DrewGS4

Here is the scenario,

My friend and I both have a 98 GS400 and we constantly race one another. We both do not have any mod's and are running completely stock except for his rims. Here's where it gets interesting. He recently got 18'' rims with Toyo T1. I am riding on the stock 16's with the Goodyear eagle garbage. Before he went to 18's he was also on stock 16's and we use to be neck and neck all the way to 80mph which was expected. Since he went to 18's, my car launches a bit quicker and I am almost a full car length ahead of him to 80mph. We only race to 80 mph, nothing over that. We did this several times and it was the same result every time with my car on 16's ahead by a full car length. We even switched cars and he pulled ahead of me in my own car ....this was to eliminate the driver skill. His car definitely handles much better, but its the 0-60 sprint time at a traffic light which really matters to most of us.

The conclusion we came too is this: With his wider tires, he has almost 2'' of extra traction per tire multiply it by 4 and you get 8'' of extra traction and more friction. This obviously helps make a big difference in the handling department but actually slows the car down a bit from 0-80 mph. Technically, wider tires have more friction, and more power is required. But since the rear wheel HP is the same in both cars, his wider tires actually slows down the car. The only reason to go to 18's or higher in my opinion is if your car's HP increases so the tires can better handle the extra power or better handeling or purely for the looks. His car also rides much harsher which was expected. I think a good compromise would be to the optional stock 17 which I am planning on going to in a couple of months with Yoko dB's. My stock 16's are just too floaty especially at speeds over 80mph.

We are both surprised and shocked at these results. He is trying to convince me to swap my stock 16 with his 18's and race again. He is the kind of person that just doesnt take no for an answer. I probalby will end up doing this this weekend and will post a followup w/results on monday providing the weather is good.

mooretorque

Decreased acceleration due to greater rotational inertia of a heavier wheel and tire unit, not increased friction. However, assuming no change in circumference, top speed remains the same, just takes a little longer to get to.

DrRick

well depending on the 18's, he has probably increased the weight over the 16 inchers. this increases unsprung weight and inertia at the rear wheels. with the increase in inertia (an object at rest tends to stay at rest) it will take more power to get them moving. and since there has been no such increase, ie mods, he will be slower of the line. that is why you see guys here that have 20s and such that are heavy complain that there car isnt as fast as it used to be. however, there really shouldnt be too much difference once the car is moving. thus ends the physics lesson for today boys and girls..........Dr. Crosthwaite at UNCC would be proud.


Doc

zushwa

I would think that rotational mass has more to do with it than just more rubber. What kind of wheels is he running?? Are they chrome?? I'm sure some of our more educated members can help with this.

DrewGS4

Seems like we have our own little physics 101 classes going on here. Just emailed him and he has the 18'' OZ Salina, they are alloys and not chrome. Suppose to be a light weight wheel designed by L-tuned.

FCobra94

That's what I was gonna say

DrewGS4: Do you know if his braking has changed at all? I was always wondering if it takes you longer to slow down if you plus size your wheels/tires because of the extra weight...anyone else know if it would not slow down as well as before?

mooretorque

Brakes have significantly more power available for stopping than motor has for going (you CAN bring your car to a full stop from top speed while remaining at WOT if there is enough brake cooling available), so, while there could be expected to be a difference in deceleration, it would be less than the difference noted in acceleration.

DrewGS4

We are going to swap rims this saturday, will post results on Monday

RON430

Not sure I have thought the physics through but this is not unexpected. If you notice on the high speed comparos that the magazines do with the tuner cars, very often the tuner cars show up with 16 or 17 inch rims even though they may sell the car with larger rims, the larger rims are more for looks than anything. The tuners know that when acceleration is involved, the larger rims have some disadvantages to them. In 16s you can go to 245/50-16 on the GS which I have been thinking is very likely one of the better compromises for getting the increased patch for handling but not the weight of the larger rims. Second thing is that the 50 series should be a little more forgiving on ride although I am not sure that you can really tell the difference between 55, 50 and 45 series unless your butt is pretty finely calibrated. Go to 40 and 35 and the wall is just so short that the sidwall stiffness has to increase a lot so the ride is going to deteriorate eventually. Should be interesting to see what happens when you swap rims.

mooretorque

I predict 16" wins on whichever car it's mounted.

(hehehe..........i said "mounted")

GS400_PUSHER

Yeah he's pushing 2" more per wheel but I rather have the handling over all if you know what I mean.

DrewGS4

Finally, here are the results:

I swapped his 18'' on my car and he ran with my platinum 16'' rims.

From 0-60
His car was up by full car length

From 0-80
His car was up by 1.5 car length's

We both were in constant contact via cell phone using hands free headsets.

Next test

Running start from 60-100mph

Tie each and every time, ran this 3 times

Running start from 80-120mph

Same result, neck and neck. No one pulled on each other.

The biggest difference is from a stop and go.

Got interesting when a IS300 decided he wanted to play. Since we are on cell phone in constant talk with one another we toyed with him for a while kept him boxed in and than just took off. Poor guy tried so hard to run with us )

So here you have it, the results are 16'' win on a consistent basis from a 0-60 and 0-80 launch. I have ordered the 17'' so I will be sure to do the same test all over again.

I am trying to get the TRD STB and LCB. Also planning on getting the Veilside side skirts or L-tuned.
Steve Gantz is one tough dude to get a hold off. Anyone know where else I can order these parts from???

enginyr

Nice to hear hard core numbers like this. So often people give numbers and situations where there could be so many different variables. Just to make sure, no one had a 300 pound speaker box in the trunk, right?

TMitchell

What size tires are on the 16" and the 18" wheels. I would think that you would lose most of your low end speed by having an 18" wheel/tire setup that is taller in diameter than the 16" setup. If you have a quality light weight 18" wheel , and 235x40s it should not weigh that much more than the 16" setup. I could see if you are running wider tires on the rear or all the way around where you add more weight.

Manaray

those results aren't surprising at all...they're expected! However, I think better handling is more important...