Yes, carseat manufacturers put 30 lbs and 3 years on their boosters. However, it is defnitely not best practice and not what is safests. For the most part the lower weight limits are for kiddos who are super duper light weights and are not going to hit 40 lbs until they are much older and the lower age limit for kids who hit 40 lbs when they are young.
It used to be that the higher weight limit seats were few and expensive. That is simply not the case any more. There are some seats with higher weight limits and that are taller that are more reasonably priced. Even the Britax Regent, which is the tallest, has sales that bring it pretty close to $200.
Here is a list of seats that was compiled an another board. Can you get his torso height? At only 34 lbs, he might actually be able to use a 40 lbs combo seat like the EVenflo Generation. If you want him harnessed longer, look at a a seat that harnesses past 40 lbs.
OH, the list does not include the Nautilus. New seat from Graco. 65 lbs weight limit on the harness with 18 inch top harness slots. Then converts to a hbb then a lbb. Hard to find right now but should be in all Walmarts soon. Might be a good one for you to look at.
Convertible Seats
Britax Marathon, Decathalon, or Boulevard (MA/DC/BV). 17 in top slots, RF 5-33lbs, FF up to 65lbs in 5 point harness. Awesome seats, allow for rf tethering, has lockoffs to replace locking clips, very easy installs, many bells and whistles that make them easier to use correctly every time, lasts most kids to age 5-6y/o. 220+ Check the FAQ sticky thread for a description of the three. - I'd skip these. For the price, you could get a REgent.
Fisher Price Safe Voyage Deluxe (FPSVD).17 inch top slots, RF 5-33lbs, FF up to 55lbs in a 5 point harness. Made by Britax, sold under the FP name- basically a stripped down Britax Marathon. Great seat, awesome price $129 (regular 199$), and will last most kids to age 5-6 y/o.
DISCONTINUED DUE TO POOR SALESBe sure to check date of manufacture before purchase as many people have been getting seats with older dom.
New Evenflo Triumph Advanced RF to 35lbs; FF to 50 lbs. Max harness height of 17". The new Triumph has the infinite harness adjuster too.. no rethreading the harness! Much nicer than the old Triumph! Much taller shell than the old Triumph too! Priced at 150$
Sunshine Kids Radian. 18 in top slots, RF 5-33lbs, FF up to 65lbs in 5 point harness. Great seat, only second to Britax because it has some compatibility issues in some vehicles when installed with seatbelt. Really good seat otherwise, allows for RF tethering, lasts most kids to 6-7y/o. 8yr lifespan (most have a 6yr) $175+
www.skjp.com has the manual available for viewing. The Raidan 80 is basically the same seat with an 80 lbs weight limit, same top harness slots and comes with a bunch of padding, nice for an infant. The extra 15 lbs is really not necessary unless you have a heavy child.
Recaro Como & Signo. Recaro makes seats for NASCAR and has made car seats for the European market and a few for the US market for years. RF to 35lbs, forward face to 70lbs, and has 19" top slots. Bottom slots of 9" so not ideal for newborns.
The outside width of the seat at its widest point is approx. 19 ½ to 20.
The Como & the Signo are basically the same shell the biggest difference is that the Signo has an infinitely adjustable harness (where the Como has to be re-threaded) and the Signo's latch straps are on a bar - similar to Britax (on all their models) - so you don't have to re-thread the latch belt if you're going from rear facing to forward facing.
Early reports on the Como The top of the seat is super narrow. Older kids seem to be very cramped in the shoulder area.
Como is $249; Signo is $289
True Fit Convertible Car seat Available 1st Quarter 2008
rf 5-35 lbs, ff to 65lbs, 10in bottom slots, 18in top slots. 3 crotch positions, Designed to fit smaller cars- headrest is removable for easier rear facing installs in smaller cars. Cover removable without unhooking the harness, lockoffs for rf & ff, harness adjusted with a knob, everything adjusts by sliding something. Covered in EPP Foam.
Available for pre order 179$.
http://gooresblog.blogspot.com/2007/07/new-convertible-car-seat-from-compass.html
http://www.amazon.com/Compass-True-Convertible-Seat-Sporty/dp/B000YBK0H8
http://i5.photobucket.com/albums/y172/murphydog77/truefit.jpg
*does not rear face tether. Compass is adamantly against rf tethers.
*Can only be used rf w/o the headrest to 22lbs. After that the headrest must be used but the seat can be installed more upright to allow more room. Older rf kids prefer to be more upright anyways.
Forward facing only seats (child must be over age 1, and 22#s)
Safegaurd GO. Harnesses to 60#s, becomes a no back booster after. Top slots are 17 to 17.5 inches, needs adjustable headrest behind it for support. Requires top tether anchor. Child must be 30#s to use. Retails for $179
Britax Regent (used to be Husky). KING of car seats is right! Harnesses to 80#s. Top slots are 20 inches. Requires a top tether after child is 50#s. Retails for $220-$260. Not good for children under 2yo. Requires college degree to read the manual.
Ride Safer Vest. A vest that comes in two sizes, Small 35-60#s, Large 50-80#s. The vest can be used with lap only belt. Requires top tether anchor & headrest. Retails for $89-$99. Great for 3 across situations in small vehicles! Tether strap HAS to be used if child is under 6 yrs old.
http://www.safetrafficsystem.com/
FF/Harness Combo Harness/Booster Seats
Cosco/Safety 1st Apex. Only higher weight Combo (FF harness/Booster) seat that harnesses to 65#s. Top slots are 17 inches high. Requires adjustable headrest or a very tall vehicle seatback behind it for support. Then becomes a very nice BUT VERY WIDE booster that doesnt fit small children well.. This seat is outgrown totally when the tips of the childs ears reach the top of the vehicle seatback. (Fully extended it has a back height of 32.5in tall) The new blue/black and all the brown ones have EPP Foam in the headrest. Retails for $99-150.
Evenflo Generations/Bolero: 80-110$ depending on model. FF ONLY to 40lbs with harness. Great harnessed seat/ great booster mode. Open belt guides. TALL 16.5in top slots. Adjusts tall in booster mode too! Flip up armrests make kids happy & make it easier to use in booster mode too!
(The Bolero is the dressed down version of the Generations. It lacks the piddle pad).
Evenflo Chase & Graco Cargo. Harness to ONLY 40lbs ff, 17in top slots. Makes ok, at best, booster. Smaller closed belt guides.. but this can be ok if your seat belts lock & you lock them every time. The Chase is about 60$. The Cargo with front adjuster is about 90$.
The Chase is good for kids/parents that keep forgetting that chest clips go on the chest!
Avoid most other combo seats... VERY low top slots or seatback heights all with 40lb limits.. Just not worth the cost. This includes all the Eddie Bauer, Cosco, Dorel, and 3 in 1's. While safe & decent seats the harness mode doesnt offer much grow room.