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Old 05-09-2016, 03:23 PM   #1
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HPDE trackday offset opinions

I have a set of wheels, originally from a C4, that I bought last fall. I mounted them on my 2001 S Boxster and they fit, albeit with a wider stance. Here's the specs:
rear: 10j x 18 ET 40 , with 265/40/18
front: 8j x 18 ET 54 , with 235/40/18

Originals are:
9j X 18 ET52, with 265/35/18
7.5j X 18 ET50, with 225/40/18

So, as I see it, this is the equivalent of running spacers of about 10 or 12 mm rear and 2 to 4 mm front, taking into consideration the difference in the rim width.
I know that this is a lot of numbers, but I've seen that some of you are quite clever with these sort of calculations.

Question 1: They didn't cause problems (rubbing) with the Michelin Sport Alpin winter tires, but do you think they could cause me grief at the track with Michelin Pilot Sport PS2 ? (I'm still in Green run group).

Question 2: Any disadvantages to this setup, either to the car or to the handling?

Thanks for your input! -James
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Old 05-09-2016, 05:35 PM   #2
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I can't answer about the offset question, but I would recommend getting better tires for track use than Ps2's

Look at getting Bridgestone RE-71, RE-11, Dunlop Direzza ZII Star Spec or Hankook RS-3. All of those are much better street tires for the track. The RE-71 is probably the highest performance "street" tire that tracks really well and is very popular for track use.

You can also probably go with wider tires on the 8 front and 10 rear wheels
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Old 05-10-2016, 11:13 AM   #3
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Quote:
Originally Posted by NewArt View Post
Question 1: They didn't cause problems (rubbing) with the Michelin Sport Alpin winter tires, but do you think they could cause me grief at the track with Michelin Pilot Sport PS2 ? (I'm still in Green run group).
Winter tires tend to have more tread than a summer tire so if you didn't have any rubbing with those, I would expect that the PS2's should be ok - but with tires its very hard to know for sure until you actually try it. I'd install them and give them a good hard drive somewhere local - and even that is no guarantee but its about all you do to know for sure.

Quote:
Originally Posted by NewArt View Post
Question 2: Any disadvantages to this setup, either to the car or to the handling?
All advantages! The extra track and reduced stagger (from 40mm to 30mm) should improve handling by improving corner turn in and reducing mid-corner understeer. The rear should remain well planted. It won't be a huge change, but it is certainly a change in the right direction.

As Jay mentioned, getting a little bit stickier performance tire will also help.

I would expect this to be a setup that will drive well and give you confidence in the car's handling.
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Old 05-10-2016, 12:17 PM   #4
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Great! Thanks to both of you for the input. It's all about the money right now: I already have the rims and I can pick up a set of used PS2s for cheap to get me through a few track days. If the wheels work out with the PS2s, then I can look into a stickier tire for later in our very short season!
Cheers, -James
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Old 05-10-2016, 02:14 PM   #5
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Be careful with used tires
Check the date codes and make sure they are not older than 4.5 years
Also inspect the tires for damage, cracks and general dryness

Bear in mind you can buy a new set of Sumitomo HTR ZII for around $500. They are a good street tire and I have tracked them with Ok results. They might be a better choice than old PS2's
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Old 05-10-2016, 03:30 PM   #6
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Actually, I'm running Sumitomos HTR ZIII all around at the moment.
These are almost impossible to find here in Montreal. I think they only sell them in the States. The PS2s are from a member of my local PCA. I asked him about the date of manufacture and they are about 3 years old. I don't expect miracles out of these tires but they will allow me to test the wheel set before I splurge on something better (pricier too!).
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Old 05-10-2016, 05:50 PM   #7
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Another thing to consider is getting a set of 17" wheels for track and AX
Tires are a lot less $$$ in 17"
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Old 05-10-2016, 06:18 PM   #8
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Yes, that I have been seriously considering! In fact, there are many 17" sets for sale. I could probably trade off one of my 18" sets.
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2004 986 S
987 air intake TB and plenum, Mantissport 2 litre sump, UDP, Bilstein B6 with H&R lowering spings, re71-rs for track, other stuff.
https://www.youtube.com/user/12shoes2

Last edited by NewArt; 05-10-2016 at 06:21 PM.
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Old 05-10-2016, 11:15 PM   #9
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Hello James,

if you want to stay the distance to the inner rim parts the same, you will need:

- 10 mm spacers in the front (wheel comes out 12 mm on the outside, rolling circumference: +1,3 %, ground clearance: +40 mm, speedo difference: -1.2 %)

- no spacers in the rear you have +1 mm that the wheel comes out on the inside (wheel comes out 25 mm on the outside, rolling circumference: 0 %, ground clearance: 0 mm, speedo difference: 0 %)

The tyre can be wider especially in the rear. So you have to check clearance in the rear anyway. The front seems to be the no difference. But be prepared that a 225 wide tyre mean that it's exactly 225 mm wide. There might be slight differences. Somme are some mm smaller, some are some mm wider. So you have to test clearance any way.

You will have less understeer.

Winter tyres i would only recommend only if you live in a colder area and need a lot of traction for a short time, or you have wet conditions. If the winter tyres are new i would not recommend them for racing they will be too soft in dry conditions. If they are older (which means the rubber is getting harder), give them a try but don't be surprised if they didn't last very long.

Regards, Markus

Last edited by Smallblock454; 05-10-2016 at 11:23 PM.
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Old 05-11-2016, 04:38 AM   #10
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Thanks Markus, I would never consider using the winter tires on the track. In Quebec, it's the law to have winter tires from December 15 until March 15. I ran the car this winter, which is why I have those tires, but as soon as spring arrived I changed over to the Sumies.
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987 air intake TB and plenum, Mantissport 2 litre sump, UDP, Bilstein B6 with H&R lowering spings, re71-rs for track, other stuff.
https://www.youtube.com/user/12shoes2
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