[SyTy]

Gents,
I'd like to see your opinnion about wheels for track use, should I go for oem or try with borbet (they are costumised already)

Thanks for the answers.

Borbet are front 8,5 and rear 10 17" dedicated for E34
OEM are 8 and 9 17"

I'd like to do survey but don't know how
Tom

 

[IvanDias]

Those Borbet wheels look nice! Shame to hide them away for track use only.

One thing that may sway you is that the Borbet's are wider, so ideally you'd be looking at bigger rubber as well.

That gives you a heavier wheel/tyre combo, with a shorter traction patch so breakaway will be faster when it goes (not fun when on a track with no runoff like the 'Ring) and also more expensive tyres which you are going to tear up on trackdays.

Unless you're a really hot driver and are already pushing the chassis to the limit, I'd save the Borbets for road use and go OEM on the track.

Whatever option you go for, once you're really familar with the car, consider proper trackday rubber like Dunlop Direzza D02G, Toyo R888 or even the awesome Bridgestone RE540. They won't last long but will be amazing on track.

Once you're an expert driver, be careful oil is not on the limit low on tracks with long hard really high-speed corners as you don't want starvation, which is also a reason to avoid true slicks. (Proper race cars are often dry-sumped to avoid this!)


Have fun!!


Kind Regards

Ivan.


P.S. When mounted, post a pic of the car on those red rimmed Borbets, I'd like to see that.

 

[Lantz]

That gives you a heavier wheel/tyre combo, with a shorter traction patch so breakaway will be faster when it goes

Ivan, I am a little confused; so with a wider rear tyre you get less rear grip?

Any explanation would be most appreciated

:cheers:

Lantz

 

[IvanDias]

Hi Lantz,

Not really, but not quite either!!

There was a thread Farrell made which explained it better than I can!



Here goes anyway!

Basically it's important not to confuse grip with traction and be aware that neither imply better handling!

Read the above line again!




A wider rear tyre will have a wider amount of rubber touching the ground, but the ratio between the width of the patch (235/255/265 etc) and its length (the 2-4cm ish front to back of the contact patch) will change too, which affects the overall grip of the tyre.

This means that although traction should be improved in acceleration and also one would hope in cornering, it would also make sense that if (say in a constant radius corner), the lateral forces the tyre can cope with would be more in a wider tyre. But, as the speed (or more correctly; load) would be more before the tyre reached its maximum grip and started to slide, there would be more lateral load being placed on it when the tyre slides, resulting in a faster and heavier sideways slide. To cut that very short, when it lets go, it lets go faster giving less time for the driver to respond.

Before everyone hit's "reply", bear in mind that a wider tyre also means that the weight of the tyre is spread over more area, so less pressure is locking the tyre to the ground.
It is possible to "over-tyre" a car, which many boy-racers have found in the past, their cars performing worse in corners than stock with wide-boy aftermarket wheels.

Also, different compounds, makes and models of tyres will have different characteristics, so will vary in the way they work, some gradually giving up the ghost, some squealing like made before a slide, some deathly quiet and some grip like mad then bang and nothing!

Now factor in the wider tyre being heavier than stock so the unsprung weight of the wheel assembly changes, then the sidewalls being under slightly different stress levels given no change in the J width of the rim, you can see that it's easy to mess around with overall grip and traction but getting a cars *handling* to be improved is a delicate dance indeed.




Without citing any actual references, I seem to recall some members having enormous fun on trackdays with their cars on factory 235 all-round tyres as the 3.6 car's suspension and antiroll-bars were originally designed for this size and it balances their cars very well.
Many owners, myself included, found the optional staggered 17" combo of 235/255 very prone to understeer. BMW agreed and the 3.8 cars with factory staggered rims got a increased rear roll-bar diameter.

I'll shut up now, especially as I don't run the proper size wheels on my car anyway, and this thread is supposed to be about the choice of track wheels above and not go off-topic into another handling thread.

Best wishes and I hope my ramblings made some sense.

Ivan

 

[nebpor]

P.S. When mounted, post a pic of the car on those red rimmed Borbets, I'd like to see that.

Amen - I generally don't care about wheels, but they are gorgeous :cheers:

And just to add my $10, I am considering moving from a 9" rear rim back to a 8" - the car has too much grip at the back and it's not helping me get a "feel" for RWD properly ... I'd like it to be easier to get the back sliding.

