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Good gear calculator
 

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Nick Payne
Joined: 10 Jan 2004
Posts: 2331
Location: Canberra, Australia

3/25/18 3:46 AM

Good gear calculator

Discovered this rather nifty gear calculator that has lots of nice features:

http://ritzelrechner.de/

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Craig
Joined: 12 Jan 2004
Posts: 528

3/25/18 5:24 PM

I was going to reply with, "oh yeah? I bet the gear calculator I use is better than yours!" and then clicked the link and, well, that's the one I use too. It's great. I especially like the "speed at a given cadence in a given gear" scale. And the "compare two setups" toggle is great too. It's a gooder.

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Sparky
Joined: 08 Dec 2003
Posts: 16237
Location: Portland, OR

3/25/18 6:34 PM

I've been using the same, albeit highly modded, spread sheet for 15 years.

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KerryIrons
Joined: 12 Jan 2004
Posts: 2891
Location: Midland, MI

3/26/18 2:51 PM

HP 11C

My gear calculator can deal with any possible combination of wheel diameter, gears, and cadence. It's called an HP 11C calculator and some basic knowledge of how things work. And when I change tires from 23 mm to 25 mm I can adjust my gear calculator to maintain full accuracy.

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Anthony Smith
Joined: 12 Jan 2004
Posts: 835
Location: Ohio

3/27/18 7:00 AM

Don't need a spreadsheet

Chainring divided by cog times wheel

ie 52 divided by 15 times 27 equals 93.6

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Sparky
Joined: 08 Dec 2003
Posts: 16237
Location: Portland, OR

3/27/18 7:53 AM

Unless you want to calc GI steps relation or my fields in SS for the Automatix hub for front and back rings quickly.

Of course the more you use the crutches the faster the simple math escapes memory. :)

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daddy-o
Joined: 12 Apr 2004
Posts: 3012
Location: Springfield

3/27/18 9:35 AM

ie 52 divided by 15 times 27 equals 93.6

ie Breaking the hour at 90 RPM

Somehow I don't think I'm the only one who made that calculation 40 years ago.

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Sparky
Joined: 08 Dec 2003
Posts: 16237
Location: Portland, OR

3/27/18 9:39 AM

28 technically, no?

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 3953
Location: Nashua, NH

3/27/18 10:50 AM

Yes and No

While 700c wheels are often referred to as 28"(the reason why is anybody's guess), with typical road tires they're actually less than 27" in diameter. If you've put 700c wheels on a frame built for 27" wheels, you have to lower the brake pads.

I played with the calculator a bit and noticed something surprising and interesting. Switching from 25mm to 40mm tires using the gearing on my gravel rig only made a 1" difference at the low end, but almost 4" at the high end (46/30, 12-32 11 speed). If is wasn't such a pain to create custom Shimano cassettes, I'd be tempted to dump the 12 outer cog for a 13 and add a 17 in the middle.

Although I usually just use a very simple spreadsheet for mapping gearing, that tool is useful for doing quick comparisons like this.

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Sparky
Joined: 08 Dec 2003
Posts: 16237
Location: Portland, OR

3/27/18 11:51 AM

Screen Cap of what my SS has DE-evolved to:

Bright green cells A/B columns last added formulas for the Automatix hub 2x ratios.

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Steve B.
Joined: 19 Jan 2004
Posts: 684
Location: Long Island, NY

3/27/18 3:20 PM

So what's 25mm tire on a 700C rim ?.

Annoying and I'd rather just use Sheldon's


Last edited by Steve B. on 3/27/18 5:45 PM; edited 1 time in total

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Sparky
Joined: 08 Dec 2003
Posts: 16237
Location: Portland, OR

3/27/18 3:37 PM

They vary a lot, mine are 2140..

The difference from 23mm=2100 to 28mm=2150 is one GI at most on most gears. It is really the MPH per RPM fields I spy most when calculating personally.

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 3953
Location: Nashua, NH

3/27/18 3:42 PM

I've never bothered with development or speed at a given cadence; gear inches tell me all I need to know. I hadn't bothered trying to compensate for tire size either, as I really only care about the effect at the low end and it doesn't make much difference there. A 1" difference is not going to make or break a ride.

If I want a quick approximation of speed, I just multiply the gear in inches, times the cadence, times .003 (or if I'm doing in in my head, times 3, then back up the decimal point 3 places).

