Measuring a stem

Mark T said:

Simple question this, where do you measure an aheadset type stem?

I presumed along the top, from the nut thing wot pops down somewhere
inside the fork steerer thingy along to the middle of wot where the
bars would be.

That is the usual way of doing it.

I *think* the official measurement is actually taken from half way down the
horizontal part of the stem (rather than along the top) - a true "centre to
centre".

Quoted message said:

That gives 95mm tho, which is a bit of a funny number.

Some stems come in "half sizes", but not many. So you've /probably/ got a
90 or 100mm. Sorry I can't tell from here ;-)

~PB

ps. Measure to the centre of the bars. Don't assume that's necessarily the
same point as the gap between stem and front plate.

~PB

Pete Biggs said:

ps. Measure to the centre of the bars. Don't assume that's
necessarily the same point as the gap between stem and front plate.

Absolutely.

Some stems are assymetrical, so the true measurement is centre of stem
tube to centre of bars.

Personally I find a change in stem length to make a _big_ difference to
the feel of the bike. Too long and it's a bit slow to react and feels
'slower'. Too short and the opposite occurs, the turn-in feels sharper.

My headset (mountain bike) is about 60mm ... Though I'm only short too
.... 😉

--
Paul - [censored]

'96/'97 Landrover Discovery 300 Tdi 'Big and Butch'
'98 Suzuki DR 200 Djebel 'Small but perfectly formed'
Dyna Tech Cro-Mo comp "When I feel fit enough'

Paul - censored said:

Pete Biggs said:

ps. Measure to the centre of the bars. Don't assume that's
necessarily the same point as the gap between stem and front plate.

Absolutely.

Some stems are assymetrical, so the true measurement is centre of stem
tube to centre of bars.

Bad form replying to one's own post, i know, but ...

If you're changing the stem you also need to make sure the angle is
also what you want. Change the angle of the stem can also give a
different feel and handling to the bike ... as can a different rise of
handlebar ... 😉

If it's a straight swap you're after it'd be easier to take the
original stem to the LBS to check it visually against any they have in
stock.

--
Paul - [censored]

'96/'97 Landrover Discovery 300 Tdi 'Big and Butch'
'98 Suzuki DR 200 Djebel 'Small but perfectly formed'
Dyna Tech Cro-Mo comp "When I feel fit enough'

Quoted message said:

If you're changing the stem you also need to make sure the angle is
also what you want. Change the angle of the stem can also give a
different feel and handling to the bike ... as can a different rise of
handlebar ... 😉

That was the idea, and it feels wonderfully fast and agile.

What's now confusing me is why stem length goes up with the frame size.
What's the reasoning behind that? Surely it'd change the handling between
the very large and very small sizes (e.g. a 120mm stem on a 60cm frame, and
a 90mm stem on a 52cm frame)?

Mark T said:

Quoted message said:

If you're changing the stem you also need to make sure the angle is
also what you want. Change the angle of the stem can also give a
different feel and handling to the bike ... as can a different rise
of handlebar ... 😉

That was the idea, and it feels wonderfully fast and agile.

What's now confusing me is why stem length goes up with the frame
size. What's the reasoning behind that?

I don't know. I don't think there can be any /good/ reasoning. Not all
manufacturers do it anyway.

As far as handling goes, yes it can make a big difference, but also you
rapidly and thoroughly get used to the handling of whatever you have. So it
doesn't really matter much in this way. Most important is the comfort or
efficiency or your riding position (depending on preference).

~PB

Mark T said:

What's now confusing me is why stem length goes up with the frame size.
What's the reasoning behind that? Surely it'd change the handling between
the very large and very small sizes (e.g. a 120mm stem on a 60cm frame, and
a 90mm stem on a 52cm frame)?

I'm no export, but is there typically a relationship between frame size
and the horizontal distance from steerer to the front wheel's contact
patch? I'd have guessed that a larger frame will have a longer head
tube and therefore a longer stem would be used to bring the bars out by
the same amount.

-dan

Quoted message said:

Mark T said:

What's now confusing me is why stem length goes up with the frame
size. What's the reasoning behind that? Surely it'd change the
handling between the very large and very small sizes (e.g. a 120mm
stem on a 60cm frame, and a 90mm stem on a 52cm frame)?

I'm no export, but is there typically a relationship between frame
size and the horizontal distance from steerer to the front wheel's
contact patch? I'd have guessed that a larger frame will have a
longer head tube and therefore a longer stem would be used to bring
the bars out by the same amount.

I don't *think* the bars need to brought out by the same amount (in relation
to the front wheel) - for the bike to handle the same.

Trail is affected by head tube angle (not length), fork offset and tyre
radius.

Then the length of the stem affects the amount of steering leverage.

~PB

In article <[email hidden]>, phil maxwell
[email hidden] says...
otherwise mean lengthening the top tube.

Quoted message said:

Lengthening the top tube would lengthen the wheel base and
thus greatly soften the handling and ride.

Wheelbase isn't that critical. A well-proportioned larger frame will
have a slacker seat tube which takes up at least part of the longer top
tube.

In article <[email hidden]>, Mark T
pleasegivegenerously@warmail*turn_up_the_heat_to_reply*.com.invalid
says...

Quoted message said:

Simple question this, where do you measure an aheadset type stem?

I presumed along the top, from the nut thing wot pops down somewhere inside
the fork steerer thingy along to the middle of wot where the bars would be.
That gives 95mm tho, which is a bit of a funny number.

Back in the old days when all bikes were road and all stems were flat
you just measured centre-to-centre along the extension. These days I
suspect the most standard measurement is normal to the steerer, so a
zero degree stem is measured centre-to-centre and an angled stem is
measured to a projection of the steerer centreline.

phil maxwell said:

A larger size frame usually implies greater leg length.

Greater leg length usually implies longer arms and\or torso

To accommodate the latter while maintaining the same riding angle
would otherwise mean lengthening the top tube.

Lengthening the top tube would lengthen the wheel base and
thus greatly soften the handling and ride.

That's a good theory except larger frames (with longer seat tubes) generally
do have proportionately longer top tubes too. So no need for a longer stem
as well when that is the case.

~PB

Mark T said:

What's now confusing me is why stem length goes up with the frame
size. What's the reasoning behind that? Surely it'd change the
handling between the very large and very small sizes (e.g. a 120mm
stem on a 60cm frame, and a 90mm stem on a 52cm frame)?

Phil's reply has reminded me that there was a time when some larger frames
didn't have much longer top tubes than the smaller frames had, therefore a
longer stem was needed to get the reach.

Maybe (some) manufacturers/suppliers just carry on suplying longer stems
with larger bikes out of habit - even when top tube and seat tube lengths
are in proportion throughout the range.

~PB