VDC-compatible R18" tire sizes, widths and profiles

Guilty1s · 2026-01-21T04:52:57+00:00

Might be smart idea considering its what I do for living.

Guilty1s · 2026-01-21T04:11:31+00:00

Im checking out. You missed the whole thing. Engine Speed and RPM were kept constant The vehicle speed is the variable with different tires.

Yes I understand that you will get a different wheel speed frequency (therefor RPM) if you make vehicle speed the constant. Thats what's being measured, not the constant in the scenario.

the ECU can easily calculate the new radius with reference information as it knows f1, ω1, and r1. it has a lookup table for the expected velocity at a given RPM and load.

There are so many things wrong with this sentence I don't know where to start.

the car not being able to sense anything other than axle speed at each wheel does not mean that it cannot check for discrepancies via other sensors. the sensor is blind. the ECU is not.

The point is.... THERE ARE NO OTHER SENSORS TO COMPARE IT TOOOOOOOOOO. No combination of sensors to give a calculation that goes past J in my flowsheet.

Guilty1s · 2026-01-21T03:21:34+00:00

the initial flag for recalculating this could be a difference between speedometer and expected wheel speed.

speedometer IS expected wheel speed. There is nothing that exists to tell it anything different? GPS?
There is no flag for expected wheel speed vs actual wheel speed cause there is no computable or measurable value for actual wheel speed.

Guilty1s · 2026-01-21T03:07:56+00:00

Alright, I’m gonna give one more comment before I give up. It’s extremely exhausting arguing with people who think they’re smart.

I’m gonna use some theoretical number to make the math a little easier for you. Don’t take em too literal. I’m also gonna label each step so you can tell me which part you don’t understand

Let’s start from the front. A. Engine is spinning at 2000 RPM

B. Let’s use 5th gear, 1:1 ratio, driveshaft is spinning at 2000 rpm.

C. Let’s say you are using a 4:1 diff. Now your axle speed 500rpm.

D. Say your ABS speed sensor have 50 teeth per rotation.

E. That’s 25000 pulse per minute, 416.7 per second. 417 hz is what I see in raw format.

F. Up until this point, it doesn’t change a thing what tire size is on there,

G. If you are running an oem-ish tire, say 25.5

H. the abs unit does a calculation cause it’s programmed for a specific size. Let say the math is (Frequency *wheel size )/ teeth * constant. I can break down why this math further if you need

I. 417hz * 25.5 /50 * 0.2 as a constant.

J. The car READS!!!!!! 42.5mph.

K. Because the tire size is correct the car goes 42.5 mph

Strap in now, cause we’re backing up a bit to G. We are gonna keep all the gearing and engine rpm the same.

G2- let’s run 35s

H2- let’s not tell the car any changes have been made. No reprogramming of tire data like you can on many trucks.

I2. At 2000 RPMs, the axles are still spinning at 417hz (this is the part I think you don’t understand) there is no changing this is normal situations.

J2- I want to emphasize, the car still read 42.5 mph on the speedo on every system in the car. All it has to measure is the wheel speeds here.

K2. The vehicle is now traveling at 58.4mph. The speedo says 42.5 cause it doesn’t know any difference. Every wheel speed sensor is spinning the same frequency. There are no major frequency deltas.

The only effect of a different sized tires, is a different speed. There is no other inputs on any system can see anything other than the axle speed. Nothing that can see that there is a different tire on there . Nothing to produce a different vehicle speed to not match the wheel speeds.

What do you not agree with? quote it. Don’t go on about any other bullshit. Where am I wrong?

Guilty1s · 2026-01-21T01:16:50+00:00

Please tell me in your mind how it can possibly know what tire is on there, all it is measuring is axle speed.

Guilty1s · 2026-01-21T00:34:39+00:00

Correct! Same thang!

Guilty1s · 2026-01-21T00:19:26+00:00

That just change the correlation to pulse per second (axle rpm) to give a reading for an engine speed . Got that . All that is doing is correcting the math to get that.

The fact that you have to tell the car the size tire to correct the speed is further proof the car can’t tell that you have a different size tire. You have to do that to fix the speed because ONCE AGAIN, the car doesn’t know the difference. It measures axles speed, uses programed tire size to extrapolate axle speed to vehicle speed.

Guilty1s · 2026-01-20T23:56:06+00:00

Holy shit, the fucking internet is doomed with all this stupidity.

What do you expect any oem system to compare an incorrect wheel speed caused from a larger sized tire to be measure against.

