Wire wheels

[Pgxxl]

Has anybody fitted 15/6.5J wheels to series 3 roadster? I have read an article where they say the tyres can foul on the tubs when loaded of over bumps . Is this true. Is there any mods you can do. I would really like to fit wider wheels but could be an expensive mistake. Please all advice appreciated

[lowact]

Yes, that is correct, the usual "off-the-shelf" 6.5x15 wheels may rub on the rear fenders, if you hit a big bump, with any sort of load in the boot. This graphic (from viewtopic.php?f=9&t=19914&p=162155#p162155) illustrates the issue. The tyre positions are: no suspension travel, full suspension travel (to the bump stop):

This issue is NOT due to the width of the rim. It is because the wheel "offset" (horizontal distance from the mounting face of the wheel hub to the middle of the rim) is different.

Oem S3 wheels (6x15) have +20 mm offset, meaning the middle of the rim is 20 mm inboard of the face of the wheel hub.

The "off-the-shelf" 6.5x15 wheels that are touted as upgrades have only +2 mm offset, i.e. the rims are 18 mm outboard relative to the oem, this is why they can rub on the rear fenders. If these wider wheels had the oem (+20 mm) offset they wouldn't rub. In fact, if the oem offset is retained even wider (7") wheels can be fitted without any modifications or compromises whatsoever.

Sometimes wider wheels are to achieve a "dished wheel" appearance; not possible with e-types due to the centre hubs always protruding outboard further than the rim.

Changing wheel offset (from oem) has other negative consequences. Imagine a straight line through the front ball joints to a point on the ground, the distance from this point to the middle of the tyre on the ground is called the "scrub radius". If this is zero the wheel (tyre) would steer/rotate about a single point. When it is not zero (+ve or -ve) the tyre cannot steer/rotate cleanly, it must also drag/scrape (scrub) sideways. Some scrub radius is beneficial, too much is not. Changing the wheel offset directly alters the scrub radius, effects the steering effort required, tyre wear rates and directional stability during steering and braking. So it is always best if the wheel offset (therefore scrub radius) is kept as per the oem design.

Ideal for S3 e-type is as also shown in the earlier post referenced above, i.e. 7x17 ET+20 with 215/55 tyres.
Imo these ones: https://www.imagewheels.co.uk/db3-alloy-wheel/

[paydase]

Hi Colin,
Interesting analysis.

I see in your picture that you assume that the camber of the wheel remains the same (wheel remaining vertical) during the rotation of the suspension arm, hence the rubbing of the tyre on the outside fender.

Should we not consider that the camber becomes negative in such a situation, hence bringing the top of the tyre more inside the fender during the compression?

[lowact]

Thanks Serge, yes I should have, I measure 3 degrees. Previous posts edited and graphics corrected, now doesn't look so bad ...
Tyres also make a difference of course, 205/70 are oem so speedo not effected and the the spare fits properly in the wheel well.

[paydase]

Thank you, Colin.

Your drawings give a good idea of what may happen when modifying the tyre width/profile and the rim offset.
In particular the comparison of 15x6 ET20 205/70 with 15x6.5 ET2 205/70 (in your other thread, shown here under) is useful to visualise the nearing of the fender under compression:

S3_camber_Wheels1a.jpg (84.44 KiB) Viewed 1803 times

Incidentally did you just guess the profile of the fender and its position relating to the axle or is it a rather accurate drawing?

I am contemplating the fitment of 5.5 x 15 Borrani rims on my S1, offset measured ET 22 in place of the standard wheels 5.0 x 15 which have an offset of ET 33.
This means that, keeping 185 R15 tyres, the top edge of the tyre will be closer to the fender by about 1 cm, which remains limited.
I assume that it will still be OK.

[lowact]

To get accurate fender profile I made cardboard templates, 1st one in sections taped together and into the fender; used this to as pattern for a one piece temple on which I drew equispaced parallel lines that I could measure and use to make cad dwg.

Hubs likewise accurately drawn and positioned. So that I could also check for adequate installation clearance. Reduced offset (rims closer to the fenders), wider rims, fatter (therefore taller) tyres will all reduce installation clearance.
Note on my dwgs there is a 2nd representation of the edge of the wheel arch, this shows the relative heights of the fender arch and the wheel hub when the car is jacked up and the hub is fully lowered, you can see that for S3 you can just about push an original wheel (668 mm rolling dia.) on directly, no necessity to tilt, lift and straighten inside the arch.
I’m not familiar with S1. Do you have to tilt, lift and straighten the wheel to fit it inside the fender before pushing it onto the spline? That monster offset, 33 mm, has to be for a reason? Off-set, inset, outset, back spacing, all terms that are confusingly defined/interpreted differently. You say S1 3.8 std ET = 33 mm, MWS web site says it is 20.6 …. One of the alternatives they list is 6x15 with ET-3.2, i.e. 23.8 mm outset relative to std, so yr 1 cm should (?) be ok ….

