worf928

Jim, adding power has almost nothing to do with it. We're not driving the front wheels are we?

I've had Fiske's 9"s and 10"s running 255f/265r on my '91 (and from time-to-time on the '89) since 1999. That was way, way before the supercharger.

Seriously: It [bigger front tires] transforms the way the car steers, brakes, and corners. And it does this even when not near the car's limits.

Whenever I now drive a 928 with 225s on the front it feels like the front end is wobbly, doesn't want to turn, and won't brake without engaging ABS.

The 928 is under-tired on the front. Period. Look at the section width per pound and compare it with front-engined cars(*) of similar weight with similar 'sporting' targets. A simple at-hand-example: the C5 and C6 Corvettes are the easiest against which to compare since they are V8 torque-tube cars like the 928. My bone-stock C5 Z06 runs 265 on the front. And it weighs 200 pounds less than the 928.

(*) It's all about moment of inertia. ***-draggers (911s) have far, far less weight on the front so they need less tire to turn-in. Similarly, mid-engined cars have a low moment of inertia since the mass is concentrated in the middle and consequently need less force from the front tires to turn-in.

Jadz928

Dave, I couldn't agree more, as long as you speaking of a car in a neutral state (travelling thru a line without power on or off)
Alls I'm saying is adding more power extends the range of speed, thus extending the limits and the need to control this higher limit with traction, when power is applied, off neutral.

Anectdotally, I find the early cars to be very neutral thru a mild corner, w/even throttle. Surface patch breaks out rather evenly front and back. Push it a little harder into a tighter corner, you get mild front end push. 225s all around.

Point is, one could over-tire a car like this rather easily, and extend the traction limits out of a fun, driveable range. Bigger is not always better.

SMTCapeCod

Dave- what offsets are your Fiskes?

Seems like an opportune time for bump, as well..

77tony

For reference. Specs on the 94 GTS. Fikse FM-5's: Fronts: 18 x 8.5, 57mm, 7.5" inner rim, 1.0" outer rim. Rears: 18 x 11, 64mm, 9.0" inner rim, 2.0" outer rim. Specs for the 80: Fikse Classics: Fronts: 17 x 8.5, 62mm, 7.5" inner rim, 1.0"outer rim. Rears: 17 x 10, 56mm, 8.0" inner rim, 2.0" outer rim. Jim, hope this helps for what your planning. I wish I knew about these 18" dials sooner because they would be going on Just Peachy. T

Imo000

Till recently, Corvettes always had more tire than they needed. Look at the C4, and the tires they had, yet the HP was the same as the 928.

worf928

Unfortunately, I can't tell you. I don't know off the top of my head so I'd have to measure and what I'd come up with would probably not be accurate to more than +/- 3mm. When I bought the wheels - almost 13 years ago - I took the very lazy route: I called Dave Roberts and ordered the Fikses though 928 Specialists. Dave's Fikse "recipe" was, at the time at least, available only through 928 Specialists because HE guaranteed the fit while Fikse would not and therefore Fikse wouldn't sell wheels with the "max 928 specs" to individuals.

About the wheels, what I can say is that Fikse doesn't (didn't at the time, at least) do offsets in mm increments. IIRC it was 1/2" increments.

The front 17x9s stick out by a couple of mm's. No more than 3 to 5 though. They will only fit late '89 through '95 where late '89 is defined as 'the point at which the front brake casting changed.' Anything before late '89 needs a few mm thick spacer to clear the earlier Brembo brakes. (Maybe its '88 although I seem to recall working on an '89S4 with the 'earlier' Brembos.)

Ok, so I don't get ...

... why HP is in the fore of this discussion. I certainly understand why more rubber on the rear is important when HP is added. My comments with regard to the front tires have been directed at handling: turn-in, fighting understeer, braking performance, and general 'feel.'

Quite right. With the weight balance of the 928, equal size tires all-'round get's you reasonably close to neutral cornering. With 245s on all four corners you get the same balance with more grip and better braking.

The latter seems to be mostly useful with the 86.5+ Brembo brakes. In my experience the floating caliper brakes can get maximum braking traction from 225 but can't quite stop a 245 (on dry pavement, braking properly and straight, etc.) But, with regard to grip, 245s is what Kempf runs on his OB and many of us have seen what he can do with that OB 928 on BRP (and it's SCARY.) He does boil his brakes.

Given the dimensions of the front wheel well, 265 is the biggest width you'll fit under a 928 on the front. After that ... its possible, but it won't be easy - not bolt-on. So, the real question is if 265s on the front are way too much tire. I think not WAY too much. Maybe a bit for 928s without GTS brakes unless the goal is maximum cornering grip.

With a 9x17" or 18" front wheel you can easily run 235 to 265. That's sufficient tire range for those that want almost no-extra front grip while at the same time allowing crazy hair-on-fire-while-cornering folks to stick the biggest tire they can under the un-modded front of a 928.

Personally, I don't really like - anymore - driving a 928 with 225s on the front. I think 245 is the minimum front tire a 928 should have.

Up to the limits of the 928's front wheel well I disagree. After that, sure, bigger is not always better.

What is certainly not better is 305s on the rear and 225s on the front. That's either way too much rear tire for the power, or a recipe for not having enough braking traction when it's time to corner the Zillion-horsepower Octo-turbocharged 928 at the end of a short straight and then understeering into the kitty litter.

Range Rover

Just skimmed through this thread. Definitely would be interested in a set when they go into production.

Jadz928

You got it, Range Rover!

Dave,
Thanks for sharing your anectodal experiences. All this is very important to me, esp when the dialogue extends beyond my "limits".

Best part of it is 225s are out, and the range of 225-265 front on 9" should appeal to most.

Just shipped out the prototype for top-class paint. Following that, will post up pics.

Speaking of Fikse... looking forward to an opportunity to work with them on this project. We will see!

Happy New Year!

mazdaverx7

the wheels are amazing! will definitely look forward to a pic of a final production version!!

Vilhuer

1/2" increments for offset comes from 1/2" steps for of the shelve rims wheel manufacturers use. They basically make one center section type to be used in many different applications and attach different width rims to it. In 928's case outer rim would have to be something which really doesn't exist meaning almost negative width piece to get offset we want. See eighties BBS RS wheels used in 928 front end for sample how 1/2" wide outer rim looks like and yet its still not enough to get correct offset for 928 when combined with available center sections. Either negative outer rim or center need to be very special shape to clear both brake caliper and have outer rim mounting point far enough inward compared to wheel to hub mounting surface. Thats why only hope we have is to get custom center section which will accomplish this. Its not easy and especially cheap task. Hopefully market is big enough to get this done and Jim can make it.

Imo000

Are you guys plannig on load testing these rims before offering them to the public?

Jadz928

I'm going to throw them on my 928, drive around my hilly neighborhood, and try to catch some air.

The plan is to load test for safety. The tests are expensive and require sacrificial wheels. What tests are performed and to what extent will depend on budget. At the end of the day, the wheels won't be produced until I'm confident they will perform on the street.

EDIT: Having closely reviewed the first prototype, I think we're in pretty good shape.

KenRudd

I volunteer to load test them. I have the perfect German engineered ~3,500 lb testing rig that will push them with about 316 HP up to ~165 MPH in some of the most grueling conditions available.

Edit: Jim beat me to the click!!!

Gonzotiki_666

Jadz those wheels look damn good! I'm really impressed by the ingenuity of you guys.
If I bought a set not only would they look sweet--my car's value would double. :-D

jWs-928

+1 for volunteer testing... at VIR - CMP & Roebling Road
:-)