Road Fan

Well, gear phreaking as I call it has a long history. I recall going into a very old LBS back in the '80s when I lived in Denver and starting to ask how do I optimize my gearing, and as the tech spoke he was intuitively selecting cogs off the wall rack and starting to fit them together for me. Easier for him to think in hardware than in abstracts! BUT, that was near 30 years ago, and the shop had been there at least 30 years then.

The best references on it are IMO Frank Berto's old Bicycling Magazine articles, his book "Upgrading your Bicycle," and Dick Marr's book "Bicycle Gearing." Berto and Marr both go into all the details of how to calculate whatever is needed.

Dunno what your math skills are, but being an engineer and former math tutor, I swim in this stuff like a math fish.

To design a half-step you have to pick some initial constraints. If your constraint is the cogset, great! count the teeth and make a table listing the tooth counts in ascending order. Take a basic calculator and for each step, divide the bigger one by the smaller one to get the ratios for each pair. Ie,

13
15 ratio = 15/13 = 1.151
18 ratio = 18/15 = 1.200

et cetera.

We'll take it up from there (next lesson? LOL!!!!). The first question is, what is the average incremental ratio and how evenly are the tooth counts spaced?

Grim

Took a quick look at a couple Suntour sets I had stashed today. I have a 14-16-18-23-28 32 and a 14-16-18-21-26-32. I think that's right. looks weird now that I see it in print.

I also have another compact free hub that I could mix and match. Didn't pay attention to it but thinking about the road wheel it came off it may be a 13-28 6 speed. Between the three loose and the one on the bike I can play around some.

Road Fan

Playing with the maths is one thing, but to engineer a working system you have to be aware of the physical limitations of your hardware. Again, I think you're thinking the right sorts of thoughts. Those 14-34's, they aren't the Megaranges, are they? The giant jump from the 6th to the 7th (usually from 25t to 34T might cause a problem.

But my previous note implied (I wasn't perfectly clear I guess) that a 14-34 7-speed would take you out of range of your intended 50/45, or at least to its edge. A 50/46 is might be a better choice in this case.

Can I post Excel spreadsheets here? Do you (and Thook) use Microsoft Excel, or actually any spreadsheet software. I think you need to model different designs and see how the gear spreads work out.

Road Fan

If you double -check the counts of all three of your freewheels I can put them in my spreadsheet and tell you if they're evenly spaced and even see if the shifts will jump evenly. Both you and Thook can benefit from looking at that.

thook

Thanks again, Road Fan. I don't have any spreadsheet type software........that I'm aware of. My computer's down and out and I'm relegated to limited use of my wife's computer and one at work on the weekend. Don't know what either contain or even how to use the software were it present.

Anyway, haven't gotten around to do doing all of my "homework" yet , but I did discover I have an SR crank 42/52 with the same BCD as the SR super custom 36/47/52.........the triple I'm wanting to go on my Perigee. I thought I'd be limited to stated ratio's until I discovered the 42/52. Soooo, I'd like to throw that 42 between the 36 and 47 and gear the freewheel to suit, if that's possible. That'll be my constraint there. It's my only other option with it. I usually find the 52 unusable unless I have a lot of momentum going and not much weight or incline to contend with. The 47 paired to the bottom cog is quite enough for a fast pace.

I've got some animals to feed and firewood to get to the house, but I'm going count that cassette and post it up. I'm really excited to learn this. Funny thing is I've been wanting to attune my mathematics skills for a while now. What a good excuse.

Later.

thook

Okay.....looks as if I actually have two HG cassettes to play with. The other.......third one.........is IG Shimano compatible only. So, the first HG cassette is 12-14-16-18-21-24-28. The second is 11-13-15-18-21-24-28.

Now, what I'm not understanding how the ratios between the two chainweels or the 7 rear cogs is obtained. I understand that the chainwheel ratio has to be half that of the cassette/freewheel progression, though. I could just use the gear calculator and have it done for me, but I'd like to know the math, eh.

