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Salvisol

Wheel Size

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Salvisol

Hey Folks. I'm a Spec Z watcher, but maybe at some point in the future a possible participant.

 

Has there ever been a discussion regarding changing the spec tire to a 17"? You can still use Brembos with 17" wheels, and also have the benefit of lower cost wheel and tire combos. Also a 17" wheel would likely be lighter which would help in getting to the the minimum weights.

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Salvisol

Hmmm I guess there are no opinions on a 17" setup.

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Salvisol

Just some info from a brief tirerack review.

 

Toyo RR 275/35/18: $284.77 per tire

Toyo RR 255/40/17: $231.29 per tire

Enkei RPF1 18X9.5: $322 per wheel

Enkei RPF1 17X9: $247 per wheel (This wheel is about 2.5 lbs lighter than the 18X9.5)

 

 

On wheel costs you'd save $300 for one set of wheels. Maybe an even bigger savings if you went with something besides an RPF1.

 

On tire cost it would be a $213.92 savings for one set of tires.

 

I bring this all up because reducing build expenses and lowering consumable costs might help attract more people to Spec Z.

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esr

Great info.

But we can't slow the car anymore, this is a good compromise of speed and reliability, i rather spend a bit more on tires than pumping up the engine.

Actually there were many request from owners to make the cars faster(more money), thankfully the directors have kept nice and simple so far, And have maintained consistency.

The car is great as it is in my opinion, actually going to Toyos has already cut the cost down from the previous BFg r1.

 

These cars are a bit heavy( but strong and safe)so we need the extra rubber, or we will be too slow out there.

 

Rafael

NorCal

Spec z #21

 

 

 

Just some info from a brief tirerack review.

 

Toyo RR 275/35/18: $284.77 per tire

Toyo RR 255/40/17: $231.29 per tire

Enkei RPF1 18X9.5: $322 per wheel

Enkei RPF1 17X9: $247 per wheel (This wheel is about 2.5 lbs lighter than the 18X9.5)

 

 

On wheel costs you'd save $300 for one set of wheels. Maybe an even bigger savings if you went with something besides an RPF1.

 

On tire cost it would be a $213.92 savings for one set of tires.

 

I bring this all up because reducing build expenses and lowering consumable costs might help attract more people to Spec Z.

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Salvisol

Hi Rafael thanks for the reply. I've taken a look at lap times for Spec Z cars to see around where they stand to other classes.

 

I focused on the 2014 Eastern Championships at Road Atlanta as during that year there was a good group of Spec Zs in the competition. Take a look a the results sheets for TT, PT, and Spec Z.

 

TTD/PTD specifies a 245mm tire max, TTC/PTC specifies 255mm tire maximum, and TTB/PTB specifies a 265mm tire max.

 

You'll notice in the results that the fastest Spec Z ran a 1:40.019.

In TT all five TTB cars ran a faster time than the SZs, four of the TTC cars ran faster or equal to the SZs, and two TTD M3s ran a comparable time to SZs.

In PT the top three PTB cars ran a faster lap than the SZs.

 

I have no idea what weight these other cars were at, what tire compound they used, or what actual tire width they used. For sure driver capability might explain why some of the TTD/TTC cars ran better or equal to the Zs. Currently the Spec Zs seem to be set at a 12:1 whp/lbs. This is equal to TTC/PTC.

 

I think the results show some evidence that a narrower tire wouldn't necessarily mean a Z would become drastically slower. Some of the cars in the results are not light from the factory (Pontiac Firebird, Chevy Camaro, Subaru Impreza, Subaru Legacy, BMW M3). All the classes I reference technically require something smaller than a 275mm.

 

There is also the tire diameter factor and tire weight. A smaller diameter will give you quicker acceleration. A lighter tire will improve suspension response and overall mass. As you can see below the 255 is only 0.1" taller but weighs 3lbs less.

 

Stock 03 350Z Rear Tire 235/50/17: 26.3"

Stock 03 350Z Track Rear Tire 245/45/18: 26.7"

Toyo RR 275/35/18: 25.6" diam, 26lbs

Toyo RR 255/40/17: 25.7" diam, 23 lbs

 

 

Results SpecZ:

http://timingscoring.drivenasa.com/NASA_Championships/Eastern%20States%202014%20Road%20Atlanta/Sunday/Group%20F%20-%20HC%20SpecZ/Group%20F%20Sunday%20Championship%20Race%20by%20Class%20-%20Official.pdf

 

Results PT:

http://timingscoring.drivenasa.com/NASA_Championships/Eastern%20States%202014%20Road%20Atlanta/Sunday/Group%20E%20-%20PT%20944Spec/Group%20E%20Sunday%20Championship%20Race%20by%20Class%20-%20Official.pdf

 

Results TT:

http://timingscoring.drivenasa.com/NASA_Championships/Eastern%20States%202014%20Road%20Atlanta/Sunday/Group%20I%20-%20TTB%20C%20D%20E%20F/Sunday%20Group%20I%20Championship%20Results%20by%20Class.pdf

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esr

You are comparing apples to oranges.

This is a spec class I think most people are willing to compromise with the current rules even if they don't agree 100%. Me included.

Cars are great.we wil see if the class grows.

We need stability and relative simplicity overall.

 

That's as much info as I got. There are other guys who run the cars more than I do. Maybe try messaging them directly.

 

Rafael

 

 

 

Hi Rafael thanks for the reply. I've taken a look at lap times for Spec Z cars to see around where they stand to other classes.

 

I focused on the 2014 Eastern Championships at Road Atlanta as during that year there was a good group of Spec Zs in the competition. Take a look a the results sheets for TT, PT, and Spec Z.

 

TTD/PTD specifies a 245mm tire max, TTC/PTC specifies 255mm tire maximum, and TTB/PTB specifies a 265mm tire max.

 

You'll notice in the results that the fastest Spec Z ran a 1:40.019.

In TT all five TTB cars ran a faster time than the SZs, four of the TTC cars ran faster or equal to the SZs, and two TTD M3s ran a comparable time to SZs.

In PT the top three PTB cars ran a faster lap than the SZs.

 

I have no idea what weight these other cars were at, what tire compound they used, or what actual tire width they used. For sure driver capability might explain why some of the TTD/TTC cars ran better or equal to the Zs. Currently the Spec Zs seem to be set at a 12:1 whp/lbs. This is equal to TTC/PTC.

 

I think the results show some evidence that a narrower tire wouldn't necessarily mean a Z would become drastically slower. Some of the cars in the results are not light from the factory (Pontiac Firebird, Chevy Camaro, Subaru Impreza, Subaru Legacy, BMW M3). All the classes I reference technically require something smaller than a 275mm.

 

There is also the tire diameter factor and tire weight. A smaller diameter will give you quicker acceleration. A lighter tire will improve suspension response and overall mass. As you can see below the 255 is only 0.1" taller but weighs 3lbs less.

 

Stock 03 350Z Rear Tire 235/50/17: 26.3"

Stock 03 350Z Track Rear Tire 245/45/18: 26.7"

Toyo RR 275/35/18: 25.6" diam, 26lbs

Toyo RR 255/40/17: 25.7" diam, 23 lbs

 

 

Results SpecZ:

http://timingscoring.drivenasa.com/NASA_Championships/Eastern%20States%202014%20Road%20Atlanta/Sunday/Group%20F%20-%20HC%20SpecZ/Group%20F%20Sunday%20Championship%20Race%20by%20Class%20-%20Official.pdf

 

Results PT:

http://timingscoring.drivenasa.com/NASA_Championships/Eastern%20States%202014%20Road%20Atlanta/Sunday/Group%20E%20-%20PT%20944Spec/Group%20E%20Sunday%20Championship%20Race%20by%20Class%20-%20Official.pdf

 

Results TT:

http://timingscoring.drivenasa.com/NASA_Championships/Eastern%20States%202014%20Road%20Atlanta/Sunday/Group%20I%20-%20TTB%20C%20D%20E%20F/Sunday%20Group%20I%20Championship%20Results%20by%20Class.pdf

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Salvisol

Yeah I just bring it up for discussion I don't think I'm the only person that has ever thought about all of this. I think it's a good point of discussion.

 

I'm not a current SZ driver so I don't have a drivers experience with the cars. I have a Z but I'm still on the fence if I'm going to build it up or not. I think all the current participants and the guys on the fence would like to see the class grow. I think lowering expenses even further would help improve car counts of course this is just my personal opinion.

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