Question about WRX Wheels on Legacy OBW

[Guest Chip Hedrick]

I'm thinking about doing the above.

 

The stock wheels on my OBW are 15 x 6".

Stock tires are 205/70R15

Stock tire diameter = @ 26.3"

Stock tire width = @ 8.07"

 

My research indicates the following about the '03 WRX:

Stock wheels: 16 x 6.5"

Stock tires are 205/55R15

Stock tire diameter = @ 24.88"

Stock tire width = @ 8.07"

 

According to the above, tire width does not appear to be a problem. My questions are as follows:

 

1. Is there a commonly available tire for 16 x 6.5 wheels (WRX size) that will give me the same tire diameter as the stock tires size on my OBW? (I'm thinking about not wanting to throw off my speedometer.)

 

2. Is there a way to adjust my speedometer for smaller diameter tires? If so how hard is it to do and how much does it cost?

 

3. Is there an inherent performance benefit in 16" wheels over 15" wheels?

 

I understand that switching to a smaller diameter tire would have the effect of lowering the OBW's gearing (which I think is good).

[Guest hocrest]

Here is a good <a href="http://www.miata.net/garage/tirecalc.html" target="top">Tire size calculator</a>

 

And here is good place to research different tires and size availability, <a href="http://https://www.tirerack.com/index.jsp" target="top">tirerack.com</a>

 

I have seen somewhere a small gear assembly that goes inline to the speedo cable but I'm not sure where I saw it???

[Guest Chip Hedrick]

Thanks. I'm hoping that someone will be able to tell me more about that gear assembly or any other way of correcting the speedometer reading.

[Guest Legacy777]

All the newer models don't have a speedo cable they have a speed sensor that is driven directly from the speedometer gear on the transmission

[Guest ShawnW]

Josh/anyone:

 

do you know what year that began?

[Guest Chip Hedrick]

Does the speed sensor setup mean that it would be difficult or impossible for me to adjust the speedometer to account for smaller diameter tires? Someone please let me know. I was seriously thinking about installing WRX wheels.

[Guest Legacy777]

Shawn,

 

Not sure what year that started, but you can still get a tranny that has just the sensor in it, and switch it over the cable kind, and vice-versa. If that's what you were interested in knowing.

 

Adjusting/calibrating the speedo may be a little difficult. To do it mechanically you would have to change the speedo gear in the tranny to a different tooth count. I'm not sure though whether on the OBD2 cars if there is an electronic way to calibrate the speedo. I know on some GM cars you can use an aftermarket scan tool to calibrate the speedo.

[Guest Setright]

Rim diameter: In general, keeping the same overall wheel diameter while increasing the rim diameter will result in better steering response and harsher ride. Both stem from the tyre sidewall height being reduced. The increased mass of the larger rim will also make your dampers work harder to control the vetrical wheel movements, which can actually reduce grip on real world roads with uneven surfaces. However, stepping it up only by one inch should not destroy your ride or grip.

 

What I personally think is far more relevant for steering response and grip is rim width in relation to tyre width. The absolute minimum is 70% rim / tyre.

 

I run 195/60 tyres on 16x6.5 rims. This gives a rim width 85% of the tyre section. Ideal for my taste. It is obvious from the very uniform wear on my tyres that the contact patch is staying flat to the road.

I really go for it in any bend or roundabout, and this usually produces a lot of wear on the outside of the tyres, but my "shoulders" show no sign of excessive wear.

Obviously tyre pressure also plays a part here, 33psi all round. 1992 Legacy EJ22 4WD.

 

A 205 section tyre on the 6.5in WRX rim will mean a ratio of 80%, which I would rate as the minimum, and probably would suit an Outback quite well.

 

(OBW Outback Wagon??)

[Guest Chip Hedrick]

Setright: Interesting info, especially about the rim/tire ratio. Yes OBW = Outback wagon.

 

I was serious about doing the WRX wheel swap (it seems like lots of WRX owners are buying aftermarket wheels and selling their OEM wheels on the net), but the prospect of throwing off my speedometer by a significant amount is giving second thoughts.

[Guest Setright]

It should be a legal speedo offset if it is no more than 5%.

 

Often, you will find that you can make do with little more than 2-3%, which is going to be hard to notice!