New Beetle tire upgrade and speed sensor problem

[silverbug99]

We followed the advice of the board and went with one up tire size change on a 1999 VW New Beetle.

We now have experienced cruise control and speedometer pulsing.

Cruise control will not lock on and stay at steady speed.

Everyone said this tire size change would not affect cruise or speedometer, how do we correct this?

Is the VAG com software useable to adjust this problem?
If so, what setting?

Thank you

[Basher]

What tire size did you mount?

[SilverSportNOLA]

Well .... I believe the ECU knows around what speed the vehicle should be going based on stock tire sizes from the engine RPM and the fact that cruise will be used in final gear, without the input from the actual speed sensor on the tranny ... but not sure. I know for the week I drove my car after the clutch replacement where they broke the speed sensor, I could not use cruise, and there were some other things that didn't work right, but, the spoiler still deployed at what seemed to be the normal 93MPH, it just wouldn't go back down automatically, some programming in the ECU deployed it regardless of the Speedo reading 0 MPH.

[silverbug99]

New tires are:
225 50 16


Thank you for your input

[yelojkt]

Switching from a 215/55/16 to a 225/50/16 should not effect your tire diameter much and therefore should not effect your cruise and speedo function. I run 235/40/18 and have no problems with cruise or speedo.

[SilverSportNOLA]

Could just be the Speedo Sensor is failing. Like the YeloMan said, that is really not much difference in diameter between those sizes. The new tires should be .4 inches shorter, which would be the difference of driving on new tires your old size and driving on half worn tires you old size, should not make a difference. Look here http://www.miata.net/garage/tirecalc.html

[silverbug99]

Code scans are showing no speed sensor defective codes.

Has anyone had a defective speed sensor that did not show codes?

[Too Cold NB1.8T]

What was the tire that you switched from?

[mel72349]

I don't know that it would make a difference, but keep in mind that tire sizes are like shoe sizes. The same size from different manufacturers will have different dimensions. Even within one brand, dimensions will vary by line.

The Miata size comparison site is a good rule of thumb, but is only an average. It's possible the specific tires are quite a bit larger than the size designation suggests.

But again, I don't know if it would be enough to cause the problems or not.

[OldSkoolVWLover]

correct me if I am wrong....

Overall rolling diameter will mainly only effect actual speedo readout. The vehicle senses speed from the speed sensor, but now you are getting more or less rotations from the tire so the speedo could be reading a few MPH faster or slower than actual speed. To my knowledge with all cars, I have never seen a car not function properly because of a mild tire/wheel change. Even when you get a wheel tire combo that is supposed to have the same rolling diameter it never is exactly the same.

Also if slight variations could cause this much of an issue you would see the same issues when tires wear (changing the rotational mass and diameter). You would also see the same issue when say switching from a summer tire to a winter wheel and tire (for those that don't live in nice weather).

[SilverSportNOLA]

That's about what I said, the new tire is about the same as the old half worn .... there is a possibility that they damaged a wheel speed sensor, I would check that. To reiterate an earlier post I made, the ECU gets speed information from more places than the speed sensor on the transmission, otherwise how do you explain my spoiler going up at speeds that felt around the normal 93MPH deployment speed when my tranny speed sensor was broken and I had no cruise control or speedometer?

[Too Cold NB1.8T]

Each car manufacturer has their own engineering concept when it comes to this and other aspects, I asked what the stock tire size was on this partiular car but never got an answer so there is no reference point.

On many of these new cars (especially ABS equipped) altered or unmatched rolling rates can cause different problems including a DTC, CEL and an ABS light to illuminate, among all the sensors these cars have, most of them also have ESP or ASR etc. along with front & rear wheel sensors that speak to the ECU.

Yes, the UTQG ratings from manufacture to manufacture often differ slightly because there are no real governing bodies in this area, however, the differences are not spectacular and in a given size this is not known to cause any issues other than maybe a fender rub.

A new tire wearing down to a bald tire is at the most maybe 12/32 of an inch, this is not nearly enough to cause a system problem and it is not an accurate comparison to the problem at hand.

[OldSkoolVWLover]

Originally Posted by Too Cold NB1.8T

Each car manufacturer has their own engineering concept when it comes to this and other aspects, I asked what the stock tire size was on this partiular car but never got an answer so there is no reference point.

On many of these new cars (especially ABS equipped) altered or unmatched rolling rates can cause different problems including a DTC, CEL and an ABS light to illuminate, among all the sensors these cars have, most of them also have ESP or ASR etc. along with front & rear wheel sensors that speak to the ECU.

