Slick size?

[mike85gn]

Hey, I'm building up for a low 12 high 11 setup and am curious as it is coming close to time to get slicks. Should I go with a 26" or 28" slick? 8.5" or 10.5 wide? Any other options you'd recommend? I'm using a modified IC, bigger 49-trim turbo and 009's, air bags, pinion snubber, seat and front end braces and other pieces. Car launches good, it cut mid 1.9's on old 215/65 Michelin XGT hockey pucks. Just wondering which slick would be the best for this speed braket.

Another question, my buddy added 4.10's to his T and wants to know which height of slick will let him race in drive without having to shift into OD. He runs 13.008 on 26" tires and wants to see 12's. I don't think a 28" will be quite enough? Maybe 29.5"?

 

[UNGN]

go with a 28X9 slick.

Tell your buddy to bite the bullet and swap the gears back to 3.42's. It's cheaper than buying special, too tall tires in the long run.

 

[mike85gn]

Originally posted by UNGN
go with a 28X9 slick.

Tell your buddy to bite the bullet and swap the gears back to 3.42's. It's cheaper than buying special, too tall tires in the long run.

Really? I always though 26x10 ET Drags were the key for 12-flat cars. Will a 28 make that much of a difference?

And I kind of figured my friend was screwed on his gears. Oh well, he built it for the street, looks like I'm going to walk away with the bragging rights this time

 

[UNGN]

Originally posted by mike85gn


Really? I always though 26x10 ET Drags were the key for 12-flat cars.

They are if you only want to run 12 flats. If a stock motored TR is running 12.0@113 and is not locking the converter, 28" tires will practically guarantee it an 11 second timeslip. Even cars locking the converter will pick up.

It's actually easier for a T-R to pull a taller tire above approximately 90 mph and this effect lasts until it runs out of RPM in Drive. On the low end, a taller tire allows a higher boost launch, so little is lost there.

A taller tire works best with Stock motor, loose converter, small turbo.

A shorter tire works best with Ported heads and cam, a "too big turbo" and a tight converter.

 

[Scott231]

Originally posted by UNGN
It's actually easier for a T-R to pull a taller tire above approximately 90 mph and this effect lasts until it runs out of RPM in Drive. On the low end, a taller tire allows a higher boost launch, so little is lost there.

TRs can pull the taller tire - relatively better than a NA motored car, only because they make more HP. ;-) Taller tires only allow higher boost launches because of their superior traction to a shorter tire (hint, going to a taller tire/same width will give you more traction than a same heigth/wider tire.) But it is harder for the engine/drivetrain to turn those taller tires. The following assumes you retain the stock gearing of 3.42 with a 200-4R...

A taller tire works best with Stock motor, loose converter, small turbo.

A shorter tire works best with Ported heads and cam, a "too big turbo" and a tight converter.

Uhhhh, some of that is right. In standard terms...

Smaller diameter tires accelerate faster than taller tires, but taller tires will attain higher speeds at the same RPM level. This applies to skateboards, race cars, etc.

I would prefer to run a shorter (i.e. 26" stock sized) tire if we are only looking at "the motor" being stock. A ported, polished, headworked engine will make more power and can moreso take advantage of a taller tire.

Same thing with the turbo. If its a stock blender, it'll have a hard time with the taller tires. Bigger turbo (like ported heads) will make the bigger power necessary to turn the taller tires.

Back to the original question - What tires on a 12.0 car to get into the 11s, if this is the only change? Given your buildup (the TA-49 with a stock headed motor is the limiting factor), I'd get a 27X9 slick from Hoosier...assuming they still make those. Do your own homework.

Tell your buddy, politely, that if he goes to 4.10 gears, he's a fool. As that much gear will screw up his tuning and shift points (unless he goes with the 29.5 tire - meaning frame notching, fender lip rolling, looser converter, etc.).

 

[UNGN]

Originally posted by Scott231

TRs can pull the taller tire - relatively better than a NA motored car, only because they make more HP. ;-) Taller tires only allow higher boost launches because of their superior traction to a shorter tire (hint, going to a taller tire/same width will give you more traction than a same heigth/wider tire.) But it is harder for the engine/drivetrain to turn those taller tires. The following assumes you retain the stock gearing of 3.42 with a 200-4R...


Uhhhh, some of that is right. In standard terms...

Smaller diameter tires accelerate faster than taller tires, but taller tires will attain higher speeds at the same RPM level. This applies to skateboards, race cars, etc.

I would prefer to run a shorter (i.e. 26" stock sized) tire if we are only looking at "the motor" being stock. A ported, polished, headworked engine will make more power and can moreso take advantage of a taller tire.

I don't think you are understanding the concept.

A Stock motored TR has a Horsepower peak around 4400 to 4500 RPM. Yet we rev them to 5000 to 5200 RPM. Because of this, At almost any mph at an RPM slightly over the HP peak RPM with a 26" tire, its easier for the motor to pull a 28" tire.

In third gear, the "crossover point" is around 95 mph. Above 95 mph, if the car had 28" tires on it, it would accellerate quicker than one with 26" tires on it, until it runs out of RPM.

Ported heads/cam and a larger turbo move the HP peak up the RPM scale and lessen the advantage of 28" tires over 26" tires. 28" tires may still help it, but the advantage isn't as great. Also, in the above comparison, I'm talking about a ported head/cam car that runs the same ET/mph as one that doesn't have ported heads/cam. Of course a ported head cam car that ran 125 mph in the 1/4 would benefit from 28" tires. If a ported head cam car ran 116 mph, the advantage of 28" tires over 26" tires would not be as great as on a stock head/cam car running 28" tires vs. 26" tires at 116 mph (measurable on a timeslip).

I've graphed out the advantage of 28" tires over 26" tires in a PDF file on my G-body homepage, starting with a typical dyno curve for a stock long block TR engine and computing the Force facture that the ground would experience from the rear tires. With 28" tires, more force is applied to the rear wheels (roughly the more RWHP) for a given mph at the top of each gear than with 26" tires. It's not magic, its science.

 

[GN/GTO]

For my car (mid 11's) I am very happy with Mickey Thompsons 28x9. They are really only a fraction over 27" tall, take very little burnout, and fit on a 8" rim like they were made for the car.