How do wheel/tire size affect speed
08-14-2009, 01:25 PM
#121
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I can’t take this anymore….. Mark, do your realize you have something like 47 posts in this thread so far, out of 116? And that most of them are fixated on an acceleration model that is grossly inferior to the GPS data possessed by the OP?
>>>>> no, im only stating physic here regarding the effects of wheel weight on acceleration performance. what does it matter how many posts Ive had. Im helping someone that wants to discuss the situation
Do you realize the differences in laptimes are being caused by what is happening in three-dimensional CORNERS on a racetrack?
>>>>>>>Yes, we are trying to remove those factors from our discussion. lap times were actually better the day before with the 18s, and faster the first half of his second day lap time as well, with the 17s. the only anomoly here is the 18s being slower down that final straight.
Your formulas relate to straight-line frictionless acceleration of a mass in a vacuum. Such formulas are useful to roughly approximate drag-strip hypotheticals, or to save money by avoiding dyno or drag strip rental time. But we are not talking about those things.
>>>>>>Yes we are. we are looking and matching speeds after the corner. If they match up, it doesnt matter what happens before hand, except for car attitude/direction.
We are talking about the dynamic interaction between a driver, a racecar at speed, and a three-dimensional racetrack. Those dynamics are far too complex to model mathematically unless you have the budget & computing power of NASA or Sony (and even then….you’d rather test it than model it).
>>>>>>>mathematical modeling is used in simulartors and is accurate. did you know that this modeling is used in airplane simulators and before your boeing 767 pilot takes you and your kids to chicago, he has never even been in the actual plane??
I’m not trying to be negative. Your effort and enthusiasm are obvious. But this thread has become a monument to the idolatry of numbers. Easily 60%+ of this thread’s total word-count has been devoted to the spurious “accuracy” of mathematical models and personal anecdotes that have next to zero relevance to this problem.
>>>>>ive done this change MANY times over the years at tracks I frequent more than most at any track. have never seen any difference like this on ANY straight for such a change. remember, we are talking about a 1 second earlier shift point on the main straight off a prior turn with similar vehicle speed. The math is clear. we can equate the change to under 1hp net difference, ignoring any grip issues.
I have nothing against mathematical models. They are useful for approximating physical outcomes that are too difficult or too expensive to test via experimentation.
>>>>>>> You are valuing the GPS data over the math, but not even understanding the GPS data that ironically is allowing us to make our assements of the situation. the GPS data is critical for analysis here.
But….from very early on in this thread we have had concrete data from an actual real-world test. The 17’s consistently enable lower laptimes.
>>>>> no they havent. how can you say this. the last test showed the 18s faster than before, and then the following day with the 17s, the 18s were faster all but the last straight. how is this concrete?????
Contrary to the pages and pages you posted above which claim it can’t possibly be true because the weight change is insignificant (in your model), the bottom line is that the time difference IS DUE TO THE WHEEL & TIRE package! The 17’s are allowing the driver to get through certain critical corners on a line, at a speed, and at a throttle position which, collectively, result in a lower elapsed time around the track. Factors causing this could relate to the 18” wheels’ effect on the vehicle’s bump-compliance over berms, steering feel, grip threshold, slip-angles, yaw rate, etc, etc… none of which are present in your models… and all of which could be affecting the driver’s perceptions about how the car is behaving in certain parts of the track and therefore impact his control inputs and racing line. Those two things in turn affect the vehicle’s acceleration mid-corner, differences in which become exaggerated all the way down any straight which follows.
>>>>>>> no, the information is not contrary to the data posted. we have tried to remove those factors that could be more subjective. remember, we have captured speeds and position and matched them up before the long straight.
Therefore, the driver should decide whether he can afford to diagnose and adjust the car’s setup to eliminate the current downsides of the 18’s, or just continue using the 17’s and enjoy the lower laptimes at this track, knowing that the outcomes may be different at other tracks.
Sorry for the long rant. I mean no disrespect to anyone. Just trying to clear the air a bit.
>>>>>> air cleared for sure, in that you are not lookng at all the data as we are. how do you explane the same lap, earlier straight, being equal to the 18s the prior day, or that first half lap being actaully FASTER? you dig into the numbers and graphs and determine what you think might be going on. the math is the guiding light. we can rule out acceleration factors of a 3lb differnce in wheel/tire weight .
>>>>> no, im only stating physic here regarding the effects of wheel weight on acceleration performance. what does it matter how many posts Ive had. Im helping someone that wants to discuss the situation
Do you realize the differences in laptimes are being caused by what is happening in three-dimensional CORNERS on a racetrack?
