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Discussion Starter · #1 ·
I'm in the processes of going 650b on the front of my prophet. I have read on post that the bigger wheels might need the bigger rotors. Should I change out the stock 160mm rotor (BB7's) for a 185mm?
 

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I prefer a 185mm rotor up front

thehogsters said:
I'm in the processes of going 650b on the front of my prophet. I have read on post that the bigger wheels might need the bigger rotors. Should I change out the stock 160mm rotor (BB7's) for a 185mm?
Its a GREAT upgrade. Do it.
 

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Mr.650b - Mr.27-5
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thehogsters said:
I'm in the processes of going 650b on the front of my prophet. I have read on post that the bigger wheels might need the bigger rotors. Should I change out the stock 160mm rotor (BB7's) for a 185mm?
I ran 160's for a while, but found I didn't have enough stopping power. I made the jump to 200mm rotors and they work great. Probably overkill, but I like 'em.

Cheers,

KP
 

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180/160 = 1.125
27.5/26 = 1.057
29/26 = 1.115 (for comparison only).

Should be about a 5% degradation in braking torque going from a 26 to a 27.5" keeping the same rotor size. (For a 26->29, about 10%.)

Going from a 160 to a 180 rotor is about a 12% improvement in braking torque.

So going from both 26 to 27.5 and 160 to 180 should increase net braking torque by about 6% (ie 180/160*26/27.5).

I have a 160mm on the front of my rigid 69er and it works fine (BB7), but it's not as powerful as the 180mm XT hydros on my 26er-- but that's changing too many things at once for a good comparison.
 

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Discussion Starter · #5 ·
So it sounds like 185mm is the way to go.

I was looking at the adapters for the BB7's and they have like 11 to choose from. Do I need the IS, PM, QR or TA for my lefty?
 
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Zak Smith said:
180/160 = 1.125
27.5/26 = 1.057
29/26 = 1.115 (for comparison only).

Should be about a 5% degradation in braking torque going from a 26 to a 27.5" keeping the same rotor size. (For a 26->29, about 10%.)

Going from a 160 to a 180 rotor is about a 12% improvement in braking torque.

So going from both 26 to 27.5 and 160 to 180 should increase net braking torque by about 6% (ie 180/160*26/27.5).

I have a 160mm on the front of my rigid 69er and it works fine (BB7), but it's not as powerful as the 180mm XT hydros on my 26er-- but that's changing too many things at once for a good comparison.
Except a 26" wheel is really about 26.52".

27.5/26.52 = 1.037 (assumes the same, 57mm tire)

I find it interesting that 650b supporters insist on calling it a 27.5 while they don't mind 559 not being called a 26.5. There is exactly 25mm difference in diameter between the two standards. Any other differences are in the tires. Claiming 26 vs 27.5 is BS.

If you see justification for 12.5% more rotor based on 3.7% increase in wheel then go for it. Greater magic is believed in here.
 

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craigsj said:
Except a 26" wheel is really about 26.52".

27.5/26.52 = 1.037 (assumes the same, 57mm tire)

I find it interesting that 650b supporters insist on calling it a 27.5 while they don't mind 559 not being called a 26.5. There is exactly 25mm difference in diameter between the two standards. Any other differences are in the tires. Claiming 26 vs 27.5 is BS.

If you see justification for 12.5% more rotor based on 3.7% increase in wheel then go for it. Greater magic is believed in here.
oi mr. 20 posts,

why are you such a frocking azzhole? the troll killer is certain you're a long time mtbr troll with a new user id.

you've obviously got an agenda. why not hang with galahs and white ants who subscribe to your brand of religion let people here enjoy what they're into? in short, piss off mate.

heez gawad,

tk
 
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troll killer said:
oi mr. 20 posts,

why are you such a frocking azzhole? the troll killer is certain you're a long time mtbr troll with a new user id.

you've obviously got an agenda. why not hang with galahs and white ants who subscribe to your brand of religion let people here enjoy what they're into? in short, piss off mate.

heez gawad,

tk
The troll killer is an arrogant idiot who, ironically, has no idea what a troll is.

