Rear Tire Traction

[541 SC]

I am fairly new to posting on this site, but I have been visiting and reading a lot for a few months and I have gotten a lot of good info from here.
I would like to get your input on rear tire traction in general on Cobras, and more specifically ERA's. I would especially value the input of Cobra owners with 650+hp and 600+ ft*lb engines. Do you find that you have addequate traction to put all of the power you have to the ground? Obviously excepting burn-outs and acceleration during hard cornering. I'm talking about when you are going in a straight line and you punch it, or drag racing. Some tire slip can be expected, but if you send the tires up in clouds of smoke, that is counter productive to going fast! I'm trying to determine to how much power you can actually get to the pavement under normal conditions using good high performance street tires. My ERA has 315/35/R17 BFG G-force T/A KD tires in the rear. For those familiar with ERA's, I have the outboard braked IRS suspension, with Jag limit slip diff. I want to get an idea of how much power will be usable and beyond what level is extra power a waste. Also what do you feel is a good balance between bottom end torque and high RPM hp? Having lots of low RPM torque makes a good drivable steet car, but how much is too much? At what point is it better to trade excessive low RPM torque for higher RPM hp?

Roy

[RedBarchetta]

Roy, I think this is a really good thread, as I have similar questions/concerns. I've driven high horsepower straight axle cars and ones with independent suspensions (i.e. Corvette).

My experiences with the former (straight axles) is that they tend to stay in a straighter line under brutal acceleration (i.e. less fish tailing). And when they do fish tail, a little less pedal ('back pedaling") usually straightens them out.

But my experiences with the 'Vette (late C4 design) are just the opposite. Power shift into second or third (at speed) and this car will literally "lurch" up to one entire lane to the left. A very uncomfortable feeling if you're not anticipating it. Perhaps some stiffer bushings on the trailing arms ("dog bones" for enthusiasts...I call it the four link portion) would correct this condition? And if that's the case, then perhaps the same medicine can be applied to a Cobra IRS?

-Deano

[Excaliber]

If I read an old thread correctly Clois Harlan (B&B with 428CJ and 4 speed top loader) was coming out of the hole in THIRD GEAR at the 1/4 mile Run and Gun recently. This was faster in the 1/4 mile than using first and second.

Down side is, it took out his clutch.

Several other guys have mentioned "short shifting" to second gear right after the "launch", or even using 2nd gear to "launch".

Bottom line? Impossible to "hook up" the torque of a big block without drag slicks at low speeds or "hole shots". It is worth noting the 289 Cobra's were very close to the 1/4 mile times of the 427's!

Even today you could make a STRONG case for a small block being more effective in the "real world" than a big block. Especially when your talking street tires! Horse power is not everything, hooking up the h.p. is everything!

Ernie

[xlr8or]

It's torque that gets you down the road.

How can you possibly understand the limit without going past it.

It's all in the application of the torque curve. Once you get good at putting it to the ground without over doing it there is nothing like the low end torque of a Big Block IMHO.

Let the debate begin.

[TerrysSPF]

.........Look out, but I think this is turning into another BB vs. SB thread!

Roy: Ernie was right on with his post. The 1/4 mile times of the 289 were very close to the 427 times, and it was mainly due to traction issues. You are already way ahead of a lot of us here, by going with the 17" tires and higher performance rubber (that is widely avail at that size vs. 15" tires). Your next step is to try and find the right "balance" for getting out of the hole and "hooking up". .........Nothing more fun than a little trial and error! :-)

[Excaliber]

The question is:

What kind of STREET tires would your run with 600 hp to be able to put that h.p. to the ground?

Answer:
Your kidding right? This can't be a serious question?

Ernie

[xlr8or]

If a 1300 lb dragster can put 2500+ HP to the ground and pull a sub 5 second quarter there is no reason a 2200 lb Cobra can't put 600 to the ground. Some sticky 17's or even the old BFG's aired down for the light car do pretty well. It's in the tire and suspension setup. Of course if you setup for drag racing it is not going to handle the twisties as well as it could.

While yes you can spin the tires when you want with a 600 HP cobra you can also put it to the ground pretty damn well with street tires if you are setup well and learn to work it.
I personally like the 20-80-20 MPH range and find that to be the fun range for a street car.


Oh yeah, Welcome to the insanity Roy.

[Rick Parker]

Ernie:

If you had a little more HP in your avitar it could grab 4th gear too! (Or a you running a 3spd??)

[Excaliber]

Hey my avatar IS a four speed, but I'm launching in 2nd gear!

,,,,,(with a small block and slicks)

Ernie

[trularin]

I sellected a small block for weight and to avoid the "wallow" effect a Big Block has on such a light car.

