Fixed gearing question

[d_douglas]

I am going to buy a fixed cog for my Indy Fab SS MTB and I am wondering what cog I should buy. I will likely want to switch out this cog for a freewheel for offroad from time to time, so bear this in mind.

It has a 38t ring. I have never ridden a fixie and am not particularly fit nor strong. I just want ideas of a safe, moderate, basic gear with a 38t ring.

I am not sure if MTB geos will make a difference - I just mentioned that in case it did mean something to some of y'all.

Thanks for your feedback!

[northbend]

where are you planning on riding - off road or city? What kind of hills will you encounter? I have no experience with off road so all I can suggest is what I used to apply for me on roads/paths not singletrack. Find a gear combination that will keep you comfortable spinning on level ground - using your existing geared bike, what gear combo do you spend the most time in while riding alone(you can use Sheldon Browns gear calculator to determine what your gearing would be with a different chainring size on your MTB) ? For me, that is around 70 gear inches or a 42x16 setup. I can live with that combo for hills and not feel like I spin out on the flats - good enough to do century rides like Flying wheels and RSVP. For you, a 38x15 would put you somewhere around 66 gear inches - that may be a good starting point for riding on the road if you are a bit apprehensive about your fitness level.

good luck

[rustychisel]

agreed.

42x16 is about the perfect FG ratio, 38x15 just a touch lower

[paczki]

That's a good gearing suggestion. As you learn to spin better, go up to an 18t. Remember with a fixed gear the work is in spinning fast down the hills more than climbing up them (at least for me).

[OtayBW]

You should be fine with these recommended gearings traveling around Lake Geneva. If you get farther out, you may be cooked....

[d_douglas]

Ooops, this is for road riding.

I hope to also buy a new freewheel for offroad - likely a 20t. is it possible to adjust the chain tension btw a 15t and a 20t just by sliding the wheel in the dropouts?

[gone]

Generally speaking (obviously terrain and conditioning dependent) somewhere in the neighborhood of 70-75 gear inches is a reasonable compromise. You should be able to manage both moderate uphills and downhills with something in that range.

I ride a 44x16 (72.6 GI) and have gone up and down 9% grades with it. Admittedly, I was really grinding at the top but I did manage it. The problem with going too easy on the gearing isn't the uphills, it's the downhills. Ideally, you want something that will allow you to manage both.

If you have a geared bike, you can try some routes in your area with the gearing you're going to try and see how it works. For example, a 39x14 is 73.5 GI. Try your route without shifting or coasting and see how it works.

Good luck! Riding a fixed gear is a fun change of pace and great training.

[markie]

What kind of hub do you have? Do you have provision for a reverse threaded lockring?

I like EAI cogs.

If you have a disc hub you could put a tomicog where the disc goes.

More questions than answers.

[d_douglas]

I have Paul Word hub - no discs....

Yes, my dignity wont be crushed if I need to get off and walk; it will however, be destroyed if I hurtle out of control down the hill from my office and crash in front of coworkers. Hills are what scare me!

D

[gone]

You shouldn't have any problems with downhills unless you're one of those way cool hipsters that doesn't have brakes and do skid stops.

Note that one conception that people new to fixed gear riding seem to have is that you can just let the pedals pull you around when you're going downhill. This isn't true. You need to stay "on top of" the pedals when going downhill - not pushing hard but definitely still pedaling.

I've found that there's a bit of a "sound barrier" when spinning really fast. As my RPM's go up, I start to bounce at about 125-130. This increases to the point where I feel I'm starting to loose control a bit but then smooths out when I hit about 145. I've gone as high as 165 with no problems (other than the fact that you're really working when you're spinning that fast).

I also find that it takes me a while to smooth out. I am not as smooth in the first 3-5 miles of a ride as I am after 5 miles or so. Also, I'm a lot smoother on the second downhill than I am on the first. Muscle memory and adaptation are amazing things :D

[RPS]

Ooops, this is for road riding.

I hope to also buy a new freewheel for offroad - likely a 20t. is it possible to adjust the chain tension btw a 15t and a 20t just by sliding the wheel in the dropouts?
Don't forget to consider the tire size when doing your math. If you are running an MTB tire like a 26 X 1.25 (what I use on my tandems and SS) the outside diameter is 25 inches, so your gearing will be different. To get the same as a 42 X 16 with road tires you’ll need a 38 X 14; and that will leave you slightly short of 70 inches. With 26 X 1.5 tires and 38 X 14 it should be close to 70 inches.

