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Post by the light works on Mar 4, 2018 3:58:07 GMT
my dad has commented that the new tires on his minivan have cost him about 10% worse fuel economy.
this would be long term observations and similar tread patterns, but different brands of tires.
so what could be done to quantify this OTHER than just a road test?
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Post by GTCGreg on Mar 4, 2018 4:55:10 GMT
my dad has commented that the new tires on his minivan have cost him about 10% worse fuel economy. this would be long term observations and similar tread patterns, but different brands of tires. so what could be done to quantify this OTHER than just a road test? You could probably build some type of single wheel dynamometer that would run one wheel with a tire on it on a roller. You would need enough force between the tire and roller to simulate the load of an automobile, maybe 500 to 1000 lbs. Then measure how much power it takes to keep the wheel turning at a given speed. Compare the power required for different tires and that should give you a pretty good indications of which tires are more efficient. You could also use an infrared image scanner to see how hot the tire is getting. A hotter tire would mean less efficiency.
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Post by silverdragon on Mar 4, 2018 8:39:38 GMT
my dad has commented that the new tires on his minivan have cost him about 10% worse fuel economy. this would be long term observations and similar tread patterns, but different brands of tires. so what could be done to quantify this OTHER than just a road test? I had a set of the "Fuel Economy" set of tires on my car once. I am glad to see the back of them. I cot more grumbles from my ABS when using them than any other tyre I ever owned?. The thing is they have "Less rolling resistance"... yep, thats the one. But what that means is you sacrifice traction for fuel efficiency. That by the way is not a myth, although, for the reasons of being shown on teevee, you can say it is, but, we know the truth here?. If you have less rolling resistance, you have less resistance all the time, which is less traction under either acceleration or braking. To test, set a vehicle in motion that has ABS to a set speed, and at a marked line, dynamite the brakes and see how long it takes to stop. More speed will mean a greater difference in stopping, so try at "freeway" speeds to show a greater difference. You need to use new tyres of both usual variety and fuel economy variety. Measure that in feet. Repeat three or four times to allow variance in road surfaces. Swap tyres. The difference between fuel economy tires and grip tyres will be obvious in feet taken to brake to a stop. You may also repeat using bot Radial and cross ply, then for education sake, show why "Off road" tyres dont have as much grip on tarmac as tarmac tyres, then carry on and show treaded tyres against "black snot" hot sticky properly warmed up racing tyres, then snow tyres against all season tyres against summer tyres, then repeat all of that again in wet sloppy greasy conditions. One of my early jobs was one day supplying tyres to a racing team, a whole container of tyres, of all different compounds, for a Rally Cross WRX race weekend. I Got an education in tyres right there and then when my eyebrows shot up all the way to the top like chapel hat pegs after being told this was probably all for one race for ONE vehicle....[ that team being in close competition for the top position...] The weekends stages were part snow part grit part tarmac and also chances of rain. They needed options for wet or dry for grit gravel or tarmac, for snow, for that stage if the snow melted, options for tarmac wet or dry and again in case there had been snow, and all that again wet or dry for the gravel/grit stages. They also needed to plan that after just one stage the vehicle may return with no working tyres because punctures, or just worn out after just one stage. There were three stages, each one to be run in both directions, making six runs in all, and the planned on changing tyres each time the car stopped. You have max 20 mis fettling time after each stage, thats mechanicking to the stop watch, pit stop on a LOT of caffeine, you choose what parts of the car need attention most, and how many spanners you can get around that car at one time. And then, my return journey, all used tyres were sent back to the manufacturers for evaluation to further their R&D on the compounds used. I was talking to one of the pit crew for about an hour, lunch break, although he didnt of course reveal trade secrets, he was quite happy to chat about many things I didnt know. Yeah, I had no idea the amount of engineering that went into tyres.
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Post by silverdragon on Mar 4, 2018 8:42:30 GMT
my dad has commented that the new tires on his minivan have cost him about 10% worse fuel economy. this would be long term observations and similar tread patterns, but different brands of tires. so what could be done to quantify this OTHER than just a road test? You could probably build some type of single wheel dynamometer that would run one wheel with a tire on it on a roller. You would need enough force between the tire and roller to simulate the load of an automobile, maybe 500 to 1000 lbs. Then measure how much power it takes to keep the wheel turning at a given speed. Compare the power required for different tires and that should give you a pretty good indications of which tires are more efficient. You could also use an infrared image scanner to see how hot the tire is getting. A hotter tire would mean less efficiency. ...But more grip?.. How the heat changes the tyres is a science all of its own. Thus some people say that Nitrogen in tyres is "better" because it expands under heat more predictably than just air that could contain any amount of pollutants.
