Tire Size Combination

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stratsix

Tire Size Combination

Post by stratsix »

Just wondering what you guys think of this tire combination:

205 40 r17 fronts
215 50 r17 rears

too big, too small...

I just need a little advise on this as I am thinking 0f purchasing tires and wheels. Still need to figure offset on wheels.
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Post by ZROSSA »

I would try to keep the rolling diameter the same front to rear. There are lots of tire size calculators on the net.

I have been using these ones

http://marksink.com/tire_wheel_offset/offset.html

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

I woul look at 225/45/17 if sticking with 17 inch

Cheers,

Douglas
Chris Wright

Re: Tire Size Combination

Post by Chris Wright »

stratsix wrote: 205 40 r17 fronts
215 50 r17 rears
205/40-17 = 23.4" diameter and 215/50-17 = 25.5" diameter, a 2" difference!

I'd go with a 235/45-17 (25.3") all around or if you want staggered, maybe a 225/45-17 (25") front and 255/40-17 (25") rear. But it does depend on what sizes are available in the tire you want.

Here is a Cut & Paste of some general info:

The size of the original rims and tires that came from the factory:

..................................... Rim Width x Diameter - Offset or "ET" (mm) - Tire Size
Stock wheels ('76 to '81) ............ 6" or 6.5" x 14" - ET22 with a 195/70 -14" tire that has a diameter of 24.74"
Stock wheels ('82 on) ................ 6" or 6.5" x 14" - ET22 with a 205/70 -14" tire that has a diameter of 25.30"
TRX (165mm x 390mm) ............... 6.5" x 15-3/8" - ET22 with a 220/55-390 tire that has a diameter of 24.88"
TRX (195mm x 415mm) ............... 7.6" x 16-3/8" - ET19 with a 240/45-415 tire that has a diameter of 24.84"

The typical replacement rim is

7" or 7.5" x 16" - ET20 or less with a 225/50-16 tire that has a diameter of 24.85"
7.5" or 8" x 17" - ET20 or less with a 235/45-17 tire that has a diameter of 25.32"

The Tire diameters range from 24.8" to 25.4" .

The rears have plenty of space and can take an 8", 9" or even a 10" wide rim with the proper offset and tires of 255 or 265 unless you have the SLS accumulators, in which case the 255 and up can hit them in hard cornering. It is the front that is the most critical and an 8" wide rim is generally the largest without a spacer or a smaller ET.

The larger the rim and tire the more stress that is put on the front suspension and the more likely to inroduce a shimmy into the front unless the front suspension is tight.

All BMW's (except the e30) use a 5 x 120mm bolt pattern and are "hub centric", i.e. they are centered by a lip on the hub, not the bolts. They all have the same size hub hole (72.56mm) with the single exception of the larger hole in the e39 which will still fit fine, but they will need hub centering rings (not spacers), $15 from Discount tire. Most after-market rims have hub rings also. The 3-series rims generally won't fit because the offset is too high, running around ET40/48 and the 7-series with an ET of 23 will generally need a hub centric spacer of 5-10mm depending on the width of the rim. Sometimes a narrower tire (215/205) can be fitted to the 7-Series rim without a spacer and not rub also (but I think is depends on the rim width).
____________________________

Here is a good Rim/Wheel Size Calculator:
http://www.wheelsmaster.com/rt_specs.jsp

--------------------------------------------------
Here is a site that lists all of the wheels that BMW made, with pictures and specs and the cars they came on:

http://felgenkatalog.auto-treff.com/
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Post by Alex E24 E30 »

What sticks out the most to me on your post is the tire width. Sound s bit skinny. What wheel width are you running? You might be going for the stretched look, but you will lose cornering and general grip as you will have a smaller contact patch. Not to mention the added stress in the tire sidewalls that I'm pretty sure wasn't a design consideration.
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sohlman

Post by sohlman »

On a 17" rim as mentioned above i would go with a 225/45/17 or 235/45/17 which is a common size. For a rear i would either go for the same or if you want a staggered look go with 255/40/17 or 265/40/17. The later is very tight and depends on your offset being perfect. 255 is safer and will be cheaper and easier to source.

