any decent AND inexpensive triple-ring 180mm cranks? I like them and plan on putting another set on the bike I build this winter. The problem I find, only the top end cranks are made in that size:

Shimano: XT($200+) & XTR($forgetaboutit)
Truvative(SRAM): none
Race Face: Atlas/Deus ($200+)
FSA: none

Any suggestions? While XT/deus level quality cranks are very nice, multiple sets of them put a big dent in the wallet. I mean, when new 175mm LX hollowtech cranks go for $50 on ebay, its tough to swallow 4-5x that for 5 more mm.

SMD

[pbayne]

I wouldn't base anything on fit calculators; even Zinn's. Ex: Two guys who are 6'2", one guy has long femur's, the other guy has long tibia's. The calculator says the same for both, but they should have different setups. Throw in foot length, flexibility, etc and the calculator is no good. It will get you close, but there is way more to bike fit than static measurements. Check out Steve Hogg's column on cyclingnews.com. This guy will blow your mind when it comes to bike fit.

On another note, look for road and cyclocross cranksets. There are plenty of long versions out there and many can take mountain rings. You'll have to do some checking to make sure everything will fit your bike, but it can be done. Lots of pro riders use compact road cranks with a double chainring for mountain biking. I've found that road rings are perfectly compatible with my drivetrain. I've even seen guys use road cassetes and dura ace derailleurs off road.

[Dirt]

Are there any decent AND inexpensive triple-ring 180mm cranks? I like them and plan on putting another set on the bike I build this winter. The problem I find, only the top end cranks are made in that size:

I'm sorry. My crank snobbery shows bigtime here. I should have been more clear. I've never even checked to see if they still make 180s in LX or lower cranks.

Truvative only makes 180s in their SS cranks if I recall correctly.

I'll see what I can find in other, more economically priced models.

Pete