Help with Cruise Control on a W210
 

OK,

So I searched around before I asked, but I think I may be stumped. My car has a cruise control issue, when my car has the cruise set above 72MPH it disengages almost right away. I replaced the brake switch, no help. I have on stock tires on 16 in stock rims. Before this problem happened I had a blowout, and my two rear tires, while the same size and pressure, are mismatched. I don't think that would cause the issue, but I am not sure. Should I be buying an amplifier next?

Thanks,

i'll be paying close attention. my 99 E320 just started doing this...at 61 mph
which is even more annoying than your 72 mph. i swapped out 16s for 18s
but the rotational measure is within 2% so should not be a factor. argh...

Tire SIZE is the most likely cause ON both cars.

Measure the circumference of all 4 tires & make sure the "shorter" tires are on the FRONT!

Even a 1/4" difference will cause that problem!

OK, so in theory, if I am running stock tires all the way around, and this is the case, I can let say, 5 lbs out of each front tire, and jack the back tires +5, so run 25 in the front and 37 in the back, and my cruise will work?

Let me know if this is a valid test, and if so, I will try it today!

The term "stock tires" means nothing in todays world.

Between tire brands there can be 1/2" difference in circumference!

Take the time to measure correctly.

Thanks for explaining this. If I was to upgrade my rims and tires in the future, how would I go about getting the cruise to work again? I have looked and can get the new tires within 2% size of the old (circumference). Is there a computer reset that needs to be done, or will it never work?

Thanks again,

Due to electronics...you need to keep circumference with-in 2-3% of original.
And remember that even 1/2" on a 100" circumference is 0.5%.

Traction systems go crazy as well as the transmission.

Remember , the computer sees Rolling Circumference/1 rev....simply meaning two tires with different wear OR air pressures will have different rolling circumferences.

So, a postive measure I use is to mark the tire at the ground and roll the car for a 5 revolution tire distance. Then devide that ground covered distance by 5..that will give you an accurate RC per Rev measure to compare each/all 4 tires. [ As DOC states, ASR systems have to be all the same b/c there are WSS on all 4 corners]

These cars are too smart for their own good. I just came back from a used tire shop, where I found the same make/model of tire that was flat, that had a similar wear amount to what was on the car. I had them mount the tire up, we put the none brand match (but size match) tire in the trunk. I drove home and the cruise worked.


This is INSANE that the car is so sensitive.