Choosing sensible tyre width - are 225s too wide for me?

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tobes
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Choosing sensible tyre width - are 225s too wide for me?

Post by tobes »

Now that I'm in a position to use my 6-series regularly, I've decided that it's time to investigate why it feels rather "dead" to drive. Turn in isn't inviting and it tends to wallow though corners. (My E30 had a much more inviting "feel" to drive.) Having checked the obvious, my attention has turned to the mix of cheap and aged rubber that shods the wheels. At the moment I've got some 15" Style 5s with 225/60R15s on them as it was when I bought the car.

I was talking to my usual tyre supplier, and he was saying that with 15" wheels becoming less common, the prices and range of tyres is getting worse. I'd do better to pick up some 16" wheels, I might well save the cost of the wheels on a set of tyres, so I've been looking at the options.

I've also seen from the tyre pressures listed on the door that these are wider tyres than it would have been supplied with, and as I understand it wider tyres lead to heavier, less inviting steering but more grip. On the other hand, I've seen plenty of discussions here about putting wider tyres than mine on.

So, having been trawling ebay and cross referencing to the available tyres, I'm thoroughly confused and no closer to working out what to go for. As I say I'm keen to enhance driving feel, probably over ultimate grip. Sets of 16" wheels seem to be pretty commonly available and at a reasonable price, but I'm still unsure whether I'd be better dropping to something like a 205 width tyre, and experimenting to see what I get on with looks like an expensive way to go.

The car tends to get used for a combination of spirited road use and longer distance touring, so no worries about track day performance, and comfort is obviously an important consideration.

So what are people's thoughts on reasonable width tyres? 225 looks to be a starting point of what people are choosing for upgrades, but has anyone who's driven differing tyre widths / rim sizes got anything to say about the relative differences in grip, feel and comfort to point me in the right direction, please?
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Re: Choosing sensible tyre width - are 225s too wide for me?

Post by slofut »

tobes wrote:Now that I'm in a position to use my 6-series regularly, I've decided that it's time to investigate why it feels rather "dead" to drive. Turn in isn't inviting and it tends to wallow though corners. (My E30 had a much more inviting "feel" to drive.) Having checked the obvious, my attention has turned to the mix of cheap and aged rubber that shods the wheels. At the moment I've got some 15" Style 5s with 225/60R15s on them as it was when I bought the car.

I was talking to my usual tyre supplier, and he was saying that with 15" wheels becoming less common, the prices and range of tyres is getting worse. I'd do better to pick up some 16" wheels, I might well save the cost of the wheels on a set of tyres, so I've been looking at the options.

I've also seen from the tyre pressures listed on the door that these are wider tyres than it would have been supplied with, and as I understand it wider tyres lead to heavier, less inviting steering but more grip. On the other hand, I've seen plenty of discussions here about putting wider tyres than mine on.

So, having been trawling ebay and cross referencing to the available tyres, I'm thoroughly confused and no closer to working out what to go for. As I say I'm keen to enhance driving feel, probably over ultimate grip. Sets of 16" wheels seem to be pretty commonly available and at a reasonable price, but I'm still unsure whether I'd be better dropping to something like a 205 width tyre, and experimenting to see what I get on with looks like an expensive way to go.

The car tends to get used for a combination of spirited road use and longer distance touring, so no worries about track day performance, and comfort is obviously an important consideration.

So what are people's thoughts on reasonable width tyres? 225 looks to be a starting point of what people are choosing for upgrades, but has anyone who's driven differing tyre widths / rim sizes got anything to say about the relative differences in grip, feel and comfort to point me in the right direction, please?
My personal preference is 16 inch rims on e24's, even so with 225/55's the ride is a bit harsher than the trx's with newer rubber, or 15's with 225/60. On my 88, a few weeks back I swapped the 225/55/16 and TSW wheels off my '87 onto the 88. The wider tires definitely increase steering effort and I suspect stress on the steering components and frame. Also, they seem too short in the wheel wells for me. Since I was prepping the car for my daughter to drive to college, I put on 215/60/16's and it drives really nice and looks better in the wheel wells to me. For me to drive, I think I'd probably still have to go with 225's but probably 60's, the extra sidewall would be a better ride/compromise and fill the wells better. May be a different story for a lowered car though.
If you wanted more handling, the 225/55/16 dunlops were great on my 87, you could turn in so hard it felt like you'd break something! But I didn't like the small diameter ghetto look on my non-lowered car. So for handling, I'd probably look into 225/55/17 for less sidewall, rougher ride, better handling, and better looks.
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tobes
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Post by tobes »

Thanks for that, so there is a noticible increase in steering effort for the 225s? How do they compare for turn-in when you're driving at normal speed, rather than parking / maneuvering speed?

I'm not sure I've got the clearance to increase the overall diameter, the tyres I've got are already pretty close to the bottom of the springs.
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Post by wattsmonkey »

225 is not wide for an E24: the Highlines came with 240s!

