More gear, Taller tires?

[BandBSTANGS 15]

My 1970 coupe with 351c init runs great, but could use more gear in it. The car went a 13:07 @ 104 mph with the car noticably starting to pull hard at 3100 rpm and being all done at 6200 rpm. Car goes thru the 1/4 at approx 4000-4200 rpm with 3:50 gear.

I feel the car would like a 4:30 or 4:56 gear (of course chasing that 12 second time slip), but the driveability on freeway goes out the window. Car currently has a 275/50 15 drag radial on it, which is 26 inches tall. I went on Wallace calculators and with 265/65 or 265/70 15 T/A radial (can't remember the exact size available) with a height of 29.1 inchs gear ratio works out to 3:60-3:65 which would be tolerable.

Will a tire this tall fit under the car?

 

IMG_9758.MOV

[Stangboy 14]

I had 28x10.5 slicks on mine 69, and they barely cleared the wheelwells. The width was fine, but they were very close to the front & rear.

[Rsanter 152]

If you have a 9" rear end you have what's called a poor mans quick change.

Get another pumpkin with the drag gears you want.

Swap the pumpkin for going to the track. Put the one you have back in for driving the streets

 

Bob

[JD08 42]

It's actually the other way around. Shorter tires would give you more gear, taller would take it away. That's why on the new Mustangs the gas sipping V6 has 2.73 gears and 28 inch tires,, just to improve MPG to meet CAFE requirements.

 

Here's an article with a little explanation.

 

 

Tire diameter will also have an effect on a vehicle's final drive ratio. As tire diameter changes, so will engine rpm at a given speed. We can demonstrate this with the simplified formula: rpm = (mph x final gear ratio x 336*) / tire diameter (*see "Formulas for Success" sidebar). For example, given 65 mph, a tire diameter of 30 inches, and a final gear ratio of 4.10, the engine speed will be approximately 2,984 rpm--(65 mph x 4.10 final gear ratio x 336) / 30-inch diameter tire. If we reduce the tire diameter to 25 inches, the engine speed increases to 3,581 rpm. By installing shorter tires, the vehicle will accelerate as though it has a 4.73 (higher numerically) gear without the expense of gear swapping.

 

[BandBSTANGS 15]

JD08 Car has 3:50 gear with a 26 inch tall tire as it sits.

 

Car needs more gear 4:30-4:56 which kills interstate driving, thus adding a taller tire (29.1) would help kill some gear ratio 4:30-4:56 down to a more driveable/interstate friendly 3:30-3:65. Thus I could drive car with taller tire and change to 26 inch tall drag radials when playing at strip

 

RSANTER changing 10 lug nuts is a lot less mess and not near as heavy lifiting as it is changing chunk out every couple of weeks when the drag strip urge hits. Plus drag radials are expensive!

[JD08 42]

You didn't say you were swapping gears, you said you wee swapping tires, thus the source of my confusion.

 

To clarify, you are talking about running different size tires after swapping your 3.50 for 4.30 gears, correct?

[BandBSTANGS 15]

Yes I intend to put another traction lock 9 inch together with either a 4:40 gear or a 4:56 gear in it and then see if I can kill some of the gear with tall tires.

 

Car goes thru traps at approx 4000-4200 and would like to have the car go thru at 5500-5800. Also more gear would get the car to 3000-3100 rpm quicker where the camshaft noticably picks up.

 

As the car sits now it dead hooks out of the hole and is a little lazy up to 3000 rpm. Car has a c-4 with a 3000 stall from TCT. 60 fts are in the high 1:80's to 2:00

 

I need to keep telling myself THIS IS A STREET CAR...THIS IS A STREET CAR...lol

[BandBSTANGS 15]

Anybody tried running a tall tire on the back of their mustang?

[DRASTiK 22]

I can't answer your tire question, but you should be able to get the RPM/gearing information by using one of the speed calculators on the net.  Here's one:

 

http://www.ringpinion.com/Calculators/Calc_RPM.aspx

[BandBSTANGS 15]

My 1st post states I used Wallace calculator, I know the math works.

 

I'm looking to see if anyone has used a tall tire on their mustang and were ther clearance issues

[det0326 179]

Pricey but have you ever thought about putting a 4R70w tranny in it. You get best of both worlds and keep your tire size the same on or off the track. the 4R is a very strong tranny stock and can be built up a lot stronger. I'm sure you could get a larger tire under there but I don't think you would be happy with the rear suspension to make it work.

 

Dave

[69volunteer 84]

265/65 or 265/70 15 T/A radial (can't remember the exact size available) with a height of 29.1 inch--Will a tire this tall fit under the car?

 

I think all he is trying to ask is will this tire fit in his wheel well without modification. I am running 225/70 15 and it fits fine....don't know the total tire height with this setup.

[BandBSTANGS 15]

I've already got a Dynamic Racing built c-4 rollerized, with hardened input shaft, good clutchs, and internal mods to drum and oiling passages. TCT 9.5 inch 3000 converter. Car has long tube headers. Too much invested

[RPM 1,190]

Nice C4! I love those mods to the C4, it'll take a beating. I've got a pan fill C5 I'll do those mods to, if I live long enough.

[det0326 179]

I've already got a Dynamic Racing built c-4 rollerized, with hardened input shaft, good clutchs, and internal mods to drum and oiling passages. TCT 9.5 inch 3000 converter. Car has long tube headers. Too much invested

I completely understand, and don't blame you I would keep that tranny too.  The tire thing is hard to call, probably not alot of people tried 29 inch tall tires. Have you checked to see if the rubber bumper on the frame rail will contact the axle tube before a 29 inch tall tire would contact the wheel housing?

 

Dave