Tires and acceleration

[Dreamcar]

I know that smaller tires increase cruising rpms, but how do they affect acceleration?

For example, with 3.23 gears the rpms at 70 mph increase by about 250 when going from 26" to 28" tall tires, but would the car feel much different accelerating? Would it be noticeable?

[crj1968]

From a dead start probably only noticeable that you can fry the (smaller) tires easily. 
After rolling along I'm not sure you would notice a difference unless you were watching your tach.   

But say in a 1/8th mile race if you could keep traction you'd see a difference, if you are consistent.

[Mike DC]

 

People have to increase the rear tire height by several inches in order to make any real decrease in cruising RPM.  It's the same thing going the other way in regards to power. 

[Dreamcar]

So, the same car will not really feel much different accelerating whether it has 26 or 28 inch tall tires?

[Kern Dog]

First off, your math is backwards. Increasing tire diameter will lower the cruise rpms because the bigger tire travels further for each revolution.
It can be a tricky thing though. Say you have a 26" tire that has adequate traction and acceleration. Going to the larger tire will result in a lower engine speed at the same road speed but the additional weight mass of the larger & heavier tire may wipe out any mpg gains from a reduced cruise rpms.

I feel though that a 2 inch difference in tire diameter will be most noticeable in a lower powered car where small changes have a greater effect.

[Dreamcar]

First off, your math is backwards. Increasing tire diameter will lower the cruise rpms because the bigger tire travels further for each revolution.
It can be a tricky thing though. Say you have a 26" tire that has adequate traction and acceleration. Going to the larger tire will result in a lower engine speed at the same road speed but the additional weight mass of the larger & heavier tire may wipe out any mpg gains from a reduced cruise rpms.

I feel though that a 2 inch difference in tire diameter will be most noticeable in a lower powered car where small changes have a greater effect.

I just read my first post...your right, my math was backwards thanks for pointing that out 

I asked the question initially because I'm always trying to figure what direction I'm going to eventually in my build. I don't want to spend all that money on wheels, tires and gears only to be unhappy with the results.

[flyinlow]

It would be like going from your 3.23 to a 3.55 which is about 9%. 28 to 26 is about a 6-7 % increase in gear reduction.

Don't change the speedo gear with the smaller tires  and  the car will seam much faster.  

(you did say going to smaller tires )

[RallyeMike]

Someone could crunch a bunch of math on this, but realistically you are not going to noticeably feel any benefit to acceleration by going from a 28inch tire to a 26inch tire. Rather, you might feel a lot less acceleration because your contact patch gets smaller and your itty bitty tires just go up in smoke.

[crj1968]

I asked the question initially because I'm always trying to figure what direction I'm going to eventually in my build. I don't want to spend all that money on wheels, tires and gears only to be unhappy with the results.

I would say most choose their street car tires & wheels based on looks alone.

[BSB67]

But say in a 1/8th mile race if you could keep traction you'd see a difference, if you are consistent.

[BSB67]

It would be like going from your 3.23 to a 3.55 which is about 9%. 28 to 26 is about a 6-7 % increase in gear reduction.

Don't change the speedo gear with the smaller tires  and  the car will seam much faster.  

(you did say going to smaller tires )

Correct, it would be like a 3.48 gear, going from a 28" tire to a 26" tire with a 3.23.

[BSB67]

I asked the question initially because I'm always trying to figure what direction I'm going to eventually in my build. I don't want to spend all that money on wheels, tires and gears only to be unhappy with the results.

I would say most choose their street car tires & wheels based on looks alone.

.....and, I woulds say that this is also the logical choice.

[440]

I would definately say so. I took the 33" tires off my pickup and put a normal sized set on for fun and it made a huge difference, much faster.

Similarly I went from a 245/60R14 to a 245/50R14 which is calculated at an 8% difference (49mm smaller). Cruise RPM's are noticably higher.

[HPP]

Rather, you might feel a lot less acceleration because your contact patch gets smaller and your itty bitty tires just go up in smoke.

A lot of people miss this one. Taller tire=more road contact= more grip=more friction.

[RallyeMike]

Taller tire=more road contact= more grip=more friction.

Taller tire=more road contact=more friction=more grip.