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Old 08-12-2018, 06:42 AM   #15
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I've seen people say the wider tires are less expensive for them. I was just looking for the details, thank you.
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Old 08-12-2018, 09:45 AM   #16
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For road racing, go as wide as you can.
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Old 08-12-2018, 10:47 AM   #17
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Much depends on the track and what your experience is. If you're new to the track it's best to leave the stock tires on until you learn proper car control and this takes some time.
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Old 08-12-2018, 09:30 PM   #18
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Originally Posted by SorryTires View Post
I hadnt considered the aero drag or rolling resistance. I suppose if you add up all these effects you might get something measurable.

Anyone have datalogs from the track with different tires they would be willing to share? It would be very interesting to see how much the lateral and longitudinal g's change
@CSG Mike - did you guys ever publish data, or just anecdotal feedback on the widths?
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Old 08-13-2018, 04:03 PM   #19
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Originally Posted by wparsons View Post
@CSG Mike - did you guys ever publish data, or just anecdotal feedback on the widths?
There's currently about 22000 laps of data in the pool, of which about 9500 was driven by me between various CSG cars, and another ~2200 laps from my personal car. I don't think that data will ever be be made public.

I can say, that you have to decide which tire is fastest based on each individual track and the track's needs.

Also, fastest lap =/= best for racing. Many of these skinnier tires being fastest are also one-lap-wonder scenarios.
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Old 08-13-2018, 04:05 PM   #20
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Originally Posted by 14stu View Post
I didn't have my AIM data logger when I took these videos; however, the first two were within 2 months of each other, the first is with 245/40-17 RE71r's (1:26.6) the second is with 225/45-17 RE71r's (1:27.6) and the third is my personal best at that track on 255/40-17 RE71r's (1:24.7).

The g's look pretty similar. All three videos are with different brake pads, but other than pads and tires there weren't any changes to the car.

245's

https://www.youtube.com/watch?v=NFUUkOPVxKU&t=729s

fastest lap starts at 5:53

225's

https://www.youtube.com/watch?v=2fDUhX4R9fM&t=864s

fastest lap starts at 13:31

255's

https://www.youtube.com/watch?v=ZMznz70P2I8

fastest lap starts at 3:53
How were the ambient temps on each of those days? Looks like the 255 tire day may have also had (by far) the best conditions between surface temps and ambient.
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Old 08-13-2018, 04:45 PM   #21
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Originally Posted by CSG Mike View Post
How were the ambient temps on each of those days? Looks like the 255 tire day may have also had (by far) the best conditions between surface temps and ambient.
The 255 day was in January, with air temps in the 60's. The other videos had almost identical temps in the 80's.

With higher temps and lows grippy Falken Azenis 615k+ in 255 I've been able to consistently dip into the 1:25's.

The 255 video was the best conditions and I really only added it because it was the only time I've run the 255 RE71r and it is my PB (I ruined the passenger side tires over those 6 sessions, they started the day as stickers).

The wider tires didn't seem to cost me any speed in the straights, and I could maintain an extra couple of mph in the long sweepers. This isn't the most scientific data and I didn't intend those track days as tire width tests (I picked up the 225s cheap after the pro solo as used take-offs specifically for non- competitive sessions).

The scca time trial program I run with uses modified autox classes and only one of the tracks we run at has long enough straights to favor a narrower tire, so I default to the 255's.

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Old 08-13-2018, 05:47 PM   #22
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Also, tires stick to the track so wider tires require more power to unstick from the track. Weight + aero drag + adhesion all add up...
Does anyone have any data on comparing a tire/wheel setup that are wider & more sticky, but weigh less vs narrower ones on stock or heavier wheels?
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Old 08-13-2018, 07:04 PM   #23
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Does anyone have any data on comparing a tire/wheel setup that are wider & more sticky, but weigh less vs narrower ones on stock or heavier wheels?
That's too many variables at once.

Light wheels are the best.

The stickiest compound is the best.

Widest tire is the best unless you have long straights.

