Any acceleration difference in wheel diameter ?
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Any acceleration difference in wheel diameter ?
Running 255-60-15 on my worked 73 350 4 speed....Have a 3:70 rear so she winds on the highway .... Wheel is 27 inches in diameter 35 lbs......
Thinking of switching to a 255-70-15....Diameter is 29 inches 34 lbs....
Revs should come down about 200 rpm on highway (65 mph ) since its a taller tire...At this point I will take any decrease...
My question is will the extra 2 inches in diameter affect acceleration even slightly ?
They basically both weigh the same...
Just figured I would throw it out there..
Thinking of switching to a 255-70-15....Diameter is 29 inches 34 lbs....
Revs should come down about 200 rpm on highway (65 mph ) since its a taller tire...At this point I will take any decrease...
My question is will the extra 2 inches in diameter affect acceleration even slightly ?
They basically both weigh the same...
Just figured I would throw it out there..
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You are changing tire diameter but the effect is similar to wheel diameter and is not worth 200 rpm.
Read the article.
https://www.carthrottle.com/post/how...t-performance/
Read the article.
https://www.carthrottle.com/post/how...t-performance/
Thread Starter
Banned Scam/Spammer
Joined: Jul 2015
Posts: 2,671
Likes: 400
You are changing tire diameter but the effect is similar to wheel diameter and is not worth 200 rpm.
Read the article.
https://www.carthrottle.com/post/how...t-performance/
Read the article.
https://www.carthrottle.com/post/how...t-performance/
The 225-70-15 is 8 pounds lighter but a half inch bigger in diameter than the 255-60-15 ....Not a huge difference...
235 and 245 60 series tires are half an inch smaller than my diameter now. but weigh less......Even though it will be very slight, I'm trying not do increase my RPM on the highway any more that what it is...
255-60-15 tires look great on a vette but I'm looking to drop additional weight from my tires when these wear out..
Just a thought...
Last edited by zrc3john; Sep 26, 2020 at 06:57 PM.
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From: Hermosa
Larger Diameter rear wheels may actually increase you ability to accelerate from a stop due to less wheel spin with that 3.70 rear diff.
i’d give it a go. You will need a different driven gear on the speedometer at the transmission or accept the error in it’s read out.
i’d give it a go. You will need a different driven gear on the speedometer at the transmission or accept the error in it’s read out.
Last edited by REELAV8R; Sep 27, 2020 at 01:10 PM.
Racer
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From: Midwest
A good point. There are many variables here.
Going from 255/60-15 (27”) tires to 255/70-15 (29”) tires, all other things being equal, will have the following effects.
They will...
> decrease RPM at any given speed.
> increase top speed.
> decrease torque.
> soften the ride.
Tire size is as relevant to RPM as your ring and pinon set.
Relative Overall Drive Ratio (ODR) = (Original Tire Dia. / New Tire Dia.) x Gear Ratio.
In the case of the OP... (27 / 29) x 3.70 = 3.44 relative ODR.
That is to say, a car with 27” tires and 3.70 rear axle will have gearing equivalent to a car with 29” tires and 3.44 ratio.
A car with 27” tires & 3.70 axle at 65mph will turn 2,983 RPM.
A car with 29” tires & 3.70 axle at 65mph will turn 2,788 RPM.
Since the OP is also trying to drop weight, another possible tire is the 235/70-15 (28” tire), which is a bit lighter than the tire he has now. I myself went from the 255/60-15 to the 235/70-15 and love the change.
In that case... (27 / 28) x 3.70 = 3.57 relative ODR.
-------------------------------
1979 L82 M21 FE7
Classic White / Doeskin
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Not really worried about the wheel spin ....Don't really drag race the car.....
Thread Starter
Banned Scam/Spammer
Joined: Jul 2015
Posts: 2,671
Likes: 400
A good point. There are many variables here.
Going from 255/60-15 (27”) tires to 255/70-15 (29”) tires, all other things being equal, will have the following effects.
They will...
> decrease RPM at any given speed.
> increase top speed.
> decrease torque.
> soften the ride.
Tire size is as relevant to RPM as your ring and pinon set.
Relative Overall Drive Ratio (ODR) = (Original Tire Dia. / New Tire Dia.) x Gear Ratio.
In the case of the OP... (27 / 29) x 3.70 = 3.44 relative ODR.
That is to say, a car with 27” tires and 3.70 rear axle will have gearing equivalent to a car with 29” tires and 3.44 ratio.
A car with 27” tires & 3.70 axle at 65mph will turn 2,983 RPM.
A car with 29” tires & 3.70 axle at 65mph will turn 2,788 RPM.
Since the OP is also trying to drop weight, another possible tire is the 235/70-15 (28” tire), which is a bit lighter than the tire he has now. I myself went from the 255/60-15 to the 235/70-15 and love the change.
In that case... (27 / 28) x 3.70 = 3.57 relative ODR.
-------------------------------
1979 L82 M21 FE7
Classic White / Doeskin
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From: Hermosa
Le Mans Master
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From: North tonawanda NY
goingfrom 31" to 32" tires on my old 5 speed 4cyl jeep made it super sluggish and I could no longer hold highway speeds in 5th gear until I swapped my diff gears to 4.56. In most cases I dont think the results would be that extreme but you are changing you final gear ratio effectively.