The only measurement for a bottom bracket you can do with the bottom bracket still on the bike is to do the shell width, which is the width of the frame where the bottom bracket installs. In order to measure the spindle length, you need to
remove the cranks and then measure the spindle length
.
How do you measure bottom bracket spindle length?
Does spindle length matter on bottom bracket?
The critical thing is your spindle length:
as long as you can set up the correct chainline you will be good to go
. But, again, best never to mix standards if you can at all avoid it. If you are looking to replace a cottered crank setup with a square taper setup, then look no further than a cartridge bottom bracket.
Are all crank spindles the same length?
Spindle length
varies depending on type of crank
(road, Mountain, Triple, etc.). Two-piece system. Crank spindle is pressed into the drive side crank arm.
How do I know what size bottom bracket I need?
To find out the size of bottom bracket needed,
measure the inside of the bottom bracket shell in your frame
, it will be 73mm, 70mm or 68mm. Some older frames may have Italian threaded bottom brackets, instead of the more modern English.
What is a 73mm bottom bracket?
The 68mm and 73mm dimension measure the width of the bottom bracket on the frame of the bike with no BB installed, simply the width of the shell. Most road bikes that use a threaded bottom bracket measure 68mm wide and
most cross country/trail mountain bikes
measure 73mm.
How do I know what size crankset to buy?
Crank length is measured from the centre of the bottom bracket axle to the centre of the pedal axle. If you’re not sure what length the cranks on your bike are, the quickest way of finding out is typically to just
look at the backside of your cranks, just below the pedal axle
.
Are bottom brackets all the same size?
There are 4 widths available with BSA bottom brackets; 68mm, 73mm, 83mm or 100mm
. This bottom bracket clearly shows you on the outside what bearings have been fitted to the bike. For road bikes, a BSA bottom bracket is always 68 mm wide. Other sizes, and particularly the 73 mm width, is commonplace with mountain bikes.
How many miles should a bottom bracket last?
Simple rule is (unless you’re starting a long trip) “if it ain’t broke don’t fix it”. Do normal maintenance, keep things properly lubed and your BB should last for another
4,000 miles or more
.
Should you grease crank spindle?
They advised: “
Grease the tapers, but make sure you only tighten the bolts once, then leave them alone
.” Their tests had shown that a “dry” spindle/crank interface did not result in a consistent press-fit between the parts.
What is an octalink bottom bracket?
Octalink Bottom Brackets. This system, designed by Shimano, was
the first successful alternative to the older square taper
. The Octalink system uses a larger and stiffer spindle with eight splines. The splines provide a greater contact area between crank and spindle for a stiffer interface.
Is hollowtech better than square taper?
Hollowtech is a bit stiffer and easier to take apart, but square taper will last much longer
.
Can I use a 68mm bottom bracket in a 73mm shell?
You could install it, but it will shift your chainline, shift the centerline of your feet, clearance issues might arise on the non-drive side, and you might be leaving some BB shell threads exposed on the non-drive side as well.
What is BB 92?
BB92 refers to the
bottom bracket shell width
, specifically: 41mm BB shell diameter. bearing with a 24mm internal diameter. 24mm diameter spindle on the crank.
What does the 90 in BB90 refer to?
BB90 and BB95
The numbers 90 and 95 refer to
nominal shell width
. This unique bottom bracket shell is not a straight bore but has an internal bearing retainer built into the shell, similar to an integrated headset. Bearing outside diameters are 37mm. BB90 shell and bearing with spindle and bearing removed.
Are all hollowtech BB the same?
Since the spindle is part of the right crank, there’s no issue of compatibility.
All Hollowtech II cranks work with all Hollowtech II bearing units
. Any crank that fits on one type of spindle will fit on all spindles of that type, but if the length is incorrect, the chainline/clearance will vary.
What is hollowtech II?
HOLLOWTECH technology is
an ultra-lightweight hollow crankarm created by SHIMANO with the company’s own proprietary forging technology that also maintains rigidity
.
What is the standard crank arm length?
THE CRANK LENGTH
The most common lengths are
170, 172.5 and 175 mm
, but it is possible to find cranks between 165 and 180 mm in the market. The goal when choosing crank length is to find the best possible balance and various factors must be taken into account when evaluating.
Will shorter cranks help my knees?
Pain is relieved.
Just by installing shorter crank arms, without any other adjustment, the knee at maximum flexion is lowered by 7.5 mm. That difference provides approximately 3° to 4° of relief
.
What is the difference between 170mm and 175mm cranks?
Whereas now 170 is ‘short’ 172.5mm is ‘normal’ and 175 mm cranks are very common. Still though, the difference between 170 mm and 175mm is
less than 3%
and leg lengths of bike riders vary by far more than that.
