Hoosier R7s on a 996 NB

I think I've read just about every thread on the R7 and fitting wider wheels and tires on a 996 NB but I thought I would try to combine that discussion in one thread here. I've been running my 996 (model year '99) in PCA's SP996 class for the last several years which means BFG R1s 245/40/R18 fronts and 285/30/R18 rears on 8" and 10" wheels respectively. However, I've been planning on doing some experimentation with a new set of wheel sizes in combination with the R7. I understand the R7 tends to run wider than their indicated numerical sizes, which adds another potential variable. I'm not sure how they compare to the BFG R1 in terms of width. Specifics on my setup: JRZ coilovers with camber plates and rotated shocks (no shims in LCA) 700#F/900#R springs ~3 deg. camber front and rear (for now) Stock Carrera uprights/knuckles front and rear Ride heights about at 996 GT3 "street" specs approximately ie. 112mm F & 125mm R I've been thinking of trying a 255F/315R combination on 9" and 12" wheels but that seems like it will be a pretty tight fit. Want to not "guess" at the right sizes and offsets but I have an idea of what may work. Does anyone have any experience in finding an optimal setup on the 996NB specific to the R7? Keep in mind this is a track/race car only so no compromises need to be made on that front.

Have you rolled your fenders yet, particularly the rear? Doing that will gain you 1/2" of clearance.

Front and rear fenders have been rolled but both could probably give a bit more. There seems to be quite a bit of room in the rear and I've seen several people on this board running a 315/30/R18 on a 18x12" ET68 wheel, but no one with the R7 from what I can tell.

I ran a similar setup on coilovers at cup car ride height. I did have to roll the rear fenders but not the fronts...but I was running 8.5s on the front. My setup was 18x12 ET63 rear on 315 Hoosier R7's and 18x8.5 front on 245 Hoosier R7s spaced out to ET38. No rubbing. Camber was -3 front and -2.5 rear. Front camber was from adjustable top mounts tipped inwards, I was not running GT3 LCAs, which might put the wheels a little more inwards than if you are getting your front camber by using shims on the GT3 LCAs. I was still able to get caster of just over 8. The GT3 LCAs will drive the wheel forward in the arch when they are shimmed way out. You may not have this if you rotated the top mounts. Rear camber was all with the stock eccentrics and then adjustable toe links. Based on what I saw running 245/8.5/ET38 on the front the limit will be the top edge of the rim hitting the coilover spring base. You may have to run spacers to maybe ET35-ish and roll the fenders to fit 255/9's.

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I have your wheels now and am not having any fitment issue with my Ohlins / Tarrett / Elephant / RSS setup.

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Cool. I had no problems with them either.

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This is very helpful, thanks. We�re running very similar setups but I am running the GT3 LCAs but rotated with no shims. I�m using the eccentric hole in the LCA for caster correction back to ~8 deg. I�m thinking I can run a 9� ET43 which should work and leave about 6mm to the strut body. If it�s too tight I will hedge with a 5mm spacer and move the radiator brackets and try to roll the front fenders more I guess. How was the balance with 245/315 split? In my current setup the rear is definitely under-tired.

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It did push just a little on certain turns on the track, but overall it was very good. I am not sure if another 10mm of front tire width would help that or not. Depending on how far out your GT3 LCAs are shimmed you should be able to run less wheel offset and still be away from the spring perch, provided you have enough negative camber. If caster becomes a problem you can run an adjustable "tuning fork" arm, but with using offset hole in the GT3 LCA you probably won't have a problem with caster unless you are going for really high negative camber like -4 or -5.

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I've been running this setup in both R7 and NT01's for a while now. There's no issue with being under-tired in the rear... I came off of running 245/285 and the car rotated a whole lot easier than with the 315.

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According to the Hoosier size chart the difference in tread width of the two tires is significant: 1.3" or about 14% bigger. The 255 is about .5" wider in section width as measured on a 9" rim. Right now I'm only running 1mm shims in the LCAs and getting the camber by the camber plate orientation and the eccentric bolt. As it sits, it's closest to the knuckle/strut body about right where the lower perch is situated. Are you saying using the shims actually buys you more inner clearance there? I was thinking that would probably push the wheel closer at the top.

