Effect of changing wheel/tire size?

[Yamazaki]

In changing an Outback's wheel/tire setup to a Blitzen setup, I will end up with a 7.56% diameter difference which will show on the speedometer as going 8.165% faster than the actual speed.

My question is - how do I get the speedometer (which will also be switched to one that came from a vehicle with the new wheel setup) to show the correct speed?

[Airgne]

are you changing the speed sensor or the gauge cluster?

you might have to get the gear out a blitzen transmission.

even my factory speedo clutster is off from the computer.

[Yamazaki]

I'm changing the gauge cluster and the wheels. Where's the speed sensor? It sounds like that's what I'm going to need....

[rougeben83]

its in the transmission housing.

[Matty2Hotty]

Yeah I read there is two speed sensors, one inside/side of the tranny housing. I'm wondering the same thing myself with my outback.

[bobbyjimmy]

Just get new tyres that keep it the same (or close) to standard.
I've got 235 40 18 on my BH Outback and the speedo is within 3% - good enough for me.

As above, 2 speed sensors - the electronic part screws into the RH side of the case, and there is a driven (plastic) gear inside the box - stuff changing them out, just buy tyres.

[Yamazaki]

Just get new tyres that keep it the same (or close) to standard.
I've got 235 40 18 on my BH Outback and the speedo is within 3% - good enough for me.

If I used a similar size tire, then I wouldnt be able to use the suspension I want. Looks like I'll be switching out some sensors...

[Matty2Hotty]

I know. I want some lower profiles to get that much lower :D

[dodik]

dont do it put the right size tires on your outback, go thru my thread there are few set of wheel/tire combo in the legacy size not outback its just doesnt fill the wheel arch they will be too small

[impreza_GC8]

The actual gear on the inside of the casing is what measures the speed. Different cars have a different tooth count. You cannot just change the electric sensor. Run whatever wheel/tire and suspension combo you want, but your speedo will not read correct.


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[chuckthefuk]

If you cant mix and match then why not recalibrate the signal

http://www.mrtrally.com.au/performance/photo/mrt161.jpg

ADJUSTABLE SPEED LIMITER and speedo signal calibrator. Designed to be fully "programmable" the electronic part simply converts the speedo drive digital signal to a setting that is "user definable". Able to redefine the speed cut to a user chosen limit and able to re calibrate the signal to suit larger or smaller dia wheels. (Great for new big diameter wheels)

http://www.mrtrally.com.au/performance/

[Yamazaki]

dont do it put the right size tires on your outback, go thru my thread there are few set of wheel/tire combo in the legacy size not outback its just doesnt fill the wheel arch they will be too smallThe wheels will look just fine since I'm changing all exterior panels, struts, wheels, etc. to look like a Blitzen6. Giant tires won't fit.
The actual gear on the inside of the casing is what measures the speed. Different cars have a different tooth count. You cannot just change the electric sensor.Does this include A/T cars?
If you cant mix and match then why not recalibrate the signal

ADJUSTABLE SPEED LIMITER and speedo signal calibrator. Designed to be fully "programmable" the electronic part simply converts the speedo drive digital signal to a setting that is "user definable". Able to redefine the speed cut to a user chosen limit and able to re calibrate the signal to suit larger or smaller dia wheels. (Great for new big diameter wheels)

http://www.mrtrally.com.au/performance/I looked through "all products" and I can't find it in their site...

[impreza_GC8]

I cannot say for sure as I've only had 5MT transmissions apart, but I doubt the design is different. The sensor unscrews from the housing, but the tooth that the sensor plug fits into is part of the interior housing. I am running an RS transmission in my Outback, but before I swapped it I took it apart and reused my Outback speedo gear. Otherwise the speedo would've been off.

[chuckthefuk]

IIRC 4EAT get their speed from wheel speed sensor or ABS.
-Chuck

[impreza_GC8]

What about early gen non-ABS cars? Were they all 5MT?

[dodik]

you do realize that if you go with H6 you will loose like 20% more fuel by rotating tiny tires? when i was on legacy wheels for a very short time i noticed that you really gotta push it to keep up with traffic instead of 2100rpm at 60 i was doing like 2800 looks are not worth it trust me. also what was the offset on those wheels is it 53?

[Yamazaki]

you do realize that if you go with H6 you will loose like 20% more fuel by rotating tiny tires? when i was on legacy wheels for a very short time i noticed that you really gotta push it to keep up with traffic instead of 2100rpm at 60 i was doing like 2800 looks are not worth it trust me. also what was the offset on those wheels is it 53?
Offset is 55. So you're saying I need to change the trans too? Looks like I'll be buying a donor car for all of this then. But that actually helps with something else I plan on doing...

[dodik]

h6 produces a bit more power most of the time i dont rev it past 2500rpms if you change the wheels you will need to find a tranny with much taller gears to keep the revs down, revving engine wont hurt but it will dent your wallet, now that i think about it legacy gt 4eat is the same as h6 4eat 4.11 just different speed sensors gears. oh and while you at it get some longer wheels studs you will not like how 55 offset looks on the outback you will need spacers

[dodik]

ok i just did some math this is approximate but with the stats you posted above you will loose about 1.5m per every gallon so if you were getting 20mpg with this tire setup you will get 18.5mpg

[Yamazaki]

oh and while you at it get some longer wheels studs you will not like how 55 offset looks on the outback you will need spacers
Huh? But if I change all of the exterior (as I am going to), then it effectively no longer has Outback measurements. Spacers would make the wheels stick out. Unless it's the chassis and not the body panels that make the Outback wider...

[chuckthefuk]

I believe this comes back to Dodik's previous posts about the Lancaster and the OB have different flares / body moldings.

[dodik]

chassis is setup a bit differently to accommodate larger wheel/tire combo the outbacks came with 48 offset while same year legacies came with 53mm, i assume you will change struts to bilsteins so that will bring the lower springs perch very close to the tire and if you do run proper tires you will rub on it with 55 offset, (with legacy tires you should be fine but your allignment will need to be dialed in differently something in between legacy and outback) when it comes to body panels you will need fenders and all four doors at the minimum which i think you already have but im not sure how all that will meet the outback quarter panels. i mean i know your car will be epic but how much work are you really willing to do/spend money on?

[Yamazaki]

i mean i know your car will be epic but how much work are you really willing to do/spend money on?
To find the answer to that, you only need to look at the two cars I have already... :smt006