rich beebe

I had a question about fitting 275/35-18s on the rear of an RSA and I was hoping that someone here has tried it. I know 18" rims aren't supposed to be run on the C2/C4, but I'm hoping someone here has tried this size on an RSA, or maybe even a carrera RS. I will be running these tires on 9.5x18 Ruf rims (8.5x18 fronts) with a 48.3 offset. I have run 265/35-18s on a set of Fikses (9.5" rears with 40.8 offset) and they fit easily, but they had the different offset from the Rufs. The other issue would be whether running a 275 in the rear and a 225 in the front would create an unwanted understeer problem. I know the 993 C4S and C2S run 225 fronts and 285 rears, so I was wondering if a similar arrangement would work OK on a 964. I'm interested in hearing anybody's accounts on this. Thanks.

Kevin

Rich;

I ran 275-17" SO2 on my RSA. My rim size was 9.5" Have you done anything to lower the suspension? I maxed the -camber, stearing was good. Good luck

rich beebe

Kevin,

I haven't done anything to lower the suspension yet, but the springs are sitting in my kitchen. Are you saying that you have to max out your rear camber to get them to fit? What rims did you have them on? I've talked to a friend of mine who says 275s fit fine on stock rims on a lowered car. That, of course, is on a 17" rim. Since the 275/35-18 tire I'm looking at is 25.5" in diameter and the 275/40-17, in the same brand, is 25.7" tall, I was hoping everything would fit fine. What size front tire were you running and how did the car feel with 275 rears? Thanks.

J richard

Rich,

I run the same setup as Kevin, plenty of room, I wouldn't think you should have a problem. If yours is an early 93 you should have the rolled rear fender lips, this buys you almost half an inch of clearance over a regular C2. I run both the turbo wheels and 993's with 55mm offset for the track.
Hope this helps.

regards

Kevin

Rich;

I installed 225's up front. I maxed the camber to get better handling and to provide more clearance between the fender lips and tires. You can just pass your finger between the fenders and tires.

You can see the gap in the rear fender/tire. What is crucial is the clearance on the right rear vs the oil line that run along the inner frame rail. I have about a 1/4" clearance. I've had no rubbing.

rich beebe

J richard,

Thanks for the info. I do have an early 93 with the rolled rear fenders, but it appears (with the correct offset, obviously) that the oil line and, for me, the trailing arm are the areas to consider. Do either of you know how close you are to the trailing arm? How close is your actual rim lip? I checked my fit again last night and I'm closer to that than I am to the oil line. My current 265s are just under 11" wide, so I tried to determine how well a 11.5" tire might fit. It seemed pretty close. What brand tire are you guys running and do you have any idea what the exact tread width is?

The other interesting point here is that you mentioned running 55mm offset rims and still not having any fender clearance issues. Clearly, with 48.3mm offset rims, fender contact will not be my problem. That 6.7mm difference certainly does put me closer to everything inboard though. If I do have clearance issues, I can obviously run a small spacer to move the rim outward. I'd just prefer not to run spacers if possible.

Kevin,

Your car looks great. What ride height are you at, looks quite low. What suspension setup are you using?

Can you tell me (if possible) how much 'tire' you have beyond your rim? I know you're running a 9.5" rim with 275s, but I'm curious how far your tire extends beyond your rim lip. Since I'm trying to 'fit' these tires without having them yet, it's hard to determine how much tire I can expect to have beyond the rim. At this point, with 48.3mm offset, that's what will make the difference for me. A ballpark figure, if you can, would be very helpful. No problem if you can't.

BTW, aren't you the guy that has the 993 exhaust on your car? I just bought a fabspeed unit from a guy who plans to do the same install on his car. He said he wasn't sure it could be done until he saw your car/installation.

Thanks for the help guys.

Kevin

Rich;
I would say that the Bridgestone S02 stick out a strong 1/4". Things are close, I have had zero rubbing. I can't tell you have things will do with the 18's. With my alignment I could probably get by with 9 3/4" rear rims. Thanks for the compliments, and yes I am the guy who has stuffed the full 993 exhaust system under the car.

rich beebe

kevin,

i realized, reading my post again, i was mistaken when i said the 48.3mm offset of my ruf rims would bring them in towards the body more than your 55mm rims. for some reason i had it mixed up, and clearly, a 48.3 offset would push my rims outwards towards the fenders more. that brings up my question, how are you guys able to fit 275s in the rear with 55mm rims? i read your posts again and you mentioned running 55mm offset on the track, what offset are the rims pictured in the photo (with the 275s)? if they are also 55mm offset, i can't see how you are not extremely close to the oil line and trailing arm. i just had my rims on the car the other day, as i mentioned, and even with a 48.3mm offset, i was close to both areas. could you also tell me what brand tire you are running? the widths vary, depending on manufacturer. one minute i'm convinced i can fit the 275s, the next i think i'm better off going with the 265s. i know one other person running the exact ruf rim combination, on an RSA, but i have no ability to view this car in person. if i could it would answer all questions. thanks.