Your wheel width is usually set by class and on a twin you're looking at something between 7" and 9" unless you are going a custom setup. The weight differences between the lightest and heaviest performance wheels is about 5lbs (the OEM wheel is about 20lbs while "light" 17x9 wheels are 16-17lbs). 5lbs of rotating, unsprung mass is nothing to sneeze at but also not a huge difference.

For tire widths, you are looking at 225-255 (I guess you could go down to a 215, but I wouldn't recommend it). There isn't a lot of difference here either and you could always just pick a middle width to hedge your bet either way.

Compound is where you can see large differences. For example: running the same 255 Bridgestone RE71r's and Falken Azenis 615k+ (both 200tw performance tires) I was seeing a 1-2s difference in lap times (I do have data for that comparison).

If you don't know what to run, you probably aren't experienced/fast enough for the slight differences to matter. If you picked the worst options in weight and width, you are looking at giving up about 2s or less. For most drivers, the performance difference fades into the background noise of their own inconsistency.

If you have fewer than 25 track days under your belt, don't sweat it. Pick the lightest wheel for whatever class you plan on running and get a 225-255* set of RS4's, Falken Azenis 615k+, or Federal 595 RSR (or whatever the 200tw version is). Don't bother tracking the Bridgestone RE71r's unless you are a competitive autocrosser and you don't want another set of wheels and tires to keep up with.

*tire and wheel widths should correspond, a 255 on a 7" wheel will be pinched (and feel terrible) and a 225 on a 9" is okay but a bit stretched (I've run a 225 on a 9" wheel without issues, and the Miata guys do it all the time)

Spend you time and money on seat time, that's where you'll get the most return on investment.
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Old 08-13-2018, 07:32 PM   #24
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Here's another gem from 949Racing's Emilio re: wheel set up.
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Old 08-13-2018, 08:15 PM   #25
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Quote:
Originally Posted by 14stu View Post
That's too many variables at once.

Light wheels are the best.

The stickiest compound is the best.

Widest tire is the best unless you have long straights.

Your wheel width is usually set by class and on a twin you're looking at something between 7" and 9" unless you are going a custom setup. The weight differences between the lightest and heaviest performance wheels is about 5lbs (the OEM wheel is about 20lbs while "light" 17x9 wheels are 16-17lbs). 5lbs of rotating, unsprung mass is nothing to sneeze at but also not a huge difference.

For tire widths, you are looking at 225-255 (I guess you could go down to a 215, but I wouldn't recommend it). There isn't a lot of difference here either and you could always just pick a middle width to hedge your bet either way.

Compound is where you can see large differences. For example: running the same 255 Bridgestone RE71r's and Falken Azenis 615k+ (both 200tw performance tires) I was seeing a 1-2s difference in lap times (I do have data for that comparison).

If you don't know what to run, you probably aren't experienced/fast enough for the slight differences to matter. If you picked the worst options in weight and width, you are looking at giving up about 2s or less. For most drivers, the performance difference fades into the background noise of their own inconsistency.

If you have fewer than 25 track days under your belt, don't sweat it. Pick the lightest wheel for whatever class you plan on running and get a 225-255* set of RS4's, Falken Azenis 615k+, or Federal 595 RSR (or whatever the 200tw version is). Don't bother tracking the Bridgestone RE71r's unless you are a competitive autocrosser and you don't want another set of wheels and tires to keep up with.

*tire and wheel widths should correspond, a 255 on a 7" wheel will be pinched (and feel terrible) and a 225 on a 9" is okay but a bit stretched (I've run a 225 on a 9" wheel without issues, and the Miata guys do it all the time)

Spend you time and money on seat time, that's where you'll get the most return on investment.
Thanks. I actually just got some wheels and tires, 17x9 Weds and continentals. Guess I'm trying to make myself feel better about my decisions lol. I get the consensus that wider & stickier tires are great for autocross so that's what I've figured. Didn't really know if it would adversely affect performance elsewhere. I will I definitely need more seat time, probably a good year or several. I'd like to get a lot better at it but I also won't sweat it as I've modded my car past STX and will likely be hard to compete even as I get better.
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