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Hello All,

Why is there a weight penalty for wheel diameters in PREPARED classes at all??

Why would a slower 285/30/18 V710 18x10 FP car need to have a 100lbs penalty over a faster 22x10x16 hoosierslicks 16x10 FP car?

Width based limits I can understand.. limit footprint to inturn limit power that can go to the ground so that low $ cars have a chance, which inturn may allow participation to remain higher.

Why the diameter based limits? How come wheel diameter penalties are up for abolishment in CP (as per the latest fast tracks) and not in other prepared classes?


 

 


 

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Vinax
1994 BMW 325i FP AutoX car.
http://www.myfastbmw.com

I'm confused, why are you comparing DOT R tires to true race rubber.  Of course the DOT tires are slower. 

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Jim Mueller
FSP 2003 Focus

Ralt25:

I'm confused, why are you comparing DOT R tires to true race rubber.  Of course the DOT tires are slower. 

Im not comparing grip of the two.

why does the 18" tired car need a penalty over a 16" tired car?? let us not worry whether they are DOT-Rs or Slicks.

 

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Vinax
1994 BMW 325i FP AutoX car.
http://www.myfastbmw.com

There are only two classes in Prepared with wheel dimaeter penalties, CP and FP.

Removing the penalty in CP is out for member comment, watch the next Fastrack for information about FP. 

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Steve Hudson
DP Miata

I have no tech on why the rules are the way they are, but bigger diameters help put more rubber on the ground just like wider widths do. They also help (often dramatically) in putting power down. They make a longer contact patch. If you can fit more tire (height), it's usually an advantage when you're running lots of power.

 

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-Philip Maynard

No weenies!

Auto-X Fil:

I have no tech on why the rules are the way they are, but bigger diameters help put more rubber on the ground just like wider widths do. They also help (often dramatically) in putting power down. They make a longer contact patch. If you can fit more tire (height), it's usually an advantage when you're running lots of power.

 

Phil,

Do you mean that a larger diameter tire puts power down better, or that a larger diameter wheel inside the same diameter tire puts it down better?  If it is number 2, do you have any tech on this?  (I know, wrong site to ask for tech :) )

We've discussed this at length on the PAC and in other places and I have been stumped to find any data either way. 

Thanks,

DaveW

Larger overall diameter, of course. I have spent a lot of time studying the effects of "plus sizing" street tires, but I don't care to make the jump to slicks with any of my data. If people are going to bigger wheels for lower-profile tires, not to get a bigger overall package, I'm just as stumped as the OP!

 

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-Philip Maynard

No weenies!

stevemhudson:

There are only two classes in Prepared with wheel dimaeter penalties, CP and FP.

Removing the penalty in CP is out for member comment, watch the next Fastrack for information about FP. 

Im not an expert on this but I think super wide tires like the ones CP uses are only available in small wheel diameters (16") so CP might not be able to make much out of removing the penalty.

FP on the other hand will have a wider tire choice based on the road racing tire choices, which inturn maybe too hard a compound for autocross use. The main point is - is there any scientific evidence to prove that 18" / 17" wheels are a distinct advantage over 16" wheels especially when either is used on a 10" wide wheel. (given the fact that a 24.8" dia tire on 18x10 wheel is the same sidewall width / profile / footprint as a 22.7" tire on a 16x10)

For me personally I will run only DOT-Rs which are good enough on asphault. - The fact that SM/SM2 cars were so much faster than PREPARED @ Nationals seems to reinforce this. I dont want my car to have a 100 lbs penalty without having any real advantage over the other "better developed" FP cars running slicks @ a lower minimum weight
 

 

 

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Vinax
1994 BMW 325i FP AutoX car
http://myfastbmw.com

Don't larger diameter wheels typically impose their own natural weight penalty by being heavier?

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Aaron Hull
Northwest Ohio Region
Occasional co-driver of: STS - '91 Saturn SC; FS - '95 Z28 1LE

NightTrain:

Don't larger diameter wheels typically impose their own natural weight penalty by being heavier?

I think it depends on how much you pay for them! 

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Ed Locke
2006 CR-SCCA XP Champion (Hey! I showed up.)
#248 SM/XP/DP/GS/BS/etc.
At Track Graphics (http://www.attrackgraphics.com)
Skull Motorsports (http://www.skullmotorsports.com)

gold325:

For me personally I will run only DOT-Rs which are good enough on asphault. - The fact that SM/SM2 cars were so much faster than PREPARED @ Nationals seems to reinforce this.

 

 

Exactly my thinking. And nevermind SM/SM2. Top CSP cars ran faster than all of Prepared save the top CP car, lol. And CSP ran the first heat on Thu/Fri too and it was freeeeezing (we were working their heat).

Ummm.....

 

Point One:  DP ran first heat on Tues/Wed, when it was freeeezing AND dirty.....

 

Point two:  I have long said I thought that the asphalt at HPT took away the advantage that slicks had....THAT said, SM/SM2 has a HUGE horsepower advantage compared to Prepared cars...just look at the index.  They are SUPPOSED to be faster than us...or at least equal... 

