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You're asking about a 3.2 M491 coupe?

225/45/17 front (or 235/40/17)
255/40/17 rear

I like the Michelin PS2 since it's a lighter weight tire.

8-9" front wheel width
9-10" rear wheel width

Make sure to get proper offset wheels, or use spacers as needed. Try and keep the scrub radius up front reasonable while planning these changes!

BTW if you're concerned about future tire availability you might want to consider going to 18s vs. 17s.
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'87 911 turbo, '10 Cayman S
In the past - '71 T, '77 S 3.6, '80 SC, '88 3.6 cab
Old 02-07-2018, 10:52 AM
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Quote:
Originally Posted by Kaefer View Post
You're asking about a 3.2 M491 coupe?

225/45/17 front (or 235/40/17)
255/40/17 rear

I like the Michelin PS2 since it's a lighter weight tire.

8-9" front wheel width
9-10" rear wheel width

Make sure to get proper offset wheels, or use spacers as needed. Try and keep the scrub radius up front reasonable while planning these changes!

BTW if you're concerned about future tire availability you might want to consider going to 18s vs. 17s.
JMO, but, Good advice!
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Old 02-07-2018, 11:11 AM
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Quote:
Originally Posted by Kaefer View Post
Make sure to get proper offset wheels, or use spacers as needed. Try and keep the scrub radius up front reasonable while planning these changes!
In regards to wheel offset, which gets tricky with the wheel widths I suggested, I STRONGLY recommend using around a +30ET offset up front on your '89 M491. If you want wayyyyyy too much info on the subject, read this. A +30 ET wheel won't fill out the front fenders much more than stock, but it'll steer nicely (as far as widebodies go with stock suspension geometry).

For the rears (assuming 9-10" width) I'd say go with -3 ET offset and adjust as needed with small spacers. Or since you're asking about Fikse wheels specifically then go with what Alan recommends for a 9-10" wide rear wheel without factory spacers.

Quote:
Originally Posted by Bill Verburg View Post
JMO, but, Good advice!
Thanks Bill! I've learned a lot over the years from you and others!
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'87 911 turbo, '10 Cayman S
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Old 02-07-2018, 11:37 AM
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Quote:
Originally Posted by Kaefer View Post
In regards to wheel offset, which gets tricky with the wheel widths I suggested, I STRONGLY recommend using around a +30ET offset up front on your '89 M491. If you want wayyyyyy too much info on the subject, read this. A +30 ET wheel won't fill out the front fenders much more than stock, but it'll steer nicely (as far as widebodies go with stock suspension geometry).

For the rears (assuming 9-10" width) I'd say go with -3 ET offset and adjust as needed with small spacers. Or since you're asking about Fikse wheels specifically then go with what Alan recommends for a 9-10" wide rear wheel without factory spacers.



Thanks Bill! I've learned a lot over the years from you and others!
The fit also depend on whether or no the stock rear spacers are retained

when first presented w/ questions about this fit fitment I asked about spacers, How aggressive a fit, use, ride height etc. he never bothered to get back to me.

So I assume he either doesn't know, doesn't care or thinks he knows better and can get an answer he likes better other places
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Old 02-07-2018, 11:45 AM
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Quote:
Originally Posted by Bill Verburg View Post
The fit also depend on whether or no the stock rear spacers are retained

when first presented w/ questions about this fit fitment I asked about spacers, How aggressive a fit, use, ride height etc. he never bothered to get back to me.

So I assume he either doesn't know, doesn't care or thinks he knows better and can get an answer he likes better other places
True. However if he's buying Fikse wheels direct from Fikse then Alan will make sure he ends up with something that fits. Same if purchased through Zuffenhaus or Jeff Alton.

The main point I tend to differ on is front wheel offset. While low offset wheels look sweet on widebodies I can't stand the increased scrub radius that comes along with them. I absolutely LOVE my 9.5x18" +44 front wheels!
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Old 02-07-2018, 11:53 AM
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Quote:
Originally Posted by Kaefer View Post
True. However if he's buying Fikse wheels direct from Fikse then Alan will make sure he ends up with something that fits. Same if purchased through Zuffenhaus or Jeff Alton.

The main point I tend to differ on is front wheel offset. While low offset wheels look sweet on widebodies I can't stand the increased scrub radius that comes along with them. I absolutely LOVE my 9.5x18" +44 front wheels!
I alluded to that too, you thread when you were looking got me thinking along those lines. again over the the years so much advice was the I did x and it's ok for me so therefore it will be ok for you and very little actual analysis of the effects

BTW I think I looked it up when thinking about your thread(I know I had a record at one time anyway), but now can't seem to find it. Do you(or any one else for that matter) have any record of the factory scrub radius, either of a stock SC, 930 or M491?

