ACR New Tires

[Purple Haze]

What can I expect on stock ACR tires when I pick up a new 2017 ACR next spring. I won't be racing the car just some street use nothing crazy. Also with the extreme aero package clearance is around 3" correct? Thanks...

[ViperGeorge]

Be careful in the rain.

[texasram]

You can raise and lower suspension, just have to remove the wheels:fpopcorn:

[NT-ACR]

I know they aren't exactly the same size but if you're just going to be using the car mainly on the street and are looking for a performance tire that would work well in a variety of weather conditions and will last longer, you might consider this setup:

Michelin Pilot Super Sports- 295/30ZR19 (F) and 345/30ZR19 (R)

http://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=Pilot+Super+Sport&frontTire=93YR9PSSXL&rearTire=43YR9PSSXL&vehicleSearch=false&fromCompare1=yes

or just wait for the Michelin Pilot Sport 4 S next year.

[ViperGeorge]

I know they aren't exactly the same size but if you're just going to be using the car mainly on the street and are looking for a performance tire that would work well in a variety of weather conditions and will last longer, you might consider this setup:

Michelin Pilot Super Sports- 295/30ZR19 (F) and 345/30ZR19 (R)

http://www.tirerack.com/tires/tires.jsp?tireMake=Michelin&tireModel=Pilot+Super+Sport&frontTire=93YR9PSSXL&rearTire=43YR9PSSXL&vehicleSearch=false&fromCompare1=yes

or just wait for the Michelin Pilot Sport 4 S next year.

I'm curious, the 295/30ZR19 Michelins are something over 1 inch larger in diameter than the stock ACR Kuhmos in 295/25ZR19. Will this effect the ESP/Traction Control of the ACR? Tire choice is the main reason I have not purchased an ACR and have stuck with my TA 2.0. When I ran a different tire size on my TA (Hoosiers) the ESP was going crazy just driving around. On the track I turned it off so no problem. I have heard that the ACR's ESP was recalibrated specifically for the Kuhmo tire sizes which are different than a non-ACR Viper.

If the Michelins really work on the street without upsetting the ESP I might reconsider my decision on an ACR.

[ViperGeorge]

If my calculations are correct (Tirerack does not list diameter for the Kuhmo) the Michelins are something like 1 inch larger in diameter. The rears are close.

[NT-ACR]

I'm curious, the 295/30ZR19 Michelins are something over 1 inch larger in diameter than the stock ACR Kuhmos in 295/25ZR19. Will this effect the ESP/Traction Control of the ACR? Tire choice is the main reason I have not purchased an ACR and have stuck with my TA 2.0. When I ran a different tire size on my TA (Hoosiers) the ESP was going crazy just driving around. On the track I turned it off so no problem. I have heard that the ACR's ESP was recalibrated specifically for the Kuhmo tire sizes which are different than a non-ACR Viper.

If the Michelins really work on the street without upsetting the ESP I might reconsider my decision on an ACR.

That's a great question, George. Unfortunately, I'm not the right person to ask. I know that Darius is running a larger tire and wheel package for the street, so hopefully he can report on his experience.

Darius is running:

iForged Icon rears are 21x13.5 and the fronts 20x11
Pirelli Pzero Neros 355/25/21 rear and 295/25/20 front

http://driveviper.com/forums/threads/15553-After-market-wheels

[Martin2000GTS]

My Gen 2 has 295/30/19 p zeros on the front that I bought from John B along with the cheap 355/30/19 rears. I would assume these would fit fine on the new ACR. (My gen 2 has after market 19in wheels) I don't know what the overall diameter is on the P zero fronts are, but that is another option besides the Michelins and way cheaper cause you can get the rears for $100 each right now. I plan on trying to put my gen 2 after market wheels on my future ACR if I ever get it!

[NT-ACR]

My Gen 2 has 295/30/19 p zeros on the front that I bought from John B along with the cheap 355/30/19 rears. I would assume these would fit fine on the new ACR. (My gen 2 has after market 19in wheels) I don't know what the overall diameter is on the P zero fronts are, but that is another option besides the Michelins and way cheaper cause you can get the rears for $100 each right now. I plan on trying to put my gen 2 after market wheels on my future ACR if I ever get it!

Good catch. Not sure why that didn't show up when I searched by size. I had to go directly to the tire itself.

