I have just bought a 2nd hand bike (Specialised Tarmac SL4) which has a 50/34 chainring, the seller says it is Ultegra 10 speed but can be 11 speed (that confuses me a little!). Most of my riding is on the flat. I have a spare pair of wheels but they have an old 9 speed cassette on them from my old bike. What cassette would I be best to buy please to put on my spare wheels which will help me maximise my speed on the flat. Thanks

Math 50 /24 is a tooth count, count teeth on the rear hub , next ..

example : a 50t turns a 25 t twice that is a 2:1 ratio.. multiply that by the wheel diameter

nominal 26,7,8,9..

more math, circumference, that is how far you go every time the wheel rotates ..


yadda yadda time for you to do the work


there are calculating and display websites to use too.

they have been mentioned, here, before.

NB 'Speeds' is not= to speed it's just how many cogs you have stacked together

50:11 is a ratio.. BTW it is 4.54545454545.... to 1.

Sheldon Brown's
Derailer and Internal-Gear Calculator

...you need to figure out for yourself what is the best gearing for you, because it varies with fitness and strength from rider to rider.

Part of the issue with speed on the flats, or anywhere else is that of cadence also known as how fast you pedal. It turns out that rookies, such as myself when beginning cycling, tend to pedal very slowly. It has been shown by people who study these things, that increasing cadence will increase speed with less effort. If you were to watch some videos of pros, it can be seen they pedal at about 90 RPM.

That was the situation with myself also until I practiced pedaling. I would put the bike in a lower gear but maintain the same speed by pedaling faster. Then I would go to a still lower gear, say for several minutes at a time and do some repeats. After a while, going to my normal gear, the usual cadence seemed really slow. Eventually, with enough repeats, you end up going faster. Just like playing piano, the more you practice, the faster you can play.

I would add that under no circumstances can I be considered a fast cyclist. Good luck.

Don't overthink this.

1. Count the number of cogs on your cassette. You want your new cassette to have the same number.
2. Most cassettes will come with an 11 tooth or 12 tooth smallest (high) gear. On a flat road you probably won't be using the 11 tooth cog very much.
3. Do you have any hills at all? Make sure your largest cog is big enough to climb your steepest hill comfortably.
4. On a flat road, you'll want to have a bunch of gears that are spaced real closely together. That lets you keep your pedaling speed constant while making minor gearing adjustments for wind or road contours.

+1 There is no gear that will make you go faster. Technique, proper fitting (saddle height and fore-aft, relative position of bars to saddle) and fitness have far more effect than things like gearing and bicycle weight. There is also little to no benefit going from a 10 speed cassette to an 11 speed. Just keep the bike drive train as it is, maintain it well and learn more about riding.

Dont get too wrapped up in gearing if you are a rookie. The simplest thing to do is just ride what the bike comes with.

Spent your time off the bike and do a little research on gearing until you have a basic understanding of what would be proper gearing for the type of riding you do. As "Retro" say dont try to over think it.

If you have 50/34 front rings combined with ANY 10-speed ultegra cassette...you ALREADY have all the gears you need to go very fast on flats.

Even if your smallest rear cog is 12. 50/12 at 90 rpm will have you going 29mph.

Thanks for your help and answers, much appreciated. I'm sure the bike is going to come with all the right gears, I just want to be able to buy a spare cassette for my other wheels (for races), and therefore wanted some advice on the right one for my roads as I don't have alot of experience. On the flat I am generally going about 32-34kph (19/21 mph) I just have little experience on what to buy, I live in a very small place without regular bike mechanics and seem to have a number of choices when I go online to look! I hope that as the season gets going I will be able to take my riding up a notch and therefore want to buy the cassette which will best suit and not leave me feeling I want an extra gear when I find a downhill!

...generally, racers with flat conditions pick cassette clusters that are close ration. That is, they pick a set of cogs that are only one or two difference in teeth. You start out figuring about what you normally find a good ration (front to back) for riding around on, then pick a middle rear cog about that one, and give yourself maybe three cogs smaller by a tooth or two, and several larger on the inside of your cassette to give you higher cadence for windy or slight uphills.

Google close ratio freewheels. Then figure out if you want a large chain ring on the front (the crank) that is 52 or 53, the most common sizes for racing on the flat.

Just a word on the number of speeds. You can't just run 10 speed one day and then use a wheel with 9 speeds the next.

Your bike has 10 speeds on the rear wheel and the shifter is designed to pull just the right amount of cable to move the chain from one cog to another. The spacing between the cogs are different for 9, 10, and 11 speeds. The more cogs the closer the spacing. When the seller said it has 10 speeds but you can run 11 speeds, that means that the rear freehub will accept 11 speeds, but you will have to swap out the shifters, chain, and probably the rear derailleur.