Facts are my "religion". Argue with them at your peril, loser.
 
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Zak Smith said:
Good point, so you'd net 8% (not 6%) more going from 26.5 to 27.5 and 160 to 180mm at the same time.
That sounds about right, or about 2/3 if the increase goes to lighter effort and only 1/3 goes to the larger wheel size. I think the justification for the larger rotor is more that you prefer the performance. Various tires can change overall diameter by 3-4%.
 

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Does anyone else see the irony of a guy who registered Dec 2007 and has 99 posts calling the guy who registered Feb 2007 and has 22 posts a troll "new account"?
 
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88 rex said:
No. My Spidy senses suspect TK has an alter ego.
Would you admire someone who keeps an alternate account for the purpose of spewing hateful messages at other forum members?

I think you are missing the irony that is being pointed out. I am neither a new forum member nor a prolific poster. TK is relatively more of a troll than I am by either of those measures. He may well have another account and be a long-time member but that's irrelevant and, if true, it calls his boorish behavior even further into question.

I don't think TK expected anyone to check his "research".
 

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back on topic boys

Yes I switched to 185 on the front of my 650b. I left the 160 on the rear which is still 26. I felt like the 160 was not getting it done.
 

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My spoon is too big!
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I have a Prophet with 650b front, and 185mm rotor, and it feels just right. I swapped out the 160 after my first ride on the bike, well before the wheel change. The smaller rotor never felt strong enough, even with the 26" wheel. I didn't feel any significant difference in braking after installing the larger wheel.
 

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craigsj said:
Would you admire someone who keeps an alternate account for the purpose of spewing hateful messages at other forum members?

I don't admire anyone on this board.

And I could care less if someone wants to call a 26" set-up 26.5" (even if the average is probably somewhere around 26.3).

26" to 650b = 25mm

650b to 29'er = 38mm

26" to 29'er = 63mm

Call them what you will. Ride what you ever you like. And use 185mm rotors to stop you :thumbsup:
 
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88 rex said:
26" to 650b = 25mm
650b to 29'er = 38mm
26" to 29'er = 63mm
These are the numbers that are important, not 26, 27.5, and 29. I dislike 27.5 for precisely the reasons some like it: because it exaggerates the difference between 26 and 650b.

Incidentally, 26.5 is the number you get when you take the same tire that makes a 29er exactly 29", that also makes a 650b exactly 27.5", and you put it on a 559 rim. Don't care what it is so long as all 3 formats are compared with a like-sized tire.
 

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www.derbyrims.com
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203

Smaller rotors have more modulation, but power is intoxicating!

203 in front. :thumbsup:

180 in back, not sure if I could handle more with current tires.

200 lb rider.
 

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mnt bike laws of physics
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craigsj said:
Except a 26" wheel is really about 26.52".

27.5/26.52 = 1.037 (assumes the same, 57mm tire)

I find it interesting that 650b supporters insist on calling it a 27.5 while they don't mind 559 not being called a 26.5. There is exactly 25mm difference in diameter between the two standards. Any other differences are in the tires. Claiming 26 vs 27.5 is BS.

If you see justification for 12.5% more rotor based on 3.7% increase in wheel then go for it. Greater magic is believed in here.
Do 650b supporter insist on calling it 27.5"? As far as I've heard, the supporters on this forum have been calling it 650b...and for myself (being a 650b supporter) I prefer to call the 559mm wheel 26.5" because that is the diameter of the tires I run on that wheel size. I have learned that blanket statements not based on real world experience are to be taken with a grain of salt.
I think a person should run whatever rotor suits their mass, riding style, terrain etc. Considering my experience with the Neo Moto, I ended up carrying more speed than any tire on a "26.5" wheel so a larger rotor would be useful.
 
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