Got Any DH Questions? Ask Them Here

PB Forum :: Downhill
Got Any DH Questions? Ask Them Here
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flag Pedro019
Posted: Sep 21, 2016 at 14:25 Quote
SmashedFungi wrote:
Pedro019 wrote:
Hi guys, I have a renthal integra II 45mm/o rise, it's fine on my old fox 40, now I wanted to buy a new fox 40, but it has a flat crown, my question is, can I mount my stem on a fox 40's flat crown?

No idea why it shouldn't fit it's still a direct mount so i guess it will.

http://p.vitalmtb.com/photos/users/2/photos/87705/s780_GWIN_VITAL_037.jpg?1426645360
This stem has 50mm, I don't think a 45mm would fit, there is less than 5mm btw handelbar and suspension...
but I already got an answer to this and it was that a 45mm stem fit if I use a fatbar, the carbon bars are too thick to clear the stanchions...
of course it fits, I only asked cuz I run my my bars low...
flag gabriel-mission9
Posted: Sep 22, 2016 at 5:30 Quote
Nobble wrote:
god damn, you can be dumb sometimes.

If you really need me to, I'll get out my bearing design textbook just for you when I get home.

Serious question, why are you so f*cking angry all the time? I have literally never seen you disagree with anyone, even over the most insignificant details, without resorting to calling them a prick. Sometimes you don't even disagree, you just take the piss cos someone who's obviously new to the sport asks a simple question or whatever. Its the internet man. Chill the f*ck out. Really, I don't feel any worse about myself because someone on the other side of the planet types into his keyboard that I'm stupid. The only person you are pissing off is yourself. Why bother doing that to yourself, its just gonna make you feel bad. I have a mate who does similar things. I once told him when he bought a new car that I'd have got a different colour. He spent the next two hours lecturing me about resale value, and hiding the dirt and all sorts. Two hours later he had worked himself into such a state I had to buy him a pint and tell him it was all ok. Now he's losing his hair. Just saying...

Anyway, have you had time to refer to your bearing design textbooks yet? I am genuinely interested to find out how loading one (possibly slightly larger/fewer balled, possibly not) bearing and repeatedly changing the direction of that load is preferable to sharing the load between two bearings, which are always loaded from one side only, and preloaded gently which should reduce the number of impacts between ball and race.

And remember, its not a competition man, just a discussion.
flag oldmanDan
Posted: Sep 22, 2016 at 6:08 Quote
gabriel-mission9 wrote:
Nobble wrote:
god damn, you can be dumb sometimes.

If you really need me to, I'll get out my bearing design textbook just for you when I get home.

Serious question, why are you so f*cking angry all the time? I have literally never seen you disagree with anyone, even over the most insignificant details, without resorting to calling them a prick. Sometimes you don't even disagree, you just take the piss cos someone who's obviously new to the sport asks a simple question or whatever. Its the internet man. Chill the f*ck out. Really, I don't feel any worse about myself because someone on the other side of the planet types into his keyboard that I'm stupid. The only person you are pissing off is yourself. Why bother doing that to yourself, its just gonna make you feel bad. I have a mate who does similar things. I once told him when he bought a new car that I'd have got a different colour. He spent the next two hours lecturing me about resale value, and hiding the dirt and all sorts. Two hours later he had worked himself into such a state I had to buy him a pint and tell him it was all ok. Now he's losing his hair. Just saying...

Anyway, have you had time to refer to your bearing design textbooks yet? I am genuinely interested to find out how loading one (possibly slightly larger/fewer balled, possibly not) bearing and repeatedly changing the direction of that load is preferable to sharing the load between two bearings, which are always loaded from one side only, and preloaded gently which should reduce the number of impacts between ball and race.

And remember, its not a competition man, just a discussion.

I've said it before Gabriel, an education is in no way a guarantee of intelligence.
Some however seem to believe it is.
flag gingy-0
Posted: Sep 22, 2016 at 8:06 Quote
Nobble wrote:
gabriel-mission9 wrote:
Nobble wrote:
bigger bearings are always better under ANY equal loading scenario. Bigger bearings equals bigger contact surfaces which equals less surface wear.