>>>>>>>Yes, we are trying to remove those factors from our discussion. lap times were actually better the day before with the 18s, and faster the first half of his second day lap time as well, with the 17s. the only anomoly here is the 18s being slower down that final straight.
Your formulas relate to straight-line frictionless acceleration of a mass in a vacuum. Such formulas are useful to roughly approximate drag-strip hypotheticals, or to save money by avoiding dyno or drag strip rental time. But we are not talking about those things.
>>>>>>Yes we are. we are looking and matching speeds after the corner. If they match up, it doesnt matter what happens before hand, except for car attitude/direction.
We are talking about the dynamic interaction between a driver, a racecar at speed, and a three-dimensional racetrack. Those dynamics are far too complex to model mathematically unless you have the budget & computing power of NASA or Sony (and even then….you’d rather test it than model it).
>>>>>>>mathematical modeling is used in simulartors and is accurate. did you know that this modeling is used in airplane simulators and before your boeing 767 pilot takes you and your kids to chicago, he has never even been in the actual plane??
I’m not trying to be negative. Your effort and enthusiasm are obvious. But this thread has become a monument to the idolatry of numbers. Easily 60%+ of this thread’s total word-count has been devoted to the spurious “accuracy” of mathematical models and personal anecdotes that have next to zero relevance to this problem.
>>>>>ive done this change MANY times over the years at tracks I frequent more than most at any track. have never seen any difference like this on ANY straight for such a change. remember, we are talking about a 1 second earlier shift point on the main straight off a prior turn with similar vehicle speed. The math is clear. we can equate the change to under 1hp net difference, ignoring any grip issues.
I have nothing against mathematical models. They are useful for approximating physical outcomes that are too difficult or too expensive to test via experimentation.
>>>>>>> You are valuing the GPS data over the math, but not even understanding the GPS data that ironically is allowing us to make our assements of the situation. the GPS data is critical for analysis here.
But….from very early on in this thread we have had concrete data from an actual real-world test. The 17’s consistently enable lower laptimes.
>>>>> no they havent. how can you say this. the last test showed the 18s faster than before, and then the following day with the 17s, the 18s were faster all but the last straight. how is this concrete?????
Contrary to the pages and pages you posted above which claim it can’t possibly be true because the weight change is insignificant (in your model), the bottom line is that the time difference IS DUE TO THE WHEEL & TIRE package! The 17’s are allowing the driver to get through certain critical corners on a line, at a speed, and at a throttle position which, collectively, result in a lower elapsed time around the track. Factors causing this could relate to the 18” wheels’ effect on the vehicle’s bump-compliance over berms, steering feel, grip threshold, slip-angles, yaw rate, etc, etc… none of which are present in your models… and all of which could be affecting the driver’s perceptions about how the car is behaving in certain parts of the track and therefore impact his control inputs and racing line. Those two things in turn affect the vehicle’s acceleration mid-corner, differences in which become exaggerated all the way down any straight which follows.
>>>>>>> no, the information is not contrary to the data posted. we have tried to remove those factors that could be more subjective. remember, we have captured speeds and position and matched them up before the long straight.
Therefore, the driver should decide whether he can afford to diagnose and adjust the car’s setup to eliminate the current downsides of the 18’s, or just continue using the 17’s and enjoy the lower laptimes at this track, knowing that the outcomes may be different at other tracks.
Sorry for the long rant. I mean no disrespect to anyone. Just trying to clear the air a bit.
>>>>>> air cleared for sure, in that you are not lookng at all the data as we are. how do you explane the same lap, earlier straight, being equal to the 18s the prior day, or that first half lap being actaully FASTER? you dig into the numbers and graphs and determine what you think might be going on. the math is the guiding light. we can rule out acceleration factors of a 3lb differnce in wheel/tire weight .
Also, in the prior data report from a previous day at Sebring, he showed a CLEAR change of when full throttle was applied, that seemed to cause the differnence of top speed on the back straight.
The physics are clear. sure, in a vacuum, and with out rolling friction, etc, but those factors are relatively consistant between the different tires tested. Same tire manufacture, same grade and type, only a change in inner wheel diameter fitting. overall diameter is the same, as I HAVE these exact tires and have measured them accurately.
