944 tyre options

[Red Panda]

Hi all I'm hoping you can help clear up some confusion around wheels and tyres for my 86 944. It has the Fuchs 7x15 and 8x15 wheels and now bald tyres I inherited from the previous owner. What size tyres should be fitted to keep the speedo reading correctly. Currently it has 215/60R15 and 235/60R15 but those are hard to find as a set and appear to have a larger diameter. If these are the standard sizes what alternatives work well? Many thanks in advance. Jon

[Buchanan Automotive]

The 944 1982 - 1986 inclusive had ( from new ) the relatively expensive option of the 15" dia Fuchs forged alloy wheels( 7X 15 & 8 X 15 ) , these wheels had the same tyre sizes as the standard 944 alloy wheels ( 1982 - 1985 ) with 7 X 15 wheels front & rear , " the cast alloy cookie cutters" =  215 / 60 /VR 15 tyres  front & rear 

You will see it also in you're owners manual, both the 7 X 15  & the 8 X 15 use the 215 / 60 / VR 15

Thats why , when these cars were new , the rear wheels always looked as if the tyres were a bit skinny for the rims ,but that is what Porsche specified 

Regards

Bruce Buchanan

[Buchanan Automotive]

I forgot to mention , as you're 1986 944 is the first year type to have an electronic speedometer ( tear drop dash ) as opposed to the earlier >1985 speed cable via the L/H/F wheel , its the rear wheel / tyre size that will have the effect on the speedo reading for you're 944 ( so long as its a 1986 > )

The rear tyres on you're car now ( 235 / 60 / 15 ) will have a very large rolling radius & will look a bit to baggy ( too much side wall height ), the 15 X 8 rear Fuchs wheels you have are the one's Porsche used earlier on the 1976 & 1977 3.0L Carrera & Porsche specified 215 / 60 / VR 15 back in 1976 / 1977 , however Porsche had another size listed as an option ( for the 1976 & 1977 3.0L Carrera ) and that was 225 / 50 / VR 15  but in the spec book it had a asterisk , indicating that if this size tyre was chosen it was " With Adapted Speedometer "

Regards

Bruce Buchanan

[Red Panda]

Hi Bruce many thanks for the reply. Yes it's an oval dash car, I thought the rear tyres were a bit oversized,  the car always over read the speed (according to gps) but that may have been a result of the turbo gearbox that was fitted. What do people tend to put on the rear, 215s seem a little narrow, 225's seem to be an option do you know how the speedo adjustment was carried out. 

[Buchanan Automotive]

I am not a big fan of a 951 trans into a 2.5NA ( didn't realise thats what you have ) because the 951trans is about ( from memory ) around 15 % high ( Taller ) final drive ratio than what the NA 1986 trans originally had , this makes acceleration a bit slower in a 2.5L NA 944 than what it was meant to be

Interestingly the fairly rare 944S ( twin cam 16V 2.5 1987 & 1988 ) has the same final drive as the earlier 2.5L 944 series , but with the larger bearings & shafts dia's that the 944S2 has ( meaning the 944S has a one off crown wheel & pinion )

All the 944 series cars we have ( as customers cars ) that have the 15 X 8 rear Fuch wheels all run what Porsche recommends in the owners manual  = 215 / 60 / VR 15 , its about all thats available when you want a set of 4 tyres all of the same brand & version 

The speedo change that I mentioned was for the 911 3.0 Carrera back in 1976 & 1977 , not for the 944 1986 , because Porsche only recommended one tyre size only for you're rear wheels 

Regards

Bruce Buchanan 

[Red Panda]

I agree about the gearbox. Was installed by the previous owner, I've just fitted a standard box, but in combination with the taller tyres it certainly was a long legged cruiser. I appreciate the input from you and I'm now looking for some reasonable 215's

[Paul Carrera]

To calculate tyre diameter the formula is 

width x (ratio \100 x 2) + rim dia

so for your tyres

215 x (.6+.6) + 15" converted to mm = 381

which equals 639mm or 25.16"

if you want to run wider tyres you just reduce the ratio ( tyre series) to get as close to origional tyre dia as poss, a 235 x 55 x15" has a tyre dia of 25.18 - close enough

hope this helps and doesn't confuse you

[cyberpunky]

Just a heads up. For some reason my speedo is pretty much exactly 10 k out regardless of speed. At indicated 60K I am doing 50k(gps verified) and at 100k I am doing 90K, at 110k I am doing 100K etc. There have been many discussions about this online and it seem that most cars are the same. There is a VDO repair guy in FTG I think that can fix it, if you can be bothered. So yeah even with tyres that are just right you still probably won't have an accurate speedo. It is accurate if you allow for the inbuilt error lol

[Typhoon]

Just a heads up. For some reason my speedo is pretty much exactly 10 k out regardless of speed. At indicated 60K I am doing 50k(gps verified) and at 100k I am doing 90K, at 110k I am doing 100K etc. There have been many discussions about this online and it seem that most cars are the same. There is a VDO repair guy in FTG I think that can fix it, if you can be bothered. So yeah even with tyres that are just right you still probably won't have an accurate speedo. It is accurate if you allow for the inbuilt error lol

Bruce,

I had a similar thing on mine where the speedo was out the same throughout the range. It was as simple as removing the speedo needle and replacing it in the correct position. The speedo now reads accurately.

 

Jeff