A Shimano or RF setup requires some degree of bearing preload which is arguably worse for them than being side loaded some of the time.

Bigger balls in the same size outer race = fewer balls = smaller contacting surface area. Same size balls on a thicker inner race = no actual difference whatsoever.

A fairly insignificant (compared to the side loads that will be applied in use) amount of preload on 2 bearings, which will only ever take side loads in the same direction as the preload, is much nicer than a single bearing taking all the loads in both directions. Especially if you consider the slop when the load changes from one direction to another, meaning the balls actually impact the inside of the race, rather than just applying varying pressure to a surface they are always in contact with as with a shimano or rf setup.
god damn, you can be dumb sometimes.

If you really need me to, I'll get out my bearing design textbook just for you when I get home.
f*cking nerd lmao
flag Nobble
Posted: Sep 22, 2016 at 9:12 Quote
gabriel-mission9 wrote:
Nobble wrote:
god damn, you can be dumb sometimes.

If you really need me to, I'll get out my bearing design textbook just for you when I get home.

Serious question, why are you so f*cking angry all the time? I have literally never seen you disagree with anyone, even over the most insignificant details, without resorting to calling them a prick. Sometimes you don't even disagree, you just take the piss cos someone who's obviously new to the sport asks a simple question or whatever. Its the internet man. Chill the f*ck out. Really, I don't feel any worse about myself because someone on the other side of the planet types into his keyboard that I'm stupid. The only person you are pissing off is yourself. Why bother doing that to yourself, its just gonna make you feel bad. I have a mate who does similar things. I once told him when he bought a new car that I'd have got a different colour. He spent the next two hours lecturing me about resale value, and hiding the dirt and all sorts. Two hours later he had worked himself into such a state I had to buy him a pint and tell him it was all ok. Now he's losing his hair. Just saying...

Anyway, have you had time to refer to your bearing design textbooks yet? I am genuinely interested to find out how loading one (possibly slightly larger/fewer balled, possibly not) bearing and repeatedly changing the direction of that load is preferable to sharing the load between two bearings, which are always loaded from one side only, and preloaded gently which should reduce the number of impacts between ball and race.

And remember, its not a competition man, just a discussion.
so, I've done a little reading while in bed before going to work, and I think it actually stems from the way loads are applied more so than bearing size. When you ride a bike and axially load the BB, say you're making a turn with the bike leaned over. You're actually only loading one bearing. Force is only applied to the "top" bearing. There is nothing applying an axial load to the bottom bearing because the other crank and cap is pushing away from the bearing rather than into it. What SRAM does is concentrate axial loading into one bearing in all loading scenarios.

According to SKF, The thrust load rating of a bearing is typically 25-50% of the radial load, and bigger bearings have higher load ratings because you're more resistant to surface deformation. Remember, only a few balls are under load at any given time so the total number of balls isn't as important.

Under side loading, static failure is probably the biggest concern. Meaning a really big force permanently deforms the balls and race surface. Bigger bearing equals bigger force for this to happen.

Also, the NDS bearing are usually the ones to wear first and making them bigger makes them last longer overall.

Apologies for my long winded and probably rambling explanation. I haven't even had my morning coffee yet.

Yes, I can be short with people on here. The amount of bullshit propagated is astonishing, like the guy the other day who was convinced that different drivetrain speeds are just a marketing ploy by manufacturers to make more money. In three weeks some guy will come into the shop and get mad at us when his drivetrain doesn't work because he read on the internet that it would.
flag gabriel-mission9
Posted: Sep 22, 2016 at 9:43 Quote
Nobble wrote:
gabriel-mission9 wrote:
Nobble wrote:
god damn, you can be dumb sometimes.

If you really need me to, I'll get out my bearing design textbook just for you when I get home.

