Tires for 8.5" wide wheels (front) - Mercedes Benz SLK Forum

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#1 Old 02-09-2015
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Tires for 8.5" wide wheels (front)

I've spent a lot of time in consternation about what to do with a set of SL R230 AMG wheels I picked up a while back for my R170 SLK. While the wheels are the same in appearance as the stock sport wheels on the SLK, they are one size larger. I even went as far as to buy a set of cheapo tires to fit to them so I could test fit them to the car. But I am having problems with the front, more cosmetic than anything but it is driving me nuts...

The stock wheels are 17x7.5 et37 and 17 x8.5 ET 34 rear, the SL wheels are 18 x 8.5 ET 30 front and 19x9.5 ET 33 rear, I bought a set of cheap 225/40/18 for the front and 255/35/18 for the rear and that is where my dissatisfaction began.


Both tires on these wheels are a stretch, both literally and figuratively, but the front is obviously way to narrow for such a wheel and looks down right wrong on the car. For the rear, I think I can fit 265's on these wheels and currently plan on doing so once I get my suspension sorted.

After more than a week of deliberation, I have almost decided to leave the stock 17x7.5's on the front and have 17/18 staggered on the car (I've been driving around like this for a week and a half with no issues). Below is how the car sits now with 18's rear, 17's front..




The question I have for those who have more experience with tires than I do; do different tire manufacturers tires of the same size differ in width from model to model, or are those who have used 225/40/18 on 18 x 8.5 wheel just lived with the stretched tire on their fronts? I have read tons of post with others who have put 18 x 8.5 and 225/40's on their R170 and other cars but to me this just doesn't look wright on these wheels.....

Safety issues aside, the look in this scenario (narrower tire on wider wheel) just looks wrong to me thus I'm trying to determine if a different brand tire might fill out the wider wheel better. I would think a 225 is a 225, but have been wrong before... Those new Puma racing shoes I bought for example... Euro shoe sizes aren't same as US.

Based on this chart, it doesn't appear that anyone has ever used anything wider than a 225 on an R170 chassis... Mercedes-Benz Fitting Chart and Wheel Fitment Guide | Alloy Wheels Direct

All indications are that we can not get any wider than a 225 on the front of our cars, but with these wheels I obviously need more tire.


While unrelated and more or less fruitless, I even test fitted the one remaining stock rear wheel to my car and it appears to fit and looks a little better than the 225/17, but since I only have one good 17x8.5 I couldn't test drive with it and again haven't heard of anyone working wider than a 225 on the front of an R170 so worry about rubbing




So what if anything will fit? Could I get wider with a different suspension setup? Lowering the car doesn't make sense to get them to fit...
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#2 Old 02-09-2015
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My manual says the rear offset on the 8.5 x17 is 30mm not that the 4 mm is not manageable.
What I don't quite understand is why you would want to run 17 front and 18 rears.
I guess it can be done as long as you match up diameters, aspect ratios etc. so overall diameter and circumference of the tires matches front and rear.
As you noted a 225 is a 225 and that is the tread width in mm. The aspect ration e.g. 45 vs, 40 is basically telling you what the wall height is relative to the tread width.
If you go up 1 inch in diameter with the same tread width, that inch has to come out of the wall height to to maintain the overall diameter. i.e, 225 x .45 = 101.25 mm wall height. 225 x .40 = 90 mm. Difference is 101.2 mm or 0.44" x 2 =.88 inches on the overall diameter of the tire on the car and not quite the 1 inch difference in the rim diameters. This translates to minor circumference errors.
Hence there will be a minor difference in peripheral speed of the fronts vs. the rears and so you have to consider is how much error there will be between the 17 and 18 assemblies as too much with throw the ABS sensors into a frizzy and you will get all sorts of ABS, ESP notices.
I am not suggesting it is something you shouldn't do but I would stay with one or the other.
Of course I don't know what suspension changes you are doing.
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#3 Old 02-10-2015
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I am not real jazzed on using 17 fr and 18 Rr, but the way the 225 looks on the 18x8.5 just isn't right to me and to be honest scares me should I take a corner way to spirited. I've heard of people "rolling the sidewall" and popping the tire right off the rim; not that I am planning on tracking the car or entering a rally stage anytime soon.


