Ok I recently got a Trek Hybrid. It has 3 speeds in front small, medium, big crank and it has 8 gears in the back. I thought I read somewhere that you do not want both your front gears and back gears to be in high gears at same time this will ruin the chain? I am riding it now on 3rd biggest crank in front and riding between a 6-5 speed on the back gears. The only reason not riding back speed at a 7 or 8 is I am concerned this would ruin the chain since both front and back gears would be in high gears which is considered bad right?

I guess what I am asking what would be the ideal gear range to be in? On the 3rd gear in front and 5th gear in back or would a better gear combo be better? That is a little too easy I would like to be in 7-8 gear range in back, but worried that might ruin the chain if both front and back gears are in high gears. I am peddling wheels very fast right now at the current gear setup I got and could switch into higher gears if wanted to.

I can't unpack what you're talking about, numbers for specific cogs vary between manufacturers.

Here's the deal: Avoid cross chaining- big ring, big cog; small ring, small cog. This adds a lot of torque and tension to your drivetrain.

Otherwise, go apey.

You likely have a setup similar to this (for a Trek FX2):
Front 3 chain rings
28/38/48 tooth chain rings
Back 8 cogs
11-32

It's best to avoid the extreme cross-chained combinations. For example, the 28 chain ring and the 11 cog. But an occasional cross chain won't cause any problems or wear out your drive train.

On the small 28 chainring, the larger 6 cogs are fine, and avoid the two smallest cogs.
On the middle 38 chainring, use any of the cogs.
On the large, 48 chainring, the smaller 6 cogs are fine, and avoid the two largest cogs.

Many riders use the middle chain ring on flatter roads, the small chain ring on hills, and the big chain ring rarely--often just on downhills.

Cadence -- pedal rotations per minute, in rpm. (To get a feel for this, on a quiet road, count the right side pedal strokes for 20 seconds, then multiply by 3.)
A good goal is to be "spinning" instead of "mashing" the pedals.
Mashing is pushing hard on each pedal stroke. It's best to save that for really steep hills.
Spinning is a fairly fast cadence, with light pressure on the pedals. It's better for riding longer rides. It uses more of your cardiovascular system, not just your leg muscles. You might try clicking one gear easier than you normally would use, and get used to that faster pedal cadence.

The chart
Here's your gears at some typical spinning cadences. the big 48 chainring is in blue, the middle 38 chain ring is in black, and the small chainring in red.

There's lots of overlap between the 3 chain rings. At 15 mph, for instance, the small chain ring is near the top end of it's range, close to being cross chained small-small. The middle chain ring can go down below 10 mph, or above 20 mph. The big chain ring is close to being cross chained big-big.

So, in general, try out using the middle chain ring, and shift to the small before you reach the base of a hill. Or if you are riding slower that day, you'll use the small chain ring most often.

Sorry, I don't know gears by number. "High" or "low" gears are referenced like a car transmission, with faster being "high"-- so smaller cogs are "higher" gears.

It sounds like you meant the small 28 chainring and the 12 and 11 cogs as "7 or 8". Yeah, if you are wanting to shift to those 12 or 11 cogs a lot, use the middle chain ring and go 2 or 3 cogs larger. That will be a similar speed range.

dok this was very helpful thank you. Yeah I am using chainring 48 and the smaller 6 & 5 cogs. It is what I figured switching to cogs 7&8 would be bad for the bike. I will try chainring 38 then and focus on getting a faster rpm. I am thinking my cadence is already pretty fast about 50-60 rpm a minute, but maybe if I got it into the 80-92 range that would be faster.

I was thinking I needed a rode bike or to lose more weight to go faster than what I am currently traveling at on my hybrid bike, but now I am thinking my problem is I am not pedaling fast enough. Maybe the best investment would be to get one of those devices that goes on the bike to measure your cadence.

50-60 rpm is quite low, better would be about 75 to 80.

I wrote a post explaining basics of gears, gearing and shifting here:

Bicycle gear ratios - speeds, gear inches

I think it will give you the answer to your questions.

good place to start is middle front & middle back. change the front gears for extremes like down or up hills. anyway that's how I started my kids

Read slaninar's comprehensive treatment - lots of good stuff there.

A brief discussion of two issues may address your concerns, though.

Mechanical things work best when they are aligned. Ideally, your bike is constructed so that if have the chain on the middle chainring (chainrings are in front) and the middle cog (cogs are on the rear wheel), the chain is perfectly straight. If you shift to the big chainring (to your right) and the biggest cog (to your left), the chain has to bend in four places (going into the rear derailler, coming off the top of the cog, and going onto the top and off the bottom of the chainring). Same thing if you have the smallest front chainring (left) and the smallest cog (right). The signficant bend in these conditions will work, but does increase friction and chain wear. Your bike's not gonna fall apart if you use these settings, but they're not necessary.

