[Jay S]

Probably the one of best overall combinations of traction, handling and adverse weather is the Avon CR6ZZ (275/55R15)road coarse tire. Tread wear is 80, and has a A rating for wet surfaces. Crazy expensive, but also the closest tire to cover traction on all surfaces..

I like the M&H drag radials for similar grip to the Mickey Thomson ET, not as good as the R’s or the Hoosier’s options, but do better on wet surfaces (but still scary). I think they look the best on our muscle cars also.

IMHO…Best bang for the buck stepping into a softer tire from the hard tire offerings is a Nitto. Best value above that for a sticky tire is the M&T ET. If price is isn’t a factor, then M&H or Avons. All out dragstrip traction, M/T E or Hoosiers.

[JLMounce]

Originally Posted by jhein

Thanks for all the replies. All very good. So it seems like street tires of any sort won't really solve this. Suspension changes would help but with potentially significant mods. Caltracs would be a fairly minor modification that's reversible. But since my car is street, not strip, just wondering how that would impact other street driving behavior, especially cornering? They say it's not compatible with the factory sway bar. It seems like if you trimmed the ends it would fit. Is there any other reason not to use the Caltracs and the sway bar? Does the Caltracs have anti-sway properties?

In general, the modifications and add-ons necessary to make a leaf spring work for straight line traction reduces it's handling prowess.

The problem with leaf springs is that they act as the suspension forward links, lateral movement control and a spring all in one. They actually do a pretty damn good job of being a jack of all trades, up until the point that they don't.

I've never run one, but theoretically, running a watts link or panhard bar with your leaf setup may help straight line traction. It takes one of the jobs away from the leaf springs and in doing so, allows the leaf to be a better spring and a better link. The propeller bolt of the watts link also takes over as the roll center (at least until bind occurs) and that is really helpful when it comes to putting power down on corner exit. If you look at vintage TA style race cars that are required by rules to run their original style leafs, almost all of them will have a panhard bar or watts link installed as well.

A Fays 2 Watts link is a completely bolt on deal and is reversible. I don't know that it's going to be as good as a cal-trac and it's certainly not going to be as good as a 4 link or torque arm.

I will say that most of the 4 link kits available are going to largely be reversible as well. The Ridetech system bolts the cradle to the frame rails and does not require physical welding to the car. Just a couple tabs that get welded on to the top of the axle tubes. This is fairly easily reversible if you're worried about that.

If you decide to go to larger wheels, that opens you up to a lot more tire options, specifically tires designed for autocross. The Falken Azenis RT615K+ is a 200 tread wear tire that will provide quite a bit more grip than what is available in 15" sizes. I had these on my previous 17" wheels and traction was really good. They aren't as comfortable as the NT555G2's are, but it's a competition tire with stiff sidewalls...some trade-offs are always necessary.

I recommend that tire, specifically because it's designed to last a bit longer. There are autocross tires with more stick, but they'll wear faster.

[jhein]

Originally Posted by JLMounce

In general, the modifications and add-ons necessary to make a leaf spring work for straight line traction reduces it's handling prowess.

The problem with leaf springs is that they act as the suspension forward links, lateral movement control and a spring all in one. They actually do a pretty damn good job of being a jack of all trades, up until the point that they don't.

I've never run one, but theoretically, running a watts link or panhard bar with your leaf setup may help straight line traction. It takes one of the jobs away from the leaf springs and in doing so, allows the leaf to be a better spring and a better link. The propeller bolt of the watts link also takes over as the roll center (at least until bind occurs) and that is really helpful when it comes to putting power down on corner exit. If you look at vintage TA style race cars that are required by rules to run their original style leafs, almost all of them will have a panhard bar or watts link installed as well.

A Fays 2 Watts link is a completely bolt on deal and is reversible. I don't know that it's going to be as good as a cal-trac and it's certainly not going to be as good as a 4 link or torque arm.

I will say that most of the 4 link kits available are going to largely be reversible as well. The Ridetech system bolts the cradle to the frame rails and does not require physical welding to the car. Just a couple tabs that get welded on to the top of the axle tubes. This is fairly easily reversible if you're worried about that.

