I'm gonna weigh my tires... Performance drop?!

[sudz]

Hi All,

As much as I hate the LOOK of my winter rims/tires (narrow kingstars on the stock 15 inch 2007 rims) I have to say, my car accelerates MUCH faster with them, vs. my 17 inch RTX Zens and nearly bald Protenzas'.

Like... For example, in my winters, If I'm not completely stopped, I do a 2nd gear start easily, and then shift to 4th directly.

With my summers, No chance - I'd be lugging it.

Even this morning, I was in the slow lane to merge get onto the highway. Dump Truck in front of me. I decide to go into the middle lane to get around him, seeing that I have plenty of room. In second gear @ around 15-20km... Buuuuuahhhhhhhhhhhhhhhh and then I feel like an ass because a Pickup went around me in the 3rd lane, and sweeped past to get into the highway

Anyone else notice a slowdown between winters and summers?

Winters: 185-65-15 15 inch stock alloy
Summers: 205-50-17 RTX Zen

[Pereira11]

i dont have a mazda3 but when i put on my enkei rpf1 with michelin pilot super sports they are much lighter than the stock wheels and tires. my rpf1's are 1" larger than stock.

not to knock you but generally when you purchase aftermarket rims that arent "performance oriented" they do weigh quite a lot. i would look into light weight rims or stick with 15's.

[Booter22]

i find my mx5 rims are lighter then my winters so in the summer it seems to be better then in the winter, mind you its not that much of a difference but there is a difference.

[Noisy Crow]

It's not (just) the weight of the wheels... it's the rotational inertia. Low profile / high performance tires tend to have more reinforcement which, which makes them heavier, with a lot of the weight in the tread area. So in many cases when you go to a larger rim you end up pushing a lot the weight to the edge... even though the overall assembly may weigh the same or less, you can can end up with increased rotational inertia. I have a speadsheet (somewhere!) that I got a few years ago from the Internet that lets you plug in things like tire weigh, size, rim weight, size, etc. and it will calculate the effective mass.

And now you know why a lot of the people who track run high-profile tires on steel rims.... cheapest way to reduce the rotational inertia.

[silverstarmazda]

same here, my wheels are actually the same dimensions as my winters since its an after market setup. but i accelerate a lot faster. due to weight and how stiff the tires r too. i set my tires at 45 which is pretty high. but the wear is good and theres less rolling resistance

[slam525i]

I put your numbers in here: http://www.csgnetwork.com/tireinfo4calc.html

your winters: 511.86 revolutions per km
Your summers: 499.56 revolutions per km

The sizes are different, so on your winter tires, all your gear ratios "become" shorter. Your acceleration would be better because of this, plus your speedometer will read high, so you're going slower than you actually think. The combination of the two, one acting on your butt dyno, and the second acting on the speedometer to make you reach desired speed earlier, may explain what you're experiencing.

[CelestSpeed3]

i dont have a mazda3 but when i put on my enkei rpf1 with michelin pilot super sports they are much lighter than the stock wheels and tires. my rpf1's are 1" larger than stock.

not to knock you but generally when you purchase aftermarket rims that arent "performance oriented" they do weigh quite a lot. i would look into light weight rims or stick with 15's.


+1 my RPF1's make a huge difference on the car.

[The Wolf]

+1 to noisy crow. The weight of the wheel is one thing, but the further out from the axle that the weight is located is another. On your winters, the barrel (bulk of the weight of the rim) is two inches closer to your axle/rotation point than on your 17's. Takes a lot more force to move weight when it is located further away from the rotation point.

[The Wolf]

+1 to noisy crow. The weight of the wheel is one thing, but the further out from the axle that the weight is located is another. On your winters, the barrel (bulk of the weight of the rim) is two inches closer to your axle/rotation point than on your 17's. Takes a lot more force to move weight when it is located further away from the rotation point.

It's like lifting a pail of water straight up vs holding the pail at arms length in front of you.

[silverstarmazda]

truee, but my new summers are 17's while my winters were 16's. im going slower than wat the speedo says. but its a very noticeable difference in acceleration. i mean same dimensions as in outside diameter, width, stuff like that. its just slightly bigger than my old oem summers. but ive never had the car accelerate better. not harder but it doesnt lag as much anymore.

[ptfire]

When I was shopping for new wheels and tires for my MS3 weight was one of my main concerns. The new combination turned out to be just over 9lbs lighter per corner and I am still running 18s with a slightly wider tire than stock.

[S.F.W.]

When I was shopping for new wheels and tires for my MS3 weight was one of my main concerns. The new combination turned out to be just over 9lbs lighter per corner and I am still running 18s with a slightly wider tire than stock.
same here. I had a specific look I wanted fr my MS3 rims, bt also weight was a huge concern.

[ericssonfan]

I notice about a 1.0L/100km on the computer increase (haven't done the real life calculations) over 2 fillups since I changed over to my summer setup. :(
I went from 16's to 18's and I should have thought of weighing them before I put them on because now I'm really interested in knowing how much they weigh.
I also didn't know about the rotational inertia. Good info to know.

[Noisy Crow]

Lot's of good info:
http://hpwizard.com/rotational-inertia.html

Same worksheet I used when I bought my Enkeis:
http://the-welters.com/racing/rotational.xls

[sudz]

Hrmmm, all very valid - I knew i'd take a bit of a hit, but yeah, it seems worse than last year. I guess its because we jumped right into 20+ degree weather, which has never really agreed with my car, Lack of torque + needing more to move the heft of my rims must have made it paticularly noticeable. Here's hoping the sumi's I've ordered from Allen are lighter than my bald Bridgestone protenza's. :-S

I knew my winters were smaller, because in the winter, I have to be careful or my nose scrapes getting into my parking garage, with my summers, no problem. I've got Car Dock Ultra on my SG2, with a car mount, I always had the GPS up there to know how fast I was actually going. at 105 ish on the cars speedo, I was actually doing 100. Also, fuel consumption dropped to 7.4

The other day was mostly the "butt dyno" Its gotten a bit less noticeable now, but definately still there. Even highway passing, I'm reaching for 3rd instead of 4th, and delaying shifting in general to keep the revs higher. I suppose its just adapting. Paticularly when the A/C is on as well :-)

One day, I'll get a car with torque... One day... lol

(but not a desiel. ... unless its s a BMW 335d. those are awesome.

[sudz]

At simplytire, allen weighed my rim, 19.2 pounds! Pretty damn good considering! They are rtx zen. Wonder what my stock alloys weigh...

[The Wolf]

I get better fuel economy on my forged BBS 17x9's than my OEM 16's :winner