My dad has been looking to change to an automatic and two of his choices so far are a Peugeot 307 and a Skoda Roomster. Both of these are Tiptronic style boxes.
Now I have never driven an auto or really taken much interest in them so excuse the ignorance.
The Peugeot is a 4 speed auto whereas the Skoda is 6 speed. Now as far as I know, you cannot buy a 4 speed manual anymore? So why would they make a 4 speed manual? Out on a test drive with my dad it just seemed to be too far between each gear?
Still to test drive the Skoda but by all accounts it is a smooth changer.
So am I wrong to compare a 4 speed manual with an auto? Also, why is the CO2 emissions on an auto so much higher than the manual version?
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2007 Seat Altea XL 2.0 TDI (140) Stylance
2005 Skoda Fabia vrS
Edited by Pugugly {P} on 31/10/2007 at 22:34
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Because of the extra flexibility given by the torque convertor, the rule of thumb has been that an automatic with N ratios performs in an equivalent way to a manual car with N+1 ratios.
Number_Cruncher
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There is little difference in performance between a Hyundai V6 Coupe with a four speed automatic and one with a six speed manual box.
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Automatics are traditionally 4 speed due to the effect the torque converter in a conventional automatic box has. As the transmission effectively 'slips' between gears (there is no solid mechanical link between the engine and wheels) it is possible to get away with less making the gearbox cheaper and lighter. Most American cars still come with 4 speed automatic boxes now.
The Peugeot is a conventional auto box like the one described, and therefore has higher CO2 emissions as it uses more fuel. The torque converter based transmission is about 7-8% less efficient than a manual gearbox hence the discrepancy. For this reason many automatics introduce "lock up" in top, where a direct physical link is made between the engine and gearbox once no more shifts are likely to be required. This makes the car more economical while cruising. Some gearboxes like the ZF HP26 6-speed auto box lock up in every gear, which is why this transmission has become very popular with many luxury manufacturers.
Looking at Skoda's website implies that this box is also a conventional gearbox like the Peugeot box. Some VAG products, especially those with the TDI engine (Golf, Audi A3, Octavia etc) use a DSG or S-Tronic gearbox which is effectively an automated manual. On the surface they work like an auto, underneath it's a manual with clutches and everything. Many people like them as they have a very small fuel economy hit, though personally I prefer either a proper manual or a well sorted auto like the aforementioned ZF unit.
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So which cars now have that top-range auto box you mention?
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The ZF Box is on:
* Audi A4-A8 Q7 Quattro models
* BMW 3-7, X3, X5 Series Autos bar the SMG models like the M3/M5
* Land Rover Discovery, Range Rover Sport, Range Rover
* Jaguar XJ, XK and most likely the XF too
* Aston DB9
* Porsche Cayenne
* VW Touareg/Phaeton
* Bentley Continental
The Mercedes 7 Speed auto and Lexus 8 Speed auto aren't the same box but they do have the same function to lock up in every gear.
Edited by cjehuk on 01/11/2007 at 19:25
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The OP is considering front-wheel drive automatics - the Aisin-Warner used in Lexus, Toyota, Volvo, Vauxhall, very recent Fords and Freelander 2 has a good reputation for reliability and longevity. Conventional VAG autos are similarly regarded. The VAG DSG box needs time to establish it's credentials.
Other front-wheel drive autoboxes do seem fragile in comparison.
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Agreed, the Aisin-Warner box is also very good indeed and has similar capabilities to the ZF unit. I seem to recall reading somewhere they make VAG's DSG box too, but I could be wrong on that.
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The Mercedes 7 Speed auto and Lexus 8 Speed auto aren't the same box but they do have the same function to lock up in every gear.
There's a bit of a discussion on one of the MB forums about the 7 speed box. Apparently in MB's application the box never locks fully, MB say it slips - by an amount that varies according to engine load, speed etc. A forum member uploaded an MB maintenance presentation which confirms this fact.
No-one has quite been able to explain this, on the face of it, odd situation on a lock that doesn't lock! Maybe MB do it to avoid the clunk of the lock engaging, which is quite noticeable on some cars.
Edited by Bill Payer on 01/11/2007 at 20:37
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There's also the hybrid option in Toyota/Lexus - they act like a CVT-style automatic but with radically simpler mechanicals.
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That's interesting. Whilst not a 7-speed I've always wondered what speeds my (5 speed?) C220CDi Sports Coupe (2002) gearbox would lock up. Where would I find that sort of information? I'd be interested in a pointer to any graphs or statistics etc so I can modify my driving accordingly.
Thanks,
Simon
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On my last (torque convertor auto) car I could tell when it had locked by watching the rev counter. Unlocked, the revs will rise ahead of the speed before lock, once locked the revs are proportionate to speed - it was very easy to see in practice. It wasn't just speed dependent, if at all - it seemed to lock once speed settled and the transmission was unloaded. This was not accompanied by any noise or clunking (Honda).
For example if climbing a gradient and accelerating I could see the revs were higher than the 1000rpm/30mph or whatever in that gear; if I lifted off a little and slowed slightly I could make it lock and then accelerate again with 'direct drive'.
If you think about it the load has to come off for the lock up to work - otherwise you would have a violent engagement.
Edited by Manatee on 02/11/2007 at 07:27
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On my last (torque convertor auto) car I could tell when it had locked by watching the rev counter. Unlocked the revs will rise ahead of the speed before lock once locked the revs are proportionate to speed - it was very easy to see in practice. It wasn't just speed dependent if at all - it seemed to lock once speed settled and the transmission was unloaded. This was not accompanied by any noise or clunking (Honda).
It's the same on our Almera, which has a Jatco box, and on a colleague's Subaru Outback.
You can tell it's locked by the way the rev counter behaves, but there's no noise when it does it. I think it only locks in top gear, but it's hard to tell.
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If you accelerate very gently from, say 40-60, you should be able to notice an extra apparent gear change where the engine revs only drop a couple of hundred rpm instead of several hundred at a normal gear change - on a car with a smooth gearbox and good sound insulation you'll have to rely on the tachometer.
When new, and for much of it's life, my Astra 1.8 auto locked up at 48mph indicated but latterly it locks up at much lower speeds (35-40) - if its a fault, it's all the better for it.
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I test drove a 7-speed Merc auto, and the changes were incredibly smooth, even more so than on a 5-speed auto of theirs I used to own (which I thought was smooth).
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I'd be interested in a pointer to any graphs or statistics etc so I can modify my driving accordingly.
There's a presentation on the 7spd box here:
mbclub.co.uk/forums/showpost.php?p=429718&postcoun...9
If you look through that thread then it started about the 5 sp box. I have that box too and I can't feel it lock - the suggestion is that it does fully lock but only very high speed.
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On modern autos with lock-up torque convertors the pressure is duty-cycle modulated by the lock-up solenoid so that lock up occurs progressively - this is no sudden 'clunk' or 'thump'. If you watch the speedo and rev counter you should see the speed stay the same but the revs smoothly fall by a few hundred rpm. Unlock is usually quite swift. A bit of pressure on the throttle and you should see the revs leap by a few hundred rpm - this is quite different to a downshift. Its quite easy to detect once you know what you are looking for.
Normally lock-up only occurs when the fluid is warm (there is a temp sensor in the transmission).
Some transmissions (like the old 4HP14) have full lock up in top (4th) and partial lock-up in 3rd (66% in the case of the HP14). This is achieved by having a shaft coming off the impeller, running inside the shaft from the turbine. There's then a little epicyclic gearset on the end of the impeller shaft so torque delivery is split between the impeller and turbine shafts. It seemed to work quite well on those 'boxes.
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