Chronos

Can you elaborate a bit on this for me please? I'm somewhat of a newbie when it comes to race mechanics...

bradrx7

If the centerline of the wheel is far away fropm the centerline of the wheel bearing, then the resulting moment will add undue forces onto the bearing. This can result in early failure. Also, the extra increase in scrub radius (in front) can unduly effect your handling when turning. In other words, don't run 18" wide wheels. <g>

SleepR1

Gee Brad, I was planning to run 285/30-18 Hoosiers mounted on 10.5 x 18 CE28Ns (45-mm offset) in back?

SleepR1

Yes, I believe this is why you should run as close to stock offsets as possible when upgrading wheels.

John Purner's CCW setup for 10 x 18, with 285/30-18 Hoosiers--offset is 2 inches (50.8 mm). Stock offset is 50 mm (1.96 inches).

Change the offset to more negative (smaller number) then the scrub radius, wheel bearing load, AND wheel rate (the overall "spring rate" of the suspension) all change.

bradrx7

SleepR1... I agree. Talk to the wheel manufacturer about your setup. If they don't know, they should. As you know, .8mm is very little and you will be fine. The wheel/tire will fit your wheel wells and you can worry about other things.

foko

i agree that if a 285 was made in 17in diameter with the proper overall diameter, this issue would be moot and we'd all have 17X 10 all around. however, no luck so 285/30-18 is the "largest contact patch" tire we can use without body mods and we're stuck with the compromise.

the 18X10 fitment uses a 50 mm offset which is not significantly different from the stock offset to worry about.

i may be off on the khumo tire weight. my khumos are still sitting at rishies shop.....still waiting on my wheelset from kinesis
rishie told me he weighed one on his shop scale at a little over 22lbs can't verify that as i wasn't there....though i agree it may be a bit optimistic.

and finally, i agree that in the end, the driver is STILL by far the most important variable. despite that, i won't mind running those 285's too much while i'm "improving"

regards
fabian

i'll post some pix if i ever get the damn things on the car!!!

bradrx7

foko,

please do post pics. I miss my old Kinesis K20s that were stolen along with my car a few years back. Alan Bayliss makes fine products.

also, 275/285 is PLENTY of tire for our cars in road race configuration. If you use slicks (not DOT) the grip is plenty.

best,
Brad

foko

yeah, i know he makes a great product but i have to admit that so far the service has been less than spectacular. rishie has been hounding the guy for months and finally the wheels are almost here. the latest word is that the wheels are just shipping....should be here next week sometime. will be installed soon thereafter and i'll post some pics.

i'll be running this setup at sears point at an open track event on 1/25.....full report to follow.

kinesis k28 18X10 all around with khumo v700 285/30.
just talked to rishie today, he gave me revised weight on the khumo's of just over 25lbs each. when the tires are mounted we'll weigh the whole setup and post it.

my present setup is oz comp wheels (very, very heavy) in 17X8.5 f and 17X10 r (235/255 toyo ra1). this setup understeers predictably even with relatively soft front spring rate (10kg/mm) and dampers full soft (j.i.c flta2).

i suspect the new setup will be better

regards
fabian

bradrx7

Fabian,

Your turn-in issues will evaporate with the 285 all around. When I converted to all 275/40 Hoosiers the car came alive again. Next time you need tires, try everything you can to go to Hoosiers. The weight savings alone over Kuhmos is amazing not to mention the grip.

SleepR1

Hoosier R3S03s are the sh*t

Say Brad, you think I can squeeze 10 x 17s CCW P4 mesh all around with 275/40-17 Hoosier R3S03s? I have stock style H&R springs, OE R1 Showa shocks, and Eibach sway bars fr/rr.

Don't know what it is about the 245/45-17 fr and 275/40-17 rr, but that setup was VERY forgiving. Must be the tallish sidewalls for both tire sizes (25.3 inch tall) ?

Anyhow, I'd like to dial out some of the understeer, and increase the car's overall cornering stick with same size 275/40-17s all around.

I read somewhere that John Purner uses two different offsets for the 10 x 17 setup. Something about the clearance from the rear trailing arms in back?

I'd like to be able to rotate the tires, so I was thinking of using 1/4-inch wheel spacers with longer wheel studs for the rear hubs; or do you think the stock studs will be fine with 1/4-inch spacers?

fluxen

This isn't the forum for it, but this discussion caught my attention. I have a set of Kinesis K10 wheels for my FD, 17x9.5" that I run 275/40's on all around. Anyone want to buy them? $1700 (compare to about $3k new)

I just bought a new race car and won't be tracking the FD much anymore.

bradrx7

Manny, you can't run that wide a wheel with stock diameter springs. With 10s you will need tubular rear control arms and 2.5" diameter springs. Nothing else will do. Even then, you will eat the front liners. Most of us hard core trackers don't care, mine are cut away in both front inside corners anyway. Also, you will need some ride height, as well. Look at the picture on my web page. I am turning right at about 90 mph in that picture so the car is up a little on that side, but yu can see I am not slammed. That is the solution, not spacers and stuff.

