Automatic and RPMs

Post by **jhoffman** » Sun Sep 11, 2011 9:18 pm

I do mostly highway driving and with the stock 195/60/14 and the automatic it turns about 3000 rpms at 70mph if the tacjh is right, has anyone tried a 205/60/14 or a 215/60/14 on just the rear. Trying to keep RPMS a little lower with a little taller tire. I know it will cause my speedo to show lower, don't know how much though. Thanks.

Found BF Goodrich TA 215/60/14 on Tire rack. Revolutions per mile will be 835 per mile at sixty, VS 869 per mile for the stock tires. If i am doing my math right it would drop my RPS by 140 RPMS. Will that size fit ok on the 5.5 rims? Thanks

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HumP · Post by **HumP** » Sun Sep 11, 2011 9:42 pm

3k at 70? I'm past 3k at 55! Your doing something right. I'd love to go 70 at any rpm below 4k!

Post by **John Brennan** » Sun Sep 11, 2011 9:53 pm

Going to 215/60's will give you the same diameter that the 15"- wheeled, later cars have (a nominal 24"). You will lose some crispness of handling, but gain in ride quality and mileage. You will also raise the already-higher switchover limits from closed to open loop, allowing you to cruise at higher speeds and save more gas. You can also get some raised white letter tires and go for a sort of retro racer look.

There are no real high-performance tires in either 205- or 215/60 14, so understand that. Of course, by the same token, there are basically no true high-performance tires left on the market that fit-- properly-- on a 5.5"-wide rim (in anything close to our diameter) anyway.

Mike McCreight · Post by **Mike McCreight** » Sun Sep 11, 2011 10:50 pm

Maybe buy some 15s?
I have a stack of 'em I'll be turing in for scrap, likely someone nearby has a pile too.
Oh, and Ian can fix your tach.
Welcome aboard!

Post by **merkurdriver** » Sun Sep 11, 2011 11:20 pm

HumP wrote:3k at 70? I'm past 3k at 55! Your doing something right. I'd love to go 70 at any rpm below 4k!

( x 2 ) 70mph in an auto XR = 4k RPMs. Tach must be reading low. You might not want to fix the tach if you thought 3k RPM was bad - you'll really cringe when you see it at 4k RPM !

Post by **DPDISXR4Ti** » Sun Sep 11, 2011 11:43 pm

I vote for a different transmission. T-9 or A4LD if you don't like the idea of shifting.

milehighXR · Post by **milehighXR** » Mon Sep 12, 2011 9:06 am

3500 at 70 is about right. I have the BBS style 15s on my car with 195/60s, and I don;t pas 4k until I hit 80, this with a C3. If you want lower rpms you need either a different tranny, or numerically lower rear ratio.

murdomino · Post by **murdomino** » Mon Sep 12, 2011 12:15 pm

i run 205/50R15's on mine with a c3, everytime i get on the freeway i pray for a fast and smooth running big-rig so i can draft behind him. i hate running 75mph here in L.A. at 3504k rpm's

Post by **jhoffman** » Mon Sep 12, 2011 5:13 pm

If my tach is off, reads 3000 at 70 mph who would be the best source for a new Tach? Thanks.

milehighXR · Post by **milehighXR** » Mon Sep 12, 2011 8:49 pm

it can be adjusted, just take it to a speedometer shop they should be able to fix it...

IceColdMikey · Post by **IceColdMikey** » Tue Sep 13, 2011 10:20 am

Mine is stock, 195/60/14's, on stock rims obviously, C3, reads 3500 at 75.

Mike McCreight · Post by **Mike McCreight** » Tue Sep 13, 2011 4:31 pm

Mike McCreight wrote:Maybe buy some 15s?
I have a stack of 'em I'll be turing in for scrap, likely someone nearby has a pile too.
Oh, and Ian can fix your tach.
Welcome aboard!

See above!
If Ian isn't here, try over at www.merkursport.com

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Automatic and RPMs

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