jesspal

I currently have a compact setup on my bike, I would like to swap the big ring for a standard 53 size chainring and leave the granny gear the same.

I think i have a 52/34, and would be changing to a 53/34.

I live in flat Florida, and end up spinning out with a 12/25 cassette on long sprints.

Would changing the cassette to a 11/25 have more of an impact?

HillRider

Changing to a 53 from a 50T chainring will increase your top gear by 6% and probably cause front shifting problems and sluggishness and possibly require a longer chain. Changing to an 11T cassette will increase your top gear by 9% and have none of the negatives associated with the chainring change.

achoo

If you do have a 52, changing to a 53 won't make a damn bit of difference.

Shimagnolo

Sure it will!
At the cadence he was doing at 35mph, he will now be doing 35.67mph!

HillRider

The OP says he has a compact crank so his current big chainring is a probably a 50T. If by any chance it really is a 52, the change to a 53 would indeed be trivial.

Kimmo 

Think about it this way: 53/12 = 4.417, so around that ratio, adding or removing 1 sprocket tooth is worth nearly 4.5 chainring teeth.

So 57/13 (4.385) and 49/11 (4.455) are about as close as you get either side of it. Dig?

fietsbob

If you accept greasy finger up- shifting, rather than expect snappy indexing,
then all sorts of combinations work.

wphamilton

Considerably more.

Six jours

And with the technical aspect out of the way, I'd like to suggest the OP start sending out his resume to professional racing teams. Anyone who can "spin out" a 52x12 on a flat road during a "long sprint" is going to attract some interest.

HillRider

Even if it really is 50/12 it's still impressive. 100 rpm in that gear (112 gear-inches) is 34 mph.

GeoKrpan

At 104rpm you would be going 34 mph with a 50/12 combination.

That's nowhere near spinning out.

Six jours

IMO "spinning out" involves a cadence of 120 rpm at the very least. That's almost 41 MPH with a 52x12.

But a rider with a half-way decent pedal stroke will find that 120 RPM isn't anywhere close to "spinning out" and can actually be maintained with no more than slight discomfort. That rider would tell you that "spinning out" isn't even a concept until 150 rpm - more than 50 mph in a 52x12.

Of course, if he's a track racer, he'll be able to flirt with 200 rpm - as long as he can manage almost 68 mph.

So my post was really a suggestion that the OP forget about his gearing and try working on his pedaling - unless he really is exceeding 40 MPH on long flat sprints, in which case my suggestion about contacting the pro teams is a serious one.

Drew Eckhardt 

It's not even fast enough to make maximum power - that takes 110-120 RPM which yields 36 - 39 MPH.

And with good fit and form 140 RPM isn't out of the question (46 MPH)

jesspal

thanks for the advice, I will swap the cassette

HillRider

For a trained racer and someone who is comfortable with high cadence, you are correct. However there are those for whom high rpm is not only uncomfortable but not obtainable. I'm one of them. I CANNOT maintain a cadence over about 85 rpm under any conditions. All I get is winded and go slower than if I upshift and use a higher gear at lower cadence. Yeah, I know I should have "trained" myself to spin faster years ago but after numerous serious attempts I realized it wasn't going to work.

That said, a 50x11 is a VERY tall high gear even for gear mashers.

shelbyfv

If you still spin out with the 50/11, get a standard, as opposed to compact, crank. You obviously will have no use for that weak 34t small ring!