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Post by the light works on Mar 4, 2018 10:53:09 GMT
I like the dynamometer study, force in minus force out gives a very good efficiency number, and being able to show thermal losses gives a very good illustration of waste energy being turned into heat.
is there a direct connection between efficiency and grip? I'm not so sure. if you lose too much grip, it takes the efficiency right with it, does it not? a "does tread make a difference in traction?" thread might be in order. which is not to say there isn't a point at which you sacrifice grip for efficiency. there's a reason why steel wheels on steel track let trains move goods very efficiently. but accelerate and decelerate more gently than race cars.
the other thing my father has said is that one brand of tires rolls more smoothly than another brand with similar tread patterns. mind you, this is not saying that touring tires roll more smoothly than mud tires. this is saying that (squawk) brand touring tires roll more smoothly than (bleep) brand touring tires.
as for putting nitrogen into tires because it behaves more consistently than putting atmosphere into tires, people agree that the science is valid, but debate over whether that makes a difference for the average driver.
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Post by Cybermortis on Mar 4, 2018 20:53:09 GMT
A dynamometer would probably work better for a small scale test using tires from RC cars, as the rig would be smaller and easier to build and fit in the shop.
A large scale test would probably be more along the classic MB lines of hooking up an external fuel tank and driving around a track to see if there are differences in fuel efficency.
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Post by GTCGreg on Mar 4, 2018 21:32:34 GMT
A dynamometer would probably work better for a small scale test using tires from RC cars, as the rig would be smaller and easier to build and fit in the shop. A large scale test would probably be more along the classic MB lines of hooking up an external fuel tank and driving around a track to see if there are differences in fuel efficency. Not sure if the RC test would tell you anything useful as the tires probably aren't even close to real tires. The track test would really be the unquestionable proof as well as give an indication of ride and handling.
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Post by the light works on Mar 4, 2018 23:15:38 GMT
A dynamometer would probably work better for a small scale test using tires from RC cars, as the rig would be smaller and easier to build and fit in the shop. A large scale test would probably be more along the classic MB lines of hooking up an external fuel tank and driving around a track to see if there are differences in fuel efficency. Not sure if the RC test would tell you anything useful as the tires probably aren't even close to real tires. The track test would really be the unquestionable proof as well as give an indication of ride and handling. it would probably be more work to build a miniature dyno for RC tires than to build a single tire drive system with an electric motor and take it to a real dyno.
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Post by silverdragon on Mar 5, 2018 10:23:24 GMT
Not sure if the RC test would tell you anything useful as the tires probably aren't even close to real tires. The track test would really be the unquestionable proof as well as give an indication of ride and handling. it would probably be more work to build a miniature dyno for RC tires than to build a single tire drive system with an electric motor and take it to a real dyno. Or have the dyno visit you?. There are now mobile Dyno's built on the back of a truck bed that can be taken to track days and car shows that allows people to run what they brung and see exactly how many horses have escaped on older engines or see how many the air scoop has caught on re-built and "Improved" engines. Getting hold of one of them in the "closed season", ie Over Winter after all the car shows have finished, could be done more easily if it provides exposure for "Daves Dyno" on the show.... and more in budget that having to go find and book space on a busy commercial dyno. However. As most vehicles are strapped down during the test, will that show the amount of grip you have, because the strapping down its self is an artificial grip?.
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Post by the light works on Mar 5, 2018 15:15:05 GMT
it would probably be more work to build a miniature dyno for RC tires than to build a single tire drive system with an electric motor and take it to a real dyno. Or have the dyno visit you?. There are now mobile Dyno's built on the back of a truck bed that can be taken to track days and car shows that allows people to run what they brung and see exactly how many horses have escaped on older engines or see how many the air scoop has caught on re-built and "Improved" engines. Getting hold of one of them in the "closed season", ie Over Winter after all the car shows have finished, could be done more easily if it provides exposure for "Daves Dyno" on the show.... and more in budget that having to go find and book space on a busy commercial dyno. However. As most vehicles are strapped down during the test, will that show the amount of grip you have, because the strapping down its self is an artificial grip?. depends on how tight you strap it. keep in mind the variables you are controlling are how many horsepower you put into the system, how much weight you have on the tire, and how much resistance the dyno is applying.
