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Apr 23, 2012 22:19:47 GMT
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I'm interested in where the MPG figures are coming from in this thread. Are folks relying on their car's computer/MFA to tell them what economy they're getting? How reliable is that? As far as I can see, the only way to accurately calculate MPG is recording every drop of fuel used and every mile covered and do the maths on it. If you can do it over many tanks of fuel in succession then you get an average figure that takes in the variation between city/motorway/country road driving/driving with an empty car/full car/clean car/dirty car/etc.
on the fuel metering at the pump issue, I seem to remember reading on the fascia of the pump that a litre delivery is calibrated to be an actual standard litre at an ambient temperature of 15 degrees centigrade. So there must be a density vs volume difference for varying ambient temperatures. Which makes me think: if a litre of fuel was denser at 0 degrees than at 30 degrees, would we get more fuel per Euro/Pound early in the morning rather than at noon or in winter rather than in summer?
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RobinJI
Posted a lot
"Driven by the irony that only being shackled to the road could ever I be free"
Posts: 2,995
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Apr 23, 2012 22:22:14 GMT
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the golf ball thing is all about how they spin when they go through the air. Something we generally try avoid with cars and aircraft, yeah? The thing with the fuel at temperature is that its less dense and when its cold its more dense and the petrol pump takes account of this when it dispenses it into your tank. You can get it as hot or as cold as you like but you only get a quids worth of petrol out either way. So I am fairly reliably informed anyway. You can get the fuel in your tank as hot as you like and you may be able to get the needle to rise, but you haven't magically made more petrol... Ahhh.. sorry, I thought when you said 'metering' you were talking about carbs/engine management ect.. not the actual pump sorry about that. Yeah, that makes sense, I'd be surprised if they didn't make sure they're metering it accurately, or at least consistently. Yeah, that sounds familiar about the golf ball, I couldn't remember exactly but I knew it wasn't as simple as dimples = better aero. Trevor, every figure I've mentioned has come from miles covered vs litres used, no computer in my Passat, just me taking note when I go to the pump. One thing I've always thought probably throws a few peoples figures out, especially on here is that incorrect tyre sizes causing your speedo to be inaccurate, then you figures will be out because the trip counter/odometer will be out just as much.
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Last Edit: Apr 23, 2012 22:27:56 GMT by RobinJI
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Apr 23, 2012 22:33:43 GMT
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Trevor, every figure I've mentioned has come from miles covered vs litres used, no computer in my Passat, just me taking note when I go to the pump. One thing I've always thought probably throws a few peoples figures out, especially on here is that incorrect tyre sizes causing your speedo to be inaccurate, then you figures will be out because the trip counter/odometer will be out just as much. fair point about the tyre size. I'm happy that my MPG calculations are good as my Passat hasn't got any fancy computer trickery either and it has stock size tyres but all my other (more) retro cars have non-stock size tyres so if I were to do the sums I'd have to have Sat-nav miles recorded and that would take serious dedication...
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Dez
Club Retro Rides Member
And I won't sit down. And I won't shut up. And most of all I will not grow up.
Posts: 11,712
Club RR Member Number: 34
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Apr 23, 2012 22:45:19 GMT
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ive never actually figured my mpg out exactly, til now. I just googlemapped my standard commute route, as I'm running much shorter tyres then stock so my odometer cant be trusted, then added on roughly what running about I do to use up the rest of a fill. I do a 44mile journey, the first 5 miles of which are heavy stop-start traffic at 8am rush-hour, then 40miles of 80mph blasting with two dead stops(busy roundabouts with traffic lights at same kind of time of day). I then have enough fuel left from a tenner to do at least 15 if not 20 miles of running about, in standard daytime traffic, say a trip into town to parts suppliers/machine mart/boc/fasteners place/bank/etc. using petrol at 141p a L(i can often get it for 139 but sometimes have to buy it at 143-144, so i took an average), that would give me a MPG of approx 38.5mpg, which is actually pretty good for a 2L 8v b3 passat running way-shorter-than-stock 165/50R15 tyres.
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Last Edit: Apr 23, 2012 22:47:55 GMT by Dez
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Apr 23, 2012 23:46:35 GMT
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.....and then, cos its got coilovers, wide rims and low pro tyres, theres no body roll so no need to slow down much at all for corners, slip roads, or clear roundabouts. in fact, its becomes a challenge to see if itll do it at 70 this time rather than 60...... with more bwaaaarp(And maybe a touch of skreeeeeek too)...... My car is French, standard and old - the body rolls when I get in it ;D
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1989 Peugeot 205. You know, the one that was parked in a ditch on the campsite at RRG'17... the glass is always full. but the ratio of air to water may vary.
