Guys,

I'm replacing my old Specialized saddle with an Sella Italia SLR Max gel flow. I want to keep the saddle height exactly the same as before. I think the rail height might be different on the two saddles. So how to do that?

Thank you!

AX

Can't be done. Oh you can measure from the BB over the top of the saddle and back down to the other side of the BB. That will get you two saddles at the same height. But what about saddle compression? When you get on the two different saddles, the two won't compress the same. Trial and error is the only answer beyond the ball park that the measurement provides.

oh stop it

Approximate with a tape measure (I always measured center of bottom bracket along the seat tube to the center of the saddle, although I'll switch to rpenmanparker's more accurate bb to bb measurement) and fine tune position and tilt until it feels the same.

Saddle curves and not sitting in exactly the same spot on different ones preclude an exact solution.

I _hate_ changing saddles and seatposts.

Mostly.

You can get close though.

Put a straight edge or ruler over the part of the saddle where you actually sit and measure to the BB center from that edge using a tape measure.

Now put on the new saddle, level it out, then put the ruler over where you will be sitting on the new saddle and match the measurement as best as you can.

Never.

I have saddles which have sagged with usage over time and have had to reset their height. Then a new one of the same type and model doesn't fit right at that height. Also I have two saddles of the same model and brand but with different density foam that have to be run at different heights to get the leg extension the same.

Drill a hole thru your bike shorts directly under your sitbone. Run a piece of string out this hole and down to the bottom bracket while sitting on the bike. Measure and replicate with the new saddle. May be easier if the saddles have a cut out.

Place a book on top of the seat and measure to the top of the book on both ends. This will not only give you the height but the angle very close, and the edge of the book is a nice defined place to measure to.

You should also consider taking some measurements from the old saddle to the stem to get it in the same fore/aft position. The saddle fore aft position will change if the shape of the new saddle is wider or narrower as you settle in at a new spot.

That's really true. So I would measure everything possible and try and come as close as you can to exact replication. Then do micro adjustments after a few rides.

There's an easy way that is "right". And once you know the dimension,, you can set up any bike's seat height fast.

It's all about getting your hips the right height above the BB and pedals so you have the most natural knee bend. (This test assumes you want the same seat "height" you had before.) So:

Sit on your old bike next to a wall so you are centered on the bike and seat. Rotate one crank, say the right, all the way down. (Always use the same crank, right or left. Different crank lengths DO put a hitch into this method.) Place your heel on the underside of the pedal so the heel bone is on the spindle with your knee straight. Now bend your knee. Don't rock your hips! If your heel lifts off, put on a thick sock and repeat the test. Still lift off? Try a low heeled cycling shoe. Perhaps a slipper. Keep going until you find that footwear where you can straighten your knee or flex it a bit and your heel does not lift off. There is one very specific point where you can pass that test. For me it is barefoot. I do best with a fair amount of knee bend.

Now just set up your new bike to pass that same test with the same footwear. And remember the footwear. It will save you a lot of time down the road.

Ben

Why measure all the way to the BB? Don't you just have to maintain the same distance from the top of the seat to the top of the seat tube? Give or take a few mm based on compression differences.

You are right for a single bike. Using the BB is standard practice to allow different bikes to be matched.

With the pedal in an identical position(both saddles), your knee should also be in same position. Set up a jig to check this.

I ride the old seat first, then just swap the saddle by eye and take a spin around the block.

I feel any height difference immediately and adjust.

Use a stick. I use a stick. ... or a rigid ruler. You can get close enough to prevent having to make big changes on your first ride.

Obviously measure from the BB shell or the pedal, and press on the saddle to see how much it flexesk, then measure. Sure, it ain't a technique NASA would use, but it's not rocket surgery

Don't forget that reading will differ with latitude and altitude, maybe as much as a mm.

Another method would be to tie a string to the ceiling and cut it off where it touches the old seat. Put the new seat on and line it up with the string.

Despite what fitters would tell you, you can't measure body parts with either accuracy or precision. No engraved marks to go by. It is all by gosh and by golly.

. It's basic geometry.

I don't know what that means in this context. I do know that it would take a metrological "vision system" to get any precision, and you would still not know you were measuring from and to the right points on the body. Where exactly IS that little bone on the knee? Skin and fat further complicate finding the right end points of the measurements. Forget it.

move it up and down as needed

you mean, if you put a permanent marker dot on your knee cap, you wouldn't be able to find it?

Where on your knee cap? How far bent? Don't say a particular angle. How would you measure that either? How much muscle flex? It all matters. Some things simply cannot be accurately or precisely measured.