paverman4u

I've got a 21 speed Surly Big Dummy. The thing is my commute is such that the highest gear could stand to be a bit higher. Has anyone ever/is it possible (and if so how) to increase the gearing on my bike so that I can get to and sustain a faster top speed on my commute?


Is this something that I could take to a bike shop to do? Would they replace just the highest gear in the rear cassette, or would it make sense to replace the entire cassette? What about replacing one of the front gears instead? Where might one get the most bang for their buck without screwing up the bike.

Thanks in advance.

dabac

Would be easier to answer this if you told us the tooth counts you have right now, but generally speaking the issue is probably not with the gearing...

A higher gearing ratio will only help if you are well and truly spinning out (cadence at 100+ rpm) with your current configuration.

I'm running a 42 big on my main commuter, and I have no trouble hitting 25+ MPH (40+ KMH) before spinning out, which I find to be plenty for commuting purposes. If you're spending much of your commute up there you should be looking at another bike than a Big Dummy.

If you insist, and unless you've got a fairly rare cassette, what you need are bigger rings up front. Depending on what's there already this might either require a whole new crank set, or the rings might be possible to replace by themselves.

fietsbob

MTB cassettes are having an 11 t for the high gear these days... but realistically above a certain speed its air resistance you are overcoming ..
If you can spin out a 46/11[4.18] or a 50 /12 [4.16] you may be doing plenty of speed .

Fast enough to be unsafe, when you decide to run late yellows rather than stop,
because you built up so much momentum.

njkayaker

What "top speed" are you talking about? What is your normal cadence?

Unless you are carrying a heavy load, it would seem that this bike is over-kill for your commute.

The only way you can get bigger gears is to change the chain rings (the "front gears").

https://www.surlybikes.com/bikes/big_dummy_complete/

Crankset/BB Surly Mr. Whirly, Forged aluminum. 48-36-26t. Black
Cassette Shimano LX-M580, 9-speed, 11-34t

https://www.sheldonbrown.com/gears/

Says that 48 on 11, will yield 26.7 mph at a cadence of 80 rpm.

BarracksSi

Bump it up to a still-reasonable 100 rpm and it'll do 35 mph. If that's too slow for me, then I'd consider a taller gear.

njkayaker

Yes, I realized that.

I picked a cadence that I'd be fairly certain he would be able to attain easily.

Anyway, it's highly unlikely that he would be able to sustain that speed on the flats for any useful length of time (which means that number is somewhat of a fantasy). It seems that even 26.7 mph would be hard to sustain for most people for any useful length of time.

He hasn't provided enough information.

Al Criner

I want to see video of the OP screaming along at 26 MPH on a Big Dummy. That must be really cool.

BarracksSi

I just figure that nearly every BF question like, "What gears do I need to change to get faster?" is from someone who isn't really a fast rider yet. If they're strong enough to really need a bigger gear, they're either racing or going for a speed record of some kind. By that point, they've been riding enough, with enough training, that they have figured out the difference between the ability of their bike and the capacity of their body, and they won't be coming to BF with a question like this.

njkayaker

Yes, which is why I asked the "what do you mean by 'top speed'" question and why I pointed him to the gear calculator!