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Post by silverdragon on Mar 6, 2018 7:22:23 GMT
Or have the dyno visit you?. There are now mobile Dyno's built on the back of a truck bed that can be taken to track days and car shows that allows people to run what they brung and see exactly how many horses have escaped on older engines or see how many the air scoop has caught on re-built and "Improved" engines. Getting hold of one of them in the "closed season", ie Over Winter after all the car shows have finished, could be done more easily if it provides exposure for "Daves Dyno" on the show.... and more in budget that having to go find and book space on a busy commercial dyno. However. As most vehicles are strapped down during the test, will that show the amount of grip you have, because the strapping down its self is an artificial grip?. depends on how tight you strap it. keep in mind the variables you are controlling are how many horsepower you put into the system, how much weight you have on the tire, and how much resistance the dyno is applying. This is where I get a bit pedantic with those that claim "My engine has 1,000 horses", and then bang on incessantly about the shape of the cam-shaft, the type of cylinder head, and all that, but, they cant tell you how many at the wheel. The Transmission for you Americans or Gear Box for the rest of the world steals some of those horses to make the cogs turn, the axles, differential, wheels and tyres all take their share, and then you have the fact that their car is as aerodynamic as a house brick turned sideways, sho am I to complain with a 900 horse engine and a "!Cab over" style truck thats the whole side of a house sized?. But then at least all 900 horses I have can be directed towards the road without me leaving half a tyre per mile in double black lines? The Dyno will tell you how may horses you have that can get transmitted to the wheel, and that is good. But what we are missing here is how many of those horses are being used per mile "Safely" when the car is in use on the road. It will tell us straight line speed, but, even you Americans in your cars that dont do corners, [/sarcasm] as the heads on TG will tell us, it doesnt tell us normal road use, which is corners, braking, acceleration. I dont know if you realise it but a change in tyre alters subtly the way you drive?. Just as a change in car should, in that you learn within about half a dozen corners how a different car brakes, all the way up to your Spongbob you drive TLW, and many are different, some you know dont like to brake mid corner, some will go round corners like they are on rails, brake or no brake, which I have to say most Toyota's I have driven excel at for such mass produced vehicles, some are more eager to stop, well, your tyres, and a change in tyre, can alter that. I notice my tyres starting to wear by when I pull out of the top of the road. Its a sharp~ish corner to a 40 speed limit, so if you see a gap, you "nail it", or you will be waiting for the next ice age at times, and if I do that when my tyres start to wear down, the inside of the corner tyre "lifts"?. As in looses traction and spins slightly... This happens about 2.0 to 1.6 mil on tyre depth, still fully legal, but at 1.8 I start to plan replacement before the next Big White.Reason I gave up on the hyper-mile economy tyre?. I lost traction quickly with them, I HAD to drive more gently, because I didnt have the grip... Therefore, I was almost driving "Hyper-mile" style... Good?. Nope. I need a tyre that stops me from 20 in the length of an eye blink when a kid on a bike doesnt look. And you may remember that happened not that long back to me. Would that tyre choice have made a difference?. Thank the lord duck I never had to find out.... Yes, Run the Dyno, but I would like to see the brake test done at the same time to show that as an educational tool. Especially the bit "In the wet"... that may scare some people into driving more sensibly when it rains, and that has to be good, yes?.