You can “approximate” how far you need to move the wheel for difference size cogs by doing a little math. For 15- versus 20-tooth cogs (5-teeth of difference) it works out to having to move the wheel about 5/8 of one inch (which is a lot) if I did the numbers right in my head. Also keep in mind that when you select the chain length to try make both work you’ll be limited to 1-inch increments unless you go with a half link. I swap between 14 and 17 tooth cogs and could go more but I don’t know the upper limit of what would work well with my frame.

Another option is to replace both cog and chainring so the number of total teeth doesn’t change too much while giving you the gear ratio you want. For example, instead of 38 X 20 maybe a 34 X 18 so the total chain length is closer to the 38 X 14. That also keeps the bike’s wheelbase closer to the same.

[d_douglas]

Math was my weakness. I even studied structural engineering in grad school and this is making my head ache.

I am using big fat 2.25 WTB knobbies on this bike. No plans to change at the moment.

It sounds like a 15 and 20t option may be a big gap.

[northbend]

who needs math when you can use sheldon brown's gear calculator. check it out. you punch in tire size, crankarm length chainring and cog size and it does the math for you. easy 'nuff.

[RPS]

who needs math when you can use sheldon brown's gear calculator. check it out. you punch in tire size, crankarm length chainring and cog size and it does the math for you. easy 'nuff.
If for no other reason it will give the person a greater and deeper understanding of the subject matter. Learning how the numbers relate and interact may very well lead to consideration of other options.

I’m not against using computers and spreadsheets to save time after one knows what is being done, but they should not replace knowledge of fundamental principles. Reading answers from what is essentially a trial and error exercise is not quite the same.



BTW: Without math how did Sheldon come up with the calculator in the first place? Apparently some of us still need math. ;)

[d_douglas]

'Learn the reasons why before finding solutions'.

I am all over spreadsheets though I know what you are sayin'!!!

[RudAwkning]

Math was my weakness. I even studied structural engineering in grad school and this is making my head ache.

I am using big fat 2.25 WTB knobbies on this bike. No plans to change at the moment.

It sounds like a 15 and 20t option may be a big gap.

Yeah. You may have an issue there. I've flipped between a 19 and a 21 and that ate up nearly 1/2 the dropout. And keep in mind that if your chainstays aren't long enough and your tires are fat, the tire may bottom out on the seat tube before it reaches the end of the droupout.

[markie]

So Umm the Paul Word hub probably does not have provision for a reverse threaded lockring.

Are you familiar with the term "suicide hub"?

[salem]

Ooops, this is for road riding.

I hope to also buy a new freewheel for offroad - likely a 20t. is it possible to adjust the chain tension btw a 15t and a 20t just by sliding the wheel in the dropouts?

To solve this problem on my single speed mtb (which I ride on the road to trail heads), I run two chainrings and two cogs to provide a 36/17 on the road and a 34/19 in the woods. Both teeth totals add to 53, so the chain length is roughly the same. Even straying slightly from the exactly equal total is fine to a point.

[d_douglas]

So Umm the Paul Word hub probably does not have provision for a reverse threaded lockring.

Are you familiar with the term "suicide hub"?


Will I DIE from riding this hub with a fixed cog?

[markie]

Will I DIE from riding this hub with a fixed cog?

Maybe.

Check to see if there are two sets of threads. One being reversed for a lockring. Without a lockring there is nothing holding the cog on if you stop pedaling.

I am pretty sure the Paul mountain hubs are set up with one set of threads for a freewheel only.

A cog will screw on, but not a lockring. You can use blue-loctite and a bottom bracket ring, but this is the "suicide hub". Opinions on it range from it'll be fine to it'll kill ya. I ran a bike that way for years and it was fine, but it is not recommended.

I like the tomicog solution that screws onto the 6 bolt disc brake hubs.

[bironi]

just to rattle RPS, here is a better gear calculator. :beer:

http://software.bareknucklebrigade.com/rabbit.applet.html

[Peter B]

To the OP:

In my experience, 70-74 GI is a good range for varied terrain and a rider of reasonable strength and flexibility. You want to be able to both climb and descend the toughest grade on your route without losing too much on the flats.

As for figuring gear swaps, you can assume one tooth change in ring or cog will move the rear wheel by 1/8". One chain link (male and female, 2 sections) will move the chain by 1/2". A 'half link' assembly (one section) will move your chain by 1/4".

Measure your dropout slot length, choose your ratio, select a ring/cog combo and go from there. Remember to allow sufficient forward movement to allow wheel removal.

I've ridden a few long fixed rides and had two dedicated fixed customs built so feel free to PM me with any specific questions.

