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I have a modern bike (ridgeback meteor '13) and It currently has a 21 speed shimano chainset. I find that going down hills (which I do a lot) and on flats I need a higher gear. Can I do anything to get a higher gear ratio (such as a bigger large chainring) or am I already at the top?

Spec: 48/38/28 Chainrings 12-32 (7 Speed) Cassette:

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I have heard of 11 tooth cassettes, but doubt 1 less tooth would be that much of an improvement –  Mark W Jan 15 at 14:38
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Serious question: Why do you need to go faster downhill? –  Daniel R Hicks Jan 15 at 17:08
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Of course, one way to increase effective gear ratio is to install a larger diameter rear tire. –  Daniel R Hicks Jan 15 at 17:40
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Assuming the frame can clear one. This thing seems to come with a 700c x 42 tire on it already, which isn't exactly small... –  Batman Jan 15 at 19:45
    
@DanielRHicks why not? - its too slow –  Mark W Jan 16 at 13:39

4 Answers 4

up vote 6 down vote accepted

You probably can't fit a bigger front chainring on that bike due to the front derailleur and chain issues. They do make 11 toothed 7 speed cassettes which you can install (but I doubt you'll gain anything from it due to the second point I want to make on cadence), which will give you a bit higher gearing but the spacing between the cogs (i.e. the number of teeth) will be worse. Note that a higher gear ratio isn't always advisable, since you need to remain in control of the bike at speed as well (there isn't really engine braking, like there is on a car, in a derailleur system). Also, if you're commuting, you don't want to be going so fast that you get drenched in sweat when you get to your destination, so speed isn't everything.

However, chances are you need to increase your cadence: http://sheldonbrown.com/gears/ says that at a 60 rpm cadence, you should be doing 19-20 mph in the 48t front, 12t back combo, which should be enough (the 700cx37 tires aren't on his calculator, but 35 and 38 are close enough). Your cadence might change if you're in an improper riding position (e.g. seat too high/low or weird handlebar positions).

EDIT: The tire size on this bike should be 700c x 42. But the point still stands (the speeds should be slightly higher at the given cadence, since increasing the tire size also increases the gearing).

You should also make sure your bike is tuned up (you may feel sluggish if your hubs are due for a repacking or your brakes are dragging on the rims or your tire pressure is too low, for example).

If your cadence is already sufficiently high for some reason, time to get a road bike then (which will probably be lighter and more aerodynamic and have higher gearing (both at the bottom and top end)). Note that there will be a geometry change, even if you go with a flat bar road bike, probably, so if you choose to go this route, make sure to get fit. What you've got is a pretty heavy (~30 lbs, which is fine for its intended purpose) and cheap hybrid which is designed to be a commuter - it isn't really worth pumping money into it to improve it, but only to fix the things which are broken and add things useful for commuting, such as lights or switching to slick tires (which you presumably already have).

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Hi Thanks for the answer. Yeah it's used for commuting. most of the downhills are on the way home, so im not worried about sweating. I find that about 20-25mph I'm turning the pedals as fast as I can in top gear. You make a good point for a road bike. And whilst the bike is serviced well you've made me think about other aspects of saftey at higher speeds for the components I have. I think I'll stick with going 'slow' for now so I dont need to fork out a lot of money. Great Answer! –  Mark W Jan 15 at 15:52
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20-25 mph isn't exactly slow for commuting - it would probably be downright dangerous in most bike commuting areas, esp. with potholes, pedestrians, etc. Also, changing your gearing may make the uphill portions (which presumably are on the way to work) harder. But, there are a decent number of commuter-type (or not commuter but often used for commuting) road bikes which do have higher gearing (that is, they have rack, fender mounts, not too aggressive geometry such as the Trek Crossrip, Kona Jake, etc.). –  Batman Jan 15 at 17:34

48/12 is actually a fairly large gear, especially since your bike has 700c wheels, the same as a road bike. 53/11 is the largest gear combination on a typical road racing bike, even on many road bikes ridden by elite racers at race speeds (e.g. 45-50km/h for an hour on time trials, or 60-70+ km/h for sprints). That's only 20% higher than your highest gear.

I'm guessing you're riding at quite a low cadence: probably 55-65rpm. 90rpm is a typical target cadence for road riders. If you can get your cadence up even a little bit to 70rpm or more your problem should be solved. I notice in your other comment you mention that you are spinning as fast as you can at 20-25mph. If you're feeling like you're spinning out the top gear at that speed, I suspect that your pedal stroke is a little rough: if you have a smoother, more circular stroke, you should be able to spin at a much higher cadence without it feeling out of control. This is easier to achieve if your feet are clipped in, but definitely possible to improve even with platform pedals.

In principle you could can get a roughly 10% increase in your top gear by either changing your front crankset or your rear cassette (assuming compatible components exist). Increasing cadence, however, doesn't require any component changes, will be more efficient and less tiring, and will be easier on your knees if you're doing a lot of riding.

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90 rpm may be high on a commute, but it is good to note that 48t and 12t is already a pretty high gearing. –  Batman Jan 15 at 19:40
    
Agreed, even getting up to 70-75rpm in that gear would likely be faster than anyone would sustain for a commute. –  user611910 Jan 15 at 21:31
    
Thats a good point about focusing on pedal technique. I was actually considering getting some clipless pedals for my MTB and learning to use them on my commuter before swapping to the MTB. I might give that a go. Thanks! –  Mark W Jan 16 at 13:55

There are chainrings going up to 56 widely available - So long as they share the same bolt circle diameter I don't see any reason why you couldn't swap out your biggest chainring (I stand ready to be corrected though). They don't even /have/ to be the same make, although it looks a bit bodged if they arn't. You should check the specs for your front derailleur to see what max/min chainring sizes it can cope with.

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The bike is fitted with MTB type components, which aren't really designed take chainrings past 48t (but some people and manufacturers do this; this is determined by the shape of the FD, and swapping MTB to Road FD's generally requires new shifters and chainline adjustment and what not or dealing with wonky shifting. They're also designed to some extent for certain changes in tooths between chainrings). In general, you also have to worry about the capacity of the RD to a lesser extent. Also, not all cranksets (esp. cheap ones) have replaceable chainrings. –  Batman Jan 15 at 17:25

If you're happy at the cadence you might find some benefit to changing the smallest sprocket to 11, I've got an 8-speed cassette with 11 then IIRC 13, half this step would be noticeable in terms of how fast before spinning out.

But with only marginally more gearing than you (and similar tyres, 700c x35, also platform pedals), I don't feel like I'm spinning out in top below about 30mph (which I've never quite managed to hit without a boost from a hill). I thought my cadence was quite low, so you might want to compare your gps logs or similar to something like http://www.bikecalc.com/gear_speed and work out your cadence and whether you should be paying attention to that first.

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