GuyinBlue

Two questions.

1. What is the best way to choose the proper chainring/cassette combination for a race?

2. Is there a way to use power output, cadence, grade, speed, etc. to select the best combination?

botto 

horses for courses.

Grumpy McTrumpy

If you are new to racing, I would suggest not looking at any of that stuff. Just pay attention to what is happening in the pack.

$.02

MDcatV

1 - 53/39; 12x25 will be fine for all but the most unique of races. youre in PA, you dont have any unique races

2 - probably, but see answer to Q1. if you're asking about during a race, experience and the speed you need to go will dictate. I hardly ever know what gear I'm in, and only if I'm cracked and going otb on an uphill or stuck due to mechanical can I ever recall worrying about it.

Apus^2

11-23, 11-25, 11-26, 11-28.
Flat...........................Mountainy

Experience will let you know. You may do one course with a good climb in it and really really need a couple more gears. I think an 11-25 is a good one to start out with. 53/39 up front.

nitropowered

Bad call on the 11-25. You lose the 16t gear which you use a whole lot more than the 11t

carpediemracing 

+1

I'd add that at the two more "mountainy" ratios, a compact crank with a 52x36 may work better.

In training I run a 53/39 x 11-25 or 12-25 (the latter just because I got one sort of free).

Racing, crits with little hills or circuit races with the same, 53/39 x 11-23.

11s are good because you can pedal slower at the same speed (or go faster) when it's fast - like descents or when it's winding up in a race.

cdr

MDcatV

only time I've wished I had an 11 was on time trials.

Apus^2

I love my 11-25. I've got enough hills here in Georgia that the 11 is very nice to have when going downhill (I also do a lot of roller work and I need the 11 for the rollers).

I have actually used my 11-28 in fairly flat crits before as the first 7 cogs are generally the same size (11, 12, 13, 14, 15, 17, 19) on a 25 and above.

I spin a lot so I climb in my 25/26 (I guess I could shift down into the 39 ). The only reason I use my 23 is if I forget it is on my wheel.

grolby

One of the great things about modern bikes and gearing is that a 53/39 crank and 12-25 cassette works extremely well for 90% of the races you could ever expect to do. You can go with a narrower or wider range cassette to get more optimum gearing for flatter or hillier courses depending upon where you live and what kind of courses you prefer, but 12-25 is extremely versatile with a modern 10-speed (or 11-speed) bike.

merlinextraligh

Yes. Find the steepest grades you'll be riding. Determine the power you can maintain for the length of the grade. Use a power/speed calculator (such as analyticcycling.com) to determine what speed that works out to, and then use a gear calculator (sheldon brown) to determine what gear you need to maintain a good cadence at that speed.

Or you could actually ride the grade, and see whether you need a lower gear than you have.

GuyinBlue

The race I'm planning for has 3,300 feet of climbing with six 1 km climbs at 15% avg gradient.

Where do you think that fits on the scale of flat to mountainy?

Apus^2

Flat

I'd probably grab my old bike with a triple and throw on my 11-28 for something like that.

GuyinBlue

Thanks!

That's exactly what I was looking to do.

queerpunk

I generally recommend a 12-25 for an all-purpose gear range. There was a time when a 12 was the smallest tooth... I had an 11 for a minute and never used it. Too big.

I use 12-23 a lot, too. For one race (actually, a unique race in Pennsylvania, MDcatV... the Fawn Grove Roubaix) the organizer sent out an email suggesting a 25, which I scoffed at... then we got there early and on a whim predrove the course and I put it on with shaking hands.

But, just ride a lot, in varied terrain, and you'll get a feel for what works well for you.

grolby

1 km at 15% = you better be able to climb that in a 39-25, or you're getting dropped anyway.

merlinextraligh

I don't think that's true. Assume 400 watts output, 160lb rider, you're going to be climbing that at 7mph.
39x25 at 7mph is a cadence of about 40.

Depending on the race category, I could very easily see someone using a much lower gear spinning it at 80 rpm, and not getting dropped on a 15% grade.

ijunes

i have a 12-22 and a 13-26 cassette on the commuter and race bike respectively.

as far as interchangeable cogs would it be okay to switch out the first and last cogs so i have something like a 13-26 and a 12-24 (this is on 8 speed cassette's btw [yes i still race an 8 speed])

edit: the reason why i don't just switch out the cassette is because one is considerably more worn than the other, however the 12 tooth has barely been tapped. The commuter cassette used to be the race cassette.

GuyinBlue

That's a good point and noted.

ridethecliche

In all honesty, if it shifted better, I'd rock a 38 instead of a 39 ring.

In fact, I might just swap to that over the summer. 53/38. It'll probably allow me to sit just a little longer on some climbs. I can't stay seated if I'm 'spinning' at 40 rpm. And I'd like to be able to alternate between sitting and standing whenever possible.

cmh

But you can stay seated at 41 rpm? The difference between a 39 and 38 tooth chainring is so small I wouldn't bother with the change unless you are buying a new chainring for some other reason.

To the OP, go out and ride the course if you can and see how you do. Keep in mind that you will probably go up those climbs faster in a race pack than you would training anyway. If it isn't obvious that you need smaller gears, just race on what you have unless it is an 80s 6 speed corn cob.

Jynx

Agreed it is small but every little bit helps. One tooth on the front or two teeth on the back arent that much but do both and it is a noticable change.

I run a 52-39 with a 12-25 and it is good all around.

ridethecliche

If I had the option of swapping cranks (I don't), I would probably be on a 52/36 setup on a compact.

grolby

Maybe it's just the crazy mofos I race with up here, but on hills like that MY 125 lb self is probably putting out close to 400 W to hold the pace.

ETA: make that 342 W for me to make 6 W/kg. For a 160 lb rider, that's 435 W. Bike calculator says that the resulting speed is 7.23 mph. For me to make the same speed requires 353 W. That doesn't quite add up to me, but whatever. Point is, you have a point, but on a wall like that the benefit of a 39-27 is nearly academic for me. Let me put it this way: for one race, I likely wouldn't bother. If I were likely to need that cassette for other races over the course of a few seasons, it might be a wise purchase.

merlinextraligh

Taking your weight and 400 watts, you're going to be around 9mph on a 15% grade which will still put you below 80 rpm in a 39/25.


15% is friggin steep. It's steeper than any portion of L'Alpe de Huez for example.

I seriously doubt people in lower categories are charging up sustained 15% grades at a pace that can't be maintained spinning a 39/27 or 39/28, or a 34/25.

Note, I'm not saying that you can't race that with a 39/25 either, but what I am saying is at the power outputs you'd expect from a typical Cat 4, you're going to be lugging it up a 15% grade in a 39/25.