Just my $0.02

[GOCATS]

Roy, I guess one question that has not been asked was what was your objective when you bought the car i.e. racing SCCA, taking out to the strip, having a street legal can of whoop A$$, or what. I don't want to turn this into a BB vs SB because that is not what you are asking about. I think this is one of the inital questions that needs to answered. As with any of these car a little right foot moderation can make the difference between winning or losing and 1st or 2nd place.

[Cracker]

I'm not aware of any street tire that is going to "hook-up" even in a straight line with that kind of power. Mine break lose with the SOFT compound Goodyear racing eagles in 1st & 2nd and I have 550 hp & 500 lbs. trq. - it isn’t going to happen! I've heard from a few knowledgeable folks that anything really over 500 hp is as much as the original chassis is really designed to handle gracefully - if you can call a Cobra under any circumstance "graceful". I could argue that threshold is a tad low but the driver’s skill is always the trump card. As Richard Huggins(?) of JBL wrote in past thread of similar topics, "if the best drivers in the world were racing the originals with 525 hp and had their hands full what makes the rest of us feel we should/could get away or even utilize the same or obscenely more?". He has a point and believe me if 300 hp can kill you - 600 hp will take half the time!!!

[jrussell]

Roy,
I have a 460 at around 540 hp +/- at the flywheel, approx. 430 at the ground, and I have a 8.8 rear end with 3.73 gears and a Tremec TKO 5 speed. I also am running 17" wheels, with 335/37/17" Michelin Pilot sports, which gives me 13" tread width on the ground. In 2002 at the Shelby Mid- America in Tulsa in June I made 2 passes at the Drag strip, with outside temp at 97 and the track at about 135! The track was "greasy" for about 100 feet or so and traction was terrible on street tires. I pulled the rpm's up to just a bit over 1000 at launch and just rolled into the gas and shifted into second as quickly as I could. I could feel the car really start to hook up at about 4500 in second and it just lept forward. I only got in two runs, with a best of 12.31 at 117.8 mph. I raced all day before at Hallet on that reack, and the only changes I made from road racing trim were to lower the rear tire pressure to about 16# and increase the fronts to 40#. I do not trailer, but drove the car to/from Hallet and to/from the Drag strip.
I think a launch in 2nd. gear will be what I do the next time I get to a Drag strip if I have the 17's on, OR put my 15's back on as I have bought a set of Drag radials that should help get the car get off the line and should get it into the high 11's.. which will be good enough for me.
I hope this information will help you a bit, and since I just replaced the 335/35/17 Michelin Pilots yesterday ($766) I think I will save those for daily driving and track use, and use the purpose built BFG Drag radials on the Drag strip( I have the 295/60/15's- and if the larger 325/50/15 has been available then I would have bought them).
John Russell

[Karl Bebout]

John, I've got the BGF 325/50/15 Drag TAs on my car and find that they work better if I lower the pressure down to 16-18#s and heat them up before trying real hard. My car is just under 2700 #s with my large body in it and the engine dyno'd out at 552 HP @ 5400 RPM and 596#s @ 3400. These are flywheel numbers and I'm sure I'd probably lose at least 12-15% by the time it gets to the rear wheels. Still, pretty perky, and real nice for the street. I can't hit full throttle until I roll out a ways and second gear usually stays fairly straight. Definitely some gas pedal feathering is used.
I'm running a Hughes TH 400 with their 10", 3200 RPM stall convertor. The rear is a 9" Ford live axle, 3.50, Powertrax, four link, coil over set up, with the pinion angle about 2* negative. The additional torque multiplication from the smaller convertor only adds to the joy and although the car is not strictly set up for either the track or the strip, it sure makes me smile on those little trips to the grocery store. The car won't pass tech at the strip so I've never been able to make any passes. ( no roll cage, 5 pt harness, trans blanket, drive shaft loops, etc) Probably just as well. I know I'd just have to do whatever it took if the car didn't get at least well into the 11's. I'm blissful in my ignorance.
Good luck with your new tires.

[jrussell]

Karlos,
Wow!! Your car really sounds like fun, and pretty close to my setup. I do believe a well set up automatic is truly the way to go for the best Drag race setup. I will definitely go with the 325's when I go through this set of Drag radials, but it is interesting to see that you also have the 1st/2nd problem in getting hooked up.
I couldn't imagine your combination not getting well into the 11's!
Have fun, as I know you will
John Russell

[541 SC]