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Post by the light works on Mar 6, 2018 15:22:24 GMT
depends on how tight you strap it. keep in mind the variables you are controlling are how many horsepower you put into the system, how much weight you have on the tire, and how much resistance the dyno is applying. This is where I get a bit pedantic with those that claim "My engine has 1,000 horses", and then bang on incessantly about the shape of the cam-shaft, the type of cylinder head, and all that, but, they cant tell you how many at the wheel. The Transmission for you Americans or Gear Box for the rest of the world steals some of those horses to make the cogs turn, the axles, differential, wheels and tyres all take their share, and then you have the fact that their car is as aerodynamic as a house brick turned sideways, sho am I to complain with a 900 horse engine and a "!Cab over" style truck thats the whole side of a house sized?. But then at least all 900 horses I have can be directed towards the road without me leaving half a tyre per mile in double black lines? The Dyno will tell you how may horses you have that can get transmitted to the wheel, and that is good. But what we are missing here is how many of those horses are being used per mile "Safely" when the car is in use on the road. It will tell us straight line speed, but, even you Americans in your cars that dont do corners, [/sarcasm] as the heads on TG will tell us, it doesnt tell us normal road use, which is corners, braking, acceleration. I dont know if you realise it but a change in tyre alters subtly the way you drive?. Just as a change in car should, in that you learn within about half a dozen corners how a different car brakes, all the way up to your Spongbob you drive TLW, and many are different, some you know dont like to brake mid corner, some will go round corners like they are on rails, brake or no brake, which I have to say most Toyota's I have driven excel at for such mass produced vehicles, some are more eager to stop, well, your tyres, and a change in tyre, can alter that. I notice my tyres starting to wear by when I pull out of the top of the road. Its a sharp~ish corner to a 40 speed limit, so if you see a gap, you "nail it", or you will be waiting for the next ice age at times, and if I do that when my tyres start to wear down, the inside of the corner tyre "lifts"?. As in looses traction and spins slightly... This happens about 2.0 to 1.6 mil on tyre depth, still fully legal, but at 1.8 I start to plan replacement before the next Big White.Reason I gave up on the hyper-mile economy tyre?. I lost traction quickly with them, I HAD to drive more gently, because I didnt have the grip... Therefore, I was almost driving "Hyper-mile" style... Good?. Nope. I need a tyre that stops me from 20 in the length of an eye blink when a kid on a bike doesnt look. And you may remember that happened not that long back to me. Would that tyre choice have made a difference?. Thank the lord duck I never had to find out.... Yes, Run the Dyno, but I would like to see the brake test done at the same time to show that as an educational tool. Especially the bit "In the wet"... that may scare some people into driving more sensibly when it rains, and that has to be good, yes?. keep in mind, my "it'll go around anything but a corner" remarks are based on turning radius, not cornering ability.
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Post by silverdragon on Mar 7, 2018 7:10:38 GMT
keep in mind, my "it'll go around anything but a corner" remarks are based on turning radius, not cornering ability. Keep in mind, I have driven American cars, and cornering ability is bad when compared to our own here in UK. Which is why we dont like live axle suspension and favour all round independent suspension, dont go for leaf springs but have coil over dampers, and cornering ability is more important than any straight line ability, therefore we dont do a lot of drag racing, unless Drag racing is a couple of queens in high heels trying to get to the bar before last orders?. Which by the way is highly entertaining when they already had a few diesel injections. If you want all out cornering ability, take a look at what we can do with the FX4 series of London Black cabs. The can turn on a sixpence and give you 5p change in metric or old money, almost not much more than three times their own width in a turning radius. Cornering ability here in UK and the wider europe, is not a "Bonus", its more a basic ability, and cornering at speed more than walking pace is a MUST, I have never ridden a bike that had to do a 3-point turn on a two lane road until I borrowed a Hardly Drivable, and the one time I drove an old ford Mustang, the lack of turning radius astounded me. There was the one time I had to do a 3point turn on a "mini" roundabout?.. [thats one of them painted on in white paint things...] You may not realise it, but cars built for your "Wide open space" roads in US, are almost painful to drive around european roads, and sometimes impossible to drive around older Roman architecture towns and cities. More so when you get to the older 50's 60's style "Land yacht's" of Cadillacs and the like.
