While both GNs are great learner/commuter motorcycles their physical similarity begs one obvious question:
What's the difference?
While the obvious answer is 125ccs that's not a helpful answer. The difference is best considered by breaking it down into power, price, resale value, and fuel economy.Power
Horse power wise, on paper at least, the GN250 is twice as powerful as the GN125 with 22hp for the 250 compared to 11hp for the 125. There is a trade-off with weight though. The GN250 weighs an extra 22kg coming in at 129kg compared to the 125s 107kg. Again, on paper at least, that translates to a more favourable power to weight ratio for the 250 (127kw/tonne ignoring the rider) compared to the 125 (~ 77kw/tonne ignoring the rider) although it won't actually double the power to weight ratio of the 125. In fact the GN250 is actually about 1.66 times as powerful as the GN125. In fact the difference isn't particularly obvious in most situations and neither bike is particularly quick. While they'll beat your standard economy car off the mark quicker drivers in bigger cars can still leave you for dead. The key difference between them becomes apparent when you travel up a steep hill at 100km/h. The 250 will keep pulling while the 125 is likely to struggle. Similarly if you're ever planning on carrying a pillion passenger grab the 250. Realistically though you should upgrade before carrying a passenger anywhere other than around town. (Horsepower and weights obtained from http://www.suzukicycles.org)Motorway Speed Capability
Originally if you wanted to hit the motorway safely(ish) the GN250 was your only option here. With an on-paper top speed of 115km/h compared to the GN125's on-paper top speed of 90km/h the choice was a no brainer. However lately some dealers have allegedly been selling GN125s with a larger front sprocket. This leads to a change in gearing that allows the bike to travel at motorway speeds at the cost of some low range pulling power. While this does mean that both bikes can travel at motorway speeds, and neither should be exlcuded on this basis, it does not change the fact that the GN250 is the more powerful bike. In fact similar adjustments can be made to the 250 if you want to gear it more towards motorway riding.Price
In terms of purchase price generally speaking they're fairly similar. The key difference is that (at the time of writing) you can still buy 125s new from Suzuki dealers while GN250s have now been superceeded by the GZ250 (a nice bike with a speedo but no tachometer) which is itself a rare sight on a showroom floor. At the time of writing this 125s are available new from dealers for around $2000 while 250s can be picked up from TradeMe from $900+ (currently the asking price for a late model GN250 with a bit of learner damage (drops from stationary rather than drops at speed) seems to be sitting between $1700-$1900). While a second hand 250 will have more kilometres on the clock than a new 125 GN250s (and 125s) are notoriously reliable and, owing to their ubiquitousness, relatively cheap to repair and maintain.Resale Value
Resale value is also worth keeping in mind. For 2 key reasons the 250 wins here hands down. First off for many people the 125 is a harder sell than the 250 because they look identical. This implies that the 125 is relatively underpowered. While this isn't exactly true, when it comes time to sell your bike perception, rather than reality, is what matters. Second if you buy a 125 odds are you will be buying it new. If you buy a 250 you will probably buy it second hand. When it comes time to sell the 250 has already dropped the showroom floor premium whereas the 125's price still has a way to fall. Odds are you will lose less on a 250 than a 125.There is an additional point to consider with resale value though. The GN250 used to represent the upper limit of allowable engine size in a learner/restricted bike. This may have caused them to hold some extra value as they may have been perceived as a powerful learner bike. While this was never factually correct this is where the difference between perception and reality in the market becomes important again. With the incoming changes on the 1st of October 2012 this may no longer be the case and, in the years ahead the value of a GN250, and other 250cc bikes, may drop more steeply than in the past.
Fuel Efficiency
However the point where these and other small engine bikes shine, and will continue to have in their favour after October 1st 2012, is fuel economy. This is also the point where people may favour the 125 over the 250 if buying on gut instinct. However the difference in fuel economy isn't overly pronounced or even particularly convincing. In fact according to registerd users of fuelly.com the difference ranges from ~10% to 0 difference with the sole GN125 rider clocking in at 71 miles per gallon (31 km per litre) with the GN250 riders coming in between 73 and 66 miles per gallon (31 or 28 km per litre). As a comparison other popular 250cc learners, the Honda CBR250 and the Yamaha Scorpio, seem to fall in about the same range while a LAMS aproved Yamaha XT660 660cc bike seems to hover around 20km/L.Conclusion
Taking all of this into account I would generally advise most people to buy the GN250 rather than the GN125. The only reasons to favour the GN125 over the GN250 are potential savings on fuel and the ability to buy a GN125 new. As we have seen the fuel savings are negligible and, odds are, if you're buying a learner bike you're going to damage your bike. If you're going to damage your bike it's better to add minor damage to a used bike that may be a little rough on the outside than a shiny new one with no prior damage.The exception to the above recommendations are cases where you will need to pay considerably more for a used GN250 than a new GN125. Currently it is not uncommon to see GN250s being listed on trademe for $2200 or more. Often these listings are for bikes with little or no WOF or Rego and plenty of Ks on the clock. Bikes like these aren't worth that sort of money unless they are in immaculate condition and/or thoroughly and convincingly customised. Realisitically a GN250 with little or no WOF/Rego time remaining can currently be obtained for around $1500 with a bit of patience.
If you move beyond the 125 vs 250 comparison many in the biker community will encourage you to avoid either GN (they are both often referred to as 'Go Nowhere's) or refer to them as good learner bikes. Essentially they are the equivalent of a mid 90s Toyota Corrolla; reliable, economical, and unexciting. If you're looking for a run about the 125 and 250 are ideal candidates. If you're looking for something that will blow your socks off then you are best to look elsewhere.
Bonus - The GN400
While the GN125 and GN250 are a common site on the roads there used to be a third bike in the GN line-up: the GN400. The GN400 was produced for 4 years and had a 400c engine producing 27hp. The bike weighed 140kg. This made it more powerful than the GN250... but not by much. The 150cc increase only yielded an extra 5hp. When this is standardised with weight The GN400 is 1.13 times as powerful as the 250 and 1.88 times as poweful as the 125. While the GN400 is regarded as a good bike given the choice between the 125, 250, and 400 I would choose the 250 as the power difference is minimal and parts for the 400 would be harder to come by.
Bonus - The LAMS power to weight ratio
While the GN250 and GN125 have been popular learner bikes the new LAMS regulations will mean that their relatively low power to weight ratio will become more pronounced. Under the new legislation a bike with a power to weight ratio of 150kw/tonne is permissible. Importantly the weight part of the power to weight ratio also allows for a rider of 90kg. This additional weight means that the LAMS power to weight ratio for these bikes are 42kw/tonne for the 125 and 75kw/tonne for the 250. To put it another way you could get a bike with over 3x the power to weight ratio of the 125 or 2x the power to weight ratio of the 250 while on your learners or restricted in New Zealand.
