Crank gears and cassette upgrade? Newbie with grand ideas

[uffstuffson]

Just purchased a CAADX disc 5 105 a few months ago, love the bike and love cycling so far. I originally thought I would be doing more trails and off-road/cyclocross with it however have been doing mainly roads and paved trails. It's come to my attention that I am spinning out around 38.5-40mph with a decent amount of hill left in front of me. Soo, I'm wondering what I should be doing as an upgrade? I made a spreadsheet comparing a few different crank gear set ups and cassettes. Currently I have FSA Gossamer BB30 46/36 crank gears and a Shimano Tiagra CS-4600 28-12t cassette. I think I understand the gear inch numbers but I'm not sure how they translate to say how hard I would have to push in my bottom end to get up a steep hill. Currently my bottom end 36x28 is 34.9 gear inches and top end is 104.2 gear inches. This is calculated off of Sheldon Brown's gear calculator. If I were to upgrade to a 50/34 crank set and 25-11 cassette my bottom end would be 37 gear inches and top end would be 123.5 gear inches. How much would I notice the extra 2.1 gear inches in the bottom end? Would I regret it on a hilly ride? Would I be killing myself in some grueling up hills? Another option going even further would be a 52/36 crankset and keep the 28-12 cassette (bottom 34.9 gear inches. Top 117.7 gear inches) or change the cassette to the 25-11 cassette (bottom 39.1 gear inches. Top 128.4 gear inches). My dilemma is how much harder will it be to make it up the same hill with the extra 2.1 - 4.2 gear inches in the bottom end? How much of a difference in the top end will I notice per extra gear inch? Here is a summary of the spreadsheet Current crank, current cassette: top - 104.2 GI Bottom - 34.9 GI 50/34 crank, current cassette: top - 113.2 GI Bottom - 33 GI 52/36 crank, current cassette: top - 117.7 GI Bottom - 34.9 GI Current crank, 25-11 cassette: top - 113.6 GI Bottom - 39.1 GI 50/34 crank, 25-11 cassette: top - 123.5 GI Bottom - 37 GI 52/36 crank, 25-11 cassette: top - 128.4 GI Bottom - 39.1 GI Spreadsheet: https://docs.google.com/spreadsheets/d/1-fEPabp2yfNTLXYt7RiCPyn0nC3vgNR3AjY0hzBRNOA/edit?usp=docslist_api Maybe I'm looking too far into it lol. I pretty good at doing that. Thank again everyone! Brent

 

[dabac]

46 to 50, that's about a 10% increase. If you're currently spinning out at 40 mph, then - your legs allowing - you should get to 44 mph. 12 to 11 is about 8%. Change that too and you might make it into 47 mph. 46 to 52 and a 12t smallest, maybe 46 mph. 11t smallest, you might break 50. While this can boost your speed thrill and bragging rights, don't expect any practical improvement outside a race setting. The reason being the time spent in that speed bracket is such a small fraction of the whole ride. Being 20% faster during, say 2% of the ride is only likely to shave seconds of your time. The 34/46 and a 25t biggest will roughly lose you (a little more than ) your easiest gear. Try a few hills while not using the biggest sprocket, and see how it feels. 34/50 and a 25t biggest will be like climbing w/o the two largest sprockets. 34/52, w/o the three largest sprockets. With a 46t biggest ring your bike might have a MTB front derailer. And while opinions about how bad this is differ, they're usually not MEANT to work well with rings bigger than 46-48t. I don't find the gear inches particularly useful, I prefer the mph@100rpm setting. Since I know my lowest climbing speed it'll show if a bike is geared low enough, and if I'm spinning out it can also show what speed I can gain by shifting the gear range one notch higher.