If you decide to go to larger wheels, that opens you up to a lot more tire options, specifically tires designed for autocross. The Falken Azenis RT615K+ is a 200 tread wear tire that will provide quite a bit more grip than what is available in 15" sizes. I had these on my previous 17" wheels and traction was really good. They aren't as comfortable as the NT555G2's are, but it's a competition tire with stiff sidewalls...some trade-offs are always necessary.

I recommend that tire, specifically because it's designed to last a bit longer. There are autocross tires with more stick, but they'll wear faster.

That Falken tire looks fantastic but I don't see a size that will work for me.

[Gator67]

I wanted more handling/cornering capability and the lack of good 15" tire choices eventually led me down the pro-touring path. I tried higher quality 17" on my 70 TA, which was an improvement, but when the car was pushed hard, weaknesses of the factory suspension became more apparent. Rather than trying to piece together something that might work better, I went with engineered front & rear suspension systems when we built my 70 Formula (Detroit Speed) and my son's 79 TA (Ridetech).

[JLMounce]

Originally Posted by jhein

That Falken tire looks fantastic but I don't see a size that will work for me.

You would be required to move to a 17" wheel or larger to run this type of tire. You should be able to run a 9" wide wheel in the back, you'd run a 275/40/17, which is close to a 26" tall tire. If you can only run an 8" wheel, you'd run the 245/45/17 which is the same height.

I put this together quickly on my lunch however. It's a "good enough" plot of the anti-squat line on my car. If you know your total vehicle weights and front and rear weights it's fairly easy to plot.

My car weighs 2000 lbs on the front and 1402 lbs on the rear for a total of 3402 lbs. My car has a measured wheel base of 107". If you take 1402 x 107 you end up with 150014. Divide that by total vehicle weight of 3402 and you get 44.10 which is inches from your front centerline. This give your your center of gravity position behind the front wheels, but does not give you it's height.

The easiest way to do this and how most people do so is to use the height of the cam. There is a formula to arrive at the exact height but it involves taking weight measurements front and rear, the independently lifting the car 10" front and rear and taking measurements again. For most purposes, using cam height is good enough.

You'll see the CG as the top most blue dot on my car door. The lower blue dot is the location of the forward spring eye on the leaf spring. This is your forward link and where all torque is being applied to push your car.

Now you can draw a line from the centerline of the bottom of the tire, up to your CG and see where your forward link is in relation to the anti-squat line. Notice on mine that my forward link is below the AS line. Not by a lot, but definitely below. This would be a percentage of AS below 100%. Lets' call it 97% here.

What this means practically is that my suspension will allow a bit of squat under power. This increases the suspensions ability to deal with uneven pavement, bumps, or even acceleration off corner. However because the suspension is allowing some squat, available power to the wheels is reduced and some traction is lost.

Notice that with a leaf spring, the physical mounting point determines your anti-squat, unlike a link style suspension. What that means is you can play around with your anti-squat by changing the relationship of the mounting point to the AS line. If you lower the front of the car, this will tend to increase AS. If you raise the rear, especially in relation to the front, your AS will increase.

Drag cars will run AS percentages between 120%-150% or so, depending on the type of suspension, tire used etc. It's not an end all be all here, but it gives you an idea of what you're up against with a leaf. All of this also assumes that you aren't overpowering the leaf and causing axle wrap. The wave that forms in the leaf pack when this occurs loads and unloads the tires. In this situation you'll either blow the tires off completely, or induce wheel hop. That's one of the things the cal-trac is aiding in. It's also adding some separation of the suspension, making it act like it's got more AS percentage.

On a performance street car that cares about more than going fast in a straight line, having AS percentages below 100 is pretty typical. This becomes somewhat neutral and provides off corner traction, braking stability and less oversteer.

Might be worth taking 20 minutes and plotting this on your car. Might be eye opening to see where it is.

[jhein]

Originally Posted by JLMounce

You would be required to move to a 17" wheel or larger to run this type of tire. You should be able to run a 9" wide wheel in the back, you'd run a 275/40/17, which is close to a 26" tall tire. If you can only run an 8" wheel, you'd run the 245/45/17 which is the same height.

I put this together quickly on my lunch however. It's a "good enough" plot of the anti-squat line on my car. If you know your total vehicle weights and front and rear weights it's fairly easy to plot.

My car weighs 2000 lbs on the front and 1402 lbs on the rear for a total of 3402 lbs. My car has a measured wheel base of 107". If you take 1402 x 107 you end up with 150014. Divide that by total vehicle weight of 3402 and you get 44.10 which is inches from your front centerline. This give your your center of gravity position behind the front wheels, but does not give you it's height.

The easiest way to do this and how most people do so is to use the height of the cam. There is a formula to arrive at the exact height but it involves taking weight measurements front and rear, the independently lifting the car 10" front and rear and taking measurements again. For most purposes, using cam height is good enough.

You'll see the CG as the top most blue dot on my car door. The lower blue dot is the location of the forward spring eye on the leaf spring. This is your forward link and where all torque is being applied to push your car.

Now you can draw a line from the centerline of the bottom of the tire, up to your CG and see where your forward link is in relation to the anti-squat line. Notice on mine that my forward link is below the AS line. Not by a lot, but definitely below. This would be a percentage of AS below 100%. Lets' call it 97% here.

What this means practically is that my suspension will allow a bit of squat under power. This increases the suspensions ability to deal with uneven pavement, bumps, or even acceleration off corner. However because the suspension is allowing some squat, available power to the wheels is reduced and some traction is lost.

Notice that with a leaf spring, the physical mounting point determines your anti-squat, unlike a link style suspension. What that means is you can play around with your anti-squat by changing the relationship of the mounting point to the AS line. If you lower the front of the car, this will tend to increase AS. If you raise the rear, especially in relation to the front, your AS will increase.

Drag cars will run AS percentages between 120%-150% or so, depending on the type of suspension, tire used etc. It's not an end all be all here, but it gives you an idea of what you're up against with a leaf. All of this also assumes that you aren't overpowering the leaf and causing axle wrap. The wave that forms in the leaf pack when this occurs loads and unloads the tires. In this situation you'll either blow the tires off completely, or induce wheel hop. That's one of the things the cal-trac is aiding in. It's also adding some separation of the suspension, making it act like it's got more AS percentage.

On a performance street car that cares about more than going fast in a straight line, having AS percentages below 100 is pretty typical. This becomes somewhat neutral and provides off corner traction, braking stability and less oversteer.

Might be worth taking 20 minutes and plotting this on your car. Might be eye opening to see where it is.

Attachment 655598

Very interesting. I'll have to go weight my car and plot that out.

As for the tires, a 25.6 inch tire is pretty small. I know we're talking about performance here but I wouldn't like that look.

[JLMounce]

Originally Posted by jhein

Very interesting. I'll have to go weight my car and plot that out.

As for the tires, a 25.6 inch tire is pretty small. I know we're talking about performance here but I wouldn't like that look.

Yeah I went back and realized you're running a 27" tire. There's only a single 27" tire offering in the Azenis line which is a 295/40/18. So you'd need an 18" wheel, which honestly is a better size currently. There's far more tire options in 18" wheels than there are 17" wheels now.

I'm fairly certain a 10" wheel with a 295 tire is possible on a stock tub 2nd gen, but you'd have to measure it out if you went that route. The problem is that there's no sizing like that available for the fronts.

Honestly, you're in enough of a quagmire here based on the look you're after as well as what you are and aren't willing to modify, that you're going to have to choose between longer lasting street tires that don't provide the level of traction you're after, or drag radials that provide the traction you're after, but need replaced often.

Edit: Completely forgot about these for 2nd gens.

https://www.pro-touringf-body.com/pr...squat-brackets

PTFB and Global West both make an anti-squat front eye mount for the leaf springs. The PTFB version raises the front eye 7/8" of an inch. It will lower the rear about 1/2" further though. Might be worth a call over to PTFB and see what they have to say about your current issues.

[b-man]

Drag or street.

Pick one.

For my Tempest I decided turning corners would be the focus of the build.

