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tj924 · Posted: Tue Jul 27, 2004 9:26 pm Post subject: Advice needed on new wheels

I have the opportunity to get some used after-market wheels cheap & I have been told they came off the same model 924 as mine so will fit (4 x 108 PCD etc).

The front are 15x7 & currently have 205/60 tyres. The rear are 15x8 & have 225/? tyres (trying to find out exactly what the rears are).

Can anyone tell me for sure whether these rims would be suitable for my '82 924?

From my research I think the original 15" Porsche rims (mine came with 14" rims) were 15x6 & used 205/60 tyres, so I'm not sure if the 15x7s & 15x8s would be suitable or not, even though the current owner says they came from an '82 924. I believe if the wrong size is used it can throw out the speedo & odometer readings?

Thanx...

TJ

tj924 · Posted: Tue Jul 27, 2004 9:50 pm Post subject:

Just found that the front are 205/50 (15x7 rims) & the rear are 225/50 (15x8 rims). Would those tyres be OK or should they be changed to something more suitable.

Thanks again,

TJ

red924 · Joined: 13 Oct 2003 Posts: 281 Location: London, England

ive got 15s on my 924 no probs, but my rear arches are falred
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tj924 · Posted: Tue Jul 27, 2004 10:09 pm Post subject:

No flares or anything. The body is standard which is why I'm a little concerned that these rims/tyres wouldn't fit properly, even though the current owner says they had them on an '82 924.

CMXXXI · Joined: 05 Nov 2002 Posts: 1939 Location: Vicksburg, MS

This part of the Tech Section lists stock sizes: http://www.924.org/techsection/9brakes.htm . The speedo would have been calibrated for the stock size, and it will differ slightly depending on replacements. There are any number of "tire calculators" (similar to this one) available on the web that will do a comparison of sizes if you want to change from stock, but "stay close" with your speedo.
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'79 Eurospec 931

Magnus K · Posted: Wed Jul 28, 2004 5:04 am Post subject:

As a bad example, the PO of my 924 has managed to use 235/60(I think?) standard 6x14 inch 924 rims at the rear wheels... It works as in it don't hit anything in the wheel well, but... No, don't go there.

I think I'll try to find 195/60-tires in 14 inch sizes for my car. It'll have about 4 per cent less diameter = the speedo will show 4% too much but I think that a smaller wheel will give a slight increase in acceleration abilities?

Over here in Europe there are other cars that use the same bolt pattern (4x108 millimeters) so the biggest problem is to find a rim with the right offset. Peugeot's 306 and 406 models has rims with a very low offset, about 15-19 millimeters, maybe they will fit?

Someone over here in Sweden gave me these recommendations:
7x15 -> offset less than 18 millimeters (0.70 inches)
6,5x15-> offset less than 24 millimeters (0.94 inches)
6x15 ET-> offset less than 30 millimeters (1.18 inches)

Could this be correct?

/Magnus
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Another curious Swede...

Asleep in Sweden, Europe, when you US guys are awake...

tj924 · Posted: Wed Jul 28, 2004 6:59 am Post subject:

Standard size for tyres for the 14" rims is 185/70 but the tyre places here want to use 195/65, which is a pretty close match (< 1% difference) according to the tyre calculators I've used.

Standard size listed for the 15" is 205/60 front & rear, so I think the tyre sizes currently on the rims are too far off to be safe (> 3% difference can cause brake failure I read).

TJ

emoore924 · Joined: 13 Apr 2004 Posts: 2822

For the street, I currently run 205/60/15 pirelli p4000 on 6x15 fuchs copy wheels. For the track I run 205/50/15 front and 225/50/15 on rear on 6x15 cookie cutter wheels. This is with "rolled" fender wells, no flairs.

For 924-zilla I have Yok AVS 225/50/15 on the front on 8.5" BBS wheels (there's room for more too) and 285/40/15 on the rear on 10.5" BBS wheels. Various spacer combinations are employed to get the tire to the right place in the wheel well. In any case, this application works under glass fenders that are +2" wider each side than a stock 944. Not normal stuff.

The fronts are probably ok except when at full lock -- but even then, they're probably ok. I'd be worried that the 225/50/15 on 8x15 will not fit in the rear without rubbing stock bodywork or hitting the swing arm (what you hit depends on the backset I guess), even with rolled fenders. I have heard of 7x15's working with 225's in the rear but I think but can't say for sure where I heard it. I run 6's but they're close, I am pretty sure 7's will work, but I'd be afraid the 8's won't work. Why not just mount them and see? Oh, and please let the rest of us know if you can get the 8's to work with *either* 225 or 235. I'd be interested for sure

The change in speedo/odo is pretty negligible, usually within a few percent. You can calculate if you want. Most people don't care. As for "brake failure", that sounds like urban legend BS to me. I've never heard of that and can't think of circumstances where something like that might occur under normal operating conditions.

I recall that there have been exhaustive discussions on this topic in the past so a search might be in order.

Also, I think JB did some compilation work on this topic a while back and he might have some good input.

tj924 · Posted: Wed Jul 28, 2004 7:36 am Post subject:

It was on some of the tyre calculators where it popped up a warning about brake failure if there was > 3% difference in the overall tyre size.

Unfortunately I can't just try the wheels on as they're in another state, so I'll actually need to put the $ down to get 'em.

If I was to get them I'd probably look at seeing if they'll do them without the tyres (which ain't new) & putting on a set of 205/60's to get back to stock. Would I still have a problem with the rear 15x8 rims?

Khal · Posted: Wed Jul 28, 2004 12:37 pm Post subject:

I'm running 205/55/15's on the front and 225/50/15's on the rear. No problems at all -and my car is seriously lowered with no wheel arch flares or anything. But I do have 5-bolt hubs. Dunno if that makes any difference.

Also, my speedo reads 8km/h fast. I don't think it's due to the wheel/tyre size because I think mine are per original for this model/year. But I'm not 100% sure...

Oh yeah, smaller wheel/tyres WILL make your speedo read fast, bigger ones will make you speedo read slow. It goes on circumference... at a given speed, smaller wheel/tyres spin faster, so your speedo reads a higher speed than you're actually doing. The opposite for bigger wheels.
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'80 924 Turbo

Lizard · Posted: Wed Jul 28, 2004 2:57 pm Post subject:

make sure the offset is correct and you should be able to fit those under with a squeeze but may have to roll the fenders abit
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3 928s,

tj924 · Posted: Wed Jul 28, 2004 5:18 pm Post subject:

Is that the offset of 33.8mm I've read about?