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Yet another wheel and tire thread. Sorry...

130
102
Exp. Type
Autocross
Exp. Level
Under 3 Years
Colorado Springs
If you're moving to wider tires I would do the brake upgrades sooner rather than later. ESPECIALLY if you decide to go 18x11. And don't forget brake cooling ducts.

Oh, and the 18x11s may need caster/camber plates to keep them tucked in under the fenders.


So got word back from SCCA, since I upgraded 2 and not just 1 of my sway bars, I am no longer able to stay in STOCK.... <shrug>, price was right, and I can already tell how much of a difference they make. However, they accentuate my 17" rims / sidewall issue. And those could only go up to 9inch wide (+1" over stock)in the stock class. So 18s (10 vs 11 tbd) but I'd like to have street tires that are a little more all season vs track tires, we still get cold and snow in CO till April and I plan on driving this thing almost year round. Looks like castor plates make sense for the next update with rims.. :) It never ends.
 

Dave_W

Cones - not just for ice cream
522
555
Exp. Type
Autocross
Exp. Level
20+ Years
Connecticut
those could only go up to 9inch wide (+1" over stock)in the stock class.
Just to clarify, SCCA Street category allows a +/- 1" change in wheel diameter, but the width needs to remain factory size for the particular car year/model/trim/option package.

That said, pick up set of camber plates (check what shocks you are running for fitment) from site sponsor Vorshlag (or Maximum Motorsports, Ground Control, Steeda, etc.), Ford Performance front hubs with ARP extended studs, a pair of 25mm spacers from site sponsor OP Mustang, a set of 18x11 wheels from site sponsors Apex or (if you have $) Forgeline, some 305 or 315 tires from Tire Rack (use the link so the site gets credit), and have fun in CAM-C or STU. BFG Rival S 1.5, Bridgestone RE-71R, and Yokohama A052 are the hot a/x tires, though the 'stones are being discontinued; you can also try the Falken RT615K. I'm recommending 18" over 19" for wheels due to tire selection - only the BFG offers a decent width in a 19.
 
130
102
Exp. Type
Autocross
Exp. Level
Under 3 Years
Colorado Springs
Just to clarify, SCCA Street category allows a +/- 1" change in wheel diameter, but the width needs to remain factory size for the particular car year/model/trim/option package.

That said, pick up set of camber plates (check what shocks you are running for fitment) from site sponsor Vorshlag (or Maximum Motorsports, Ground Control, Steeda, etc.), Ford Performance front hubs with ARP extended studs, a pair of 25mm spacers from site sponsor OP Mustang, a set of 18x11 wheels from site sponsors Apex or (if you have $) Forgeline, some 305 or 315 tires from Tire Rack (use the link so the site gets credit), and have fun in CAM-C or STU. BFG Rival S 1.5, Bridgestone RE-71R, and Yokohama A052 are the hot a/x tires, though the 'stones are being discontinued; you can also try the Falken RT615K. I'm recommending 18" over 19" for wheels due to tire selection - only the BFG offers a decent width in a 19.
Ah, tall vs wide.. Got it. Either way, my sway bars kicked me up... so as you indicate, just go all in now....

hahaha. That becomes the debate.... do I just sink the money now, stick to my guns and NOT spend that for a year or find a medium that is better and then commit the full $ in a season? :) I do think I want a set of street vs track and if they are both 18 it makes life easy.

But I am looking for cheaper options, I simply don't want to commit that much money to wheels currently. Guess I am trying to fight the slippery slope.
 
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130
102
Exp. Type
Autocross
Exp. Level
Under 3 Years
Colorado Springs
No, opted to go 9.5 since this will still be a street car for a while, no other changes needed with 9.5. Chatted with the Apex folks and since I don't want to commit the full camber plates/hubs / etc until next year, should be fine for a street car. Then just get a second set for track only and make that leap next year. My office is 55 miles away so when I drive it, I will put some serious miles commuting until I decide if I want to fully commit to a track designated car.
 
