Stock 17's Vs aftermarket 18's...1/4 mile time

[mmarfan]

Debate is going on about how much getting 18 inch wheels will effect the 1/4 mile time.

What I have data on is 18's with shorter tires compared to the stock 17's. (225/40/18 Vs 215/50/17) This tire size is the most common in a wheel/tire package.

The approximate difference for the 18's is about 7 mm (0.3'') shorter; which in turn, topping out in 3ird, it will be 93.5mph instead of 95mph (which does hurt).

The weights (which I haven't weighed yet) are very close between them (within 2 lbs).


Each best run was done with very similar conditions - ~75 degrees and decent humidity.


Best time with stocks:

60' - 2.281
330- 6.277
1/8- 9.557 @ 74.91
1000 12.375
1/4- 14.750 @ 94.94

Best time with 18's:

60' - 2.291
330- 6.384
1/8- 9.677 @ 74.49
1000 N/A
1/4- 14.929 @ 93.15

Difference:

60' - (+.010) - Barely enough to be a difference
330- (+.107) - 2ond gear shift possibly slower, but not bad.
1/8- (+.120) - kept around the same split.
1/8- (+.42MPH) - lost MPH, not good, wheels dragging the engine a bit, even though the tires are shorter - i.e. better gearing.
1000- I really wanted this data, oh well
1/4- (+.179) - Lost more time, and there is no gear change between the 1/8 and the 1/4.
1/4- (+1.79MPH) - The big one, Lost almost 2 mph, and I didn't hit the rev limiter until AFTER the traps. This means the 18's are definitely more effort for the engine, even with tires that might make up the difference.

So if you are thinking about racing with 18's, you are better off putting stock wheels back on, UNLESS you have super light wheels.


I will go back to the track (hopefully) and try both wheels in the same day.

That's my spill...

[flarearrow]

Hopefully I can one day add to this thread. I plan on getting Kosei K1 TS on 215-50-17 Kumho ASX (stock size and stock weight). So we shall see how much of a difference it makes keeping the tire specs the same, but dropping 8 lbs of rim weight.

[Stretch]

It surprises me that the stock rubber you probably have on the 18's doesn't compensate for their extra size and weight. Sticky rubber can be better than light rubber. I'd of expected the first 60 feet to be much faster on 18's, with the car being slower thereafter.

[GreenNuggs]

Interesting data. I can tell you that my times were nearly identical if not worse when I went from stock to the wheels I have now which arguably should provide better times. However, the conditions between the two nights were not even near the same.

[flarearrow]

Originally posted by GreenNuggs@Oct 25 2005, 03:20 PM
Interesting data.* I can tell you that my times were nearly identical if not worse when I went from stock to the wheels I have now which arguably should provide better times. However, the conditions between the two nights were not even near the same.

[snapback]542417[/snapback]

Well, the stock rim and tire weigh 22 lbs and 23 lbs = 45 lbs
A 17x8 Rota Torque (according to Machiii.net) weighs 19 lbs, and a 235-40-17 94Y tire (like a Kumho SPT on Tirerack) weighs 24 lbs = 43 lbs

I don't think 2 lbs is going to make much of a difference, especially since (according to the guesstimate) you're adding tire weight negating the weight savings of the rim.

[Crewin323]

The problem with heavy wheels is that it is rotational mass. A good rule of thumb is that for every pound of rotational mass removed from the car is like removing 10 pounds of actual weight.

Take two wheels at 2lbs difference. Thats 4lbsX10 would mean for 2lb wheels, it is like dropping 40 "actual" pounds from the car. Figure that every 10 extra pounds is like 1hp and you can see that light wieght wheels can pack a punch.

The other thing to concider is how many times did you run with 17s and 18s to get a good comparative base. You could run the same car on the same day, and depending on different variables get the same results with the car that you got by switching wheels. The differences that you posted could be attributed to a shitty launch.

If you want real results, you are going to have to make runs on the car under similer conditions, but get atleast 5 in with each setup to make a decent comparison

[charles]

Originally posted by Crewin323@Oct 26 2005, 06:55 PM
The problem with heavy wheels is that it is rotational mass. A good rule of thumb is that for every pound of rotational mass removed from the car is like removing 10 pounds of actual weight.

Take two wheels at 2lbs difference. Thats 4lbsX10 would mean for 2lb wheels, it is like dropping 40 "actual" pounds from the car. Figure that every 10 extra pounds is like 1hp and you can see that light wieght wheels can pack a punch.

The other thing to concider is how many times did you run with 17s and 18s to get a good comparative base. You could run the same car on the same day, and depending on different variables get the same results with the car that you got by switching wheels. The differences that you posted could be attributed to a shitty launch.

If you want real results, you are going to have to make runs on the car under similer conditions, but get atleast 5 in with each setup to make a decent comparison

[snapback]543188[/snapback]

i totally agree on this one. Back when i was really new to the TRACK not dragging but the track i could take my car down the qtr with what i thought was my best that i cought do and then i let my friend drive it and he pulled about 3-5 tenths over what i did. THe point that i am really trying to make is there are many variables when you do this test. How hard can you launch with the stock vs. upgraded tire or is that tire better than stock at all? How much weight did you add or lose. Is you rotation between each wheel the same or more or less? This plays a part of your gearing also which can make a difference. All these differences may NOT be that much to warrant too much to fuss over but they are variables to be looked at.

[charles]

Originally posted by Crewin323@Oct 26 2005, 06:55 PM
The problem with heavy wheels is that it is rotational mass. A good rule of thumb is that for every pound of rotational mass removed from the car is like removing 10 pounds of actual weight.

Take two wheels at 2lbs difference. Thats 4lbsX10 would mean for 2lb wheels, it is like dropping 40 "actual" pounds from the car. Figure that every 10 extra pounds is like 1hp and you can see that light wieght wheels can pack a punch.

The other thing to concider is how many times did you run with 17s and 18s to get a good comparative base. You could run the same car on the same day, and depending on different variables get the same results with the car that you got by switching wheels. The differences that you posted could be attributed to a shitty launch.

If you want real results, you are going to have to make runs on the car under similer conditions, but get atleast 5 in with each setup to make a decent comparison

[snapback]543188[/snapback]

well i am not sure of those figures of losing 10lbs from 2lbs of wheel rotating mass also the one about 40 pounds dropped from the car because of this? I don't think so, that is like losing a small child worth of weight???

[mmarfan]

Just as a side note, I'm no stranger to the track. I can tell you that those 2 best runs there are backed up by at least 4 other runs within about one tenth of that time. So that data is close to accurate, but can only tell for sure if I do the test in the same day...

[GreenNuggs]

Originally posted by flarearrow@Oct 25 2005, 05:18 PM
Well, the stock rim and tire weigh 22 lbs and 23 lbs = 45 lbs
A 17x8 Rota Torque (according to Machiii.net) weighs 19 lbs, and a 235-40-17 94Y tire (like a Kumho SPT on Tirerack) weighs 24 lbs = 43 lbs

I don't think 2 lbs is going to make much of a difference, especially since (according to the guesstimate) you're adding tire weight negating the weight savings of the rim.

[snapback]542516[/snapback]

My stock combo weighed in 46 on the bathroom scale and the new combo (T1R tires) weighed in at 41. So I saved 5lbs and 4% diameter. It is still possible as you say though that even though the overall I'm lower, the center of weight inertia is actually farther out on average than it was on stock. I still think it should have saved time. Honestly though, even Dragon6 could break a 15.6 that night and he's got the same combo adding revised clutch and flywheel, so I think it was just a slow night.