Same goes with your 9 speed wheel, except you might be able to use the current rear derailleur. But you'll still need 9 speed shifters and probably a 9 speed chain.

John

Thank you John, so simply put if I want to use my race wheels and the bike I've bought is currently a 10 speed bike I need to buy a 10 speed cassette for my race wheels to fit - if I've understood correctly. That makes sense thank you. I then just have to choose which one, 11/23, 11/25, 11/28, 12/23, 12/25 or 12/30... that's where I get a bit confused. The terrain is pretty flat here, only one short sharp hill (12% climb over 1/2 a mile) and another more gradual one, other than that it's just the wind I'm fighting! So I just need to figure out what cassette I need to pick....

52/53 is no longer "common" since the advent of 11 tooth rear cogs. It's common only among elite racers, and they are not running compact cranksets. The OP has no reason to move larger unless he finds he actually needs that tall a gear, which would be good for 40 mph.

I'm a fan of range over tight spacing. I'm ok varying my pedal cadence a bit, so if you have any 12% climbs, I would get a 10-speed 11-28 cassette, and be done with it. You'll have the high and low range covered. Just make sure those wheels will take a 10-speed cassette.

What cassette you get for racing wheels depends on what racing you will do - crits, road race or time trials, and the terrain for each. You are not going to want to be shifting a compact between chainwheels much in a race (personally I would not race on one) so don't go too tight. Besides, with 10 cogs you have some room to go larger. Keep in mind that for decades racers managed to go fast with 5 cogs in the rear and downtube shifters. To retain some hill climbing ability and still keep the gears close I would think an 11/28 or 12/30 would be fine, but if you only race flat crits you could go tighter. Again, it depends on your fitness level.

...I had the impression that's what he is looking for. C'mon, your legs were young once too.

...honestly, nobody really needs an 11 tooth rear cog. It's a gimmick.

Take your bike out as it sits now on a windy day, somewhere approximating where you might race in terms of up and down hill, and then pedal off into the wind. shift your gears until you get what feels like a comfortable cadence into a strong headwind on a slight uphill. Now stop, get off your bike, and look at the gear you are in in terms of how many teeth are on the rear cog, and how many teeth are on the front chain wheel.

That is now your preferred low gear measurement point. You probably want to go one or two teeth more for the low gear you choose for your racing cluster, as a bailout for when you get tired. Possibly three teeth as your low reserve. Use 12 for your high. Nobody really needs an 11.

He never said he needed more than a 50 tooth. I raced Cat 3/4 when I was younger. Did not win any races, but often finished top 5. I ran a 52/14, and nobody had smaller than a 14 when I first started racing. Fastest criterium I was in had average speed of 30 mph.

Correction - actually on that crit I was on tour, changed my freewheel to a tight cluster but I was running a 48/38 in front.

...or this, just start out with 12-30 and see how it goes. If you really intend to race on any sort of regular basis, you will be buying plenty of cassettes in the coming years, and you can also have a selection for races on different terrain or conditions. They're easy to change out, just buy a chain whip and the proper lock ring tool and a wrench to turn it.

Make certain you stay with compatible stuff. Shimano is pretty good about compatibility/interchangeability.

...please don't start with me on this. It's still early here, and I'm not up to it.

Unfortunately 11 teeth is starting to become the default small cog these days.

Ultegra 10-speed cassette

For crits or flat road races, I'll use a 12-23. If there's going to be any climbing more than a roller, I'll go with a 11-28.

Indeed, very unfortunate.

Camper, take a look at this gear calculator. You can try any gear combination that is available and slide the gears around for a very visual representation showing what each combination will do. Bicycle Gear Calculator

Appropriate 10 speed cassettes for road riding are
11-12-13-14-15-16-17-18-19-21
12-13-14-15-16-17-18-19-21-23
13-14-15-16-17-18-19-21-23-25 (or 26 for Campagnolo riders)

50x13 is a 30+ MPH cruising gear and 40+ sprinting which is plenty, so it's about having a low enough gear to make it over your hills at a reasonable cadence, when you need to change rings, and what the chain line is like in your most used gears - 50x21 will be quieter when that's the third largest cog than when you have a 21 big cog.

You might run an 11 starting cog with a 34 ring so you can stay on your small ring longer with terrain that's not quiet flat, and either the 12-23 or 13-25 with a 53-39 crank based on whether you spend more time in small ring x smaller cog or large ring x larger cog.

Gearing is about terrain, rider weight, power output over durations of interest, and personal preference which vary a lot between people. You'll do better figuring out what works for you over taking advice from internet forum denizens.