 Poster: A snowHead
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| ski3 wrote: |
@Judwin, "And power isn't really how it works anyway. You need to think in terms of torque not power. Torque is directly related to the amount of air you can get into the cylinder. Double the air means double the torque. There is no use having 250bhp at 4K RPM if the torque curve is so peaky that the power drops off rapidly either side of 4K."
Worth expanding for explanation......torque is the effort the motor can put out and usually stated as peak @ given rpm (eg 250 lb / ft @ 2000rpm) and so it can enact that effort in total at that running point.
Bhp is something of a notional figure that takes into account time/work rate as a component of the calculation. Effectively it takes torque and uses the rpm at which the peak occurs as a gain factor to give bhp. The M in rpm being minutes.
Two engine having torque of 250 lb/2000 rpm and 250 lb/4000 rpm produce the same "power" but with the occurrence at 4000 rpm giving a higher bhp.
Ordinarily this is fitted into real usage by having a lowered gearing for the higher rpm example which then has the output of 250lb then enacted through more power pulses over a given distance.
Pressurised intake has the ability to increase however it's delivered, turbo has more options to control over a range, how that is trimmed and generally at lower cost. Hot and cold sides of turbine can be tailored individually, most now are configured with a variable geometry to alter boost on demand via altering the internal flow of the hot side primarily to bring speed at low rpm and avoid overboost at peak, normally doesn't need a waste gate to bleed of excess pressure either. They are very neat integrated units that are fitted.
All engine will vary in combustion and power with intake air temp too, intercooling (air to air heat exchange for intake cooling) is a fundamental to making power while not detonating the engine. |
I'd go further than that.
Power = K * Torque * EngineSpeed.
K is just a constant used to convert the various (non SI) units used in the measurements. If you measure EngineSpeed in revs per min, and power in BHP, then K is 5252. So show me a torque curve, and I can give you a power curve. The opposite is obviously also true. However since we know that Torque is directly related to the amount of air/oxygen being burnt (and power isn't) it's better to start by thinking about Torque.
Highly tuned normally aspirated engines do things like optimising the inlet manifold length so they are resonant at a certain frequency (RPM). This can allow the air pressure in the inlet manifold to exceed ambient so more air gets into the cylinder - but only at/close to that RPM. This produces a peak in the torque curve at that RPM. The resonant RPM is usually chosen to about 15-20% below than redline. Therefore you get a peak in the power reading at that RPM. Trouble is, the more tuned the engine, the more difficult it is to drive at anything other than that narrow power band. The thing gets lumpy and flat and generally unpleasant to drive.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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| Masque wrote: |
edit: Winter tyres are NOT defined by their tread pattern (though it is part of the construction parameters) but primarily by the construction and compounds used . . . However Michelin seem to have struck some sort of deal with the Devil to enable a competitive winter tyre to function and last well in summer use! |
As I understand it the conventional product being enabled by, mostly, rubber compound and sipes etc, has been the baseline in understanding. Transformative thinking (if that's what you'd label it) has given us the Michelin "Cross" type tyre that is principally the tread geometry without recourse to really soft compounds, hence a sideways step in product and performance envelope.
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You need to Login to know who's really who.
You need to Login to know who's really who.
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@ski3, I have been very impressed with Kleber Quadraxer all-season tyres, which interestingly look almost identical to the Michelin Crossclimate, and are made by Michelin as well - just about £15 per tyre cheaper!
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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@RobinS, yes they are a good manufacturer. I've used their "Hydraxer" wet weather (northern Europe  ) tyres that work well, also with considerable snow capability as an aside too in my experience.
Their "Krisalp" pure winter tyre for those located more extensively in alpine domain is a very good tyre.
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You'll need to Register first of course.
You'll need to Register first of course.
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Kwikfit are doing 15% off a set of Vector 4Seasons Gen-3, and 10% off CrossClimate2. I reckon it's probably the best time of year to buy right now.
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If you could make one tyre that was ideal in summer and winter, then we'd just have, well, 'tyres' - there wouldn't be this distinction between summers, all-seasons and winters.
The 3-Peaks-and-Snoflake standard is very useful but doesn't set the bar particularly high in terms of snow-handling.