As far as the driver's feel for the tire over birms, on, off line, etc, that is up to him to post. One thing, that stands out, contrary to your comment is that we KNOW that the speeds and positions are near identical coming off the turn, at any point independent of the factors you list. Lets grab data off the turn and compare them, eliminating those factors as much as possible. Again, the main evidence here is the first 75% of the laps were identical. infact, the first part of the lap was BETTER with the 18s. why do you think that was?
why do you think that the very last straight had the effects of near 50hp diff and didnt show this diff on a similar straight with similar matched exit speeds half a lap earlier. this is the type of things that we need to look at to see what could be the cause of the differences. the physics for wheel weight are clear and if we were doing a similation, which can be very accurate, the 3lb wheel weight factor would be a rounding error at best. any differences mid corner do not mulitply down the straight, IF the speeds at the same point further downt the track, are the same. You are not looking at the data.
To put in bold print, that you know the reason, is complete BS. you are looking at so little to make that assumption.
I'm curious about this also, published tire dimensions don't mean much. Brinkley, maybe you could put the 18s on the rear, mark the pavement and sidewall at the same spot and roll the car forward 3 rotations of the rear wheels and then mark that distance and measure. Then do the same thing with 17s on the rear...
Sorry to reinforce the imposable but I have felt the same thing with my low hp car.
He is not, you are. You are making some strong blanket statements and outright dismissal of the careful real world observations offered up by others.
My read as well. Still getting to know the tires. I bet there is a little of everything at play here. True rolling radius, wheel weight and where the weight is, driving style and car setup. Interesting thread, fluffy figure flouting filler aside. I think some are trying to measure chain saw cuts with a micrometer and find a trend. This is not a closed condition lab test it is a driver on a track and with that comes the human element. Stop at Saturday's data and the 18s are faster. Go on to Sundays data and the 17s are faster. Calculate that without factoring in the human element.
He is not, you are. You are making some strong blanket statements and outright dismissal of the careful real world observations offered up by others.
My read as well. Still getting to know the tires. I bet there is a little of everything at play here. True rolling radius, wheel weight and where the weight is, driving style and car setup. Interesting thread, fluffy figure flouting filler aside. I think some are trying to measure chain saw cuts with a micrometer and find a trend. This is not a closed condition lab test it is a driver on a track and with that comes the human element. Stop at Saturday's data and the 18s are faster. Go on to Sundays data and the 17s are faster. Calculate that without factoring in the human element.
One other thing to consider from the lastest traces. Turn 15-16 anc Back Str. It is clear the vehicle accelerates out of the corner sooner with the 17s. It looks as though there's a bobble with the 18s. This leads to a 1-2 mph advantage of the 17s out of the corner. Now, make the assumption that acceleration is equal between the two. That 1-2 mph difference in exit speed is equal to __% difference. If acceleration is equal that __% difference will be the same down the entire straight, which means the speed difference at the end of the straight percentage wise is equal. That means that your speed difference at the end of the straight is now 5-6 mph. Which describes the above trace.
Brinkley, I'm confident that if you can match the exit speed of the 18s with the 17s then your time loss over the last section of the lap will be zero. This is probably a portion of the track you'll want to focus on as elsewhere in the lap the differences are rather subtle.
Brinkley, I'm confident that if you can match the exit speed of the 18s with the 17s then your time loss over the last section of the lap will be zero. This is probably a portion of the track you'll want to focus on as elsewhere in the lap the differences are rather subtle.
Last edited by mark kibort; 08-14-2009 at 02:37 PM.
08-14-2009, 01:46 PM
#122
Three Wheelin'
agreed. I think you need to look at the mid lap straigth vs the last straight to see why one is a mirror image with both tires, proving that there is no differnce earlier, and then see why the last straight, why there is a 5mph+ difference. even comparing at any point post handling, setup for turn and exit, etc. the acceleration through the straight vs position and mph, is clearly faster, where it wasnt a half a lap earlier. Ignoring any handling issues or differences that the two tires might possess.
08-14-2009, 03:11 PM
#124
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Brinkley, one thing to keep in mind it that the distance scale on your charts reflects distance travelled since the start-finish line. So just because the 2 laps' lines touch at a certain point in the corner before that back straight, does not mean the cars were actualy in the exact same location when their speeds were identical. In my own data, I have seen 30ft variances in total distance travelled per lap, due to different lines taken. So the car with the 17s may be in a different location than the car with the 18s at the moment the chart shows them both at the same speed and same distance from S/F.
If your D/A application allows you to replay the two laps in realtime and watch the dots travel around the track map plotted by the GPS, you might be able to see if the car with the 17's had achieved greater rotation earlier than the 18's car, thereby allowing it to have a straighter steering wheel and accelerate faster forward from that moment when their speeds were identical. Just an idea.