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Post by the light works on Mar 7, 2018 15:43:03 GMT
keep in mind, my "it'll go around anything but a corner" remarks are based on turning radius, not cornering ability. Keep in mind, I have driven American cars, and cornering ability is bad when compared to our own here in UK. Which is why we dont like live axle suspension and favour all round independent suspension, dont go for leaf springs but have coil over dampers, and cornering ability is more important than any straight line ability, therefore we dont do a lot of drag racing, unless Drag racing is a couple of queens in high heels trying to get to the bar before last orders?. Which by the way is highly entertaining when they already had a few diesel injections. If you want all out cornering ability, take a look at what we can do with the FX4 series of London Black cabs. The can turn on a sixpence and give you 5p change in metric or old money, almost not much more than three times their own width in a turning radius. Cornering ability here in UK and the wider europe, is not a "Bonus", its more a basic ability, and cornering at speed more than walking pace is a MUST, I have never ridden a bike that had to do a 3-point turn on a two lane road until I borrowed a Hardly Drivable, and the one time I drove an old ford Mustang, the lack of turning radius astounded me. There was the one time I had to do a 3point turn on a "mini" roundabout?.. [thats one of them painted on in white paint things...] You may not realise it, but cars built for your "Wide open space" roads in US, are almost painful to drive around european roads, and sometimes impossible to drive around older Roman architecture towns and cities. More so when you get to the older 50's 60's style "Land yacht's" of Cadillacs and the like. yes, our trucks have to back and fill to make a turn that your cars can make. as I've said, my work truck has a larger turning radius than our fire engines. that's because its independent suspension, to I can't turn the front wheels as far as the straight axle on the fire engines will allow. the new car is much better in that regard, as they've figured out how to make the control arms a sharper angle at the pointy end. so the pickup and work truck are the worst for turning radius - we've got a four lane divided road in the area, and from the left turn lane in the middle, I can make a u-turn, using a side street for overflow, and not run up on the sidewalks. the car, I haven't checked, but I would suspect I could do a u-turn straight into the outside lane without crossing the fog line. the jeep, an old straight axle four wheel drive, can almost do a u-turn on a two lane road without crossing the fog lines. as far as fast cornering is concerned, so far, the truck, before the service box went on it still is king. if you could keep the grip, you could make the corner. and as far as harleys and cornering ability: maybe you just went to the wrong riding school
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Post by silverdragon on Mar 8, 2018 8:16:23 GMT
Show that again with my last bike if you can find one Ducati 907ie, note that on that vid, at several points, he is "almost" scraping the exhaust, the Duke will get so low you can not just touch the floor with hand and elbows, it has you screaming how the hell do you get that kind of grip off the sidewall of a tyre.
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Post by the light works on Mar 8, 2018 15:16:48 GMT
Show that again with my last bike if you can find one Ducati 907ie, note that on that vid, at several points, he is "almost" scraping the exhaust, the Duke will get so low you can not just touch the floor with hand and elbows, it has you screaming how the hell do you get that kind of grip off the sidewall of a tyre. I believe the question at hand was making a u-turn, not how far you tip the bike before something contacts the ground. I was taught the secret of good cornering was having your center of gravity closer to the ground, not further from it. and what is it that happens when you break a tire loose on a sport bike, again?
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Post by silverdragon on Mar 9, 2018 6:44:49 GMT
When you break loose a sports bike, if your that daft and try to hard, it either regains grip or it doesnt, if it doesnt, kick it and slide, if it does "High side". That vid with the harley, until he broke grip with the rear tyre, most of those corners wouldnt even cause me to drop a cog on my old Duke, those aint corners, thems just slight bends. It isnt all about speed either, most bikes I have had can make a U turn at low speed in a single lane road without hitting either kerb, rider skill can do that without putting your foot down, but it makes it easier parking up, and no bike I have ever owned came fitted with a reverse gear, although I have ridden Goldwing Aspencade, 1500 engine, you need a reverse on that beast. I know some harleys dont need reverse, but the bigger ones do, and they dont get a turning circle as good as my current car. But this wasnt all about Bikes, it was the general discussion, our roads have less space and tighter turns that American ones, including that one with the hairpins on a hill you have in SF. which you may see as extreme... In truth, that one in SF is probably about Normal on those turns for some of our roads, in that we do have tighter, but not that often. Most bikes I have had could manage that as a hill climb at a reckless speed, and most times, wreck-less as well, we have speed bumps bigger than that over here?. Some may call those speed bumps the hills of Wales, but I see them as a challenge. But back to what I am challenging, european and UK cars have better turning ability in general than most US cars, I know its a PITA, but one I know you have got, as an example, the Toyota Prius, thats about average for a larger family affordable sized vehicle in UK. We have smaller, the Golf, maybe you know it as the Rabbit?. thats a average 5seat family car for smaller people in UK. Even that can turn on a sixpence and give you change when compared to the radius of say a Mustang. Unless you light up the tyres that is... Golf are FWD, useless at power sliding. I can drive one, but the drivers seat is so far back with me in it you wont get anyone behind me comfortably.... But they are a lot of fun if fettled correctly. You have more space than us, and quite often, better roads as well, we have to manage with a right mess of roads built for horse and cart that used to make a chicane if there was a tree in the way, and in some places, went around bigger houses if the cost of a straight line was too much in demolishing the house. We didnt plan our roads, they started as sheep tracks, and in some places, the harder ground around boggy areas?. Most just happened, and some have been there since stone age times.
