various hubs - track increase?

[mccusername]

My Tii has Turbo front brakes (and hubs) and while trying to fit some new wheels, I discovered/learned that Turbo hubs add about half and inch of track on either side compared to stock Tii hubs. 

 

Does anyone know the relative width of an early E21 hub compared to a Tii hub?

 

And does anyone know if Turbo drums (which I believe require Turbo stub axles) add to the rear track? My wheels fit better in the back but still poke a little more than I anticipated.

 

Thanks, Michael

[kbmb02]

8 hours ago, mccusername said:

My Tii has Turbo front brakes (and hubs) and while trying to fit some new wheels, I discovered/learned that Turbo hubs add about half and inch of track on either side compared to stock Tii hubs. 

 

Does anyone know the relative width of an early E21 hub compared to a Tii hub?

 

I learned that when tearing down and restoring the Hyde Park #34 race car (image, below). That car has turbo hubs, vented rotors, and later-model calipers. 

 

Re: E21 vs Tii hub -  if I’m speculating correctly in what you’re thinking, you may have to pre-fit each set-up on a strut with the appropriate rotor and caliper to confirm the width and/or fitment.

 

Bryon / @Preyupy has a good handle on the differences, perhaps he’ll chime in. -KB

 

[visionaut]

I’m running the full Turbo brakes conversion on my 76er.  Yes, the conversion adds track width to the front and rear vs. a regular 02 or tii.

 

I’ve done all the calcs for the differences in track widths, and what contributes to the changes — let me go dig through my archives to find that info…

 

IIRC, it wasn’t a full 1/2” additional per side up front (it’s less)…

 

[mccusername]

Thanks for the picture, Ken-- although that's not as much of a difference as I thought/hoped. I have some H&B 15" wheels that are 6.5" wide with an ET of about 19. They-- should-- fit but are poking out too far. I'm trying to figure out if Tii hubs + Alpina repro (thinner) rotors will tuck them in enough.

 

The rears fit OK but a little more poke than I expected. That's why I was wondering if Turbo and/or 320i rear brakes increased track at all.

[mccusername]

@visionaut I'd appreciate it if you could check your notes, especially on the rear. Not much info out there.

I had read that the Turbo front hubs are 10-12 mm longer than Tii hubs.

Edited October 1, 2023 by mccusername

[visionaut]

Okay, I found my old calculations.  Looking back over it now, the only bit of a puzzle I ended up with was the narrowness of the 2002 Turbo Rear hubface distance.  I was expecting it to be wider than 2002tii due to the beefier Turbo Rear stub axle and drive flange...

 

Here ya go.

Tom

 

=======

Quote

 

2002 Turbo - Wheel Track calcs

 

BMW published the 2002's Wheel Track (vs. Axle Track) measurements. Axle Track is measured Hubface-to-Hubface, and doesn’t change with wheel offsets. Wheel Track is a wheel centerline-to-wheel centerline measurement.  Note that Tire & Wheel widths don’t factor into Track Width. ;)

 

Wheel Track = Hubface width - 2 (Wheel Offset)

Hubface Width = Wheel Track + 2 (Wheel Offset)

 

— The 2002tii —

Early 2002tii  Front Track = 1348mm

Early 2002tii  Rear Track = 1348mm

Early 2002tii Wheels = 5J x 13, et26

• Front Hubfaces = 1400mm

• Rear Hubfaces = 1400mm

 

Late 2002tii Front Track = 1342mm

Late 2002tii Rear Track = 1343.6mm

Late 2002tii Wheels = 5J x 13, et29

• Front Hubfaces = 1400mm

• Rear Hubfaces = 1401.6mm

 

2002tii Early vs Late Track differences are from:

a)  Late has 6mm less Front & Rear Track due to wheel offset differences (3mm x2)

b)  Late gains 1.6mm Rear Track  due to Late tiis having  thicker rear drive flanges

 

 

— The 2002 Turbo —

 

2002 Turbo Front Track = 1375mm

2002 Turbo Rear Track = 1362mm

2002 Turbo Wheels = 5.5J x 13, et18

• Front Hubfaces = 1411mm

• Rear Hubfaces = 1398mm (?!)

 

2002 Turbo has 33mm wider Front Track than Late 2002tii

2002 Turbo has 18.4mm wider Rear Track than Late 2002tii

 

2002 Turbo vs. Late 2002tii Wheel Track differences are from:

a) Turbo has 22mm wider Front & Rear Track due to the lower offset Turbo Wheels (biggest part of it).

b) Turbo has 11mm wider Front Track due to the 5.5mm wider Turbo Front Wheel hubs

c) The Turbo Rear stub axle/drive flange combo, while beefier, is actually 1.8mm less wide than Late 2002tii (?!)

d) The Turbo Wheel outer lip would sit 17.25mm farther outward than the Late 2002tii Wheel if both were mounted to the same hub.  But the Turbo Front hub actually extends 5.5mm farther, and the Rear axle/flange is actually 1.8mm narrower than on a Late 2002tii…

 

 

[mccusername]

Thanks for that info, Tom. Hub face to hub face is what I'm interested in, since I'm trying fit wheels that are 2.5" from the outer lip to the mounting surface. If going from Turbo hubs to Tii hubs is only going to get me 11mm total, that's probably not going to do it.

 

I could use Dunlop Direzza ZIII's which are almost an inch more narrow than my current tires although both are 195/55r15. But I'd still be on 6.5" rims so anybody have a guess how much room that change would get me?

[visionaut]

32 minutes ago, mccusername said:

But I'd still be on 6.5" rims so anybody have a guess how much room that change would get me?

 

Most seem to successfully run a 195/50 on 15x7 et 25-28 wheels (no rub/no roll). A 55 being a taller profile tire may be more likely to rub…just sayin’.

 

So your wheels are 6.5J x 15, et19? That wheel spec should have virtually identical poke to the 15x7 I cited above (.3mm diff) but will sit 1/2” closer to the strut… Of course then add 5.5mm additional poke for your Turbo front hub…

 

FWIW I don’t like working with backspacing cuz you never know whether folks are measuring to edge of lip or edge of tire bead… (a 6.5J wheel measures 6.5” between the bead surfaces).

Edited October 1, 2023 by visionaut
Added note about Turbo hub…

[mccusername]

8 minutes ago, visionaut said:

So your wheels are 6.5J x 15, et19? That wheel spec should have virtually identical poke to the 15x7 I cited above (.3mm diff) but will sit 1/2” closer to the strut…

 

Yes, strut clearance seems fine (fingers crossed). These should fit like the 15x7 but I think the small added width from the Turbo hubs isn't helping.

I went with 195/55 because the outer diameter is almost an exact match for OEM. 195/55 are smaller OD but the difference in width was miniscule. But yeah every mm seems to count now so maybe I should have. I have some 195/50s but in a much worse tire...

 

 

[TobyB]

that's what they make tinsnips for.

And dead- blow hammers.

 

t

bkuz racekar