Car feels slower or not as aggressive when accelerating

[5ohaejun]

The wheel MIGHT be 6 lbs less. But without weighing them, it's impossible to know. If you didn't weigh rim and tire vs rim and tire, you wont know. And again, I go back to, more mass is concentrated at the edge of the circle, not the center, so it takes way more work to get a wheel rolling.

Yea that is true

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[5ohaejun]

Probably could just be mainly because you have better traction. Unless you were dead hooking on the old tires.

yea definitely this. I was still hooking completely fine with the old setup. I just need more power now

 

[Idaho2018GTPremium]

The diameter difference between new 265/35/20 and 315/35/20 tires is about 5% for new tires. If your previous tires were somewhat worn, that 5% could be actually 7% due to the tires losing diameter as they wear. That difference causes higher overall effective gear ratio, which is probably noticeable from a seat of the pants perspective. That's like reducing your engine torque 7% (e.g., from 410 ft-lbs to 381 ft-lbs assuming 7% drop). If the car was near but not quite sluggish before, that 7% gearing change could put it over the edge. From an overall acceleration standpoint, it'll be slightly slower in a given gear assuming same rpm range, but you'll be able to hold lower gears to higher speeds (5-7% higher depending on old tire wear) due to the extra gearing, making up some of that lost ground over the course of acceleration through multiple gears. One thing to note is that you didn't actually reduce horsepower your engine produces, just the effective torque multiplication from the drivetrain. It's similar to changing a rear end differential gear from 3.55:1 to a 3.37:1 (or 3.30:1 factoring in tire wear).

I think the diameter difference is the biggest factor, but additional friction due to larger contact patches and possible much heavier tires x 4 (despite lighter wheels) also might contribute to the overall sluggish feeling.

 

[5ohaejun]

The diameter difference between new 265/35/20 and 315/35/20 tires is about 5% for new tires. If your previous tires were somewhat worn, that 5% could be actually 7% due to the tires losing diameter as they wear. That difference causes higher overall effective gear ratio, which is probably noticeable from a seat of the pants perspective. That's like reducing your engine torque 7% (e.g., from 410 ft-lbs to 381 ft-lbs assuming 7% drop). If the car was near but not quite sluggish before, that 7% gearing change could put it over the edge. From an overall acceleration standpoint, it'll be slightly slower in a given gear assuming same rpm range, but you'll be able to hold lower gears to higher speeds (5-7% higher depending on old tire wear) due to the extra gearing, making up some of that lost ground over the course of acceleration through multiple gears. One thing to note is that you didn't actually reduce horsepower your engine produces, just the effective torque multiplication from the drivetrain. It's similar to changing a rear end differential gear from 3.55:1 to a 3.37:1 (or 3.30:1 factoring in tire wear).

I think the diameter difference is the biggest factor, but additional friction due to larger contact patches and possible much heavier tires x 4 (despite lighter wheels) also might contribute to the overall sluggish feeling.

Wow, thanks for this information.

 

[Pistol_91]

Install 4 skateboard wheels then come back and tell us how much faster it is. Lol

 

[robvas]

You basically turned your 3.55's into 3.35's and have big ol steamroller tires now.

(or you turned your 3.15's into 2.97's....)

 

[sk47]

Bing Videos

Hello; Might gain some insight from an old Julius Sumner Miller video= The strange behavior of rolling things.

 

[Torched10]

You basically turned your 3.55's into 3.35's and have big ol steamroller tires now.

(or you turned your 3.15's into 2.97's....)

The way I look at the stock wheels turn 3.55 times witn each turn of the axle.the 3.15 is turning slower so your acceleration drops a bit but your mpg will go up a little.im sure I n probably didnt say it exactly right and someone will correct me,

 

[Balr14]

Something else that hasn't been mentioned, but always effects me... you simply got used to how the acceleration felt. You need more to get that feeling back.

 

[ORRadtech]

The way I look at the stock wheels turn 3.55 times witn each turn of the axle.the 3.15 is turning slower so your acceleration drops a bit but your mpg will go up a little.im sure I n probably didnt say it exactly right and someone will correct me,

So yeah, l'm sure you meant the drive shaft rotates 3.55 times for every tire rotation.

 

[Torched10]

So yeah, l'm sure you meant the drive shaft rotates 3.55 times for every tire rotation.

That's what I meant sorry

 

[RocketGuy3]

Yeah, you increased your rear tire height by almost 1.5” or over 5%. This effectively raised you rear gear ratio which reduces the the rate of acelleration making the car feel slower from the jump. Whether or not you can actually feel this amount of difference is debateable or it could be a placebo effect but the fact is the car will have less off the line acceleration because of the taller rear tire.
The good news is you could get better fuel economy ifyou do much highway driving. Whoot!

But worse fuel economy if he does much city driving, heh.

 

[GrabberBargeCaptain]

One of my last cars was an FR-S which makes 160whp on a good day, 1000 lbs lighter than my GT. I switched from the stock 21 pound 17" wheels to a 15 lb wheel and felt zero difference in performance at least in a straight line.. it did make the car feel spritelier during VERY quick and sudden turns but it was by no means a night and day difference.

I don't think it's the wheel weight especially not on a 450+hp car. The much taller tire giving you a taller final drive ratio i can definitely see though. Go drive one with stock wheels to confirm

 

[Obiton]

New tires are usually quieter and softer than old tires…. Less sound and fury reduces the perception of speed. That said, the effective gear ratio changes may also be felt if big enough. If you changed your effective ratio a full 7%, you will stay in each gear 7% longer. Your actual time to speed (0-100 or whatever) probably did not change significantly. Your extra (7%) time in lower gears and fewer gear changes may offset the 7% decreased torque in each gear. But… Your time through each gear and your time to speed on your (now incorrect) speedometer will have increased 7% or more, making it feel slower. My daily is a Jeep Wrangler with the crappy old 3.8 engine and 4A. Moving from 32” to 35” tires REQUIRED a gear change to make Overdrive work on the highway. You are probably good with the gears you have for street driving, but as others mentioned, you should adjust your speedometer.

 

[ShadesOfBloo]

sorry, I don’t understand this part. How is it higher? And is there a way increase the rate of acceleration somehow?

Your tires are like big rubber gears. By changing the outside diameter you've changed your overall gear ratio.

If you had a 3.31 rear end gear, and put on a tire that was 5% taller than before, that's the same effect as changing your rear end to a 3.145. It's a small change but as GrayMater22 also said,
the wider tires also increase your rolling friction.

And, since the new tires are likely heavier than the old ones, that weight difference is way out from the axis of rotation, so you have more rotating inertia like WItoTX was saying. If you look at the math, rotating inertia includes mass multiplied by the square of radius from the center. A 5% difference increase in radius (even if you didn't change the mass) gives about a 10% increase in inertia.

...So, you have 3 effects adding up to a difference you can feel.

You can fix that right up with a 3.9 rear end.

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