Serious question, why are you so f*cking angry all the time? I have literally never seen you disagree with anyone, even over the most insignificant details, without resorting to calling them a prick. Sometimes you don't even disagree, you just take the piss cos someone who's obviously new to the sport asks a simple question or whatever. Its the internet man. Chill the f*ck out. Really, I don't feel any worse about myself because someone on the other side of the planet types into his keyboard that I'm stupid. The only person you are pissing off is yourself. Why bother doing that to yourself, its just gonna make you feel bad. I have a mate who does similar things. I once told him when he bought a new car that I'd have got a different colour. He spent the next two hours lecturing me about resale value, and hiding the dirt and all sorts. Two hours later he had worked himself into such a state I had to buy him a pint and tell him it was all ok. Now he's losing his hair. Just saying...

Anyway, have you had time to refer to your bearing design textbooks yet? I am genuinely interested to find out how loading one (possibly slightly larger/fewer balled, possibly not) bearing and repeatedly changing the direction of that load is preferable to sharing the load between two bearings, which are always loaded from one side only, and preloaded gently which should reduce the number of impacts between ball and race.

And remember, its not a competition man, just a discussion.
so, I've done a little reading while in bed before going to work, and I think it actually stems from the way loads are applied more so than bearing size. When you ride a bike and axially load the BB, say you're making a turn with the bike leaned over. You're actually only loading one bearing. Force is only applied to the "top" bearing. There is nothing applying an axial load to the bottom bearing because the other crank and cap is pushing away from the bearing rather than into it. What SRAM does is concentrate axial loading into one bearing in all loading scenarios.

According to SKF, The thrust load rating of a bearing is typically 25-50% of the radial load, and bigger bearings have higher load ratings because you're more resistant to surface deformation. Remember, only a few balls are under load at any given time so the total number of balls isn't as important.

Under side loading, static failure is probably the biggest concern. Meaning a really big force permanently deforms the balls and race surface. Bigger bearing equals bigger force for this to happen.

Also, the NDS bearing are usually the ones to wear first and making them bigger makes them last longer overall.

Apologies for my long winded and probably rambling explanation. I haven't even had my morning coffee yet.

Yes, I can be short with people on here. The amount of bullshit propagated is astonishing, like the guy the other day who was convinced that different drivetrain speeds are just a marketing ploy by manufacturers to make more money. In three weeks some guy will come into the shop and get mad at us when his drivetrain doesn't work because he read on the internet that it would.

This all makes sense. And yes bigger bearings (when looked at individually) suffer less from surface deformation. Absolutely relevant for downward loads when standing on the cranks with the bike upright, as only a few balls at the bottom of bearing are taking the load.

However surely for side loading situations, all balls are loaded at once, as the whole inner race tries to exit stage left. This means then the load is shared between all bearings, and suddenly the number of contact points becomes relevant to the total surface area the force is being put through.

Shit, lights being turned off at work. i gotta go....
flag Arnoodles
Posted: Sep 22, 2016 at 9:49 Quote
You're never gonna get a pure axial load on a bottom bracket bearing so you can't simplify it to all balls sharing the load equally.
flag TinyTim10
Posted: Sep 22, 2016 at 10:34 Quote
Look what I've started... haha!
flag bromando
Posted: Sep 24, 2016 at 5:22 Quote
should I go to a 35 bar
flag jfkusa
O+
Posted: Sep 24, 2016 at 6:30 Quote
bromando wrote:
should I go to a 35 bar
do you need a new bar? If yes, maybe, if no, don't waste your money.
flag Arnoodles
Posted: Sep 24, 2016 at 7:07 Quote
I like my 35 stuff but I simultaneously went carbon, so no clue if the size itself is better or worse per se. Certainly doesn't seem too harsh like some people say but that might be the carbon working its magic.
flag goytay
Posted: Sep 24, 2016 at 8:30 Quote
Arnoodles wrote:
I like my 35 stuff but I simultaneously went carbon, so no clue if the size itself is better or worse per se. Certainly doesn't seem too harsh like some people say but that might be the carbon working its magic.

Same here, went 35 carbon and won't go back.
flag sherbet
Posted: Sep 24, 2016 at 11:21 Quote
On alloy 35 here. Difference is not large. Little stiffer.
flag fredro
Posted: Sep 24, 2016 at 13:25 Quote
More girth is significant difference. Wink

 


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