Ya you've heard this one before. I'm thinking a 46:16 A guy at a shop recommended 46:17 I'm a skinny guy about a buck 40.

Not a huge difference between 16 and 17. The nice thing about having a 17t cog is if you increase your gearing, you won't have any problems with skid spots unless you run a 51t ring.

trevor ... i was thinking of switching from 44 to 51 for the thur. mit races with my 17t cog, what do you mean by skid spots?

If you skid, you probably skid with your feet in a similar position each time (usually around 9 & 3 o'clock) or so.

Basically the the number of factors your chainring and cog don't have in common determines the number of spots on the tire which receive this abuse. The worst case scenario is that your ring is an even multiple of the cog so every time you skid with your legs in the same position, you're skidding on exact same part of the tire.

It's not just theoretical. People here have skidded through tires in one spot while the rest of the tread remains in good shape.

By going with a chainring and cog that are relatively prime, you have as many skid patches on your rear wheel as teeth on your cog.

But we don't skid on the track, so it's fine for a track gear.

gotcha ... learned somthin' new thanks.

What is your comfortable crusising speed? What is your comfortable cadence?
What is you top desired sprinting and/or downhill speed? What is your max cadence?
What are the hills like where you live?
Do you get lots of serious headwinds?
Do you have lots of start/stop riding?

This will help with comparing ratios and skid patches (assuming non ambi skidding)


Al

Noisebeam, I've carried that chart in my wallet for months now. Thank you for such an invaluable resource!

*blink*

Do you really change up your gearing often enough that it's worth carrying around with you? Is this sort of like the condom I have in my wallet?

Everybody's got their gearing sweet spot. I found mine in 45x18.

41x14 floats my boat. Oh yeah all that skid stuff is true. I went through 4 tires in a few months with 42x14. Since I've switched to a 41t chainring, I've managed to keep the same tire with hardly any wear. Go me!

Don't forget to take into consideration the crank length. It will make a difference in the effective gear. On a fixed gear, they vary quite a bit. Most people use shorter that 175 cm to avoid the very unpleasant contact between pedal and road.

Wow, trevor, that correlation between flatspotting your tire and even multiple gearing has to be the craziest **** I've heard in a long time. I would have never expected that to be the case, although in hindsight, it makes a good sense. Of course, my only experience with flatspotting a tire came from Skip Barber racing school (and now, watching F1 on TV). I really do learn something new here every day.

[Edit: And I'm glad I'm rolling on 46/17 and 49/18, respectively.]

Flat spotting is a real problem. I had an old rear tire, and just learned to skid a couple weeks ago. I had some spare time on Sunday, so I spent some time skidding with my other leg as dominant. I was having fun, until I checked the wheel to see threads on the top. I ride a 48-16. I only did like 10 skids (of medium length) and that tire was shot. Downside was that my rear wheel is an old-ass 27" rim, so I had to pay up for the tire. Bogus. Definitely looking for a 44t-46t ring for the winter.

46-16 here.. It's pretty good for every day riding, but I sometimes feel myself craving some more speed. My commute is pretty flat though, so I'm thinking I'm best keeping this gear in case I encounter any hills.

No, I used it for building up my fixie (still waiting on QBP for my hub) and comparing my chainrings (40 and 52) to some standards (42x16, and 46x16).

I use 49x18 fixed on the road. I find it very good for flats and rolling hills. I can climb pretty much anything in my area, but it gets pretty anaerobic on steep sustained grades. My typical rides are in the 20 to 30 mile range.

I use 36x16 free on my mountain bike. That is a bit steep. Most people go with a 2:1 ratio around here for mountain biking.

Um on the skidding, couldn't you release the rear wheel and put the tire/cog in a different spot every other time or so? that' would make more sense than putting a flat spot on your tire.

Yes you can rotate the cog on the chain, you can rotate the tire on the rim. You can also spread the skid over a wider area by moving the pedals a bit as you skid (which can also give you more control of the skid) which can spread it over 1/8th of the circumference of the tire or so (but still mostly in the middle of that range)

But it takes discipline to rotate tires/cog and over skidding a spot can happen on just one ride. So its much easier to just make sure you have more than a few skid spots (I picked 7 in my above chart to fit the 1/8th diameter skid area, assuming you always skid with same foot forward, hence the bold text for 7 and over skid spots)

But after having fun with skidding for several months and wearing out tires I pretty much don't skid any more and rely on hard rear resistance on verge of skid and front brake added for hard stops. End up saving a lot of money.

Al

Learning to skid ambi would compound the equation ... right? i was just f'in around last night to see where my skid spots are with a 44X17 skidding ambi which I do (seemed natural for me right away) there seems to be a load of skid spots on my setup. Noisebeam your chart is for non-ambi skidding right?

Yep, just as I said when I posted chart "assuming non ambi skidding"
If you skid equally* with left or right forward then you simply double the number in the chart, which for me means I'd want at least 3 or 4 non ambi skid spots if I didn't want to rotate tire, etc.

*I can skid equally well left or right and when goofing around do both. But when out riding hard or in emergency situation I find I always skid with left foot forward.

Al

My seven fixies range between a 42/16 to a 52/16. For rolling terrain I like a 44/16 (74") and I've done a 67 miler in that gear. Higher gears are fun for flat rides or hilly routes under 30 miles. My lightest geared fixies have racks and bags for commuting and usually get less than 15 miles per day.

I was thinking it sounds more like an item that one carries around always, but rarely uses.