Pirelli P-Zero Corsa overall diameter- 26.1" (295/30/19) and 27.4" (355/30/19)
Pirelli P-Zero overall diameter- 26.1" (295/30/19) and 27.4" (355/30/19)
Michelin Pilot Super Sport overal diameter- 26" (295/30/19) and 27.2" (345/30/19)

http://www.tirerack.com/tires/tires.jsp?tireMake=Pirelli&tireModel=P+Zero+Corsa+System&sidewall=Blackwall&partnum=53YR9CA&tab=Sizes

[NT-ACR]

Just got done talking to TireRack (great people who are extremely helpful) and I got the diameters for the ACR's Kumhos.

295/25-19 is 24.8" and 355/30-19 is 27.4"

[ViperGeorge]

Just got done talking to TireRack (great people who are extremely helpful) and I got the diameters for the ACR's Kumhos.

295/25-19 is 24.8" and 355/30-19 is 27.4"

Consistent with my calculations. So the question remains does a more than 1 inch change in diameter effect stability control/traction on an ACR? As a point of reference the 315/30/18 Hoosiers I ran on my 2015 TA 2.0 screwed with the stability control big time and the Hoosiers are only about 1/2 inch larger in diameter than the TA's stock 295/30/18s. The rear Hoosiers were only about 2/10 inch smaller. Seems to me that the 1 inch larger diameter would in fact screw up the system. I've sent an email off to SRT for clarification.

[jpgunn123]

On my ACR-E on the street I am running 305/30/19 Bridgestone RE-71R in the front and the Kumho 355/30/19 in the back.

The Bridgestone 305 has a 26.2" diameter. So far no issues with any systems, and they clear everything fine. I am going to run them for a bit at ButtonWillow in just over a week to see how they do vs. the Hoosiers I run on 18s.

[NT-ACR]

On my ACR-E on the street I am running 305/30/19 Bridgestone RE-71R in the front and the Kumho 355/30/19 in the back.

The Bridgestone 305 has a 26.2" diameter. So far no issues with any systems, and they clear everything fine. I am going to run them for a bit at ButtonWillow in just over a week to see how they do vs. the Hoosiers I run on 18s.

Please keep us updated, JP.

[Purple Haze]

Thanks everyone. Do you think I'll get 1000-1500 miles on the stock ACR tires no racing...???

[NT-ACR]

Thanks everyone. Do you think I'll get 1000-1500 miles on the stock ACR tires no racing...???

Yes.

[ViperJon]

Thanks everyone. Do you think I'll get 1000-1500 miles on the stock ACR tires no racing...???

Way more than that. I have 1350 on mine and they are not even worn.

[ek1]

What can I expect on stock ACR tires when I pick up a new 2017 ACR next spring. I won't be racing the car just some street use nothing crazy. Also with the extreme aero package clearance is around 3" correct? Thanks...

If you dont track your car, just leave the tires alone and enjoy. They are perfectly fine for street use. They are also cheaper than other brands (Pirelli, Michelin, etc).

[ek1]

Thanks everyone. Do you think I'll get 1000-1500 miles on the stock ACR tires no racing...???

I drove my ACR home for over 1,500 miles when I picked it up from Woodhouse and the tires looked almost new after that. My car currently has about 3,000 miles and I am STILL on the original set of rear tires - this includes 4 track days and 1 auto cross day.

If you do street driving with no burnouts or drifting, I'm thinking you'll easily get 7,500 miles out of them, if not more.

[NT-ACR]

I drove my ACR home for over 1,500 miles when I picked it up from Woodhouse and the tires looked almost new after that. My car currently has about 3,000 miles and I am STILL on the original set of rear tires - this includes 4 track days and 1 auto cross day.

If you do street driving with no burnouts or drifting, I'm thinking you'll easily get 7,500 miles out of them, if not more.

Lol. Who would be drifting on the street? That person would have to be an even bigger imbecile than the people like Junkie who street race.

[Policy Limits]

What about the second part of op's question in regards to extreme aero ground clearance? I thought I read 4 inches with stock suspension setting. Does that change to 3 with the extension piece installed or does it remain at 4? My GTS is 5 and I just received my race ramps order which mitigates front splitter exposure on driveway slope.

[Purple Haze]

Thanks guys and gals...By the way I plan to sign up as a member here love this site!!!

[sadil]

Someone with experience dealing with ESC and TC system, please correct me if I am wrong.

