Reducing vibration/tyre pressure

I think now you should try in mountain biking, It is more adventures and enjoyable too. 

But you should take your eyes carefull on safety otherwise all will be gone to vein. I think change your one get a latest one with full suspension and i read here https://coolidealbike.com/

a lot of reviews on mountain bike with full suspension and it will resolve your problem.

A steel frame is not the solution. Defy is already one of the best alu frames in this regard. Wheels are an expensive option but if you choose wisely they *may* bring a slightly smoother ride.

Lighter, more compliant tyres (Schwalbe One or ZX, GP4000S, Michelin Pro4) will ride better than heavy tyres with their stiff sidewalls and thick puncture belt.

Position and angle of your handlebars and shifters can make a difference to comfort and weight distribution, as can saddle (both height and fore/aft setting).

Drop pressure in 10 psi increments until it gets draggy and/or you are at risk of pinch punctures - probably around 40 psi front & 50 psi rear for 60kg lightweights, higher for heavier riders. Front can go lower than rear, as you've already tried.

The other factor is modern deep rim low spoke count wheels. They are stiff and efficient but very uncomfortable on rough roads.

Back in the day on the pavé the pros used to go for a low profile rim and 32-26 spoke wheels because the rims were more flexible and gave a softer ride. It's something worth thinking about, any wheelbuilder can make them and they're not even expensive.

This written after getting a bit sick of bashing over bloody speed bumps (CS1) on my commute on my Canyon Ultimate AL with Zondas, which is normally a beautifully smooth ride thanks to the carbon/basalt seatpost and carbon forks, but now feels to harsh.

A steel frame soaks up vibrations - aluminum delivers them to your brain.   Aluminum bikes are great in countries like Germany or Japan where the roads are kept in good condition.  GB and US roads are full of bomb craters.

It's not only tire pressure and size, but also material and thickness.  I find a flxible and thin skinned  28mm Conti GP4000II @ 95 psi to be softer riding than a tough thick puncture proof 38mm Conti Top Contact @ 70 psi.  

How slammed is your stem?
I discovered, when I moved just one spacer, I got headaches as you describe on rough ground.

Fit the widest tyres your bike can accomodate and keep lowering the pressure until you're happy. If it's still not good enough and you can't fit anything wider, you've got a wrong bike for the task.

Correct pressure depends partly on weight (amongst other factors). So a heavy rider like me (north of 100kg) might use 100psi on 28mm never mind on 25mm.

Having said all that I do find 28mm to be better for me. Though a lighter rider has more options.

100 PSI in 25mms is way too high anyway.

60 and 80 is more like it - but headache ? Are you drinking enough ?  

My old Giant TCR was awesome for soaking up road vibration - you could ride over a drain and not feel it.  I'm sure you could pick up an old carbon TCR for pennies. 

listerine wrote:

On smooth roads I typically run 100psi in my 25mm tyres. But I often ride in the area around my flat in London, and the roads are absolutely disasterous, filled with cracks and speed bumps. A 10km ride, even when running 60psi on the front and 80 on the back, will usually leave me with a headache. Short of riding my mountain bike, are there any decent ways to reduce the sheet amount of vibration which is transmitted through the bike? I have just bought a 28mm rear tyre, and will try that this afternoon. I also looked at Canyon's suspension seatpost, but, with only 10cm of exposed post on my frame, am not confident it will have a substantial effect.  I ride a Giant Defy aluminium bike.

(from the page source)

Eh ?