95BlueBomber

I am finally starting to get these 28" tires under my car. How much is this going to effect my gear ratio? Should I start looking for a 3.90 gear?

95BlueBomber

nobody?

AlwaysInBoost

if you're running the stock 3.42 rear its going to hurt you big time.
I forget the exact numbers but you would be in the 160MPH range IIRC at the end of 4th gear with that size tire.
unless you're making over 1000whp or have shorter gearing then 3.42 you don't want that sized tire.

vrybad

Based on mn6 ratios, with a 3.42 rear diff, 26" tire,
your current mph@6500 rpm in each gear equates to

1st 55
2nd 83
3rd 113
4th 147

With the 3.90's and 28" tire,

1st 52
2nd 78
3rd 107
4th 139

You didn't specify which gear you currently have, but this info should help.

I agree that 3.42's with a 28" tire will make 4th too tall, and puts top end in 4th right at 158-160 @ 6500 rpm.

95BlueBomber

so basically I need to look at maybe stepping down to a 26" tire?

vrybad

Well, I don't spend alot of time at the drags, but I think the 3.90 with the 28" tire may help your e.t., depending on how much power you are making.

You'll run out 3rd and 4th quicker, so it may be a benefit.

With the overdrive 5th and 6th, highway driving will still be pleasureable, if that is a consideration.

Hopefully you'll get more direct feedback on this potential change from someone who has done it.

95BlueBomber

From what I can figure it will be like putting in a 3.17 rear gear... does that sound right?

ChopperLoco

Sound about right-but this may not be so bad on a FI car...

vrybad

3.17 and 26" tire will give you a 1st gear speed of 59mph @6500 rpm, so it's a bit taller than the 3.90 and 28" tire.

I agree, that might work out with a boosted car.
Being able to run 1st to 60mph might be a good thing.

Just note that with 3.17 and 26" tire, 2nd thru 4th become

2nd 89mph
3rd 122
4th 158

You'll end up shifting into 4th very late.

I would think it would be best to shift into 4th as close to or slightly earlier than the 1/8th mile point.
Again, depends on power level.

highpockets

Anyone have any hard on paper esults running a hugher HP FI car both ways on the same gearset(3.42) ? I would love to have more traction and think the 28s would help off the line.

396375

A 26" tire with a 3:42 is optimum for a 10.5 or slower car.If you are going faster then that then the 28" wouldn't hurt you that much as long as the car has big power and leaves hard.I know some one running 9.80s with a 3:42 and a 26" and went to a 28" and picked up nothing in the 60'.If you are going slower then 10.5 or so you will need more gear to make up for the 28" tire.IMO.
Good luck.

easyvette

How well does the 28" slick fit under the wheel well? Curious maybe consider the 28 inch slick for myself. I am currently on a 26 with 3:90 gear and trapping just a the rev limiter 4th sometimes just in it some. It all depends on wheel spin and making sure hit my shifts at max rpm to keep it out of the limiter when I hit the trap.

ChopperLoco

Most guys have to remove the inner fender liner for clearence,and the car can not be lowered in the rear-maybe try a 27" tire?

AlwaysInBoost

I'd have to disagree with that statement. you wouldn't want to run a 28" tire with a 3.42 rear unless you were making BIG power. IMO, 26" tire would be optium for anyone who is high 9's and slower with the 3.42 rear.

keeping in mind that you want to be just about on the rev limiter in 4th gear while finishing the 1320', in order to use all your available power, and the trap speed at most tracks is an average of the last 66':

with a 3.42 rear:
a 26" tire will net you 147mph @ 6500RPM
a 28" tire will net you 163mph @ 6500RPM

with a 3.73 rear:
a 26" tire will net you 135mph @ 6500RPM
a 28" tire will net you 147mph @ 6500RPM

so running a 3.42 rear with a 26" tire is basically the same gearing as running a 3.73 rear with a 28" tire.

easyvette

Thanks, think I am gonna have my rev limiter bumped up 200 rpm that should give me some room. The cam was speced to be at 7K so looks like its going that way...

396375

I don't think you would see a big difference in your ET with either setup as long as the car hooks.Obviously the 28" tire will hook a lot better with a larger tire patch on the track then the 26" tire.Gettting deeper in the nines would be hard on the 26" tire even though there are guys who have done it.It all depends on how fast you plan on going.I have never seen a big reduction in ET with a step up or down with the next ratio in a gear change.Going threw the lights at the exact rpm you are looking for is great but getting the car to cut a better 60' has always been more important to your ET.What is your combo Always in Boost?
Take care.

AlwaysInBoost

396375, you would see a difference in ET & MPH with that tall of a tire because the car would be way out of its powerband at the end of the track. basically it would make the gearing too tall with a 3.42 rear unless you had a TON of power to trap in the low 160's.

a 26" tire is enough contact patch to pull low low 1.4 sec 60's and maybe even some 1.3's, although I don't know of anyone who has gone THAT low on a 26" tire. Its all about the right setup. take a look at robz car, 4.10 rear & 28" tires, he is using all his available power for the whole 1320' and running low low 10's.

my combo is in my sig, let me know if you have questions.

396375

So what tire and gear are you running?

AlwaysInBoost

stock z06 3.42 rear, stock mn12 trans & 26 MT ET Streets

Z06wanted

I will tell you this I have a Kene Bell 2.8 on stock motor making nearly 600rwh with my 28 inch drag pack it bogs pretty hard out of the hole. 1.60 60ft and on the dyno in 4th gear I hit 172mph running to 6800rpm. this is all with a 3.42 gear. I have a set of 3.90 for mine.