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Tracking / Autocross / HPDE / Drifting What these cars were built for! |
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12-14-2022, 10:43 AM | #29 |
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Wheel width is not measured outside edge to outside edge, it is measured bead to bead. Also, tread width is not section width.
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12-14-2022, 10:56 AM | #30 |
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True, but it's pretty obvious the tire is stretched. You can't even see the tire on the trailing edge of the wheel. Compare that to how much you can see on the leading edge and you'll appreciate how great the difference is.
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12-14-2022, 11:04 AM | #31 |
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edit: nevermind
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12-14-2022, 12:39 PM | #32 |
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Just throwing a few of my two cent thoughts in here.
For fastest lap times you match tire section width to rim width. This gives the best feedback, wear and lap times. The only time that we shove larger tires on smaller rims is when we are rim width limited in classes, such as scca since they rule by rim width versus tire width like nasa does. Something people seem to get focused on also is the number printed on the sidewall of the tire, that number is nothing meaningful in the performance world. Like RedReplicant mentioned earlier, a radial slick's number on the sidewall is not something to use as a size reference. A 225 hoosier, goodyear or bfgoodrich is more like a 245 - section width is pretty much 10" on those sizes - and a 245 is a roughly a 10.5" section width. Now you take most street performance tires like a goodyear supercar or a Yokohama ao48 and 225 is 9" section width, a 245 is a 10" section width. Just a FYI, I am rounding a little on the section widths for quick explanation, manufacturers vary on all of this a little like one is 9.8, another 10 or another 9.9 for a given section width, aspect ratio causes variance as well. Hopefully this helps a few making size choices. |
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12-16-2022, 08:25 AM | #33 |
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Another variable to throw out that I have done some testing on with my track Miata, in low HP cars like the Miata and the Twins, I found that carrying an inch of wheel and tire around a high-speed track can hurt your laptimes. You will not make up the drag of those inches down the straights with the extra corning grip from the wider set-up. There is a balance that you have to figure out for your set-up and track. My Miata at 145WHP was faster around Sebring and Homestead on a 7" rim than 9" rim with the same 205 NT-01R's.
Also, keep in mind that the tread-wear number is almost meaningless as there is no industry standard for what it means. In other words, a 400TW Bridgestone may be a 200TW to Toyo or vice versa. The only thing I can say for sure is to test it yourself.
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12-16-2022, 10:47 AM | #34 | |
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Quote:
Thats another valid thought, something I have forgotten about since I haven't played with sub 200whp cars in a really long time. Rolling resistance of the larger contact patch plus added rotating mass, be it larger tire or wheel, will have a pretty great affect on low hp cars. Good points! |
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12-16-2022, 11:46 AM | #35 | |
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12-16-2022, 03:56 PM | #36 |
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That is part of why you get the people working around restrictive aero rules in certain classes by using larger than usual stick on fender flares that cover some of the frontal area of the tire, the big airdams that are bowed out in front of the tires, and the front of fenders bent out with the rearmost front bumper mounts spaced out wider than stock.
The competitive BMWs and Miatas running in NASA usually have one or more of these so they're easy to find examples of on ye olde google images.
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12-17-2022, 10:38 AM | #37 |
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Good discussion guys. Ran a 2:04.6 at Buttonwillow on CW13. This is my PB. The weather was very favorable. Really enjoyed the kumhos. Next test will be the same 225 on my 17x8 wheels. I think the car has some time to loose in the right hands but this size might be go forward to use.
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01-07-2023, 06:15 PM | #38 |
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I will be at BW at the end of this month. Plan to put my 225 kumho v730s on my lighter smaller 17x8 rims and will do my best to compare things.
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01-16-2023, 11:28 AM | #39 | |
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Tirerack did some testing, as posted by nissanfanatic over in the tire subforum
https://www.tirerack.com/tires/tests...y.jsp?ttid=296 Quote:
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01-16-2023, 12:32 PM | #40 | |
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The wet results are not surprising. Water creates drag and a wider tire is going to have more of it. In a straight line the narrower tire is going to be faster because of less drag. The wider tire has the opportunity to make up for this in turns where the lateral grip is greater. In the wet the water acts as a lubricant and therefore reduces lateral grip for everyone which effectively nullifies the advantage. It would be kind of neat to see a track map of speeds/times comparing these tires against each other. |
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01-16-2023, 02:49 PM | #41 | |
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01-20-2023, 10:54 AM | #42 |
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Speaking in terms of autocross only, it's common that everyone is putting as wide of a tire on as possible. All our second gen guys (and there's a lot of them) are running 245's and even 255's on a 7.5". They do extended studs, spacers, and max offset per the rules to achieve this. Note that I'm just talking about autocross, but our courses are very much like smaller tracks similar to the TireRack testing facility.
I personally run 225/45/17 because it's what you can get away with without going the spacer/stud route... and because having Brembos limits your wheel choices heavily. Interesting to see what 225 on the proper wheel generally is even with 245's on the same width... at least per TR's testing.
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