Update and summary: I’ve noticed a lot of people hitting this page by Googling “Tomtom 930 vs 940″. If you want to know which is better, I’d say the 930 – it’s around £45 cheaper on Amazon, but with the 940 you’d need to buy the remote, and you might also want the TMC receiver (more on that below), so it’s actually £90 cheaper to get the 930. And with the Tomtom “Latest Maps” gaurantee, you won’t be buying an out-of-date unit – you can download the latest map for free, same as on the 940. For more of my thoughts on the two units, read on…

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Earlier this year, I bought the TomTom GO 930T Satellite Navigation System.Since I had a new car, I figured I might as well get a new Satnav to go with it, and I’ve always been a TomTom fan so it was the obvious choice. It’s a lovely bit of kit, as Satnavs go, and has done a great job so far – although it does have a couple of drawbacks.

The first problem, and this is only a minor thing as it can be easily turned off, is the “Lane Assistance” option. This is a great thing in theory, but in reality it is quite possibly the most stupid and potentially dangerous “feature” you could have on a Satnav, and I’ll tell you why. The theory is that as you approach a motorway junction, it will replace your usual map view with a 2D “picture” of the junction, complete with gantry signs and even scenery. It will then flash big-ass green arrows on the screen showing you exactly which lane you should be in.

Here’s the thing, though. Most junctions are fairly straightforward – you get in the exit lane and keep left or right as appropriate. No use for Lane Assistance there. Where you do need Lane Assistance, though, is on complicated junctions – and that’s exactly where it’s completely useless, if not dangerous. The reason is that the TomTom will flash up the junction image around half a mile before the junction, and complicated junctions tend to have multiple exits quite close together. Because the usual map view has been replaced, it is very difficult to work out which exit you should be taking, and a couple of times I’ve followed the Lane Assistance instructions only to realise, at the last moment, that I was too early and was taking the wrong exit. We’ve all seen idiots join the exit lane only to swerve back onto the main carriageway for no apparent reason, and this isn’t going to help!

So, that’s my first moan about the 930, but I’ve turned off Lane Assistance so it doesn’t bother me (unless TomTom Home installs an update, in which case it gets turned back on… Gah!).

My second moan is a bigger issue, and what led to this entry. The 930 comes with the RDS-TMC receiver, usually an optional extra. The RDS-TMC receiver picks up traffic data which the 930 can use to avoid traffic jams. Only problem is, it’s not very useful near north London or the northern half of the M25; for some reason, it just can’t lock on to a frequency and get data with any reliability. As soon as I get 15-20 miles outside the M25 it’s OK, but I can never get a signal on the M25 or thereabouts. It worked fine all the way to Europe and back, but as soon as I got within signage distance of the M25 it gave up. I figure there’s too much radio “noise” around London so the RDS signal isn’t strong enough. I was all set to buy the Traffic HD device TomTom were advertising, as it used a mobile phone data connection (with a built-in SIM), but it never appeared.

Instead, they’ve launched the next range of Go devices – the x40 range. They’ve got the Live service built in, meaning there is a mobile SIM card in the Go, and it receives traffic – and other – data over GSM instead of the less reliable RDS-TMC method. I was sorely tempted to upgrade and sell my 930 on eBay, but after careful consideration, I might give it a miss, and here’s why…

The TomTom GO 940 Live,and indeed the TomTom GO 740 Liveare cheeky little teases! They go on about how you get traffic information and petrol prices and whatnot, but it’s only if you dig a little deeper that you find out that these services only work in the country where you bought the device. Now this might sound fairly obvious – it’s using a GSM connection which has a fixed monthly subscription and would therefore be hard to allow for roaming charges – but the main selling point of the Go 740 Live and Go 940 Live are that they include maps of Europe, and even America in the case of the 940. So, you can drive all over Europe, but you can forget about getting traffic info as soon as you leave Blighty! So, on the one hand, you’ve got a great Traffic info service; on the other, it’s only available on a small percentage of the maps the device includes.

You can now buy an TomTom RDS-TMC Traffic Receiverfor the Go x40 which plugs into the USB socket, but it’s an extra £28 (on Amazon) on top of the Go itself. Plus, they don’t include the remote control any more, so you’ll need to buy the TomTom GO Bluetooth Remote, £25 from Amazon.So, in order to match the 930 I have to spend at least another £50 on the 940, and that’s on top of the fact it costs around £50 more than the 930. And then you’ve got the monthly sub for the Traffic service which you won’t always be able to use if you’re not in the country.

So, all in all, I think the 940 is a giant leap backwards for TomTom. Looks like I might be updating my 930 maps instead…