By pure chance I have been flying two almost identical C172S models during the last 10 days. One has the wheel pants, the other not. Although these flights were rather short hops in the L.A. basin, so no real cruise performance comparison, the one with the pants does about 7-10kts more than the other. Quite a difference, given the top speed of these things!
I think the Dakota is the only PA28 that I would buy if I had to buy one 
Ahhh, my RG flies 2 MPH slower with the gear retracted, so I leave it extended much of the time….
It is simply that retractable gear is not cowled so it drags when hanging out
I think it’s more than that – I think many retract gear systems are extra draggy due to all the other bits that fixed gears don’t have, such as gear doors, the various extra struts to make the gear go up and down, and the big hole in the wing that’s left when the wheels are down (the Bonanza with inner gear doors is draggier when the gear is in transit and all the gear doors are open than when the gear has finished extending and the inner gear doors are once again covering the big hole where the wheel was).
Incidentally that’s how you tell if a Bonanza/Baron pilot is telling the truth when you go out to their aircraft sitting on its belly on the runway and they say the gear collapsed. If the gear really did collapse, the landing gear is crumpling the inner gear doors up into the wheel wells. If the gear is still behind the inner gear doors, well, the truth is that for whatever reason the gear was still retracted on touchdown…
The 230 HP dakota loses 7 knots without the wheel pants. Max cruise is 143 per book.
Some schools here operate them like that because they can then take more abuse during landings.
.. and more easy to inspect the tires after all that abuse…
comparing TB20 cruise performance with gear exetended and retracted. The difference (IAS) was 22 kts.
That’s about right. There is also a huge hit on the operating ceiling – at a guess FL120-140 instead of FL200.
The TB20 gear was designed to produce a lot of drag
That cannot be right. Why would they design gear for max drag?
It is simply that retractable gear is not cowled so it drags when hanging out. If you look in the POH for even the slowest (100kt) fixed gear PA28 you find there is a ~7kt loss of speed just by taking off the wheel cowlings. Some schools here operate them like that because they can then take more abuse during landings. So with a 150kt plane (which needs 1.5 ^ 3 more HP) I would expect to lose 23kt (cowled wheels versus bare wheels).
I do recall doing a TB10 v. TB20 MPG comparison but don’t have the details handy now. The difference was very substantial.
The one downside of the C182RG is the annual landing gear check.
Takes about 20 minutes but requires jacks for the C82R which are much bigger than for the other low wing planes. My shop has jacks from German Luftwaffe surplus, were used to jack Hercules transporters. They just manage to lift my C82R
I’ve seen a maintenance company not only use the tall tripod jacks but also suspend the aircraft from the roof using the eye-bolts located over the cabin in the carry-through spar.
The C82R does not have a carry through spar (the reason the cabin is so roomy). It was most likely a floatplane conversion which adds extra stabilizers in the cabin and is suspended for float installation/removal.
I made a check yesterday comparing TB20 cruise performance with gear exetended and retracted.
The TB20 gear was designed to produce a lot of drag where as the TB10 gear is designed to do the opposite. Better compare a TB20 to a TB10 flying at the same altitude with the same fuel flow. Same comparison can be made between the C82R and the C182 which have identical airframes down to the last rivet.
I made a check yesterday comparing TB20 cruise performance with gear exetended and retracted. The difference (IAS) was 22 kts. I set 125 KIAS at 8000 ft on autopilot in stable and smooth air, extended gear and speed dropped to 103 KIAS. Retracting gear lead to speed increase to 125 KIAS. Repeated once more with exactly same result.
The one downside of the C182RG is the annual landing gear check. I've seen a maintenance company not only use the tall tripod jacks but also suspend the aircraft from the roof using the eye-bolts located over the cabin in the carry-through spar. Belt and braces I suppose!