I agree alan, or Jeff will provide good information as to what fits, I don't think that they overly concern themselves w/ some of the other issues that we always seem to get caught up in
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Old 02-07-2018, 12:03 PM
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Quote:
Originally Posted by Bill Verburg View Post
BTW I think I looked it up when thinking about your thread(I know I had a record at one time anyway), but now can't seem to find it. Do you(or any one else for that matter) have any record of the factory scrub radius, either of a stock SC, 930 or M491?
Unfortunately I don't recall ever seeing any factory info on scrub radius. I just know it's wayyyy too much on the widebody cars, and can also easily get out of hand on narrowbody cars.
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Old 02-07-2018, 12:15 PM
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Quote:
Originally Posted by Kaefer View Post
Unfortunately I don't recall ever seeing any factory info on scrub radius. I just know it's wayyyy too much on the widebody cars, and can also easily get out of hand on narrowbody cars.
It's big on an SC/Carrera too, at least an order of magnitude larger than is seen on the water cooled cars, which I do have good data on.

Guess I'll have to try and measure an SC or Carrera next opportunity on an alignment rack
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Old 02-07-2018, 12:39 PM
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I have 17x9 17x11 on a SC with Turbo flares running 245/40 17 fronts and 285/40/17 rears. I know there is a chart around that offers the correct sizes for certain cars. Will see if I can dig it up.




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Old 02-07-2018, 04:46 PM
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Quote:
Originally Posted by nippy View Post
I have 17x9 17x11 on a SC with Turbo flares running 245/40 17 fronts and 285/40/17 rears. I know there is a chart around that offers the correct sizes for certain cars. Will see if I can dig it up.





Are those Continentals these from TireRack?

https://www.tirerack.com/tires/tires.jsp?tireMake=Continental&tireModel=ExtremeContact+Sport&partnum=84WR7ECS&

Those 285s look really good on an 11x17!
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Old 02-07-2018, 05:03 PM
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No not the new tire. mine are the Extreme contact DW. I will try the new tire next time if they have my sizes. I love Michelins and the singer runs the PS2 on the cars. I found them to be way to stretched for my liking. I think they run 225 45 17 fronts and 275 40 17 rears. Not big enough for me. The 245 and 285 were perfect for my application.

We did the tire lettering which is a love em or hate em thing. I love em and the tires are pretty good so far.




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Old 02-07-2018, 05:07 PM
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How well a given tire size fits on a given wheel depends on the brand and type of tire. There are brands that run small and brands that run huge. When you narrow down the approximate size you want to run then it's time to do homework on the real world sizes. You'll find that some sizes that are normally thought of as too narrow or too wide for a given wheel actually are not and may produce the look you are after. If you don't do this homework or don't size the wheels and spacing to match then plan on using spacers to get the wheel/tire combo centered in the wheel well exactly where you want it as the variability of section width will alter the measured total width of the wheel/tire combo.
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Old 02-07-2018, 07:10 PM
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Quote:
Originally Posted by Bill Verburg View Post
The fit also depend on whether or no the stock rear spacers are retained

when first presented w/ questions about this fit fitment I asked about spacers, How aggressive a fit, use, ride height etc. he never bothered to get back to me.

So I assume he either doesn't know, doesn't care or thinks he knows better and can get an answer he likes better other places
Greetings all, I just returned from a business trip that started at 4a this past Monday morning.

Thanks for all the responses. In turn, I owe some of my own and I have a few more questions as a result of the discussion to date. I want to be as thoughtful and mindful about responding as you all have been with your comments, so I will do so when I've had a chance to digest everything that has been written. In the interim...

Bill, my apologies if you feel that I never "bothered" as that certainly was NOT my intent. In fact, setting your inaccurate assumptions about me aside... I am HUGELY appreciative of the expertise you've shared here and elsewhere on Pelican.


Thanks everyone.
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Old 02-07-2018, 10:59 PM
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There is an overload of info on this subject.
Bill Verburg always has great advice.
My M491 has Fikse 9" / 11" X 17 (no rear spacers) with Nitto 235/45 Front, 315/35 Rear.
Allan at Fikse will guide you with proper size/ ET's.
Old 02-08-2018, 04:01 AM
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I have the Fikse Fuchs/Zuchs on my stock 930. 9x17 fronts and 11x17 rears. I am running 235/40 front tires and 275/40 rears (Nitto NT05).

Realistically, my tire options were either 275 rears or 315 rears. As my car is stock and I often do canyon driving, I went with the narrower tires for lower unsprung weight (and lower cost).

I would not recommend any narrower of a tire on 11" wide rear wheels. My 275s already are a little bit stretched. If you're considering a narrower tire for your NA car, then consider going with a 10" rear wheel (and 8" front).
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Old 02-08-2018, 08:52 AM
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If it were my car w/ a stockish engine and trans, both reduce scrub radius from stock for better steering feel
17" option that is less costly in terms of torque loss, total loss ~11lb-ft


18" option, total loss ~10lb-ft
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Old 02-08-2018, 10:09 AM
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Alan no longer works for Fikse. I do a lot of the spec info for Fikse on these wheels now. And I know I am concerned about the same stuff many of the posters are here, not just what will fit. If anyone is interested in a set or has any questions, just send me an email and I will be happy to answer them as best I can.