I hate to point out obvious stuff that you've doubtless already considered, but an E30, with its low kerb weight and rack and pinion steering, will turn in more positively and directly than an E28 with its steering box. The E24 is, aesthetic qualities apart, a fat-arse E28 with massive overhangs all over the shop!

The standard suspension setting is good for ground clearance, but not for going round corners without rolling around a bit.

New rubber versus old trx will provide an amazing difference.

My preference is 225/50/16, although the Hartges will be rocking 245/45/16 on the back.

You certainly won't want to increase the rolling diameter, so using one of the online tyre-size comparison calculators is a good idea.

Cheers,

Rob
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Post by GazM3 »

Hey there.
Good rubber will help but if u want less dead feeling I'd tidy up the chassis a little. Start with the front end bushes and if u haven't done so install one of those strut stowed stress bars. A rear tower stress bar also helps. Actually I'd probaby do the strees bar or bars first even before the tyre/wheel change.
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84 E24 M635csi
90 E34 M5 3.6
94 E34 540i/6 SC E85
97 E36 M3 euro SC U/C
97 Z3 2.8 widebody

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Post by tobes »

Hi, thanks for the thoughts. I agree that a) it's never going to be the same driving experience as the E30, though I don't think that the top of the line "Ultimate Driving Machine" should be this much less "fun" than the three-series was. Also b) I should look over the rest of the suspension setup. I've been over it several times, and while obviously much of it is thirty years old, anything that's broken or showing obvious play / wear has been changed.

I'll consider a strut brace, though I've always thought that if it was that much of a difference, they'd have come with one from the factory.

Tyres seem an important starting point as having been a believer in "a tyre's a tyre," a set of Goodyears transformed the driving of my daily Passat for not much more than a set of budget tyres, so I thought that a set of better rubber was probably a good starting point.

A set of 16" wheels and a set of 225/50/16s look to be the consensus on a good compromise of comfort / handling / grip / price / etc..
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Post by wattsmonkey »

I can't recommend a strut brace highly enough: I dare say our cars have even more flex in the chassis than when they were new!
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Post by GazM3 »

The humble 6 can be made to handle even better than e30.

When I first got my e24 handling was just awful and olde worde almost bordering on dangerous I'll list the things I done with a points score out if 100 for improvement/effectiveness and in chronological order with a small comment after.

1/ replaced metric tyres with 17". 50/100 well straight line traction a lot better and copes with wet weather
2/ future lowered h&r springs 15/100. Good aesthetics buoy little handling benifit.
3/ added missing under car brace bar 25/100. Tightend up front end significantly and better cornering feel
4/ fixed broken steering box bracket and adjusted free play on steering 35/100. Hallelujah. No London bus style few play in the wheel. Noticeable turn in improvement
5/ upgraded all front end bushes and steering arms. Much smoother and no shimmy at 100kmh.
6/ added offset roll centre adjusters to give -2deg front camber 50/100. Sharp turn in and more confidence in the cars handling
7/ installed front strut tower brace 100/100. Wow. It's like someone tune d the handling up majorly. Prob brought the car 20yrs more modern improvement. Front turn In now instant and lots of confidence.
8/ installed rear strut tower brace 50/100. Whoa. Like someone fed it red bull. Now oversteer on demand and probably needs the rear end adjustment done to balance out chassis.

I still run OEM 30yo shocks and have non adjustable rear geometry.

Overall the car has made astonishing improvement in handling. Corner speeds are as good as or even beyond my e36m3!!
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84 E24 M635csi
90 E34 M5 3.6
94 E34 540i/6 SC E85
97 E36 M3 euro SC U/C
97 Z3 2.8 widebody

OTHERS
11 Audi S5 3.0 SC
19 VW Amarok V6
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Post by tobes »

Great list, that sounds like just what I've been looking for!

Funnily enough I was looking at an E36 M3 not so long ago. A lot of fun for the money, especially as it doesn't have a lot to give it away as not a regular 3-series...

I shall have a think about that, get under the car and have another check that everything is as it should be, but then it sounds like a strut brace needs to go on the fabrication / shopping list.
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Post by Brucey »

225s (with the right offset) are about the right width to work properly with the stock steering geometry, provided the rims are not too wide. 225/60-15 (on skinny 7" rims) is really an E34 fitment (and is a fraction larger diameter than most other E24 fitments) but I think it works very well on E24. Of all the setups I've tried this gave the lightest, most accurate steering. It would be my choice if you want to drive the car a lot of miles in all conditions, on stock suspension.

If you go to 16s, 17s, 18s etc then you trade grip etc for more noise, worse tramlining etc. Dynamically the suspension works best if you have the least unsprung weight; the lightest wheel/tyre setup you can get for reasonable money is a set of 15" BBS cross spokes and a decent tyre (they vary quite a lot). If you really want to 'push on' when using bumpy roads the smaller rims are best until you get to the corners.