Yes, the UTQG ratings from manufacture to manufacture often differ slightly because there are no real governing bodies in this area, however, the differences are not spectacular and in a given size this is not known to cause any issues other than maybe a fender rub.

A new tire wearing down to a bald tire is at the most maybe 12/32 of an inch, this is not nearly enough to cause a system problem and it is not an accurate comparison to the problem at hand.

My point being I HAVE put aftermarket wheels or other wheels and tires on cars and have not duplicated this issue. As well, even full size spares on vw's are not the same as a stock wheel and tire. So this should then lead to the same exact problem. My point being that in my history of modifying cars I have yet to see catastrophic failure of systems like that due to a wheel and tire change let alone slightly altering the tire size on a known working wheel.

My point with the worn tire analogy is that if the systems were this sensitive you would see things like this happening MUCH more frequently. Dealerships put aftermarket wheels and tires on cars before they sell them, not to mention the ability to upgrade or change the specific wheels on a car. As I said above I have never taken a wheel and tire off a car and had the new wheel and tire be exactly the same, this speaks for a set of factory alloys, a set a factory steelies (from a MK1 Cabrio), and 2 different aftermarket wheels.



I personally would put the odds on a damaged sensor at a wheel, seeing that even if the new rubber caused this problem I would guess the sensor was probably damaged before the car ever saw the new rubber.

[OldSkoolVWLover]

Originally Posted by SilverSportNOLA

That's about what I said, the new tire is about the same as the old half worn .... there is a possibility that they damaged a wheel speed sensor, I would check that. To reiterate an earlier post I made, the ECU gets speed information from more places than the speed sensor on the transmission, otherwise how do you explain my spoiler going up at speeds that felt around the normal 93MPH deployment speed when my tranny speed sensor was broken and I had no cruise control or speedometer?

I am with you.

[Too Cold NB1.8T]

I was and still am completely clear on what you have stated in your posts on this thread, I am also clear as to what point(s) you were trying to make, I thoroughly understand what you have said in both of your last replies, however, my previous post stands.

This simply means, I don't agree with some of what you stated and/or how it was termed.

[SilverSportNOLA]

Originally Posted by Too Cold NB1.8T

I was and still am completely clear on what you have stated in your posts on this thread, I am also clear as to what point(s) you were trying to make, I thoroughly understand what you have said in both of your last replies, however, my previous post stands.

This simply means, I don't agree with some of what you stated and/or how it was termed.

Well .... I said that the difference between the stock tire, which he stated was a 215/55/16 and his new tire a 225/50/16 would be .4 inches and should not make the difference to cause the problems he is seeing. Now the difference in diameter of a new tire with a 12/32" tread depth and one worn slick is about 3/4" or 24/32". All of my Beetle tires have had 10/32" which when half worn would reduce the diameter by 10/32" and I have worn many a front pair to 3/32" tread depth with no mechanical or electrical problems.

I still beleive that there is a sensor problem with the car, and hooking it up to a VAGCOM will tell what's up, mine threw a few non CEL/ABS errors due to the speedo sensor being broken for the short time I drove it that way.

[Too Cold NB1.8T]

For a question that I already knew the answer to, I was fishing for information when I posed the question multiple times, -What was the tire size that you switched from?-, I was trying to see exactly what tire was on the car before the change.

I don't see where silverbug99 wrote what size tire was on the car before the switch, there was only an implication which has lead to assumptions.

The fact is that the car came stock with a 205/55R16 tire on it and not a 215/55R16, although this still should not cause the trouble being experienced, it is always wise to have accurate facts and specifics at hand before attempting to trouble shoot a problem.

Also, FYI, a one up or plus one tire size increase on this car would require the wheels to be changed as well and take it to a 225/45R17, "not" a 225/50R16, a plus two increase would be a 225/40R18 etc.

However, the question still remains, what size tire was on the car before the change??

[silverbug99]

I appreciate all of the input regarding my question/problem...


The tires were stock/original size before the change.
Thank you

[Too Cold NB1.8T]

Ok, along with everyone else here, I'm really trying to assist with resolving your car problem if I can, complete answers to the following questions might lead to at least narrowing it down.

1. Have you attached a scan tool/vagcom to the car and if so, what DTC's were store if any?

2. Have there been any dash warning lights illuminating and if so, what are they?

3. Have you checked to see if your brake lights are functioning properly?