Running different width tires, with different thread: Is it safe?

[coolgraymemo]

*I searched and didnt come up with an answer*

I just picked up some cheap 18" wheels, but two of the tires have heavy camber wear that wont be safe to drive on.

The tires that the wheels have on right now are P235/40/R18. I plan on taking the two bad tires off and replacing them with some 215's (P215/40/R18). I would run the narrower tires up front and the wider tires in the back.

My questions are:
- Would it be safe to ride on two tires that have 60% tread (235's; rear), and two new tires (215's; front) without messing up the QUATTRO?
- Should I look to see if I can find two used tires with the same tread as the 235's so they can all be the same?
- Does running different width tires mess with the QUATTRO?

FYI: 1999 Audi A4 1.8T (Pre-Facelift) Quattro. Wheels are 18"x8"



**Please read all replies, before replying**

[stevejones19]

i don't know how that would work to be honest, defintely wanna keep the rolling diameters within 1/4 inch or so they say...

[coolgraymemo]

That would be a quarter of an inch in height right?

So just a different tread that isnt too different wouldnt matter?

Or ahould i run 225's upfront?

[EErie B6]

would be 1/8th inch ride height, but measuring on car is not the safe way to do it, you should go off the actual tire specs.

215/40R18 depending on the maker is about 24.8" diameter
235/40R18 depending on the maker is about 25.4" diameter

personally, i wouldn't do it

a 215/45 might be do-able (25.6")

Tread (design?) does not matter. width does not matter. rolling diameter matters. from a safety standpoint, so does speed rating.


EDIT:
just saw the comment about the rears being worn... you could get away with the 225/40s but that would put you right at the 1/4" limit.

[Greedo]

I'd be more concerned about matching brands for even treadware than worrying about the width. I would assume that as long as the sidewall of the tires is the same, the width won't matter, but if you run two different brands with different patterns they may (and probably will) wear unevenly causing you problems eventually.

In other words: replace all four tires with the same brand/wear of tire (because if two tires are bad, the other two must be used meaning they will have less tread than two new tires.).

[walky_talky20]

It is all about rolling radius, also known as circumference. Quattro doesn't really care about the width on it's own, BUT the circumference is a function of both the series *and* the width.

Even if you have 4 tires that are exactly the same, even the wear on the tread makes a difference. Audi's official recommendation is to stay within 4/32" of tread depth for all 4 tires. They don't give a specific recommendation for allowable circumference differences other than they must be "the same". I would take that to mean as close as possible.

You can, however, use their tread wear recommendation to extrapolate a circumference difference recommendation. Let's do some math. Here we go:

- Given the stock size of 205/60/15
- Diameter when new = 24.7"
- Circumference when new (diameter*pi) = 77.6"

Now factor in the tire wear:
- Wear of 4/32" changes diameter by 8/32" (4/32 each on the top and bottom)
- 8/32 = .25"
- Worn diameter (24.7 - .25) = 24.45"
- Worn circumference = (24.45*pi) = 76.8"
- Difference compared to new = .8"
- Difference percentage (.8/77.6) = 1%

A difference in circumference of about 3/4", or about 1%, given maximum allowable wear difference on the stock 15's. So you should stay within 1% in circumference.

For comparison: Subaru, who's AWD system is more sensitive than ours(uses variable locking clutches), recommends staying within 1/4" in circumference. I'd recommend staying closer to that if possible.

[somebody5788]

Not worth it

[coolgraymemo]

I didnt know that a 235/40 tire was a different height than a 225/40 tire. I just thought that because they were both 40's, they were the same exact height.

i am probably just going to be a full set of 215/40/R18 tires from a tire shop and just keep the two spare tires as spares or something.

[Alan]

The second number [40] is a percentage of the width

[coolgraymemo]

Since i got the wheels for free, i guess it wouldnt hurt to spend a few bucks on some new tires.

Thanks for the help AZ!

[EErie B6]

hope you have nice roads, around here, a 215/40 would wreck an 8" wide rim ...they are going to have a fair amount of stretch to em.

they will also most likely look small inside your wheel well

[coolgraymemo]

Cali roads suck.

