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-   -   7->8 spd...should I be concerned about the chainline? (https://www.bikeforums.net/bicycle-mechanics/901440-7-8-spd-should-i-concerned-about-chainline.html)

stephr1 07-14-13 04:21 PM

7->8 spd...should I be concerned about the chainline?
 
Hi all,

This is somewhat related to my previous post (http://www.bikeforums.net/showthread...=#post15828314).

I've decided to take my '99 Specialized HR from 7 spd. to 8 spd. (wish I had considered this *before* I bought a new 7 spd freehub and cassettes late last year...very poor planning :( Setting aside the fact I know I'll have to re-dish the rear wheel (good news is rear dropout is 135 mm and a 5 mm spacer that sits on the axle opposite side from the freehub can be removed or maybe replaced with a 1.5 mm spacer to make room for the new 8-spd freehub and cassette), I was curious if I need to be aware of any issues that might be related to how critical the chainline setup would be relative to the cassette. Here's why I ask....

Based on chainline specs from Specialized, cassette dimension data from the Sheldon Brown site and my best ruler/eyeball process |^( it looks like the rear chainline sits pretty much on center (give or take) with the 4th cog/gear of the 7 spd cassette. When I install the 8-spd freehub, (again using Sheldon Browns data) it looks like the chainline would then line up almost 1/2 way between the 4th and 5th gear/cogs (~.1 mm closer to 5). So, it still looks like the chainline sits in the center of the cassette.

Intuitively, it would seem that this is a nice, ideal arrangement and that, other than getting the dishing right/straight and aligned, it should be a no-brainer process. If there is anything anyone thinks I should know about or be aware of in this, please speak now or I am off to potentially screw up my bike when the freehub arrives next week ;)

Thanks in advance...Steph

IthaDan 07-14-13 04:49 PM

Dish it and ride it. Suboptimal Chainline isn't nearly the deal breaker that everyone makes it out to be.

Retro Grouch 07-14-13 04:51 PM

I've never worried about it.

Think about your smallest rear cog. It's going to reside in pretty much the same place regardless if it's 7-speed or 8-speed. That's as good as you can get it.

sreten 07-14-13 05:01 PM

Hi,

Chain line is a poor excuse for upgrading and not much of an issue.

However its nice my big front lines up with ~ 5
of 7 and the small front lines up with ~ 2/3 of 7.

For a single front the best chain line is in the middle of the gears
you most use, not physically in the middle of the rear cassette.

rgds, sreten.

I don't use the top two gears of 7 much, the rest a lot.

FBinNY 07-14-13 05:07 PM


Originally Posted by IthaDan (Post 15850567)
Dish it and ride it. Suboptimal Chainline isn't nearly the deal breaker that everyone makes it out to be.

+1,
Don't obsess. It's a derailleur bike so spends very little time in an "in-line" combination anyway.

bradtx 07-14-13 05:10 PM

Steph, A couple of years ago I did a similar 7S to 8S change to my 135 mm spaced touring bike. Your cassette's small cog will be the same distance from the chainstay as before with the large cog about 4 mm further inboard. Inconsequential IMHO. The only issue that popped up in the change was my RD required the L stop screw adjusted fully out to allow the RD to travel the extra difference.

Brad

Bill Kapaun 07-14-13 05:53 PM


Originally Posted by FBinNY (Post 15850616)
+1,
Don't obsess. It's a derailleur bike so spends very little time in an "in-line" combination anyway.

+1
I tend to ride a lot on the middle ring & smaller cogs, so I've actually set my chain line a bit "wide".

IMO, "upgrading" from 7 to 8 is rather a waste. IF you really need more gears, go straight to 9. A lot more available cassette combinations.
I went 7>8>9 and basically wasted good money on 8.

stephr1 07-14-13 07:45 PM

Thanks to everyone for the comments. I really appreciate the feedback and input.

A special hello and thx to Retro Grouch and FBinNY who I remember have been kind enough to help me in the past.

After doing the rough calcs, chainline wasn't really a concern (tho, re-dishing the wheel is). It looks like everything shifts just right (or close enough). I just wanted to check in with the xperts and see if I had missed something in doing this.

Some interesting comments...

Re: use of gears...I am more of an urban MTB'er so I mostly use the upper gears (3-7...top gear is 11T to get a little more speed) and I'm in the middle chainring for 99.9% of the time.

Re: 9 spd. Yeah. I get it. However, I don't know that I could make good use of 9 cogs, given how few I normally use. I had trouble deciding to go to 8 spd. The main thing pushing me was that the 7-spds have gotten cheap and there aren't as many 7 spd cassette options around as there were a few years ago. I could go to 9 spd sometime down the road (freehub supposedly can handle it, not sure of the RD). But I see myself in 8 spds for quite some time.

Again, thanks for the help on this.

Cheers...Steph

FBinNY 07-14-13 08:10 PM

It's hard to critique anybody's gear selection, but there are three things to consider.

1 ride the gear that's comfortable n\for you in any situation. This is the main objective, but if when you have choices between two comparable combinations the following may help decide.

2- larger sprockets are more efficient, and produce less wear. So if you can choose between the outer and a larger rear instead of the middle and a smaller on, larger is usually better.

3- sprockets that are better aligned are more efficient, so outer with outer half of the cassette, middle with middle, etc. This isn't digital as in good and bad, just a matter of degrees.

Rules 2 and 3 are often in conflict since using the larger chainring may force you inboard on the cassette, and the middle with a smaller sprocket may be better. So throw it all into the hat and remember that rule 1 is what drives the process.

FastJake 07-14-13 09:09 PM

If your chainline was fine with 7S it will be fine with 8S. Just don't try using that first cog with the big ring.


Originally Posted by IthaDan (Post 15850567)
Dish it and ride it. Suboptimal Chainline isn't nearly the deal breaker that everyone makes it out to be.

I mostly agree with this, but terrible chainline can definitely be a deal breaker. I had a beater once setup so bad that I literally could not use the big ring with the first two or three cogs. The chain would fall off the ring if I tried. That's what really bad chainline can do.

ThermionicScott 07-14-13 09:30 PM


Originally Posted by stephr1 (Post 15851057)
Re: 9 spd. Yeah. I get it. However, I don't know that I could make good use of 9 cogs, given how few I normally use. I had trouble deciding to go to 8 spd. The main thing pushing me was that the 7-spds have gotten cheap and there aren't as many 7 spd cassette options around as there were a few years ago. I could go to 9 spd sometime down the road (freehub supposedly can handle it, not sure of the RD). But I see myself in 8 spds for quite some time.

Actually, the selection of 7-speed cassettes is nearly as good as it's ever been (certainly better than 8-speed) and Shimano has recently started making HG50 cassettes in silver again: http://www.niagaracycle.com/categori...settes/7-speed

So I wouldn't be in too big a hurry to switch. (Unless you want more gears.) :thumb:

fietsbob 07-14-13 10:30 PM

Doing the frame spreading, too ?

ThermionicScott 07-14-13 11:13 PM


Originally Posted by fietsbob (Post 15851479)
Doing the frame spreading, too ?

He's already at 135mm, so I would expect not. ;)

fietsbob 07-14-13 11:16 PM

ideal chain line is center of cluster.. 4 0f 7 or the space between 4 & 5 of 8.,.

rebelLT 07-14-13 11:50 PM

I too find that I ride 99 percent in the middle chainring. All of my bikes are 7 or 8 speed and I have contemplated taking off the front derailleur and two chain rings and running my bike as a seven speed. Hhmmm.


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