front center calculation

[soulspinner]

If the head tube is slackened from 73 to 72 degrees, fork rake is changed from 45 to 50 and top tube remains the same, how much longer will the front center be?

[mosca]

What are the ST and TT lengths?

[Dave]

This would depend on the distance from the center of the wheel to the TT/HT intersection point, so it's c-c frame size dependent. The formula to use is (cosA-cosB) x length, where A and B are the two head tube angles and the length is the distance I just described.

For small frames, like the 51cm c-c that I ride, the HTA change would increase the F-C by roughly 8mm. For a 10cm larger frame, the change would be about 9.5cm.

The change to the F-C due to the change in fork offset (rake) is proportional to 1/sinH. For all practical purposes, it's 1/1 so that would add another 5mm.

That makes the answer somewhere in the 13-15mm range. No sense worrying about fractions of millimeters.

[soulspinner]

What are the ST and TT lengths?

ST=52.5 c-c
TT=54c-c

[soulspinner]

This would depend on the distance from the center of the wheel to the TT/HT intersection point, so it's c-c frame size dependent. The formula to use is (cosA-cosB) x length, where A and B are the two head tube angles and the length is the distance I just described.

For small frames, like the 51cm c-c that I ride, the HTA change would increase the F-C by roughly 8mm. For a 10cm larger frame, the change would be about 9.5cm.

The change to the F-C due to the change in fork offset (rake) is proportional to 1/sinH. For all practical purposes, it's 1/1 so that would add another 5mm.

That makes the answer somewhere in the 13-15mm range. No sense worrying about fractions of millimeters.

Thanks Dave, I googled but couldnt find the answer. As always I value your input on this board and RBR. Cheers and watch 4 black ice...

[mosca]

Yep, my expensive CAD program tells me it would be about 14mm. In other words, "what Dave said."

[brians647]

Yeah, after my post the other day about head tube angles, I've been goofing around on Bikecad here and there to figure things out. It's helpful, especially for the geometrically challenged like me.

[swoop]

hold it, isn't 'front center' the measurement from the center of the bb to the center of the front axle (and nothing else but that)?

[Viper]

If the head tube is slackened from 73 to 72 degrees, fork rake is changed from 45 to 50 and top tube remains the same, how much longer will the front center be?

If a 54 cc top tube was heading east at 18mph, leaving the station at 12:30pm EST and another top tube which was ~13-15mm longer left the same station at 1pm EST traveling west at 22mph, by 8pm EST that night, how far apart are the two top tubes? Note, the track is straight, there is a bar car, DarrenCT is drinking and the Olsen twins are in tow.

:beer:

[manet]

hold it, isn't 'front center' the measurement from the center of the bb to the center of the front axle (and nothing else but that)?

me 2

[Tobias]

hold it, isn't 'front center' the measurement from the center of the bb to the center of the front axle (and nothing else but that)?If you are implying that there was not enough information given to calculate an exact answer you are correct. However, for comparing relative toe clearances or changes to weight distribution it’s more than good enough IMHO.
I don’t know how much accuracy some people need. Would a guy ever pass on a bike because the front center is 2 millimeters too long or too short? How about having a custom bike designed so the front center matches the numbers in his wife’s birthday? It's probably been done.

[soulspinner]

Just a toe overlap calculation.

[Grant McLean]

I'm not a bike builder, but I play one here:

http://www.bikeforest.com/CAD/bcad.php

-g

[thwart]

Thanks much, Grant! :banana:

[Tobias]

Just a toe overlap calculation.If overlap is very important to you maybe you should also consider smaller wheels as a possible solution rather than limit it to odd geometry -- not that your question suggests an odd geometry for certain riding styles.

[Ti Designs]

Look, strange women lying in ponds distributing swords is no basis for a system of government!

[swoop]

If you are implying that there was not enough information given to calculate an exact answer you are correct. However, for comparing relative toe clearances or changes to weight distribution it’s more than good enough IMHO.
I don’t know how much accuracy some people need. Would a guy ever pass on a bike because the front center is 2 millimeters too long or too short? How about having a custom bike designed so the front center matches the numbers in his wife’s birthday? It's probably been done.


i'm not implying anything.. i'm just stating the term 'front center' is the measurement form the center of the bb to the center of the front axle.
there's no hidden message.