 

[uffstuffson]

Thanks a ton for the information. I actually read this the other day but wasn't able to reply, which gave me some time to play around with the gearing on a hill like you said. I think I am going to go with the 34/50 crank and the 25-11t cassette. My LBS showed me a hand full of compact crank gear sets that will just bolt on in place of my current gears and work with my front deraileur. Currently I just have platform pedals which hopefully in the next few months I'm going to upgrade the crank gears, cassette, and pedals to clip less. My wife is going to kill me when I drop another $450-550 on the bike but oh well. Lmao. I was able to climb some pretty long/steep hills (the same I'm spinning out on going downhill) in my 46/28 gearing. Not that it was efficient but I was testing my limits. I almost had to secede and drop to the 34/28 my made it. My legs definitely weren't thanking me. Lol

 

[dabac]

Keep in mind that unless you are a track sprinter, bike riding is a Lot more about endurance than it is about strength. Unless you're a rare anatomical freak, you'll do best at an average cadence between 80-100. Pushing hard-and-slow is a lot more likely to cause knee problems than spinning light-and-fast. Dirty Harry quote:"do you feel lucky?" Do yourself a favour and get yourself a cyclocomputer with a cadence counter, make sure you're not establishing any bad habits that'll come back and bite you later. You can get your clipless pedals now already. Pretty much all bikes apart from ones with one-piece Ashtabula cranks take the same 9/16" pedal thread. The gearing you're suggesting is pretty close to what's on drop bar road bikes with compact cranks. Just keep in mind that those bikes are meant to work for group rides, which thanks to improvement aerodynamics and shared effort, are a fair bit faster than solo rides. Don't get into the habit of grinding it out! Stamina and fitness should be your Focus, not strength.

 

[AyeYo]

I think it's pretty safe to assume he's not a grinder if he's successfully spinning a 46/12 to 40mph. My 50/12 is useless for me after 35mph, which according to this awesomest of all bike gear calculators, is about 110rpm. A 46/12 at 40mph is like 135rpm. That's impressive spinning, especially with platform pedals.

http://www.bikecalc.com/speed_at_cadence

 

[dabac]

I think it's pretty safe to assume he's not a grinder if he's successfully spinning a 46/12 to 40mph.  My 50/12 is useless for me after 35mph, which according to this awesomest of all bike gear calculators, is about 110rpm.  A 46/12 at 40mph is like 135rpm.  That's impressive spinning, especially with platform pedals. http://www.bikecalc.com/speed_at_cadence

But that was during descents. Doesn't say much about how he handles the flats.

 

[uffstuffson]

I do very much appreciate the advice and guys like you looking out for us newbies. Thank you for that, dabac. I don't normally push like that on flats or if it can be avoided on up hills. I do prefer using my gears to my advantage. That's what they are there for after all, isn't it? I've never really attempted a push quite like that one so I was curious how I could handle the situation if it arose. That was my main reason for that experiment. I figured I would be more likely to encounter a scenerio where I would have to push that hard if I upgraded to the 11-25 cassette. If I couldn't handle it there would be no reason to even entertain that idea and I would just have to accept the 12-28 cassette advantages and disadvantages. I do very much wish I had a computer that I could track my cadence, speed, and time. For now I am using a combination of strava (highly inaccurate speed - according to strava I should be in the damn Tour de France lmao), endomondo, and a friend of mines speedometer/computer. Comparatively, endomondo is fairly accurate when it comes to speed. I don't necessarily trust it that much though. The 40ish +/- MPH was calculated off a combination of endomondo and my comparison to the friend with the computer. Endomondo said 38.5 mph, his computer said 39.1 mph and I was increasing the gap between him and I. So my closest guess is somewhere between 38.5 and 40mph. I'm glad to hear I'm doing something right and impressing someone lol. I don't have much of a baseline to compare how well I'm doing since I'm pretty new at this. As a side note, anyone have any recommendations for a computer? I may be using the wrong terminology. I'm comparing it to my dive computer for scuba diving and just throwing throwing that verbiage in there, right or wrong, lol. Any correction in terminology is much appreciated. It might help me hide my newbie-ness a little better, lol.

 

[uffstuffson]

Oh, and the clipless pedals! I would love to have them right now. My wife may murder me in my sleep though if I dropped the money on them right this moment, lmao.

 

[AyeYo]

What makes you think Strava's speed is inaccurate? If you have good GPS signal for the entire ride, Strava's speed should be very accurate.

Since you're looking to track a lot of info with the computer, I'd skip the standard computers and get entry level GPS headunit like the Magellen Cyclo 105. Those go for $150 or less and do everything you're looking for and more (you will have to buy a cadence sensor separately).

http://www.magellangps.com.au/Products/Fitness/Cyclo_Series/Cyclo_105

 

[uffstuffson]

For any distance above about 10mi I use endomondo and strava simultaneously. For some reason strava has a tendency to give me a higher max speed by a few miles per hour than endomondo. I've compared multiple rides with my friends computer and endomondo is usually with less than 1mph different which could be just out difference in speed. Here are screen shots of the exact same ride which I was able to compare to my friends computer.

Distance and average speed they are usually very close but max speed I've noticed can be wildly different between the two apps. I'm not real sure as to why. Endomondo seems to calculate calorie burn much higher than strava as well. Not sure the algorithm they are using but I use a HR monitor that syncs up with both while I ride as well. The only explanation I have been able to justify for the max speed deviation in my head is maybe endomondo marks gps waypoints more often than strava? Not sure if that would cause the deviation in max speeds or not. Comparing the timeline and ride I know the exact hill I hit my max speed on, it was fairly obvious lol. There was only one large hill during the ride.

 

[uffstuffson]

Although here is a ride they matched up fairly closely on. This is a ride through the hilly area I usually wind up spinning out on and where I did that experiment. This was not the day I was experimenting though.

 

[uffstuffson]

Please excuse my ignorance but I saw the unit gets mounted to the rear wheel, how does it measure your cadence? Does part of it get mounted to the crank arm or something? Here is the sensor I matched up with the Magellen Cyclo 105 through their website. http://www.magellangps.com.au/Products/Accessories/Accessory_List/Speed_and_Cadence_Sensor

 

[AyeYo]

I wouldn't worry about max speed too much. Average speed is far more relevant for progress and training purposes. For some reason, all online ride data analysis programs vary greatly in their results, even within the same program. I've gone on rides with friends all recording with Garmin GPS units and after upload to Strava we have average speeds that differ by up to 0.5mph and elevation gains that differ by up to 1,000+ft. Unfortunately that just seems to be normal margin of error for these type of devices and programs. I'd agree that it most likely has to do with GPS position update intervals.


The speed/cadence sensor mounts on the drive-side chain stay where it sits between magnets that are on both a wheel spoke and a crank arm. Also, you don't need to buy the expensive Magellen unit. Any ANT+ compatible sensor will work, like this one:

http://www.amazon.com/Garmin-Speed-Cadence-Bike-Sensor/dp/B000BFNOT8

 

[maydog]

Here is another way to look at descending.

A 150 pound rider, in the drops coasting down a 8% grade will top out at about 40mph. I that rider puts 200 watts to the ground, he gets to 43.5 mph, 500w gets to 47.5mph. If you were to go for the gusto 800w will get you to 50.7mph. Quadrupling power from 200 to 800 nets a, short lived, 27% increase in speed.

On the flat, 200w gets you to 21, 500w gets you to 30 and 800w get you to 35. Quadrupling power get you a 67% increase in speed

Going up that 8% grade, 200w = 6.5, 500w = 14.8 and 800w = 21.2. Quadrupling power gets you a 326% increase in speed.

Being able to push big gears and lay down the power on a descent increases speed by a small margin. It may be worth the effort to change gearing if you have long downhill courses, but even then you will gain more speed just by improving your aero tuck.

Judging by your ride data, you are not spending a lot of time going downhill and based on you average speed are not really being limited by the gearing's top end.

 

[dhk2]

Good stuff maydog. You've clearly illustrated why pedaling downhill at speeds over 40 mph is a waste of effort. Rather than trying to put out 200 watts or more, I believe most of us recreational riders can gain that 3.5 mph just by geting into a good aero tuck anyway. I vote for coasting, watching the road ahead and enjoying the free speed.