And remember: Don't stop pedaling!

[RPS]

just to rattle RPS, here is a better gear calculator. :beer:
I don’t use one (have my own system I prefer) but if I were going to use a standard, I’d use Sheldon Brown’s Gain Ratios. I find it superior in concept than the inch-gear approach. ;)

[ericspin]

dd, do you have an iPhone? If so there are several good drivetrain calculator apps. I have one in my phone that gives me more information than I need but I use it a lot. Check 'em out.

As for fixed gear advice.........mine is to set the bike up with some kind of benign gearing and ride it. My fixed has been the most intuitive setup I have ever ridden. It is amazing how quickly my body adapted. When it comes to sheer fun on the bike it is a real toss up between fixed gear on the road and single speed on the dirt. My geared road bike is more of a tool compared to these two. Not a tool as in "dude, you're a real tool". A tool in the true sense of the word. I don't have the same love affair with my geared bike that I have with the fixed. Do it man, you have the ultra cool indyfab as the platform to build from.

Did you see the Starsky and Hutch movie? If so, hear them in your head when you read me saying DO IT! :banana:

[ericspin]

And remember: Don't stop pedaling!

Right on. But be guaranteed you are almost sure to do it at least once. And probably around aa crowd of people. Your mind will remember pretty quickly.

[RudAwkning]

I've ridden a few long fixed rides

really Peter? :D

http://fixhistio.blogspot.com/
http://wheelsnorth.campyonly.com/

btw, Nov 21st a bunch of us (myself, Ken Emerson, Mike Melville and 2 friends on their first fixed century) are riding from Berkeley to Davis for a Murder Burger. We'll take the train back and reminisce about the days antics. You're more than welcome to join us (as are any other fixed forummites!)

[RudAwkning]

Fixies make old routes and roads new again. It really is like being a kid on the bike for the first time. I'm hooked and have gotten 3 of my friends addicted to it :D

dd, do you have an iPhone? If so there are several good drivetrain calculator apps. I have one in my phone that gives me more information than I need but I use it a lot. Check 'em out.

As for fixed gear advice.........mine is to set the bike up with some kind of benign gearing and ride it. My fixed has been the most intuitive setup I have ever ridden. It is amazing how quickly my body adapted. When it comes to sheer fun on the bike it is a real toss up between fixed gear on the road and single speed on the dirt. My geared road bike is more of a tool compared to these two. Not a tool as in "dude, you're a real tool". A tool in the true sense of the word. I don't have the same love affair with my geared bike that I have with the fixed. Do it man, you have the ultra cool indyfab as the platform to build from.

Did you see the Starsky and Hutch movie? If so, hear them in your head when you read me saying DO IT! :banana:

[woolly]

Maybe.

Check to see if there are two sets of threads. One being reversed for a lockring. Without a lockring there is nothing holding the cog on if you stop pedaling.

I am pretty sure the Paul mountain hubs are set up with one set of threads for a freewheel only.

A cog will screw on, but not a lockring. You can use blue-loctite and a bottom bracket ring, but this is the "suicide hub". Opinions on it range from it'll be fine to it'll kill ya. I ran a bike that way for years and it was fine, but it is not recommended.

I like the tomicog solution that screws onto the 6 bolt disc brake hubs.

If you're going with a standard freewheel hub (i.e. without a reverse-thread lockring), I'd recommend the loctite and a a standard-thread lockring from an old English-thread bottom bracket for a little extra security. And at minimum a front brake (maybe a rear too). Skidding a brakeless fixee without a proper track hub is a recipe for disaster.

[woolly]

dd, do you have an iPhone? If so there are several good drivetrain calculator apps. I have one in my phone that gives me more information than I need but I use it a lot. Check 'em out.

Which one do you like the most? I grabbed one called simply "FixGear". It was inexpensive, and I liked the simple & straightforward interface. But I think either his logic or his math is a bit askew - when you change the crank length, it actually changes the calculated mph for a given crank RPM (with no other changes to tire size, chainring, or rear cog).

[ericspin]

Which one do you like the most? I grabbed one called simply "FixGear". It was inexpensive, and I liked the simple & straightforward interface. But I think either his logic or his math is a bit askew - when you change the crank length, it actually changes the calculated mph for a given crank RPM (with no other changes to tire size, chainring, or rear cog).

On my app screen it is just called BikeGears. I think it was like 4 or 5 bucks.

[Peter B]

On my app screen it is just called BikeGears. I think it was like 4 or 5 bucks.


+1 Great app.

[beungood]

whats the differance between fixed gear and SSd?

