7 speed / 8 speed compatability?

[Chris Zacho "Th]

It's getting harder and harder to find 7 speed shifters, and I have no intention of getting any more
cogs on my rear wheel. There's enough chain deflection with the seven!

Is it possible to use an eight speed shifter with a seven speed cassette (Shimano)? Maybe by
swapping spacers?

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner

 

[Jon Isaacs]

>It's getting harder and harder to find 7 speed shifters, and I have no intention of getting any
>more cogs on my rear wheel. There's enough chain deflection with the seven!

>
>Is it possible to use an eight speed shifter with a seven speed cassette (Shimano)? Maybe by
>swapping spacers?

If you are looking for MTB shifters, they are out there still BNIB.

If you are looking for road shifters (or MTB for that matter), you can use 8 speed shifters with 7
speed cassettes and they work just fine.

jon isaacs

 

[Per ElmsäTer]

Chris Zacho "The Wheelman" wrote:
> May you have the wind at your back. And a really low gear for the hills! Chris

That is exactly the reason I have nine speed cassettes, so I can combine those two
--
Perre

Remove and/or replace the DOTs as needed to reply

 

[Sheldon Brown]

Chris Zacho The Wheelman wrote:
> It's getting harder and harder to find 7 speed shifters, and I have no intention of getting any
> more cogs on my rear wheel. There's enough chain deflection with the seven!

Chain deflection depends mainly on operator choice of gears, and is also very much related to
chainstay length. The stupidly short chainstays currently fashionable creater more of a problem than
the switch to 8 & 9 speeds.

> Is it possible to use an eight speed shifter with a seven speed cassette (Shimano)? Maybe by
> swapping spacers?

Shimano 8-speed shifters generally work just fine with 7-speed clusters. It isn't usually even
necessary to fiddle with spacers.

Attaching the derailer cable slightly closer to the nearest of the parallelogram pivots is
sometimes helpful.

Sheldon "Not Rocket Science" Brown +--------------------------------------------------------------+
| If you pick up a starving dog and make him prosperous, he | will not bite you. | This is the
| principal difference between a dog and a man. | --Mark Twain |
+--------------------------------------------------------------+ Harris Cyclery, West Newton,
Massachusetts Phone 617-244-9772 FAX 617-244-1041 http://harriscyclery.com Hard-to-find parts
shipped Worldwide http://captainbike.com http://sheldonbrown.com

 

[Jon Isaacs]

>That is exactly the reason I have nine speed cassettes, so I can combine those two
>--

There's always the old "Half step-granny" that allows for the wide range of closely spaced ratios
without a bunch of extra cogs.

Jon Isaacs

 

[Chris Zacho "Th]

Thank you so very much (everyone) I have seen deraileurs, and shifters, advertized as "7-8 speed
compatible" but always assumed they meant with an adapter, as with Shimano's "6-7 speed" (indexed)
bar end shifters.

As for those who asked, I was referring to road shifters. I am thinking of dumping the dual
control levers on my touring bike and returning to regular brake levers and bar-ends. The dual
controls didn't really give that much of an advantage, and never could pull quite enough cable for
the canti's.

Thank's again :-3)

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner

 

[Chris Zacho "Th]

26 - 44 - 48 12 - 14 - 17 - 20 - 24 - 28 - 34

Work it out and graph it, you'll see why ;-3)

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner

 

[Jon Isaacs]

>1.public.lawson.webtv.net>
>
> 26 - 44 - 48
> 12 - 14 - 17 - 20 - 24 - 28 - 34
>
>Work it out and graph it, you'll see why ;-3)

Here it is:

@ 90 RPM SPROCKET SPROCKET

5.425022 .7647059 26 34 20.20333
5.425023 .9285714 26 28 24.53262
6.685447 1.083333 26 24 28.62139
7.180806 1.294118 44 34 34.19025
8.222536 1.3 26 20 34.34566
9.01542 1.411765 48 34 37.29846
10.85004 1.529412 26 17 40.40667
11.14812 1.571429 44 28 41.51674
12.16159 1.714286 48 28 45.29099
13.00614 1.833333 44 24 48.4362
14.17505 1.857143 26 14 49.06524
15.18852 2 48 24 52.83949
16.37089 2.166667 26 12 57.24277
17.60737 2.2 44 20 58.12343
18.02622 2.4 48 20 63.40738
19.36161 2.588235 44 17 68.38051
20.03085 2.823529 48 17 74.59692
21.29624 3.142857 44 14 83.03347
22.32317 3.428571 48 14 90.58197
23.01228 3.666667 44 12 96.87239
24.37704 4 48 12 105.679

There are some redundent gears but they all involve the 26 tooth. Using the standard half step split
between the 48 and the 44 the ratios are nicely spaced and a nice wide setup of ratios. I see 16
different useable combinations, not bad for 21 total gears.

(Note: with 7 speeds and the small difference between the diameters of the 44 and 48 chainrings,
cross chaining is not a problem. Also note that with such a small difference, those shifts are fast
and do not require a partial revolution of the rear wheel to become effective.)

Those top ratios are indeed nice and close. For comparison, here are the top six ratios that one
gets with a 52 13-18 straight block:

Speed RATIO FRONT REAR Gear inch @ 90 RPM SPROCKET SPROCKET

25.49453 2.888889 52 18 76.3237
26.70009 3.058824 52 17 80.81333
27.05634 3.25 52 16 85.86416
28.59343 3.466667 52 15 91.58844
29.3501 3.714286 52 14 98.13047
30.37704 4 52 13 105.679

Some might complain about wanting a taller gear and that is also a possibility, just depends on what
one wants.

But what this shows is that the 7 speed half-step granny scheme provides ratios that are as close as
a 9 speed setup and at the same time providing a wide set of ratios that are practical for just
about any riding one chooses to do.

Jon Isaacs

 

[Chris Zacho "Th]

In response to Jon Isaacs in depth research (which in too long to paste here):

Wow, I never really meant to imply such a review! LOL!

Yes the spacing is very even, that was what I was striving for. If you'll notice the spacing is
consistent at approximately 8.2% between each of the ratios on the half-step.

This way, each successive ratio requires 8% more (or less) effort than the one adjacent. Or 16%,
if you shift from cog to cog. I found that my legs interpret this change as more evenly spaced
that a direct "linear" increase . for example 10 gear inches between all the ratios across the
entire range.

It varies slightly, of course. Such is the down fall of working with set differences offered by a
cog/sprocket system. But by less than +/- 2%.

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": http://www.geocities.com/czcorner