I bought a used spin bike (Keller racer), but can’t seem to get it pedaling smoothly. I can dial up the tension, but it goes from easy to very hard quickly. And if I have the tension at medium, I can get pedal with some resistance, but as soon as I stand it feels like there is no tension at all. I am hoping this is a simple adjustment. Thank you in advance for your suggestions!

Is the resistance controlled by magnetic resistance or a felt/cloth pad? Never heard of a Keller? Kettler maybe?

I guess check to see if the felt pad is worn, and replace if it is.
If it’s magnetic make sure the magnets move closer to the flywheel without touching and the movement is smooth when turning the resistance dial.

If it is a Kettler Racer,

there appears to be a complicated function that might be the issue.

"Pressing “P = Fix/Var” will shift from rotation-speed independent to rotation-speed dependent operating mode.A double-headed arrow in the pedal rate display shows the rotation speed dependent operating mode. The limitation of performance is canceled. A change is only possible during training."

I tried a spin bike once. Had to quit because I got too dizzy...

Fanciest looking coat rack I've ever seen

Spin bike riding doesn’t transfer to out door riding gains for me. Would rather have a smart trainer.

https://www.kettlerusa.com/fitness/e...3677?fullSite=

Computer manual---https://s3.amazonaws.com/kettler-manuals/fitness/exercise%20bikes/7988-727.A.pdf

As far as how quickly the resistance ramps up, I have no idea ... that could be idiosyncratic to that machine. Check the manual, make sure all the tolerances are correct, contact the manufacturer (Phone:
866.804.0440 Monday thru Friday 9:00 a.m. to 4:30 p.m. EST ---- email: parts@kettlerusa.com) and ask the pros.

Pretty obviously you put out more power when you stand (you are dropping your body weight onto the pedals plus the force of your muscles) so you can spin stiffer resistance than you can sitting---just as you would need (generally) to shift up when standing on a bike when climbing and switching from sitting to standing, you would want to increase the resistance when standing.--or spin the same resistance with higher revs, depending on how you wanted to exercise.

I did a lot of spinning when I wanted to train for a cross-country charity tour several years back. The work doesn't seem to translate directly, but you are using similar muscles in similar ways, and I found it to be an enjoyable workout, so it worked. Also, on a spin bike (or a trainer) you can go all-out because if your body gives out, you are at home, not 20 miles from home. On the spinner I was willing to work to failure--complete exhaustion---because I could ride by time, not distance---I never went anywhere, so I never had to ride back. Also, when weather refuses to cooperate, the spin bike is always ready to go.

Hope you work out your issues and enjo your opurchase.

spin bikes can give you a nice workout if you have a decent one.