Outnumbered

If i go from a 46 to a 50 in the front do I need to lengthen the chain and if so how much longer would I have to make it?

I am replacing the front gear (to give a different gearing a try) and the chain (cause its worn) at the same time.

Thanks,

Kevin

SkyDog75

Yes, you'd likely have to replace the chain. Otherwise you risk a too-short chain when you shift into your big chainring + big cog combo, which could cause serious damage to your bike.

I don't know how many links longer your new chain might need to be, in part because that depends on how your current chain was sized. Why not ignore the current chain length and measure anew? There are a few different techniques to do so, including Sheldon Brown's "big big plus 1" method as described on his web site.

cny-bikeman

You aren't just going to different gearing, but rather 8.7% higher gearing on the large chainwheel. You are also introducing a larger jump between the large chainwheel and the next smaller one. The first issue may produce problems with gear selection and the amount of shifting you have to do in the rear every time you shift between chainwheels, and also may introduce gears that you will very rarely use (such as 50/11 or 50/12). The second may cause less crisp shifting, or with some derailleurs and chainwheel combos, more problematic shifting. Of course the second set of issues is moot if you have only one chainwheel. It may help to state what you hope to gain with such a change (Hint: "More speed" is the wrong answer).

AlexCyclistRoch

What he said....

I've recently reduced my chainring size. I'v gone to a 'half step' setup, and decided that with a common middle-ring cassette, I needed a 3-tooth difference in chainrings, and also needed a smaller 'large' ring so that all gears would be useful. Now I generally ride with a 45/48 ring setup, unless I'm doing a hilly ride, when I change the setup to 42/45.

Outnumbered

OK being new to this gearing change thing, then I was looking to do this with the wrong answer. I was looking for the same/more speed with less effort for the same speed and same effort for faster speed. I will have to look into this gearing, speed, cadence, effort grouping a little more.

Thank you all for the help.

dabac

Unfortunately, the true answer to how to ride faster is usually to "pedal harder, and more often".

Or possibly, "get a better aero tuck". Or "buy a more appropriate bike/Wheels/tires/clothes etc etc".

At a rough average, MTBs tend to let an average rider stay on power up to about 25 mph, while road bikes let you stay on power into the 30s.

Unless you're spending important amounts of time at the top of that range, you should probably be working on pedalling technique rather than bicycle technology.

And/or overall fitness.

And while a power descent might be fun, and kick your personal top speed record up a bit, increased gearing very rarely has any impact of travel times and average speeds.

It's rather the opposite that's more common.
By reducing the overall range (sacrificing a little top end) you can get closer/tighter ratios in the range where you ride the most, making it easier to be just right WRT effort level for a greater part of a ride.
Doing a climb 2 mph faster will save you more time than topping out 5 mph higher during a power descent.

Most people do best at a cadence (= pedalling pace) of 80-100 turns-per-minute.

AlexCyclistRoch

At some point, taller gearing is just not going to provide enough torque. Mashing along at too high a gear will cause knee and leg cramp issues as well. You want to be in the correct gear to keep your cadence above about 60 rpm at all time. I used to have a 53-12 choice, which I NEVER used, even on downhills. You must always keep your spin going. There is no "overdrive" on a bike. Faster spinning does NOT require less effort, and often a very tall gear requires MORE effort to spin more slowly.

Where you live, unless you are riding in the Berksires, you need more or less "flat land gearing", where you have a lot of moderately tall to moderately short gearing (no extremes), with short steps between to compensate for headwinds.

cny-bikeman

Thank you for being open to questioning your assumptions. That seems a rarity lately, even when faced with facts that challenge those assumptions. As I would not expect you to just take on faith what we are saying, and want you to know the basis of it, here's an overview:

The relationship of the above factors is affected by the realities of both physiology and physics. It's true that at a given rpm a bike will go faster in a higher gear, and also true that at a given speed you have to turn the crank fewer times in a higher gear. The problem is that either way you need to exert more force/effort at any given moment to achieve those goals. Gears are spinning levers, and a higher gear is the same as a shorter lever, so you have to push harder to move the other end. The other, somewhat smaller factor is that using a higher gear results in short bursts of stress to the bike frame and drive train, which is reflected by a less straight path of the wheels and waste heat from parts flex.

Faster cadence works because the force is distributed over a longer distance/time, so muscles are allowed to work more smoothly with less lactic acid buildup and more oxygen, and a given amount of energy is transmitted to the bike over a longer period, resulting in less wasted flex.

Alex also makes some very good points regarding the practicality of higher gearing. Getting a few more mph on a downhill (often achievable just by tucking down and coasting) will work against you on the next uphill and also when you can't get an efficient gear due to too-large spacing between gears.

SkyDog75

In general, speed equals effort. Increasing the size of your big chainring will increase your speed per revolution of the pedals, but that doesn't mean less effort since it'll be harder to turn the pedals.

In part to be kind to your knees, many people advocate "spinning" the pedals at a relatively high cadence (say 90 RPM or so) to achieve your top speed instead of "mashing" the pedals at a slower speed but more forcefully. With a 46 tooth chainring and a 12 tooth cog on your cassette, a 90 RPM cadence would put your speed at 27.5 MPH. That's plenty fast for most of us.

Outnumbered

Thank you I guess I will just stick with my 46/34 and 11/18 cassette in the rear as I do have headwinds out here.

I have found through my years that when you are open to a challenge on something you assume you make out better and have more fun in the end.

Harder and more often sounds good even at 58 . Tiring but good. Thanks for pointing out the aero position it is something that has gotten away from what I am trying to do.

My cadence is about 75 or so but I can see from everyone's comments that picking it up will definitely help along with better aero position which is actually lacking more than my cadence.

Again thanks to all.

dr_lha

As I think I pointed out in another post, going from a 46T to 50T front ring gains you one higher gear (50x11), the next gear down (50x12) is essentially the same as your highest gear with a 46T front chainring (46x11). IMHO that's not worth bothering with.