2018 TIRE INDEX ADJUSTMENTS

Parking lots and traffic cones.
Post Reply
User avatar
hufflepuff
Posts: 226
Joined: Mon Jan 25, 2010 11:12 am
Car: 2005 Mazda RX-8
CDC Member#: 512
Location: Alexandria, VA

2018 TIRE INDEX ADJUSTMENTS

Post by hufflepuff » Mon Dec 04, 2017 8:02 am

All,

Tire technology and performance has changed significantly from when the CDC tire index was last updated. Given similar car prep and driver talent, a driver that shows up on Rival S or RE-71R is pretty much guaranteed to beat someone showing up on "last generation" autocross tires.

To level the playing field in 2018, I suggest we work together to update the CDC tire index. I also know that i'm far from an autocross tire expert, and that the folks here have more data than i do (i'm hoping those who do contribute below for the more fair and accurate recommendations). But from what data i've been able to gather, the following seem like fair index values:

< 100TW slicks ? (no data)
100TW tires 1.00
RE71R 1.00
Rival S 1.5 1.00
N FERA SUR4G 1.00
RS4 1.00
RT615K+ 0.99? (no data)
VR1 0.98
SSII 0.98
RT615K 0.98
N FERA SUR4 0.98
Rival 0.97
AD08R 0.97
595 RSRR ? (no data)
> 200 Street Tires ? (no data)

During registration, we could give the option of having folks either choose their tire index as we do currently, or have a drop-down menu for their tire type.

The data I used: https://docs.google.com/spreadsheets/d/ ... sp=sharing

With other variables being wide open (especially tire width and suspension modifications), a realistic tire index seems like an easy win to help promote parity.
'05 RX-8 - HPDE and Time Attack
'95 Miata - Daily driver and AutoX
http://www.youtube.com/mchuffman/

User avatar
wrathe74
Posts: 377
Joined: Fri Aug 29, 2008 12:18 pm
Car: 1974 Opel Manta
CDC Member#: 523
Location: Maryland

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by wrathe74 » Mon Dec 04, 2017 8:08 am

Let's do a drop-down ... keeps it simple and avoids complications
-- Jason

gimp
Posts: 49
Joined: Sun Oct 07, 2007 11:58 am
Car: What do you have?
CDC Member#: 0
Location: Catonsville, MD
Contact:

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by gimp » Mon Dec 04, 2017 8:17 am

You might be taking things too far. What about vehicle weight and tire make - some tires work better on heavier cars, and some on lighter. If a heavy car shows up with a better "light" tire are you going to factor that all in?

I think you are starting to split hairs, IMO.

JayPar
Posts: 76
Joined: Wed May 01, 2013 9:25 am
Car: '96 Gray Miata (LATRL G)
CDC Member#: 96
Location: Boyds, MD

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by JayPar » Mon Dec 04, 2017 9:30 am

I think this is a good idea, but I don't quite like the level of model-specificity. When I think of tires, I think of these classes:

- R comps
- State of the art AX (latest gen) (Rival S, RE71R, RS4, ...?)
- Last gen AX and/or "track tires" (RS3, R1R, non-S Rivals, ...?)
- All seasons

I would be in favor of this breakdown, and think that it would make the club more competitive based on driving ability. What we're missing now is a differentiation between tier 2 and 3.

Also, CDC doesn't account for suspension, but I think we probably should. Suspension classes might be:

- High end aftermarket / stiff
- Basic aftermarket / firm
- Stock (moderate roll) (Miata, modern sedans)
- Stock (seriously...that passed tech?!)

(The challenge of course is assigning numbers to these, which I'm not even going to attempt, but I think we could come up with something).

Note that both of these proposals would probably hurt my car (TicTac) relative to others, but I think it would be better for the club. It would reduce the cost of entry to be competitive.