The stance with 17x7.5 front is the look I am looking for, but again not my preference. Based on all my calculations I am less than 1% off in diameter with this setup and after two weeks of driving do not notice much of a difference in handling characteristics. The idea of putting the rear 17x8.5 on the front was just a way of pushing the fronts out to the edge of the fender to again, match the appearance of the rears, but a nice set of spacers could do the same and after living with this setup, may not be necessary.


as you can see in the last photos I attached to my first post, the problem is rooted in the fact that 225's are stretched on 18x8.5 wheels in a too narrow of a way and the protruding lip of the wheel just doesn't look right. I would gladly get a wider tire upfront, but fear that it would rub since I can not find anyone who has successful used anything wider without mention of rubbing. I have not ruled out lowering the car with springs, but don't see that adding the ability to go wider... I have done lots of reading and experimentation but am really out of my depth here and unfortunately my wife is not much help; when I ask her opinion, she just glazes over and says "chesse burger, cheese burger". My neighbor likes low riders and protruding wheels, so neither are much help, so I value the opinions here.
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#4 Old 02-10-2015
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I wouldn't have thought that a 225 would look that stretched on a 8,5 J wheel , although , obviously a 245 would fit better on that width !
Maybe it's because it's a cheap model tyre ?
Do the tyres have rim protectors , this might change the look ?
Can you go to where you fitted them and compare/measure them against higher end tyres ?


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#5 Old 02-10-2015
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I had the same thought when I read conelyjb's last comment. A 245 would work well I am thinking. I know they look OK on my 18 x 8.5 on the wagon although I must say I still prefer the ride in the wagon on the 17s my winters are on. The handling of the wagon is much the same as the 18s but the ride better. They take a pot hole better too.
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#6 Old 02-10-2015
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Here's the specs for my R171 Sports Pkg:

F: 225/40/18 ET 37/7.5
B: 245/35/18 ET 30/8.5

The last number is rim width. BTW, TR will give you the range of rim widths a tire will work on.

My solution would be to put the SL 18" on the rear with the 255/35/18. I'd use the 17" for the front with perhaps a wider tire. The inch difference would be hardly noticeable. What's left over you can easily peddle, since OEM wheels are always in demand.
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#7 Old 02-11-2015
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At this point I am leaning towards doing what DSSG suggested and have made arrangements to return the 225/40/18 tire for a refund, since I technically never used the tires (drove on it) they are willing to take it back and issue a full refund.


Having used the 17 Fr/ 18 Rr for a couple weeks now with no major issues; although there is some slight wandering on HW, that too could probably be attributed to the cheapo tires. My next step I guess is to get my suspension sorted and then I can order my Michelins in 225/45/17 Fr and 265/35/18 Rr and buy them with proceeds from selling the front SL wheels and the rear SLK.


I am still perplexed however as to how so many others seem to have done the same setup (SL 8.5's on front with 225's) and not either notice, or take issue with the stretched appearance of the combo.
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#8 Old 02-11-2015
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One bit of advice. When you select tires, check their diameters. If you want the car to sit level, you'll want the same number. You might want a rake hopefully down hill. Another thing to look at is section width to make sure they fit the rims properly.
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#9 Old 02-12-2015
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I'm very familiar with how the numbers work on tires, my challenge is how a 225mm wide tire which equates to 8.8inches, sits so wrong on an 8.5" wheel. All indication is that a 225 should have fit, but as you can see in the photo they do but are stretched b/c they are to narrow on the wheel. Either its the manufacturer doing something squirrely and not all 225 are actually 225mm, or my math is off.
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#10 Old 02-12-2015
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Unhappy Really?

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Originally Posted by conleyjb View Post
I'm very familiar with how the numbers work on tires, my challenge is how a 225mm wide tire which equates to 8.8inches, sits so wrong on an 8.5" wheel. All indication is that a 225 should have fit, but as you can see in the photo they do but are stretched b/c they are to narrow on the wheel. Either its the manufacturer doing something squirrely and not all 225 are actually 225mm, or my math is off.

You are confused and don't understand the numbers. The 225 refers to the section width of the tire, that's the fat part of the tire. What you want to know is the appropriate rim width for that size of tire.

Look at the front tire on my car. It's a 225/40/18 on a 7.5" rim. That tire would look as goofy as hell on an 8" rim which is exactly what you are experiencing.

Look at the back tire or 245/35/18 or a section width 20 mm wider which looks OK on a 8.5" rim or 1" larger. Also note that 20/25.4 = 0.8".

Go to Tire Rack and look up the specifications for the tire of your choice. Look at the various section widths and the range of rim widths they'd fit. Also remember just because it fits doesn't mean it'll look good, your interest being cosmetic.
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#11 Old 02-13-2015
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Thanks. Just what I needed to start my day. Being called out as the idiot I am... the 18 x 8.5 wheels are going up for sale this weekend. If anyone is interested let the idiot know...
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#12 Old 02-13-2015
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Quote:
Originally Posted by DSSG View Post
You are confused and don't understand the numbers. The 225 refers to the section width of the tire, that's the fat part of the tire. What you want to know is the appropriate rim width for that size of tire.

