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here is the situation – I have a quasi-vintage 7-speed bike that still has the original front and rear derailleur (Deore DX) in very good condition. I have recently took a wheel building class which, naturally, resulted in a nice new set of wheels that I would like to use on this bike. However, the freehub on the new rear hub is for a 8/9/10 cassette.

Now, I realize that I could buy a spacer and place a 7 speed cassette on that bad boy. My question is this – Could I put an 8 speed cassette on the new hub, avoiding needing a spacer, and then adjust the limit screws on the rear derailleur to accommodate the extra gear on the cassette? I’m currently using a set of dura ace 8-speed bar end index shifters at the moment, so that wouldn’t be a concern. I also believe a 7 speed and 8 speed drivetrain uses the same chain, too.

Thanks for any help!

  • 8-speed bar-ends are designed to work with 8-speed cassettes. Set the limit screws and adjust the indexing. It should work perfectly. – Carel Mar 6 at 17:23
  • Awesome, that's what I was hoping to hear. Thanks! – Big Al Mar 6 at 17:26
  • Please answer in answers, not comments – ojs Mar 6 at 17:41
  • @ojs I put it as a comment because it was a bit on the short side. – Carel Mar 7 at 7:56
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    @Carel sometimes correct answers are short. – ojs Mar 7 at 8:55
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Dura-Ace 6/7/8-speed used different cable pull ratios from other models. To get your shifter to work properly with your DX rear derailleur you may have to try alternate cable routing. As always, Sheldon has the details: https://www.sheldonbrown.com/dura-ace.html

  • Interesting...I'll give this a look over and if I run into any problems I'll give that alternate cable routing a go. Thanks! – Big Al Mar 6 at 20:44
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Well, if you have 8 speed shifters an 8 speed cassette those will work together. (I'm a bit confused about how you were getting this to work with a 7 speed cassette as the spacing between sprockets is 0.2mm different (see here).

If you have a putatively 7 speed derailleur, it will still work OK because Shimano used the same derailleur actuation ratio for 7, 8 and 9 (and road 10) speed systems.

Yes, 7 and 8 speed chains are the same but you'll want a new chain to run on the new cassette.

  • Yep, you are right, the spacing is off by just a little bit (0.2mm), but it didn't seem to affect the shifting. I asked a local bike shop if it would be a problem before I installed it and they said no, so I went with it. I can't say I notice it, but I'm sure there will be a nice placebo effect when I get my 8 speed shfiter paired up with an 8 speed cassette, ha. – Big Al Mar 6 at 20:40
  • @BigAl So my answer is actually wrong because I forgot DA 6/7/8 has a different actuation ratio than anything else - see Noah's answer. – Argenti Apparatus Mar 6 at 20:51
  • @ Argenti Apparatus I may be wrong about this,but it appears the info on Sheldon's page is only applicable to older Dura-ace 6/7/8 shifters? I purchased mine about two years ago, new, so it might not apply. I would think that if it did apply, I wouldn't be able to use the shifters on my current 7-speed setup, as the cable travel would still be different. Here is a link to the barend shifters I bought - jensonusa.com/Shimano-SL-BS64-8SPD-Barend-Shifters-8-Speed – Big Al Mar 6 at 21:08
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    @BigAl I see on that page that it specifically says "NOT compatible with 8 speed Dura-Ace". Also, I see on some pages that the SL-BS64 is labelled as DuraAce and some it's labelled as Ultegra. I'm not knowledgeable to say which it is. – Noah Sutherland Mar 6 at 22:51
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Congrats on the new wheels! I'm sure they will roll for many years.

What you described will work perfectly. That is because as you said 7 and 8 speed systems use the same width chain and the shifter assumes the same distance between the gears.

On the other hand, if you wanted to put a 9 or 10 speed cassette, you would also need to get a new chain and shifter and the front crankset would be slightly wrong.

  • Same width chain yes, distance between sprockets no. Shimano/SRAM 7 speed spacing is 5mm, 8 speed is 4.8mm. See sheldonbrown.com/cribsheet-spacing.html. – Argenti Apparatus Mar 6 at 19:29
  • Something tells me you haven't actually tried this... – Kris Mar 6 at 20:19
  • So maybe it works - I got no problem with that, but the statement 'shifter assumes the same distance between the gears' is not technically correct. – Argenti Apparatus Mar 6 at 20:20
  • Well I learned something new today! Thanks for the correction. – Kris Mar 6 at 20:27
  • Thanks for all your help! I'm excited to get the new wheelset up and running. I'll throw the new 8 speed cassette on and hopefully get the limit screws and indexing done this weekend! – Big Al Mar 6 at 20:42

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