Alright, we all know the debates b/n 215/40/17 & 215/45/17.

But, can someone out there quantify the difference in 1/4-mi & 0-60 acceleration b/n the two sizes?

And, what's the affect on interstate speed acceleration?

I'm not a drag racer, I just haven't heard the sizes compared in this manner.

Thanks.


ZM

 

About 3% deviation

Alex

 

Going from the 45-series to the 40-series will cause your speedometer to read about 3.4% too high (Not a big difference - about 2MPH at 60MPH).

The effect on your acceleration is harder to predict. Normally, smaller-diameter tires will increase your acceleration by lowering your overall drive ratio, but it may not be noticeable.

Even if it is noticeable, it might not be helpful. If you're doing 1/4-mile runs, and you're currently hitting redline right as you cross the finish line, then shorter tires could actually hurt you, because you might have to upshift right as you're crossing the traps. The time you saved from the extra acceleration could be lost because of the extra upshift.

There are some pretty sophisticated software packages out there that let you change variables such as horsepower, torque, transmission ratios, differential ratios, and tire sizes, and predict the effects on things like 0-60MPH and 60-80MPH times, and 1/4-mile elapsed times. They're not 100% accurate, but they're fairly close.

Scott

 

The difference between the two for street use is not significant.

The size of the tires is not as important as:
Reaction time to start a 1/4 mile race or 0-60 run.
The stickness of the rubber for the given tire you choose- i.e. either size tire with sticky rubber will work best for acceleration as long as traction is kept- if you spin wheels then neither sized tire will help you.

Generally given the same rim and same tires but only changing the size, the smaller outer tire diameter will be of gearing advantage but only a little. Probably not enough to tell the difference for acceleration purposes.
The weight of the rim and weight of the tire are also factors, the lighter the total weight the better- this will vary with the tires choosen.

If you have a limited slip differential and a smooth acceleration style you might be able to notice something but it would be difficult in a blind test- where the driver doesn't know which tire he is using. If you have a stock differential and the older MCS with tall gearing then I would predict it would make little difference which tire you use.

These tires ARE very different for cornering, turn in responsiveness, and ride firmness.

 

but 0-60, about 3% slower for the 45 series tires..... And that is if your car will do 60 in second. Mine's an 02, and it hits just about 70 in 2nd....


In general, for small changes, you can just do a linear approximation... So if torque is down 3%, it will take 3% more time (or whatever) to get to the same place. Not perfect, but a good gide to the eye, so to speak. Of course, when you start introducint extra gear shifts, all bets are off....

Matt