If your D/A application allows you to replay the two laps in realtime and watch the dots travel around the track map plotted by the GPS, you might be able to see if the car with the 17's had achieved greater rotation earlier than the 18's car, thereby allowing it to have a straighter steering wheel and accelerate faster forward from that moment when their speeds were identical. Just an idea.
08-14-2009, 03:17 PM
#125
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Good point. you can see that the entry point to that last straight, vs any others prior, was very different. I have to think about the exit speed's effect on the top speed for a minute. we have to remember we are talking speed vs positon as well. But, i think you are on to something here.
in thinking out loud, if you are racing someone, and you are 1 second back off a slow turn, you can be equal in HP and acceleration and always be 1 second behind, but the distance back will double at double the speed, even though at the same position on the track, you will be at the same speed.
If you look at the two curves it sure looks like if the two were matched up from the beginning they would overlap, almost identically.
in thinking out loud, if you are racing someone, and you are 1 second back off a slow turn, you can be equal in HP and acceleration and always be 1 second behind, but the distance back will double at double the speed, even though at the same position on the track, you will be at the same speed.
If you look at the two curves it sure looks like if the two were matched up from the beginning they would overlap, almost identically.
The resolution isn't clear enough on the early straight you're referring to to make a call, but its obvious on the back straight that the exit speed difference is the cause of the time AND SPEED loss on the straight. Acceleration is non-linear, so a 1 mph exit speed difference can become a 5mph difference on a long enough straight even if accleration is 100% equal between the two.
08-14-2009, 03:25 PM
#126
Three Wheelin'
Got the solution! Should end the discussion...I hope.
Brinkley, the maths channels in I2 Pro should have the solution. There should be a derivative function. Plot the derivative of speed for the back straight and overlay them. Obviously this is acceleration. If they are the same then there is no difference due to wheel size/weight/drag/etc or the opposite is true.
Brinkley, the maths channels in I2 Pro should have the solution. There should be a derivative function. Plot the derivative of speed for the back straight and overlay them. Obviously this is acceleration. If they are the same then there is no difference due to wheel size/weight/drag/etc or the opposite is true.
08-14-2009, 06:02 PM
#128
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Regarding position on track being based on the distance i've traveled from start/finish, I don't know. The car doesn't have a Speedometer, and I don't think the DA is looking at a wheel speed sensor to be able to calculate distance traveled by multiplying revolutions?
The start of a lap is based on gps lat/long coordinates not a lap beacon.
2bwise, I don't know how to do the calculation you suggested. IF you have i2Pro I can email you the file and you can do the math. That is, if i2Pro can process an i2Standard file, as I do not use i2Pro.
The start of a lap is based on gps lat/long coordinates not a lap beacon.
2bwise, I don't know how to do the calculation you suggested. IF you have i2Pro I can email you the file and you can do the math. That is, if i2Pro can process an i2Standard file, as I do not use i2Pro.
08-14-2009, 06:05 PM
#129
Rennlist Member
BINGO.
Now, if there was any difference due to wheel sizes, wouldnt it show up here?
2BWISE has a great idea as well to determine acceleration rates on the suspect straight.
This clearly shows almost identical speeds vs position, slight advantage on the blackline (17s) as it is showing earlier shifts by fraction of a second, but the end result is near identical speeds. IF there was an advantage, it would show up here. the math proves this also. Now, the largest variable is your engine output and driver inputs, even down the straight. But, i have to believe that if you are running 1:25s, you know what you are doing.
As another note. look closely at the throttle position at the start of the straight. notice the 17s (black) have an advantage that pays off slightly before the first shift, which is earlier. even that doesnt create that much of a difference, even though at the end, you are off the throttle a little earlier with the 18s ( red/green).
Thanks for posting that. great info.
mk
Now, if there was any difference due to wheel sizes, wouldnt it show up here?
2BWISE has a great idea as well to determine acceleration rates on the suspect straight.
This clearly shows almost identical speeds vs position, slight advantage on the blackline (17s) as it is showing earlier shifts by fraction of a second, but the end result is near identical speeds. IF there was an advantage, it would show up here. the math proves this also. Now, the largest variable is your engine output and driver inputs, even down the straight. But, i have to believe that if you are running 1:25s, you know what you are doing.
As another note. look closely at the throttle position at the start of the straight. notice the 17s (black) have an advantage that pays off slightly before the first shift, which is earlier. even that doesnt create that much of a difference, even though at the end, you are off the throttle a little earlier with the 18s ( red/green).
