tire height and rpm?

[Fern]

I have 2 questions, first what is stock tire height on a 70 challenger?
The reason I ask is I'm looking to buy new tires and rims and was wondering what rpm I would have at 70mph.
I have a 440, 4-speed manual with 355 rear.  If the rpm's were too high I could go with a higher wheel to bring them down.
I don't even know if it is possible.
Any help would be great,
Thanks

[Katfish]

Yes, taller tire will bring down the RPMs.

http://www.richmondgear.com/101032.html

[Chryco Psycho]

or if you want a Mopar designed one
http://vexer.com/automotive-tools/speed-rpm-calculator

[blown motor]

Whoa, that link is just way cool!!

[moparman82]

Nice link CP!   

[Fern]

or if you want a Mopar designed one
http://vexer.com/automotive-tools/speed-rpm-calculator

Great site answers a lot.
what is the correct size tire that a 70 challenger came with and overall height?
Thanks

[Raw Untamed]

I believe the original sizes were labeled F70x14 and G60x15(bias ply sizes), but they were both right around 26 inches tall.  The compatible radial size is 205/75R14 or 205/70R15.http://www.musclecarclub.com/library/tech/tires.shtml (scroll down to bottom of page.)

If you're trying to keep the rpms the same, then you should run a 26" tall tire.  If you want to lower them, then run a taller tire.
With a 205/75R14 tire, you're rpm for an 833 4speed in 4th with 3.55 gear ratio at 70mph is 3200rpm.

Decide what width you want to run, such as 205, 215, 225, 235, etc., then choose the correct aspect ratio 75, 70, 65, etc., on whatever diameter wheel you want 14, 15, etc.  Your rpms won't change drastically until you plus size an inch or more in tire height.

Ex: 235/70R15 is a 27.95 inch tall tire!  It would give you 3000 rpms at 70mph.  235/70R14 is a 26.95 inch tall tire.  It would give 3100 rpms at 70mph.

Here are the sites I use: http://www.f-body.org/gears/

http://www.discounttire.com/dtcs/infoTireMath.dos

Hope this helps,

Joe

[Fern]

Thats a great site
http://www.musclecarclub.com/library/tech/tires.shtml

I see a lot of people run 145/45/17,  how acurate is the spedo with this combo?
Thanks

[brads70]

Thats a great site
http://www.musclecarclub.com/library/tech/tires.shtml

I see a lot of people run 145/45/17,  how acurate is the spedo with this combo?
Thanks

you can make any combo work by changing speedo gears. 

[Chryco Psycho]

original tire was a F 70 15 , 25" tall I believe

[HP2]

Ultimately you will not see a huge difference in rpm with tire changes. Swapping from a 26" to a 28" tire will only net you a 250 rpm drop. Step all the way up to 31" diamters and you can get around a 500 rpm drop.

Similarly, swapping a 3:55 for 2:94 with your 26" tall tire will also get a 500 rpm drop. Step up to th tall 31" tire and you finally reach 1000 rpm under original, but, how will the car look with a truck tire under it.

This is why OD units are so popular. Without changing the gears or tires, a .86 OD unit will drop that 3:55 to a 3:05 and almost net your 500 rpm drop with still have brisk accelleration froma standstill adn look original. All comes down to how you use your car and what your budget for improvement is.

[Raw Untamed]

I think you meant 245 45 17 . Yes that size is close to stock diameter at 25.6 tall.

[swede-cuda]

 :dunno:dont know height,but in the import papers it says my -70 383 cuda came with F-70 14 tires.

[Fern]

Thanks everyone, you guys answered all my questions! 
Where do you find all those great sites.  Its like being a kid in a candy store 
I think I'm going with 17" either torque thrust m in chrome or the year one rally.
245/50/17 which will get me where I want to be in overall height.

[Fern]

Looks like I have to go with either 245/45/17 or 255/45/17 to get the tires I like.

will 255/45/17 tires rub on the front of a stock suspention?