TYRE HELP
- Thread starter jason
- Start date
Diver944
Active member
Jason, I will be able to confirm this at the end of the week as I am finally chucking my Pirelli P zeros and getting some Kumhos.
Acceptable sizes on 7inch rim are 205/50/17 (standard) and 215/45/17 (I have 215s on the Turbo and 205s on the S2 as it doesn't need as much tyre IMHO)
Acceptable sizes on 7inch rim are 205/50/17 (standard) and 215/45/17 (I have 215s on the Turbo and 205s on the S2 as it doesn't need as much tyre IMHO)
andymorris
New member
I too am having Kumhos fitted all round this week on my refurbed wheels[
]. This was on the advice and guidance from an Independent Porsche specialist. I maybe teaching you to suck eggs here, but from my own recent experience the wrong profile tyres on my 90 S2 caused my ABS not too work.
]. This was on the advice and guidance from an Independent Porsche specialist. I maybe teaching you to suck eggs here, but from my own recent experience the wrong profile tyres on my 90 S2 caused my ABS not too work.
All 17" are "wrong" on a 944 as they were never supplied with 17" wheels.
However, many of us have subsequently fitted 17" wheels for a variety of reasons - aesthetics, availability of tyres, clearance for brakes. This doesn't make them wrong, just different.
Different tyre manufacturers will have different rim tolerances so it is worth checking the manufacturers data.
Pauls sizes tie up with my own. Some manufacturers might even allow 225/45's.
http://ssl.delti.com/mytires/start.html
I quite happy with my vredestein tyres, they only 15"s but can get the 17"s, good write up too,
Vredestein[/b] ***
[/size]Tyre producer from the Netherlands in mid price segment[/size] [/size]![[FONT=verdana,geneva"]](/forum/styles/default/pcgb/space.gif ". [FONT=verdana,geneva\"]")
[font=verdana,arial,helvetica]ULTRAC[/b] 225/50 ZR17 94W Rim-protection
[font=verdana,arial,helvetica]
JB
I quite happy with my vredestein tyres, they only 15"s but can get the 17"s, good write up too,
Vredestein[/b] ***
[/size]Tyre producer from the Netherlands in mid price segment[/size] [/size]
[font=verdana,arial,helvetica]ULTRAC[/b] 225/50 ZR17 94W Rim-protection
[font=verdana,arial,helvetica]
- Summer tyres
- Test results
- TyreTest.com
- ADAC (german)
- ÖAMTC (german)
- Speed W: the speed capability of this tires is up to 168 mph/270 km/h !
- We only supply the tire. If there is a rim shown on the picture, it is just to symbolize.
- Search for fitting station
JB
sawood12
New member
Was the outside diameter of the wheel calculated correctly? Sounds like it was out of limits. The ABS system somehow knows if you've got the wrong dia wheels on and will cease to operate according to the handbook.ORIGINAL: andymorris
I too am having Kumhos fitted all round this week on my refurbed wheels[
I've got 205's on my car and I find they can push wide, i.e. understeer slightly when pushed hard mid corner, but only slightly. This is cured by carrying speed through the corner rather than accellarating through it. Other than that I think it is generally well balanced. Are 225's OK on 7J rims? I thought the max tyre they could take was a 215?
225s should be OK on 7" rims. The Audi RS2 has 17x7" Cup 1's and came originally with a Dunlop tyre designed for the model that was nominally 245 section, but in reality was much narrower. Those Dunlops are no longer available, but some people still fit 245 tyres which are far too wide for the rims and can also touch the track rod end. The owners in the know fit 225 tyres as they more closely match the original "245" tyre size.
