repickrel

I have a 2008 Lemond Poprad that I'm using as a road bike. It's got Schwalbe One tires on it and rides good. However I need a bigger chainring as I spin out on slight downhills.
It has 12-27 10 speed with 46/38 chainrings. Can I just slap any 53t chainring on it as long as it has the same 130 bcd?

thumpism 

You'll need to move the front derailleur up, and probably get a longer cable.

thumpism 

Might need a longer chain.

thumpism 

Existing rear derailleur might not wrap the new chain.

MRT2

You sure you need a bigger chainring? At 90 rpm, 46 - 12 combination would have you moving at 27 mph. At 100 rpm (still not spinning out, IMO) 46 - 12 combination has you at 30.2 mph. Change out the 12 tooth for an 11 tooth and you are at 33 mph. And frankly, if you can sustain speeds in excess of 33 mph on flat ground, you should consider turning pro. Going downhill, aerodynamics are more important for sustaining speeds in excess of 33 mph and frankly, I don't see how a person who just started with cycling doing this.

Put another way, if you really need a bigger gear, it would be far easier, and cheaper to switch out your cassette for one with an 11 tooth small cog, and leave the chainrings alone. A 46 - 11 gear is 110.5 gear inches. A 53 - 12 gear is 116.0 gear inches.

gl98115

Yes. The shifting pins may not line up perfectly, but it should work.

BlazingPedals

You don't have to sustain 30 mph in order to justify the bigger chainring. It's important to plan your gearing so that you're in the middle of your cassette at normal cruising speeds. It's more efficient and leaves you with more options as your speed varies. Besides, using those small cassette gears is hard on the chain! The guys who tell you that you don't need a bigger ring are the ones at the back of the group in a sign sprint.

MRT2

My sprinting days are long over, so I wouldn't know about sign sprints. But I do know how to read a gear inch calculator. If you can do an all out sprint using a 53 - 11 or 53 - 12 gear, that means you are capable of sprinting at over 40 mph. As opposed to 46 - 12, which at 120 rpm would put you at a pokey 36 mph.

But back to the middle of the cassette at a more leisurely 90 rpm. In the middle 4 gears, 53 tooth chainring puts OP at a range of 16 to 25 mph, where as the 46 tooth ring puts OP at a range of 14 to 22 mph. Not much of a difference and IMO the 46 tooth is closer to the real world needs of most recreational riders.

wphamilton

53-38 is a fairly common standard. Most short cage DR's should handle the wrap capacity with that and the 12-27 so, no problem.

I'd personally throw a 50 on there, but OP didn't ask that question and if you want to spin downhill, bigger is better!

Lazyass

The only thing gear calculators are good for is finding gear ratios. For MPH they're less than worthless.

redlude97

What? If you are pedaling, a gear calculator tells you exactly what speed you are going at a given cadence

Lazyass

Yes, I know their purpose. Accuracy is another matter.

MRT2

If you have an accurate idea of your cadence, they are extremely useful. And, for those who say they are spinning out on their biggest gears, a gear inch calculator is a reality check.

BlazingPedals

I'm 62 now, maybe when I'm 65 I'll stop doing sign sprints. NOT!

I'm pretty much red-lined at 100 rpm. While I can spin faster, it doesn't help my overall power output. That puts my 53/12 at a touch under 35 mph. Using the calculator as a validity check, that sounds about right; with the 11T in reserve if there's ANY downhill grade to the road or if 100 rpm is starting to be uncomfortable. I generally don't coast a downhill unless a) I'm going over 45 mph, or b) I'm deliberately trying to limit my speed.

Trsnrtr

Saw a 73 tooth ring at the Hostel Shoppe in Wisconsin if anyone feels they need a bigger ring.

mstateglfr 

Er?
Are you saying this because the calculator cant take into account weight, wind, and air resistance?
Because other than that, im not sure how it isnt accurate. And its hard to fault a calculator for not taking into account an unknown variable.


The mph

02Giant 

I believe it isn't faulting the calculator, it is faulting the strict adherence to the calculator only with no consideration of the many variables. And, basically ridiculing the OP for suggesting he is wanting a gear change.

.02

MRT2

No, trying to save OP some time and money, and trying to put things in perspective. I would do the same for any friend, acquaintance, or internet stranger who just started riding 3 weeks ago.

corrado33

I often spin out of my bikes that have 53-12 or 53-13 gears. I've considered going to bigger chainrings. For me it's NOT easier to replace the "cassette" mainly because the bikes are classic, and they don't make freewheels with smaller gears than 12 or sometimes 13 tooth. There are many long drawn out hills around me that I'll cruise around 30-33 MPH for 10 miles or so. Sometimes with wind I can hit sustained 35 for a few miles. It's nice to be able to pedal at slightly normal cadences when going that fast instead of pedaling furiously.

OP: Yes, as long as the BCD is the same you can replace your chainring with something bigger. If you go too big you may run into problems with either of your derailleurs not being large enough to accommodate them.

corrado33

This doesn't make sense to me.

Those calculators ARE accurate. When pedaling with a certain gear ratio and at a certain cadence, the wheel WILL be turning at a certain rotational velocity. Add in a wheel size and you have a bike speed. It's simple gear ratios.

Wind, weight, and air resistance have absolutely nothing to do with it. Sure, those factors will affect how quickly you, as a human, can pedal, but that doesn't change the fact that if you are pedaling at a certain cadence, in a certain gear, with a certain wheel size, you WILL be traveling at a certain speed. There is NO ambiguity other than the slight differences between tire sizes(23c vs. 28c have slightly different diameters), which some calculators even account for.

indyfabz

+1.

jefnvk

Once you know gear ratio and tire size, you know how far the bike travels with every pedal rotation, therefore you can determine speed at a known cadence.

Whether or not the cyclist can maintain that cadence due to fitness and environmental considerations is beyond the scope of the calculator. When that bike is in that gearing at that cadence, it will be traveling that speed.

fietsbob

IMHO, pedaling down hills is just not that important.

ksryder

He didn't ask if anyone thinks he *should* replace the chainring, he asked if he *could*.

As long as the BCD is the same, sure. Probably.

Iride01 

Well the OP said he was spinning out on slight downhills. So the suggestion to replace the rear cog seems a good choice to me. It is the cheaper alternative for most people with cassettes. We have no idea what gear the OP uses the most. So to say that the OP would be cross chained because of that is of little significance. Sometimes you just have to be cross chained. For the time it takes to get to the bottom and decelerate it's of little consequence.

Cross chaining isn't a bad thing if your setup will let you do it with out making noises.

It also is not wrong to suggest other remedies just because the OP asked about a specific one.