The tyre sizes you originally put down i don't think would work.

J
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Post by sharkfan »

As Sohlman says; 235/45 all around or 255/265 on staggered sets of wheels but beware that going up to 235's from smaller sizes can expose the dreaded 'shimmy' that comes from worn upper thrust arm bushes and steering linkages.

Sharkfan.
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Post by sohlman »

That is true.

Fundamentally the six was originally designed around a 195x14" tyre width on a 70 profile. The more you load this up at the front the more chance it has to expose the limitations in the track control arms. These however can be upgraded with 750 bushings pressed into the E24 arms.

Personally i feel a 225 tyre is perfect on the six and run 225/50/16"s on my car all round. There is a case for the M cars or cars with 250+bhp to have a wider rear to keep the tail in check. However many owners put on big rims and wide tyres for looks reasons and they do look good. I try and limit changes to maximise the handling and drivability of the car.

The important thing is to ensure that the rolling radius is the same as the standard wheel and tyre combination. This then ensures your speedo is accurate.

J
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Post by Brucey »

+1 on that;

I'm running wide staggered 18"s at the moment and the grip is mental, but the steering feel and lack of tramlining etc is nothing like as good as it was when I was running 225s on 15" rims.

Probably there is a compromise for most folk in the 16 to 17 " range of wheel diameter, but given a choice of a 225 or a 235 at the front on suitable rims I'd stick with the former, and dial out any understeer by tweaking the suspension.

just my two pence worth....

cheers
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Post by wattsmonkey »

+1 on the above, I know I've posted the same thing before, but I can't get over how much I - personally - prefer the drive on 16" wheels(currently with 205/55 all round, soon to be 225/50 at the back) compared with the 17s with 235/45 front and 265/40 rear. Exactly as per Brucey's post, steering feel is much more alive, and there is no tramlining.

17s looked unbelievably cool though.

I'm holding out for a set of 16" staggered Alpinas, but am very happy with the Style 8s at the mo.

Cheers,

Rob
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Post by sharkfan »

Sohlman wrote:That is true.

Fundamentally the six was originally designed around a 195x14" tyre width on a 70 profile. The more you load this up at the front the more chance it has to expose the limitations in the track control arms. These however can be upgraded with 750 bushings pressed into the E24 arms.

Personally i feel a 225 tyre is perfect on the six and run 225/50/16"s on my car all round. There is a case for the M cars or cars with 250+bhp to have a wider rear to keep the tail in check. However many owners put on big rims and wide tyres for looks reasons and they do look good. I try and limit changes to maximise the handling and drivability of the car.

The important thing is to ensure that the rolling radius is the same as the standard wheel and tyre combination. This then ensures your speedo is accurate.

J
I completely agree with this with regard to power; the M635's were designed for the 240/45 x 415 TRX's and I suspect that running with something along the lines of 225 at the front would induce significant understeer, and 225's at the back, well I suspect lunatic oversteer.

The staggered setup does suit the M635's and I would suggest 235 at the front and 255's at the rear is normally sufficient for all but on-the-edge driving styles but as James says you'll almost definately have to upgrade the thrust arm bushes and even then my experience suggests to expect some accelerated wear in steering linkages.

My 635CSi auto runs equally well on 225/60x15's or 235/45x17's if a little soft on the former and a little sporty on the latter - I suspect 16 inch rims with 225's would suit most 635's on most road surfaces and 17's with 235's and upgraded bushes on M635's.

But it's down to individual taste and how you like your car to ride AND look.

HTH

Sharkfan
dividedbydrew

Post by dividedbydrew »

I have no opinion on what is best yet but very much appreciate the discussion in this thread. I have staggered 17x8 is20 and 17x9 is26 wheels off of an e39 with shot tires. I was originally thinking I might do 235/45-17 in front and 265/40-17 in the rear but based on this discussion maybe I'll go with 225/45-17 and 255/40-17. The latter sizes provide a lot more choices in tire brand+model which will hopefully mean less cost. I do have the upgraded thrust bushings installed. We'll see. Keep up the good discussion. I've seen lots of posts on wheel size but not nearly as much discussion on tire size before.