[Peter B]

Fixed gear aka fixed wheel employs a single rear cog threaded directly to the hub. It does not include and sort of freewheel mechanism and cannot coast. When the wheels move, the cranks also move. A singlespeed also uses a single gear but incorporates a ratcheting freewheel mechanism so that coasting is possible. Best to use front and rear brakes with the latter as slowing with the legs or 'backpedaling' is not possible.

[Oirad]

I am going to buy a fixed cog for my Indy Fab SS MTB and I am wondering what cog I should buy. I will likely want to switch out this cog for a freewheel for offroad from time to time, so bear this in mind.

It has a 38t ring. I have never ridden a fixie and am not particularly fit nor strong. I just want ideas of a safe, moderate, basic gear with a 38t ring.

I am not sure if MTB geos will make a difference - I just mentioned that in case it did mean something to some of y'all.

Thanks for your feedback!

d_douglas,

Wheel size is important. If you're mtb singlespeed is a 26" then a 38 t chainring and a 19 or so, if you're not a fixed gear convert yet, gives you a 2:1 ratio, and is easier than, let's say, 42x21 with 700c wheels. Many offroad singlespeeders/fixed riders swear by 34x20, or similar gearing because it gets them over the rough stuff and climbs. But don't underestimate yourself. So what if you have to walk up a hill after having struggled pedaling halfway up it. You'll become a stronger rider.

In all honesty, I'd settle for a compromise gear, one you can ride to the trailhead with and then on the trail, and back home again. Salem's advice about the same number of teeth but a sort of dinglespeed is actually the smart choice, but, hey .... since when are fixed gear riders smart?

-- Oirad

[DRZRM]

I do the same thing, but I set up my travel bike (S&S) with a Phil Wood Kiss-Off fixed-free flip-flop hub with a duo freewheel in back (17-19) and 42-40 rings up front so I can ride it to the trail (42-17) then loosen the rear wheel and move the chain over to 40-19 for trails. I also have a 16 tooth fixed chain ring on the other side of the hub for slightly faster fixed riding. I can take up a tooth or two by moving the rear wheel and still get the brake to hit the rim cleanly. There's a better description in my sig below (Travel Sled), but it gives me enough flexibility to ride most geography and it packs up quickly without any shifter cables to put back on.

To solve this problem on my single speed mtb (which I ride on the road to trail heads), I run two chainrings and two cogs to provide a 36/17 on the road and a 34/19 in the woods. Both teeth totals add to 53, so the chain length is roughly the same. Even straying slightly from the exactly equal total is fine to a point.

[Peter B]

<<snip>>

Many offroad singlespeeders/fixed riders swear by 34x20, or similar gearing because it gets them over the rough stuff and climbs. But don't underestimate yourself. So what if you have to walk up a hill after having struggled pedaling halfway up it. You'll become a stronger rider.

-- Oirad

A popular offroad SS gearing is 2:1 + 1. 32-17 has worked well for me.

[toasttoast]

A popular offroad SS gearing is 2:1 + 1. 32-17 has worked well for me.

for 700c or 26"? are we talking 35mm cross, or like a puglsey 4" tire?

[MarcusPless]

Are you familiar with the term "suicide hub"?


IMHO this isn't really a problem unless you're riding without brakes and insist on doing skid/skip stops. Most of the people I see at the track never use a lockring. They (obviously) don't have brakes; they just don't to skid/skip stops. My road going fixie is geared at ~70 gear inches, I run front and rear brakes, and I used to start every ride by riding down a 15% grade (rode up a different hill to get home). :D I've never had a cog come loose.

--Marcus

[Peter B]

for 700c or 26"? are we talking 35mm cross, or like a puglsey 4" tire?


Sorry for the omission. 26" SS.

[d_douglas]

All this talk about dying, so I bought an 18t White Industries trials FW. Maybe I will get the courage up to put a fixed cog on there soon, but for now, too scared (of the thought of the cog coming off, not Fixed riding....)

[ericspin]

OK let's see a show of hands...........

All you fixed gear riders that have spun a cog off off your hub while riding your bike..........

Anyway, enjoy the ss. But that fixed cog is going to be whispering in your ear, trust me.

[billrick]

YMMV, but I ran a suicide hub (fixed cog on SS hub, loctite, no lock ring) for a year with no issues. There are some really detailed instructions out there - look them up and follow them closely. I had to use a torch to get the cog off later.

Currently running a flip-flop hub on my 650B mountain bike with 34x18 SS and 34x16 fixed (Tomicog) options.

:)