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7am Backcountry ;- )
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Discussion Starter · #1 ·
"8 inch rotors on 150mm QR forks are for tough guys with good dental insurance."

This was posted in a thread about upgrading to 8" Rotors - which i'm running with a Shimano QR.



Anyone else see a problem with this?

Advice on making it safer (I don't want to have to use a spanner and bolts to get my wheel off!)
 

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dontcha?
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TheProphet said:
I was always under the impression that you couldnt run 8" rotors on a QR fork just because its too much force for the drop outs. But I could be wrong.
I think it depends on the fork, some are "approved" while others it will void your warranty..
 

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I have been told the same thing by some trusted mechanics at my local shop. You might not have a problem, but for me the risk was too high. Its your call, but I would advise against it.
 

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dontcha?
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I've been running 8" rotors up front on my all-mountain/trail bike, and haven't run into any problems, but I run BB7's and they are not that powerful compared to hyrdo's.. My headset has been rattling loose maybe as a result of the big rotors.. has anybody actually heard of anyone's wheel/fork/hub/ falling apart because of 8" rotors?
It sounds like another debate that's always on the car/auto forums I post on about stretched tires. Everybody says it's really dangerous and really bad, but yet nobody actually has first hand experience of anything bad happening or any pictures to back it up..
 

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yeah thats a load. Some of these rumours that come up amaze me... Look at trials bikes or even some DJ bikes, QR's work OK. Like others have said, it depends on the fork. All marzocchi forks with 130mm travel or more are approved for 203mm rotors.

Do you need a 20mm TA? If you are going huge it's a good idea.

I've been running 8" rotors on my trail bikes for 3 years with no problems.

I also had a QR-20 system break on me several times.

If you're getting a new fork then 20mm is a good idea, but if you like the QR fork you have I woudn't hesitate to run a 203mm rotor as long as the MFG approves.
 

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7am Backcountry ;- )
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Discussion Starter · #12 ·
Anyone any experience or info on a Marzocchi Drop Off (standard on Kona Coiler 05) and handling an 8" rotor?

BUT from what ive been reading on the web it seems the smaller the rotor the more force it puts on the QR.

"It seems like another misunderstanding of the bicycle industry. The larger the disk, the lower the forces. In fact when the contact diameter of the disk pads reach that of the rim (as in rim brakes) braking forces are minimized.What is going on here?"
 

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gnar, brah
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TheProphet said:
Gotcha. IMO, anything over 150mm you should be using 20mm.
I don't think so. Any bike that doesn't have Hope minis (or another 140mm system) is going to have 160mm rotors. That includes 99% of bikes that come stock with discs. The vast majority of those are going to be QR axles. New Stumpjumper FSRs come stock with 203mm Juicys, on a QR Fox fork. Plenty of other examples too. I run a 185mm rotor on a 3.2 lb XC fork with no problems whatsoever. I have run 203mm on several QR forks...again, no problems. It will depend on rider weight and riding/braking style, more than anything else. If you are a clydesdale who is bombing downhills and braking heavily with your front, an 20mm is going to be a good idea no matter what rotor size you are using. I think that the 20mm's main advantage over QR is stiffness; rotor size is not really a big issue in most cases. I would say that 185mm rotors are fine for vitually all QR systems, but that's just me. Above all, be honest about your size and riding style to determine if you need 20mm (It's usually worth it), but you shouldn't limit your rotor size just because you have QR.
 

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Hey just a thought on one thing that IS important- check your caliper bolts! especially if you use and adaptor to run a larger rotor.

I've had two buddies whose caliper bolts came loose, for one his fork lowers got wrecked and he had to finish a ride with no front brake. :madman:
 

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7am Backcountry ;- )
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Discussion Starter · #15 ·
FM said:
yeah thats a load. Some of these rumours that come up amaze me... Look at trials bikes or even some DJ bikes, QR's work OK. Like others have said, it depends on the fork. All marzocchi forks with 130mm travel or more are approved for 203mm rotors.

Do you need a 20mm TA? If you are going huge it's a good idea.

I've been running 8" rotors on my trail bikes for 3 years with no problems.

I also had a QR-20 system break on me several times.

If you're getting a new fork then 20mm is a good idea, but if you like the QR fork you have I woudn't hesitate to run a 203mm rotor as long as the MFG approves.
So I take it my Marz fork with 150mm would be cool?

What is a 20mm (sorry if this is a really stupid question!) is it the two bolts and a spanner method?
 

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Monte Su Bici Maldita
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The new Specialized Stumpy in a large comes w/ an 8" rotor on the front, and a QR Fox Float.
 

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capoz77 said:
So I take it my Marz fork with 150mm would be cool?

What is a 20mm (sorry if this is a really stupid question!) is it the two bolts and a spanner method?
yeah you'll be fine- just make sure your QR is tight & of decent quality (salsa or shimano)

20mm is a big hollow axle that fits trhough the fork, then bolts secure it from each side, and also through teh fork drop-outs. Like you see on most all dual-crown forks.
 

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gnar, brah
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mtnbykr06 said:
The new Specialized Stumpy in a large comes w/ an 8" rotor on the front, and a QR Fox Float.
Yeah, I built two at work...a large and an x-large. I thought they might all be like that.

The L/XL FSRxc Pro also comes with an 203mm Juicy on the front, the fork is a Reba SL, QR of course. Obviously Specialized sees no problems with mounting a big rotor on a QR fork...at least for the bigger riders.
 

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Glad to Be Alive
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my Z-1 on my stinky was a QR with an 8 inch and also the 2002 Jr T was 8 inch on a QR.....better to have 20mm IMO though
 

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Meh.
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I believe that I explained this in the other thread.

Btw, that's not a Shimano QR. Shimano QRs are true cam-action.

It largely depends on the fork. But the braking force may cause accelerated wear of the fork bushings.
 
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