Running a compact crank on a tri bike (Page 2)

UWMadTri - 2010-11-04 2:17 PM

Good point. I was running an 11/23 with my 50 and a 12/27 with my 53. For flatter races, I toss the 11/23 with the 53 now. Didn't even think about that. Not an absolutely enormous difference, but still significant.

Dave Luscan - 2010-11-04 1:13 PM Here is an even easier rule of thumb with no power knowledge required:

You should use all of the gears on your bike. So the biggest climb you regularly see should have you in your smallest gears. The biggest descent should find you in your biggest gears.

If most of your riding finds you towards one end of your total gearing range or the other, consider some gearing changes. 

the bear - 2010-11-04 8:03 PM

I rarely use all my gears, the ones on the ends stay shiny and new. But then a hilly ride for me has total climbing elevation of 50 feet.

dalessit - 2010-11-04 1:15 PM

Another good way to think about it is how many times do you wish you had a bigger gear going down hill vs. how many times have you clicked and then looked down at your casette just to check for the 5th time to make sure there aren't any more gears left when you're going up a hill.

tri808 - 2010-11-04 7:24 PM

Hard to believe that you spin out on 50/11 and not on 53/12.   Being that 50/11 is a bigger gear than 53/12

UWMadTri - 2010-11-04 7:48 PM

I clearly got faster. :p

tri808 - 2010-11-04 9:24 PM

Hard to believe that you spin out on 50/11 and not on 53/12.   Being that 50/11 is a bigger gear than 53/12

JohnnyKay - 2010-11-04 1:18 PM

Yes, I've only managed to go about 52mph downhill on mine.  Really sucks.

UWMadTri - 2010-11-04 1:25 PM I've personally found that compact cranks leave me spinning out on descents and with plenty of gears on the cassette for the worst (read:best) climbs that I encounter. My typical cadence is around 90-95 and my power numbers are well within my FTP ranges.

Here's a nifty calculator that lets you toy around with some gearings with the related speed output.

http://home.earthlink.net/~mike.sherman/shift.html

GoFaster - 2010-11-05 3:43 AM So if you're running a compact crank, is an 11-25 the way to go to get the best of both worlds (top and bottom end)?

otee453 - 2010-11-04 8:26 PM

You can pair a compact crank with a high geared straight stack cassette (11-23) and have more top and bottom end than a wider spaced cassette (12-26) paired to a standard crank/rings.
And IIRC, you have one or two fewer duplicate gear combos with the 11-23/compact setup. 
Put the calculator to it.

GLC1968 - 2010-11-05 12:50 PM

I would like to mention that I can spin out on a 52-12 combo on a flat on my road bike...so tucking and coasting wouldn't do anything but bring me to an eventual stop.

JohnnyKay - 2010-11-05 7:03 AM

Not to muddle with your decision anymore, but to do so means you are likely travelling over 30mph on the flats.  That's not impossible, but it is hauling and I suspect you don't do so regularly.  Regardless of what combo of crank, wheels, cassette you are riding, I suggest you get more comfortable at a wider range of cadences.  We all, of course have our "preferred" cadence, but it is good to be able to move that around for a time when conditions warrant.

And the effect likely won't be that significant in moving to a tri bike as you'd be down in the drops at those types of speeds in a road bike anyway.

GLC1968 - I would like to mention that I can spin out on a 52-12 combo on a flat on my road bike...so tucking and coasting wouldn't do anything but bring me to an eventual stop.   Again, I know my case is different since I'm on 650's, but I wanted to point out that I wasn't talking about a downhill situation.  I am making the assumption that this would be even worse on a TT bike that is going to be significantly more aero.

mjengstrom - 2010-11-05 10:11 AM

Out of curiosity, what does spinning out mean to you and how long can you do this for?

Even with your 650's, a cadence of 100 is still over 31mph and a cadence of 120 is almost 38mph.  That is very impressive, especially if this is done at or below your LT.

tri808 - 2010-11-05 10:06 AM

I agree.  Don't let your short term capabilities decide what gearing to get.  I've spun out 50/12 on my road bike going 38 mph on the flats with a tail wind...but I can only hold that for a few seconds...and with a strong tail wind.  That doesn't mean I should be riding a 53/11 top gear for all of my normal riding.  As a previous poster mentioned...that's what the pros ride...and I'm far from that.

GLC1968 - 2010-11-05 1:21 PM Actually, with 650's and a 90rpm (my average), that puts me at about 28.4 mph according to the calculators and yes...I can do that or faster easy enough (yes, in the drops).  I don't maintain it for more than 10-20 minutes at a time yet (except in a paceline), but I'd hate to be in a race and be limited by my bike.  You are right that if I work on my cadence, I can do better...but this is just giving me an initial guideline so that I can choose the right combination for my new bike.

A 50-11 combo gets me 5 more gear inches and a 29.8 mph speed.  The 53-12 is still only 2 gear inches better than the original combo and a 29.0 mph speed.

Frankly, I was surprized at how large a difference the 650's made compared to 700.  I should have looked at this a long time ago!

GLC1968 - 2010-11-05 7:21 AM Actually, with 650's and a 90rpm (my average), that puts me at about 28.4 mph according to the calculators and yes...I can do that or faster easy enough (yes, in the drops).  I don't maintain it for more than 10-20 minutes at a time yet (except in a paceline), but I'd hate to be in a race and be limited by my bike.  You are right that if I work on my cadence, I can do better...but this is just giving me an initial guideline so that I can choose the right combination for my new bike.

A 50-11 combo gets me 5 more gear inches and a 29.8 mph speed.  The 53-12 is still only 2 gear inches better than the original combo and a 29.0 mph speed.

Frankly, I was surprized at how large a difference the 650's made compared to 700.  I should have looked at this a long time ago!

tri808 - 2010-11-05 2:34 PM

I take back everything I said...carry on.