Just leaving this here for the next time I need it
Back in the '70s, to arrive at seat height, we would take an LP album cover, back up against a wall barefoot, tuck the album cover in the crotch and, using the cover as a T-square, mark the wall and multiply the measurement by 1.09. The resulting measurement was then applied to theoretical center of the pedal spindle, crank arm paralleling seat tube, to the seat top. It worked perfectly.
is the 0.09 factor to account for foot extension?
Over the weekend, I noticed that when I’m pedaling on my full squish, it feels like I am making much better use of my glutes than when I’m on the road bike, where my power generation feels really quad-dominant. I feel a lot more powerful on the mountain bike and even realized that I PR-ed a long road straightaway that I ride a lot. I think my two or three fastest times are all on the full squish. It probably has something to do with the more upright position catching the constant tailwind better, but all the same, I would expect my road bike on 30mm slicks to be faster than a full suspension mountain bike on 2.5" Minions and 760mm bars maxing out at 32/11 gearing. I feel like I’m just not making as much power on the road bike.
I’m going to try to replicate the saddle position of the mountain bike on the road bike, but I don’t know if that will actually work given the totally different arrangements of everything else.
What are the things I can/should think about here? Forward? Back? My cleats are scooted all the way back on the shoe. Should I look at that?
Trying to resist the urge to just try everything and never know what made what difference.
Compare the saddle height and saddle setback. The crank length is the same between both bikes?
Mountain bike has 165 mm, waiting on the 165 cranks I ordered to come back in stock for the road bike.
Working on comparing the saddle positions relative to the BB.
Well, I spent a little time trying to get a rough comparison of the two bikes and their saddle positions. The mountain bike has the saddle a little forward of center on the rails and somewhere in the 74.5º to 75º effective seat tube angle by my back of the napkin math. Dropper has basically no setback.
On the Endpoint (74º STA), I had the saddle slammed all the way back on a 25mm setback post from a little while ago when I wanted to take some weight off my hands. Scooted it forward a bit and didn’t raise or lower the saddle at all. I took it for a very quick sprint up and down that short straightaway near my house (San Jose ave for SF people) and it feels a lot better. I think I was pointing my toes too much? I probably also should have lowered the saddle a bit when I scooted it back.
I don’t think I am going to actually try to replicate the saddle position of the mountain bike just yet. Seems like the weight distribution would get all fucked up.
Anyway, I’m probably going to keep tweaking this, but does this seem like I am on the right track? I’m stabbing around mostly in the dark here.
To compare saddle setback, you should measure from the center of the BB spindle to the nose of the saddle in the horizontal direction. If you have a laser level, it’s a little easier. You can also hang a pumb line so it intersects the spindle.
I usually start from my reference measurement and make adjustments. From talking with a fitter, that’s about they do for MTB fit, too: just put the saddle in the same place and tweak.
I feel like you should measure horizontally from your sit bone position to the BB on each saddle, because saddle nose lengths differ
Lucky for me I am using a Fabric Scoop on both bikes, so we’re good there. Right now the nose of the saddle on the mtb is about 10mm in front of the center of the bb, road bike is 5-10mm behind. Measurements are rough because my plumb bob is a piece of thread from a sewing kit tied to a washer and it it gets blown around a lot.
I might experiment with scooting it forward a bit more on the road bike, but I am going to wait on making more drastic changes until I’ve really had a chance to ride set up like it is now.
Dave Kirk wrote about a method to make that easier. Put the rear wheel of the bike against a wall/corner, and measure the BB and saddle from the wall. Then do the same with bike #2 and compare numbers.
Also mine, but with dental floss.
oh, that’s clever. I like it.
I think I am going to get a plumb bob. I don’t need it that badly, but they look cool and it probably won’t take up too much space in my tool kit.
hate my plumb bob, love my tape measure and floor/wall combo
I can almost guarantee that I will be using it for some non-intended purpose almost immediately. Or playing with it at my desk.
So wife’s niner is really uncomfortable now after years of use a kid then significantly less use. She keeps trying to scoot back on the saddle. She’s got a Thompson setback on there now with a cambium saddle and a 100mm stem. She feels too over the bars. She doesn’t really like the look of the VO post much. So what other options are there that have a decent amount of setback. I have a service course on my soma I could swap on to see if it works better but that’s marginal gains. Maybe that and a longer crank might help.
IIRC, the Thomson setback has less effective setback (range of saddle adjustment) than some straight posts or something like that because of the shape of the head. I’m going off of a memory from like 8 years ago, but I don’t think it’s changed at all since then.
I bet almost any post with any setback at all would give a little more than what’s on there.
backing dfl on this. start with whatever regular setback post you have and work from there.
Cheap laser or gtfo.
Swapped my zipp service course into her bike which lists 25mm offset vs 20mm for Thomson. Gained a half inch of setback. Now I need to buy myself a new seatpost I think since I’m pretty sure it’s stolen now.
Are you taking sagged/loaded suspension into account? I think on my full squish the effective ST is about 70 degrees.
Er damn it is actually more complicated than I thought
Not really taking sag into account, just because it’s going to change a bit kind of no matter what. Also the math just gets too complicated for me to bother with, tbh.
That 74.5º to 75º is my attempt at finding the effective angle based on my saddle height, but I have a fairly limited measuring capability and my geometry skills are a little rusty. Typically my effective STA is pretty close to or a bit steeper than listed for most bikes since my saddle height is so low (580mm BB to saddle rail with a 165 crank).