Bicycle Mechanics - Gearing Question?

Hi, newbie here. I recently upgraded from a Raleigh Hybrid to a Trek FX 7.1. I bought it used, the previous owner upgraded it to be more like a road bike and I added a carbon fiber post. Anyhow, this bike really moves out, but it is set up for 21 speed and I find myself in 3-7 way too often, and maxing out on downhills. Looks like changing out to a higher gear set up is more than what the bike is worth. But I am probably a year away from getting a "real" road bike. The question is; Could I change out the 48 tooth large chainring for a 50 or 52 and increase my top speed without screwing up the current deraileurs? Seems like a possible solution if it would work for about $50, but short of adjusting the gears, I have limited experience in this field.

You can but you have to raise the front derailleur and then loosen and retighten the derailleur cable and then adjust to be able to go to all 3 chainrings.

I have a 52 chainring and I never use my 3 smallest cogs in the rear with it but I don't go over 30 mph except downhill and then I'm not pedaling. Are you sure you need to replace it? Is your cadence at 100 rpms or much slower? If much slower than you don't need to change your chainrings, you need to turn faster.

I cadence 100+. On a slight downgrade with the wind to my back I will be in 3-7 and do about 22mph, but on steeper downhills I am cadencing well over 100 and will only do about 25mph. I would like to take more advandage and get more speed. Now on a normal flat with no wind I usually cruise in 3-5 and average 16 or 17 mph. Does all of that sound normal? My current gear set up is really for a hybrid, and I am trying to find an affordable way to get more top end speed until the day I can buy a real road bike.

..on steeper downhills I am cadencing well over 100 and will only do about 25mph. ...Does....that sound normal?

That doesn't sound normal. Doing the maths with some nominal numbers 100+ cadence, 28" wheels, 48T ring and a 14T sprocket should put you at about 30 MPH. Using 26" wheels, 48T ring and a 14T sprocket should put you at about 27 MPH. Using 26" wheels, 48T ring and a 11T sprocket should put you at about 34 MPH.
Either you've got a cassette/freewheel with a really big smallest sprocket, or your cadence counting is way off. Do you get the cadence from a cyclocomputer, or are you trying to count it out by yourself?

Pull the wheel out of the frame, count the teeth in the rear. Sheldon Brown has a nice gear calculator wich gives you speeds at different RPMs, see what it will say.


..Now on a normal flat with no wind I usually cruise in 3-5 and average 16 or 17 ...Does....that sound normal?
The 3-5 doesn't say much w/o knowing the tooth count, but 16-17MPH is a perfectly decent average speed on a hybrid, particularly if you're doing it in an urban environment.

Thanks for the info. I will have to recheck my cadence numbers. I just use a wrist watch and count cadences in 15 seconds and X 4. For speed I use a GPS. So there is a good margin in error in both I suppose. Maybe I am going faster than I think, all I do know is I am wanting another couple gears quite a few times during a normal 12 mile ride.

you need bigger rings up front. I have a road bike and on some mild downhills i'm outspinning 52/14. At that point I'm doing 30+mph so I just coast and enjoy! It's a freewheel so it's tough to get anything lower than that though some 13-28's and 13-32's out there but then you sacrifice some with your gaps between gears. I just got a truvativ elita 52/42/30 crank off of ebay for $35 shipped because my bigger issue was needing a granny gear to get up the hills.

http://cgi.ebay.com/TRUVATIV-ELITA-TRIPLE-ROAD-CRANKS-CRANKSET-170MM-170-/400133179651?cmd=ViewItem&pt=Cycling_Parts_Accessories&hash=item5d29cbc903

I bought mine from them. Mine were 175 mm not 170mm and didn't include the bottom bracket. I really wanted 175mm cranks so I paid $40 for a bottom bracket from my lbs. This is an insane deal.

Be careful about the 7.1 - it's likely a one piece unit with non replaceable rings (you'll have to swap out the whole crank). Something to consider.

bikepedia says a 2006 trek 7.1 fx has a Suntour XCC-100, 28/38/48 teeth front, and a 7-speed, 13 - 34 teeth rear.

I'm almost positive that front is a welded steel triple, you'd need a whole different crankset for different ring sizes. you can, however, get a 12 or even 11 tooth rear in 7 speed as long as its a cassette. freewheels have a 13 tooth minimum. going from 13 to 12 is a much bigger jump than 48 to 50 in the front. There's a $17 12-32 from SRAM.

hey, when you count that 100 cadence, you're only counting one leg, right?

The simplest solution is to replace the rear cassette. Currently the smallest cog is 14 teeth, replacing it with a cassette that has an 11 tooth cog will give you a 23% increase in speed at the same cadence (and the oppertunity to get rid of the megarange jump). Changing the front chainring to 52 teeth will only give you an 8% increase.

My suggestion is the Shimano CS-HG30-I 11-28.

Thanks again for the advice, you are all correct! The front chainrings are welded and I looked up the ratios on Sheldon Browns site and changing the cassette would do much more. My smallest cog is 14. I haven't taken it down yet, but if I could just switch out the 7th gear for a 12 or 11 cog, that may be the best solution. Better yet replacing the smallest three would be better to give me smoother transitions in that range. Then again it will create larger jumps elswhere, so I am still undicided. Going to do more research on the cassette.