So, either of the two HG cassettes and then I will modify the Sugino AT to suit. Hopefully with the high of 50. I mean, it's just such a pretty chainring, too.

My choices of chainrings: a 46, a 45, a 42, a 36, and it seems somewhere around here I think I have a 40. Couldn't locate it earlier.

Anyway.......teach?

thook

So, maybe I should read when I'm not tired.

The ratios for the first HG cassette:

12
14 ratio = 14/12 = 1.166
16 ratio = 16/14 = 1.150
18 ratio = 18/16 = 1.122
21 ratio = 21/18 = 1.111
24 ratio = 24/21 = 1.144
28 ratio = 28/24 = 1.166

The average is 1.143. So, the crank has to match half that = 1.0715? I'd have to go 46/50, then. Unless, I did 42/45. But, that 45........the only one I have... is an inner ring. Would look kinda odd though the gearing is optimal. Hmmmm.........will it make that much difference in the operation of everything? Given what you said earlier, you're probably going to say yes.

thook

Blah.....what do I do?

I guess I'll start playing numbers between the two cassettes and see what I can conjur.

Later.

BL4zD

Here's mine, but I don't know what the numbers mean other than they don't look like a half-step setup
14-16-20-24-30 | 52-42

Road Fan

Yes, but I need to check with the spreadsheet. Sorry I wasn't on before, had a class and choir rehearsal.

You are catching on to the math pretty well!

I can't really say if the 45 middle ring would work as an outer ring. But, what outer ring do you need? How high a gear do you need? I think previously you said you wanted to go 50/14? With a 700c wheel you'd get a 96 inch high gear, which means you'd travel 307 inches (multiply 96 times 3.14159) in one crank revolution (this number is called the development). To get that same gearing with a 12 tooth small, you need a 43/40. If you keep the 12 tooth small and the 50/46, you'll get a 112 inch big gear, with a development of 358 inches.

I'd suggest looking for a top gear between maybe 95 and 108 inches. That would cover your 50/14, 50/13, and the same with up to a 53 tooth big ring.

How do your other cassettes line up?

Roll-Monroe-Co

Will this help?

https://www.sheldonbrown.com/gears/

thook

I've got about 6 or 7 steno pages of calculations with different combinations of a number of the chainrings and freewheel or cassette cogs I have at my immediate disposal. I've not counted two other freewheels I have, and all the pages are at home, and I'm at work right now. So, I'll have to get back with that info tomorrow to answer your question.

Yeah, I've really caught on to the math part. I've even noticed how you can engineer everything to target ratios/gains at key areas (for lack of a better word) of the set up. For example, seems to me you'd want to keep the gain ratio transitions smoother/in smaller increments in the gears for cruising. That way it's easier to keep momentum. Seems when you're dropping in the low or granny gear/s it wouldn't matter so much. That is unless you intend to be doing a lot of travelling through hilly regions......like me and where I live. Maybe I'm wrong, but I think I'm seeing a trend.

Anyway, you've gotten ahead of me, teach. I hadn't figured gear inches, wheel size, development, or any of that into my figures so far. I've just been trying to match numbers between the cogs and rings. I mentioned the 5spd ProCompe freewheel earlier. Well, that mates perfectly with the SR 52/47/36 (or 47/42/36 combo) and the Sugino 50/45/28 (the original set up.....not the proposed 50/46/28). I do have a set of 700c wheels with freewheel hubs, but I wasn't looking to use them on the Lotus since the rims are narrower more suited for 28c down to 20c........not 32c's like I wanted to use on it. But, oh well. I can put some 30c's on them at some point and call it good for the Lotus. I plan on riding it mostly down highways and through towns with hill exposure and light loads...... just not alot of loading like with the Trek or the Dawes I'm wanting to build. With those I'd like to keep the ratios lower.