ESC - Electronic Stability Control - Monitors the direction of the steering wheel in relation to the direction of the vehicle (via lateral acceleration, sensors, etc) and corrects if it notices an inconsistency which can lead to skidding or loss of control. It can apply the brakes and even reduce engine power on some vehicles.

TC - Traction Control - Monitors wheel slip by relating engine torque and throttle input to available grip on the given road surface. Applies ABS braking when one tire seems to be spinning faster than the other. Only applies to driven wheels.

Given the overview above, I cant come up with a reason that a non-driven wheel (Viper front) that has a larger diameter will have an effect on either of these systems.

[ViperGeorge]

Someone with experience dealing with ESC and TC system, please correct me if I am wrong.

ESC - Electronic Stability Control - Monitors the direction of the steering wheel in relation to the direction of the vehicle (via lateral acceleration, sensors, etc) and corrects if it notices an inconsistency which can lead to skidding or loss of control. It can apply the brakes and even reduce engine power on some vehicles.

TC - Traction Control - Monitors wheel slip by relating engine torque and throttle input to available grip on the given road surface. Applies ABS braking when one tire seems to be spinning faster than the other. Only applies to driven wheels.

Given the overview above, I cant come up with a reason that a non-driven wheel (Viper front) that has a larger diameter will have an effect on either of these systems.

I believe you are correct in your definition of ESC and Traction Control. However, a different size tire can cause the systems to think one axle is spinning at an incorrect speed vs. the other. The system is calibrated to know, based on tire diameter, what the relative speed of the fronts should be in relation to the rears. Based on this it determines whether there is excess slip and if so it intervenes. This is information I obtained directly from Erich Heuschele who designed the system. The problem is I don't know how much of a difference the system will see as acceptable. I've sent Erich an email to see if he can clarify.

Again, at least with the calibration in my 15 TA, it sensed something was amiss when I was running Hoosiers (315/30/18 front and 345/30/19 rear) and it intervened big time. Now I suppose if this were to happen on an ACR with the Michelin PSSs then you could always turn it off but that is a pain since the car has to be stopped to do so. If you were to start driving and it the system intervened you'd have to pull over to shut it off. Maybe Track Mode would desensitize the system enough so it wouldn't intervene though.

Here's the first info I received directly from Erich in response to a question I had asked about ESC on the ACR (my questions are first followed by his response). As you can see I had asked him about the traction control on the ACR and the possible use of standard Viper wheels and tires from a non-ACR if I ordered an ACR with steel brakes (which would allow easy fitment of 18" wheels in the front). Notice his comment about the construction of the Pirelli PZeros and Corsas and their use on an ACR. His comments on the tires would be most relevant on the track when down force comes into play.

My question:

"When I was at Hastings I ran Hoosiers for the first time on my TA. 315/30/18 front and 345/30/19 rears. On the track with the ESC off they were great. I drove to get gas and left the ESC on and it was kicking in all the way to the station.

So that raises a question on an ACR-E. If I were to buy an ACR-E with steel brakes (really don't want the carbon for the track) could I run standard Viper tires in 18/19 without having issues with the ESC kicking in? Also which non-ACR Viper wheels can handle the downforce? Someone said that the Sidewinder IIs aren't strong enough. What about street tires can the Michelin PSSs or the Pirelli PZeros handle the load?"

From Erich:

"The traction control was giving you trouble with that large diameter front tire. It is spinning slower, so the car thinks the rear tires are slipping. You should be fine with a front tire that has a diameter closer to stock.

None of the non ACR wheels are designed to manage the downforce of the ACR. Neither are the Corsa or Pzero tires. Since there is less grip on the Pirellis, that helps reduce the stress the wheel can see, but we haven’t analyzed that scenario. I would keep a close eye on the 18” front wheels for cracks in that scenario and inspect regularly on the inboard and outboard face of the wheel."

[sharmut]

None of the non ACR wheels are designed to manage the downforce of the ACR. Neither are the Corsa or Pzero tires. Since there is less grip on the Pirellis, that helps reduce the stress the wheel can see, but we haven’t analyzed that scenario. I would keep a close eye on the 18” front wheels for cracks in that scenario and inspect regularly on the inboard and outboard face of the wheel."

Interesting, did Erich mention the load ratings on the Sidewinder-2 & ACR 19" wheels?