SleepR1

Got pics? How posting a bit more info?

SleepR1

Yeah, but that stuff costs money

bradrx7

Old saying:
Speed costs money, how fast do you want to go?

foko

yeah, i expect the understeer to disappear.

i will definitely consider the switch to hoosiers after i cook this set of khumos. unfortunately, i may need to use the same wheelset for dry and wet....(yeah it rains up here in north. calif. ) and since i actually like running in the rain, i may need to stick with the treaded tire until i get a second wheelset for rain tires.

the wheels arrived today and are being mounted tomorrow. should be on the car this weekend....yippie!

fabian

racedriver

brad, where did you get the idea to use 1000 & 700 lb springs? I run 650 & 450lb. Whats the difference in feel.
Did you do it because of a switch from performance dot to slicks?

bradrx7

racedriver,
I was running 800/600 on my old car (the one that was stolen) after moving up from 650/400. The idea was to eliminate roll from the car. My track driving friend Jim O'Brien had taken the increases to the next level and went to 1000/700 on his car. We were at Watkins Glen for an open track event in 1999 amd I drove Jim's car. I was impressed and was planing on the increase for my car when it was stolen. As things worked out, Jim ended up selling me his car. I've since changed almost everything on the car BUT the spring rates. It helps that I run a lot of downforce and a very stiff front bar (Tri-Point .25" wall set to full stiff). After switching to slicks I was afraid the car might need some changes, but I only needed to take a little camber out to get my tire temps perfect. Like anything on a race car, it works for my tracks and my driving style. On my home track, Texas World Speedway, I am in long fast sweepers where the stiff chassis works great. At tracks like VIR with a lot of quick fast transitions, the chassis has been very happy.
Hope that helps,
Brad

racedriver

thanks

redrotorR1

So, even the CCW "special" 17 x 10 fitment won't work without tubular rear control arms? And if so, what about 17 x 9.5's on both F&R? I'm looking at 'new' wheels and I want to go as wide as possible. And will 275's fit on a 9.5-in rim?

bradrx7

10" wide wheels will fit statically but you will run into problems under cornering when the tire offsets. It will rub the control arm. the tubular bars are slightly narrower than the stock ones and you can gain a little more room with offset bushings at the Heim joint. On my current setup, the tire is 3/16" from the bar and it rubs a little when I corner.

275s on a 9.5 is pinching the tire. you may get it to mount, but thesidewalls are not happy. My suggestion is to take the high road, get the correct wheel/tire/suspension fitmet for your setup. You don't want to cut corners on your set up and drive 155mph into turn one.

CrispyRX7

iTrader: (139)

Great thread guys....keep it up
Regards,
Crispy

PS Brad, the wheels are almost finished

SleepR1

Seems reasonable to me, Brad. Definitely agree with the 275/40-17 Hoosier preferring a 10-inch wide. I'd go with 255/40-17 Michelin Cup Comps or 245/40-17; 245/45-17 Hoosier R3S03s on 9 or 9.5s. FWIW 245/45-17 and 275/40-17 Hoosier R3s03s are identical in height 25.3 inches. Rim widths would be 9 wide for 245 and 10 wide for 275.

redrotorR1

Thanks for info. If this is going to be the case with the rear control arms, then what is the ideal spacing so that no rub occurs? And is there a way to approximate this using front/backspacing calculations?

in2twins

Brad, I have the utmost respect for your opinion, but in looking at both the Hoosier, and the Kumho sites, the 275-40-17 measured rim width for both brands is 9.5". It seems to me that given this, a 9.5" rim is certainly not pinching the tire. On the Kumho, which I have on my Supra(17x9.5"),the sidewall of the 275 is both straight, and vertical. It behaves predictably, and shows perfect temps across the tread. Kumho lists 9-11" as usable rim width. The Hoosier as most of us know is a little different story, as they tend to like a little larger rim, still hoosier lists this tire as having a 9.5" rim width(9.5-11 usable). There was a nice article recently in Sport Compact, that talked about using various rim widths on the same size tire to vary the turn in and break away characteristics of a given tire size. One suspension tuner was using a wider rim on the front, for a vertical sidewall, and good turn in. On the rear they used a narrower rim, for a slightly rounded sidewall, and more gradual break away. Granted there are other ways to accomplish the same thing, but ity does represent another tool for getting the car just right. On a side note, I believe someone on the forum has run the 9.5" Supra rims on an FD. Does anyone know what's required to accomplish that? I would like to run these all the way around on my FC with 275-40-17s. (Already working on the widebody). Best regards, Carl Byck