Praxis rings on SRAM hidden bolt cranks - experience & ??'s.

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VTBike
Posts: 383
Joined: Mon May 16, 2011 8:14 pm

by VTBike

So this has been circuitously talked about in another thread that's 20 pages long, and gets on many different tracks. Posting again here to have focused discussion.

I recently bought a set of Praxis standard (53x39) rings for my 2014 exogram hidden-bolt SRAM Red 22 cranks. Based on the other thread, it seemed like some simple 'filing' would allow this set of rings to fit.

I actually had to do more than some simple filing - basically for the mounting tab that goes behind the crank arm, i had to file it shorter - but also file the face down probably a 1/16th (or more). Before filing the face of the mount down, i found that the chain-ring bowed significantly inward at the hidden bolt location, and wasn't a true circle. So after a bunch of filing/testing/filing/testing - it's pretty close to true.

Meanwhile, the to the other point of this thread, i've found that when in 39 ring, I really can't use the 11 or 12t cog as the chain rubs to closely to the 53t ring. The 13t (3rd) cog is OK, but still rubs a tiny bit. I recall years ago that the new Red rings were a slightly different thickness - and forgot all about it. I didn't read anything about this in the bigger threads on the cranks, so wondered if anyone else found this issue? I think i can deal with it just fine - if I'm in 39x12 i should probably be shifting to 53 anyway.

Overall, after a single 30 mile hilly ride, I'm quite happy with the change. The shift from 39x53 and back down is significantly better than with the Red rings (and I didn't think the shifting was bad before). They are quieter (though my red rings were pretty worn, so might not be a completely objective comment); and I am enjoying the change in look. I used a grinding wheel to do the work on the rings - it would have been a huge PIA to do it with a file by hand.

Oh - the new rings are around 40g lighter. The RED rings came in at 182g; and the Praxis at 144g.

Ozrider
Posts: 1018
Joined: Sat Nov 20, 2010 6:06 am
Location: Perth, Western Australia

by Ozrider

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It works fine. I just rotated the chainrings 180 degrees to keep the ramp and pin timing the same (chain rings can't tell whether the power or downstroke is from left or right leg) No filing was required.
The Exogram rings also work perfectly on the older SRAM cranks.
On my Parlee I upgraded to DA 9000 but kept the SRAM Exogram crank as it is a BB30 frame. And the Exogram crank is lighter than a DA9000 crank with BB30 adaptor.
I swapped the new Red groupset to my Madone as I had damaged the shifters and rear dérailleur in a fall.
There is a tiny bit of chain rub on the 11 cog the 39 inner ring with both, but I never use this combination due to the extreme chain angle and increased chain wear this causes.
I swapped things over about 10 months ago and have raced Crits on the Madone and done a 5 day race on the Parlee with no issues at all.



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Ozrider - Western Australia
Parlee Z5 XL (6055g/13.32lbs) Trek Madone 5.9 (7052-7500g)Jonesman Columbus Spirit (8680g)
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Doolop
Posts: 550
Joined: Wed Jul 08, 2009 9:19 pm

by Doolop

I hate hidden bolt cranks so much. My quarq is a sram red hidden bolt setup and with the switch to DA9000 it is a huge pain in the ass to get rings to look good on the setup. I have just been switching my rings 180° but there is still creaking issues and they don't look good.

VTBike
Posts: 383
Joined: Mon May 16, 2011 8:14 pm

by VTBike

Hmm, interesting. I didn't rotate my rings 180.. I placed the pin right below the crank arm when the crank arm is at 3pm. I don't know how rotating further would have eliminated the need for filing though - there was significant overlap between the mounting tab, and the hidden bolt mount. Looks wise, i think it's solid though.. and fortunately, no creaking.

As for me having chain rub in 39x11&12, and you not -- no idea about this. It doesn't seem like a function of the chain ring mounting, but rather an overall spacing issue. Are you on 11sp? Perhaps my wheel/cassette is just spaced further outboard than yours, or perhaps it's a frame geometry thing?

Ozrider
Posts: 1018
Joined: Sat Nov 20, 2010 6:06 am
Location: Perth, Western Australia

by Ozrider

The Exogram crank is fitted to a Parlee Z5 using a DT 240 hub and Ultegra cassette. I do get slight chain rub in 39/11, but I don't often ride with the chain at such an extreme angle.



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Ozrider - Western Australia
Parlee Z5 XL (6055g/13.32lbs) Trek Madone 5.9 (7052-7500g)Jonesman Columbus Spirit (8680g)
Chase your dreams - it's only impossible until it's done

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