Hyundai Genesis Forum banner
1 - 20 of 20 Posts

·
Registered
Joined
·
75 Posts
Discussion Starter · #1 ·
I drove a 14 3.8 GT with 18" rims and then a 15 3.8 ultimate with 19" rims, does the rim size affect final drive?

I guess the overall tire / rim height could affect the final drive so are the overall height the same or different?

The 19" car felt much faster.
 

·
Registered
Joined
·
283 Posts
While the circumference is obviously different, it's not THAT different. That being said, if anything, the 18's would yield better performance than the 19's, but I sincerely doubt it would be picked up by the butt dyno.

However, it is entirely possible that the 15's engine was in better condition. Or, it could have been psychosematic.
 

·
Registered
Joined
·
75 Posts
Discussion Starter · #3 ·
Thanks for the info. It could have just been me but i do believe some motors in same stock form are just better runners, I remember this from riding in several different muscle cars back in the 70s.

The first car didn't really feel more powerful than my 2012 3.8 but the second sure did.
 

·
Registered
Joined
·
239 Posts
The 245/40 x 19 tire size is almost exactly the same rolling circumference as the 245/45 x 18. Or about 2 tire rotations different in a mile. Assuming the stock tire size on the cars, that would have no bearing on "gearing" or acceleration. Like has been said, some cars may simply run stronger than others. Maybe one car was running 87 octane (not a great idea) and the other 91 or 93??

ominousone
 

·
Registered
Joined
·
283 Posts
IIRC both the LSD and open diff have the same ratio... Also FWIW having a taller ratio would result in slower acceleration, not faster... It's easy to mix up though. The octane difference is a good point that I also forgot to mention though.
 

·
Registered
Joined
·
486 Posts
IIRC both the LSD and open diff have the same ratio... Also FWIW having a taller ratio would result in slower acceleration, not faster... It's easy to mix up though. The octane difference is a good point that I also forgot to mention though.
Yes, my typo. Meant a low gear, ie 3.90, etc.
 

·
Registered
Joined
·
283 Posts
Yes, my typo. Meant a low gear, ie 3.90, etc.
Probably one of the easiest mixups/typos lol. I have seen several posts on FB lately regarding people swapping their diff's for shorter and also taller ratios, so it's also possible that one of the aforementioned cars could have been swapped as well.
 

·
Registered
Joined
·
486 Posts
Yes, my typo. Meant a low gear, ie 3.90, etc.
Probably one of the easiest mixups/typos lol. I have seen several posts on FB lately regarding people swapping their diff's for shorter and also taller ratios, so it's also possible that one of the aforementioned cars could have been swapped as well.
Which makes me feel more like an idiot as I used to build and drag old American muscle in Gainesville. Sometimes the fingers dont type what the mind means to say lol.
 

·
Registered
Joined
·
2,032 Posts
All 6mt 2013 - 2016 v6 have same ratio - 3.5.
Automatic bk2 v6 has 4.1 final drive for all years.
I am asumming he drove automatic in both cases.

Nonly logical explanation for diferance between the two - grade of gas, or transmission learning (if differance was felt non in WOT driving)

Sent from my SAMSUNG-SM-G900A using Tapatalk
 

·
Registered
Joined
·
75 Posts
Discussion Starter · #13 ·
All 6mt 2013 - 2016 v6 have same ratio - 3.5.
Automatic bk2 v6 has 4.1 final drive for all years.
I am asumming he drove automatic in both cases.

Nonly logical explanation for diferance between the two - grade of gas, or transmission learning (if differance was felt non in WOT driving)

Sent from my SAMSUNG-SM-G900A using Tapatalk
The cars i drove were both autos and think both would have 3.909 final drive.

I drove both in auto sport mode also
 

·
Registered
Joined
·
2,032 Posts
The cars i drove were both autos and think both would have 3.909 final drive.

I drove both in auto sport mode also
Prety sure that website is incorrect, as all 13 and newer autos (2.0 or 3.8) come come with 4.1 dif, while 2012 and older with 3.9

Sent from my SAMSUNG-SM-G900A using Tapatalk
 

·
Registered
Joined
·
150 Posts
There are a few replies here, but I would like to go back to your original question:
Title of your thread: “Do stock 18 and 19 " rims affect final drive ratio?”

I drove a 14 3.8 GT with 18" rims and then a 15 3.8 ultimate with 19" rims, does the rim size affect final drive?

I guess the overall tire / rim height could affect the final drive so are the overall height the same or different?

The 19" car felt much faster.
It is the tire size (the tire’s diameter) and not the wheel’ diameter, that affect final drive ratio. You can have 18” and 19” wheels with the same final diameter if the tires are sized correctly. For example, a 275/40-18” tire has nearly the same diameter as a 275/35-19” tire.