Look at the front tire on my car. It's a 225/40/18 on a 7.5" rim. That tire would look as goofy as hell on an 8" rim which is exactly what you are experiencing.

I have 225s with rim protector mounted on 8Js and they look perfect !



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Last edited by curro101; 02-13-2015 at 11:51 AM.
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#13 Old 02-13-2015
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looking at Tirerak.com a 225/40/18 should fit a rim of 7.5"-9" looked at some BBS wheels that are 8.5" and the tire size recommended is 225/40/18

can you have the shop fit a good tire that you would purchase and use, not the cheap one and just see how it fits? And I hate to ask this, but are you sure the rims are 8.5", have you measured them? I ask, because something is not adding up.

My 2012 SLK350 runs this tire with a 8" rim and I can't see the extra 1/4" on each side making the tire fit that bad.


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#14 Old 02-13-2015
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Unhappy Skinny Tires on Wide rims!

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Originally Posted by NMBruce View Post
looking at Tirerak.com a 225/40/18 should fit a rim of 7.5"-9" looked at some BBS wheels that are 8.5" and the tire size recommended is 225/40/18

can you have the shop fit a good tire that you would purchase and use, not the cheap one and just see how it fits? And I hate to ask this, but are you sure the rims are 8.5", have you measured them? I ask, because something is not adding up.

My 2012 SLK350 runs this tire with a 8" rim and I can't see the extra 1/4" on each side making the tire fit that bad.
Are you sure?

It doesn't matter if you have 17" or 18" OEM wheels, the rim width in the back is 8.5" and 7.5 " in the front. The section width on the front tires in either case is 225 and the back is 245.

The wider rim width is necessary for the rear tire with a 20 mm greater section width.

What is the purpose of this? Cosmetic mostly and perhaps handling. If you decide to change wheels, you must pay attention to wheel diameter, rim width, bolt circle, and offset. When picking a tire, you must pay attention to tire diameter, what range of rim widths it fits on, but also section width.

If you put a skinny tire on a wide rim even though it may be OK specification wise, it will look goofy as hell, and you will be laughed out of your neighborhood!
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#15 Old 02-13-2015
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I have 8Js all round , 225 on the front and 245 on the rear !
You can see the front above and the rear here below ...



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#16 Old 02-13-2015
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Quote:
Originally Posted by DSSG View Post
Are you sure?

It doesn't matter if you have 17" or 18" OEM wheels, the rim width in the back is 8.5" and 7.5 " in the front. The section width on the front tires in either case is 225 and the back is 245.

The wider rim width is necessary for the rear tire with a 20 mm greater section width.

What is the purpose of this? Cosmetic mostly and perhaps handling. If you decide to change wheels, you must pay attention to wheel diameter, rim width, bolt circle, and offset. When picking a tire, you must pay attention to tire diameter, what range of rim widths it fits on, but also section width.

If you put a skinny tire on a wide rim even though it may be OK specification wise, it will look goofy as hell, and you will be laughed out of your neighborhood!
I stand corrected on my wheel size, 7.5 in front and 8.5 in back for a SLK350 and the manual says 8 in & 9 in for the SLK55 which uses a 235/40/18 in front.


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#17 Old 02-13-2015
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A 245 width is what is required.
Go back to the shop or a second hand tyre place and fit just one used 245 tyre and see if it clears the suspension strut on the inside, and fits under the guard on the outside.

If ok then great, if not you should resell the nice rims, and put it down to a learning experience.
Nice looking rims though.

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#18 Old 02-14-2015
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get 17'' 8' for the front and 9's for the rear. Fit well and look good
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#19 Old 02-20-2015
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i am looking at buying the same size wheels for mine.wonder if 235 would fit?look better.
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#20 Old 02-21-2015
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I'm selling my 18 x 8.5's and going to stick with the 17 x 7.5 until I can source some 18 x 8, or 18 x 7.5 in this same style (assuming they are made). If I don't sell them, I may try them on the rears so I can get away with 255's and not add the expense of 265 or 275 which the 9.5" wheels need
Mercedes R230 SL Ronal Front 18x8 5 AMG Wheel A 2304012002 | eBay

Last edited by conleyjb; 02-23-2015 at 04:25 PM.
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