18x9 all around with 245/40 and 275/40 tires, will switch the fronts to 245/45 next time.

Previously ran 17x8 steel wheels with 235/45 tires all around. Very nice handling and fun to drive, the short 25.3” tires worked well with the 2.56 rear end and somewhat limited room up front (wheels could have used a little more backspace).

[jhein]

OK. Here's what I think.

1) JLMounce knows more about suspension than I ever will. His insights are amazing and very helpful.

2) I talked to both Caltrecs and Ridetech today and both said their systems would help with wheel hop but not spin. Essentially they both said if you don't have a sticky tire, their systems wouldn't fix that.

3) I watched some videos of the Caltracs system in play and I think it does some stabilization of the rear end that is overall beneficial. It seems to dampen the vibrations in the leaf spring which don't seem to be beneficial to anything.

4) I think I may try Caltracs and see what that does. I wouldn't expect a big change in spin but maybe just having it plant a little better would be good.

[ta man]

I run Caltracs with their split mono leaf and Nitto 555s .It is a good combo for the street. Controllable chaos. If I heat the Nittos up I can roll into the throttle rather quickly with minimum wheel spin.

[jhein]

Originally Posted by b-man

Drag or street.

Pick one.

For my Tempest I decided turning corners would be the focus of the build.

18x9 all around with 245/40 and 275/40 tires, will switch the fronts to 245/45 next time.

Previously ran 17x8 steel wheels with 235/45 tires all around. Very nice handling and fun to drive, the short 25.3” tires worked well with the 2.56 rear end and somewhat limited room up front (wheels could have used a little more backspace).

Yes, maybe I'm trying to have it both ways. As you previously said, I'm more of a "canyon carver". So if I had to pick just one, cornering would be it. Do you think the Caltracs would have any adverse effects on that type of driving?

Your car looks great with either set of wheels on it. Maybe I'm weird but when I see those big wheels on 2nd gen F bodies, most of them just don't look good to me. It's the combination of the thin sidewall and how well it fills the opening. Also wondering about ride quality. As Formulabruce points out with a stock suspension it can be harsh. How do those feel to you?

[JLMounce]

Originally Posted by jhein

Yes, maybe I'm trying to have it both ways. As you previously said, I'm more of a "canyon carver". So if I had to pick just one, cornering would be it. Do you think the Caltracs would have any adverse effects on that type of driving?

Your car looks great with either set of wheels on it. Maybe I'm weird but when I see those big wheels on 2nd gen F bodies, most of them just don't look good to me. It's the combination of the thin sidewall and how well it fills the opening. Also wondering about ride quality. As Formulabruce points out with a stock suspension it can be harsh. How do those feel to you?

Cal-Tracs change the angle at which force is applied to the front spring eye. As power is applied and the pinion starts to climb the ring gear, that force is sent through the cal-trac bar upwards towards the spring mount. This creates separation in the chassis from the suspension, pushing the tires into the ground. It straightens the leaf instead of the minor amount of tilt going on, so as the car is leaning into a corner, you're actually picking up the inside tire. Basically it creates a lot of bind which initially creates understeer as your losing contact patch on the inside tire, then you reach a point where there's too much bind, the suspension unloads and you have snap oversteer.

It's important to note that this happens with leaf springs naturally. Because they are also an axle locator, they tend not to want to tilt. They do a minor amount due to compressibility of the bushings, flex in the shackles as well as in the leaf itself. It's not a lot though and as you take up that bit of tolerance, you get a rising spring rate and an axle that is picking up the inside tire. The CalTrac makes it worse.

It's also why in many situations, leaf sprung cars don't run rear sway bars unless the springs are very soft or there is a very wide and sticky tire in the back.

The CalTrac is of course adjustable and as the lower bar is leveled, it's effect is less. You could of course try a set and play around with them. You could leave them in their least effective state for most street driving and canyon carving, then drop the bar if you know you want to play around with hard acceleration runs.

Really, the cure where leaf springs are concerned here is a leaf that can support the power you're making. You probably need more than a 200 lb rate and the leaf pack should be built so that the second leaf in the pack extends all the way to the eye and is banded there to help control spring wrap. It's probably gonna ride incredibly stiff though.

