Strip tires for my setup

[bigpappy33]

Ok so reading up there seems to be alot of opinions on what tire to run for the track, so I am going to ask what would be best for my set up

My car has a 2.3 Whipple, and 4.10 gears. I will be running Jegs 15x8 Sport Stars on the rear, and unfortunately my 20s on the front due to the brembos (wish I could afford those GT500 bogarts) Making around 470-490 (est) at the wheels on the bigger pulley, thinking I should get a 27-28 inch tire? What affect will this have on my gearing and what size tire should net me the best ETs?

Also I should get the Drag radials, not the slicks right? I hear your not supposed to run a slick with a radial tire on the front.

I was looking at Mickey Thompson 295/55/15, little over sized but a bigger contact patch. 27.8" tall.
Are the 275/60/15 a better option? or 275/50/15? I was confused shopping for the 27 x 10.5-15s because some sites said they are a slick and I'm trying to find a radial, do the radials only come in metric sizes?

Thanks all for the help

 

[Vapour Trails]

thinking I should get a 27-28 inch tire?
What affect will this have on my gearing and what size tire should net me the best ETs?

I agree, ~ 28" tall. It will reduce your overall gear ratio, or lengthen your gears. It would be the equivalent of 3.95 gears or so.

I was looking at Mickey Thompson 295/55/15, little over sized but a bigger contact patch. 27.8" tall.

I think you have the right one picked out, Part # 3755R

 

[bigpappy33]

I want to be coming through the trap around the top of 4th right? Would I want to lower my gear ratio or raise it? I know some people run 4.56s, so wouldn't a little shorter tire like a 27" or maybe even a 26" help me?

 

[dysan]

With my set-up, E-force around 11.5psi on a 302 stroker 28" tall M&H DR's on my stock 17" rims and 4.10's I go through the traps around 6200 rpms in 4th gear. Now that is with it pulling timing due to high IAT's so when I install my new trunk intercooler reservoir and pack it with ice I don't know what I'm going to go through at. I would say do the 28" DR's.

As far as doing a bias-ply VS radial, if you're going to have radials up front then I would do radials in the back. If you can do bias-ply's on both I'd say go with that since you have a stick shift and the bias-ply's will absorb some of the shock and you won't stress your drivetrain as much.

 

[Vapour Trails]

I want to be coming through the trap around the top of 4th right? Would I want to lower my gear ratio or raise it? I know some people run 4.56s, so wouldn't a little shorter tire like a 27" or maybe even a 26" help me?

You have a blower, you don't have to over-gear your car like that.

I do run a short tire (275/40/17) but I have 3.55 gears. The overall gearing ends up being 3.76 which about perfect in my eyes.

 

[bigpappy33]

ok, so it looks like Ill be getting the 295/55/15s. Those should fit and be able to squat without hitting the fenders right? I know alot run the 275/60/15 with no problems, but why not go a little wider right? haha

 

[tjm73]

I think you should expect a trap speed of around 120 mph if your car weighs about 3600 lbs with you in it.

As a result if you are gearing for the 27.8" tall 295/55 tire you need to do a little math to see what ratio puts you closed to that trap speed with your tires at the RPM you plan to finish the race at.

(target RPM * tire height ) / (336 * trap speed ) = gear ratio

So let's set your known values...
target RPM = 6200 (a good place to start)
tire height = 27.8"
trap speed = 120

Plug it all in and you get a ratio of 4.27. 4.30's would be a great ratio at that power level. 4.10's won't hurt much so you are golden. I'd run the 4.10's, see what you get and if the revs are too low then consider changing the axle ratio.

This is, of course, all speculative. But it's a good place to start.

 

[tjm73]

As to your separate question about running bias ply and radial together...

Lot's of people do it without any problems. My brother does it regularly. The trouble comes when you jump in and expect the vehicle to act like anything you are used to.

Short story, it can be done. Long story, it takes more forethought and planning. runthe radials and don't worry about it. it'll be more predictable and is likely to do what you expect it to do. Bias ply's can be a little disconnectd feeling at times.

 

[bigpappy33]

I think you should expect a trap speed of around 120 mph if your car weighs about 3600 lbs with you in it.

As a result if you are gearing for the 27.8" tall 295/55 tire you need to do a little math to see what ratio puts you closed to that trap speed with your tires at the RPM you plan to finish the race at.

(target RPM * tire height ) / (336 * trap speed ) = gear ratio

So let's set your known values...
target RPM = 6200 (a good place to start)
tire height = 27.8"
trap speed = 120

Plug it all in and you get a ratio of 4.27. 4.30's would be a great ratio at that power level. 4.10's won't hurt much so you are golden. I'd run the 4.10's, see what you get and if the revs are too low then consider changing the axle ratio.

This is, of course, all speculative. But it's a good place to start.

Thanks for the math man! The car has trapped 117+ on street tires, so hopefully after figuring out the launch i can see around 120-122. 4.10s are as high as i will go for now, might move down to 3.73s one day since its a DD.

 

[firestang70]

OK hope this helps. I run a Whipple with 4.10s manual tranny and same power range. I run a 28" bias ply 28 by 11.50 by 8 on the Jegs star wheels 15 by 8. Its actually a narrow tire with a contact patch less than 8.5" and sometimes is not enough honestly. My car traps between 117 and 122 depending on heat, DA etc. I would say run the bias ply and skip the DRs. The DRs cannot recover fast enough esp the 1-2 shift in a car that heavy with a manual tranny. I would say DRs would be OK with an auto car. The bias ply will last ALOT longer than the DRs. I don't run below 12.5 psi at the track, the car gets a little too "goosey" for my tastes. My car 60s in the 1.5s, ETs best in the 11.3 with my crappy driving skills. Bottom 11s are possible with great DA,track prep, driver mod etc. Good luck!

 

[bigpappy33]

Yea i hear it can get goosey on the top end with the bias ply, Id like to sometimes be able to run these on the street too (and drive to the track), so i think I might just stick with the DRs. Have you run the Drag radials before? That's a great ET btw. I need to get myself an aluminum driveshaft!

 

[firestang70]

The learning curve is quick on the the tires. Now I don't really notice much if I run 12.5-15 psi in the tires. I have not run DRs with the Whipple. I run them NA and they were fine, I ran them with a 100 shot and they would blow off the line and 1-2 shift. They were MT 275/40/17s.

 

[Vapour Trails]

RTCTTFMF