Kevin

Rich;

A 9.5" rim and 275 will fit with the proper offset. You need to max the camber out. If you can ask for someone to give you a used tire so that you can mount it up in your neck of the woods I think that you would see your situation alot clearer. I'll check to see what my offset is. The rims are close to the trailing arm, but there is plenty off clearance.

Jeff Curtis

I use 275s on the rear as well...I had a little bit of rubbing on the oil line and trailing arm. I have a factory set of 17" Cup II wheels, 7" in front w/225s and 9" in the rear, all four have 55mm backspacing.

What I wound up doing is using 6mm (1/4") spacers from Performance Products, which effectively gives you 49mm backspacing...so that matches up with Kevin's formula.

There was just enough thread left to be legal when using steel lug nuts at the track.

I plan to purchase a set of studs that are slightly longer than stock, so that I may use these spacers with my aluminum lug nuts during street operation, using up all the threads.

rich beebe

thanks for your post jeff. what you write does bring up some interesting points. i have done a ton of research on this for the last 2 weeks (talking to other RSA owners, taking measurement after measurement and having friends, who have offered, do the same) and here's what i have come up with/found out. apparently, a 275/40-17 will fit an RSA/C2 on a 9-9.5" rim with an offset range of 55mm to 48.65mm (your 55mm with a .25"/6.35mm spacer), but a 275/35-18 will not fit under the same circumstances. the info on the 18" tire fitment is only coming from web sites, i have found, that list the widest tires for the 964. i always find the 275/40-17 and 265/35-18 listed as the widest options. the strange thing about that though is, with every tire brand i have checked so far, the 275/35-18 has a smaller overall diameter than the 275/40-17. if that's the case, how is it that the 275/35-18 won't fit? i've thought that possibly the tire's shoulder has a more squared off corner (because of the shorter profile), but i can't see that being the only thing that will not allow it to fit. if it was, an offset in the 52mm range should make it fit. as of yesterday, i was ready to order 265/35-18s because i know they will work. then i get to thinking about it again and looking at all the numbers and i can't figure out why 275s won't work. unfortunately, i haven't run across anyone that has 18" rims with 275s yet. everyone with 275s is running 17" rims. here's one more point of reference, i know another RSA owner who is running the exact rim combination that i am (rufs) and he's running 265/35-18s in the rear. i've looked at photos of his car and it appears that 275s would fit without any real difficulty, but when he asked his mechanic (or tire guy) he was told that they "strongly recommended against 275s". i wish i was close enough to look at that car, but we don't live anywhere close to eachother and it's not that convenient for him to supply me with measurements.

when i think that you (jeff) have 275s on a 9" rim with an effective offset of 48.65mm, it just makes me think that 275s are possible on an 18" rim with a 48.3mm offset. jeff, what type of clearance do you have between your fender and tire? that's the critical area. also, what brand tire are we talking about (i'd need to find the section width of that tire)? you don't happen to have any pics of your car (rear tire) that you could send me, do you? i know i could just order the tires and hope they fit (they're VERY, VERY close), but if they don't, i have a situation where i can't do anything (ie. spacers) to make them fit. i'm surprised i haven't run across anybody who has tried this on 18s yet and knows if they fit or not.

thanks for all the info guys.

Jeff Curtis

Rich, at first I would say, "give it a rest" and go with the 265s...after all a 10mm difference in tire size, i.e. 265 when compared to a 275 is likely not even 10mm...more like 7.5 maybe 9...not much of a visual difference, which is, what I'm sure you're looking for. But, that would be the safe route...and I certainly understand your pain. (my first usage of the "bold" option )

I use the Kumho ECSTA 700 track tires in 275/40-17, they are a bit on the "skinny" side when compared to some other 275mm sized tires. I would say that 275s on an 18" would fit better than 275s on a 17" simply due to less sidewall flex...but this is just using simple reasoning, no facts. You apprently have the facts laid out to a tee...probably using the well documented stats on www.tirerack.com - as I did.

While I don't have pics of my car with the "new" track wheels (I JUST upgraded to 17" Cup II wheels for the track)...I can tell you that there's ample clearance left to the fenderlip, even with the 1/4" spacer...and my car is lowered quite a bit.

Just to rehash, I am using 55mm backspacing plus a 1/4" (approx. 6mm) spacer on a 17" x 9" Cup II (factory) wheel to achieve a rough 49mm backspacing...without the spacers, the wheels rub the trailing arm, secondary muffler guard and oil line under track conditions. The rubbing was eliminated with the 1/4" spacers.