If you calculate the gear ratios for these "high bend" combinations, you'll see that you can get the same ratio in other ways. So instead of big chainring/big cog, you can use middle chainring and a big smaller cog. Same ratio, less bend. Worth working out all your ratios on a spreadsheet to know where they overlap.

The other issue is when you have the large chainring and large cog. Especially with some of the hug cogs folks like nowadays. In this case, you have the bend, but you also have the derailler idler stretched to its max. It should be able to handle this if the bike is setup with enough chain length and a properly sized cage, but it does put maximum bending moment on the derailler. Again, if you drop both the front chainring down one size, and the rear down one or two cogs, you get a very similar gear ratio.

Bottom line: there's no reason to use big chainring/big cog, or small chainring/small cog. It can cause friction and chainwear, and (in the case of the big/big) it puts the derailler in the highest tension condition.

The chart
Here's your gears at some typical spinning cadences. the big 48 chainring is in blue, the middle 38 chain ring is in black, and the small chainring in red.

I use the same chart its really excellent, you dial in the numbers & it shows you exactly where you are for different gears, there are several others for download on the web, then you can see where you are going wrong.

sorry it did not copy over last time ?

Tom's right. To get optimum efficiency from your muscles, you want to be doing his higher (75-80) range. This allows for good aerobic work. When you try to maintain speed at the lower cadence you have to mash down on the pedals pretty hard. This puts you into the anaerobic range. Your legs will get tired quickly.

I'll keep it real simple. First, you don't want to cross chain and you will be more efficient the straighter the chain is. Don't worry about all the technical stuff and just focus on your bike. Here is a guide for you to follow:
Front High (largest ring, left hand) goes with gears 8-7-6 in back (right hand)
Front Middle (left hand) goes with gears 3-4-5-6 (right hand)
Front Low (smallest ring) goes with gears 1-2-3 (right hand)

If you pay attention to your shifting (watch the gear indicators) and align your front gears (left) with the back gears (right) outlined here, you will be in good shape. If want to extend your middle range to gears 2-3-4-5-6-7 you will be fine as well.

Good luck.

when I 1st got my Trek Marlin 5, it was my 1st multi-geared bike. I watched a lot of youtube videos explaining how gearing works. I mapped my components and created a chart to tell me my ranges. Each chain ring gear has an optimal set of cassette (cog) gears for normal use, to avoid stressing the chain / components.

I understand not crossing the chain but don't get why you would only use 3 cogs of 8 speed cassette with the outermost chainrings. That seems excessively conservative to me.

The chart is saying you shouldn't use only one gear in your big ring, and showing how small the steps between gears COULD be if you were really obsessed with small differences. There is no reason you shouldn't use any of the gears that aren't red.

My reply was directed [MENTION=379539]practical[/MENTION] post, sorry should have been more specific.

You could be right about my advice being too conservative, but if someone is trying to figure out how best to use "all those gears" then I hope it works for them.

Imo, you can use all the combinations marked in black no problem. I see no reason to be overly conservative. The big gear overlap helps reduce the amount of chain ring shifting.

Click the link HTML5 Gear Calculator

Many riders make this process way, way, way more complicated than it needs to be:

Think of your bike as having 3 gear ranges: One for steep uphills, one for fairly level ground, and one for either downhills or for the two times per year that you have a significant tail wind. Use your front derailleur to shift into whichever chainring matches your condition. Fine tune your gearing within those ranges with your rear derailleur.

That's all that you really need to know.

I got an electronic device this weekend from Trek Store that measures cadence and mph for my bike. I initially started riding bike in higher gears like I was doing before at a slower cadence and it was reading 15 mph. So then I adjusted to a much lower gear and went for a 90 cadence on bike path and my mph range was about 17-24 mph. I felt like I was going slower since I was pedaling more, but the evidence was on my readings on the electronic device and the time it took me to travel the same distance. I wasn't going slower, but was actually traveling faster even though it felt strange pedaling that fast on lower gears.

I had my girlfriend get on the Trek Bike and pedal in lower gears at a higher cadence. She pedaled at about 70-75 RPM and she was traveling at about 11-13 mph which is really good for her.

My girlfriend and I both agree that pedaling at a higher cadence is a lot easier on the lighter Trek Hybrid than the heavy steel Schwinn mountain bike. I tried pedaling at a higher cadence on the Steel Schwinn Mountain Bike before and it was too hard for me.

Thanks for the advice it helped.