User avatar
echan
Posts: 2518
Joined: Fri Sep 28, 2007 10:50 am
Car: 1973 Triumph TR6
CDC Member#: 4

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by echan » Mon Dec 04, 2017 10:32 am

JayPar wrote:
Mon Dec 04, 2017 9:30 am
Also, CDC doesn't account for suspension, but I think we probably should. Suspension classes might be:

- High end aftermarket / stiff
- Basic aftermarket / firm
- Stock (moderate roll) (Miata, modern sedans)
- Stock (seriously...that passed tech?!)

(The challenge of course is assigning numbers to these, which I'm not even going to attempt, but I think we could come up with something).

Note that both of these proposals would probably hurt my car (TicTac) relative to others, but I think it would be better for the club. It would reduce the cost of entry to be competitive.
I think adding a suspension index would be almost impossible because each make a model have different levels of suspension in the stock form and then it gets more complex when the suspension is modified. For instance, my TR6 suspension is modified but a stock Miata out handles it out of the box. If a softly sprung family sedan is modified, it still may be inferior to a BMW. I don't know how to really address this issue, while making it simple and fair.

User avatar
Nathan Atkins
Posts: 285
Joined: Mon Mar 12, 2012 6:28 pm
Car: 2005 Mazda RX8 Red
CDC Member#: 10
Location: Bel Air, MD
Contact:

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by Nathan Atkins » Mon Dec 04, 2017 10:55 am

I agree that this is getting too detailed, I can contribute that the Federal RSRR is at least on par with the RS4, and the RSR is part of the older generation.

Spankin’ new RSRR will outperform aging RE71R, which we don’t account for either.

I like the way it is, I think we all know what “autocross tires” are. Anyone gunning for CDC championship knows what tools they need to make it happen. Get some top tier tires if it’s important to you. Most of us are here for driver development anyway which is a benefit regardless of what tire you’re on and how competitive it is.

User avatar
BugBomb
Posts: 1060
Joined: Mon Oct 08, 2007 5:28 am
Car: '02 Whorevette
CDC Member#: 33
Location: PA

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by BugBomb » Mon Dec 04, 2017 11:47 am

I'm a firm believer in the KISS principle for CDC's index. Here are the problems I see with this:

-Right now, the tire multiplier uses a code from the tire manufacturer (easy) and splits into 4 categories. This option would add who-knows-how-many choices, and has to be updated every time a new, competitive tire comes out.

-Looking at results, you would have to reference a table to figure out what tire someone used.

-The timing system and registration system have to update any time this tire list changes.

-Although not as many people would have to look up their treadwear rating, people running registration or timing have to deal with all these extra options as well. For example, "Are you positive you're running the N FERA SUR4 and not the SUR4G?"

The following is MY OPINION and should not be taken as official CDC policy:
I believe the spirit of CDC represents the fun of this sport rather than the competition. Many clubs and types of motorsports go through immense effort to "level the playing field." You probably won't find a better example than the SCCA, and that's why I took steps to make sure SCCA PAX got back onto CDC results. The CDC index will never be as comprehensive as SCCA PAX, it has just been a way to encourage some competition for what is otherwise a social event. In the history of CDC, we see many people who have worked to become the big fish in this pond, and almost invariably they move onto the real competition areas (SCCA Solo or Road Racing for example), if that is what they desire. We are lucky that some of those big fish still drop by as it offers participants a good gauge for those higher competition events like Nationals. I'm just trying to give some perspective because this is how many organizers and regulars view this club. We are all open to leveling the playing field in any way possible, as long as it doesn't add complexity.
Mike M
"There’s no way you can eat a hot pocket and do this." -Ed Chan
The views expressed herein are my own and are not intended to sound like a "dick."

marauder
Posts: 4
Joined: Mon May 05, 2014 3:50 pm
Location: Tysons Corner
Contact:

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by marauder » Mon Dec 04, 2017 3:54 pm

I agree that going to specific would just cause to many problems for registration and new comers. One of the best parts about CDC is the low cost of entry for new people. You don't really know your car, thats fine the organizers can roughly guess because of the index system.
I suspension class would be nice but there's a lot of variables. You could do stock, springs(or upgraded stock), coilovers, adjustable coilovers. but as Ed said that could give an advantage to miatas over other stock cars.