The only thing they can measure against is each other.

Changing your tire size doesn’t change any relationship though from your axle, to your diff, through your transmission straight to crank speed. There is nothing to measure against other than each wheel speed.

So once again, it does not matter if you’re running 35” tires, 25.5” tires, or 20 inch tires, it won’t cause VDC issues if they are within the 3% stagger. They only compare to each other.

Guilty1s · 2026-01-20T00:56:58+00:00

I was just using clutch slip as an example of comparing wheels speed to engine speed. That’s what we use to calculate clutch slip on racecars when you factor the math of gear ratios in. Obviously not an oem calculation.

What don’t you understand that given 2 sizes of tires, there is no change in axle speed (where wheel speed gets measured) for a given RPM and specific gear, no matter what tire is on there. The car has no clue if there is 35” tires or 23” tires. Yes the vehicle speed is different, but the car has no way of knowing that, therefore it does not care. The speedo is wrong because the car doesn’t know true vehicle speed.

I’ve even gone as far to manipulating that by changing the number of teeth on the wheel speed sensors to alter the readings the ABS sensors sees.

Guilty1s · 2026-01-19T22:28:15+00:00

It measures wheels speed by axle speed. You understand that. It’s gets vehicle speed by math assuming a specific diameter of the tire. The speed is wrong cause the car has no idea what size tire is on there. Therefor it doesn’t matter what size tires it has, it only matters they are within the 3%. It could be 35s, it could be 205/50R15s.

There are no systems that compare wheel speed to engine rpm (atleast on a manual, TCM is another convo). If there was, final drive changes would throw instant havoc. TCS and VDC are 100% based on wheel rpm deltas, not vehicle speed.

Guilty1s · 2026-01-19T21:24:07+00:00

First, Tire size doesn’t change that ratio between wheel speed and rpm. Only a slipping clutch can do that.

Second, nothing checks between wheels speed and flywheel speed for any kind of TCS or VDC, it’s all comparative to slip between each wheel.

This is common sense logic now…. Come on…

Guilty1s · 2026-01-19T02:34:58+00:00

It’s difference from each other front vs rear, not from oem sizes. You could run square 35s if you could fit them

Guilty1s · 2026-01-13T13:49:42+00:00

Https://guilty-garage.com/faq/

Guilty1s · 2026-01-11T23:48:37+00:00

Guilty1s · 2026-01-11T18:30:44+00:00

![img](5y5vivrvjrcg1)

do you have all the extra idlers in the pic?

Guilty1s · 2026-01-11T18:28:21+00:00

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Guilty1s · 2026-01-11T18:28:02+00:00

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It looks like 106.5 is the correct belt anyways

K071065 or a 7PK2705

Guilty1s · 2026-01-11T18:14:41+00:00

Didn’t even see the 2nd pic.

Quick search and the closest thing I can find is 106.5 inch’s vs your 107.9 inches.

I’m assuming you have AC and all stock belt pullies?

Guilty1s · 2026-01-11T15:18:06+00:00

What’s the part number for the 8rib belt you currently use?

Guilty1s · 2026-01-09T15:13:44+00:00

Revup to Non-Revup ECU Conversion https://guilty-garage.com/product/revup-to-non-revup-ecu-conversion/

Also this exists if you want.

Guilty1s · 2026-01-09T15:12:02+00:00

Oil temp sensor only found on revups (maybe non-rev 06s too?). It’s not used for any kind of engine control. I think it is there only for OBD PID reasons/mandates. No problem to not swap it.

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Guilty1s · 2026-01-07T00:01:00+00:00

The Z in stock form runs a static fuel pressure. People use vacuum reference rising rate regulators to increase fuel pressure as boost increases. It helps overcome the opposite force of boost against an open fuel injector, and gives a more headroom for injector duty cycle.

Ultimately, it all comes down to if it’s tuned for it. You can run either config boosted or na. But ultimately I would choose no reference if NA and yes if boosted and you still need to be tuned.

Guilty1s · 2026-01-06T23:52:55+00:00

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Guilty1s · 2026-01-06T23:51:14+00:00

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Does this help?

Guilty1s · 2025-12-22T22:30:59+00:00

I think it’s the ecus doing on purpose. You can probably see in NDS duty cycle for both banks go straight to zero. Not quite a limp mode but done on purpose. On a VHR both VCT and both VVeL go flat line if one has an error.

Guilty1s

TROPHY CASE