16 mm less offset: need advise

[ADAMS997]

I purchased a 2006 C2 997 cab. I am able to purchase some new takeoff 2008 C4S wheels and tires. The C4S front wheels and tires are the same size and same offsets as those now on my car. HOWEVER, my current rears are 11x19" (67 mm) 295/30 ZR 19 and the ones I am thinking of installing are 11x19" (51 mm) with 305/30 ZR 19. THUS, the rears would have a 16 mm smaller offset. MY QUESTION: What are the issues with reducing the rear offset by 16 mm? Thanks in advance for your comments.

Edited July 18, 2008 by ADAMS997

[gandrade1]

I purchased a 2006 C2 997 cab. I am able to purchase some new takeoff 2008 C4S wheels and tires. The C4S front wheels and tires are the same size and same offsets as those now on my car. HOWEVER, my current rears are 11x19" (67 mm) 295/30 ZR 19 and the ones I am thinking of installing are 11x19" (51 mm) with 305/30 ZR 19. THUS, the rears would have a 16 mm smaller offset. MY QUESTION: What are the issues with reducing the rear offset by 16 mm? Thanks in advance for your comments.

If you are reducing the offset by 16 mm, that means that the new wheels will be moving outward by 16 mm, so the tires might rub your car. That will be amplified by the fact that the tires you are thinking of using are wider than the ones you currently have by 10 mm (305 - 295). So we are in theory talking about 16mm (from offset change) + 5mm (1/2 of the extra tire width) in extra space you need between the tires and the fenders in your current setup to be able to accomodate the new wheels and tires. Measure it, if you have much more than 21mm between the tires and the fenders currently the wheels will fit. If you are close to the 21mm mark it is too risky - after all this is not precise math!

BTW, spacers will not solve your problem - assuming one exists - since all they do is to move the wheels out even further.

Best of luck,

Gus

Edited July 18, 2008 by gandrade1

[ADAMS997]

I purchased a 2006 C2 997 cab. I am able to purchase some new takeoff 2008 C4S wheels and tires. The C4S front wheels and tires are the same size and same offsets as those now on my car. HOWEVER, my current rears are 11x19" (67 mm) 295/30 ZR 19 and the ones I am thinking of installing are 11x19" (51 mm) with 305/30 ZR 19. THUS, the rears would have a 16 mm smaller offset. MY QUESTION: What are the issues with reducing the rear offset by 16 mm? Thanks in advance for your comments.

If you are reducing the offset by 16 mm, that means that the new wheels will be moving outward by 16 mm, so the tires might rub your car. That will be amplified by the fact that the tires you are thinking of using are wider than the ones you currently have by 10 mm (305 - 295). So we are in theory talking about 16mm (from offset change) + 5mm (1/2 of the extra tire width) in extra space you need between the tires and the fenders in your current setup to be able to accomodate the new wheels and tires. Measure it, if you have much more than 21mm between the tires and the fenders currently the wheels will fit. If you are close to the 21mm mark it is too risky - after all this is not precise math!

BTW, spacers will not solve your problem - assuming one exists - since all they do is to move the wheels out even further.

Best of luck,

Gus

Gus

Thanks for the quick reply. I have 26 mm+ from the top of tire to the bottom of the wheel well (the top of the wheel well arch). How much do I need for wheel up/down suspension travel?

Thanks

Walter

[gandrade1]

Gus

Thanks for the quick reply. I have 26 mm+ from the top of tire to the bottom of the wheel well (the top of the wheel well arch). How much do I need for wheel up/down suspension travel?

Thanks

Walter

Hi Walter,

The distance between the tire and the top of the wheel well should not be a problem at all.

You should be concerned with the distance between the outer edge of the tire and the fender.

Take a look at this website...it might help you

Wheel Offset Calculator

[Kazzz]

I purchased a 2006 C2 997 cab. I am able to purchase some new takeoff 2008 C4S wheels and tires. The C4S front wheels and tires are the same size and same offsets as those now on my car. HOWEVER, my current rears are 11x19" (67 mm) 295/30 ZR 19 and the ones I am thinking of installing are 11x19" (51 mm) with 305/30 ZR 19. THUS, the rears would have a 16 mm smaller offset. MY QUESTION: What are the issues with reducing the rear offset by 16 mm? Thanks in advance for your comments.

If you are reducing the offset by 16 mm, that means that the new wheels will be moving outward by 16 mm, so the tires might rub your car. That will be amplified by the fact that the tires you are thinking of using are wider than the ones you currently have by 10 mm (305 - 295). So we are in theory talking about 16mm (from offset change) + 5mm (1/2 of the extra tire width) in extra space you need between the tires and the fenders in your current setup to be able to accomodate the new wheels and tires. Measure it, if you have much more than 21mm between the tires and the fenders currently the wheels will fit. If you are close to the 21mm mark it is too risky - after all this is not precise math!

BTW, spacers will not solve your problem - assuming one exists - since all they do is to move the wheels out even further.

Best of luck,

Gus

I have a 997 and did the exact same upgrade with c4 carrera classic wheels with 11x19 ET51 on rear with the 305 michelins dropped with H&R springs. They fit perfectly without any rub. I also had them on with the stock suspension and there weren't any problems. Some might say that they may look a bit too aggressive but they in fact are almost the exact same offset as the techart formulas for the porsche which in my opinion look great on the 997s. (They are only 1mm wider offset). The other nice thing is that you wont need to add any spacers for the rear. The fronts are the exact same wheel as on the regular carrera so they will need some spacers to bring them out a bit. I recommend 7mm.

Here are some pics

[ADAMS997]

I purchased a 2006 C2 997 cab. I am able to purchase some new takeoff 2008 C4S wheels and tires. The C4S front wheels and tires are the same size and same offsets as those now on my car. HOWEVER, my current rears are 11x19" (67 mm) 295/30 ZR 19 and the ones I am thinking of installing are 11x19" (51 mm) with 305/30 ZR 19. THUS, the rears would have a 16 mm smaller offset. MY QUESTION: What are the issues with reducing the rear offset by 16 mm? Thanks in advance for your comments.

If you are reducing the offset by 16 mm, that means that the new wheels will be moving outward by 16 mm, so the tires might rub your car. That will be amplified by the fact that the tires you are thinking of using are wider than the ones you currently have by 10 mm (305 - 295). So we are in theory talking about 16mm (from offset change) + 5mm (1/2 of the extra tire width) in extra space you need between the tires and the fenders in your current setup to be able to accomodate the new wheels and tires. Measure it, if you have much more than 21mm between the tires and the fenders currently the wheels will fit. If you are close to the 21mm mark it is too risky - after all this is not precise math!

BTW, spacers will not solve your problem - assuming one exists - since all they do is to move the wheels out even further.

Best of luck,

Gus

I have a 997 and did the exact same upgrade with c4 carrera classic wheels with 11x19 ET51 on rear with the 305 michelins dropped with H&R springs. They fit perfectly without any rub. I also had them on with the stock suspension and there weren't any problems. Some might say that they may look a bit too aggressive but they in fact are almost the exact same offset as the techart formulas for the porsche which in my opinion look great on the 997s. (They are only 1mm wider offset). The other nice thing is that you wont need to add any spacers for the rear. The fronts are the exact same wheel as on the regular carrera so they will need some spacers to bring them out a bit. I recommend 7mm.

Here are some pics

That's one sexy machine.