Regarding tires, a change would be nice. I think an additional breakdown is needed as right now Super Sports are categorized the same as RE-71s and Rivals.
Maybe use the tire classing system of Max Performance, Extreme Performance, etc similar to how they are on tirerack. That would allow quick and easy lookup for people who don't know.

User avatar
hufflepuff
Posts: 226
Joined: Mon Jan 25, 2010 11:12 am
Car: 2005 Mazda RX-8
CDC Member#: 512
Location: Alexandria, VA

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by hufflepuff » Tue Dec 05, 2017 7:55 am

Agree that CDC is a casual club with the spirit of having fun. However, there are plenty of talented folks, and people who are interested in a fair yardstick to gauge their own driving. Other members voiced this desire on the facebook post. Not because we're overly competitive, but because we desire to gauge our own driving.

Agree we need to keep things simple to understand, and simple to manage.

I don't think we should account for "old" tires, as this would be very tough to quantify.

I've thought of suspension indexes, but I agree that it might be complicated and not in the spirit of CDC simplicity. The easiest ways I can think of are:
1. a single suspension "mod" is free (i.e. springs, or shocks, or swaybars), but two or more is assessed an index.
2. completely stock suspension gets a credit.

But i'm not pushing for a suspension index.

Finally, for tires, I like Jay's recommendation, because it's simple. I would suggest the following:

< 100TW tires - 1.0X?
100TW and current-gen AutoX compounds (currently Rival S, RE71R, 595RSRR, RS4, SUR4G) - 1.00
Last-gen AutoX compounds (all other extreme performance summer tires) - 0.98
> 200 TW tires (all) - 0.9X?

The "current gen" AutoX tires could be listed in the FAQ, or listed for reference during registration. Most of us are enthusiasts and would know what we're rolling on. ;-) And if you DON'T know what tires you have on your car, you probably aren't worried about the index!
'05 RX-8 - HPDE and Time Attack
'95 Miata - Daily driver and AutoX
http://www.youtube.com/mchuffman/

JayPar
Posts: 76
Joined: Wed May 01, 2013 9:25 am
Car: '96 Gray Miata (LATRL G)
CDC Member#: 96
Location: Boyds, MD

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by JayPar » Tue Dec 05, 2017 12:29 pm

From the Facebook discussion (which is now quite a mess), there does seem to be some support for having a tire index that accounts for differences between the latest gen 200 TW tires vs the older generation and other extreme performance 200 TW tires. (There was no similar consensus on suspension, so it's probably not worth further discussion.)

But back to tires, it might be as simple as just changing the labels on the select boxes and adjusting the index values.

I think doing this would be good for the health of the club because, as I argued on Facebook, most of the younger and/or newer members use their daily driver cars and do not have as much disposable income to be buying the latest and greatest tires, maintaining multiple sets of wheels, etc. Not only would it be cheaper in terms of initial purchase price, but it also would allow people to buy somewhat longer-lasting tires which would be cheaper on a cost-per-run basis. Lowering the cost of entry to be competitive would help club membership.

Over and out.

User avatar
hufflepuff
Posts: 226
Joined: Mon Jan 25, 2010 11:12 am
Car: 2005 Mazda RX-8
CDC Member#: 512
Location: Alexandria, VA

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by hufflepuff » Wed Dec 06, 2017 8:32 am

Based on real-world data and feedback from club members:

< 100TW tires - 1.02
Current-gen 200TW and 100TW R-comps - 1.00
Last-gen 200TW - 0.98
> 200 TW tires (all) - 0.96

The current "cheater 200TW" are the benchmark (Rival S, RE71R, 595RSRR, RS4, SUR4G), since that's what the vast majority of the fast folks use.

