Setting a bike up for a turbo

I have an original Tacx Neo, and since a recent bike fit I've been meaning to get the turbo bike setup correctly.
One thing I have, is the saddle quite far forward, and this is where I'm confused. With the riser block in place, the saddle is 3 cm further back from the BB than I would like. Without the block, it's spot on. The riser is the standard one that comes with the Neo.
So should I setup my bike off the riser? Other than stopping the wheel twisting during the session, what's the purpose of a riser?
One thing I have, is the saddle quite far forward, and this is where I'm confused. With the riser block in place, the saddle is 3 cm further back from the BB than I would like. Without the block, it's spot on. The riser is the standard one that comes with the Neo.
So should I setup my bike off the riser? Other than stopping the wheel twisting during the session, what's the purpose of a riser?
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And that's the block I have.
The detail that I might have missed on my first post is that I'm measuring how far behind the BB the tip of the saddle is. the distance that's shown here as '5cm Tolerance'
NOT the height of the saddle.
Yes, every time. I take a lazer level, tape measure and plumb line with me every ride. Some of the guys I ride with find it annoying, but they can't say too much as I crush them up every hill...
Desmond Tutu
Only if I take my MIG welding kit, which is helpful for both mild frame tweaks and resistance training.
If you're also going to do some outdoor rides on it over winter, either adjust things each time you ride in/outdoors, or set the bike up for outdoors and find a height for the front wheel off the floor that works for you.
2020 Voodoo Marasa
2017 Cube Attain GTC Pro Disc 2016
2016 Voodoo Wazoo
Secondly, I don't appreciate being called a "complete idiot", I've come with what I thought was a reasonable question, and have been treated to a stream of sarcastic replies, which I've stooped to with a couple of my responses.
However, my question still stands, and I'd like to understand what I'm seeing and in which position I should set the bike up.
On both occasions the red line goes through the centre of the BB (click on the image to get a clearer version)
So, what's the difference I'm seeing? What am I missing? Happy to have it explained to me, but if the only answers are rude or sarcastic, I'll rather be left floundering in the darkness for an answer.
Thanks.
I am not sure. You have no chance.
My understanding of what the riser does, is that balances out the lift occurs when mounting the bike on the turbo. So why should the measurements be different from when it's on level ground if that's the case? They are the same without the riser as they are on level ground.
Also, the angle of the saddle is out by a couple of degrees, which would further suggest that it's not flat when on the riser.
So there are 3 states
Level ground: Correct
Trainer without riser: Correct
Trainer with riser: Incorrect
I'll say it again though, your fit does not change simply by putting the bike on the turbo. Sorry to say, this really seems like a complete non-issue.
No need to apologise, I'm happy for it to be a non issue, it just seemed to contradict what I thought the purpose of the riser block was. I was just surprised when the difference came out at 2cm, which is a fairly decent amount.
Interesting, where did you read that?
Wrong. Direct drive and wheel on turbos are all different. Some need a riser, some don't. Measure the height of your rear axle from the ground and compare it to the height of the front wheel axle to know if you need or want a riser block. Some prefer to have a slightly more elevated front wheel on the turbo for a perceived more comfortable position like putting a couple of spacers under the bars.
OP, if you're going to ask a question, ask the right question. Claiming that your saddle is moving from its position behind the BB because you've put it on the turbo is factually wrong. Your set up hasn't moved at all.
Your bike set up doesn't change, it's just that your front wheel is lifting because of the block which is there to correct for the additional height of the back wheel in the turbo and to help 'simulate' going up a hill. If you don't like the way the bike feels than just use a smaller (thinner) block. It may look like it's moved if you're using a plumb line to measure it.
BTW you don't need a anything special, my front wheel has sat on a piece of chipboard left over from some work in my loft for years.