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 Post subject: Rock Shox Mag 21 forks
PostPosted: Sat May 15, 2010 4:06 pm 
Dirt Disciple

Joined: Thu Apr 08, 2010 2:06 pm
Posts: 56
I now have another Rock Shox Paris Roubaix (Mag 21) fork. The maximum tyre size is the standard 25mm - anything bigger and the tread hits the underside of the brake brace arch. I was wondering though if one of the mtb Mag 21 braces has a higher arch and would allow a taller tyre, say a 27mm/ 28mm tubular, to fit? There seem to have been two or three different mtb braces, with and without cable hangers/ centre holes, but it isn't clear to me if the arches give greater tyre clearance than the 700c brace.

Thanks, Jason.


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 Post subject:
PostPosted: Sat May 15, 2010 4:17 pm 
retrobike rider
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First problem is there would be no bolt through for the calliper so you would need and alternative braking system.
I do not know the dimensions of the P-R brace, but I could scan an.or measure the MAG brace if you wish. May take a while though.


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 Post subject:
PostPosted: Sat May 15, 2010 4:32 pm 
Dirt Disciple

Joined: Thu Apr 08, 2010 2:06 pm
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Thank you.

I was thinking of using the Paul Moto BMX brakes.

Knowing the measurement of the mtb Mag brace would be helpful (better than buying a whole mtb mag fork just to find out if the brace has more height than the PR brace). I guess the measurement would be dropped down vertically from the centre of the underside of the arch to the intersection of the horizontal line passing through the bolt-on holes. I can then compare that to the height of my PR brace and decide if there is extra room for more rubber.

Cheers, Jason.


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 Post subject:
PostPosted: Sat May 15, 2010 4:50 pm 
retrobike rider
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First estimate is the height is the same, but the width at that section is wider.


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 Post subject:
PostPosted: Sat May 15, 2010 5:02 pm 
Dirt Disciple

Joined: Thu Apr 08, 2010 2:06 pm
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It looks wider visually, which would be expected for fat mtb tyres.
If it's no higher then I may need to scout around for a third party Mag 21 brake brace/ booster with extra clearance.

I precise measurement would seal it :-).


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 Post subject:
PostPosted: Sat May 15, 2010 5:50 pm 
Dirt Disciple

Joined: Thu Apr 08, 2010 2:06 pm
Posts: 56
...and, my brace is the champagne coloured original PR one (part no# 48988)
and the vertical measurement from the underside of the arch centre to the bolt-on holes centre line is 95mm. So I need a brace that has maybe 5mm more height to fit a pair of nice fat tubulars. That should still give me 15mm- 20mm of shock travel for those crazy cobbles.


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 Post subject:
PostPosted: Sat May 15, 2010 8:45 pm 
retrobike rider
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101mm +-1mm I just went and measured 2 braces I have off the forks.
These are 94+ era braces.
Unless the original MAG20 brace is any taller, then you gain just 5mm but extra width.
Probably a bit close :lol:


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 Post subject:
PostPosted: Sat May 15, 2010 9:09 pm 
Dirt Disciple

Joined: Thu Apr 08, 2010 2:06 pm
Posts: 56
Well, that's good news. An extra 5mm may be enough additional space for the tubulars I have in mind.

Just to be clear, was the 101mm +-1mm measurement taken as a vertical line tracking up to the inner arch top from the mid point of a horizontal line passing through the centre of the four bolt? Or, taken from the very base of the 'feet' of the arch and then up to the upper most point of the inner arch top?

My brace would measure 101mm +-1mm if the vertical was taken from the very base and not from the centre of the four bolt holes. Just want to clear up that possible confusion.

Are your braces with or without cable hangers? If you have the five digit part numbers available stamped on the back I can see exactly which ones you have from my Rock Shox parts list. It may be no# 48998.

Many thanks Fluffy, Jason.


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 Post subject:
PostPosted: Sat May 15, 2010 10:04 pm 
retrobike rider
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Line placed through bolts and canti hole. Then to inner side as you measured.

It's hanger version latest revision (which would be 48998 as you say since it's black originally) but in black (1994+ model). I don't remember seeing any numbers stamped on them but not a part i've looked at closely and from memory don't think the inner arch altered between from the older versions (1993). Like I said not sure about my MAG20 original brace though, long since good and was made differently. You probably wouldn't want to use that on a road bike anyway.
I have 3 of them to check against ;) I also don't think the hangerless version was any different on the inner arch.


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 Post subject:
PostPosted: Sun May 16, 2010 10:41 am 
Dirt Disciple

Joined: Thu Apr 08, 2010 2:06 pm
Posts: 56
So it sounds like all the mtb versions have a little more clearance than the Paris Roubaix brace I have. That extra 5mm of height should be more and enough for fat tubular PR tyre, and may even be enough for the smallest of cross tyres with a smooth pimple tread pattern. Lots of fun and experimenting to come then - I love it. Thanks Fluffy, Jason.

P.S. If you ever decide to sell a hanger let me know :wink:


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