Edit: An idea I've had in my head is to run a split mono leaf which a heavy enough front section to keep up with the amount of power and of course the lighter rear section to help with ride quality. This type of setup sucks as an axle locator though, so I would employ a watts link to take care of that. That's all theory though and I have no idea how that might actually play out. Considering the cost of a good split mono leaf and a watts, I'm not sure it's anything I'll ever try.

[b-man]

You could run 255/45-18 (27.035”) all around and they’re just about exactly the same height as the 255/60-15 tires (27.047”) you have now. Some black wheels visually don’t look all that big and they’re a nice contrast on a white car. It’s the giant size honeycomb and Rally II wheels that look visually huge because of the silver color.

Of course when you get rid of that tall squishy sidewall of a 60-series 15” tire and go to a 40 or 45-series 18” the ride will stiffen up. But fhen your T/A will start to handle like it should.

Another bonus is the 18” wheels allow you to upgrade to 13 or 14 inch brake rotors. 14” and 13.4” C6 Z06 on the Tempest. Can’t have enough braking.

I can’t say whether or not Cal Tracs will help or hinder handling but suspension mods intended for drag racing may not be what you’re looking for and may cause a harsher ride.

[jhein]

Originally Posted by b-man

You could run 255/45-18 all around and they’re exactly the same height as the 255/60-15 tires you have now. Some black wheels visually don’t look all that big and they’re a nice contrast on a white car. It’s the giant size honeycomb and Rally II wheels that look visually huge because of the silver color.

Of course when you get rid of that tall squishy sidewall of a 60-series 15” tire and go to a 40 or 45-series 18” the ride will stiffen up. But fhen your T/A will start to handle like it should.

Another bonus is the 18” wheels allow you to upgrade to 13 or 14 inch brake rotors. Can’t have enough braking.

Well, now that you have me talking about 18" wheels, for the rear I could run a 275/40/18 or if it would fit a 285/40/18 which are 26.7 and 27 inches respectively. Also, Nitto makes drag radials in those sizes.

Edit: and they do make 18x9 wheels in a Rally II style....

[76TA462]

On my second gen TA I ran with the Nitto NT01 on the rear with 15-inch wheels and really liked them but needed to go the larger wheels for a brake upgrade. I now run the NT555 G2 all round. 245 45 18 (8”) up front and 285 40 18 (10”) rear. Very happy with the street performance, but I can still spin them easy - they are still street tires but are better than lots out there. No mods for the 285s other than moving the seat belt bulge in. I get the 27” height I want. For fit, I might have been able to go to 295 but tight and didn’t want to take the chance since I will not modify the tubs - it might work. Perfect world would be the 285 in a 45 but its not made except in a Perelli as far as I know.

[jhein]

Originally Posted by 76TA462

On my second gen TA I ran with the Nitto NT01 on the rear with 15-inch wheels and really liked them but needed to go the larger wheels for a brake upgrade. I now run the NT555 G2 all round. 245 45 18 (8”) up front and 285 40 18 (10”) rear. Very happy with the street performance, but I can still spin them easy - they are still street tires but are better than lots out there. No mods for the 285s other than moving the seat belt bulge in. I get the 27” height I want. For fit, I might have been able to go to 295 but tight and didn’t want to take the chance since I will not modify the tubs - it might work. Perfect world would be the 285 in a 45 but its not made except in a Perelli as far as I know.

Good to know the 285 will fit. Would you be willing to post some pics?

[76TA462]

Just took the pictures on the hoist, not the greatest angle. The picture of the car on the road was before I added about 3/4 inch to the spacing between the top of rear tire and fender. Did that to get the perfect road clearance for me.

[Steve C.]

Posted here for general interest. Magazine material from years ago, and before NASCAR changed their wheel sizes....

"Wheels: How big is too big?