Thanks for posting that. great info.
mk
08-14-2009, 06:10 PM
#131
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On i2Standard I have the ability to drag each laps distance to different areas (look at the horizontal portion of the graph). Notice below I have the same 6500 feet zoom but I have moved the BLACK trace to match the first shift. You will notice it is -28 feet difference. But know everything looks "out of wack". This causes the discussion of DA to get even tougher to comprehend when you shift time and bend it back on itself!
Last edited by Brinkley; 01-26-2013 at 10:47 AM.
08-14-2009, 06:20 PM
#132
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Brinkley, another intersting plot, since you were so excited to do a P.R. on Saturday, with the 18s, would be to plot that lap to the 17 lap of the prior month weekend. Now, you have different weekends, different temps, etc and style possibly, and see where you made up the time, vs what you thougth at the time, was the faster tire (i.e. the 17s on that prior weekend). We can then focus in on the straights again and see if there is a different in raw acceleration times, speeds, distances on that same back straight.
08-14-2009, 06:28 PM
#133
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Mark,
You ask and I can try.
Below is a zoomed in look at the same straight. BLACK is July in Florida at 90 plus degrees. Lap 2:25.0
RED is January at Winterfest and it was 45 -50 degrees and no humidity. Lap 2.25.8
Note across the bottom I have matched first shift points and there is a -57 foot difference this time.
Also note that I concluded shifting into 5 was not worth it so I eliminated this practice and I hold 4th up to 6800 rpms. That is why the speed is faster in the black trace. At least that is what I think.
You ask and I can try.
Below is a zoomed in look at the same straight. BLACK is July in Florida at 90 plus degrees. Lap 2:25.0
RED is January at Winterfest and it was 45 -50 degrees and no humidity. Lap 2.25.8
Note across the bottom I have matched first shift points and there is a -57 foot difference this time.
Also note that I concluded shifting into 5 was not worth it so I eliminated this practice and I hold 4th up to 6800 rpms. That is why the speed is faster in the black trace. At least that is what I think.
Last edited by Brinkley; 01-26-2013 at 10:47 AM.
08-14-2009, 06:43 PM
#134
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Mark, what is a P.R.?
Anyway I have the answer below for the entire post. Below is a zoomed in lap that is NOT distance shifted. The RED is on 18's and the BLACK is on 17's. (The previous post is comparing 17's to 17's in two different temperature settings, 50 degrees no humidity vs. 95 degrees 90% humidity.) The speed is identical once you look at throttle. I think the whole thing goes back to getting on the throttle sooner and maintaining higher corner speed, as said by many over the last pages.
Anyway I have the answer below for the entire post. Below is a zoomed in lap that is NOT distance shifted. The RED is on 18's and the BLACK is on 17's. (The previous post is comparing 17's to 17's in two different temperature settings, 50 degrees no humidity vs. 95 degrees 90% humidity.) The speed is identical once you look at throttle. I think the whole thing goes back to getting on the throttle sooner and maintaining higher corner speed, as said by many over the last pages.
Last edited by Brinkley; 01-26-2013 at 10:47 AM.
08-14-2009, 07:30 PM
#135
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sorry, track and field talk (P.R. =personal record)
yep, those graphs are also telling. You are getting pretty good at this!
What I was really looking for was that final straight 17s, which is where you beat the 18s, even though they were faster for the first half of lap, vs the 17s on the prior month's weekend. That is the biggest delta in speed vs distance ,but it also has the biggest positon delta entering the turn.
I think its now clear to see that where you get on the gas, is the main component here.
Again, you also have the calculations of HP vs weight on the tire. you can see what the HP gain or loss would be at near any speed range. As they show, we are talking about a very minimal difference, especially at the speed ranges you were worried about. (i.e. 60mph to 120mph of over 10 seconds)
Great topic of discussion! Thanks for all the info.
mk
yep, those graphs are also telling. You are getting pretty good at this!
What I was really looking for was that final straight 17s, which is where you beat the 18s, even though they were faster for the first half of lap, vs the 17s on the prior month's weekend. That is the biggest delta in speed vs distance ,but it also has the biggest positon delta entering the turn.
I think its now clear to see that where you get on the gas, is the main component here.
Again, you also have the calculations of HP vs weight on the tire. you can see what the HP gain or loss would be at near any speed range. As they show, we are talking about a very minimal difference, especially at the speed ranges you were worried about. (i.e. 60mph to 120mph of over 10 seconds)
Great topic of discussion! Thanks for all the info.
mk