Thanks to all who have given their input. I would like to hear from anyone else who has an opinion as I value many different view points. It was looking like this might turn into a big block vs. small block "discussion", I'm glad it didn't. To answer a couple of questions, I want my Cobra to be a very powerful all around car. Mostly for street use, but I do plan on taking it to some open track events, and occasional drag an autocross use. I am willing to trade off some handling for the power and sound of a big block. I agree that for pure drag racing a well set up automatic is best, but I want to shift the gears in my Cobra, so I'm using a Richmond 6 spd. Having the O.D. will be nice for cruising. As far as need or practicality, I don't think those words really apply to Cobras. Who really needs a Cobra with any amount of power? Practical?......Please! Cobras are all about wants. Having said that, the point about professional drivers having difficulty handling the original cars is well taken. Just about any Cobra needs to be driven judiciously if one wants to stay above ground a while longer. I am of the opinion that just because you have mountains of torque and hp, doesn't mean you have to use it all the time. On the other hand, having more power that you can really put to the pavement, doesn't not help you. I would consider getting a set of drag radials or slicks for drag racing, if I got into that more seriously. Of course that increases the chances of breaking a diff, U-joint, or axle. Can a Jag rear end and half shafts handle all of the power that can be put to the ground with street tires before they slip? This is without dumping the clutch at 6000 rpm in 1st.
Another issue is safety and track rules. I am not well versed in drag racing safety rules. Mostly written by the NHRA I believe? I know most drag races and tracks require certain safety equipment (i.e. roll cages,etc) if you run under a certain time. Although what I have seen of events like Run & Gun there seems to be Cobras that run in the 10's with little more than a helmet, standard roll bar, and racing harness. These articles never talk about required safety equipment, but that doesn't mean there isn't any. Is there places and events that a Cobra can run in the 11's or 10's in just the standard S/C trim (i.e. roll bar and harnesses)? Obviously the driver is accepting greater risk by doing so.

[coyled]

541sc, no, if your under 12.00, the standard cobra roll hoop is not enough at most drag strips. If you truly have 650hp, it won't hook up well with street tires until your above 50mph. The bfg drag ta's work pretty well, I have used them. On the track, get slicks and it will hook once you get your damper and spring rates right. Good luck, Scott.

[scottj]

Here are a few things I’ve learned for the track running that much power with 13” Hoosiers, 3.54 gears, and a Richmond 5spd. To start with, I need to run the rear percentage in the 55-56% range. I also need softer rear springs and stiffer front springs (with matching shock valving) than would be optimal for maximum skid pad performance. I need the smallest rear bar available for my chassis.

This set-up will get full power down in 4th while 3rd takes a little throttle modulation off corners. With 335/35-17 street tires and 58% rear it, it will spin the tires some from a 3rd gear roll-on and continue spinning slightly in 4th. I can’t hook up 1st or 2nd at all with either tire and I’ve never run a drag slick to compare.

Re: "at what level power becomes a waste" and "bottom end torque vs. top end HP". If I were to do another engine I would reduce the stroke from 4” to 3.5”(380cid) to lose some of the bottom end torque and turn more RPM. I would build 700hp with around 550 ft/lbs torque, making it more usable than what I have now. With less torque and more rpm(hp), I could balance the chassis for better handling and improved laps. In my opinion the throttle should be an asset not a detriment to good laps.
Scott

[541 SC]

Scott,
Do you like your 1st gear ratio in your Richmond? Assuming that you have the standard 3.28 Richmond 1st. I have read other posts suggesting it is a little low for a Cobra's power to weight ratio. I am planning on using a 3.04 1st in my 6spd, along with 3.07 rear gears to keep the RPM's down in 6th. I want to be able to cruise at 70mph at about 2200 RPM. The 3.04 1st narrows the split between 1st and 2nd to be more in line with the 2nd to 3rd split. It sounds like not having enough power in 1st to get off the line is not a problem, and a little taller 1st should be a little more streetable with a lot of torque. What type of rear diff/suspension do you have in your EM?
What you said about crank stroke is exactly the info I'm looking for. I'm trying to decide on what stroke to go with in my big block. I think I should go with a shorter stroke, that will set the engine up for higher RPM and drop off the torque a little. That is why I was trying to get some idea of how much torque you can expect to get on the ground with a typical Cobra. Torque makes the car go, but it also sends the tires up in smoke! There is to much of a good thing.

Roy

[LETSRCE]

I have a 514" 429 in my SPF making 550 RWHP and 618 RWTQ.
With the TKO trans and 3:73 gears anything past 1/2 throttle in 1st is all tire spin, 2nd is about the same and if your not careful 3rd will spin pretty good. I have 295 BFG's. It's all about finese.
I can blow the tires away in 4 gears screwing around but I can also drive the thing were it hooks up. Like rolling in to the throttle in 1st,2nd & 3rd gears. I'm going to change my rear springs to 343# instead of the 400# the cars come with to try and help plant the tires. My motor makes most of it's TQ from 1800 rpm to 6200 rpm, I find myself shifting off the rev limiter more than I like as the motor rev's very fast.