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GraemeH View Drop Down
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Direct Link To This Post Topic: E24 handling
    Posted: 03-November-2005 at 04:32

Hi, New to E24 ownership, having owned E34 & E38, I'm wondering if those more expert than I can confirm: I'm thrilled with the car (635csi, '85), but worried about family members ending up in a ditch!! It's a manual (M535 gearbox, LUK clutch, LSD, 265/17 M-Series deep dish on rear), and seems very lively indeed in the tail. Exciting and terrific but wondering if it's simply the E24 in general or possibly the nature of the 265/17s or gearbox or . . . Well, basically, humbled by those with far more E24 expertise me: I'd value any tips on how they generally perform -- mostly, I'm thinking, to prevent my early demise. ;-) best wishes, Graeme.

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UKDaveJ View Drop Down
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Direct Link To This Post Posted: 03-November-2005 at 13:28
Welcome Graeme!

When you say its lively at the rear, are you talking about in high-speed cornering or applying lots of throttle coming out of junctions etc?

There is huge knowledge on this forum, as there is HERE.

Please post up some pics & a few more specs, interior spec, colour etc.

My 635's.
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GraemeH View Drop Down
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Direct Link To This Post Posted: 03-November-2005 at 13:54

Thanks for the warm welcome. Much appreciated. Yes, I'm talking about simple cornering. It could be aquaplaning, I guess, as the 265s are quite a chunk of tyre, and it has been damp down this way. But it seems to be that the gear ratios are such that even a touch on the accelerator in a corner in 4th has some key grip, and she's ready to fly. Also, what's interesting (well, to me who has only owned E34 & E38!) is that I can't get out of 4th into 5th in built up areas with the M535 gearbox; it simply has more legs than that. The car was set up, they tell me, by Capel Engineering, who do 635 work I believe (In case anyone knows more??)

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Direct Link To This Post Posted: 03-November-2005 at 14:33

I think the LSD provides for much of the entertainment. A lot of 635s are set for about 3000rpm at 100mph (overdrive top gear, 3.07 diff) which makes them super autobahn blasters.

If your is on long gearing, and its a bit frisky, just imagine what it'd be like with a dogleg box (straight through top) and a shorter diff ratio....

I've never driven two identical spec cars back to back with and without the LSD, but others report that the rear end is more prone to break away with the LSD, but easier to control when it goes....

265s are about the biggest you will fit at the rear, if they are worn they will aquaplane like crazy, likewise if they are a bit hard through age. Tyres this wide only make any kind of sense in the dry- the car is nose-heavy anyway, so a loose rear end comes as standard....

cheers

 


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GraemeH View Drop Down
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Direct Link To This Post Posted: 03-November-2005 at 14:38
Many thanks. Thus, I think it might be combination of heavy front and older 265s. What's a recommendation on rear tyre width? I guess that's a "how long is a piece of string" question. I'm thinking 255, as I have run those on an E38 for a few years and found them excellent. But will defer to E24 long-termers on any recommendation! ;-)
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Direct Link To This Post Posted: 03-November-2005 at 15:08
Depends on rim width.

My Highline runs BBS/BMW Style 5's, think 8.5 front 9.5 rear.
234/45/17 front, 255/40/17 rear.
The rears were 245/40/17 as bought, but once I knackered them out, the 255's went on. Oodles of grip.

Mine is an auto, has an lsd.

3100 rpm is approx 85mph in mine.
2500 rpm is approx 85mph in my 84 auto (non-switchable non-lsd car)

Also tyre brand & pattern will affect grip in the wet, as will tyre pressures.

A couple of pointers, some obvous for which I apologise;

A tyre with higher pressures will have the following, a smaller footprint, less friction generated heat, stiffer tyre overall resulting in less grip in the wet as the tyre carcass won't flex as much & a harsher ride. Grip in the dry will also be lower, but the more rigid tyre carcass will appear to give greater grip, mainly due to less tyre flex, working your suspension harder.
Too hard will create prounced wear in the central tread area.