Cheers
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Old 02-10-2018, 12:07 PM
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Wow, what a surprise. Are they still making the Zuff's? Thanks for posting Jeff.
Old 02-10-2018, 01:54 PM
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Quote:
Originally Posted by Bill Verburg View Post
however if the the advice is erroneous or otherwise bad expect to be called on it.

track or not isn't the real point here

The cost of larger wheels and tires is something that has been elided over for years, I've finally gotten around to getting at least a preliminary grip on it.


telling someone to put a 265 on an 11 is in the category of poor advice, telling someone that it works fine on a 400hp turbo so it will work fine on their 200hp M491 is also bad advice or at least in the category of maybe some more thought could be put in to this.
i dont think a 265 on 11's is poor advice or dangerous. its well within reason imo.
there production cars out there with 195 on 8inch, 205 on 8-1/2, 225 on 9s,

michelin TBs recommended width size for 215 is 6 to 7 1/2 and 270 8 1/2 to 10 1/2. how many TBs have you seen recently just here on pelican with these sizes mounted on wider 9 & 11 braids ? this rim to tire ratio size is very similar to the gr4 micholotto 308 and the stratos they have been running consistently 4 decades on TB's and P7's without issues and rallying is a much harsher environment than the streets or the circuits.

the reason tire and wheel companies are now extremely conservative in the width of tire to wheel ratio is warranty claims. there has been an exponential increase in claims with the lower profile tires being available even mundane cars and our potholed roads aren't getting any better.

even parking and car-wash rail curbing for cosmetic damages rather than structural have become an issue. this have become liability for the oem's and some of vendors. hell, back in the early 90's the nsx guys were even blaming and suing acura/honda for excessive tire wear not lasting more than 12k miles like their accord if you can believe that. hard to not blame the oem's, tire and wheel companies for not being conservative on there tire to wheel width ratio's.

showroom stock type racers and other american race series have something to do with this trend too with the regulatory limits on wheel widths. companies like hoosier and goodyear design ginormous tread width to squeezed on to narrow width wheels. not ideal but if you wanted the most grip you run with these muffin top tires which is a huge advantage

i work with a couple racers who's day jobs is are oem wheel/tire engineers. they would go for the wider than recommend wheels on their personal cars every time primarily for the increase tire response.

for what its worth.
Old 02-10-2018, 03:56 PM
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Quote:
Originally Posted by panzerfaust View Post
i dont think a 265 on 11's is poor advice or dangerous. its well within reason imo.
there production cars out there with 195 on 8inch, 205 on 8-1/2, 225 on 9s,

michelin TBs recommended width size for 215 is 6 to 7 1/2 and 270 8 1/2 to 10 1/2. how many TBs have you seen recently just here on pelican with these sizes mounted on wider 9 & 11 braids ? this rim to tire ratio size is very similar to the gr4 micholotto 308 and the stratos they have been running consistently 4 decades on TB's and P7's without issues and rallying is a much harsher environment than the streets or the circuits.

the reason tire and wheel companies are now extremely conservative in the width of tire to wheel ratio is warranty claims. there has been an exponential increase in claims with the lower profile tires being available even mundane cars and our potholed roads aren't getting any better.

even parking and car-wash rail curbing for cosmetic damages rather than structural have become an issue. this have become liability for the oem's and some of vendors. hell, back in the early 90's the nsx guys were even blaming and suing acura/honda for excessive tire wear not lasting more than 12k miles like their accord if you can believe that. hard to not blame the oem's, tire and wheel companies for not being conservative on there tire to wheel width ratio's.

showroom stock type racers and other american race series have something to do with this trend too with the regulatory limits on wheel widths. companies like hoosier and goodyear design ginormous tread width to squeezed on to narrow width wheels. not ideal but if you wanted the most grip you run with these muffin top tires which is a huge advantage

i work with a couple racers who's day jobs is are oem wheel/tire engineers. they would go for the wider than recommend wheels on their personal cars every time primarily for the increase tire response.

for what its worth.
Thank you for your opinion

I make no judgement on whether or not you or anyone else want to disregard the engineers advice, IMO it's generally not a good idea, sure you can skirt the issue and you probably won't have a problem

This is a great look, who wouldn't be proud to have a similar one on their car, Safe too.





If someone wants to use oversized overweight wheels and tires on their car fine, I just feel that all the factors need to be considered, if you don't, well once again, thanks for your opinion

in this day of fake news everyone needs to do their own due diligence

but some facts that all but flat earthers can argue w/
torque loss is proportional to mass of the wheel/tire and where that mass is located,
torque loss is proportional to the radius of the tire in 2 ways, first gearing and second mass and the location of that mass

The less torque a given engine has the larger will the % of torque loss due to oversize/overweight wheels

Any reasonably sensitive driver will be able to feel even fairly small differences in back to back sessions, I know I do
some will be more concerned w/ torque loss than others, just as appearance is more of a concern to some than others

I have always advocated the use of the widest wheel for which a tire is spec'd, sure you can stretch the spec, many of us have done so, it's not usually going to be the best idea though.
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Old 02-11-2018, 09:47 AM
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