|
|
|
KEEP M3POST ALIVE BY DOING YOUR TIRERACK SHOPPING FROM THIS BANNER LINK! |
Post Reply |
|
Thread Tools | Search this Thread |
10-18-2011, 11:26 AM | #1 |
New Member
13
Rep 28
Posts |
For track, why 18 inch wheel instead of 19?
Hi, guys, is there any good reason of choosing 18 instead of 19 wheels for the track day? I saw lots of you have 18 inch setup when you go to track.
The reason why I'm asking is that I want to install new BBK. But I am afraid that 18 is too small for 6 piston 380mm kit. thx |
10-18-2011, 11:41 AM | #2 |
Brigadier General
97
Rep 3,246
Posts |
I run 19's at the track, but think the 18's are used because there is a larger selection, they're cheaper and don't think r-comps come in 19's.... other than that have yet to hear a compelling argument as to why 18's are "better" than 19's....am sure there's more to follow....
__________________
mods: track ready stuff
|
Appreciate
0
|
10-18-2011, 11:49 AM | #4 | |
Captain
15
Rep 751
Posts |
Quote:
I’m using 18X10 Apex wheels all around with 275/35 tires, and StopTech brakes, 380mm rotor with ST-60 caliper in front, and it works fine, no spacers needed front or back. |
|
Appreciate
0
|
10-18-2011, 12:29 PM | #5 |
GODXSPD
12
Rep 157
Posts |
Larger diameter wheels have higher rotational moment of inertias and tend to decrease stopping times and reduce acceleration.
How much are they reduced? Depends on the wheel. Is it a huge issue for a weekend racer? No.
__________________
e90m / ssii / foxred / wedssport sa-55m 19x9.5 et24 + 265/35r19 square / 15mm rear spacer / no chrome |
Appreciate
0
|
10-18-2011, 02:14 PM | #8 |
Major General
1571
Rep 8,076
Posts
Drives: 11 E90 M3 Individual
Join Date: Mar 2006
Location: Houston, TX
|
Price
__________________
2018 F30 320iX Melbourne Red
2011 E90 M3 Monte Carlo Blue 2004 E46 M3 Imola Red 2000 E36/7 Z3 Steel Blue |
Appreciate
0
|
10-18-2011, 02:28 PM | #10 | |
Lieutenant General
923
Rep 15,818
Posts |
Quote:
I know many non-M guys run 17s when they drag and it improves their times. When you see race-spec cars, they don't generally run large rims 380mm 6 piston ST will fit APEX, but brembos do not. you would need TE37s, TC-IIIs and such to fit 380MM Brembos with an 18 in rim
__________________
|
|
Appreciate
1
6ixSpd6014.50 |
10-18-2011, 02:52 PM | #11 |
Second Lieutenant
11
Rep 293
Posts |
F1 car runs 13s.
Part of it is having two wheels or equal overall diameter (with tires) and having different rims will result in the smaller rim being lighter due to just the rubber/nitrogen versus aluminum in the wheel. |
Appreciate
0
|
10-18-2011, 03:37 PM | #12 |
Brigadier General
97
Rep 3,246
Posts |
Fair enough. Just seems that these days the technology is making that moot, the BBS lightweight FI's are the lightest wheel out there and they're 19's, also thought that wheel width has more to do with weight, than size, but get that a bigger wheel has more weight further away, but just seems like we're getting to the point where metal is getting lighter than rubber and the whole wheel weight, not just rims, becomes important, but that's just me thinking out loud
__________________
mods: track ready stuff
|
Appreciate
0
|
10-18-2011, 03:41 PM | #13 |
Major General
285
Rep 6,007
Posts |
I thought the 19s for this car were actually lighter??
__________________
|
Appreciate
0
|
10-18-2011, 03:49 PM | #14 | |
GODXSPD
12
Rep 157
Posts |
Quote:
A large portion of the wheel's mass is the rim itself, not the hub-mounting face and spokes, and that's the portion that's farthest away from the center of rotation. I = mass * dist_to_center^2 (in general for a thin-walled cylinder). For a two-piece wheel, a 19" rim will have a MoI of about 11.4% more than the 18" rim. The face/spoke center piece will also have a somewhat larger MoI, though maybe less pronounced. MoI is used to calculate the energy needed to maintain or change motion (e.g. go fast or stop going fast). This also discounts the additional weight / MoI of the 18" tire combination you would need to run, but the overall mass of the added tire is very small and, at the radius at which you are adding material, does not span the entire width of the wheel providing for a relatively small MoI.