If you want to save the potential for MUCH heartache...go with the 265s...and be happy that you're fortunate enough to outfit your ride with 18" wheels!

rich beebe

jeff,

thanks again for your reply. i got a good laugh from the 'give it a rest' suggestion. i realize i'm obsessing over this decision quite a bit (friends tell me i'm a bit obsessive), but at some point this became more about 'would it work' than 'what should i buy'. yes, the easy thing would be to buy the 265s and be done with it, but what fun would that be?

you're right that the difference in the tire widths is marginal and wouldn't make much difference overall - visually more than anything, i guess. i will admit that i am drawn to having a 'big' tire in the back. my friend's C4S has 285s in the rear and they look great. although, at this point, it's all about whether this application is actually possible or not and why if 275s on a 17" rim fit, why wouldn't a 275 on a 18" rims fit? i know, i'm obsessing again. i was just hoping to run across someone who was running the 275s on 18" rims.

you also mentioned the kumho ecsta 700 as being slightly thinner than other tires in that size. i'm actually considering the kumho 712s for the car and they are also listed as being slightly thinner than the S03s that were on my other rims. so, if the 265 S03 fit easily, than a slightly thinner 265 kumho would fit that much easier again. so, that should give the 275s from kumhos a chance. one more question on the kumho ecsta 700s -
how do you like them as an 'R' tire? i've run the victoracer 700s a lot in the past (big fan of those - cost vs. performance/life), along with toyo RA1s, BFG R1s and the hoosiers. i'm planning on buying the ecsta 700s as my next 'R' tire, as i like the new tread design. what are your impressions so far?

you mentioned "ample" clearance. is your car lowered to the point that the tire sits within the fender or does it still sit just below the fender lip? when you say ample, is that 1/8", 1/16"? i assume you also do not have any contact under load? that's my last 'tire' question.

thanks for all your help jeff... and i am happy that i can fit 18" rims on the car. i will post pictures of the car to this board, once i have the rufs on the car. i may not have the car lowered at that point yet, though. it will look MUCH better once lowered.

MadMarkie

Hi Rich,

Let's just see if I can generate a few more questions from you! I had a set of Fikse FM/5 18x10 with Hoosier 275/35/18s mounted in the rear. The offset was 50.8mm, but remember, these were 10" wide wheels, so you would need to adjust this value to the equivalent for a 9.5" wheel. With the car lowered and aligned to European RS specs (not as low as Kevins RSA, and -1.5 degrees of camber, not maxed), I could drop a plumb line from the outside of the fender lip, and it would just miss (2mm) the outermost part of the tire sidewall at the top of the tire (the Hoosiers have a wheel protector bead). If the line was long enough, it would hit the bottom rim lip. On the inside, there was perhaps 5 to 7mm between the tire sidewall and the control arm, and just a hair more between the tire and oil line. This was a very close fit... pretty much the most rubber possible on an RSA, really for track use only. Any lower or less negative camber, and fender contact would have been imminent. Any more width, and those control arms and oil lines would shine up nicely. I sold them with the intent of running 17" wheels for street and track, but have been putting off any more expenditure untill after Christmas. I think you could get away with 275s on your wheels... but I would just go with 265s for the street, as Jeff suggested. Not only would it be hard to tell 265s from 275s visually, but the larger diameted of the 275s (?) would throw your speedometer off and result in more tickets, or possibly more sluggish accelleration. Have fun deciding, and don't go cross-eyed staring at tire spec and wheel off-set charts! Mark.

rich beebe

mark,

i remember when you had your fikses for sale recently, we spoke (emailed) a few times while you still had them. you're the first person i had heard from that actually fit/ran the 275/35-18s on the rear of a RSA. but, as we discussed earlier, that was with a 'track' setup that allows for wider rims/tires. even with the 'perfect' offset, i'd have to think that 10" rims would be an incredibly tight fit. the 50.8mm offset is clearly the right number for 10" rims. when i first spoke with jeff at fikse, i inquired about 10" rims and they said they would only suggest that with a track setup. my 9.5" rims were built with the same 50.8mm offset though. as most of you have suggested, i have decided the safest thing to do is to order the 265s. i don't want to be in a position of having 2 'used' 275s and have to pay for dismounting and mounting of the new 265 tires. looking at the photos once again, i'm almost certain the 275s would fit, but it's not worth the chance. i'll use 265s this time around and consider 275s next time. thanks very much for your post mark. this was exactly the info i was looking for. i find it interesting too that you were able to fit 275 hoosiers, which we all know are wide. i checked and tirerack does list the 275 hoosier and the 275 kumho as 11" though.