[ViperGeorge]

Interesting, did Erich mention the load ratings on the Sidewinder-2 & ACR 19" wheels?

No sorry, he did not. He only said no other OEM non-ACR wheel was strong enough for the ACR. That has been something I've wondered about too. Would an aftermarket wheel hold up to the down force? No way to know I guess until cracks appear.

[NT-ACR]

No sorry, he did not. He only said no other OEM non-ACR wheel was strong enough for the ACR. That has been something I've wondered about too. Would an aftermarket wheel hold up to the down force? No way to know I guess until cracks appear.

I'm sure that, should you have a custom wheel made, that the company could do a structural analysis of the stock ACR wheel and match it to one of their designs.

A company to talk to might be BBS's Motorsports division:

http://www.bbs-usa.com/race_wheels/contact.cfm

[Brian GTS]

From the factory, my front clearance is ~4 1/4" with track extension installed. Take note that the track extension does not alter ground clearance. It simply extends the splitter forward. However, you DO need to be careful of your approach angle with the track extension installed because you chin is hanging out a bit further.

Where you need to be most concerned is with the rear diffuser extensions. They have less clearance than the front extension.

[NT-ACR]

From the factory, my front clearance is ~4 1/4" with track extension installed. Take note that the track extension does not alter ground clearance. It simply extends the splitter forward. However, you DO need to be careful of your approach angle with the track extension installed because you chin is hanging out a bit further.

Where you need to be most concerned is with the rear diffuser extensions. They have less clearance than the front extension.

Not to get this thread of track but you have a beautiful vehicle, Brian. What color is it?

[ViperGeorge]

Ok, so I heard back from Erich on the choice of tire sizes for the ACR. He says that the traction control system compares the rear wheel speed to the front wheel speed. If you went with the Michelin or Pirelli in 295/30/19 he says the traction control system will think the rear tires are slipping relative to the fronts and it would intervene. The tire sizes front to rear get closer as the 295/30/19 is taller than the stock size and the ESC system is calibrated to stock tire sizes.

He says that Ralph tried those tire sizes and had the issue in his ACR. Ralph had to either put ESC in "Track" mode or turn it off. Track mode turns traction control off. While turning ESC off would solve the traction control issue he says it won't address the issue with the ABS system. The larger front tire would cause the ABS system to release pressure to the fronts as it would sense there is more slip. (Not sure I completely understand this part but hey I'm not the engineer.) He says there is nothing you can do to address the ABS tuning like you can with the ESC. I experienced the problem with ESC on my TA running the Hoosiers. I was running a front size of 315/30/18 which is not as tall as the 295/30/19 and I had to turn ESC off or the traction control would interfere like crazy.

Lastly he said if you could run 18" wheels in the front which I know some have tried on ACRs with CCBs then you might be able to run 295/30/18 tires. These would be somewhat smaller than stock sizes in 19 but would preserve a greater difference front to rear. This would prevent the traction control from kicking in as soon. He also said the Corvette's Michelin PSS are quite sticky and fast. Also important to note that if you bought an aftermarket non-Corvette spec Michelin you would get a different compound and they would not be as sticky or as fast. You have to specify the Corvette tire.

Bottom line is I still see no good solution for tires other than the Kuhmos. Certain aftermarket 18" wheels do fit the ACR but they are very close to the calipers and debris could get wedged in the gap causing issues. If you have an ACR with the TA's steel brakes then 18" wheels would be a very good solution and give you more choices for the front. Still have to watch wheel for cracks though due to the down force.

[Brian GTS]

Not to get this thread of track but you have a beautiful vehicle, Brian. What color is it?

Thanks....it's very similar to Jeep Hydro Blue metallic.

[Purple Haze]

All interesting data thanks...

[Bruce H.]

Ok, so I heard back from Erich on the choice of tire sizes for the ACR.

I wonder if he might comment about their discussions with other tire manufacturers to provide an alternative for the ACR which they mentioned in the SRT panel discussion at NVE2? A Pirelli rep was on the panel as well and acknowledged that on-going discussion.

Tires are such a critical component for track rats that I'm rather surprised SRT designed the car around a single tire, and one that's apparently designed as more of a qualifying tire than an actual track day tire. Having to potentially change tires each track day must make it a non-starter for many.