I’m not sure of a reason the “19 inch wheel on that car felt much faster.” In fact, it should have been opposite, all other things being equal. A 19” wheel is heavier than an 18’ wheel; and therefore, overcoming inertia will be greater for the 19” wheels, and it will be slower while accelerating. That is the reason people who track their cars never go over 18” wheels and often go with 17” or even 16” wheels. They want better acceleration, and you get that with smaller and lighter-weight wheels. A good example of this is Formula 1 race cars that run with 13” diameter wheels. The tire compound weighs less than a metal wheel.
 

·
Registered
Joined
·
2,032 Posts
There are a few replies here, but I would like to go back to your original question:
Title of your thread: “Do stock 18 and 19 " rims affect final drive ratio?”



It is the tire size (the tire’s diameter) and not the wheel’ diameter, that affect final drive ratio. You can have 18” and 19” wheels with the same final diameter if the tires are sized correctly. For example, a 275/40-18” tire has nearly the same diameter as a 275/35-19” tire.

I’m not sure of a reason the “19 inch wheel on that car felt much faster.” In fact, it should have been opposite, all other things being equal. A 19” wheel is heavier than an 18’ wheel; and therefore, overcoming inertia will be greater for the 19” wheels, and it will be slower while accelerating. That is the reason people who track their cars never go over 18” wheels and often go with 17” or even 16” wheels. They want better acceleration, and you get that with smaller and lighter-weight wheels. A good example of this is Formula 1 race cars that run with 13” diameter wheels. The tire compound weighs less than a metal wheel.
You will minimize efect of rotational enertia on accelaration, as long as weight of the tire does not increase when you go from 19 to 18 rim.
Weight of a tire has more affect on accelaration then weight of a rim (because total weight is further from center of rotation ).

I dont belive that anyone will feel a diferance in case of GC, but I will try to find weight of the rims and tires to calculate the diferance in power.


Sent from my SAMSUNG-SM-G900A using Tapatalk
 

·
Registered
Joined
·
150 Posts
Wheels weigh much more “per unit measured” than “rubber” tires. The compounds used in making modern tires are extremely light weight.

There is NO factual basis in your statement: “Weight of a tire has more affect [sic: effect] on accelaration [sic: acceleration] then [sic: than] weight of a rim (because total weight is further from center of rotation).”

The tire is so much lighter than the wheel weight that the inversion effect is not significant.

You will minimize efect of rotational enertia on accelaration, as long as weight of the tire does not increase when you go from 19 to 18 rim.
Weight of a tire has more affect on accelaration then weight of a rim (because total weight is further from center of rotation ).

I dont belive that anyone will feel a diferance in case of GC, but I will try to find weight of the rims and tires to calculate the diferance in power.

Sent from my SAMSUNG-SM-G900A using Tapatalk
 

·
Registered
Joined
·
2,032 Posts
F1 regulations prevent them running larger rims, and tires are completely different composition.
Street tires weight as much as rims.

My point is purely baced on physics. The further weight is from center of rotation, the more it affects accelaration. What i did not considered, was the fact that by going to 18s, you are decreasing your rim weight distance to center. (You gain equivalent of 5hp just going from 19 to 18" rims without changing weight)

I looked up GC weights and it looks like 18" tires are diferent model and weight 1lb less. And rims weight 2lb less.

Plugging it in into a formula - going from 19" to 18" package is same as gaining 11whp on GC v6, OEM tires.


If you were to run same brand and model of tire in wider spec, 245f and 265r on 18 and 19 rims, 18" tires will be a bit heavier (1lb) - this would minimize benefit of smaller and lighter rims. You'd be looking at 4hp diferance between 18" and 19" wheels.
 

·
Registered
Joined
·
2,032 Posts
This is how tire plays into rotational inertia.

If you save 4lb per rim (same diameter) - it is equivalent to 5hp gain.

If you save 4lb per tire (same diameter) - it is equivalent to 12 hp gain.

This Calculation was done for 19" rims and tires using physics.

Picture shows what I am using to a proximate weight to power relation.


 

·
Registered
Joined
·
150 Posts
There is a very good thread on this site that describes and defines some points in our discussion.

http://www.gencoupe.com/new-member-section/216521-ultimate-genesis-coupe-newbie-guide-modding-must-read-2.html

There is a great deal of information in this thread. This is a great read for anyone, owning any performance car. The author did a great job posting useful and accurate information. He is also a very good and interesting writer. --Spike

F1 regulations prevent them running larger rims, and tires are completely different composition.
Street tires weight as much as rims.

My point is purely baced on physics. The further weight is from center of rotation, the more it affects accelaration. What i did not considered, was the fact that by going to 18s, you are decreasing your rim weight distance to center. (You gain equivalent of 5hp just going from 19 to 18" rims without changing weight)

I looked up GC weights and it looks like 18" tires are diferent model and weight 1lb less. And rims weight 2lb less.

Plugging it in into a formula - going from 19" to 18" package is same as gaining 11whp on GC v6, OEM tires.


If you were to run same brand and model of tire in wider spec, 245f and 265r on 18 and 19 rims, 18" tires will be a bit heavier (1lb) - this would minimize benefit of smaller and lighter rims. You'd be looking at 4hp diferance between 18" and 19" wheels.
 
1 - 20 of 20 Posts
Top