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Tracy Ramsey
Team Blenderblaster
2000 MR2 DP Spyder

Haha, ok point one taken, but first heats on thu/fri were dirty as well from the wind blowing the dust around, and yes thu-fri had better condition, but still... you gotta admit that a CSP Miata/CRX has no right even being in the same time zone vs. a DP/EP Miata/CRX?

We didnt make the move to slicks yet. But who here thinks given more normal temperatures (say 70-75F) the DOT tires would've still been faster? Obviously the weather last year was not normal for the region, but does happen and will happen again. Will it come down to top Prepared/Mod people showing with an extra set of DOT tires as insurance? Is this a viable option for those with a radial slick, or even a bias setup?

 Sorry for the OT...

 

Well, I will answer it this way.   I am one of two current DP cars that run on 15" rims.  Then I heard there is a proposal about upping DP rim width to 10".   Hmmm...15 x 10.  Just take a guess what the first thought that went through my head was

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Tracy Ramsey
Team Blenderblaster
2000 MR2 DP Spyder

Zauskycop:

Just take a guess what the first thought that went through my head was

 

275-35-15 A6?

jsi:

Zauskycop:

Just take a guess what the first thought that went through my head was

 

275-35-15 A6?

DING DING DING...we HAVE a winner!!! 

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Tracy Ramsey
Team Blenderblaster
2000 MR2 DP Spyder

I think the weight penalty for larger diameter wheels in FP should be removed. Smaller diameter wheels have less rotating mass and create a shorter final gear, these two conditions are helpful for autocross.

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Rad

2003 Toyota Celica GT-S, 6-speed Manual
2004 911 GT3 with some upgrades (Sold)
2007 BMW 335i Sedan, 6-speed Manual
2008 BMW M3, 7-speed DCT

NJGT3:

I think the weight penalty for larger diameter wheels in FP should be removed. Smaller diameter wheels have less rotating mass and create a shorter final gear, these two conditions are helpful for autocross.

Well, the less rotating mass may be true - may not be (depending on the rim choice - and the tire weight to go along with it).  The gearing effect is a non-issue, since you can change your final gear to anything you want anyway.  The overlooked, but probably greatest benefit to smaller diameters is the opportunity (assuming the correct tires are available) to lower the car without messing with the suspension geometry a great deal.  The overlooked benefit to the larger diameter wheels is the ability - given the proper tire choice - to utilized lighter tires to achieve better / as good turn in - not having to utilize super-thick sidewalls to get enough rigidity (since for a given tire height the sidewalls will be shorter and therefore more rigid without having to be thicker).

I don't know enough about what is available in tire choices for the different rim diameters, but I do find it hard to believe that there would be a great benefit to larger diameter rims.  BUT if there was a benefit, I can see this becoming a higher cost component... 
 

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Ed Locke
2006 CR-SCCA XP Champion (Hey! I showed up.)
#248 SM/XP/DP/GS/BS/etc.
At Track Graphics (http://www.attrackgraphics.com)
Skull Motorsports (http://www.skullmotorsports.com)

gold325:

Im not an expert on this but I think super wide tires like the ones CP uses are only available in small wheel diameters (16") so CP might not be able to make much out of removing the penalty.

 FYI - Many CP cars run between 16x10 and 16x12. However, for the newer CP cars (like my 2000 Trans Am), 17s and 18s are the logical choice. I run 17x11s. There are more than a few 18x12 wheels out there - expensive, but they're there. 17s or 18s are a must if upgrading the brakes. And upgraded brakes are a must if doing any road racing with these cars. So, removing the penalty for CP makes a lot of sense if you want newer cars to compete.

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2000 Trans Am
Delta Region #14 CP

00 Trans Ram:

gold325:

Im not an expert on this but I think super wide tires like the ones CP uses are only available in small wheel diameters (16") so CP might not be able to make much out of removing the penalty.

 FYI - Many CP cars run between 16x10 and 16x12. However, for the newer CP cars (like my 2000 Trans Am), 17s and 18s are the logical choice. I run 17x11s. There are more than a few 18x12 wheels out there - expensive, but they're there. 17s or 18s are a must if upgrading the brakes. And upgraded brakes are a must if doing any road racing with these cars. So, removing the penalty for CP makes a lot of sense if you want newer cars to compete.

No class - FP or CP needs any wheel diameter penalties.

Cars like ours need all the help that they can get - no more extra penalties.

My expensive 18x10 SSR + 285 30 18 V710s are 46 lbs each.
16x10 Real Wheels + 22x16x10 slicks are like 32.5 lbs each.

Running 50 - 60 lbs extra in unsprung weight is penalty enough! ;) 

Minimum weight for my car is 2100 lbs. With penalty its 2200 lbs. I run DOT-Rs because they are cheaper, more consistent, last much longer and are grippier on asphault.
 

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Vinax
1994 BMW 325i FP AutoX car.
http://www.myfastbmw.com