I'm prepping my car for running in RTR. The setup has to match my Touring V2 wheels, so I have to get Enkei RPF1 (F1 Silver on Nogaro Red) sized 18x8 +35 and 18x8.5 +30. I'm planning on getting Bridgestone Potenza RE-11s 245/40R18 and 275/40R18. Is this a good size and tire to start out with? Thanks.

 

The RE-11 would be a great tire for that. Great dry grip, sharp steering response, decent wet traction, and can be daily driven. Many happy customers on those. Sizes look fine as well.

 

Thanks, Neal! I just bought the RE-11s from you guys last night. I bought 245/40R18 and 265/40R18s. Tire rack mounted and balanced them for free and they're on their way.

 

I would probably run a 275/35 rear for that class, the gearing change will help a lot and have a shorter sidewall for less squirm since it is a narrow wheel. 255/35 should fit fine up front. Then also space the wheels out as much as the rules allow. Typically 5mm from stock

 

IMHO,

The car needs as much front grip as possible for autocross. The 245/265 combo will probably work and later I would run a 265 up front on the 8" rim as an experiment. Only space the fronts out as much as the rules allow. Keep the rear track as narrow as possible. This moves roll stiffness forward which helps with the under steer issue.

Some of the local autocross Gods have been doing back to back testing of the new gForce Rival prior to the NT and are very, very impressed.

 

Looks like I'm going to be trying a few tires this year. I don't know about the differences in RTR, but with C-Stock rules, my front rims can't be spaced out anymore. Offset is the major reason I went with the RPFIs. The rears can be spaced out more, but shouldn't be? Stock is 33m, 8.5" rim is 30m, max is 39 I believe(+- 6.35mm).

 

Stock front is 18x8 +30 , so you can install a 10mm front spacer. The rear is 18x8.5 +33 , so the most you could do is a 2mm shim.

 

Enkei RPF1s: 18x8 +35(already +5 from stock) and 18x8.5 +30(33 + 6.35 = up to 39.35mm allowed)

Now back to my question. Do I use the 5mm spacer in the back? Is just 5mm worth it?

 

Hello Rex08Z. The offset you are looking for is ultimately +25 and NOT +35. The higher the number, the narrower your track becomes. (I know it seems confusing but, take a look at the wheel guide on tirerack.com)

http://www.tirerack.com/wheels/tech/...jsp?techid=101

http://www.tirerack.com/wheels/tech/...urrentpage=101

Being that you bought wheels that match the same width as the stock wheels, the offsets will line up identically when referenced from the centerline of the wheel to the outer edge of the wheel.

So with that in mind, your target offsets are +23.65mm in the front and +26.65mm in the rear.

So, by taking the advice of terrasmak, adding a 10mm spacer will put you at the desired +25mm offset for the front. Close to your target of +23.65mm and well below the 6.35mm allowance.

For the rear the target spacer you are ideally looking for is a 8.35mm spacer to put you at +23.65mm. So a 5mm spacer is what you would commonly find unless you look for a 'custom' spacer set. That put's your rear at 30mm which is 3mm (well below the 6.35mm allowance).

Hope this helps.

 

your calculation is off in the rear. +33 is oem in the back

 

I didn't realize my goal was to go backwards, but now it makes sense. More offset puts the wheels further INTO the wheel well would would never happen with a spacer. Now I see. I will get 2x10mm for the front for a target of 25mm. The backs could take a custom 4mm if there is one, or stay where they are.

Wait a minute. If the offset can go backwards, I could have gotten a wheel with a different offset. OH MAN I wanted TC105n's so bad, I just needed a 10mm spacer for the front. I thought only RPF1s could replace my stocks since they were so close to stock offsets.

 

Good advice. Under steer has been a bit challenging!