A tyre with lower pressures will have a larger footprint, more friction generated heat (driving with seriously under-inflated tyres can result in blow-outs), more compliant tyre which will allow greater flex, more comfort, etc.

It can be fun playing with tyre pressures, but in reality people don't tend to tune them regularly, unless of course they are track-daying etc.

A tyre when adjusted/checked from cold will increase its pressure by as much as 4-5psi or greater at higher speeds.

Tyre temperature & grip levels are directly linked via the pressures you run, according to road conditions.

I'd stick to manufacturers pressures, experiment a few psi or more either way - just be aware that you are also affecting your grip!
My 635's.
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GraemeH View Drop Down
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Direct Link To This Post Posted: 03-November-2005 at 15:17
Ta. Might try lower pressures for starters. 'course now you have me wanting to go off and buy all manner of 6ers to try them and see the differences. I'll be at trouble at home in no time! Least I can blame someone else now, though! ;-) 
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Direct Link To This Post Posted: 03-November-2005 at 15:40
Like Dave I'm running 255/40 x 17's on the rear (Goodyear Eagle F1's all round),

They are very good in the wet.

AndyS
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Direct Link To This Post Posted: 03-November-2005 at 16:57
The problem is that the semi trailing arm
suspension wasn't designed for fat, low profile tyres
- as the rear suspension compresses, it takes on
some fairly severe negative camber which in turn
means that the tyres are only giving full grip on the
inner section. When this suspension was designed
back in the early sixties for the 1500 saloon, tyres
were skinny with a tall profile for lots of flexibility.
The first really wide tyre on a BMW was the Michelin
TRX which had been previously used on the Ford
Granada 2.8i, various Ferraris and big Peugeots with
success. However big BMW's like the 635CSi and
735i didn't like them at all due to the very stiff
sidewalls. The worst car was the E28 M535i which
frankly was dangerous in the wet and almost
uncontrollable. They are in fact banned in Australia
and no BMW can be imported with TRX tyres or any
other Metric wheel - bad news travels fast!
However on the M5 E28 and M635CSi they worked a
lot better because the roll bars were so much stiffer,
keeping the suspension in check.
With standard anti roll bars, I'd say having a good
tyre with loads of tread is about as good as you can
do. As for mods, the first thing to do is add stiffer anti
roll bars and leave the standard springs and
dampers alone, although new shocks are always a
good idea after 100'000.

A 635CSi with a manual gearbox - that's the only way
to go IMO. The best one was the old T and V reg
79-80 cars with the dog leg box and 195-70 x 14's.
They really had an edge missing in the later cars,
along with most of the wings and sills
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GraemeH View Drop Down
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Direct Link To This Post Posted: 03-November-2005 at 18:06
Ta. What shocks do you think are best in that instance? The car seems firm at rear at present and, beyond having a bunch of people ride around in the back seats on a regular basis, I'm figuring you might well have pointed to something worth investigating. . .
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Direct Link To This Post Posted: 03-November-2005 at 18:17
I found a huge range of sliding behaviour depending on the rims / tyres I had fitted. On the 16" rims, I had the best balance between fun, comfort and ease of driving. The metrics were just plain horrid, skittish, harsh and slippery. On the 18" rims, I found the comfort was good, but the tyres gripped very well indeed and I was not really able to make the back step out unless I provoked it quite severely; sadly they also made the car quite heavy to drive.
Ciao,
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Direct Link To This Post Posted: 03-November-2005 at 18:22
What about on 17's then Spokey?
My 635's.
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Direct Link To This Post Posted: 04-November-2005 at 05:14

I've only driven my 6 with the standard TRXs (220/55/390) and it only gets lively in the damp. I put that down to the LS diff though, in the dry I've never had an issue with tail-happiness (accidental tail-happiness that is!!)

I've just bought some 16" rims with decent kumho tyres (sport 104 or something) which are 225/50/16 at the rear and 205/55/16 at the front but they're not fitted as yet so I can't comment but I hope to get a better, more secure, feeling in the wet than the TRXs give.