I'm a noobie so anyone chime in and correct me if I'm wrong but

1. On a modern bike if it's 7 speed in the back it could definately be a FREEWHEEL and not a casette. We just had this come up yesterday with somebody on a specialized hybrid. It's very common practice on these hybrid and flat bar road bikes apparently.

2. The link I gave you was for an entire crank and bottom bracket. $40 is hard to beat. My lbs charged me $20 labor to remove the old and install the new. So for $60 your looking at having a new road crank in place.

3. After installing this crank the 34 tooth megarange in the back is largely useless though i suppose if i were literally climbing up a mountain road it would work. my flat bar roadie has 30-28 granny gear which gets me up pretty much whatever I need it to. I'm going to put on a 13-15-17-19-21-24-28 free wheel and be good to go. I would think you would be in the same situation since your granny gear up front must be even smaller than mine

There are still 7 speed, and even some 6 speed cassettes out there....I know because I have an old 6 speed uniglide.

Swapping the 14 for a 12 or 11 would make a HUGE difference because small differences at the end of your block feel much larger due to wind resistance at higher speeds. You might find the 11 too large honestly...

Or, install a rack and panniers and with the extra weight you'll probably never hit the end of the block -- that's what happened to me ;).

Or, just coast if you are maxing out -- most racers I've ridden with (I'm not a racer) say that newbies tend to focus on descending too fast and should instead focus on climbing faster. Just a tid bit.

Careful when you are descending at speeds like that -- that's a lot of speed for an exposed body!

I am looking at an Shimano CS-HG30-I 11-28 that was suggested above and don't think it will work, as I do have the freewheel type. I tried a search for a 7 speed megaforce with smaller cogs to no avail.

"But I am probably a year away from getting a "real" road bike."

You say you are getting a Road bike next Year, Might be better to just use what you have, as is ,

and save the money for the Go-Fast bike by not spending it on fussing over your current price point limited parts pick rig.

I am looking at an Shimano CS-HG30-I 11-28 that was suggested above and don't think it will work, as I do have the freewheel type. I tried a search for a 7 speed megaforce with smaller cogs to no avail.

smallest possible gear on a screw-on freewheel is 13. you can get a 13-32, 13-28, etc. IRC makes some nice quality ones.

smallest possible gear on a screw-on freewheel is 13. you can get a 13-32, 13-28, etc. IRC makes some nice quality ones.

save your money, shimano makes 13-28 and they are $20 not $50 like IRD. I honestly think you should consider the crank swap as well. I just got back in from a ride and on gentle downhills i was easily out spinning 52-14 so simply going to 48-13 from 48-14 isn't gonna cut it. I do agree, I know I tend to want to go fast and pedal too much downhills when I should just tuck and coast and conserve energy for the climbing portions but I can't help it, I love speed!

Thanks CP, I did find the Shimano 13-28 for just under $20 shipped. I am going to start there and then consider the crank later. I will probably put so much time and effort into this bike that I will end up building my own someday, that's what I do with everything it seems.

bikepedia says a 2006 trek 7.1 fx has a Suntour XCC-100, 28/38/48 teeth front, and a 7-speed, 13 - 34 teeth rear.

I'm almost positive that front is a welded steel triple, you'd need a whole different crankset for different ring sizes. you can, however, get a 12 or even 11 tooth rear in 7 speed as long as its a cassette. freewheels have a 13 tooth minimum. going from 13 to 12 is a much bigger jump than 48 to 50 in the front. There's a $17 12-32 from SRAM.

hey, when you count that 100 cadence, you're only counting one leg, right?

Exactly what I was going to say. 48/13 is a pretty big gear. 48/11 is higher than what many road bikes have. My road bike runs a 50/12 and spins up to 40 mph. 48/11 would be similar.

I'm a noobie so anyone chime in and correct me if I'm wrong but

1. On a modern bike if it's 7 speed in the back it could definately be a FREEWHEEL and not a casette. We just had this come up yesterday with somebody on a specialized hybrid. It's very common practice on these hybrid and flat bar road bikes apparently.

7-speed cassettes are also pretty common.


3. After installing this crank the 34 tooth megarange in the back is largely useless though i suppose if i were literally climbing up a mountain road it would work. my flat bar roadie has 30-28 granny gear which gets me up pretty much whatever I need it to. I'm going to put on a 13-15-17-19-21-24-28 free wheel and be good to go. I would think you would be in the same situation since your granny gear up front must be even smaller than mine

The low gear depends on what type of riding you do. Loaded touring? A 28/34 isn't a bad idea. Around town? A 28/28 is generally low enough for anyone.

My new gear set arrived.

Here is the old:

http://i28.photobucket.com/albums/c221/banddr2/100_3591.jpg

And here is the new installed:

http://i28.photobucket.com/albums/c221/banddr2/100_3592.jpg

Tried it out and is a definate improvement. Added an extra 2 to 3 mph on the top gear, and the 1 st gear is much more useful than the old 36 tooth granny gear. Only gear that is the same tooth count is 2nd, 3 thru 7 are one tooth less.

Only problem is for some reason 3rd gear is rough, don't know why since the others are smooth.

Next will be a new crank, but that will be after I build on my new carbon fiber frame that I just acquired.