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I've tried looking at trig calculators but i'm too stupid to understand.
Can anyone tell me is there a rough and ready calculation that relates bar height to head angle? ie if i stick a -2degree slackset in, all other things remaining the same, by how much will this drop my bar height?
Thank you.
Depends, but not a lot.
The easiest way would be using sin/cos/tan using known angles and assume one is a right angle. I think a change of 2 degrees will amount to bugger all because if I am imagining it right the " fulcrum of the change in angle is at the top of the head tube? So the ngle is only acting on the length of your stem above that point? I think?
With small angles, swap to radians and then calculate by length of stem.
2 degrees is 2x3.14x(2/360) radians. Add on a 70 mm stem on and it will move 70 times this angle in radians. So 2.44 mm. Or nothing really.
If you use tired's formula, doesn't the end of the stem go UP not down? The top of the steerer will go back and slightly down, which means the end if the stem at the handlebars go up and back?
I've never even heard of radians, but thank you. I think i'm grasping that the answer is essentially bugger all.
If you use tired’s formula, doesn’t the end of the stem go UP not down? The top of the steerer will go back and slightly down, which means the end if the stem at the handlebars go up and back?
Yes, but with the head angle being greater, the whole front of the frame will also be slightly lower and the wheelbase will also increase.
And don't forget to also factor in how much the headtube drops due to the slacker fork angle. Because of the longer arm I'd guess this is more significant.
Edit: too slow, busy multi tasking doing the kids breakfast.
Yes, but with the head angle being
greater, the whole front of the frame will also be slightly lower and the wheelbase will also increase.
Lesser?
Smaller head angle, slacker and lower.
Doesn't 10mm get quoted as average BB drop for -2degs? Which seems a lot, and would be even more at the bars.
Lesser?
Smaller head angle, slacker and lower.
Aye, sorry.
That calculator is useful, thanks. It shows me that reducing the head angle by 2 degrees is in itself going to have very little effect on bar height - even though i'll be dropping the front end by reducing HA, obviously the stem will be clamping to a steerer that is also at the new relaxed angle so it will have the effect of adding a couple of degrees of rise.
What i was really trying to work out in all of this is whether fitting a works components 49mm external bottom headset cup which has a stack of 14mm from a hope internal cup (so about 10mm difference in stack) is going to raise my front end or whether the 2 degree slackening of the HA would cancel this out. Probably a better question to ask is if i'd even bloody notice anyway... thank you for indulging me.
Use this:
Based on my rough figures, your head tube will drop by exactly the same amount due to the angle change as the external lower cup pushes it higher. The end result will be the head angle slackens by a bit over 2 degrees whilst everything else stays the same.
Magic. Thank you. Knew there'd be a clever thing out there somewhere - and the answer is pretty much what i expected.