experience of fsd with 17 and 18 inch wheels ?

anyone got direct experience to compare 17 inch wheels with koni fsd and m033 to 18 inch wheels under the same conditions ? I'm currently thinking of a switch from 17 inch wheels to 18 inch but have seen a few mentions of the ride being impacted for the worse with 18s, but not sure if this is just with harsher shocks and springs on the car.

i like the way the car runs on 17, but like the look of 18...but on balance if its likely to degrade the ride, I'll stick with 17.

wilsonny, sorry I have no direct experience of the specifics that you request but until someone comes along with that which you request I am happy to share aspects of my limited experience which may provide you with a slightly wider perspective.

As I have typed elsewhere my Porsche experience of the variation in a 1" difference in wheel size all be it 15" to 16" on 911 SC models, was the difference between the SC at 15" and the SC Sport at 16". Both set-ups equated to each having the same rolling radius (overall diameter) thus maintaining speedometer accuracy and tyre to bodywork clearances. The Sport version also was fitted with different shock absorbers.

The difference was that the sport had sharper handling as the result of having less tyre sidewall flex but the downside of that was that you DEFINATELY felt the road surface more accutely as having less sidewall to absorb bumps and thumps.

Ultimately much depends upon your priorities be they looks, handling or a degree of additional comfort.

Given the above was my experience around the time the 993 introduction, as I walked towards the 993 looking at the very low profile tyres (compared to MY non-sport SC), I mentally prepared myself for a bumpy ride.... Well I sure got that wrong, as the then new suspension was DESIGNED to match the low profile tyres thus the ride and handling were greatly improved over the SC Sport cars I had experience of..

If the original Porsche suspension set-up does not match the choice of replacement tyre and wheel combo, then it seems logical that there will be a difference in the driving experience.

Of course going too large in the wheel/ tyre department can also affect body clearance too. There can be wheel/tyre issues relative to diameter, width and off-set as well as the aspect ratio of the tyres.

Using logic it does seem that increased shock transmitted to the monocoque may also create unforeseen issues in time..?

Apologies if this comes across as all too obvious.. :?:

I've got exactly this set up and switched from 17" cups to 18" hollow spokes.

I barely noticed any difference in the ride quality and so have been more than happy to stay on the 18s. I had been expecting a significant deterioration before I switched but in the end I was surprised how comfortable the car remained with the bigger wheels.

Of course, it will always come down to personal preference ultimately but I do not consider myself to be someone that would put up with too harsh a ride quality for long.

Edit: just for completeness, my tyres are Michelin Pilot Sport 4.

madge said:

I've got exactly this set up and switched from 17" cups to 18" hollow spokes.

I barely noticed any difference in the ride quality and so have been more than happy to stay on the 18s.

Edit: just for completeness, my tyres are Michelin Pilot Sport 4.

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spot on... just what I needed, sounds like I'll be happy with the 18s

Hi wilsonny - not able to help sadly as my car currently having FSDs fitted on the stock 17 Cup 2s. Am planning on graduating up to 18s though as the car becomes more RS'd so would be keen to hear how you get on.

Also what 18s are you going for?

pierrebear said:

Hi wilsonny - not able to help sadly as my car currently having FSDs fitted on the stock 17 Cup 2s. Am planning on graduating up to 18s though as the car becomes more RS'd so would be keen to hear how you get on.

Also what 18s are you going for?

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I'm trying to keep mine as a compromise between comfort and a little better performance for the odd track day. one of the reasons is tyre choice....new stuff doesn't seem to be available at 17 inch.

wheel choice... not sure I should admit to it on here... there may be disapproving comments because I'm almost certainly going for non Porsche items, oz alleggerita hlt in dark grey, so will look like this...

https://images.app.goo.gl/Ghfpub43Dh2bEzgJ7

Luddite said:

wilsonny

If the original Porsche suspension set-up does not match the choice of replacement tyre and wheel combo, then it seems logical that there will be a difference in the driving experience.

Apologies if this comes across as all too obvious.. :?:

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thanks... looks like from other comments that it should be ok. 18 inch was of course an option for our cars so wouldn't expect a major problem.

i know its a popular topic so thought I'd bump my original thread with an update having finally made the move to 18" wheels and fsd/m033... my original quest was for first hand experience so it's only right I share.

so I was making the move from old Monroes and m029 springs with 65k on them, running 17 inch cup2 with ps2 Michelin 205/255, shocks in ok condition but worn and slight leak on front drivers, already done rear engine mounts, geometry checked and to spec. std roll bars. std tyre pressure.

my intended use is to suit a weekend fun car without comprising the ride for Europe trips but reducing the excess roll and turn in understeer which was just spoiling my track day fun a little... https://youtu.be/V6g8vWyo8ec ... not expecting the impossible, just a good compromise.

so first change was oz 18 alegerrita with pilot sport Cup 2 225/265 std pressures but no other change to suspension. with this set up and old suspension, the grip and turn in was what I wanted, but the ride was a bit harsh and very unstable over bumps. tyre noise was also worse.

I tackled the tyre noise first by following the other threads on here and insulating rear and doors with skinz products...a little extra weight, but a huge difference to annoying noise reduction.

next i did the fsd/m033 and all new mounts, drop links, arb bushes. i checked out all the other bushes and couldn't see any excess movement or issues so for now, I've left them alone. set camber myself using a magnetic tool and rechecked over a couple of weeks as the suspension bedded in.

result...magic... just what I wanted... once settled, the ride is great, no harshness and more comfort on fsd/m033/18 than with old Monroes/m029/17, initial woolyness on turn in has gone, no understeer and high speed stability is great. can't wait to try out on a track day, although its obvious they are not a track focused shock/spring. height of car also looks right to me (i will post a follow on pic).

so if your needs are anything like mine... I'd certainly recommend the combination.

https://photos.app.goo.gl/tMbyBBottW5VPATRA

koni

Good to hear. I have 18 inch BBS LM's on standard suspension and to be honest I could hardly tell the difference when moving from cup wheels. I am about to fit Koni Special Active (FSD replacement) with Eibach pro sport kit for the lowered look but hopefully keeping a degree of comfort!

Wilsonny, thanks for coming back with an update. Nice looking 993.. (-:

I start by stating the obvious in that it is unlikely that changing wheel diameter is the principal factor in altering the way a car feels to it`s occupants..?

In my limited experience the defining factor in terms of wheel diameter alteration relative the the vehicles "feel," is that if the rolling radius will require to be maintained, in order that both the gearing, speedo read out and ride height of the vehicle are not altered...?

Given the above it may come as no surprise whatsoever that if you seek to maintain the rolling radius while fitting a larger diameter wheel, in doing so it is then necessary to fit a tyre with a reduced aspect ratio (sidewall depth), and in doing so the handling will sharpen up though as with any such modifications it seems logical(?) that there may be a knock-on, or domino effect..?

Reducing the aspect ratio is likely to remove a degree of flex out of the suspension, and in the case of a Porsche the hope/expectation would be that those who designed the the 993 had a reasonable idea of the best match of tyres and wheels to suspension..? Another consideration may be the actual weight difference of one wheel and tyre combo against that which was originally fitted which affect the unsprung weight within the suspension set-up..?

My experience is circa 20 years out of date, but a similar difference existed between the 911 SC and the 911 SC Sport where the cookie cutter wheels on the SC (comfort as it might be recognised as today) had 15" wheels and the SC Sport has 16" Fuchs wheels.

Given both 911`s wheel/tyre options had the same rolling radius, the wheel and tyre combo could be swapped between the models... However, Porsche being Porsche the dampers/shock absorbers differed between the sport and non-sport, the latter fitted with Boge units and the former fitted with Bilstein, no doubt providing the required characteristics to match the tyre/wheel combo..?

Whether the torsion bars(spring equivalent) differed between SC and SC Sport, I have no idea, however I suspect Porsche would have matched all suspension components to each other on both yet different systems

In my experience the Sport was a more harsh ride than the non-sport, which seems to be expected..?

As I have typed before, when I first saw the aspect ratio of the standard tyres on the first of the 993 models, I expected to be in for a harsh ride as in the SC Sport, but was both pleased and surprised to discover that the feel was logically minus the need to settle into corners, but more importantly such was the improvement in the suspension design that the 993 was far more comfortable than I expected... Best of both worlds..?

As ever Porsche and other marques owners will ever seek to modify much, and in so doing may not understand that in altering any one item, tends to just be the start of a domino effect which then may create the need to attempt to re-set the now off-set and all important balance of the machine by further alternative means, and which may not be understood at the time of the first component change, more so perhaps if style has been prioritised over basic engineering principals ...?