__________________
e90m / ssii / foxred / wedssport sa-55m 19x9.5 et24 + 265/35r19 square / 15mm rear spacer / no chrome |
|
Appreciate
0
|
10-18-2011, 04:03 PM | #15 | |
Major General
285
Rep 6,007
Posts |
Quote:
__________________
|
|
Appreciate
0
|
10-18-2011, 04:11 PM | #16 |
Brigadier General
97
Rep 3,246
Posts |
I understand the math, as I stated, just seems like technology is making things moot, like all other things. Wheels are heavier now, but seems to me that trend is changing that's all and soon we'll be bitching about what tires weigh. I get the argument about size of wheel, I'm just taking it a step further saying tire weight, which is furthest away, will matter more than wheel weight as wheel mfg gets better, stronger, lighter. Tire companies aren't as concerned with weight, more about other things.... Wonder what the differences in tire weights are between 18's and 19's and if that weight being furthest away to move becomes more of an issue than wheel weights. Just seems like people throw out equations w/out thinking about all the variables, and that it's a bit deeper than expected. Wonder if the few pound difference in tire weight further away could make more of a difference than a larger weight diff on the rim, that's all. Not sure if I'm wrong or right but just seems like a logical question to ask.
__________________
mods: track ready stuff
|
Appreciate
0
|
10-18-2011, 04:26 PM | #17 | |
Lieutenant General
923
Rep 15,818
Posts |
Quote:
You aren't comparing apples to oranges here I'm sure if BBS made FIs in 18s, they'd be lighter than their 19in counterpart
__________________
|
|
Appreciate
0
|
10-18-2011, 04:36 PM | #18 |
octane chick
79
Rep 1,187
Posts
Drives: ex-M
Join Date: Oct 2010
Location: Colorado
|
18 is easier for square setup, no? I think 19" square setup could be a bit tough for finding the right clearance up front. I have square 275/35R18 on Apex Arc-8s. They're much lighter than my ZCP rims. It looks sexy and works well for track. (It took some getting used to, mind you!)
On the other hand, I've had lots of fun on the stock 19s with AD08s in staggered setup. Tires are more expensive for 19s, though. With square, you can rotate tires. With staggered, you get less risk of oversteer. |
Appreciate
0
|
10-18-2011, 04:51 PM | #19 |
World's Foremost Authority
1181
Rep 4,535
Posts
Drives: M4 Cab - Cayenne GTS - Jag XK
Join Date: Jul 2007
Location: Upper East Side Manhattan - Boca Raton FL - Lime Rock CT
|
There is a sweet spot for rim size and too large of a rim can decrease performance and so can too large of a rim. Many race series have a limit for rim size so the fact that a particular race car runs a particular size rim may be because it is the maximum allowable size.
There are many factors at play here, unsprung weight, rotational mass and slip angle among others. These tend to interact with each other and as you change rim size to improve one parameter to gain performance you may actually be downgrading performance by making another area worse. I can tell you what I was told by someone who has a lot of experience in this area. The coach for the Drivers Club at Lime Rock told me that the Club's M3 is fastest around the track with 18s and the suspension on the second stiffest setting. This is coming from someone whose job is driving an M3 around a race track. CA
__________________
Drivers Club at Lime Rock - International Motorsports Research Center - Society of Automotive Historians - Madison Avenue Sports Car Driving and Chowder Society (0nly a VP) - BMWCCA - Porsche Club of America - M Gruppe - Polish Race Drivers of America (PDRA) - Glen Club (Watkins Glen International) - Jaguar Club of Southern New England Last edited by captainaudio; 10-18-2011 at 07:11 PM.. |
Appreciate
0
|
10-18-2011, 04:53 PM | #20 | |
Lieutenant
25
Rep 596
Posts |
Quote:
OP,you do not need to go as big as 380mm.. No real advantage over the 360mm's other than looks.But a real disadvantage in added rotating mass.Car will stop and perform just as well on the 360mm setup with Motul 660 or Castrol SRF. Last edited by ManAndMachine; 10-18-2011 at 06:19 PM.. Reason: brake fluid type added |
|
Appreciate
0
|
10-18-2011, 05:20 PM | #21 |
GODXSPD
12
Rep 157
Posts |
It's just 19^2 / 18^2 (mean rim diameter into I = 1/4*m*D^2). I can do the long-hand calc if you'd rather
__________________
e90m / ssii / foxred / wedssport sa-55m 19x9.5 et24 + 265/35r19 square / 15mm rear spacer / no chrome |
Appreciate
0
|
10-18-2011, 05:30 PM | #22 | |
GODXSPD
12
Rep 157
Posts |
Quote:
Make no mistake, tire manufacturers are gaining ground in traction technology. It's just not readily apparent because there's a dearth of publicity on the matter and the layman is unable to really understand the gains. I-beam spokes? Marketable. Reorganization of ply direction or slight tweaks to the rubber compounds used? Impossible to explain.
__________________
e90m / ssii / foxred / wedssport sa-55m 19x9.5 et24 + 265/35r19 square / 15mm rear spacer / no chrome |
|
Appreciate
0
|
Post Reply |
Bookmarks |
|
|