Traction?

[Jimtmich]

So with the FIA body requiring smaller tires, how does everyone feel about the traction they are getting? Are you getting enough? Do you feel like you are driving rolling artwork and cannot enjoy the car?

Possible configurations:

245/60/15 Front 275/60/15 rear
Avon CR6ZZ Radial vintage DOT approved sticky racing tires. This is probably the perfect tire if you want the 15" look but your going to be into $1,700 for a set of tires.

Hoosier Quick Time DOT drag tires are DOT approved and sticky, but bias ply so they might not track as well, Look fantastic like the AVONS and only about $840 from Summit.

Mickey Thompson S/R radials. I cannot tell if there is a good match size wise

Cooper Cobra and BFG Radial T/A are fine tires but I gather they shouldn't be pushed as they aren't really High Performance tires

17" offers a lot more selection
Any feedback here on plenty of traction available with modern Extreme Performance or High Performance tires?

I'm still trying to decide what to build, so many compromises....

Thanks,

[Jim1855]

I've never run a tire that provides sufficient traction, acceptable but never enough. 275 & 315/335 17s, still not enough. Goodyear GS-D3s, Sumitomos, Vredesteins, Michelin PS2s, still not enough. BFG R1s might be OK and Hoosier R6/7 are good but you can still overpower all.

Wouldn't run drag radials, they aren't designed for corners.

The Coopers and BFGs look like tires. I have friends that run the MT S/Rs, they seem to like them but run them as wide as possible and run street not track. You'll still overpower them.

The Avons get great reviews and would be my choice if I was planning on or had to run 15s. You'll still overpower them.

Modulating the skinny pedal is the key.

Happy to help another Michigan guy.

Jim


What prompts you to be concerned with FIA regs? Will you be racing under their rules?

[GoDadGo]

Jim,

The traction question can get a bit messy as the other Jim has stated so here are some stupid question from yours truly:

1. What is the intended use of the car?
2. How much horsepower and torque do you expect do be making?
3. Are you a Lead Footed Tire Burner or a Cool Daddy Cruiser who likes to light them up on very rare occasions?

From my perspective the power to weight ratio and use really dictates the tire selection. I'm a real fan of the 15 inch wheels, but compromised with 17's to get a better selection. I'm running 245/45-17's up front with 285/40-17's out back to give me the tallest sidewall possible.

Shown below is my Red Gel-Coat Cruiser:

https://youtu.be/CaRlqMmKIzk

[mike223]

What prompts you to be concerned with FIA regs? Will you be racing under their rules?

He's talking about the reduced tire / fender clearance on Mk4 289 USRRC kit as opposed to the Mk4 roadster - I think.

"Street" tires I've had pretty good luck with for the price:

R888, NT05.

I found the much maligned Sumitomo to be a pretty reasonable street tire, especially at the price point - but they certainly don't offer the grip of NT05s or R888s - definitely requires some operator adjustments due to "less grip".

But I'm not sure how you could wear the (300TW) Sumitomo out before it ages out (excepting major abuse).

Modulating the skinny pedal is the key.

Learn this and you will always be "one of the most agile" cars anywhere - because you're the lightest + fastest and have the most tire - comparatively.

[chuckster]

I’ve got an 289 FIA with a 306 putting out 330 RWHP and 320 TQ. Tires are FRT 245/45 17s. RR 275/40 17s. I’ve yet been to 1/4 mile the car, but I can light them up when I want to no problem. I can also accelerate like a rocket sled without any tire spin, depending on what I do with my feet.

[CobraboyDR]

I’ve got an 289 FIA with a 306 putting out 330 RWHP and 320 TQ. Tires are FRT 245/45 17s. RR 275/40 17s. I’ve yet been to 1/4 mile the car, but I can light them up when I want to no problem. I can also accelerate like a rocket sled without any tire spin, depending on what I do with my feet.

(On my soapbox)

I am constantly amazed about how many people don't understand what horsepower and torque really are.

Anything over 400hp in a 2300lb. car is nearly absurd and makes these cars more than a handful to operate on the streets safely. Especially in damp, wet or cold tire conditions.

I know, I know, some people can do it. Some can launch on dragstrips and go straight. Most can't. And overall it is not nearly as enjoyable to drive a Cobra with huge power vs. one that is under 400hp. It's like shooting a .50 Desert Eagle vs. a slick 9mm.

Carroll Shelby himself has stated a 289 slab side was much more fun to drive than any 427 was, and they had what? 271-320hp, depending?

You can't put enough tire on a 450+hp 2300lb Cobra to ensure traction.

My SPF had a 525hp/535tq side oiler in it, and weight 2450lbs wet. I had to make sure it was lined up straight before slamming the skinny pedal, less my rear view mirror became the front. Yes, fun, but I knew I had to be much, much more careful lest a bad outcome would certainly result. Too much throttle or too little clutch and squirrelly didn't define it.

My first Cobra, a 2350lb. CMC, had a 350hp 351w. Bubba, lemme tell you: it was stinkin' fast, and actually more fun to drive hard because I didn't have to worry much about being overpowered when I didn't want it. And my butt dyno couldn't tell all that much difference, friends and wives and girlfriends couldn't notice a big difference, and folks sharing the road couldn't tell, and priests still prayed they'd survive when I got it on.

