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Discussion Starter #1
I got back from a track day at Pacific Raceways yesterday and was reviewing some in-car cam of a couple of sessions. One of the benefits of taping (besides being able to assess driving line, etc.) is that you get a built-in timing feature.

I noticed that when I was out of traffic and in the clear, I appeared to be a couple seconds faster than my visit a few of weeks ago to the same track under nearly the same conditions (clear and warm). I was running about 1:53.xx yesterday vs 1:55.xx the other week.

The only difference here was the wheel/tire combination.

In my last visit I was running RA1s in 205/40-17 on the stock 2004 SVT wheels. This time I was running on Falken Avenis RT-215s in 215/45-16 on Rota Slipstreams. That setup is a bit lighter, but the wheel diameters are very close.

Question: Can the swapout of the wheel/tire combination alone explain the overall delta in lap time? I didn't feel like I was driving any more aggressively. Both days I was driving with a "new" (to me) group of drivers so I was not wanting to push too much.
 

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All things being the same, the RA1s should actually have more 'stic-tion' than the Falkens, but the unsprung weight indeed helps. Curious to see how different the weights of just the tires are...as the Falkens tend to run on the heavy side.

I would just chalk it up to having more experience; it tends to be pretty easy to chunk time off as you learn the line and just get more comfortable in the car and being on track. Nice work!
 

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Remeber the rule of thumb us 1lb of unsprung weight is worth 3lbs of sprung weight. From SVT wheels (21 lbs) to 16" Rota Slips (14.5 lbs). That's 6 lbs per corner. 24 lbs total plus the tire weight difference (and R's are almost always heavier than street radials).

But just looking at the wheel, thats 24 lbs of unsprung weight which should help the car act as if it lost about 75 lbs up top!

Lighter wheels also allow your suspension to work better, keeping the tire in contact with the pavement moreso than a heavier tire/wheel would.
 

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I'd chalk it up 75% to the fact that you "slept on it".

Doing a repetitive task, you can only get so good on a given day. When you sleep, your brain does some more stuff, and you get even better the next day. It works in all facets of life, that's where they phrase "sleep on it" comes from.

So, I say the gain was just from experience.
 

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and R's are almost always heavier than street radials).
kumho712 24lb,710 24lb,goodyear 24lb
2 sconds? Probably helped you had been there before, maybe feeling a little froggier.
gas is 6 lb per gallon, how much did you have both days?
Not sure 24 lbs is worth 2 seconds. "feels" like 75, but you still have to move 2700 lb vs 2676 lb +- gas difference.
 

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Discussion Starter #6
gas is 6 lb per gallon, how much did you have both days?
Not sure 24 lbs is worth 2 seconds. "feels" like 75, but you still have to move 2700 lb vs 2676 lb +- gas difference.
Hmmmm. Well, on the prior visit I went out at lunch to reload on gas (was down to about 1/4 tank). Yesterday, I did not and ran pretty much down to about 1/8 tank for the trip home (which nearly got me back, although I stopped for gas a few miles from the house). We had fewer, shorter segments.

The car didn't feel much different, although the Falkens did talk more and didn't seem to hang on quite as well when I would try to get on the throttle a little early on corner exit. Not being very experienced really, I like the audible feedback that the Azenis provide, although RA1s feel more planted in the same situation.
 
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