One of the guys I was riding with last night raised this as a point, and I couldn’t think of a sensible answer, so I thought I would open myself up for ridicule on here.

Clearly I understand it won’t change the actual HA, but he made a good point, or was very convincing in his argument!

If I understood him correctly, the point was regarding the relationship between hand position on the bars and front axle position. Thus the longer the stem, the closer the hands are to the axle and thus creating an effective ‘steeper’ HA. The shorter the stem, the more slack it effectively becomes?

I was trying to relate it to top tubes, and seat tube angles, as they both have different measurements,but I gave up, as we were in the pub, post ride by then and the beer was fuzzing my brain.

Is there any science behind what he’s talking about? Or am I just a nugget for not scoffing immediately at his stupid suggestion?

it will change the handling which you could call effective HA. I can see where they are coming from but it sounds more like trying to associate a change with another measurement.

No, head angle and reach are two different things.

No, it’s quite separate. By having a shorter stem the steering becomes quicker, having a steeper head angle the steering becomes quicker.

Having a long stem i.e. 100mm plus, especially with shorter bars will also give a sort of tiller effect, where you need to move your hands from side to side, rather than in an arc to steer, with the shorter stem giving more of a forward/rear motion of the hands.

Head angle will make a bike more nervous or twitchy the steeper the head angle and more stable or lazier with a slacker head angle

No

As far as I understand it a long front centre (centre of BB to centre of front hub) can add high speed stability to a bike. A slacker HA will give a longer front centre.

Lengthening top tube and at same time reducing the stem length will keep the reach the same, but lengthen the front centre without having to use silly slack HAs (with other undesirable characteristics). It’s what Kona and Mondraker have done.

So you could say a bike with a short stem (and a long top tube) will have similar characterisics to a bike with a longer stem (and a shorter top tube) and a slacker head angle.

Tell your friend he is thinking too much, or drinking too much! 😉

There’s some effects that are similiar though, increased slackiosity or decreased stemmage both move the hand position and default ride position further back from the axle which can be positive on steep stuff etc. But lots more to it than that.

Best thing to do, imo, is fanny about with it, easy to change stem lengths and see how it feels.

I suppose, moving your weight further back will cause the rear suspension to sit lower in its travel kind of slackening your front end

but I suppose you are just affecting the sag really

More to it than that. you can call hand to axle angle “effective HA” if you like, but it’s not very halpful. A shorter stem will change your hand position relative to the front axle, but the “effective” changes are limited to stem length effects on steering (tiller effect as above) and body position on the bike. These changes will be to quicken the steering and make it more twitchy, which is the opposite of what you’d expect from slackening the HA.

Compare it to the changes from moving the axle forward, rather than your hands back – changes to rake, trail, and wheelbase will all have a much more substantial effect on how the bike behaves.

Yes. Kind of. But only in certain circumstances.

If the rear wheel is off the ground, the bike doesn’t “know” what the head angle is, therefore your only relationship is your COG position relative to the tyre contact patch, which would be affected by the stem length (all other things being equal).