Taller tire for lower RPM on highway?
03-30-2016, 07:08 PM
#1
Melting Slicks
Thread Starter
Taller tire for lower RPM on highway?
73 CONVERTIBLE....WORKED 350..275 HORSE TO THE REAR WHEELS WITH 349 TORQUE TO THE REAR WHEELS..
My stock 336 rear went last week...Got a good deal on a complete 370 rear......Currently running 255-60-15s all around on 15x8 American racing outlaws.......
Thinking of going to a 275 in the rear,it is one inch taller...Should tach around 115 -120 less at highway speeds as far as calculations..
Anyone have any experience with this before I change? Also how much will acceleration be compromised with a little bigger rear tire? Not much im guessing....I figure they are maybe a few pounds more than the 255s.....
My stock 336 rear went last week...Got a good deal on a complete 370 rear......Currently running 255-60-15s all around on 15x8 American racing outlaws.......
Thinking of going to a 275 in the rear,it is one inch taller...Should tach around 115 -120 less at highway speeds as far as calculations..
Anyone have any experience with this before I change? Also how much will acceleration be compromised with a little bigger rear tire? Not much im guessing....I figure they are maybe a few pounds more than the 255s.....
03-30-2016, 09:26 PM
#2
Racer
This isn't completely related to your question, but if you want to run 275 tires, you should relocate your parking brake bracket to the top of your trailing arm, assuming you haven't already done that.
03-30-2016, 09:42 PM
#3
Race Director
Is that really enough of a significant reduction in RPMs to make a difference? I don't really think so. While not easy or cost effective an overdrive trans would be the way to go if you want to stick with the 3:70 rear.
03-30-2016, 09:52 PM
#4
Nam Labrat
Member Since: Sep 2013
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Rookie suggestion: If you want performance and you are NOT concerned about MPG on long trips.....it sounds like you have chosen the correct size tires.
If you plan on making long road trips....buy tires with a diameter that will keep the engine UNDER 2600 rpm/OVER 2000 rpm at 70 mph.
Stay close to 2500 rpm at 70 mph for a balance between performance and MPG.
If you plan on making long road trips....buy tires with a diameter that will keep the engine UNDER 2600 rpm/OVER 2000 rpm at 70 mph.
Stay close to 2500 rpm at 70 mph for a balance between performance and MPG.
03-31-2016, 12:31 AM
#6
Melting Slicks
Thread Starter
You would be suprised,it doesnt sound like much but my thinking is every little bit helps....Like the way the 275 compliments the rears on the older stingrays...
03-31-2016, 12:34 AM
#7
Melting Slicks
Thread Starter
My rear was so damaged absolutely nothing was salvageable,not even the housing which cracked.....Unreal.....
03-31-2016, 02:01 AM
#8
Race Director
A taller tire is going to put more drag on the engine. You'd be more efficient with 3.55s and a 27" tire than 3.70s and a 28" tire, FWIW.
Personally, I'd use a modern transmission to get RPM down.
Personally, I'd use a modern transmission to get RPM down.
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zrc3john (03-31-2016)
03-31-2016, 02:22 AM
#9
Le Mans Master
The 3.70/28" will feel very similar to the 3.36/27".. I doubt you'll notice much difference at all.
I have 3.36 and I use both 27"s and 28", the 28"s do have a slight effect on acceleration but not anything you won't get used to after about a 10 min drive.. The 28s will knock about 100 rpms off at 3000...
With my 3.36/28s I'm 70 mph at 3000 rpms with just the slightest bit of converter slippage..(auto).
I have 3.36 and I use both 27"s and 28", the 28"s do have a slight effect on acceleration but not anything you won't get used to after about a 10 min drive.. The 28s will knock about 100 rpms off at 3000...
With my 3.36/28s I'm 70 mph at 3000 rpms with just the slightest bit of converter slippage..(auto).
03-31-2016, 05:42 AM
#10
Team Owner
Member Since: Oct 2004
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St. Jude Donor '05
Is that really enough of a significant reduction in RPMs to make a difference?
255s look great on the car. Whats 100 rpm or so sure wont hurt anything?
03-31-2016, 10:39 AM
#15
Melting Slicks
Thread Starter
The 3.70/28" will feel very similar to the 3.36/27".. I doubt you'll notice much difference at all.
I have 3.36 and I use both 27"s and 28", the 28"s do have a slight effect on acceleration but not anything you won't get used to after about a 10 min drive.. The 28s will knock about 100 rpms off at 3000...
With my 3.36/28s I'm 70 mph at 3000 rpms with just the slightest bit of converter slippage..(auto).
I have 3.36 and I use both 27"s and 28", the 28"s do have a slight effect on acceleration but not anything you won't get used to after about a 10 min drive.. The 28s will knock about 100 rpms off at 3000...
With my 3.36/28s I'm 70 mph at 3000 rpms with just the slightest bit of converter slippage..(auto).
04-02-2016, 10:46 PM
#17
Le Mans Master
I ran a set of 9.15-15's on my '63 with 3:73 gears and a posi back in the late 60's. The 9.15-15's were about an inch and a half taller than the previous 7.75-15's. I could no longer break the tires loose, but I could sure smoke the clutch! 
Good luck... GUSTO
Good luck... GUSTO
04-03-2016, 09:21 PM
#18
Melting Slicks
To the OP, not sure if you mentioned if stick or auto...
but swapping tires is a waste. Bite the bullet and select the rear you want.
Or go with a overdrive tranny...perfect for the 3:70!!!!!!!!!
but swapping tires is a waste. Bite the bullet and select the rear you want.
Or go with a overdrive tranny...perfect for the 3:70!!!!!!!!!
04-03-2016, 11:39 PM
#19
Melting Slicks
Thread Starter
04-04-2016, 12:28 AM
#20
I have a 235/70/15 BFG on the rear of my 69 for the same reason. It has a big block, and i was trying to get the rpms reasonable on the freeway. They look good and fill the wheel well plus give the car a little higher stance in the back so it sits level when 2 people are in it. I have 225/ 60/ 15 on the front
Last edited by centuryoldracer; 04-04-2016 at 12:33 AM.