62
34
Exp. Type
HPDE
Exp. Level
Under 3 Years
Cantley
I am like you but I just got started. Had my first HPDE event yesterday and I plan to attend 20-25 twenty minute sessions this season.
read
I have a dual use car that I play with at the track. I am not running competitive classes, just HPDE groups for fun. If I was building a dedicated track car I would certainly look at 11" wide wheels (class permitting) and everything that goes along with making them fit, but I don't think it is that import for someone getting started. Remember that NASA Spec Iron cars are restricted to a 9.5" wide wheel with a 275 wide tire.

I think it is more important to get out on track. Plan modifications/upgrades as you gain experience to correct handling characteristics that you do not like or that are holding you back.

I have a dual use car that I play with at the track. I am not running competitive classes, just HPDE groups for fun. If I was building a dedicated track car I would certainly look at 11" wide wheels (class permitting) and everything that goes along with making them fit, but I don't think it is that import for someone getting started. Remember that NASA Spec Iron cars are restricted to a 9.5" wide wheel with a 275 wide tire.

I think it is more important to get out on track. Plan modifications/upgrades as you gain experience to correct handling characteristics that you do not like or that are holding you back.
I am like you but I just got started. Had my first HPDE event yesterday and I loved it. I plan to attend 20-25 twenty minute sessions this season. Like OP I read everything I could find on tires. I have a 2019 GT with CP and 19x11 forgestars that came with mostly worn Dunlop Maxx sports and I need to change them before I go back to the track. I think they handled great but I have no idea what it should be like :I'm a complete beginner. There are those who say beginners like me should spend a year on 300+ TW tires like the firehawk or the Cooper, others who say get PS4S, and others who recommended going to 200-240 TW like the rivals or sport cup. I'm not sure what to do. I tend to think the performance of the sport cup or equivalent would be wasted while I'm learning my way around a race track, let alone getting close to the limits of the car. But then many people say I will not learn properly without a proper tire for the job. I am kind of thinking about middling the difference and going with PS4S, since they seem to be regarded as the best street tire in this harder compound tire bracket. Thoughts?
 
42
22
Exp. Type
HPDE
Exp. Level
Under 3 Years
Pittsburgh PA
After reading this thread and many others, I thought I'd ask the following question on overall tire diameter in this thread and not create a new one...

After 2 yrs of TNiA's (approx 14) and 4 PDE's at my local track with factory 19x9 / 9.5"s, I am making the next step to a track-only set of wheels / tires. My 012 is stock and I have no plans (at the present time) to upgrade the factory front struts. Maybe in a few years.

After lots of reading, I am leaning towards a square set-up of 18x10 wheels. I'd like to go with 285's. 285x30x18 tires seem fairly common and 285x40x18 tires don't seem to be as common. I'd like to go with Falken RT660's but the 285x40x18 is not available.

My question is..how big of a deal is it going with a 285x30x18 which has an approx overall diameter of 24.7"? My factory size tires are approx 27" dia. as would a 285x40x18 be approx. 27" dia. I understand the handling benefit of an aspect ratio of 30 vs 40 and I get the final drive ratio effect, but a 2" dia difference seems like a fairly big difference.

Lastly, I'm running stock Boss springs. I don't care how it looks, but I was curious about the 1" larger wheel / fender gap. Is it pretty much a given that when one goes to track tires, they at the same time go with the Ford Racing Boss springs or other lowering springs?

I appreciate any and all comments / advice.

Thanks.
 
1,211
997
Exp. Type
HPDE
Exp. Level
5-10 Years
Philly Metro Area
Perhaps you can consider the Falken's (in either RT615K+ or RT660) in 295/40-18. They are 27.2" or 27.4" in diameter. I run the 615K+ on Apex EC-7 18x10 (ET42) wheels with a 3mm spacer up front. I also used the Roush steering rack limiter to prevent them from rubbing on the inside of the wheel wheels and brake ducting.

I also have the Steeda HD strut mounts that allow for some additional camber adjustment. I can get about -2.2 degrees with them. I have Roush springs and Koni yellow struts/shocks.

If you are running the stock suspension up front you may not be able to get much more than -1.5 degrees of camber. This will cause some premature wear on the outside edges of your tire.