We built an SPF for a guy who wanted a 570hp/600tq 460 crate motor in it and could not be persuaded otherwise. Besides being literally impossible to change spark plugs without raising the engine, It was also nearly impossible to adequately control that car, and last I heard he scared the bejeezus out of himself with the wifely babe as co-pilot, and it ended up just sitting in his garage.

We built an SPF for a guy with a 375hp 351w crate motor from Ford. An absolute blast to drive. There is nothing like a 6-7000rpm screamer. Loved it.

We built a nice SPF roadster, no side pipes, scoop or rollbar, with a strong 375hp 428PI, lots of torque. Very, very pleasant car to drive on the street, with more grunt than a sane man would want when you added some serious throttle.

IMO, the "sweet spot" for power in one of these cars is 350-400hp from a small block, a .64OD Tremec and 3.73 gears. They are light cars so gobs of torque isn't necessary to launch. They'll wind past 6000rpm. The 3.73 give a fantastic stoplight-to-stoplight performance, and the .64OD allows relaxed highway cruising at speed.

The only problem is the original 427's had FE's in them, and the small blocks seem a little out of place in a 427 replica.

(Off soapbox)

[Jimtmich]

Thanks for the feedback guys!
Yes, I’m planning on building a 289 Usrrc ffr mk4 an am trying to decide that key component, wheel size as so much depends on this.
I will not be racing but could see some auto cross and track days when life allows down the road. I definitely enjoy spirited driving, have been driving mustangs as daily drivers for 30 years. The latest is a 14gt, just a phenomenal car!
What I have to determine is how much rolling art I have to sacrifice to get a performance that is equal to or better than the 14 GT.
I would like to build a replica of csx 2000, but realize I will have to compromise on looks to meet performance and drivability goals.
I would really like to stay with 15”, willing to give up the fia knock offs and run 15” hilabrands to get the irs.
Hp goals would be similar power to weight ratio to the 14gt so 350 flywheel. Would enjoy a period engine compartment. Probably roller 302, heads, cam, Holley snipper hiding under the chrome round air cleaner. Not ready to do floor mounted pedals and fiberglass foot boxes at this time due to lack of free time.

If I should go 17’s I would probably us an f150 coyote and get to use the free brakes from the salvage yard 2015 irs.

[GoDadGo]

Jim,

My HP/Weight ratio is some place around 1.0/5.0 and the car is a tire shredder at roughly 450 HP with similar torque figures running 3.73's gears out back.
An acquaintance of mine has a nearly identical MK-4 (Professionally Built By Mike Everson) and makes about 350 HP with a 331 SBF (4.030" X 3.25") with 3.55's.
With a HP/Weight ratio of roughly 1.0/6.3 his car is fast, but far more manageable to drive than mine but he still needs to pay attention to the gas pedal in 1st and 2nd.
Your 2014 GT has a ratio of roughly 1.0/8.6 and the computer's stability programming is likely holding that Coyote back a lot more than you think.
The only things I'd suggest if you are going to Auto-Cross the car is to add power steering, hydro-boost power brakes and sticky very tires.
The lack of weight really gets these cars start spinning their wheels a lot quicker than you can imagine.

Good Luck From The Dark Dart Side!

Steve

[NAZ]

When it comes to traction there can never be too much. When it comes to power, too much is just enough.

[ehansen007]

I wanna reference an article I've been reading over and over for the past 4 years. It's an article in Road and Track based upon a quest to find the ultimate sports car. The narrowed down a group of legends of their time.. of a group that included a 67 911, a MG TC, a 300SL, an 88 BMW M5, an 01 Acura Integra, a 20 Mazda Miata, THE 95 Mclaren F1, and a little 289 Cobra. I'll spare you the suspense, the 289 won by a unanimous vote of the editors.

Mind you, these are people who have driven everything over the years and in that moment they picked the smallest of the Cobras as the greatest sportscar, Ever. The 427 wasn't even mentioned. The car was CSX 2230 and had over 110K miles on it with only two owners. With only 270HP and skinny little Pirelli P600s the editors talked about how friendly it was, with a wide torque curve and ease of use. The best quote however came from the Porsche-file whom everyone swore would stay with his tribe- "Holy $hit," he laughed, Best thing ever. This is hard to believe, but I can't even come up with the words for it. You could do 1000 laps in it."

So with that I leave it to you to decide how much traction and HP you really need to have a good time and get around the track or the neighborhood. The rest is just talk. This mantra literally motivated me to build another 289 but one that will be a lot more fun to drive. Even the BP 302 with 350HP I bought might be a bit much along with the sticky Blue Streaks I might buy. Then again, I might just detune it with some Cats and put some smaller Mickey Thompson's on it just to keep it real; even though my 18yr old son wanted a big block and the biggest tires we can find. We'll see. LOL.

[gbranham]

I've had a lot of cars over the years that would shred tires, and the best tire I've had, bar none, is the R888. Downright sticky. I am building my MkIV with R888Rs. Sure, I can't drive on them when it's under 40 degrees or they'll crack, but that's OK. I know when it's warm out, they'll help with traction immensely.

Greg

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