[allans]

This whole tire issue is somewhat confusing, I ran Hoosier 315/18s on both my SRT TrakPac and my T/A. I had absolutely no issues with traction control or ABS. Some on here are running 335 fronts and 345 rears , on their ACR with good results. I think we need more info. Anyone? Best, Allan

[reshetov]

So I had the same exact consideration when ordering my ACR, more so actually because of the 25 profiles in the front which make that front tire just so damn thin against bumps especially here in New Jersey. That was one of the bigger reasons I went with the TA brakes rather than the CCBs when ordering the 1 of 1 also, so I could run the Sidewinder II wheels while still getting the ACR. I actually like the way the Sidewinders look better than the ACR wheels.

What's interesting is that Mark and Bill at Woodhouse told me that they had to double check all the same considerations with the Viper engineers if I could actually run 18s in the front on the ACR - the ABS, traction and stability controls and they were looking for the same diameter. So when you run 18s in the front as you guys know those get the 30 profiles, so with less rim and more tire your overall diameter is within tenths of an inch of the 19s with the 25 profiles.

However, what's interesting is that while you can configure everything to hell with the 1 of 1, one of the very few things they didn't let me do is actually order the Sidewinder IIs with the ACR package and that if I wanted that package I had to get the stock ACR 19s with the Kumhos. So I ended up doing that, and getting an additional set of Sidewinder IIs separately for a spare set, with more tire options.

Having said all that, my goal was to just run the 18s all year and then when hitting the track or such events to run the 19s w/ the Kumhos. Well let me tell you how glad I am that they forced me to get those 19s because the grip in that setup is so good that I ended up just keeping them on and switching the Sidewinder IIs with the P Zeros for the late fall/winter/early spring. The Kumhos started getting really squirmy below 50 F, and the regular Viper tires are at least rated to be ok at lower temps which works out well since I plan on keeping the car active throughout the year.

[MK2_Viper]

The extensions do not come installed by the way .

[1of1TA1.0]

I'm sure it had to do with the downforce of the ACR actually. The Sidewinders while awesome, do not allow for the amount of downforce the Full Extreme ACR can apply to them. Brakes are only part of the equation. Good looking combo you have and I'm sure you will be happy.

As for the extensions, they do NOT come installed from the factory. A dealer may install them but the factory includes them in plastic and the dealer/owner has to install them.

[ViperGeorge]

This whole tire issue is somewhat confusing, I ran Hoosier 315/18s on both my SRT TrakPac and my T/A. I had absolutely no issues with traction control or ABS. Some on here are running 335 fronts and 345 rears , on their ACR with good results. I think we need more info. Anyone? Best, Allan

Did you leave ESC full on or turn it off?

[jpgunn123]

Did you leave ESC full on or turn it off?

On Track I run the Hoosier 335 and 345 18s with Everything off or in Track mode. Just driving around (to track and back) I don't turn anything off. I don't go fast on the street, but never see warning lights.

I can see the ABS thinking the front may have some slip, but I have not noticed any decrease in braking when on the 18s.

I honestly think the Kumhos are a great tire. They just won't put up with a lot of lapping. I would prefer to run the 19s with a more durable tire. I am going to try the 19s this weekend with a 305/30 Bridgestone RE-71R. It has plenty of load rating but is 26". Will see how this works, but I am not expecting it to be faster than the Kumho, just more durable.

We need other options in the factory diameters... Hoosier, Nitto, BFG... I wish one or more would come out with a 24.7 by 11.1"+ tire...

[ViperGeorge]

On Track I run the Hoosier 335 and 345 18s with Everything off or in Track mode. Just driving around (to track and back) I don't turn anything off. I don't go fast on the street, but never see warning lights.

I can see the ABS thinking the front may have some slip, but I have not noticed any decrease in braking when on the 18s.

I honestly think the Kumhos are a great tire. They just won't put up with a lot of lapping. I would prefer to run the 19s with a more durable tire. I am going to try the 19s this weekend with a 305/30 Bridgestone RE-71R. It has plenty of load rating but is 26". Will see how this works, but I am not expecting it to be faster than the Kumho, just more durable.

We need other options in the factory diameters... Hoosier, Nitto, BFG... I wish one or more would come out with a 24.7 by 11.1"+ tire...

Interesting. With 315/30/18 Hoosiers on the front of my car the traction control was constantly engaging. I had to drive to a gas station about 1/2 mile from the track and I thought something was wrong with the car, it wouldn't accelerate. Then I saw the traction light on and realized what was going on.