My daily driver is a mk2 gti which is so much better planted on high speed corners. I suppose it helps to be about half the weight though

 

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Direct Link To This Post Posted: 04-November-2005 at 05:30
Horsetan (Ivan) is over the moon now he's running his 635 on 16's, having finally seen the light & ditched the metrics.

He can't praise the quality of ride difference enough now.....
My 635's.
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Direct Link To This Post Posted: 04-November-2005 at 06:50

Originally posted by UKDaveJ UKDaveJ wrote:

Horsetan (Ivan) is over the moon now he's running his 635 on 16's, having finally seen the light & ditched the metrics.

He can't praise the quality of ride difference enough now.....

Thats odd Dave, Ivan IS over the moon, but it was 15" wheels he got from you wasn't it?

My 6 obviously has a completely different rear end, but I'm happy with how it handles, but am still looking forward to getting the 14" wheels changed to 16"s

And so says Jimbob.
1981 635csi 81k miles. Will be fixed, but not by me.
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GraemeH View Drop Down
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Direct Link To This Post Posted: 04-November-2005 at 07:54
It sounds like, from discussions, that my 17" would be as large as anyone would want to go (?) And perhaps larger than most would prefer (?) best, Graeme
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Direct Link To This Post Posted: 04-November-2005 at 08:41

Graeme, spokey seemed reasonably happy with his 18s (see above) whilst other members prefer the comfort/handling balance of smaller wheels. Once Mr Sohlman sees this thread, he'll probably chip in his (always valuable!) opinion. If I remember rightly, he's tried a number of different sizes, ending up with Alpina 16" wheels.

I personally wont go bigger than 16" puerly from a looks point of view - as other series 1 cars I've seen with big wheels look odd.

Having said that, I really like the look of 17" wheels on the newer cars, especially on Shadowline and Highline car.

And so says Jimbob.
1981 635csi 81k miles. Will be fixed, but not by me.
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GraemeH View Drop Down
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Direct Link To This Post Posted: 04-November-2005 at 08:59

Those that are on it - 17s - certainly seem right (to my mind at least) from an appearance point of view ('85 mod). M-series, turbine: "very sharky" I thought when I first saw them! But it would be interesting if they're having an impact on performance to a large extent. They are deep, and wide, and points made above suggest that's not the original idea. Fair enough; but cry in my coffee if it was the case     ;-). I saw a vehicle recently, and is still advertised on . . . ., with Alpinas and thought it looked very good - though, on inspecting, the beast itself was so rusty that it might as well have been a nice set of wheels on an old tin can, I'm afraid. I'm a little unconvinced by the appearance of the standard shoeing that I've seen on some 6s - but it's probably sacrilege to say that. Apologies. I'll wash my mouth out. ;-)

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Direct Link To This Post Posted: 04-November-2005 at 09:13
Originally posted by GraemeH GraemeH wrote:

I'm a little unconvinced by the appearance of the standard shoeing that I've seen on some 6s - but it's probably sacrilege to say that. Apologies. I'll wash my mouth out. ;-)

No sacrilege to my mind, "standard" wheels on early 6s was 14" - much too small (as the pic in my profile shows), and most later cars were fitted with the 390 metrics, also pretty small (about 15 and bit inches?). Post some pics of yours as soon as poss!

And so says Jimbob.
1981 635csi 81k miles. Will be fixed, but not by me.
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Direct Link To This Post Posted: 04-November-2005 at 13:18
Originally posted by Jimbob Jimbob wrote:

Originally posted by UKDaveJ UKDaveJ wrote:

Horsetan (Ivan) is over the moon now he's running his 635 on 16's, having finally seen the light & ditched the metrics.

He can't praise the quality of ride difference enough now.....

Thats odd Dave, Ivan IS over the moon, but it was 15" wheels he got from you wasn't it?

My 6 obviously has a completely different rear end, but I'm happy with how it handles, but am still looking forward to getting the 14" wheels changed to 16"s



I stand corrected!! I meant to say 15"'s, only a woman would notice an inch difference.......

Only joking!!
My 635's.
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