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From 53/39 to 49/39?(17 posts)

From 53/39 to 49/39?schimanski
Jan 6, 2003 2:55 AM
I've been playing with Sheldon Brown's Gear Claculator for a
couple of days and have decided to change from 53/39 chainrings
to 49/39. As I see it this change would give me more useful gears
and get rid of ones I have no use for.

I currently have 12-25 cogs and would be going for Ultegra 11-21
with the 49 chainring. I have never ever needed to be on 39x23
and certainly not 39x25 so it would be nice to get rid of these.

Is there a reason why I shouldn't be going this way with my gearing?
Will there be other factors besides IMHO improved gear range?
Will the 49 chainring be causing chain rub somewhere I can't think of?
The chain angle should be less severe for 49x19 than it is for 53x23, correct?
What about front derailleur with 49, will it rub with the chain where 53 didn't?
Will 39x13 be usable? What about going as low as a 48 up front?

OK, I'm done.

Answers from people who've done something similar
with their setup would be highly appreciated.
reduced range...C-40
Jan 6, 2003 6:09 AM
Apparently you ride on pretty flat terrain. The change you are proposing does not change your top gear.

You would get the same effect from changing to a more common 53/42 or a 52/42 chainring combo and a 12-23 cassette. You should be able to use all cog and chainring combos expcept the 53/23 and 42/12.

The 49/19 combo that you're proposing won't be any less extreme than your current 53/23. It's still the large chainring and next to largest cog.

The primary effect of changing from a 14 tooth chainring difference to a 10 or 11 tooth difference is the number of cogs that must be shifted after you shift from one chainring to the other. With the larger difference, a 2-cog shift is generally made. With a 10 tooth difference, only a 1-cog shift is generally required.

The larger chainring difference became popular with the introduction of indexed shifting that makes precise, multiple cog shifts quite simple.
plusDougSloan
Jan 6, 2003 6:53 AM
The 49 you find likely will not be pinned and ramped for smoother shifting. Your stock 53 may shift better.

I agree with going with the 53/42 and 12-23 in instead. It might be slightly heavier, but then weight does not appear to be an issue for you.

Nonetheless, a 42 and 39 are almost exactly the same, but with one cog difference in the rear. Run the numbers and you'll see it. Same is true for a 53 and 49. They are almost the exact same gear ratios, just one higher and one lower at the ends of the range. YOu can run the numbers here: http://www.midcalracing.com/gears.xls


Bottom line: You just want to leave it alone. You don't really gain anything changing.

Doug
Thanks. Still a couple of questions...schimanski
Jan 6, 2003 3:41 PM
Thanks for the answers.

Seems I was only too excited about shaving a few grams, that it never occured
to me to check the effect of a 42 chainring. The thought simply didn't cross my
mind at all. Wow.

Interesting though with the 42 I'd be getting pretty much the things I wanted from
that 49 chainring. Makes me think. How much is the indexing likely to be worse with
the 49 than a 53 and what gears are most likely to suffer from poorer shifting if
I decide to go for the lighter version?

What I mainly want from this change is to get higher gears for the smaller chainring
so I can ride easy rides from there. I like to spin rather than mash and when the
average speed is below 35km/h, I currently don't need the 53 at all. I kind of want
to go to the big ring only when serious speed increase is needed. I don't know if this
makes any sense but I guess with the kind of climbes we've got around here, I hate to
have a 25 or a 23 back there for nothing. There are a couple of nasty ones but they're
very short, the longest serious climb I know is around 400 meters with highest gradient 13-15%
and this for only a couple of meters.

More middle range gears is what I want instead of real climbing gears.
How about 53/42 plus 13-23Kerry
Jan 6, 2003 5:10 PM
You get a 13-19 straight block to cover the range well in the 53, which is both lower friction and lower wear than running the small ring. If you "need" a 53/12 (nearly 38 mph at 110 rpm!) then consider a 12-21, still getting that straight block. You can't get gears closer together than that!
I agreeDougSloan
Jan 6, 2003 8:21 PM
either one would work; at some point, we start talking about differences that are more esoteric than real. I think anything close would work fine.

Doug
the ideal set up?colker
Jan 7, 2003 7:22 AM
53/42 and 13/26.... you can climb, you can spin, you can't mash though.
thanks for all the suggestionsschimanski
Jan 8, 2003 8:01 AM
Lots of good advice and interesting suggestions here.