[NT-ACR]

Thanks....it's very similar to Jeep Hydro Blue metallic.

Did you ever make a post about it? I'd love to see larger images of it!

- - - Updated - - -


Ok, so I heard back from Erich on the choice of tire sizes for the ACR. He says that the traction control system compares the rear wheel speed to the front wheel speed. If you went with the Michelin or Pirelli in 295/30/19 he says the traction control system will think the rear tires are slipping relative to the fronts and it would intervene. The tire sizes front to rear get closer as the 295/30/19 is taller than the stock size and the ESC system is calibrated to stock tire sizes.

He says that Ralph tried those tire sizes and had the issue in his ACR. Ralph had to either put ESC in "Track" mode or turn it off. Track mode turns traction control off. While turning ESC off would solve the traction control issue he says it won't address the issue with the ABS system. The larger front tire would cause the ABS system to release pressure to the fronts as it would sense there is more slip. (Not sure I completely understand this part but hey I'm not the engineer.) He says there is nothing you can do to address the ABS tuning like you can with the ESC. I experienced the problem with ESC on my TA running the Hoosiers. I was running a front size of 315/30/18 which is not as tall as the 295/30/19 and I had to turn ESC off or the traction control would interfere like crazy.

Lastly he said if you could run 18" wheels in the front which I know some have tried on ACRs with CCBs then you might be able to run 295/30/18 tires. These would be somewhat smaller than stock sizes in 19 but would preserve a greater difference front to rear. This would prevent the traction control from kicking in as soon. He also said the Corvette's Michelin PSS are quite sticky and fast. Also important to note that if you bought an aftermarket non-Corvette spec Michelin you would get a different compound and they would not be as sticky or as fast. You have to specify the Corvette tire.

Bottom line is I still see no good solution for tires other than the Kuhmos. Certain aftermarket 18" wheels do fit the ACR but they are very close to the calipers and debris could get wedged in the gap causing issues. If you have an ACR with the TA's steel brakes then 18" wheels would be a very good solution and give you more choices for the front. Still have to watch wheel for cracks though due to the down force.

Great info, George.

[allans]

Did you leave ESC full on or turn it off?

Both ways.

[Jack B]

We probably will never have hard data that answers the question, it is going to take trial and error. The front tire change introduces a 4% speed error. There were non-acr cars running 3.73 gears without any issues, this introduces a 5% error. The pcm has a parameter, that looks for a match between speed and rpm, the value is 9%. In other words it does not want to see more than a 9% difference from what is expected. What we do not know is what happens when you go beyond the 9%.

I personally have run a 25.75" tire on the rear, that is close to a 9% difference. i have also run a 26" tire on the front, versus the stock 25" tire, that is a 4% difference, neither was a problem.

All this sort of means nothing until someone tries the smaller combo.



Consistent with my calculations. So the question remains does a more than 1 inch change in diameter effect stability control/traction on an ACR? As a point of reference the 315/30/18 Hoosiers I ran on my 2015 TA 2.0 screwed with the stability control big time and the Hoosiers are only about 1/2 inch larger in diameter than the TA's stock 295/30/18s. The rear Hoosiers were only about 2/10 inch smaller. Seems to me that the 1 inch larger diameter would in fact screw up the system. I've sent an email off to SRT for clarification.

[Jack B]

Was that the TA2, I have run the same tire on my 2013 without an issue.



Interesting. With 315/30/18 Hoosiers on the front of my car the traction control was constantly engaging. I had to drive to a gas station about 1/2 mile from the track and I thought something was wrong with the car, it wouldn't accelerate. Then I saw the traction light on and realized what was going on.

[ViperGeorge]

Was that the TA2, I have run the same tire on my 2013 without an issue.

Yes, TA 2.0. There are probably different calibrations for traction control and ABS between the non-ACR Vipers and the ACRs. Why there would be any difference between a 13 and a 15 Model Year, I don't know unless they just updated the parameters for some reason.

[jpgunn123]

OK -- half the day at Buttonwillow down, so here is the report on tires so far:

I have not driven this track in about 10 years, so I needed to get some time to remember the track. Even after all morning, I am still remembering things. Plus the Viper can just go through things like Riverside and the Bus Stop so fast if you trust it. So, learning the track, the car, etc. Anyway -- now for my findings..