The general rule is to only use as big a wheel as you need to clear brakes and suspension components. The weight of an average car for road racing usually requires brakes that are too big to fit inside 15-inch wheels, so larger ones are used.
So the question becomes what is the best size wheel to use ? It's natural for us to think that bigger is better, and it's true that the general public prefers the look of larger wheels, but don't let that trick you. Oversized wheels will slow you down. It all comes down to moment of inertia. The excess weight of a larger wheel is an important issue, but the diameter of it is a much more important factor. The effect of a 10-pound weight at the end of a 12-inch string is much less than a 10-pound weight at the end of a 36-inch string. The larger-diameter wheels are not only heavier, but are much harder to control the rate of rotation like the weight at the end of the string.
Now let's look at overall tire diameter and the effects of sidewall flex. Let's say you've decided on a tire diameter and are looking at what combination of wheel diameter and sidewall height to run. The taller the sidewall, the more flex it can have. This is a good and a bad thing, but mostly a bad thing. When the sidewall is tall, it can deflect quite a bit, throwing away any sense of your suspension alignment settings. Too short of a sidewall a sidewall can be oversensitive to surface conditions, and gives you far less warning before traction is lost. The trick is to find the right balance.
The sweet spot for most of our muscle cars and track cars is 17- or 18-inch wheels. this isn't just our opinion, but that of many industry insiders. The 12- or 13-inch rotors usually chosen by the road racing crowd fit in these wheels just fine, and don't need the additional clearance given by a 19-inch or larger wheel. Consistent with that, BFGoodrich doesn't even make their sticky road race R1 tires for any wheel larger than 18 inches in diameter.
So why does NASCAR still use 15-inch wheels ? The rules mandate these 15-inch wheels and have for many years; knowledgeable fans speculate that this rule won't change. It can be argued, however, that oval track cars use this tall sidewall as a part of their tunable suspension. Since their quickness is defined by how they can plant power out of the turns, tire pressure can be used to improve that.
That brings us to ask why new Corvettes and Vipers use such large wheels. The simple answer to that is because they look cool. There is no advantage to these larger wheels except their looks. The laws of physics would suggest that using a smaller wheel while still clearing the brakes would make the car faster.


.

[JLMounce]

For what it's worth, modern 17 and 18" aluminum wheels and their accompanying tire weigh less than older steel based wheels and larger tires. Given the same overall tire diameter, you can actually decrease moment of inertia with modern larger wheels when compared to old steel wheels.

That doesn't make that article wrong, but it assume that overall heights change as well, when in reality, most people stick with the same overall tire height.

I always look at what parts people are running that are winning in whatever discipline you are interested in. Autocross is the best analogue for our street cars, because the speeds are largely the same and the maneuvers tend to be tighter, vs long fast sweeping corners present with open road racing. For a "canyon carver" autocross is the best comparison.

We can use Mary Pozzi's second gen Camaro for this comparison. This car is well put together and has a great driver behind the wheel.

Wheel and tire package includes Forgeline Wheels in 18" square setup. 315's front and back. It uses a 27" overall tire diameter.
It may have an independent rear now, but for a long time it used a speedtech torque arm and coil overs up front.

Efrain Diaz's 69 Camaro is setup very similarly. It uses 18" wheels with 315's front and back, again on a 27" overall diameter. It too is on a torque arm rear.

Now if you want to look at cars that are winning shows and are less concerned with performance, the hot setup that I personally like and see a lot of is C6 GS/Z06/ZR1 fitments. 18x10 in the front with a 19x12 in the rear. These will run a 27" diameter in the front and a 28" diameter in the rear. Very high performance tires are available commonly in these sizes, as are all season tires.

The point I'm trying to make here is that sometime you have to follow market dynamics, which don't always care about physics. You may have the perfect setup with a 17" wheel, but then find that the perfect tire you need doesn't exist. But you might be able to get that perfect tire if you upside to 18" or 19", and unless you're chasing every 10th, that type of deal is going to take precedent over perfect physics.

[jhein]

Originally Posted by 76TA462

Just took the pictures on the hoist, not the greatest angle. The picture of the car on the road was before I added about 3/4 inch to the spacing between the top of rear tire and fender. Did that to get the perfect road clearance for me.

That looks good. Thanks for posting. Is that a stock height suspension or is it lowered just a bit?