Spec B wheels & tires on a regular LGT

Since some Spec B owners will be selling their stock rims and tires to owners of regular LGT's, I just wanted to point out that using the larger-diameter Spec B tires on a regular LGT will throw off the speedometer and odometer readings (besides slightly hurting acceleration).

By my rough calculation, the sidewalls of both the stock Spec B tires and the stock LGT tires are around 3.75", for a total diameter of ~25.5" for the Spec B tire vs. ~24.5" for the regular LGT tire. That means the Spec B tire is approximately 4% larger in diameter (and therefore, circumference). So, the speedometer and odometer should read ~4% lower than actual speed and distance when running the Spec B tires on a regular LGT. This is as opposed to a "plus-one" sizing, where a tire with a lower-profile sidewall is matched to a larger rim, in order to keep the outside diameter approximately the same.

This problem of speedometer calibration can be avoided or minimized by putting a lower profile tire on the Spec B wheel for use on a regular LGT.

some tires are different than others too, even with the same advertised sidewall size.

there is a chart somewhere on the web that levels the field by doing measurments all the same way.

dR

it's not going to matter that much.. I run oversized for a long time.. with 25.5" tires.. it's only to your benefit anyways as it lowers your odometer reading as you drive

which would be a crime in most states if you don't disclose actual mileage. Just because you do it doesn't mean it's right nor in the best interest of most people on this board.

it's not going to matter that much.. I run oversized for a long time.. with 25.5" tires.. it's only to your benefit anyways as it lowers your odometer reading as you drive

It may not be huge, but it's 4%. At 75 mph, that's a difference of 3 mph on the speedo. In other words, if you're running the larger tires and your speedo says you're going 74 (say, in a 65 zone), you are actually going 77. If you're like me, and you believe that you are less likely to get pulled over going 9 over the speed limit than if you are going 11 over the limit, it makes a difference. I don't think the judge is going to let you out of the ticket based on the "Spec B wheel defense".

I just thought that it might be something people wouldn't realize or think about, and it's something they should be aware of. I'll bet many people think the Spec B tires are simply a plus-one size vs. the regular LGT tires.

A question I don't know the answer to: Since ride height would be changed by putting the Spec B tires on a regular LGT, would the car need an alignment?

There's gotta be some slop allowed in the reported mileage laws... even with the factory wheels the odo isn't 100% accurate... any idea what the allowable slop is? +/- 5%?

that's different. To do it intentionally and not to disclose it is a crime. I don't think it's anything to worry about, but for a member to encourage it as a benefit is nothing short of

it's only to your benefit anyways as it lowers your odometer reading as you drive

Might as well crack open the odometer and roll it back

Didn't I read on here somewhere that the ECU, or whatever calculates and displays the speed and mileage can be changed as to what size wheels / tyres you have on ? Can only be changed with the Subaru select monitor thingy ?

Very interesting; I never read that. It would be great if you could do it with an AccessPort.

Someone (Opie maybe?) noted a LONG time ago that the Select Monitor could change readings for 18" wheels. Long before we knew the Spec.B would be a trim package or that they would offer 18" wheels. It was speculated, though, at that time that Subaru might be planning on offering an 18" wheel option. Speculation was apparently correct.

Now ... to get our hands on a Select Monitor and see if we can make this work.

Someone (Opie maybe?) noted a LONG time ago that the Select Monitor could change readings for 18" wheels. Long before we knew the Spec.B would be a trim package or that they would offer 18" wheels. It was speculated, though, at that time that Subaru might be planning on offering an 18" wheel option. Speculation was apparently correct.

A minor point: it's really the tire size, not the rim size that is the issue here. You can have 18" tires that are (basically) the same overall diameter as the stock 17" tires (e.g. 235/35/18, or the more common but not as close to stock 225/40/18). You can also have 17" tires that are considerably larger in diameter than the stock tires (e.g. 235/45/17, which are close to the diameter of the Spec B tires).

I would assume that most of the people on this board who have gotten 18" wheels tried to stay close to the stock tire size in overall diameter, rather than going with a larger-diameter tire like the 215/45/18 Spec B size.