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Sparky
Joined: 08 Dec 2003
Posts: 16237
Location: Portland, OR

3/27/18 3:59 PM

"then back up the decimal point 3"

I never thought about that, not sure why being I do most math in my head normally. This last year playing with 14-28 cassettes etc, I spy the top gear MPH/RPM to see if I want to see the 108 GI spin out speed. ;)

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dan emery
Joined: 11 Jan 2004
Posts: 5887
Location: Maine

3/27/18 5:44 PM

My gear calculator

If pedaling is too hard, I shift to an easier gear, and vice versa.

Really, do you guys find it helpful to know the speed at a given gear and cadence (that is when you're not training for the world hour record).

About once every 8 years I might want to know the gear inches of something like a 46/12 or 42/11 but I don't needs a spreadsheet for that. But if you need to know the difference with a 25 or 28 tire, by all means go for it!

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Sparky
Joined: 08 Dec 2003
Posts: 16237
Location: Portland, OR

3/27/18 5:52 PM

Dan, you obviously have either gotten past being a control freak, or maybe just never gave enough of a shit to be one in the first place. ;)

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 3953
Location: Nashua, NH

3/28/18 5:44 AM

For comparison only

I calculate gearing mainly so I can compare variations with each other. In particular, I can figure out comparable gearing with different cranksets I own (53/39, 50/34, 46/30, 39/24) when I'm setting up bikes for specific types of riding. As I mentioned earlier, I'm generally only concerned that the low-end gearing is sufficient for the purpose.

As for speed, it's only relevant when I'm on the bike and the Garmin takes care of that.

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Anthony Smith
Joined: 12 Jan 2004
Posts: 835
Location: Ohio

3/28/18 8:27 AM

tires

Measuring the tires becomes important if you are interested in minutia or have to meet a rollout.

For example with a 49x15 my track bike rolls out to just under 88" with Vittoria Corsa Evo tires labeled 700x21, but rolls out to only a shade over 86" with Vittoria Pista Evo tires labeled 700x22. Yes you read correctly and I have no explaination. Tire pressure also makes a difference in rollout. As a junior (more than 40 years ago when the limit was 93.6") I could use a 53 on the front and make rollout as long as my rear tire pressure was under 90 psi, so I would always pump it up to 85 psi, go to rollout, then inflate it to 120 prior to the race which gave me almost 95", then let some air out on the cooldown lap since many events had post race rollout if one placed in the money. Since the racing at Lexus Velodrome has a restriction of 88" I can go to a 50 ring and still meet rollout with the track tires but not the road tires.

On the road with normal applications, this difference is so small it shouldn't make any difference at all.

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Brian Nystrom
Joined: 26 Jan 2004
Posts: 3953
Location: Nashua, NH

3/28/18 12:15 PM

I would assume that track-specific tires are going to have much thinner tread than road tires (for less squirm/better control), hence the potential for them to be smaller in diameter. Tire companies are notorious for not being particularly accurate on their stated sizes and unless you have the same rim and know what pressure they used, you're likely to get different results even if the tires were actually measured accurately by the factory.

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KerryIrons
Joined: 12 Jan 2004
Posts: 2891
Location: Midland, MI

3/28/18 4:59 PM

Actual diameter


quote:
28 technically, no?



No, no, no. On a Velocity Aerohead rim, a 23 mm Conti GP 4000 gives a 26.25 inch diameter. On a Velocity A23 a 25 mm Conti GP 4000 gives 26.45 inch diameter.

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Nick Payne
Joined: 10 Jan 2004
Posts: 2331
Location: Canberra, Australia

4/18/18 8:27 PM

Here's a spreadsheet I've used for many years. Allows comparison of two different setups, and gives gear inches, development, and kph at a specified cadence for each gear. For those living where mph is used instead, just modify the kph formula to divide the result by 1.609. Sheet is in OpenOffice/LibreOffice ODS format, but Excel (for the last ten years at least) has been able to read ODS files.

https://www.dropbox.com/s/3vf2umc7p1cacjv/gears.ods?dl=0

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Sparky
Joined: 08 Dec 2003
Posts: 16237
Location: Portland, OR

4/18/18 8:59 PM

Nick, that 'IS' the one I use, with a ton of mods and additions over 20 years basically.

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