Recommendations for replica wheels

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Aug 9, 2019 | 07:08 AM

#16

mujeriega

Racer

Joined: Dec 2018

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If you're going to just drive the car on the street then you should be fine with replicas.

Aug 9, 2019 | 09:34 AM

#17

Acroz

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Quote:

Originally Posted by GoldenGorilla

That's not going to work well. The 305 is typically mounted on a 11" rim and to put that in perspective, 305mm = 12". When you try to mount on a narrower rim, two things happen.

You’re right, I didn’t think about that, and it would probably mean the side wall could separate more easily from pothole damage. Also, it turns out that it will void the tire warranty (with Michelin anyway) since it’s below their recommended wheel width for the size.

Quote:

Originally Posted by GoldenGorilla

You could probably do a 285 tire on that rim, though a 265 would fit better, but then you have to match the outside diameter to the 305/30 R19 so that the AWD system has the correct offset it is designed for. If you try to drive the AWD system at the wrong offset, you will damage your front differential.

Can you explain what you mean by offset in this context? I assume you’re not referring to the wheel offset (which doesn’t matter for rear wheels)? In that case do you mean the difference in outer diameter between the front and back tires? And that the computer may detect the front diff to engage due to a noticeable difference in rotational speed, which in turn would wear it out since it’s not designed to be transferring power all the time? Or are you referring to something else? I don’t see how the front diff working can ruin it because coupling different speeds is what it’s designed to do. However if the diff’s clutch is constantly engaging and disengaging I agree that could wear it out.

Quote:

Originally Posted by GoldenGorilla

And in addition, you'll be giving up some mechanical grip on the rear. I know because I intentionally run a 265/40 R18 on a 18X10" wheel in the winter.

I have 275/40/17x10 for winter rears, I haven’t tried to drive it hard in winter so I haven’t noticed loss of grip, just wondering how much grip you’re noticing you’re losing with a 265?

Also, with my winter setup the rears are undersized (smaller outer diameter than the fronts by about a half inch). This was a mistake at the time of ordering/installation and wasn’t noticed until they were used for a season. Since this basically is the same case as above that you say will damage the front diff, are you saying it’s damaged already from a season of winter driving with wrong rear sizes and I just don’t know it yet, or is it something that should be noticeable?

Aug 9, 2019 | 10:53 AM

#18

GoldenGorilla

Racer

Joined: May 2018

Posts: 347

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From: Golden, CO

Quote:

Originally Posted by Acroz

Most AWD drive systems are designed around all four tires being the same size. The 911 AWD system is not. The differential is geared for the front tires to have a smaller diameter/circumference than the rear. If you vary too far from the spec, front differential will be constantly overdriving or underdriving when it is engaged, which will cause wear to the differential. It is the same reason why on a regular AWD car, if the tires are worn and one is damaged in a way that cannot be repaired, you have to replace all 4. You want the ratio from front to back diameter to be close to the specified winter sizes in the manual.

Quote:

Originally Posted by Acroz

I chose the 265mm specifically because the narrower tire will bite down through thin snow cover and get to the tarmac a little better in the type of winter conditions we have in CO. It is a Porsche C4S specific fitment from Pirelli. Roads tend to snowpack or go slushy here, but rarely do we have ice. With regards to grip, what I mean is that if you are on dry roads, you can cause the 265 to lose traction more easily that the 305 summer tire (given proper air temps for each). But for driving on the type of snow we have, it gets better traction in the snow and helps keep the car running straight.

Aug 9, 2019 | 11:04 AM

#19

Acroz

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Joined: Aug 2019

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Quote:

Originally Posted by GoldenGorilla

The differential is geared for the front tires to have a smaller diameter/circumference than the rear. If you vary too far from the spec, front differential will be constantly overdriving or underdriving when it is engaged

Do you know that spec is exactly and how much room it has, or what the ratio between the front and back tires is supposed to be?

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