Powertap Pro+ need spacer?

[tomUK]

Hi -

Hoping someone can help. I've just brought a new Powertap Pro+ and I have Dura Ace 7900 Cassette. Do I need the spacer?

I think I do because in the manual it says that the Powertap is compatible with 8, 9 and 10 speed Shimano systems.

Anyone got an ideas?
Thanks,

 

[daveryanwyoming]

If your cassette has an 11 tooth cog you almost certainly need the spacer or the cassette won't fit tightly. At least that's the case on the older SL style powertap freehubs as the splines don't have the slight notching required for 11 tooth cogs. I only run 11's on my race wheels but put the thin shimano spacers on all my PT wheels so that the derailleur adjustment stays the same when I swap from training to racing wheels even though I don't need the spacer on the cassettes with 12 tooth top end gearing.

-Dave

 

[tomUK]

I do have an 11-tooth cog. When I put the spacer in I gain about 4mm of space on the spoke-side. Saris tell me I don't need the spacer, however, without it I don't see how this is compatible with 9 or 8 speed.

Shimano suggest it in most cases...

http://techdocs.shimano.com/media/t...001/SI_1Z80B_001x13_v1_m56577569830648477.pdf

feeling a little confused...hrm...

 

[daveryanwyoming]

...feeling a little confused...hrm...

Perhaps Saris has updated their freehub body designs, but the SL style freehub certainly isn't compatible with 11 tooth cogs without the spacer.

Check out the section on 'hyperglide-c' freehub bodies on this page: Shimano Cassettes & Freehubs, by Sheldon Brown

That page also discusses compatibility between 8,9 and 10 speed cassettes and freehub bodies. Seven speed cassettes need a 4.5 mm spacer, but the others are all the same width, the 9 and 10 speed cassettes just cram more gears into that same space by reducing the spacing between gears. The Shimano tech note on adding the thin spacer for 9 speed freehubs just adjusts for the lack of notched splines in the older non hyperglide-C freehubs which is basically what you have with a PT hub (at least the ones I've owned but I haven't owned any wireless versions).

Bottom line, if you can engage the threads and tighten the lockring then the spacer isn't hurting anything and if you install a cassette with an 11 tooth cog, tighten the lockring and the cogs (all except the 11) rattle then you really do need the spacer. Remember the Shimano tech note assumes you are mounting on a Shimano freehub, not a PT freehub.

-Dave

 

[tomUK]

Thanks for the reply and input, Dave. I appreciate you taking your time to reply to my thread.

I've taken a good look over the freewheel and it appears that no spacer is actually needed. Maybe this is the reason Saris negate to mention it in the instructions?

The freewheel appears to have a 'step' on it. This means that a 10 speed can only make it down so far on the spline. A 9 or 8 speed would most likely? be able to surpass this step.

Either way, I find myself asking would a 0.5mm spacer make that much difference? Who knows, but I don't think it will do much harm.