Note that the original 390 and 415 metrics have the exact same working (i.e. exposed) sidewall height as 15" and 16" fitments respectively; rims are measured at the bead seat and the TRX ones have smaller lips.

If you fit very much lower profile tyres (with stock bushings and stock geometry) and drive a lot in the corners you can expect the tyres to wear less well than you would like. The reason for this is that the suspension is designed for a tyre with a reasonable sidewall height, and you need the sidewall to move around to keep the tread on the road in the right way once the car rolls.

So if you increase the roll stiffness, lower profile tyres start to make more sense. Because of the way the bumpstops work on this chassis, simply lowering the car about 3/4" (i.e. to M-car height) gives increase roll stiffness, provided the bumpstops are in good shape. [NB; If your bumpstops are more than about five years old, they'll be kippered, and you should change them].

So my take (and BMW's too I suppose) is that a 415 metric or a 16" rim is going to work best with M-tech suspension or other slight lowering.

But.... all this talk of tyres is meaningless unless the steering is sorted out. There are several known issues with the control arms, as well as other things that should be looked at. Now, a steering box is never going to feel quite like good rack but many E24s are woeful for other reasons.

Some things to check;

1) upper TCA bushings (NB many alternate types have the bushing centre in the wrong place and may give bump steer)
2) Ball joints. There are eight in total (in the front alone) and they all need to be perfect.
3) Dog bones. These are on the rear suspension but they can very greatly affect the turn-in; the reason is that they control the passive rear wheel steering as the rear end loads up.
4) Idler arm condition.
5) steering box mountings; these are known to crack up and even if in good shape it is worth using a reinforced mounting onto the subframe beam; the reason is that the stock mounting is tied into the upper skin of the beam only, and it simply isn't all that stiff; you can flex the box section quite easily using a set of water pump pliers. Something welded into both the top and the bottom skin is a much better idea.
6) The steering box. These can wear or be set up badly so that there is too much free play in the straight ahead.
7) The centre link. This is often the real problem that gets overlooked.

There is a special RHD issue here, which is that the steering box/ idler arm balljoints on RHD links are usually configured as per a LHD link. The balljoints each side are different to one another (the steering box one should have about x5 the preload and about x5 the backing spring stiffness vs the other one) and the result is that the highly loaded steering box balljoint on a RHD car can often move ~ +/- 2mm in normal use. No wonder the steering feels crap; a new centre link provides temporary relief only simply because the parts are a tight fit in the bore; trust me, this won't last a year. BMW seen unwilling or unable to make the correct RHD part and so do the aftermarket people. I built my own modified centre link which is adjustable on the steering box joint. Needless to say it was like having a new centre link, but it carries on working properly.

hth

cheers
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Post by tobes »

Thanks Brucy some great technical points there. Unfortunately that leads me back to the problem of a limited choice of tyres in the current size. Though I've found some Conti Premium Contact 2 for sale which look a reasonable known brand / cost / grip rating compromise.

Some good points on the steering too. I've looked at most of them in the past however it's probably going through systematically at this point and checking everything. When it comes to bushes am I right that levering with a big screwdriver should result in negligible but detectable flex? (rotating by a couple of degrees / 1mm or so.)

Having been for a decent run in the beast yesterday, I think that the steering box adjustment may we be worth looking into, there is a vagueness in the straight-ahead that's not helping.

Box mountings have been repaired, but ever since I did, I've liked the idea of the reinforcements that are available (from Ed someone, IIRC - I've still got the email somewhere). Again I shall add to the desirable list.

The center link issue sounds interesting. Am I missing something, why isn't it just a LHD linkage mounted the other way round? Or are differing ball joints only needed in RHD configuration?
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Post by Brucey »

The rubber bushes on the control arms vary in their stiffness; the front (lower) bushings should be pretty stiff radially, slightly less so axially.

The rear (upper TCA) bushes are meant to have an 'easy' stage when compressed under braking, and then to go firmer once two parts of the bushing contact one another. They are not especially stiff in any other direction. The idea is that you get a nice compliant ride but when the brakes are on the toe settings are well controlled. The stock E24 Upper TCA bushings are pretty flimsy; the E32 ones (which need to be shortened to fit) are a lot stronger, and contain a stiffening insert.

Straight ahead vagueness can be the steering box itself (worn/badly set), the steering box mountings, the centre link (or other) ball joint, or just bad toe settings (normally slightly toe out).

The RHD centre link should be configured with the different balls joints ball joints simply exchanged in position vs the LHD one. There is a separate part number for the RHD part and everything. The basic problem is that some f-wit somewhere has decided to sell the LHD part labelled as a RHD part; they superficially look identical to one another part from the shape of the backing cap on the ball joints. The same part is made by several different vendors and they all appear to be the same; in fact I have never seen a correctly manufactured RHD part.

If you take the centre link off your car you can check the ball joint preload quite easily; the joints also look different to one another as well. You can see more here;

viewtopic.php?t=7915&highlight=center+c ... hd+problem and here

viewtopic.php?t=20635&start=0


cheers
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