Dodgensince74

I have a 2010 Trek fx 7.3 that i really like but would like to have more top end speed. I talked to my lbs where I bought it and was told that they could change my cassette but they didn't say anything about changing my crank gears and am wondering if just changing the cassette without changing the crank gears would make enough difference to justify the cost? I was hoping to see at least 5mph increase in speed. Below is what my bike has for gears right now.





Crank Shimano M361 48/38/28 w/chainguard
Cassette Shimano HG40 11-32, 8 speed

DiabloScott

You won't find anything bigger than an 11t... you'll have to get a bigger chainring up front... or bigger wheels.

Edit:
OK... there are some 9 and 10t cassette cogs but they only fit special hubs.

contango 

^ this

I don't think it would even be possible to make a 10t sprocket that would fit around the lockring so you're stick with 11-something, and at the high end it's the 11 that counts.

You may be able to put bigger chainrings on - moving from 48/38/28 to 50/39/30 (as on something like a Tricross) would give you a marginal gain but probably not worth the cost. You might get a 52 or 53t outer chainring which would give you about a 10% increase in gearing.

When you say you want more high end speed, are you already using the highest gear you have (i.e. 48/11) and spinning fast? If so you should already be moving around 30-odd mph (at ~90rpm). Bumping up to a 53t outer chainring and keeping everything else the same would increase that to 36mph, assuming you had the strength to spin the pedals at the same rate in your new highest gear.

HillRider

There is no cassette that will increase your gearing and your current high is 118 gear-inches which will produce 35 mph at a cadence of 100 rpm. Can you really ride At 35 mph except down a big hill? So, changing the gearing on your current bike isn't going to give you the speed you want.

Your bike is a hybrid with flat bars and an upright riding position so aerodynamic drag is a big factor. A bike with drop bars will give a better riding position and getting in better physical condition will make you faster.

reddog3

The highest gear you have is when you are in the big ring up front, and the smallest cog in the rear. To gain more speed you need to go bigger in the front. What was the LBS thinking?

Really though changing to a bigger ring up front may not get you there if- you can't pull the larger gear. First I'd work on getting the cadence up, and make sure your tires are fully inflated. Assuming you have a computer and it's programmed correctly, what kind of speeds are you getting now? Hybrids ain't real speed demons in the sense race bakes are.

fietsbob

FWIW Shimano's Caprio system for small wheel & folding bikes ,
only cassette made for that hub is a 9 to 26t..

DiabloScott

48x11 and 100 rpm is 34mph. 5 mph faster puts this dude on the podium at the olympics... on his hybrid.

CACycling

+1 Even at 90 RPM, he'll be above 30 MPH. That's flying on any bike.

contango 

Yep. Reminds me of a while back when I thought I was pushing the top end of what my Rockhopper could do and was thinking about replacing the chainrings, only to realise I still had two more sprockets at the back I could use and in gear 7 of 9 at the back I was pedalling around 50-60rpm. Lots of scope to go a lot faster without replacing anything on the bike. In the end I concluded what the bike needed most of all was a better engine.

contango 

If he didn't already have an 11t sprocket at the back there could have been scope to gain gearing by replacing, say, a 14-34 cassette with an 11-34. It would mean the highest gear went from 48-14 to 48-11, which would be a significant boost.

LeeG

This is like saying you can only bench press 200lbs but if you could put on 50lbs more you would be able to lift it. What is limiting you isn't the gears, it's your inability to put out the power.

RollCNY

Just a thought.. I think you all may be thinking of the OP as an experienced cyclist, and not a rec cyclist. I was researching cadence last year, and found something that kind of matched my experience. The average rec cyclist has a natural cadence of 60 rpm, which matches a natural running cadence. Once that starts to vary, it feels unnatural. So all of your statements about 30 mph at 90 rpm may be 50% more than he is seeing.

Op.. I started with a Spec Sirrus with the same gearing you have, and I switched to a road crank because I lacked top end. The crank change helped, and I loved it. Then I learned how to increase my average cadence from 62 to 83-85, and the crank change became irrelevant. This isn't an easy change, and took 6 months to get comfortable with, but oh what a difference.

Buy a cadence sensor before you spend money on cranks. Just my 2 cents.

Homebrew01

^ This

Al1943

Replacing the gearing will not make you faster. Turning the cranks faster will. A computer with a cadence meter can help you learn to ride at a higher cadence. Pick a gear that will let you stay above 80 rpm and then gradually learn to maintain a higher cadence until you are comfortable in the 95 to 100 rpm range. Upgrade to a road bike when you are ready, but first learn to spin.

DannoXYZ 

Yes, learning to spin faster and using 2-3 gears lower will result in that +5mph increase the OP's looking for. Will take several months of training.

In the 10-years I worked in a shop, we constantly sold larger chainrings & smaller rear-sprockets to beginners (3-years or less experience) who were looking for more top-speed. Gave upon explaining all the above information about spinning, power vs. RPMs, etc. Just sold them the taller gearing and installed it. A large percentage of these came back in to get their money back as using the bigger gears actually made them slower.

Dodgensince74

I hear what you guys are saying about faster spinning = faster speeds. The reason I asked this question is because I am at a point where I really can't spin much faster due to back issues(4 back surgeries), if I spin much faster for very long my back will put me out of commision for days. I can maintain 20-22 mph on my fx right now for quite a few miles on nice smooth paved roads, unless the wind is blowing in my face. I usually ride for 20-30 miles, I can't use a drop bar road bike due to my back. What I am gathering from all the experience on here is that my best bet is to continue using what I have for now. I do thank you guys since you guys not only help me from possibly wasting some $$ but also helped to prevent me from some possible dissappointement, thanks again.

DCB0

Most people find spinning faster puts less strain on the body, not more.
I just did a quick calculation at https://sheldonbrown.com/gears/ and worked out that if you are going 22 MPH then you are likely turing your cranks at ~60RPM. As most people said, 90-100 is considered a pretty good cadence, but you have to do what you are comforatble with.

Also, 22mph was just slightly shy of my time trial speed the last season I raced on a lightweight road bike with narrow high pressure tires... not very fast but decidely middle-of-the-pack among the cyling enthusiasts at the local club. 27mph puts you among the fastes recreational riders (on racing bikes) anywhere.

Edit: Also, you should consider a recumbent bike if you like speed and you have back issues. They are faster than road bikes on flat ground.

Looigi

Trueness.

Al1943

[QUOTE=DCB0;13582779]Most people find spinning faster puts less strain on the body, not more.

+1
I've had 5 knee surgeries and still have rotten knees. I can ride much faster at a higher cadence (95 - 105) in a lower gear than at a lower cadence in a higher gear.

dabac

When I read this, I'm thinking posture-related. One thing pushing harder on slower cadences will do (apart from increasing the load on your knees), is to make it easier for you to brace your upper body against the pedalling action. Lose that bracing action, your torso will try to tilt forward more, and that force will have to be soaked up somewhere. Most probably by the arms stepping in and carrying more weight. And that will then transfer over to your shoulders and your back.

Or maybe you're running the seat a tad too high, and get that funny looking pelvis tilt at each stroke? I can see that messing up a back real easy too.

So maybe there are other things that you can research. A cadence of 60 is the kind of thing you find as a specific strength exercise, in tailored cyclist training schedules. But I can't think of anyone that'd suggest it for regular use.