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Post by the light works on Mar 9, 2018 16:05:57 GMT
When you break loose a sports bike, if your that daft and try to hard, it either regains grip or it doesnt, if it doesnt, kick it and slide, if it does "High side". That vid with the harley, until he broke grip with the rear tyre, most of those corners wouldnt even cause me to drop a cog on my old Duke, those aint corners, thems just slight bends. It isnt all about speed either, most bikes I have had can make a U turn at low speed in a single lane road without hitting either kerb, rider skill can do that without putting your foot down, but it makes it easier parking up, and no bike I have ever owned came fitted with a reverse gear, although I have ridden Goldwing Aspencade, 1500 engine, you need a reverse on that beast. I know some harleys dont need reverse, but the bigger ones do, and they dont get a turning circle as good as my current car. But this wasnt all about Bikes, it was the general discussion, our roads have less space and tighter turns that American ones, including that one with the hairpins on a hill you have in SF. which you may see as extreme... In truth, that one in SF is probably about Normal on those turns for some of our roads, in that we do have tighter, but not that often. Most bikes I have had could manage that as a hill climb at a reckless speed, and most times, wreck-less as well, we have speed bumps bigger than that over here?. Some may call those speed bumps the hills of Wales, but I see them as a challenge. But back to what I am challenging, european and UK cars have better turning ability in general than most US cars, I know its a PITA, but one I know you have got, as an example, the Toyota Prius, thats about average for a larger family affordable sized vehicle in UK. We have smaller, the Golf, maybe you know it as the Rabbit?. thats a average 5seat family car for smaller people in UK. Even that can turn on a sixpence and give you change when compared to the radius of say a Mustang. Unless you light up the tyres that is... Golf are FWD, useless at power sliding. I can drive one, but the drivers seat is so far back with me in it you wont get anyone behind me comfortably.... But they are a lot of fun if fettled correctly. You have more space than us, and quite often, better roads as well, we have to manage with a right mess of roads built for horse and cart that used to make a chicane if there was a tree in the way, and in some places, went around bigger houses if the cost of a straight line was too much in demolishing the house. We didnt plan our roads, they started as sheep tracks, and in some places, the harder ground around boggy areas?. Most just happened, and some have been there since stone age times. keep in mind our police, back in the 80s, got the bright idea of buying Mustangs as interceptors, and then switched to Camaros when the mustangs showed a habit of sailing straight off into the scenery if the driver came into a corner too fast. now most of the police are favoring the Exploder Interceptor, which you over there would classify as a large family SUV. they started buying them when attorneys started filing cruel and unusual punishment complaints when the suspect was put in the back seat of a Taurus. (the next size up from a focus) and yeah, our roads have turns as sharp as yours, and occasionally as apparently pointless as yours (a chicane around a tree that fell down and rotted out generations ago) we just have more distance between them. our farm country roads tend to follow the borders of fields, which means you have a mile ruler straight, and then a 90 degree corner, and then another mile ruler straight. then you go up into the hills, and you get roads that follow deer trails, that they drive these at speed on; so I'm sure you're proud of Bealach na Bà. try this: www.dangerousroads.org/north-america/usa/233-going-to-the-sun-road-usa.htmlbut back on the subject of tires - if you have too hard a compound, you will have slip, which will rob you of mileage, but too soft, and you're wasting energy flexing the tire.
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Post by silverdragon on Mar 10, 2018 5:18:43 GMT
I agree with the tyres thing, too hard, you nmeed to warm them up to get grip, and they are great at lasting long, but dont give you the grip, too soft, you waste energy in rolling resistance, but sure as heck they grip like black snot round the tight stuff. This is why Wagon tyres are hard, and sports vehicles prefer racing compound.
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Post by c64 on Aug 22, 2018 20:36:52 GMT
so what could be done to quantify this OTHER than just a road test? The German "Auto, Motor-sport" magazine used to have a simple test to find out how efficient a car rolls and gather hard figures. They had simply accelerated the car to 100kph (60mph) and drove it over a line where they had hit the clutch. The further the car rolls until it stops, the less aerodynamic drag and rolling resistance it has. The distance you get from this test is proportional to how efficient the cars body, wheels and drive shafts are. So all you need to do is to take the very same car just using different tires to get nice hard figures quickly. Since transmission and aerodynamics remain a constant, you get a percentage how much less power the engine needs to deliver to keep moving.
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