So, if I used the ProCompe freewheel with the 50/45....starting at 14 in back.....that would be in your recommended range, right? Well, I'm at a loss because I was hoping to get a 7spd behind that crank. But, I don't how I'm going to match a 7spd starting at 14 and get the same gain ratio as the 50/45. What.......end at 38 on the low? Lol!

To summarize again, for the 50/45 I have a freewheel of 14/17/21/27/32. What would I have to do to make that a 7spd and still make it work on 700c's? On, eventually, a width of 30c? Hmmm.....

Off to do some math, I guess. Later.........and, thanks.

thook

Well, after deciding the Perigee was just too big of a frame for me, I've rethunk everything. However, this thread was intended for pics of the builds, so I'm just going to start another thread.

See ya there............anyone.

Thanks.

happycheapskate

I found this forum looking for stuff related to "corncob cassettes" to go along with a discussion about the new Sram group (definitely not a cob.)

It has 2 front rings and a big-gap but even 11-32 10x cluster.

I like the classic stuff on here a lot. It was a real treat to see the Sturmey/Shimano custom bike. My first road bike had 52/42 and 12-25 6x. I hated it till I put a 39t on the front.

After that I've been a fan of closely geared triple cranks and 11-26 rear.

So is the aim of the half-step style group to avoid duplicate ratios, or to facilitate small changes to a driving ratio for slight grades? (a shift down and up with the front once on a light grade, instead of clicking a bunch of rear gears)

happycheapskate

Some posters had complained of thick front crank spiders that caused skipping. Its easy to file spiders down, esp with something to use as a measurement for preserving concentricity. But is the skipping (or chain stuck between cogs) caused by using two "outside" rings? Can you alleviate the problem by sharpening or shortening of any of the teeth, installing rivets as pickup pins, or dialing the outside ring to alternate existing ramps or pins?

John E

The problem is indeed that spiders have gotten wider over the years, to accommodate larger steps between the two outer chainrings. I get nervous about filing or grinding down the ears of the spider, because one has to be so precise to avoid chainring wobble. One partially satisfactory solution was to do a half-step-plus-overdrive, sort of half-step-plus-granny in reverse: 39-42-50. With a 2- to 3-tooth progression in back, this gave me 1.5 step on the two outer rings, half-step on the two inners, and crossover with a little somewhat acceptable redundancy between the outer and inner chainrings. THe only downside is the jump at the top end, where I would have liked an in-between half-step ratio.

Edoctus

Take 2. Hey Cyqlist - I was just Googling "The Low Gear Bulletin" and came across yours and other posts, plus the National Library reference, which seems to hold just #1 & #2. I joined the
Forum af few minutes ago to ask if anyone knows why Shepherd only published 2 bulletins? I joined his Low Gear Fellowship when he launched it, got Number 1 (September 1975) and Number 2 (December 1975) and didn't hear anything ever again, despite Number 2 promising some really interesting stuff for Number 3! I have shepherded (no pun intended) both my copies these last 35 years, and both are as pristine as the day I originally got them. I think I learnt more from Shepherd's two short Bulletins about gearing than anything I have read since.

balindamood

A couple of thoughts based upon my experience:

1). If you divide the range of the freewheel by the number of cogs, and number less than three will generally mean you need a chainring difference of 3. More than three generall means 4; and over about 3.5 means 5. This results in nearly all 7-speed clusters having only a 3 chainring difference on the front. This is better figured on a spreadsheed, but if you are daydreaming in a meeting, this seems to work.