Drew
sohlman

Post by sohlman »

sharkfan wrote:

I completely agree with this with regard to power; the M635's were designed for the 240/45 x 415 TRX's and I suspect that running with something along the lines of 225 at the front would induce significant understeer, and 225's at the back, well I suspect lunatic oversteer.

The staggered setup does suit the M635's and I would suggest 235 at the front and 255's at the rear is normally sufficient for all but on-the-edge driving styles but as James says you'll almost definately have to upgrade the thrust arm bushes and even then my experience suggests to expect some accelerated wear in steering linkages.

My 635CSi auto runs equally well on 225/60x15's or 235/45x17's if a little soft on the former and a little sporty on the latter - I suspect 16 inch rims with 225's would suit most 635's on most road surfaces and 17's with 235's and upgraded bushes on M635's.

But it's down to individual taste and how you like your car to ride AND look.

HTH

Sharkfan
The first M635 actually had a split rim style 5 rim on the metric sizing and they were all recalled as they lost air. The cars then went to the 415 metric rims from the 7 series. I would argue that these are over tired and induce understeer by being too big. They work at the rear, but at the front they don't work IMO. By comparison the M5 e28 had 16" rims of 225 diameter all round. This was actually in a lighter car with more BHP per ton. Alpina's of the day used an even narrower track of 205 at the front.

J
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Post by sharkfan »

Sohlman wrote:
The first M635 actually had a split rim style 5 rim on the metric sizing and they were all recalled as they lost air. The cars then went to the 415 metric rims from the 7 series. I would argue that these are over tired and induce understeer by being too big. They work at the rear, but at the front they don't work IMO. By comparison the M5 e28 had 16" rims of 225 diameter all round. This was actually in a lighter car with more BHP per ton. Alpina's of the day used an even narrower track of 205 at the front.

J
Agreed on those points - but the 3 piece split rims were the same 415 size and 240/45 fitment and it was 1983, and a little before mass produced cars, well BMW's, were generally being fitted with staggered wheel sizes. Yes, the 240 weren't perfect all round on the M635's but then perhaps due to the increased rear tyre width they didn't share the E28 M5's questionable reputation of too-easily induced oversteer and rear end step-outs, perhaps another case for the tyre/wheel compromise not quite working.

Alpina's have always been accepted as more precisely tuned vehicles by their low volume and exclusive nature - so perhaps they had it right - but did a B7 or B7S really have 205's on the front......

Most owner decisions can lay somewhere between ride comfort/firmness, looks and wheel availability - mine have - as opposed to the original design Engineers who had to design for a market and to other decisions, i.e. the TRX decision.

Have fun choosing :D

Sharkfan
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Post by wattsmonkey »

Am sure Alpina 16"s had 205/55/16 on the front and 225/50/16 on the rear, on staggered 7" and 8" rims. Same as the contemporary E28-based cars.

Completely agree with all of the above, but my opinion is that the E24 is naturally prone to oversteer with the nature of the weight balance and the rear suspension design, hence I feel that wide tyres on the front are unnecessary (and possibly counterproductive). My personal opinion is the same with both my M535i and the sixer: the 16" Alpina tyre set up suits me brilliantly and transforms the car.

I know the M535i was famed for frightening oversteer with the TRXs, but always understood that the M5 was a revelation in comparison, presumably down to the tyre change, lower suspension and the thicker anti-roll bars.

Different with the Alpina Highlines, which had thee E34-spec 17" Alpinas, I've been told.
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Kent Klein

Re: Tire Size Combination

Post by Kent Klein »

[quote="stratsix"]Just wondering what you guys think of this tire combination:

205 40 r17 fronts
215 50 r17 rears

too big, too small...

I just need a little advise on this as I am thinking 0f purchasing tires and wheels. Still need to figure offset on wheels.[/quote]

Hi, [-X
You can find here new model and good tires that's you need. http://jaxtires.com
sohlman

Post by sohlman »

205/40/17 is too small in diameter.