I guess that may be part of the reason that some folk may prefer to seek out cars in original spec in the passage of time..?

GREAT that you are content with the outcomes relative to your modifications, and thanks again for sharing the processes you utilised to arrive at your personal ideal... :thumb:

yes, thanks for sharing... my focus here is to share the practical experience on the specific combination that myself and others will be considering on a 993. there are lots of threads and other sources regarding principles and opinions.... but you know what they say about everyone having one of those

all our cars at this point will be needing a suspension refresh if not already tackled. original shocks aren't available, you may or may not fancy porsches replacement offer. 17 wheels aren't getting all the good new rubber any more, so if you use the car, 18 is attractive as it widens choice. of course, 18 tyre size and m033 springs I've used ARE original, just not on my car. but at this point if a 993 has ITS original suspension then its not a positive, either for driving experience or the impending cost to renew.

maybe it wasn't clear, but of course i don't expect any change is due to wheel diameter... hence quoting tyres and pressures and also describing the gradual upgrade process. clearly harshness on original suspension is due to reduced tyre side wall on old suspension, but at same time a reduction in woolyness from increased rubber width and reduced side wall flex.

none of this was unexpected, the point in sharing is that suspension change can't be avoided for any owners and to give a practical round up or pros and cons of a potential option combo. I'm sure it's probably all been said by previous generations here in the forum of course !

There is no substitute for first hand knowledge when it comes to running old sports cars when original parts bins have been emptied, and substitutes have to be considered. The ability to be able to continue enjoying such machinery on the road depends on folk as on this forum sharing their much valued and bang up to date experiences... The ramblings of an old duffer.... Less So.. ld: :floor:

Hi wilsonny I am going through a similar process but in reverse as I am looking at going from 18" to 17" as I find the car tramlines quite badly and has a tendency to shift position on any undulation given the bad state of roads where I live. I have booked the car into Centre Gravity to look at the suspension set up as my cars PO had set the car up quite rigidly for track use and the shocks are also looking past their best. However my 993 is going to be a daily driver when the salt is not on the road and will probably se 1 or 2 trackways a year as I compete in a historic doing hillclimbs and sprints. The additional problem with mine is that it is an early 993 made the first quarter of 1994 so according to Porsche should under no circumstances run 18" wheels but knowledge on here leads me to believe with the strengthening bar it will be fine. Subject to what CG say I would like to run 17 on the road and 18" on the odd track day but interested to see if this is possible. Im going for non-standard Otto Fuchs wheels as I like the look on my Guards Red car.

912Polo said:

Hi wilsonny I am going through a similar process but in reverse as I am looking at going from 18" to 17" as I find the car tramlines quite badly and has a tendency to shift position on any undulation given the bad state of roads where I live. I have booked the car into Centre Gravity to look at the suspension set up as my cars PO had set the car up quite rigidly for track use and the shocks are also looking past their best. However my 993 is going to be a daily driver when the salt is not on the road and will probably se 1 or 2 trackways a year as I compete in a historic doing hillclimbs and sprints. The additional problem with mine is that it is an early 993 made the first quarter of 1994 so according to Porsche should under no circumstances run 18" wheels but knowledge on here leads me to believe with the strengthening bar it will be fine. Subject to what CG say I would like to run 17 on the road and 18" on the odd track day but interested to see if this is possible. Im going for non-standard Otto Fuchs wheels as I like the look on my Guards Red car.

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my understanding is that it's just the brace you need to fit, but others might know better.

I thought I might be in the same position regarding a switch back to 17s... the car was pretty scary at high speed on 18s in the brief period before I changed the suspension, but now it's better than it ever was regarding stability.

might be of interest before you go to CoG...i checked my camber using a cheap magnetic camber tool... there's some pics on here of me using it and also comparing the overall diameter between 17s and 18s being virtually identical...

https://photos.app.goo.gl/VRmzHfstSZJjtPbP6

Luddite said:

There is no substitute for first hand knowledge when it comes to running old sports cars when original parts bins have been emptied, and substitutes have to be considered. The ability to be able to continue enjoying such machinery on the road depends on folk as on this forum sharing their much valued and bang up to date experiences... The ramblings of an old duffer.... Less So.. ld: :floor:

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I think you need to get a 993 and join in the fun !