Going to 406 will not be comfier, but, u do have way more tyre sizes selection up to size 20 x 2.0. So, its more comfier in that sense.

If the tire size is equal width for 451 and 406...the 451 will be a tad comfier due to bigger diameter rolls over road irregularities better.

I think ur feeling bumpy, maybe ur Java Pro comes with very thin tires like 1 1/8 inch. Go look for wider 1 3/8" tires and there is a few in the market, pump around 60-65 psi, that should do the trick.
There are some cheaper innova/kendas tires that is price ok, and should be fine tires.

If u really prefer squishy feel, haha..no choice u will have to resort to 406 and its wide tyres like ..like the Marathons, Big Apples, Maxxis Torch and DTH...I used to favor this squishy,.. but now im on bone shattering skinny tires Durano.

Here is my experience of using a child seat on the rear of 20" foldie, rear carrier mount kind. Polisport Models, or Decatlon models.

- The foldie will be very unstable once the child on it...the front tend to lift if ur weight is not on the saddle.

- Using those proper ones like Polisport / Decathlon models..ur heels will likely hit on the child's foot that protudes from the chair...too close to pedals.

- U can get away with the leg collision issue, if ur mount type on the rear is on the seatpost...but my strong opinion, ur putting ur child at risk. Im very concern of the single seatpost have to support ur weight, togther with side load from the seat mount.....not worth the risk to me. Not to mention, your bike will tilt over easily.

I tried the cheap ones like those below RM100 selling online..rear rack mounting...but the mounting tools/ strap seat quality/safety..i rather not for any further journey or child is heavy.

If ur child is still lightweight, can try those that mount on the front between u and the handlepost..at least the weight support is loaded on the seatpost and body frame..and ur there to secure the kid.

So, long story short...Big bikes like mtb or touring bikes..still the way to go for using rear mounted child seat for me.

Deli,

I'm with bro Azam, if u want good ride and solid feel, spend a few hundred more to get the Tern ( Verge D9 is only RM2600++ now).
I'm lean more towards 451 wheelset nowadays...

I have just ridden the Java Pro 4 hard...thru dragonbacks and on heavy back load ( baby chair with kid), i know not supposed to do that...just helping lady friend....but on load stress and high speed, frame stability just ain't there, whole bike very flexy and handling wobbly. I can benchmark it as i used to do that on my dahon Vitesse, and yet its way more stable than the Java pro.

Presumably u are willing to spend this range of budget ( RM1800-1900 ??), ..if u want better ride feel on longer distance...get the Tern. or if u just planning to ride taman..still get the Tern...hahaha.

Not to put down the Javas, they are nice bikes for the money...just that for a few hundred more..u can get a Tern D9 now...in shopee rodalink Tern sale...act quick!!

Yup..even the new R7000 Short Cage RD looks long now...macam MTB RD styling.

Any ideas of decent dedicated 1X Hollow cranksets ( besides Litepros, Prowheels ) and the SRAM 1X...( mahal giler).
Been keeping an eye but so far havent came across one yet that suits..

The Litepro crank with its Narrow Wide Chainring has been serving its purpose well tho, without the need of chain catcher or guide. Cheap and Cheerful.

Already can buy a Mid end Dahon or Tern with this reel...