I'm not all that made up with my mind anymore and I guess that's what I was
looking for, to question the first and 'such obvious' choice I came up with.

I'll be banging my head against the wall here for a couple of days to get some sense into it until I make the final call...
whatever that may be.

Thanks.
nothing is permanentDougSloan
Jan 8, 2003 9:48 AM
I've tried dozens of things like this. Sometimes what you think might be a perfect solution has some hidden flaw that sends you back to square one. I guess all we can do is to help avoid a few blind alleys we've been down. Nothing wrong with experimenting.

Doug
re: From 53/39 to 49/39?Funston
Jan 7, 2003 7:56 AM
I have a 50/39 on one of my bikes, and this year I'm going to try it out in some crits. THe gear ratios in the big ring are closer together, and the first race of the year finishes up a hill where I'm betting the closer ratios will work to my advantage at the finish.
not quite...C-40
Jan 7, 2003 8:44 AM
Changing to a 50/39 does not make "the ratios in the big ring closer together". The spread between ratios in a given chainring is governed by the cogs.

If you have to switch from the big ring to the little for an uphill finish, the only difference is having to shift one cog instead of two after the chainring shift. With indexed systems (especially campy) a two cog shift takes a fraction of a second. Shouldn't make any significant difference.
yeah, my bad, but...Funston
Jan 7, 2003 5:52 PM
You correctly corrected me on the phrase, but what I wanted to say was that the final drive ratios (or whatever the bike world term is) would be closer from gearchange to gearchange with a 50 ring, differences that would best be noticed while climbing and while shifting under full-bore power and speed conditions which is where I expect to find myself as I'm blowing around the final turn at 30mph and begin the last several hundred yard climb to the finish line. That's going to be run in the big ring.
a 50...schimanski
Jan 8, 2003 8:08 AM
Should be interesting with that 50.

I'll be doing the numbers for a cassette I'd like for a 50 chainring since Dura-Ace/Ultegra
do have a 50 on offer. Though I'm still undecided which way I'll be going.
Which cassette are you going to be using with yours?
Funston
Jan 8, 2003 7:35 PM
Hey shimanski, did you ever play football cause that's a classic name for the sport, expecially when you gotta grit whatever teeth are remaining in your mouth and focus on smacking the stinking slimeball crouching opposite you within the next two seconds, all the while a freezing rainstorm is raging above your bodies and cold, wet mud is ooxing between your sprained and taped up knuckles...

I'll use a 12/23 in this crit race. You gotta look at what your strengths are, what your weaknesses are, and how all that will match up with the road you'll be riding. Then make your choice.
Racing is not the same at allLC
Jan 8, 2003 1:27 PM
Racing is different than just riding because if you have to slow down to shift your front ring then you are at a disadvantage. In the final lap all it takes is just a momentary hesitation and your out of the race. Really in any lap, anyone that had to shift to the small ring was done for. I used a 50T last year on hilly crits, but if there are up hills then there are down as well. You are going to need a 11 cog so you don't spin out.

The other way to accomplish the same thing with a 53T (which is what I plan to do this year) is instead of a 12-23 is to use a 12-25 instead. Keep in mind that because you don't want to cross it all the way over your only going to use the gear next to the largest so your really going from a 21 to 23.

I would not worry about all this going into the finish even if it is uphill, since you will be in a higher gear than think if your in the front part of the pack. I would do most laps grinding the hill in 50x21 or even 50x23 after a hard attack, but for the finish I would use about 50x15 and hardly feel the hill with all adrenaline. BTW, if you blow up in the last lap before the hill, then even the 39x23 feels hard and you will barely be able to turn the pedals over ;)
Sweet 16Funston
Jan 8, 2003 7:40 PM
12/25s don't have a 16 cog. Having a 16 cog is more important to me than a 25 cog in this race because the hill is only around 2-300 yards long with the rest of the course pretty flat. As its a crit, I'll be doing it arount 15 or so times, and a 12/23 is just fine.
Not so fast!LC
Jan 8, 2003 10:50 PM
11/23's don't have a 16 either and with a 50T chainring you need the 11 or your going to be in more trouble down hills when you get over 40 MPH which is often seen in crits that have hills. At 40 MPH in a 50x12 you need to do over 120 rpm, which is going to waste alot of energy.

Of course you could put on a 11/21, but that kind of defeats the whole reason for the 50T in the first place.