Would i be able to run 225/40's all the way around without modification?

The wheels have an offset of et35, would i need to roll my front fenders to be able to fit 225's?

[coolgraymemo]

Sorry to bring this up again but:

what if I run 215/35/18 tires all around? would i get a stretch? would the car look weird with some wheels with such a small sidewall?

[EErie B6]

the 225/40s are the ideal size for an 8" rim on a B5... touch of stretch, but very little. (when i say stretch, im refering to the sidewall being pulled out wider than the tread in order to seat on the wheels)

This is stretch, its more extreme than we are talking about, but its a good example.


i have 235/40R18s on my B6 with 8" wheels and the tread is about dead even with the wheel. (even sidewall)

the 215/35R18 is going to look stretched, itll be too small in diameter, and make your wheel wells look bigger. its also going to make your speedo read high.
215/35R18 = 33.9" in diameter you need something that is (or close to) 25".

[EErie B6]

Heres 225/40R18s on an 8" wheel...

this photo belongs to a fellow AZ member, i hope he does not mind me using it. (if so, pm me and ill remove it)

I love the way this car looks.

[black99.5a4]

The whole tire size thing on quattro cars is really laughable at best from a lot of people.. you guys really do get worried.. hell 1 guy in the s4 forum got flamed for replacing 1 tire instead of all 4.

you need to be withing 3% rolling diameter of each other. I know 3-4 quattro guys running 2-3% differences for thousands of miles (not 2 or 3, try 30-40 if not more) with no problems at all.

you will be fine on what you're doing.. i drove my car 13 hours straight from chatanooga, tn back to lancaster ,pa with 3 yokohoma's and 1 idk i had to borrow due to cords showing on a tire when I went to pick up some parts. oh nooozzzz my quattro was about to blow away.... lol its not going to.

[sean1.8t]

^amen to that!

3% is what the books states, but you can get away with a bit more. i've had more of a difference than 5% for 10's of thousand's of miles.

[EErie B6]

I agree for the most part. just because you can, does not mean you should, or that its not bad for the system.

if the system was super-duper fragile, the middle-aged women that bought these things when new, that dont know jack about cars other than you put gas in them and they go would be blowing them up all them time.

im the type to replace 1 tire if it needs it... i had to on mine due to a sidewall puncture. i did keep the size and brand the same, and people told me i was crazy... mainly the tire shop as they were trying to sell me another tire... guess what, the car never blew up and the world kept turning.

[sean1.8t]

I agree for the most part. just because you can, does not mean you should, or that its not bad for the system.

if the system was super-duper fragile, the middle-aged women that bought these things when new, that dont know jack about cars other than you put gas in them and they go would be blowing them up all them time.

im the type to replace 1 tire if it needs it... i had to on mine due to a sidewall puncture. i did keep the size and brand the same, and people told me i was crazy... mainly the tire shop as they were trying to sell me another tire... guess what, the car never blew up and the world kept turning.

haha i had a bunch of douches at a Les Schwab try to tell me that they couldn't let me replace only 1 tire. it was unsafe and could cause an accident if the AWD system failed. i laughed and threatened to have my car towed over to big O if they didn't sell me 1 tire

[EErie B6]

lol, the same shop also tried to charge me $50 to swap out the rubber. I laughed and told him he was crazy. he gave me some bs about the machine that he had to use was very expensive and thats why the price was high. i tolf him i wasnt trying to buy his machine, i just wanted my tire put on. I offered to mount it myself on one of his standard machines using 2 tire spoons... he grumbled and changed the price.

[coolgraymemo]

so now the people that are more like me come out. lol.

i am probably just going to buy 225/40 tires.

[black99.5a4]

are the wheels staggard at all?

i just picked up 8.5 and 9.5's.. plan to run 215/45's front and 225/45 rears....17's of course.