215/50/17 is too big

You want a 45 profile tyre on either a 225/45/17 or 235/45/17.

J
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Re: Tire Size Combination

Post by Hachi »

Resurrecting the topic as I am looking for some advice on what tires to get.
I just picked up a set of staggered RC90s (aka Style 5):
17x8 ET20 (front)
17x9 ET22 (back)

I was looking to use some 235/45/17 Michelin PS I have for the front.

I was wondering which way to go for the rear, 255/40 or 265/40? I believe hubcentric rings are needed but are spacers?

Note the car is slightly lowered on H&R Sport with Bilstein B8s.

Thanks in advance.
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Re: Tire Size Combination

Post by 86_6series »

Rings yes, spacers not needed on RC090's
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Re: Tire Size Combination

Post by sharkfan »

Hachi wrote: Sun Oct 21, 2018 9:15 pm Resurrecting the topic as I am looking for some advice on what tires to get.
I just picked up a set of staggered RC90s (aka Style 5):
17x8 ET20 (front)
17x9 ET22 (back)

I was looking to use some 235/45/17 Michelin PS I have for the front.

I was wondering which way to go for the rear, 255/40 or 265/40? I believe hubcentric rings are needed but are spacers?

Note the car is slightly lowered on H&R Sport with Bilstein B8s.

Thanks in advance.
265/40 on the rears will exactly match the rolling diameter of the 235/45 fronts but on standard suspension tend to wear heavily on the inner edges, and far quicker on lowered cars. 255/40's wear considerably less on the inner edges and still provide sufficient grip in 95% of circumstances, as well as being near enough on rolling diameter not to upset the ABS system.
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Re: Tire Size Combination

Post by Hachi »

After purchasing the wheels I was able to find out they came off an E34:

9JX17 ET:‪22 - 36 11 1 182 305‬ E34 - 72.56 (BBS RC038)
8JX17 ET:‪20 - 36 11 1 182 217‬ E32, E34 - 72.56 (BBS RC035)

This being the case no hub rings.
Would 235/45 in the rear look odd?
What would be the ideal set if I were to disregard the 235/45 I already have?

I installed e31 lower control arms and Moosehead Engineering upper control arm spherical bushings so maybe suspension wear is not as much of an issue going with 265/40?
The 255/40 option is appealing because of price/availability but being a bit shorter when paired with the 235/45 on the front won’t it look and feel off?

Thanks again
Last edited by Hachi on Fri Nov 02, 2018 11:37 pm, edited 1 time in total.
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Re: Tire Size Combination

Post by GRNSHRK »

Been running the same exact combination of wheel and tires sizes and offsets for years, without issue :-"

You could still opt for the 265/40's out back if you're really concerned about the slightly reduced diameter of the 255's, they are only 10mm wider, although the issue of accelerated wearing of the inner edges may be an issue, if your 6er is lowered and you don't have the ability to dial out some of the negative camber :-?

I'll post a pic if you want to see a side profile view =D>
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Re: Tire Size Combination

Post by Hachi »

So you are running 235/45 and 255/40 right? Yes a pic would be most appreciated.
Thoughts on running the 235/45 on the back? It is within the tolerance of the tire but may look too stretched :-k
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Re: Tire Size Combination

Post by GRNSHRK »

Hachi, yes, 235/45 up front and 255/40 out back =D>

Same size wheels as well, including offset :shock:

You could probably stretch 235's onto 9" wide wheels, if you prefer that look :-?

Not for me, however [-X

Okey doke, photo attached :-"
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Re: Tire Size Combination

Post by Hachi »

It looks great.... too much sexy to even pick up on that 10mm difference.
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Re: Tire Size Combination

Post by 88m6 »

Been trying to source 255 40 17 rears in a tire recently discontinued to match up with what I already have up front and it's a problem. Plenty of 255 45's show up. Upon all the recommendations of a 255/40 what would I be up against if I pulled the trigger on the 45's?
All these numbers have me :roll:
Will be installing them on style 32
TIA
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