- People on a budget receive a fair index.
- Things stay simple.
- People can make a more accurate assessment of their driving.
'05 RX-8 - HPDE and Time Attack
'95 Miata - Daily driver and AutoX
http://www.youtube.com/mchuffman/

User avatar
echan
Posts: 2518
Joined: Fri Sep 28, 2007 10:50 am
Car: 1973 Triumph TR6
CDC Member#: 4

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by echan » Fri Dec 08, 2017 4:19 pm

Here's the latest draft with combining everyone's suggestion:

Tire Index:
Low-performance/All-season tires (Over 300 Treadwear Rating) = 0.99
High-performance Street Tires (205-300 Treadwear) = 1.00
Tires With Treadwear Rating 200 - 204 = 1.02
Tires With Treadwear Rating < 200 = 1.03

HP Index (measured at the wheels):
100 HP or Less = .099
101 to 150 HP = 1.00
151 to 180 HP = 1.01
181 to 220 HP = 1.015
221 to 250 HP = 1.02
251 to 300 HP = 1.025
301 and above = 1.03

User avatar
hufflepuff
Posts: 226
Joined: Mon Jan 25, 2010 11:12 am
Car: 2005 Mazda RX-8
CDC Member#: 512
Location: Alexandria, VA

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by hufflepuff » Sat Dec 09, 2017 1:40 pm

i think the power index looks good, Ed.

the proposed tire index doesn't seem to map to the real-world performance data, or to distinct UTQG rating ranges (TW 200 - 204???). The Parsons and I had recommended the following, which has buy-in from a few members:

> 301 TW : 0.98
300 - 201 TW : 1.00
200 - 100 TW : 1.02
< 100 TW : 1.04

Basically, the above is equivalent to:

- low performance all seasons and basic summer tires = 0.98
- high performance summer tires = 1.00
- autocross tires and budget, hard compound r-comps = 1.02
- soft, high performance r comps = 1.04

There was a time when 100TW tires were faster than street tires. this just isn't the case anymore; the "cheater" 200TW tires are just as fast or faster than the budget 100TW tires, so the system above has them grouped together.
'05 RX-8 - HPDE and Time Attack
'95 Miata - Daily driver and AutoX
http://www.youtube.com/mchuffman/

User avatar
echan
Posts: 2518
Joined: Fri Sep 28, 2007 10:50 am
Car: 1973 Triumph TR6
CDC Member#: 4

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by echan » Sun Dec 10, 2017 9:00 pm

OK. Here's the latest for the Tire Index:

> 301 TW : 0.98
300 - 201 TW : 1.00
200 - 100 TW : 1.02
< 100 TW : 1.04

Is everyone (or almost everyone) good now?

User avatar
BugBomb
Posts: 1060
Joined: Mon Oct 08, 2007 5:28 am
Car: '02 Whorevette
CDC Member#: 33
Location: PA

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by BugBomb » Mon Dec 11, 2017 3:05 pm

I'm not opposed to the new TW and HP categories. Should we also look at vehicle weight categories?

After taking a rough survey from some of our participants on their car specs, I believe we could add 2 weight classes and change the categories to 300-lb sections as follows:

<1700 - Nothing currently in attendance, but we could eventually see things like Exocets, Sprites
1701-2000 - DP cars like TicTac and Bumblebee, lightweight Hondas like the CRX
2001-2300 - TR6, most normally-aspirated Miatas, older Civics
2301-2600 - NC/ND Miatas, Mazdaspeed/Aftermarket turbo Miatas
2601-2900 - S2000s, FRS/BRZ Twins, Mini Coopers, the Suxass
2901-3200 - Most Corvettes, Solstice/Sky, Civic Type R
3201-3500 - FoST, WRX/STi, Lighter Pony cars, Porsches/Bimmers
>3500 - Land Yachts


This seems to group similar cars better than the previous 500-lb categories. Thoughts?
Mike M
"There’s no way you can eat a hot pocket and do this." -Ed Chan
The views expressed herein are my own and are not intended to sound like a "dick."