[coolgraymemo]

sorry to bring this back up but I found this calculator and found the measurements in diameter; from what I understand, there's 1.2% between the 235/40 and the 225/40 tires. I think the 1.2% will be compensated with the newer tread on the 225/40 tire. can someone make sure I'm looking at the correct measurements?



thanks!

[coolgraymemo]

^
the calculator can be found here:

http://www.rimsntires.com/rt_specs.jsp

[speedydragon]

I'm running 225/40 on my 18x8s. I plan to run 215/40 once I have to buy new tires. I live in the bay area, I'm always trying avoid every imperfection on the road lol.

[EErie B6]

Coolgraymemo:
you will be fine. and yes thats the correct % you are looking at.

Speedydragon:
I hope you have staggered wheels or that might look a little funny. to the average person, its just going to look like you put the wrong size tire on.
If i understand correctly, Coolgraymemo is just doing it temporary to save some money b/c he just dropped his cash on wheels.



**To any one just tuning in, please read the whole thread before you comment. Thanks.

[somebody5788]

Heres 225/40R18s on an 8" wheel...

this photo belongs to a fellow AZ member, i hope he does not mind me using it. (if so, pm me and ill remove it)

I love the way this car looks.

I steal keef's pix all the time lol.

As to 225 rubbing. You'd have to be trying pretty hard to get them to rub..... My 235's have only rubbed 1 time. I had 5 people in the car taking a tight off ramp at 50mph and a couple bumps in it. If it takes that much for me to rub a 225 just shouldnt rub.

[somebody5788]

Heres 225/40R18s on an 8" wheel...

this photo belongs to a fellow AZ member, i hope he does not mind me using it. (if so, pm me and ill remove it)

I love the way this car looks.

I steal keef's pix all the time lol.

As to 225 rubbing. You'd have to be trying pretty hard to get them to rub..... My 235's have only rubbed 1 time. I had 5 people in the car taking a tight off ramp at 50mph and a couple bumps in it. If it takes that much for me to rub a 225 just shouldnt rub.

[coolgraymemo]

Coolgraymemo:
you will be fine. and yes thats the correct % you are looking at.

Speedydragon:
I hope you have staggered wheels or that might look a little funny. to the average person, its just going to look like you put the wrong size tire on.
If i understand correctly, Coolgraymemo is just doing it temporary to save some money b/c he just dropped his cash on wheels.



**To any one just tuning in, please read the whole thread before you comment. Thanks.

Thanks fot the help.

I got the wheels for free. Im trying to save money because I am broke (college student).

[onemoremile]

Find a used pair of tires that match the usable pair. Then when they all wear out you can do it right with a matched set. That approach saves you money now and gets you a proper setup later.

[speedydragon]

Speedydragon:
I hope you have staggered wheels or that might look a little funny. to the average person, its just going to look like you put the wrong size tire on.
If i understand correctly, Coolgraymemo is just doing it temporary to save some money b/c he just dropped his cash on wheels.



**To any one just tuning in, please read the whole thread before you comment. Thanks.

18x8s all around. I might stagger it with spacers. 20s in the back and 15s in the front

[J Ozzie]

Yeah 225 40 is the Sweet Spot.. I was running 235 40 last year.

Id say depending on the wheel, the backs need spacers to make em flush with the fenders. the fronts dont seem too bad.

[coolgraymemo]

I decided on running 205/45/R18 in the front and 235/40/R18 out back (the old tires).

its the best setup I can do; the back tires are just .06% taller than the front whereas the 225/40 would be 1.3%.

[EErie B6]

going to be stretching em.

[coolgraymemo]

I decided on running 205/45/R18 in the front and 235/40/R18 out back (the old tires).

its the best setup I can do; the back tires are just .06% taller than the front whereas the 225/40 would be 1.3%.

nevermind, I cant find that size on tirerack. i dont think they make em.

[coolgraymemo]

215/45 is just 0.9% smaller...

[EErie B6]

why are you trying for skinny tires?

[coolgraymemo]

to get a staggered tire look.

[EErie B6]

post pictures once its done.

[royal_b7a4]

Think I would have any issues running a 35/20 profile tire on a 20in wheel on a B9 S4?