I am moving up to a 29er frame and rigid fork and need to buy new disc brakes. Both the forks and frame are post mount and I want to run 160mm on the front and 140mm disc on the rear. Since I am running Sram XX on my build, I want to stay with Sram XX brakes if possible. I see on Ebay and other sites a ton of brakes listed. The front brake seems easy to sort out because the post looks like it is designed to run 160mm without any adapters. From what I have seen on the rear, pretty much all of the Sram XX brakes have a bracket on them to get them to 160mm and 185mm.

Would I be wrong if I bought a 185mm and just ditched the bracket, that it should be able to do 140mm on the rear or would it be 160mm at that point.

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BIG DADDY B FLOW
AERO & LIGHT is RIGHT

Cervelo SLC 5890g/12.98 lbs

It all depends on the frame.
You are correct that it will work fine, if your frame will let it happen

This is what I am thinking of buying and by all accounts it looks like if I buy any front XX brake and any rear XX brake it should work by ditching the IS bracket that comes with the brakes. This is just a bike to ride around with the kids on hard packed trails and city paths and such. Also while I am trying to rehab my back I will put slicks on and do some road riding. Has to be a XX if possible as I like to match it up when possible.

Oh and if the powers that be do not like me posting this pic, I will take it down.

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BIG DADDY B FLOW
AERO & LIGHT is RIGHT

Cervelo SLC 5890g/12.98 lbs

Can you ask the seller if it is post mount 140 compatible? It's hard to tell from looking at that picture, my friend couldn't run a 140 on his Niner A9C, but it works fine on my Stumpjumper. It looks like it should be able to work...
That will be a cool ride

I could actually care less if it had to run 160mm rear but since we are WW's it would be better to run a smaller rear disc for a bit of savings and lets face it, I am not going to be racing down a mountain or doing anything stupid at this point with my back. Shit at this point I could run BB7 and it would be fine and I might be able to do that and go lighter with a very light lever. lol.

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BIG DADDY B FLOW
AERO & LIGHT is RIGHT

Cervelo SLC 5890g/12.98 lbs

How about Scrub rotors front and rear?

I know that for some aggressive heavier riders, that Hope 2 piece floating roads don't work. because the carrier/spider cracks after hard use. The 29er puts more torque on the brake rotors.

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http://www.hackracer.com/

I currently own some Ashima ARO-08 rotors so I might just stick with them in 160mm but I will contact the seller and see if I can run 140mm on the rear.

So I might be able to save some weight on the rotors if it works out.

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BIG DADDY B FLOW
AERO & LIGHT is RIGHT

Cervelo SLC 5890g/12.98 lbs

SRAM XX front and rear callipers are identical - they are post mount.


From the frames I have seen that have the brake calliper inside the chain and seat stays, they have been for 160 mm discs, but you need to check with the frame manufacturer.

You should be able to fit the caliper without any adapters and in the worst case scenario, 160 mm disc would be the smallest you could have on the rear.

I ran 160/140 on my 29er for a while. 2 Observations:

1) yes it works with 2 standard callipers (assuming you've got clearence for the calliper, mine was on the chainstay and IS mount so needed a 160mm front addapter).

2) 29ers need bigger brakes due to the lower speed of the wheels (they're bigger so at a given speed over the ground they're rotating slower), energy = force*distance, so power=force*speed, drop the speed the brake track on the disk is moving through the calliper at and you need more force to achieve the same braking power. So either brake harder or use larger rotors to bring the speed of the disk back upto what it would have been on a 26er.

I ended up going to 180/160 and using aligator aries rotors to keep the weight down which produced braking power that was adequate (but then I'm 95kg's and use it for techy off road so maybe I just need more brakes than you )

I did send an email to the seller yesterday night to see what the minimum that I could go on the rear but have not heard back yet. I am fine with 160mm all the way around becuase I already have rotors that size so saves a bit of money. So once I hear back from the seller, I will buy the frame/fork and brakes and then sort out the crank issue.

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BIG DADDY B FLOW
AERO & LIGHT is RIGHT

Cervelo SLC 5890g/12.98 lbs

heads up, a-baygoods also sells from their website flyxii.com I'm not sure what the prices are at the moment, but they offer free shipping when ordered from their website. Not affiliated, just been considering ordering from them for a while now...

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Trek 5500 - 13.75lbs on a $1400 Budget
20 gram 1x10 chain guide

Thanks for the heads up Maniac. That will allow me to put more towards a try BB30 cranks set.

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BIG DADDY B FLOW
AERO & LIGHT is RIGHT

Cervelo SLC 5890g/12.98 lbs

The frame is designed for double 160mm rotors so it looks like I can pull the pin on the frame, forks and brakes now. I just have to sell off my 26" wheels and buy some 29er wheels and life is good.

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BIG DADDY B FLOW
AERO & LIGHT is RIGHT

Cervelo SLC 5890g/12.98 lbs

Wish I had hack bikes like this!

You can.

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BIG DADDY B FLOW
AERO & LIGHT is RIGHT

Cervelo SLC 5890g/12.98 lbs