? The ABS works with a magnetic sensor reading a castellated ring around the hub. How can it have the faintest idea what tyres you have on? [
] I can only assume that if the front and rear tyres are of significantly different radius it will confuse the ABS as it then can't compare the change in speed of the front and rear wheels. Provided you use the correct profile relative to width you should be OK.
sawood12
New member
I'm not sure how it works but it says in the manual that you must fit tyres of the same or similar outside diameter or it will cause problems with the ABS system and lead to it not functioning. I can only guess that maybe the system assumes a specific outside diameter of the wheel to relate the rotational angle of the wheel as measured by the ABS sensor and the castellated ring in the hubs with the speed of rotation at the edge of the wheel and maybe comparing that to the speedo input. So if the actual size of the wheel is different then there will not be the correct correlation between speedo and the speed the sensors are measuring, and the system will not know the speed of the car as it doesn't know if the actual diameter of the wheel. Anyway it's only a guess!
sawood12
New member
In fact I just happen to have my drivers manual at hand and it says:
"The control of the ABS brake system is set for standard tyre sizes. If non-standard tyres are fitted the control of the unit may misinterpret the speed of the vehicle because of the variant data it received from the sensors on the axels. If the difference in rolling radius exceeds approx. 17% the control unit deactivates the ABS system and the ABS warning lamp lights up".
"The control of the ABS brake system is set for standard tyre sizes. If non-standard tyres are fitted the control of the unit may misinterpret the speed of the vehicle because of the variant data it received from the sensors on the axels. If the difference in rolling radius exceeds approx. 17% the control unit deactivates the ABS system and the ABS warning lamp lights up".
andymorris
New member
Scott - thats right my tyres were completely different profiles, put on by the previous owner. 60's on the back and 50's on the front therefore confusing the system. However the ABS light only came on when doing 70/80MPH + I guess the acceptable tolerances became too different the higher the speed.
Andy
Andy
Diver944
Active member
This is a really useful website when you want to determine what tyre sizes are similar to eachother:
http://www.1010tires.com/TireSizeCalculator.asp
You can see that 205/50/17, 225/45/17 and 255/40/17 are all within 0.4% of eachother. The 215/45/17 is 1.8% smaller which is still well within tolerance and works perfectly fine on my Turbo with 255/40 on the rear.
When I weant to 215s a short while ago most of the tyre manufacturer websites listed their brands were suitable for a 7" wheel. I could find no current manufacturers that included a 225 tyre on a 7" wheel, as Fen and John have said you need a 7.5" rim for those. It's worth noting that some manufacturers 225 tyres will measure at around 220mm and some 215s will measure up to 219mm
It is not an exact measurement [&:] Arrrrg []
http://www.1010tires.com/TireSizeCalculator.asp
You can see that 205/50/17, 225/45/17 and 255/40/17 are all within 0.4% of eachother. The 215/45/17 is 1.8% smaller which is still well within tolerance and works perfectly fine on my Turbo with 255/40 on the rear.
When I weant to 215s a short while ago most of the tyre manufacturer websites listed their brands were suitable for a 7" wheel. I could find no current manufacturers that included a 225 tyre on a 7" wheel, as Fen and John have said you need a 7.5" rim for those. It's worth noting that some manufacturers 225 tyres will measure at around 220mm and some 215s will measure up to 219mm
It is not an exact measurement [&:] Arrrrg [
]Yes you should be able to find out the rolling radius of the prospective tyre from the maker, fitter, or website. I would have thought that you'd have to come up with a pretty strange sized tyre to fool the abs but maybe not. I think when I was getting my 285's x 18" they had a smaller overall radius than my previous 255 x 17" so you can possibly go up to a much larger tyre. I would agree with Fen that you should be able to go 245's?
mik_ok
New member
I ran 225/50/16 on a 7" on my Leon for ages without issue (although that combo does have a bit more sidewall to accomodate differing rim widths).
Toyo list recommended rim widths of 7.0" to 8.5" for a 225/45/17.
CLICK HERE
I'd be happy with that personally ~ 205 on the front with 255 rear seems like waaaay too big a difference for such a well balanced car.
Toyo list recommended rim widths of 7.0" to 8.5" for a 225/45/17.
CLICK HERE
I'd be happy with that personally ~ 205 on the front with 255 rear seems like waaaay too big a difference for such a well balanced car.
Only slightly off topic but if you are considering new tyres try COSTCO if there is one relatively near you. They only deal in Michelins, can order any of the Michelin range including Pilot Cup Sports, will fit them for free up to one year after purchase and (until Sunday 18 Feb) have a 20% discount despite already being cheaper than any other outlet I have found.
Posts made and opinions expressed are those of the individual forum members
Use of the Forum is subject to the Terms and Conditions