Might as well crack open the odometer and roll it back

Huh... OK... I guess I never considered putting aftermarket wheels & tires being the same as cracking open the odometer and rolling it back... even if there's a side "benefit" with the larger tires & wheels of showing "only" ~100,000 miles on the odo after an "actual" 104,000 miles. Wear & tear on the engine & drivetrain would be pretty much equivalent between a car with the stock wheels at 100,000 actual miles and a car with the aftermarket wheels at 100,000 indicated miles given that the car is covering more distance at the same RPM, so not only is the indicated mileage still a fairly accurate indication of the life of the mechanicals, it's also such a piddly amount that it's not enough to change the resale value of the car. I simply can't imagine anyone purposely putting larger wheels & tires on their vehicle specifically to reduce the odo reading by a mere 4% any more than I can imagine someone going through the trouble of cracking open their odometer to roll it back by a mere 4%...

Now if Xenonk had said something like "I highly recommend you get a 20" wheel with a 245/55/20 tire in order to knock 20% of the actual miles off the odometer so that you get better resale value;" then I'd totally be with you saying that's not something that ought to be recommended on this board...

To each his (or her) own, I suppose...

Didn't I read on here somewhere that the ECU, or whatever calculates and displays the speed and mileage can be changed as to what size wheels / tyres you have on ? Can only be changed with the Subaru select monitor thingy ?

So it could be changed to say I have 16" wheels & tires and then I could save 4% of actual miles on my odo without having to buy larger aftermarket wheels & tires...?? Cool! I could make a killing on resale...

many cars (especially german) speedos read artificially high from the factory and often make up for customers putting larger wheels/tires on. my m coupe reads roughly 10% high

If I am not mistaken, there is a law in Europe(an Union) that states that speedometer might never show lower speed.

Manufacturers fulfil this by calibrating speedometer for largest wheel/tire combo that still fits into the wheel well.

Krzys

If I am not mistaken, there is a law in Europe(an Union) that states that speedometer might never show lower speed.

Manufacturers fulfil this by calibrating speedometer for largest wheel/tire combo that still fits into the wheel well.

 

Krzys

i have heard that as well. one of the car mags (car & driver i think) published a full article on the issue a few years ago and i believe they gave the same explanation.

ive learned to use the tach instead of the speedo to figure out how fast im going

which would be a crime in most states if you don't disclose actual mileage. Just because you do it doesn't mean it's right nor in the best interest of most people on this board.

Driving 40,000 miles with a 500 mile difference on the clock aint gonna kill me.

Driving 40,000 miles with a 500 mile difference on the clock aint gonna kill me.

then why tout it as a benefit?

Might as well crack open the odometer and roll it back

as long as the owner knows what the modding does to the car, it's their responsibility to handle it in their own manner, hopefully a legal manner.

It's like all those people running around messing with exhaust and tampering with cats.. that's a larger offense than not mentioning "btw, these wheels are not stock, that is all".

then why tout it as a benefit?

it's a benefit for those that see it as a benefit (see my original post if one was to go oversized, in any case, that last note about the mileage was just a minor sarcastic joke, hence the " ").. for me, I plan on keeping this car til it rusts out and just vanish into carbon bits. So regardless if the motor had 200,000 miles or 500,000 miles, as long as the body is still intact, I'll put in another motor in it and start all over again.

Now if Xenonk had said something like "I highly recommend you get a 20" wheel with a 245/55/20 tire in order to knock 20% of the actual miles off the odometer so that you get better resale value;" then I'd totally be with you saying that's not something that ought to be recommended on this board...

 

To each his (or her) own, I suppose...

:lol: :lol: :lol:

I would love to see someone even try knocking just 5% difference.. RippinRoo, you are correct about the 4% difference being moot as the miles go up. But it's how people see the car was used if someone was that anal-retentive about the actual mileage on the car. Maybe the person looking into buying a used car really wanted to know how many miles your motor actually ran.. but again, it's how you view 50,000 miles on the odometer vs. 52,000 miles on the actual chassis.

And then there are people that run some obsurd tire sizes that is greater than 10% of the original size.

And then there are people that run some obsurd tire sizes that is greater than 10% of the original size.

Courtesy of jazzymt & his photochop skillz: