How much stack height does a Chris King No Thread Set buy me?

[Wayne77]

I'm running an integrated HS in my Klein at present. It has a flange that sticks up about 7mm above the top of the HT. I plan on using a CK for my new Serotta and was wondering how much stack height this will buy me. I can see from the website that the total stack height is 31.8mm with a lower stack height of 13.4mm. Do I use the total stack height or do I need to subtract the lower stack height from the total?

Thanks!

Also, does anyone know how much setback a Shimano DA, or Campy Centaur seatpost has, compared to a zero setback Thomson? I'm looking for a nice polished aluminum post, but I'm not sure that I'm sold on the looks of the Thomson zero setback post yet.

[lnomalley]

as i remember the rule of thumb for chris king is 3cm. now, my memory usually is a little soggy so i'd say i am only 95% sure on this one.

[dave thompson]

.....Also, does anyone know how much setback a Shimano DA, or Campy Centaur seatpost has, compared to a zero setback Thomson? I'm looking for a nice polished aluminum post, but I'm not sure that I'm sold on the looks of the Thomson zero setback post yet.
According to the catalog, Campy seatposts (all) have 25mm offset and Shimano 20mm.

[dirtdigger88]

dave you beat me too it- I was going to guess Dura Ace to be 1.75cm to 2cm offset because I just changed from a Thomson to a Dura Ace-

Jason

[Smiley]

Height of Chris King head set above the head tube is 1.8 cm .

[Dave]

If all fork were the same length, then all you'd have to do is add the head tube length to the headset stack height to make a valid comparison. Unfortunately, forks can vary in length from 365 to 374mm, so this could affect the accuracy of any calculation that ignored fork length.

BB drop should also be considered. If the Kein has a more common 7cm drop and the Serotta has an 8cm, then the saddle will be 1cm lower relative to the head tube.

As for the seatpost setback, a measurement taken to the center of the seat rail clamp doesn't quite tell a completely accurate story with regard to the limits of saddle setback. The front of the seat rail clamp limits the rearward travel. A front of the clamp on the Thomson is 2cm ahead of the seatpost centerline, while traditional posts like Campy and Shimano wil be located very close to the centerline of the post. Campy's long seat rail clamp limits the forward travel of the saddle more than some other brands.

Personally, I'd never buy anything but a 2-bolt clamp, which permits very fine adjustment of the saddle angle. I also prefer to center the saddle as close as possible on the clamp. I like the ITM/Selcof or FSA K-force models. The FSA now comes in two differnt setbacks. The model with the most setback has the front of the seat rail clamp 1.5cm behind the centerline of the post. The ITM/Selcof model has the front of the clamp about .5cm behind the centerline of the seatpost.

[Wayne77]

Assuming forks of equal length, same bb drop, would I only add the CK upper stack height of 1.8cm or do I use the total stack height of 3.18 cm?

I've got 4cm of spacers now and I'm wondering how much I can eliminate with the use of a CK compared to my current integrated HS. (adjusting for HT length differences, BB drop differences, stem angle differences, and fork length differences)

I guess this thread probably belongs in the Fit discussion...


Thanks!

[Dave]

Just measure from the bottom of the head tube to the top of the headset on your Klein. For the Serotta, add the head tube length plus 31.8mm for the king headset.

Ignoring a big difference in BB drop isn't wise. The lower Serotta BB will effectively lengthen it's head tube, by 1cm.

[Richard]

Dave, you've lost me. Don't the "internal" or "cockpit" dimensions hold constant with a change in BB drop? All I see happening is a change in the angle of the chain stays and down tube while all else holds equal. Please explain what you mean by your statement.

[Wayne77]

Just measure from the bottom of the head tube to the top of the headset on your Klein. For the Serotta, add the head tube length plus 31.8mm for the king headset.

Ignoring a big difference in BB drop isn't wise. The lower Serotta BB will effectively lengthen it's head tube, by 1cm.

Thanks Dave,

I will include the lower BB in my calcs.

[Wayne77]

Dave, you've lost me. Don't the "internal" or "cockpit" dimensions hold constant with a change in BB drop? All I see happening is a change in the angle of the chain stays and down tube while all else holds equal. Please explain what you mean by your statement.


Dave, correct me if I'm wrong, but I'm pretty that since lowering the BB lowers the pedals, the saddle will need to come down by the same amount to preserve the same BB>top of saddle distance, which will then reduce the saddle to bar drop. (Bar height being unaffected by lowering the bb)

[Dave]

Remember that the idea behind lowering the BB is to lower the rider and the center of gravity of the bike (relative to the ground. A given rider should have a fixed saddle height relative to the BB. If the BB is 1cm lower, then the saddle will also be about 1cm lower relative to the ground, but the position of the fork crown race does not change. Therefore any given head tube length on a bike with an 8cm BB drop will be about 1cm higher relative to the saddle, than the same HT length on a bike with a 7cm BB drop.