The thing that sucks the worst about the X is that although it has identical gearing to the IX, it has a shorter final drive.

Because of this (and the extra weight does not help either), the fuel economy is worsened. The biggest problem I see, though, is for drag racers. Once you start making decent power on an aftermarket turbocharger, you're going to either have to raise the rev limiter or shift to fifth.

I'm not scared to bump the rev limiter around 200rpm max, but that's about it.

Lets look at gear speeds in 4th. Bear in mind, the stock rev limiter is 7599rpm:



RPM MPH
6000 89.5
6100 91.0
6200 92.4
6300 93.9
6400 95.4
6500 96.9
6600 98.4
6700 99.9
6800 101.4
6900 102.9
7000 104.4
7100 105.9
7200 107.4
7300 108.8
7400 110.3
7500 111.8
7600 113.3
7700 114.8
7800 116.3
7900 117.8
8000 119.3
8100 120.8
8200 122.3

I have 7600 and 7800 both bolded. 7600 because its the stock rev limiter; 7800, because that's where I'd flash and not feel a lot of anxiety about it.

So without tearing into the tranny, what would I do? Well, I think I might upsize my tires a little bit. The OEM A013s have a diameter of 25.6" according to Tire Rack.

I look at something to replace them with, such as Star Specs. Star Specs in stock size are 25.7", but if you go from 245/40/18 up to 245/45/18, the diameter jumps to 26.6". And look at what happens to the gear speeds:

RPM MPH
6000 93.0
6100 94.5
6200 96.1
6300 97.6
6400 99.2
6500 100.7
6600 102.3
6700 103.8
6800 105.4
6900 106.9
7000 108.5
7100 110.0
7200 111.6
7300 113.1
7400 114.6
7500 116.2
7600 117.7
7700 119.3
7800 120.8
7900 122.4
8000 123.9
8100 125.5
8200 127.0


This (to me) is a whole lot more exciting. This makes the gear speeds actually ever so slightly higher than an Evo IX. This will allow you to trap higher in the quarter mile if you have a decently modded car with turbo upgrade, it will increase fuel economy, and it will reduce a bit of wheel gap.

There are downsides. The heavier tires will effect whp ever so slightly. Taller sidewalls have more flex than shorter sidewalls. And the overall height of the car will increase ever so slightly.

But IMO, its a compromise worth testing. For Dunlop Z1 Star Specs, the 45 series are a measley $2 more per tire. My car is brand new, but I think its worth trying when the Advans are toast.

What do you guys think? Has anyone tried this already? Are the 45 series too much of a handling compromise? Thanks in advance.

 

Someone's been playing with their favorite spread sheet again I see

 

Yuo shuts up!
I'm trying everything I can to figure out how to make this car faster.

 

problem is, 245/45's rub even on stock suspension on lock and uneven roads.

 

^ that's what I think the main issue might be. Apparently people were trying it with their winter tires and it was rubbing.

I'm not sure how, since lowered, with 285/30 on 18x10.5+15 wheels I get the slightest of rubs at full lock on the liner in front and behind the wheel...

 

Oh YOU are a buzzkill.

 

Seth,
According to Moteigi, "...the overall diameter of the tire/wheel combination should be close to the original sizing". How close you ask? From another source, which I ID'ed as "SCC", the diameter should be within a few percent. So going from OEM diameter of 25.7 to 26.6 equates to ~3.4% > 2%. That said, I do not know the rational for this recommendation.

Later, Ken

 

Compromise. 1.7% increase.

Azenis RT615 in 255/40/18 (Becasue I am too poor white trash for Neovas and they're probably not any better). Azenis are low stock, might be discontinued, but are a smoking deal at $171/tire at Discount Tire.

RPM MPH
6000 91.2
6100 92.7
6200 94.3
6300 95.8
6400 97.3
6500 98.8
6600 100.3
6700 101.9
6800 103.4
6900 104.9
7000 106.4
7100 107.9
7200 109.5
7300 111.0
7400 112.5
7500 114.0
7600 115.5
7700 117.1
7800 118.6
7900 120.1
8000 121.6
8100 123.1
8200 124.7

 

Upping to 19's would solve the sidewall issue... but doesn't help at all for the rubbing

 

You might slow the car down a bit with the taller tires (heavier?), but gain from not having to shift out of 4th gear. Also. tires wear down more than a 1/4 in diameter.

I'd be happy to pull 105mph with the stock turbo, just a road car to me. I bet a different final drive ratio would dyno higher because the drive components would be spinning slower at peak engine rpm and over the whole range. There would be less diff and axle loss/friction. if i went up in tire size, I'd try to get wheels that were 1 lb lighter to make up for it. They say that 1 lb off the wheel is like 7 or 8 for accel due to rotational forces.

 

These might get you some more gear:

http://www.myride.com/images/non-veh..._(544x408).jpg


Just kidding.... for the guy asking for the rationale of keeping it below 2%. My guess would be for speedometer accuracy purposes.

 

Depending on what hits roll the fenders & get some spacers or attack the fender liners with a heat gun and ball peen hammer.

 

Why not just do some fender rolling to deal with the rubbing. This is great info and it really should be more looked into.

Nice job Noize!

 

I could be wrong but I think it is more than inaccuracy of the speedo that drives the recommendation for 2% or less; perhaps handling characteristics?

Later, Ken

 

in using larger tires, what you gain in speed, don't you lose in acceleration? does that really make your car "quicker"?