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Surprised no1 clocked on to the mention of fuelly. I think the most effective way to improve energy consumption (in this case fuel) is simply to be more aware of it. Since installing a visible electricity meter in my living room and having a linked in smart-phone app with alerts and the such like, my electricity usage has gone down just through increased awareness of habits and costs. Surely, 'fuelly' could do the same and if you can do it from your phone would only take the time it takes you to queue to upload the info and find out for yourself. www.fuelly.com/
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'88 Toyota Supra Turbo
'88 Honda VFR 400 NC24
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I'm pretty anal about recording litres taken and miles covered. I have MPG histories on a spreadsheet for loads of the cars I have owned. I have each tank MPG and then a running average (from total miles and total litres not averaging the tank MPG)
Yup, changes in tyres and final drive will affect your readings.
I tend to look at it as a way of plotting trends rather than an absolute figure. It also keeps your mind on the MPG a bit. Maybe I'm just sad. Who drives a big yank car and then whitters about the fuel consumption?
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1937 Austin Street Rod - 1941 Wolseley Not Rod - 1956 Humber Hawk - 1957 Daimler Conquest - 1966 Buick LeSabre - 1968 Plymouth Sport Fury - 1968 Ford Galaxie - 1969 Ford Country Squire - 1969 Mercury Marquis - 1970 Morris Minor - 1970 Buick Skylark - 1970 Ford Galaxie - 1971 Ford Galaxie - 1976 Continental Mark IV - 1976 Ford Capri - 1976 Rover V8 - 1994 Ford Fiesta
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edwell
Part of things
Posts: 199
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I was always under the impression that the dimples in golf balls were to aid stability, not range. If it worked at reducing wind resistance then the aerospace and motorsport industries would have cottoned on a long time ago. I think the golf ball dimples thing is a red herring as it is a special case. (they apparently reduce the pressure drag of the ball in some way but actually increase the surface drag, but the properties of the ball, maybe because it is relatively small the one out-ways the other) What does work however are "riblets," these are like the dimples on golf balls but a lot smaller and are used on lots of stuff from airliners to boats and even those all in one swim suits that were banned. I think riblets work by sticking a layer of air to the object, which itself has less surface drag than the object.
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mjd
Part of things
Posts: 46
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Are folks relying on their car's computer/MFA to tell them what economy they're getting? How reliable is that? Must be fairly reliable. They're hooked in to the ECU, which knows how much fuel's going in (because it's the thing deciding how much that is). Distance should be as reliable as the odometer (ie not bad assuming stock tyres) because it's the same signal. All methods are flawed -- you can't be sure if you've got a full tank every time, you can't be sure every pump meters the same (or even the same pump a fortnight later). I guess you could fill a petrol can, keep it in your boot until you run out, tip the can in and then monitor mileage with a GPS until you run out again, that'd be as close as you'd get I think. Obviously a second petrol can would be a good idea I quite fancy fitting one of these: www.dschmidt.com/MPGuinoJBD.htmlbut I've got a mechanical speedo and no electronic vehicle speed sensor, so that'll need some gentle bodging
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EmDee
Club Retro Rides Member
Committer of Autrocities.
Posts: 5,920
Club RR Member Number: 108
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Unless you have a Fiat ;D According to a lot of Fiat owners on various forums the Italians in their infinite wisdom set the bleedin thing up for US gallons. The digital display on my 1.9 JTD rarely gets over 40 mpg, but if I do brim to brim and do some basic maths I'm getting way better milage than that.
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Apr 24, 2012 10:17:04 GMT
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29.9mpg is still curse word in my opinion for a modern 1.4 engine. I agree, are you sure there's not something wrong with it? What van is it? 2005 1.4 Corsa Combo LPG, think the manufacturers figures are only about 34 ish mpg running on petrol and i try to avoid that whenever possible;) I know its not very retro but i am looking for something else I have averaged the mpg figures going fill to fill on LPG at the same pump with the van pointing uphill on the same gradient (get more in that way;) I always log down the mileage and litres anyway for the taxmans benefit if nobody elses!
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mjd
Part of things
Posts: 46
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Apr 24, 2012 11:41:13 GMT
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Nice dodgerover: If it's meant to do 34mpg on petrol then 30 on LPG sounds about right -- you'd expect to get 10-20% less on LPG.
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Apr 24, 2012 11:43:48 GMT
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According to a lot of Fiat owners on various forums the Italians in their infinite wisdom set the bleedin thing up for US gallons. Impressive. Even Austin-Rover got it right: the SD1's trip computer had a switch to select between Imperial, Federal and Metric measurements.