The side benefit of running a 295 on a 10" wide wheel instead of a 10.5" or 11" wheel is that the tires are ever so slightly "pinched" and the outside edges don't get as much wear as they otherwise would going around the corners. The tire pretty much rolls so the wear line is just even with the little arrows below the tread.

You may also want to research the difference between the two versions of the Falkens. I've heard that the 660 are better for autocrossing and the 615Ks last longer for HPDE. The specs on the 660s indicate that are a little bit wider so they may require a thicker spacer. If you don't have camber plates you may need to run thicker spacers for that reason too.

Apex's fitment guide mentions the 295s. It states to use 12mm spacers but as I indicated about, I did not need anything nearly as thick. The latest generation of EC-7s 18x10 are ET40 so you gain an additional 2mm. If I had ET40's I probably wouldn't need the spacers at all.

 

Dave_W

Cones - not just for ice cream
522
555
Exp. Type
Autocross
Exp. Level
20+ Years
Connecticut
Circumference is Pi times diameter. The 27" tall tire is 84.8" around; the 24.7" tire is 77.6". So the smaller tire travels 91.5% of the distance of the larger one per rotation. The rpm needed for 65mph on the larger tire will only get you going 59.5mph on the smaller tire. So you need to be aware of that speedometer error, though it goes to the "safe" side for tickets. But the smaller tire effectively gears you for 8.5% more torque at the ground - it's like changing the 3.73 ring & pinion for a 4.08. With the shorter tire, you'll accelerate faster but have to shift sooner. That's the math of it.

I don't think most folks swap springs because of the wheelwell gap. Most of us probably don't even care about the gap if it doesn't affect lap times. I think the spring swap happens because it's relatively easy to do and should improve lap times.
 

xr7

TMO Addict?
492
515
Exp. Type
Autocross
Exp. Level
5-10 Years
Minnesota
After reading this thread and many others, I thought I'd ask the following question on overall tire diameter in this thread and not create a new one...

After 2 yrs of TNiA's (approx 14) and 4 PDE's at my local track with factory 19x9 / 9.5"s, I am making the next step to a track-only set of wheels / tires. My 012 is stock and I have no plans (at the present time) to upgrade the factory front struts. Maybe in a few years.

After lots of reading, I am leaning towards a square set-up of 18x10 wheels. I'd like to go with 285's. 285x30x18 tires seem fairly common and 285x40x18 tires don't seem to be as common. I'd like to go with Falken RT660's but the 285x40x18 is not available.

My question is..how big of a deal is it going with a 285x30x18 which has an approx overall diameter of 24.7"? My factory size tires are approx 27" dia. as would a 285x40x18 be approx. 27" dia. I understand the handling benefit of an aspect ratio of 30 vs 40 and I get the final drive ratio effect, but a 2" dia difference seems like a fairly big difference.

Lastly, I'm running stock Boss springs. I don't care how it looks, but I was curious about the 1" larger wheel / fender gap. Is it pretty much a given that when one goes to track tires, they at the same time go with the Ford Racing Boss springs or other lowering springs?

I appreciate any and all comments / advice.

Thanks.
I'm have Falken 295/40-18's on my car. 18x11 Apex wheels, 19mm spacers on the fronts. Stock struts and shocks, I have Ford Racing Springs, T's I think, would have to check to be sure. Vorshlag caster/camber plates. I went 18x11 so if I ever go to 315 rubber I won't need new wheels. Buy once, cry once? Also if I go to 315/30-18 tires I would probably need to change the rear axle gears. I have 3.73's and I rarely have to use 3rd, mostly run 2nd and 1st autocrossing. I don't need any more torque in first as I can break the tires loose pretty easily but loosing 5 mph at the top of second would probably put in 4 more gear changes per run, don't need that. I did buy an appropriate Black Friday gift for the Boss, 4 fresh Falken 660's, 295/40-18's. Should be arriving Friday.
 