User avatar
BugBomb
Posts: 1060
Joined: Mon Oct 08, 2007 5:28 am
Car: '02 Whorevette
CDC Member#: 33
Location: PA

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by BugBomb » Mon Dec 11, 2017 3:46 pm

hufflepuff wrote:
Sat Dec 09, 2017 1:40 pm

> 301 TW : 0.98
300 - 201 TW : 1.00
200 - 100 TW : 1.02
< 100 TW : 1.04
I'm not sure I agree with these numbers. What data are you using? We don't have a huge amount of people using >200TW tires, and even fewer people actively testing the differences between these tires. Using your numbers, someone could show up on Conti DW or Conti Sport tires (which are decent street tires, but 320TW) and if someone were at the top of the index on Rivals with a 45-second run, they could be beaten by someone on the Contis running a full 1.8 seconds slower (all else being equal). That does not seem right to me. I would rather see a more moderate change for 2018 and then reevaluate at the end of the year. Something like this:

> 301 TW : 0.99
300 - 201 TW : 1.00
200 - 100 TW : 1.01
< 100 TW : 1.03

That puts someone on Contis at a 9-tenths advantage on a 45-second course compared to Rivals/Bridgestones, which sounds more reasonable in my experience.
Mike M
"There’s no way you can eat a hot pocket and do this." -Ed Chan
The views expressed herein are my own and are not intended to sound like a "dick."

User avatar
hufflepuff
Posts: 226
Joined: Mon Jan 25, 2010 11:12 am
Car: 2005 Mazda RX-8
CDC Member#: 512
Location: Alexandria, VA

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by hufflepuff » Mon Dec 11, 2017 7:54 pm

BugBomb wrote:
Mon Dec 11, 2017 3:46 pm
hufflepuff wrote:
Sat Dec 09, 2017 1:40 pm

> 301 TW : 0.98
300 - 201 TW : 1.00
200 - 100 TW : 1.02
< 100 TW : 1.04
I'm not sure I agree with these numbers. What data are you using? We don't have a huge amount of people using >200TW tires, and even fewer people actively testing the differences between these tires. Using your numbers, someone could show up on Conti DW or Conti Sport tires (which are decent street tires, but 320TW) and if someone were at the top of the index on Rivals with a 45-second run, they could be beaten by someone on the Contis running a full 1.8 seconds slower (all else being equal). That does not seem right to me. I would rather see a more moderate change for 2018 and then reevaluate at the end of the year. Something like this:

> 301 TW : 0.99
300 - 201 TW : 1.00
200 - 100 TW : 1.01
< 100 TW : 1.03

That puts someone on Contis at a 9-tenths advantage on a 45-second course compared to Rivals/Bridgestones, which sounds more reasonable in my experience.
.

The data I had was really focused on comparing 200TW cheater vs 200TW last gen vs 100TW tires; I did not have data for 200TW and greater so I swagged. Although: the data I have shows a 0.98 modifier for cheater vs non cheater 200TW tires, and I would think the Delta from a Hankook rs3 to a continental dw could be almost as large.

But starting conservative is no issue with me since we're lacking data... If folks are willing to test and tune, that would help us sort things out. I think where we're at tentatively is already a nice progression.

I think the weight index recommendation is fine and translates pretty well to the vehicles commonly seen at CDC. Might help some of the folks who are unfavorably right on the edge.
'05 RX-8 - HPDE and Time Attack
'95 Miata - Daily driver and AutoX
http://www.youtube.com/mchuffman/

User avatar
echan
Posts: 2518
Joined: Fri Sep 28, 2007 10:50 am
Car: 1973 Triumph TR6
CDC Member#: 4

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by echan » Tue Dec 12, 2017 10:51 am

BugBomb wrote:
Mon Dec 11, 2017 3:05 pm
I'm not opposed to the new TW and HP categories. Should we also look at vehicle weight categories?

After taking a rough survey from some of our participants on their car specs, I believe we could add 2 weight classes and change the categories to 300-lb sections as follows:

<1700 - Nothing currently in attendance, but we could eventually see things like Exocets, Sprites
1701-2000 - DP cars like TicTac and Bumblebee, lightweight Hondas like the CRX
2001-2300 - TR6, most normally-aspirated Miatas, older Civics
2301-2600 - NC/ND Miatas, Mazdaspeed/Aftermarket turbo Miatas
2601-2900 - S2000s, FRS/BRZ Twins, Mini Coopers, the Suxass
2901-3200 - Most Corvettes, Solstice/Sky, Civic Type R
3201-3500 - FoST, WRX/STi, Lighter Pony cars, Porsches/Bimmers
>3500 - Land Yachts


This seems to group similar cars better than the previous 500-lb categories. Thoughts?
What do you propose the indexes for each weight class be? I'm open to what the participants think is fair.

