Difference in tire sizes to throw off cruise control?

[Denlasoul]

Hello all-

I was curious as to how much of an incorrect tire size difference it takes to throw off the cruise control?

for example: 225/40/18 and 245/40/18

[MrSpace]

throw off??

I use my cruise control and went from the original rims+caps to 225/40/18 and 255/35/18 and my cruise still works.

Wltough I need to check with my friend is my speedo is correct, I'm pretty sure it writes a little less than what I'm actually going.

Etienne

[edub]

I use 225/35/19 & 245/35/19 and cruise control still working good...

[Denlasoul]

Originally posted by edub
I use 225/35/19 & 245/35/19 and cruise control still working good...

225*.35 = 78.75
245*.35 = 85.75

So, about a 7mm difference in diameter. Must be within the threshold of limitations.

What I mean by "throw off" is that with incorrect sizing of tires, there seems to be a tendency of cruise control not working.

In edub's case, I can only conclude that his tire sizes do not have a large enough variance to throw off or not have the cruise control working.

I am running 225/40/18 and 255/35/18 and have no problems whatsover. I am looking into other tire sizes and was curious as to how much of a variance I can get away with.

Is there anyone who's cruise control is not working possibly due to a change in tire size?

[Rocky]

I had the stock 225-45-17 on front and 245-40-17 in back on my C36. I had toyos in the front and michilins in the back and that threw off my cruise control. Took the dealer 3 days to figure that one out. They swapped it witht he wheel in tired from a C43 in the showroom and it the cruise worked. A week later I put on my snow tires, 4 X AMD Mono II's with same tires, 225-45-17 all around and ther cruise worked.

This only afftected my cruise control speed above 120km/hr.

I got a feeling it calculates all four tires for a certain tolerance.

[98_Benzo]

I just got my new rear tires this weekend and I put the cruise control on and it worked perfect. I will try again when I get my new front tires. My original tire sizes were 245/45-17 all around.
I just ordered my new tires:

255/40 - 17 (Front)
275/40 - 17 (rear)

After seeing my new rear tires, I think I am going to go a little bigger (305/35 - 18), they just don't look big enough.:D That should throw my cruise control off then.

[MrSpace]

305x18

you are NUTS

;)

Etinene

[joesc280]

i have 215/35 in front and had 265/35 out back.....it didn't go into cruise control at all....i recently switched to 255/35 now it will work to speeds up to like 60mph...after that it will not work...and actually after i hit 60mph it will not work again for speeds under that until i restart the car...its almost as if it triggers a failsafe or something and shuts it down...?

[nokia8860]

Originally posted by 98_Benzo
255/40 - 17 (Front)
275/40 - 17 (rear)

OH MY!

This works huh? How does the front clear? I know from reading speedybenz's post that he has to widen his front fenders. What did you do to make it fit.

Thats crazy!!!

[Denlasoul]

Originally posted by nokia8860
OH MY!

This works huh? How does the front clear? I know from reading speedybenz's post that he has to widen his front fenders. What did you do to make it fit.

Thats crazy!!!

Nokia-

It's for his Mustang, remember. He got rid of the 202.

[nokia8860]

Originally posted by Denlasoul
Nokia-

It's for his Mustang, remember. He got rid of the 202.

check out bboy jeff's post in the RS thread.....

[Denlasoul]

Originally posted by nokia8860
check out bboy jeff's post in the RS thread.....

Hubba hubba. That's fat! Let's see some pics Jeff. :)

[98_Benzo]

RS thread????? I will post some pics of my 275's, when I get some.

[nokia8860]

RS Thread (http://www.club202.com/forums/showthread.php?threadid=4155)

[98_Benzo]

wow, I didn't realize those would fit....but, I guess after a little modification to wheel wells, anything will fit. That should look sweet!!! I wanna see pics....

[98c43amg]

Originally posted by Denlasoul
Hello all-

I was curious as to how much of an incorrect tire size difference it takes to throw off the cruise control?

for example: 225/40/18 and 245/40/18

Mine's working 100% with wheels & tires upsized by one.

The defacto tool to determine the % difference in this regard IMO is:

http://www.miata.net/garage/tirecalc.html

Enter your stock size & new size, and it'll give you all the differences. Newer MBs take the speedo signal off the front tires I believe, so that's new size that matters for speedo differences, and if you set it to 55mph [ya, right :) ], by what percent it will be fast or slow.

So what you're saying is you've heard of situations where the difference between the speed the car determines that it is going -- based on the front tire's size -- is so different then the RPM the engine is turning in a gear -- based on revolutions of the rear wheel affected by the size of the rear tires -- that it stops the cruise control from working? ...that's a first for me.

My cruise conrtol did stop working once, but that was an electronic/water problem I believe.

[Denlasoul]

Originally posted by 98c43amg

So what you're saying is you've heard of situations where the difference between the speed the car determines that it is going -- based on the front tire's size -- is so different then the RPM the engine is turning in a gear -- based on revolutions of the rear wheel affected by the size of the rear tires -- that it stops the cruise control from working? ...that's a first for me.

I'm not too sure if that is the correct cause of it, but I have heard on many occasions that members have had cruise problems and the common denominator happened to be funky tire sizes. For example, running a wider tire in the rear while keeping the same series.

I stepped up my wheels to 18's and am running 225/40 and 255/35. The difference here is very very very minimal. No problems for me whatsoever.

I am interested in going wider in back (I like the front sizing) but do not want to vary the difference so much that it can cause cruise problems.

So, I want to know what kind of variance I can get away with without sacrificing cruise.

I really like to cruise at 90-100. :)

[98c43amg]

Originally posted by Denlasoul
I really like to cruise at 90-100. :)

err, where? [!] Assuming you can do that w/o hassle, I want to come visit.
:D