4,384
4,775
FWIW and has been alluded to bhut not exactly mentioned, there is 2 ways to get contact patch, one is by simply widening the tire, the other, is by running a taller tire. Now that can create some other issues, such as a taller (I hesitate to say larger) side wall can also affect spring rate, this is why a lot of race tires actually have their "spring rate" published (to give engineers something to do) and to give racers the ability to adjust their suspension between tire sizes and pressures.
 
42
22
Exp. Type
HPDE
Exp. Level
Under 3 Years
Pittsburgh PA
Circumference is Pi times diameter. The 27" tall tire is 84.8" around; the 24.7" tire is 77.6". So the smaller tire travels 91.5% of the distance of the larger one per rotation. The rpm needed for 65mph on the larger tire will only get you going 59.5mph on the smaller tire. So you need to be aware of that speedometer error, though it goes to the "safe" side for tickets. But the smaller tire effectively gears you for 8.5% more torque at the ground - it's like changing the 3.73 ring & pinion for a 4.08. With the shorter tire, you'll accelerate faster but have to shift sooner. That's the math of it.

I don't think most folks swap springs because of the wheelwell gap. Most of us probably don't even care about the gap if it doesn't affect lap times. I think the spring swap happens because it's relatively easy to do and should improve lap times.
I get the final drive ratio smaller tire effect and could see how that would be good in Autocross.

Curious of opinions of those running full track / time trials with 285x30x18’s and their thoughts on overall drive ratio on the higher speed stuff.
 
4,384
4,775
Because most autocrosses are insured by companies like KnK insurance, they only allow a maximum speed limit of 60 - 70 mph, which makes most autocrosses a point and shoot affair. If I could, I'd run 4.88s in the diff , to match the longest gear in the trans, and the engines power band, then never shift
 

xr7

TMO Addict?
492
515
Exp. Type
Autocross
Exp. Level
5-10 Years
Minnesota
Because most autocrosses are insured by companies like KnK insurance, they only allow a maximum speed limit of 60 - 70 mph, which makes most autocrosses a point and shoot affair. If I could, I'd run 4.88s in the diff , to match the longest gear in the trans, and the engines power band, then never shift
Most of the autocross I attend is run at the track at Dakota County Technical College near Rosemont Minnesota. The autocross courses can be configured in 100's of ways. I don't think I have ever run exactly the same course there. If you Google the college and zoom in on satellite you get a good look at the track. They do trooper training and truck driver training at this site. The pavement is old, mostly asphalt with one three lane stretch of concrete. Elevation changes, off camber transitions and off track is highly discouraged. 4 wheels off twice and you are done for the day. Even with the RPM range on the Boss 302 some course set ups require first, second and third gears for the best times. Some course setups favor the Miata's, some the Corvette's. I like running there vs the usual parking lot courses. Throwing in some gear changing adds to the challenge. My friend runs a '19 GT350 and with the slightly taller gearing and added rev range he only needs 1st and 2nd. The tight hairpin turns that show up in the courses require a drop to first to get thru and out of quickly, speed is too low for 2nd, acceleration is king. Length of course is also another advantage at DCTC. Shortest around 3/4 mile and longest maybe a mile and a half.
 
4,384
4,775
Most of the autocross I attend is run at the track at Dakota County Technical College near Rosemont Minnesota. The autocross courses can be configured in 100's of ways. I don't think I have ever run exactly the same course there. If you Google the college and zoom in on satellite you get a good look at the track. They do trooper training and truck driver training at this site. The pavement is old, mostly asphalt with one three lane stretch of concrete. Elevation changes, off camber transitions and off track is highly discouraged. 4 wheels off twice and you are done for the day. Even with the RPM range on the Boss 302 some course set ups require first, second and third gears for the best times. Some course setups favor the Miata's, some the Corvette's. I like running there vs the usual parking lot courses. Throwing in some gear changing adds to the challenge. My friend runs a '19 GT350 and with the slightly taller gearing and added rev range he only needs 1st and 2nd. The tight hairpin turns that show up in the courses require a drop to first to get thru and out of quickly, speed is too low for 2nd, acceleration is king. Length of course is also another advantage at DCTC. Shortest around 3/4 mile and longest maybe a mile and a half.

You're very fortunate, all the auto X around here are in parking lots.
 

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