I set the car alignment again; Front is -2.8 camber with 6 degrees caster and 0 toe (pretty much Factory, and Rear is Factory.

1. 305/30/19 RE71-Rs in front with Kumho 355/30/19 rear. Bridgestones worked great with the Kumhos. Tried a session with Traction Control in Sport mode and everything was happy, and then did a couple of sessions in track mode. Traction control ABS, etc. all worked just fine with no complaints. Did 25 laps on them (which is roughly 50 minutes of track time). Was able to get down to a 1:52.08 before I took them off. I did run in to some traffic during these laps, and the predicted Virtual Best was a 1:51.08 on these tires. Here is how the RE71-R looks:
21079

Track Map with G's overlaid (anything red is over 1.1G, anything yellow is over 1G)
21081

I ran 35psi hot rear and 32 psi hot front. Seemed like starting pressure (at 76 degrees ambient) needed to be about 25 rear and 24 front.

I think these would last about 4 hours of track time, maybe even 5 hours (depends on track and driver) which seems to be about what the rear are good for. The car was very neutral. I ended up running the front rebound at 6 with these (vs. 5 factory).

2. 18" Hoosiers in 335/30/18 and 345/35/18. These were the leftovers from about 2 hours of running at Chuckwalla a few weeks ago. Did 30 minutes on them, and there is still plenty left. Pressures were best at 33 psi front and rear at 31psi. I ran front rebound on 7, and the car felt good once the tires got up to pressure (started at 24 front and 23 rear). Picture of Front:
21080


Video of CW #13 in the ACR where I ran a 1:48.54. I had open track, did not take huge risks, but it was a solid lap. It was my predicted virtual best by Harry's Lap Timer.

https://youtu.be/d6FDgduEO2k


Track Map with G's overlaid (anything red is over 1.1G, anything yellow is over 1G)
21082
The Viper is a beast. It really rewards keeping the entry speed up.


Afternoon Update. Hoosiers made it another 40 minutes before letting go, so I got 4 hours out of them with a sub-optimal alignment in the front. I think they should last about 5 hours next time. Fresh Hoosiers are going on for tomorrow.

Got the time down to a 1:48.01.
Other things of note:

Brakes are still looking good (first set of pads)
Coolant never went over 205
Car burns no oil
Wheels are 12" in front and 13" in rear.

[BlueAdder]

What can I expect on stock ACR tires when I pick up a new 2017 ACR next spring. I won't be racing the car just some street use nothing crazy. Also with the extreme aero package clearance is around 3" correct? Thanks...

4" Front and 5.5" Rear (or at least those are the settings on the ACR manual)

[Dr.Ron]

On Track I run the Hoosier 335 and 345 18s with Everything off or in Track mode. Just driving around (to track and back) I don't turn anything off. I don't go fast on the street, but never see warning lights.

I can see the ABS thinking the front may have some slip, but I have not noticed any decrease in braking when on the 18s.

I honestly think the Kumhos are a great tire. They just won't put up with a lot of lapping. I would prefer to run the 19s with a more durable tire. I am going to try the 19s this weekend with a 305/30 Bridgestone RE-71R. It has plenty of load rating but is 26". Will see how this works, but I am not expecting it to be faster than the Kumho, just more durable.

We need other options in the factory diameters... Hoosier, Nitto, BFG... I wish one or more would come out with a 24.7 by 11.1"+ tire...

What width 18" wheel were you running the 335 Hoosiers on?

Thanks!

Ron

[jpgunn123]

What width 18" wheel were you running the 335 Hoosiers on?

Thanks!

Ron

I am running a 12" front. They would work on an 11" well enough.

[allans]

Jp, So your happy with the RE71s and they are good for an additional hour of track time but, the hoosiers are 2+ seconds faster. Great info. Thank you. Allan

[Arizona Vipers]

I'm curious, the 295/30ZR19 Michelins are something over 1 inch larger in diameter than the stock ACR Kuhmos in 295/25ZR19. Will this effect the ESP/Traction Control of the ACR?

No. There are many many posts about this already. I've run 335-30-18 Hoosiers up front with zero issues on all traction control settings from full on to full off.

[Dr.Ron]

I am running a 12" front. They would work on an 11" well enough.

Have you or anyone run them on 11" wheels up front? How would a 335/18 be on an 11" wheel vs. a 315/18 on a 11" wheel?

Ron