[paydase]

Good point on the offset.
MWS indicates 20.6 inset but 97 mm backspacing for the 5 inch (127 mm) rim.
In principle inset and offset (or outset) should have the same value (actually with a negative sign) as per the following drawings:

Backspacing(4).jpg (110.47 KiB) Viewed 1724 times

But when I make the calculation, that does an inset of 97 - 63.5 (half of 97) = about 33 mm towards the inside of the car.
So it does not add up...

Anyway, what matters is that the MWS 5.5 inch rim has a backspacing of 89 mm and a strongly reduced inset of 6.35 mm (my 5.5" Borrani has a similar backspacing of 92 mm).
So basically, the 5.5" rim has an inset reduced by about 1 cm compared to the standard 5" rim, meaning 1 additional cm outwards for the tyre.
I think indeed that it will be ok for the S1.

Thank you for your explanation wrt fender profile, you made very comprehensive measurements and drawings!

[mgcjag]

Hi Guys.....you need to take care just useing the inset/offset/backspace measurements that are just taken off the rear face of the wheel center hub.....not all center hubs are the same and the distance between the hub taper face and the rear face can vary with wheel model....so 2 wheels could have the same inset/backspace but the whole wheel can sit much further in/out depending on the taper mounting position relative to the rear of the hub....MWS can give you the hub dimensions for their wheels......for other makes check with the manufacturer.... note the drawings below with different measurements from taper to rear of hub.....Steve

[paydase]

Hi Steve,
Thank you, very useful and helps understanding.

In my case I made the measurement of backspacing as is shown on your picture for wheels XW472 (the "standard" 5" wheel for the S1) :

IMG-20210201-WA0011.jpg (194.7 KiB) Viewed 1668 times

I assume that MWS also made their measurements in the same way, although I do not understand how they can reconcile their figures of "inset" and "back spacing" for their wheels.
In your picture they indicate an inset of 12 mm while on their website they indicate 20.6 mm...

[mgcjag]

Hi Serge...the photos I posted above do not show any inset or backspace measurements.... they are just showing hub dimensions from taper to rear of hub.. Steve

[paydase]

I made a mistake in my calculations and I wish to share it so that there is no misunderstanding in the ET measurement of wire wheels (and hence in buying wheels having the correct specs).

The picture from Dayton here under helps understanding the data used in the measurements:

Dayton backspace.jpg (66.33 KiB) Viewed 1552 times

Actually a so called 5" rim (measured rim width) has a total width of 6" (overall rim width) because you have to add one half inch by side to account for the edges that maintain the tyre centered in the rim.
My calculation of the inset using the bakspacing was correspondingly wrong by one half inch.

The MWS indications for the standard 5" Jaguar wheel (MWS XW455) are correct: 20.6 mm inset rightly corresponds to 97 mm back spacing:
https://www.mwsint.com/custom/FitmentGu ... A&CarYear=

For my 5.5" Borrani wheel, my measured 92 mm back spacing actually corresponds to a 8.5 mm inset.
That is close to the inset of the 5.5" Jaguar competition wheel (here MWS XW5744) which has an inset of 6.35 mm.
It still means however as I indicated previously that, by using the same 185 R15 tyre, this tyre will be closer by 20.6 - 8.5 = 12 mm to the fender.

Also, noteworthy is the way the inset/offset is measured for knock off wheels using Rudge-Withworth hubs where the contact surface between the wheel and the hub is conical, not a plane parallel to the central plane of bolted wheels for which the measurement of the inset/offset (distance between planes) is traightforward.
The Borrani drawing here under confirms how, for such RW wheels, the inset/offset (here 30 mm) is measured:

Borrani-Ferrari knockoff.jpg (240.62 KiB) Viewed 1552 times

[mgcjag]

Hi Serge...im not following you here. ....your Borrani drawing above shows a backspace of 30mm and an offset of 41mm (24+17).....Steve

[kashma77]

Has anybody fitted 15/6.5J wheels to series 3 roadster? I have read an article where they say the tyres can foul on the tubs when loaded of over bumps . Is this true. Is there any mods you can do. I would really like to fit wider wheels but could be an expensive mistake. Please all advice appreciated

Hello Pgxxl,
yes I have on my Series 3 Coupe the Dunlop (MWS) wire wheels 6 1/2 x 15" with 215/70VR15 tires (Pirelli P4000 Super Touring)
So far no issues with the clearance, even when the car is fully packed with four passengers, but yes it is very tight also at the front axle (Have some scratches in the front inner housing of the hood, only on the right side) but it only happens by steering in low speed e.g. getting into a parking lot.
Btw ordered the same size now as an alloy wheel (unfortunately did not arrived yet) to give you some feedback
Hope that helps.
kindly regards
Ralf

[paydase]

Hi Serge...im not following you here. ....your Borrani drawing above shows a backspace of 30mm and an offset of 41mm (24+17).....Steve

Sorry Steve, of course it is a 30 mm back spacing (not offset).
The offset of 41 mm (here broken down as 24 mm + 17 mm) can be calculated from the measurements of the rim width and of the back spacing.