MY17/MQB Platform Tiguan Discussion Thread
Quote:
Originally Posted by
Delewin
Hi REGS12,
Thank you.
Trendline & Comfortline use 17x7 ET40 and 215/65 R17 with overall wheel diameter of 711 mm
Highline use 18x8 ET38 and 235/55 R18 with overall wheel diameter of 716 mm
R-Line use 20x8.5 ET38 and 255/40 R20 with overall wheel diameter of 712 mm
The space-saver is
18x4 ET 27.5 and 145/80 R18 with overall wheel diameter of 689 mm This is why you cannot exceed 80Km/Hr with the space-saver.
It is all about the difference in the rolling diameter and how that can cause problems with the diffs, axles and steering if it is on the front.
While patiently waiting for my 162 TSI to arrive I am trying to work out just what tyre /rim combo will replace the Spacesaver wheel and still fit under the tray top when it is placed on the higher position.
This brings up a question on how does one re-calibrate the speedo when you change the overall wheel diameter from standard?
Also has VW used the same calibration for all of its Tiguan models?
If so, then the Trend line, Comfort line and R line would be OK, but the High line would show a lower speed that actual based on the larger overall diameter tyres??
Does anyone know if the speedos are calibrated to the supplied tyres or does VW just assume all tyres are equal?
David
The difference between a 711mm and 716mm rolling diameter would result in a difference of 0.7% or less than 1km/hr at freeway speeds. This is significantly less difference than a new tyre vs one due for replacement as the tread is reduced on the same tyre.
Of note, on this subject, is that the Australian Standard for speedo calibration states (well at least it did a few years ago when I first researched it) that for a speedo to be in accordance with the standard it must not under-read at all, but can over-read by up to 10% + 6km/hr. So a true speed of 100km/hr could see your speedo read 116km/hr and still be considered correct.
You can thank the nanny state "speed kills" nonsense and the proliferation of speed cameras for this. If you stay below the limit on your speedo you will always be below the limit, sometimes by a long way. The worst car I've seen for this was my MY07 Subaru Liberty 3.0 RB which over-read by 10%. The MY13 A6 Allroad I currently drive over-reads by 2%. The easiest way to check this is on the freeway with the cruise control on, at a constant speed, on a straight road. Check the speed against a GPS. GPS speed does have a small time lag and works through a principle of time rate of change of position, so if you're accelerating, or going around a corner, the GPS will under-read slightly. It is far more accurate than most car speedos though.
So the Highline would be the more correct using your diameters above. The other models would over-read more, slightly.
Yes, speedo calibration can be changed with VCDS, but if I recall correctly can only be changed in steps which equate to 3-5% so more than the error in most modern VAG cars. You can't fine tune it to the accuracy of less than 1% using VCDS. If you're changing tyres from the manufacturer spec my suggestion would be to check the over-read of your speedo with standard tyre first. Then work out what the change will be with the new set. If the new tyres have a larger rolling diameter it will reduce the over-read. This is what I did with the Liberty. Using the same 18" wheels, and the same aspect ratio tyres I increased the width by 10mm. As aspect ratio is a measure of sidewall height as compared to width, this increased the sidewall height by 5mm and the diameter by 10mm. This reduced the over-read in the speedo by a small amount.
Of interest is that different brands of the same sized tyre can have a variance in rolling diameter of up to 1%. Even though they may be the same wheel size, width and aspect ratio they should mathematically be the same rolling diameter they're not.
I hear what you say about the space saver speed limit being based on diff stress, I hadn't heard that. I'd been told it's based on the structure of the sidewall of the space saver not being able to handle stress of cornering or impact at high speed. It's possible what you say is correct, but I would have thought distance travelled with a space saver would be more of a consideration than speed if this were the case.