Rear end ratios
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Rear end ratios
Posted: July 15 2008 06:20 PM
 
George Abel (aka ahotrod33) [ View ] [ gaabel@sunocoinc.com ] [ Car Ads ] [ Blogs ]
Glen Mills, Pennsylvannia
(484) 840-1379
 
OK.....I think I must be getting senile, or just slow. Anyway, I wanted to check the rear ratio on the roadster. Jacked it up, put trans in neurtal, marked the tire, had my bride rotate the tire while I counted the turns on the driveshaft which I also marked. First time the drive shaft rotated slightly less than 2 full revolutions. Seemed weird, so had her do it again with the same result. I've always thought you took the number of turns of the driveshaft to one turn of the wheel. Drive shaft turns 3.5 turns to one turn of the wheel and you've roughly got a 3:55 rear gear. Am I losing it or just being an idiot. Either way, anybody have an idea what those numbers might work out to. BTW--going down the road @ an indicated 60 mph, the tach's showing +/- 3 grand. Thanks!
 
 
Comments
 
Posted by ahotrod33  -  07/15/2008 06:22 PM
Also, the 37 in the picture is gone. The roadster in this post is what I now have. I can't seem to get the roadster pic to come up on a new post. Help?
ahotrod33 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Glen Mills, Pennsylvannia Charter Member since June 2003
 
Posted by da34guy  -  07/15/2008 06:46 PM
could b 4:11, how tall a tire?
With a 29" tall tire 3000 rpm @ 60 = 4:10
Don [ View ] [ Email ] [ Blogs ] [ Car Ads ] Prescott, Arizona Charter Member since October 2001
 
Posted by ahotrod33  -  07/15/2008 06:49 PM
Don, That's sounds right the way the car pulls. Close ratio Muncie 4 spd. Go through the gears really quickly. Thanks! I just seem to remember something about being able to count the turns on the driveshaft vs. a tire rotation.
ahotrod33 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Glen Mills, Pennsylvannia Charter Member since June 2003
 
Posted by da34guy  -  07/15/2008 07:00 PM
No MPG, but a blast to drive on short hops.

Don't think it would work 4 me as a freeway flyer with all the LONG HAULS I do.

I like my 3:25 gear with a 31" tall tire. On the newest roadster on it's maiden voyage( enginee only had 175 miles on it) Drove over Wolf Creek Pass (12000 ft read no air) and the 1st 800 real miles got right @ 20 mpg. Not too bad for a new motor.

Great bottom end( it'll smoke em any time) yet cruise the interstate @ 75- 85 no problem( around 2300 rpm)

Still will pull real hard up to 110 or so.

Kruzin and Smokin em in AZ
Don [ View ] [ Email ] [ Blogs ] [ Car Ads ] Prescott, Arizona Charter Member since October 2001
 
Posted by da34guy  -  07/15/2008 07:04 PM
George- Just checked out the pic of Ur roadster.

Looks as if the rear is a little far back or is it just the pic?
Don [ View ] [ Email ] [ Blogs ] [ Car Ads ] Prescott, Arizona Charter Member since October 2001
 
Posted by Crazyhorse Rod Shop  -  07/15/2008 07:07 PM
sounds like a 3:55 to me.
dont poke the porchdog........he bites [ View ] [ Email ] [ Blogs ] [ Car Ads ] BLUFF DALE, Texas Charter Member since March 2003
 
Posted by hotrod39  -  07/15/2008 09:24 PM
is rear a posi unit if not you need to hold the left or right tire till they roll together did same thing and i came with a 1 to 1 ratio after a couple of cold ones figure out what i was doing wrong. but in the area of 3;50 sounds good
Tom [ View ] [ Email ] [ Blogs ] [ Car Ads ] somerset, Massachusetts Charter Member since January 2008
 
Posted by jimmothershead  -  07/15/2008 09:30 PM
George.......close but no banana. Put the rear axel on jack stands....carpet to protect nice paint. Chalk tire at six o clock. mark Companion flange at 6 o clock. Lay on your back under rear in center. Spread arms out. Now, turn each tire identical and watch chalk on pinion. Make one full revolution of tires. If pinon rotates 3 1/2 times = 3.50. 2 3/4 times = 2.73. 3 times = 3.08. This is for open rear. If positraction, both wheels turn in same direction so only need to rotate one tire.
Keep kroozen, jim
Jim [ View ] [ Email ] [ Blogs ] [ Car Ads ] Huntingtown, Maryland
 
Posted by ahotrod33  -  07/16/2008 04:35 AM
Thanks to all.

Don-good eyes-the rear is just slightly back, something I want to address at some point. It's definitely not a freeway flyer at this time. I made the run from Philadelphia to the Nats East. Managed to get about 10 mpg, but got up to speed really quick.

Tom and Jim--It's an open rear so I'll be crawling back under the car when I get back home. I think it's something stronger than 3:55's but I'll know when I check it.

Thanks again!
ahotrod33 [ View ] [ Email ] [ Blogs ] [ Car Ads ] Glen Mills, Pennsylvannia Charter Member since June 2003
 
Posted by Ghengis  -  07/16/2008 09:31 AM
check out this website it makes all kinds of ratio calculations for you. You can figure gear ratio from speed and tire size or vice versa. Pretty Cool! www.freewebs.com/soslo/formulas.htm
Ghengis [ View ] [ Email ] [ Blogs ] [ Car Ads ] Weston, Wisconsin
 
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