2). Current availability causes a problem here. If we ignore TA, the only odd-tooth ring presently made that I know of (that is 3/32nd...not track) is a 45, so you are locked with either a 45 high, or a 45 low. Frankly, moving to half step with more than 7 speeds in the rear results in such a fine difference between gearing that I question its value. I see little use for a chainring larger than 48 tooth with a 7 speed anyway becasue you will be pushing a 13T or smaller anyway. 48/13 at 700C is about 99 gear inches which is useless unless you are a racing or have the desire pedal down really long, steep hills. Most of my riding with loads is between 40 and 70 gear inches. Depending upon the bike, I try to focus the center of the band in this area, with one additional cog up and down for hills (up or down)

3). I have had occational problems with chainrig differences of 4 or less where the chain rides along the top of the inner rear. This is a width issure which can be solved only by filing, bending, or adjusting the front derailluer and deliberate shifting.

4). Anything above a 6-speed you are in troublesome cross-chaining area such that it migh be advisable that the highest and lowest cog are half the difference of the others. e.g. if you were in the big ring and the 2nd smallest rear cog, the next shift would simply be to the smallest cog, rather than a double shift.

ricohman

Nishiki Continental.

Ruffinit

I've been preaching 1/2 step for years and have set up many bikes with it for others. My Bridgestone T700 came out in 85 and 86 with the HS+G on a 5 speed freewheel. Over the years and 50,000 plus miles, I've worn out a number of chainrings and freewheel cogs. I just collect Suntour, 600 and DA freewheels which work very nicely. I just pull them apart and build the ratios that I want. My very favorite setup is on the BS, which is 50/44/28 with 13, 14, 17, 21, 26, 34. I used the original derailleurs up until a few years ago which was friction shifted Deore XT Superplate rd with Deore XT fd (Stagheads). I switched to the Suntour XC Pro rear and kept the XT front with Sprint indexed shifters (downtube). I like being able to double shift with one hand.

Sixty Fiver

On a 20 inch wheel a 40 tooth chain ring is a granny and it gives me a low of 26 gear inches.

Range is 26-71 with that 40/48/53 and have swapped out the 5 speed for a 6 speed block which has a 14/16/18/21/24/28 and over a 100 mile test run found that I always had the perfect gear at hand save for speedy descents.

happycheapskate

I am still trying to understand what "half step" gearing means. I can see that the 2 front chain wheels are close together, but what measurement are you halving to choose the rings? I like the idea of avoiding duplicate gears.

Ruffinit

Half step is basically like having a high/low for each of your cogs on your freewheel. The number of teeth between each of the freewheel cogs is determined by your chainrings and given the total package you would have (on a 6 speed freewheel) 12 distinct non-duplicated gears which are evenly spaced. This gives you not just efficiency in your geartrain but a very smooth transition between gears. The "+Granny" or "+Alpine" equates to your third chainring which is small enought to give you a whole separate set of gears below the normal 12 (in this case). When completed you have 18 distinct gears.

khatfull

Wow, I'm glad I saw this thread as I have a new Fuji Touring Series III setup with half step. I started a thread myself on this but I thought I'd drop my info here to see what the obviously knowledgeable folks here think.

The bike is setup stock with 50/45/28 up front and a 14-28 on the back and the chart looks like this:



I came across a 14-32 6 speed freewheel at the co-op which I picked up because it was in good shape and cheap. Switching to it gives me this:



I believe that the former is a much better half step system...am I correct? If I'm going to try this I'd prefer to have it setup properly and with decent ratios from the start.

Thanks.

Ruffinit

Well, neither freewheel gives you a great setup for a 6 speed. For the cogs you have, you need to pull the freewheels apart and used the 14, 17, 21, and 28. You need a 13 and a 34. That way you could use 4 of your cogs anyway. BUT if you want to do it right from the start, go with 13,14,17,21,26,34.. Check that out with your calculator.

If you are already riding the bike, just make a note of the cogs you have and start picking up the ones that you need. I like the way Suntour freewheels work, but keep an eye out for the older Dura Ace and 600s also. Collect until you have the needed ratios and then put the freewheel together. OR you can use a 5 speed freewheel set up to begin with. Your Fugi came out with a 5 speed and someone changed it to 6 along the way. Right now your shifting is probably confusing.