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Good feedback thanks

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Assuming the same camber if you shim out the bottom and also move the top mount outwards you would get more clearance as the wheel will be moved outwards from the centerline of the car. The expense of this would be possibly driving the wheel forward in the arch and throwing caster off (even with the offset hole in the LCA) and then needing to roll the fender. The caster issue could be corrected with an adjustable tuning fork arm, then you could return to the center hole in the LCA and let this adjustable arm do the caster work instead. Going up by 1.3" is a 0.65" increase on each side of the tire, that's quite a bit, I have not tried this so I can't comment on if it would fit or not. There's a thread going now over on the 6-GT3 forum about putting wider tires on the front, they are talking about going up to 275! Maybe you can find an answer from one of the guys there: https://rennlist.com/forums/996-gt2-...h-996-gt3.html

Thanks, I;ve been following that thread and yes if people can make the 275 work on a 10" rim surely this can be done. It's interesting that the 255 R7 has the same tread width as the 275 but it would have a slightly larger overall contact patch thanks to the larger diameter. The sidewalls of the 255 would also be better supported on a 9" rim. I think it will be a good compromise. I'm trying to keep the suspension as-is for now but if I have to invest in some adjustable caster arms or pucks for the LCA, I'll do it. The good thing is a 255/35/R18 is about the same overall diameter as a 225/40/R18 and is smaller by 6/10" than the 245/40 I'm running now, so I'm betting that combined with the right ride height adjustment and working the fender and radiator brackets will make it work. Raising the front ride height a bit more is not a problem. Overlowering a 996 on the stock uprights is a common mistake I see people make and really hurts the geometry at the front.

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This is true. My 6-GT3 is new to me, setup by the last owner and his shop. When I took it to the local race shop that I work with one of the first things they did to optomize the front end setup was to raise the ride height a little. It was so low at the front that the ends of the coilovers were sitting on top of the ball joint studs! Yes everything moves together up and down but wow.

Couple of notes. Blow off the R7 and go straight to the the Pirelli DH. I got in a bind once and bought a set of R7 stickers at a PCA event. Ran them for 2 days and then sold them on Rennlister for enough to replace them with DH scrubs. It's obviously personal preference but I find the slip angle on the DH a lot more predictable and the car feels more planted. On geometry, my PB in my GTB1 996 was with 3.75"F/4.25"R. I had Cup car shocks with less travel in the rear. Conceptually I understand what this does to the geometry but the extra half inch of drop seemed to fit the car well. Go with caster arms instead of the pucks. They are one of the places that it's really worth the extra money, especially if you do your own alignment or pay by the hour. I have an extra set of used GMG if you are interested. I'm running them front and back on my 996TT but honestly, for the rear, stock thrust arms and LCAs with solid inner bushings work just fine. With RSS adjustable dog bones and Tarett toe arms I can get -4.0 rear camber without shims.

hey Brandon, thanks for the advice. I'll probably stay on a DOT tire if I decide to run NASA as you have to take a power/weight ratio penalty if you run a full-on slick. Right now I'm more or less right on the money for GTS3 at my current HP/weight so I'll probably stick with a DOT tire for now. Either way the R7 will be a major upgrade over the spec BFG R1 I've been running. On the geometry, are you still running the stock C2 uprights? The GT3/Cup uprights differ in that their attachment points for the outer ball joints for the LCA and tie rod end are dropped lower in relation to the ground and with the inner points staying equal corrects the geometry and allows the lower ride heights indicated for the GT3 and Cup. Going too low with the body on the C2 uprights and thus dropping the inboard pivots increases the angularity in the wrong way and basically puts the roll center too far underground which can actually increase weight transfer even at the lower ride heights which can increase bump steer and understeer and make everything generally less predictable, on paper at least. Consider that the factory ride height measurement reference points are basically the low points for the inboard pivots, both at the front and rear. If you go out and look at your car (as is mine currently) you will see that your LCAs (and tie rod ends) are probably sloping pretty steeply downward from the outside in with the inner pivots much closer to the ground. Notice how the lower control arm in this diagram is parallel to the ground. Given that the angle at the top mount is fixed on a MacPherson strut design and that makes your effective "virtual upper wishbone" angle, that means your roll center is underground. Dropping the outer pivot points with the Cup/RS uprights, using lower control arms with shimmable ball joints, raising the ride heights or some combination of all three will restore the geometry where it theoretically needs to be. Also have to keep in mind that changing the total diameter of the wheel/tire combo larger or smaller also changes the overall effective ride heights and roll centers. Just for reference I've got my front heights set at about GT3 "street" settings at ~113mm at the front on the 245/40 series tire and just by putting the 245/35 Hoosier rain tire on it drops the front ride height to about 99mm! I'm definitely in agreement with you that using the lowest possible ride heights for best cornering within practical limitations helps. Everything is a trade off at the end of the day and if you are more comfortable and the car is going faster, it's a good setup for you. That's a good point about the ease of alignment with the adjustable caster arms vs. the center pucks. I'll PM you about them.