User avatar
BugBomb
Posts: 1060
Joined: Mon Oct 08, 2007 5:28 am
Car: '02 Whorevette
CDC Member#: 33
Location: PA

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by BugBomb » Tue Dec 12, 2017 11:54 am

Ed,
As I get time, I'm playing around with index values on the spreadsheet where people have contributed their car specs. It's going to take a while, but I am working on it.
Mike M
"There’s no way you can eat a hot pocket and do this." -Ed Chan
The views expressed herein are my own and are not intended to sound like a "dick."

gjenks
Posts: 16
Joined: Sun May 01, 2011 1:52 am
Car: Chevy Corvette Z06
CDC Member#: 642

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by gjenks » Tue Dec 12, 2017 1:28 pm

BugBomb wrote:
Tue Dec 12, 2017 11:54 am
Ed,
As I get time, I'm playing around with index values on the spreadsheet where people have contributed their car specs. It's going to take a while, but I am working on it.
We're looking at a data driven analysis of the vehicles to determine what breakdowns make the most sense, mathematically, to create meaningful divisions between classes such that vehicles are more balanced across the board.

scheherazade
Posts: 27
Joined: Wed Jul 11, 2012 10:15 pm
Car: 09 GTR
CDC Member#: 684
Location: nova

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by scheherazade » Fri Dec 29, 2017 6:07 pm

I like the idea of assigning tire rack categories a point value. They are a bit more granular, and they don't hang onto treadwear as a magic bullet.

Every system will have cheater tyres. That changes year to year. Unless you're in it to win it, that isn't a serious concern. If you are, you are probably running cheater tyres anyways. That's just life.

Really, the only true wholistic way to compare cars is to have a hot shoe drive each car to the point of personal proficiency with that specific vehicle, and put down a baseline run. Then individual performance is graded relative to baseline as a percentage better/worse.

Not really feasable, given time and resource constraints, and the fact that not everyone is willing to hand their keys over. But personally, I'd be down for it. I'd love to know if my driving is worth a darn compared to someone who knows what they are doing.

P.S. I drive a land yacht, and it does ok. Even weight classes have exceptions (given decent dampers, etc).
Heck, track and wheelbase matter more than weight when it comes to slalom or u-turns. IMO*

-scheherazade

User avatar
Rock Star
Posts: 80
Joined: Tue Jan 17, 2012 4:32 pm
Car: 93 Rx-7, 83 SPEC7, 70 GT6
CDC Member#: 515
Location: NoVa

Re: 2018 TIRE INDEX ADJUSTMENTS

Post by Rock Star » Tue Jan 02, 2018 3:03 pm

Matt, I still think we should use the actual weight/hp entry system that we discussed a couple years back.

viewtopic.php?f=11&t=2536
^this coupled with the new tire system you guys are suggesting would be best.

I've never liked that the weight and power levels were categorized. This lets the cars that are near the limits to inherently have an advantage over others. By making it a formula you level the playing field at the same time as eliminating the extra costs that would come up from people trying to build their cars to the edge of the spec.

The way I see this implemented is for the person signing up to run to type the weight of their car into an entry blank. At that point in the background the index would be calculated via a formula and that number would be used for their weight index.

Then have another data entry blank for HP. This would also have a check box for Motor vs Wheel HP (noobs entering hp numbers from the dealership stickers may not know their wheel.) This box when checked would automatically reduce the number to account for drive train loss (~15%?) before running it through it's own equation to determine index.

I think this system would be a lot cleaner/easier to understand as well. Simply type in weight, type in HP, check off class of tire, done.


If there is any interest I could come up with an equation that still hits the same values for your existing indexes, its been a bit since I've done that kind of math but I'm sure I can figure it out.

Post Reply

Who is online

Users browsing this forum: No registered users and 1 guest