Profile race crank spindle length

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12/26/2018 4:14 PM

I decided to install the profile cranks I have on my mongoose. The bottom bracket is a mid. The spindle I have is 5 1/4”
Per this https://www.profileracing.com/faq/q-and-a-which-spindle-do-i-need/ I need a 5 5/8”
I thought my 5 1/4 would be too short but without any spacers it was too loose. I installed a couple spacers on the drive side and 3 on the non drive. Q factor is pretty narrow. I used the profile tool to install so the arms are definitely on there plenty.

Seems a bit strange to me that profile recommends a longer spindle for a mid. Is the idea that one typically installs spacers to take up the slack? perhaps my frames chainstays are narrower than other bikes?

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12/26/2018 4:53 PM

Some frames have narrower/wider BB shells than others. Most aftermarket frames nowadays use a wider BB shell to accommodate wide chainstays & tires. There is a good chance your Mongoose has a narrower BB.

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12/26/2018 5:14 PM

FWIW my mongoose is a 2017 or maybe 2018 l100

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12/27/2018 10:59 AM

mid is the bearing size, not the BB width.

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12/27/2018 11:52 AM

Thanks for the clarification!

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12/27/2018 11:58 AM

pnj wrote:

mid is the bearing size, not the BB width.

Mid and American take the exact same bearings. Mid is a press fit (goes directly into the frame) design with bearings coming from the old American standard.

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12/27/2018 11:59 AM

On this same note, is there a reason why so many bikes are mid/spanish?
I'm so used to BSA on road bikes (threaded) so european. From the road bike world, press fit always creaks so it's weird to me to see press-fit bearings on BMX bikes

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12/27/2018 12:13 PM
Edited Date/Time: 12/27/2018 12:14 PM

belopsky wrote:

On this same note, is there a reason why so many bikes are mid/spanish?
I'm so used to BSA on road bikes (threaded) so european. From the road bike world, press fit always creaks so it's weird to me to see press-fit bearings on BMX bikes

My guess is that it's because they have less pieces & are easier to slap together. Most BMXers want a simple, easy to maintain rig. I could also see the bearing cups getting damaged from certain grinds/stalls.
Also, with how often BMXers break/replace stuff, I'm sure it is much cheaper to replace a Mid BB rather than a Euro/Threaded style BB.

Spacing could also be an issue, a lot of Modern BMX bikes already have poor chain alignment from trying to accommodate for 2.5+ tires. I imagine they would have to make the BB & thus also the Chain Stays narrower to make space for the cups, which means no massive tires for all the trend whores.

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Refs : SnM An1mal, GThompson121, Chuck8273, blizzbikes, bmxsteve99, kevin.brock.338, zinum, Brian_Griffin, billyhandyjunior, riverM, tomdon
Instagram : @timhankinsbmx


12/27/2018 12:15 PM

belopsky wrote:

On this same note, is there a reason why so many bikes are mid/spanish?
I'm so used to BSA on road bikes (threaded) so european. From the road bike world, press fit always creaks so it's weird to me to see press-fit bearings on BMX bikes

Euro sucks. They blow up in next to no time.
Spanish is OK but it's not usable with the 24mm cranks that have appeared on the market in recent years.
Mid can take one hell of a hammering without a problem and can accommodate every crank spindle size.
American is typically just a Mid bearing in a cup.

I can't say I've ever had a problem with a BB creaking or even thought about why road/mtb/etc. have such a problem with press fit creaking but I'd imagine the difference is largely the frame material.

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12/27/2018 12:19 PM

belopsky wrote:

On this same note, is there a reason why so many bikes are mid/spanish?
I'm so used to BSA on road bikes (threaded) so european. From the road bike world, press fit always creaks so it's weird to me to see press-fit bearings on BMX bikes

Press fit bearings creak on road bikes because it's a poor design. Even pf30 with the nylon cups creak. Basically, there's a lot more flex on a road bike, and the bearings are narrower. If they used a mid bb with a tube spacer, it wouldn't creak as much. They suck.
And euro bb's (bsa shell) just didn't last in bmx. The bearings were too small and blew up all the time.

Fun fact. Fbm invented the mid bb by making a shell a profile bearing would press into (pw moto frame, Phil wasson's signature). And before it became the norm, no one made a bearing that fit for 22mm axles.

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12/27/2018 12:24 PM

belopsky wrote:

I decided to install the profile cranks I have on my mongoose. The bottom bracket is a mid. The spindle I have is 5 1/4”
Per this https://www.profileracing.com/faq/q-and-a-which-spindle-do-i-need/ I need a 5 5/8”
I thought my 5 1/4 would be too short but without any spacers it was too loose. I installed a couple spacers on the drive side and 3 on the non drive. Q factor is pretty narrow. I used the profile tool to install so the arms are definitely on there plenty.

Seems a bit strange to me that profile recommends a longer spindle for a mid. Is the idea that one typically installs spacers to take up the slack? perhaps my frames chainstays are narrower than other bikes?

Careful you don't install the cranks flush to the spindle ends; you need to leave some space so that the bolts are always acting in tension(if you bottom the bolt out, it's not going to do anything for keeping the cranks tight)

BTW, Q-factor isn't even really a consideration in BMX; as long as the chainline's OK and the cranks are evenly spaced from the frame it's fine. By design, BMX cranks have an atrocious Q-factor but it serves the purpose of keeping the rider's ankles away from the cranks and preventing ankle injury.

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My Sunday Soundwave V3 Build
Insta: @p.gibbons

"You can't educate pork"
- grumpySteve

"Life should not be a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside in a cloud of smoke, thoroughly used up, totally worn out, and loudly proclaiming "Wow! What a Ride!""
- Hunter S. Thompson

12/27/2018 12:54 PM

JPC wrote:

Mid and American take the exact same bearings. Mid is a press fit (goes directly into the frame) design with bearings coming from the old American standard.

correct.

and the size has nothing to do w/ the width of the spindle or BB shell width.

over the years, BB widths have changed and there is no real standard. Especially with a company like Mongoose.

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12/27/2018 12:56 PM

Thanks so much for all the info. Yes, my crank is on the spindle properly with enough room for the tension bolts to add the tension. Guess nothing to worry about!

Now to get a different set for my Klunker..don't really want to spend the money on another Profile set for a 69 Schwinn I paid $50 for..but have since spent more money on smile

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