I did my first ride yesterday on my new bike and after the 34 mile ride my left knee what aching.

Never had any problem with knee pain before. What could be causing this pain?

Last time this happened to me my seat post had dropped some. It was gradual so it wasn't obvious that it happened. As soon as I raised it back up to it's correct position the pain went away.

YMMV though. It's my story and I'm sticking to it.

Ride today and see how it feels.

Get fitted

Might be an IT band if the post didn't move. Stretch it out good over a couple of days and see if the pain goes away.

where specifically does your knee hurt?

how much do you normally ride, i.e. was a 34 mile ride an epic ride for you or something you do daily?

are the fit measurements for this new bike identical to your old bike? if not, what is different?

likely a fit issue, change from what you're biomechanically accustomed to, and riding fitness issue

ice and advil. then stretch.

Pedals: clipless or platform? Same as your old bike?

Another vote for fit issues.

I highly recommend a professional "fit". I hated the thought of spending the money on something that wasn't visible and touchable but it was very well worth it. I did a BG fit from a specialized dealer. They also follow up with you so it's not just a give them your money and hope it works thing. They let you come back and continue working with you until it's right.

https://www.bikefit.com/forefoot.htm

My 1-sided knee issue was caused by heel rotation. I had speedplays with too much float, allowing my heal to come in. Fixed by switching pedals and aligning cleats so my foot was closer to the crank, more in-line with my knee mechanics.

A friend of mine got a new bike, got fitted at the shop, felt great... at first, then his knee started hurting and got worse to the point that he was regretting his new bike. He got his fit adjusted just a little and all the pain went away. Get fitted.

Fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit fit

Did anybody say get a fit?.... cuz that's what I'd tell you.

Hodie
If you ride with a road shoe with cleats, you can do damage with a poorly aligned shoe over the pedal.
you could also have a pre existing condition for all I know, maybe a runners knee?
Anyhow, bike shoes pedaling at an angle that doesnt closely match your natural gait is one sure way to strain them, so try different cleat angles to see what feel right to you.I have a problem with straining my IT band on the outside of my right knee from having my heel too far out.Now that I re positioned my right side fixed cleat to bring in my heel about 2mm, my knee is getting better, but I still have to watch it, and not push too hard until my tendons feel strong again.
Even with float cleats such as the Yellow pad shimano spd-L model, you want to have the cleat well within range so that you do not have the shoe angled way in or way out in order to get your own approximate "Natural Angle".
The fore aft of the cleat should have the ball of the foot not far ahead of the pedal axle, and last of course is having proper saddle height, too low will strain the front part of the knee for sure, and too high will murder the hamstring tendons and have you on the front of the saddle nose

Also Folks,
when Time came out with their hot new rage in road racing pedals and shoes,(1988) they insisted that having float helps the knees.This is helpful to some with bad bio mechanics which need it, but was a bad idea for riders like me, who need carefully aligned zero deg cleats such as the Black LOOK cleats that prove that excess or even a few degrees of float can strain the knees as well. The Look type of pedal allows a choice here which is great. Look includes Shimano SPD-L since theyre offsprings of LOOK
hope all this helps

Fit is one important aspect, but only one.

There are all kinds of reason for general knee pain, general posture, systemic condition like OA or RA, poor skin condition, weakness, neurological conditions, mal alignment of the hip, biomechanical adjustment due to other sports/work nature, amunst many other factors. Even Sexually Transmitted
diseases can cause knee pain.

The "correct" treatment might be to strengthen the glutes roles in maintaining rotational stability of the femur, or encouraging the glide of the knee cap to track better. More information is required as to the nature,location of the condition to rule anything in or out. See a physiotherapist and get a differential diagnosis.

And yes, also make sure your "fit" is optimal.

This is 2010, can some road cyclists realise than "fit" is not the only answer to knee pain!

bravo. i get aches and pain occasionally in one place or another and then it may go away or it may not. it is affected by how i rode that particular day or how out of shape i am at that point. i can go for a long ride and feel no back ache but if i go to the sharpest climbs available to me i will get lower back pain. that is probably due to bad technique.

If it becomes a recurring problem over severl rides after making tweaks and you can't get rid of it, then maybe get a fit.

"Go get a pro fit" because i got a sore whatever. Yeah right. Let some pseudo scientist with a computer dazzle you and it will cure all.

Your saddle "dead on straight?" Change your cleat position with the new bike? Did you forget to HTFU before mounting the bike?

Bingo...

I've had the gammit of body aches and it all started with me knees...

Got a number of so called 'pro-fits' and each one fit me slightly differently an none helped...

What helped me was reading countless articles on fit and making slight adjustments myself and then listening to my body. I still have issues that I am working through, but things are definitely much better then they were...

I also find that as I start to feel better, less pain, I push harder....Then a new pain begins....Of course at this point I have to figure out if it's a change I have made, or just the fact I stepped it up!

RETUL pro fit. By an experienced professional fitter. Good tools in the wrong hands are useless.

Having said this, there is always the chance that you have some physical condition that is being exacerbated by riding. If your other bikes don't bother you, get a fit.

i've seen advice by fitters on youtube that said that "you should always go to the most expensive fitter you can afford". hmmmmmm

"quality is definitely indicated by the cost where bike fitting is concerned". yeah. ok.

While getting fit is crucial, definitely check out some IT band stretches. I started doing them a few times a day after the outside of my right knee started to ache and I'm feeling much better on and off the bike.

fixed

I've been working through a soreness issue in my left knee over the last few days as well. The pain originates on the inside of my knee, but after about 20 minutes of warming up, it doesn't go away, but instead goes 'numb' to the point where its no longer an issue.

My body tells me that when I push down on the pedal, I want to have equal inside/outside leg forces by the knee pushing down on the pedal. first I tried moving pedal closer to the bike, but keeping the fore/aft setting. this did not help, so i figured it was a fore/aft setting. Last night, I tried moving the cleat forward on the pedal. This cleared the pain in my knee suprisingly but my ankle rotation didn't feel locked into a particular motion like on my right leg. I think the cleat is now too far foward. Im thinking my left leg is slightly shorter than my right , but it did not show up on the professional fit.

This is just an example of how to play and work through your setup, as it seems like your problem could be a fit issue.