For an 'average' car, it is possible to make a tyre that makes the grade for this standard but at the same time, doesn't give up too much in terms of summer capability. Which is what Michelin has done with the Cross-Climates™. If I look at my CrossClimates on my little run-around, I can't see any sipes and I assume that the compound chemistry is such that it can handle summer temperatures without too much wear, but will still warm up faster in the cold compared to a summer.
Unfortunately, for any one with a performance vehicle, all-seasons will represent the worst of both worlds, rather than the best. They give up too much in summer compared to a summer tyre, and too much in winter compared to a winter tyre. Quite a lot of performance car owners who have to regularly use their car in the winter come what may (even just in the UK), have separate sets of winter and summer wheels. As I do for our other, performance vehicle.
Tread pattern tends to be important in terms of water dispersal as well as braking and traction. The optimal orientation for tread drainage channels is around 20°-40° from the direction of travel (with the caveat that this is in conjunction with other important metrics for the tread pattern, like optimal breaking). What a lot of cheap tyre manufacturers do, however, is to design exotic and impressive tread patterns that have no scientific basis: they just look good and are a diversion from the cheap compounds used and fewer number of components (a quality tyre will have about 600 separate components, a cheap one perhaps half that number but visually, they both look the same).
On winter tyres, there is a subtle additional design element to the tread: it also has to hold snow - but not too much. As anyone who's made a snowball knows, snow sticks to snow better than to, say, rubber. So winters are designed to trap snow on their surface to give optimal traction in the snow. But there's a limit to how much snow you want to carry, so you may see some of the tread with curved channels that encourage the rotation force to throw the snow off when it gets too thick.
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@ski3, it's the 'grab and release' function of the tread design with mixed compounds and structures to allow cold temp flexibility and not self destruct in summer temps. I don't think that any multi use tyre will beat a pure snow tyre but they've become far closer in performance over the last couple of decades.
There's one effect of fitting snow tyres that I see far too often over here . . . and voiced in the complaining whine of a crash instigator "my tyres stopped working"
Winter tyres only work if you drive within their limits.
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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@HilbertSpace, thanks, glad I went for CC 2s
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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No doubt there's some intersection, but good all season tires are pretty expensive. I think -- but could be wrong -- that the key advantage to snow/winter tires is their pliability in colder weather vs summer or all-season tires.
I'm going to plump for a set of -1 steel wheels (16" from 17") and higher-profile "pure" winter tires this year. I read an interesting article from a Canadian guy who went -3 (18" to 15") for his snows, but he's probably dealing with much more extreme weather.
When I was younger I had a Saab 99, and ran 75 series Hakkapellittas snow tires vs 60 series tires (and the famous saab soccerball wheels) for the rest of the year...nearly unstoppable in snow but not the best handling on dry roads, needless to say...
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@Pasigal, my CCs were about the same price as the P7000 they replaced. If you go for budget tyres there will be a big difference of course.
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You know it makes sense.
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I live in California and drive a Subaru Crosstrek with Nokian WR G4s that they describe as 'all weather'. I suspect they are mostly tread pattern with maybe a slightly different compound, as they've done well in +44C in Joshua Tree as well as -22C in Colorado (and winter weekends in Tahoe). They're not as 'sticky' feeling as proper winter's can be (based on renting cars from GVA) but there's never been a moment where I've not felt in control.
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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Poster: A snowHead
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Useful, @Weathercam. Having always had chains in the past (and fitted them fairly often, at least once a season) I found myself driving to the Alps at Easter in a new car, with no chains to fit. I did have all-season tyres but decided to buy snow socks. However, when I did a "practice fit" before the drive I found them an absolute PAIN to fit, as the expert in your article notes. Would prefer to fit chains, any day.
Fortunately I didn't have to use the socks. I did encounter one tight uphill bend, covered in wet slushy snow (the worst kind......) which might have been problematical with summer tyres, but the all-seasons were fine.
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FAQ
I knew about the A/C cutoff on some cars at full throttle but never heard anything about windscreen wipers, any power saving must be really minimal so seems like a strange design decision.