Grip is the enemy of fun - that's why modern cars are rubbish!

 

[Mmm-Five]

Amen - I generally don't care about wheels, but they are gorgeous :cheers:

And just to add my $10, I am considering moving from a 9" rear rim back to a 8" - the car has too much grip at the back and it's not helping me get a "feel" for RWD properly ... I'd like it to be easier to get the back sliding.

Grip is the enemy of fun - that's why modern cars are rubbish!

Keep the staggered set-up but put some Avons on the rear - they'll teach you the art of oversteer :hihi:

 

[nebpor]

Yeah, I was thinking that my stout defence of PS2s on the car might actually be the problem :nono:

 

[Lantz]

Thank you Ivan, very informative post!

Lantz

 

[davidoli]

Thank you Ivan, very informative post!

Lantz

+1 ...... That boy Faz really knows his stuff .....good post ......

Sebring Sienna is on 235/45/17 ps2s all round ......8 j rims , all round ....handles like she's on rails !

 

[IvanDias]

+1 ...... That boy Faz really knows his stuff .....good post ......

Yes, he does.

Just to clarify in case I got anything wrong and it tries to comes back and bite the wrong person, my post is not a cut'n'paste from a Darren Farrell post, it's something I wrote yesterday to help Lantz.

The info contained in it is what I have absorbed from Faz and other sources, so any errors in it are definately from my poor brain and not attributed to him.



David, I bet that car handles lovely with all the weight out and on the original designed spec of 235's. Once you're truly finished with it, it might be worth getting a few cars together. How cool would it be to see a drag down an airport runway on video showing the difference from 20-140mph between a stripped 3.6, my 3.6 with it's (still) dead resonance flap, a 3.6 in working order and a 3.8. That would be a fun experiment I'm up for!!

Regards

Ivan

 

[davidoli]

Yes, he does.

David, I bet that car handles lovely with all the weight out and on the original designed spec of 235's. Once you're truly finished with it, it might be worth getting a few cars together. How cool would it be to see a drag down an airport runway on video showing the difference from 20-140mph between a stripped 3.6, my 3.6 with it's (still) dead resonance flap, a 3.6 in working order and a 3.8. That would be a fun experiment I'm up for!!

Regards

Ivan

Sounds like a great idea Ivan .........

 

[Sebring NL]

Gents

I tend to agree with above statements, but some key elements have been left out too IMO.

1) Using R-compound will wreak havoc with the car. Especially a heavy, non-trackcar that is being used as such. We're not just talking reversable damage here.

2) The whole grip vs handling thing is indeed often overlooked by the 'bigger is better' crowd. However, I think a lot is up to the individual driver. I have toyed with offsets on my car ( yes I got it wrong at the Ring once with the tire scrubbing the control arms) but now I am quite pleased with the wider track of the car at the front but tires only slightly wider than stock. However I have the feeling that even wider tires -could- work when the offset is wider than stock. I can perfectly live with the handling now, since the oversteer has been reduced (but not like my driftcar) and the car feels more neutral than OEM .

However, this would only be case in the dry, as in the wet I wouldn't dream of going wider.

There is just a frame of reference in which the engineers made the car. Changing offsets, diameters and width of the wheels will tamper with that. I am arrogant enough to think that for my desires, I can alter it for the better.

Many people have difficulties understanding how small technical differences in car can make a HUGE difference in handling. On my E28, I raised the rear by 1 cm in order to reduce rear end grip through altering the negative camber. It was a day and night difference, in some corners the car would engage drift 10 km/h slower than before. Ofcourse most people want the opposite effect, but its just an example of how easy things can affect handling when pushing outside the envelope that Motorsport made.

 

[Jon Baker]

David, I bet that car handles lovely with all the weight out and on the original designed spec of 235's. Once you're truly finished with it, it might be worth getting a few cars together. How cool would it be to see a drag down an airport runway on video showing the difference from 20-140mph between a stripped 3.6, my 3.6 with it's (still) dead resonance flap, a 3.6 in working order and a 3.8. That would be a fun experiment I'm up for!!

Regards

Ivan

Great idea, name the time and place and I will be there!!

 

[legacy260]

Ring up Bruntingthorpe in Leicestershire and book a time / day!!