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bortaf
Posted a lot
Posts: 4,549
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Apr 24, 2012 11:55:00 GMT
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Trip computers in my car lol sorry though we were on RETRO rides I only disscuss my retro which don't have any trip/fuel computers in em ;D I brim to brim for fuel calculations, I even have a few demijons maked off in Ltr cos I blend my own fuel in the "lab" but if we are talking modern cars i'll get the paperwork out for my modern (ok R reg) escort but thats as modern as I can go without resorting to self flagellation that will return 35 round town no matter it seems how i drive it? on a run 45 but that has the longest diff ever in the history of long diffs, redlining it in 3rd takes so long the tide goes out and back in again (hense the great millage on a run) whereas my P100 has a diff so low it passes under a snakes belly so i max it at 55 and NEVER ever use motorways (aint been on a motorway in 3 years in it) pluss A and B roads are so much nicer to drive, ooo a tree, look another tree, a squirrel !! i saw a squirrel!!! ect ect makes for a more relaxed trip and the more relaxed i am the less fuel i use. What I am looking forward to is putting the 47Mpg TD in my 1/2 ton lighter cotrtina and then really peeing off the modern diesel owners with my miles per gallon ;D
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Last Edit: Apr 24, 2012 12:02:08 GMT by bortaf
R.I.P photobucket
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Apr 24, 2012 22:49:07 GMT
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All methods are flawed -- you can't be sure if you've got a full tank every time, you can't be sure every pump meters the same (or even the same pump a fortnight later). I use fuelly.com and have done for more than 10,000 miles so far, as far as I can see the best way to work out your average fuel consumption is to do so over as long a time period as possible and be methodical about it. That way you allow for pumps that under-serve, pumps that over-serve, whether you've filled the tank at one fill and missed a couple of litres on the next fill, it all averages out over time/miles. The only flaw I can see is that I'm relying on the mechanical odometer to tell me how many miles I've driven and even with stock height tyres the speedo reading it out my a few mph when checked against sat-nav speedo so I presume the odometer is out a few % too. this isn't a great way of testing your MPG as you're only doing it over a very short distance. Granted you now exactly how much fuel you've used up but you can't predict the next stint of driving is going to be an average snapshot of your driving routine. What if you got stuck behind a tractor? Were driving into a strong headwind or being helped by a good tailwind? Again, the only way to get a reliable average is to work it out over a long period of time, many fills of fuel and thousands of miles.
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Nice dodgerover: If it's meant to do 34mpg on petrol then 30 on LPG sounds about right -- you'd expect to get 10-20% less on LPG. Yep not saying different but the point was its pretty crappy for a small 1.4 engine in a modern vehicle, too much weight as standard (darn safety standards) and a cat etc doesn't help the MPG
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mjd
Part of things
Posts: 46
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QFT
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Apr 25, 2012 11:21:37 GMT
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Unless you have a Fiat ;D According to a lot of Fiat owners on various forums the Italians in their infinite wisdom set the bleedin thing up for US gallons. The digital display on my 1.9 JTD rarely gets over 40 mpg, but if I do brim to brim and do some basic maths I'm getting way better milage than that. This is true - you need to add 20% to a Fiat-computer MPG if your car is set up with US gallons, which makes my 72mpg in a Multipla (see earlier in thread) 86.4mpg imperial. Shame I only managed it over about 5 miles - it's normally showing as mid 40's though, which is 50mpg imperial. I drive slowly on motorways if I'm not in a hurry, and you get used to it - you only get hassle off other cars if you are on the fast side of slow (60-70mph) - stick below 60 and no-one bothers you. It is nice every now and again when time is of the essence and I can drive at a more 'natural' speed with justification. Anticiapation is key, as others have said: I hate stopping my car because acceleration eats fuel, and generally you can avoid it by looking a long way ahed - traffic lights change to green and small queues at roundabouts disappear if you approach at the correct speed. I also try not to brake; if I get to a roundabout I lift off early enough so that I can go around at the speed I arrive at it at - it helps if there is little traffic and you can use the full width to straighten out the bend. I also make good use of hills. Although I do drive slowly on the motorway, if it's an undulating one (M6, M1 north etc) I will gain as much speed as I think I need on the downhill bits to give momentum on the following uphill. Momentum is king on uphill bits too. I don't have an instant readout, but it seems that it's sometimes better to just get the hill out of the way than to trundle up it. I think riding a push bike is a great way to get used to knowing which bit of your drive is using the most energy, by the way.
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