Welwynnick

Hi Guys,

I've spent the last 12 months fixing stuff, and only in the last week have I been able to even drive my car and play with it. The weather was nice and spring-like today, so I tried different combinations of wheels & tyres. I've owned four different W220's, with different wheels & tires - 16's, 17's, 18's & now staggered 18's - the Segin style below.



The 16's were super smooth and quiet-riding, while bigger tyres had more grip. Subjectively, it felt to me that it took 18's to give ABC suspension enough "work" to do, and that was quite a sweet spot, as long as I had the 45 profile tires. 40's and lower are rather harsh. It is a luxo barge after all - the party trick is being able to go very quickly AND very comfortably.

On my car, the fronts are 18x8 ET 44 with Michelin Pilot Sport 245/45/18's, and the rears are 18x9 ET 46 with Goodyear Eagle F1 265/40/18's. I've been sensitive to the noise and harshness that the bigger rears bring, so I've been reluctant to go any bigger. It makes me cringe when I hear people talk about fitting 20's and 22's on their cars - people are always asking how big they can go, how wide, how low? Bigger is always better. But why spoil a good compromise?

I drove a Lexus Soarer with active suspension for a long time, and with Supra Turbo wheels and tires fitted, its roll-free cornering was astonishingly grippy and agile. I always hoped my newer and faster S600 might bring back some of those memories, but good though it is for a luxo-barge, it was never quite the same.

However, when I bought the Lexus, it had the stock 225/55/16's, and again they never quite put enough "work" in to the chassis to make the most of the active suspension. It was only when I went up to the Supra's 235/45/17's that the potential was realised. Which got me wondering if there's more to the S600's chassis. I know the S65 & CL65 use 245/40 & 275/35 19's. Folks always say they're harsher than 18's, but I'm curious about the handling benefit.

I'm also curious about where the tire limits are. There are countless forum debates about moving up through 265's, 275's, 285's and even 295's. What profile to use? What wheel offset? But all this discussion centres around the rear wheels. Nomatter where I look, the fronts always top out at 245's, be it 245/45/18, 245/40/19 or 245/35/20. So it seems like accepted wisdom that 245 is as far as you can go at the front. Maybe larger tires rub something, or they're too noisy, or too harsh, or they stick out too far, or they corrupt the steering and cause kick-back, tramlining or shaking. Or wear and tear.

The are lots of reasons not to have over-size front tyres, but in the name of scienctific curiosity, I tried fitting my rear 265/40's on the front today (and ran the 245/45's at the rear).

Did they even fit? Yes.
Did they rub the wheel arch? Yes if the ABC fails, but not otherwise.
Did they foul the suspension on full steering lock? Nope.
Did they fill the wheel arch out, and did they look good? They sure did!
Time for a test drive then!

As I said, I'm sensitive to all the effects over over-large tires, but the dreaded pitfalls never really materialised. Sure, the ride was a little bit lumpier, given that I could isolate the contributions from the front and rear, but if anything it was quieter. The Pilot Sports that I have at the front are quite coarse and droning, something that I've proven by substituting them on several ocassions, and putting 265/40 Goodyears in place of the 245/45 Michelins was quite an improvement, much to my surprise.

And what about steering? Fat tires can spoil steering, but I never noticed the steam-roller effect (where the wheel only wants to roll forwards) and I didn't feel any tramlining over ridges, cambers or white lines. I've modified cars before - bad steering a show-stopper for me - and I was fearing the worst. Although I went up two sizes in width and dropped one size in profile, which is quite a significant change, and 265 is pretty big to go on the front of a refined luxury car, I never felt like I'd gone too far with the wheels & tires. They look big too!

I don't like staggered wheels & tires, as I like balance and commonality. I don't like front ends that push wide, and I like being able to fit any wheel on any corner. So if I can find two more 18x9 wheels and 265/40 tires, I rather like the idea of having the same all round.

Surprising result, really.

Nick

ibeforreal

My car came with 245/45/18 in the front and 275/40/18 in the rear from the factory. Although I would prefer the same size tires all around I have continued using the setup that came on the car. I suppose the Mercedes engineers know a lot more about the optimum fitting than I do. The car rides just like it is suppose to.

I have been told that I could change the rears to 265/40/18 but haven't ever tried them.

tusabes

The 265 40 18 will certainly fit in the front but you risk fender damage if cornering while the syspension is low (abc or airmatic ) . I've seen quite a few s classes with bent fender arches

Welwynnick

Yes, OK, but that happens with 245's as well (rather to my surprise). I've had the front suspension collapse on my car twice - first with a burst hose, second with a failed level sensor. In both cases a front wheel was buried in the wheel arch. I could still drive slowly, but I could only put on half a turn of lock, so there's no fail-safe with the stock tires, either.

In normal operation (big qualification there) ABC keeps the wheels out of the arches pretty well, and I'd never contemplate trying this without it. Firstly, there'd be no point - I'm only interested in using the roll-free cornering to capitalize on wider, low-profile tires. Secondly, Airmatic rolls a lot, and I couldn't depend on it to keep the wheels out of harm's way.

I'm not a fan of staggered wheels. Powerful RWD cars often have them, supposedly to put the power down better. However, you can also improve dynamic traction with softer rear (or firmer front) suspension. Of course, that corrupts the handling by increasing the cornering weight transfer at the front, and hence increases the understeer. But staggered wheels do exactly the same thing! All V12's suffer from the big, heavy engine, and I was hoping to get away from the nose-led balance.

Of course, staggered wheels look good - even 265's fill out the rear arches nicely. But they do a great job with the front arches too! The 8" & 9" wheels have about the same offset, so the latter spread about half an inch both inside and outside. Its not a big difference, but it fills the arches out nicely. I don't have before & afters, but here's a picture of my old NA S600 with 245's all round, followed by my TT with 265 front and 245 rear:

Nick

Quadrobenz

Given you are driving an S600 rear traction is important. I have 255x40-19 front and 285x35-19 rear tires on stock S65 wheels. They work without issues, hook up well and with proper inflation handle fine. A square setup on 18" wheels would be max 265 section width limited by the front clearance and would not provide adequate rear traction with the V12 Biturbo.

Welwynnick

Is your car a W220 or W221? I'm surprised that 285's fit OK, as 265's look very tight on mine. I'm tempted to fit 275/40/18 at the rear, but the wheel is really close at the corner of the arch/fender/bumper. To me, it looks like the 265's have more space around them at the front than they do at the rear.

I drove mine to work this morning with 265 front and 245 rear, and it wasn't bad at all. I have a section of fast, narrow, bumpy country road, and a good trustworthy chassis and steering is very important. Other than the steering being a bit heavier, it was fine. No rubbing, crashing into potholes, bump-steering or pulling and weaving. If anything, it was smoother and quieter just because I got the Michelins off the front.

Regarding traction, I think wide tires are needed for cornering, but don't help traction much. I had a puncture and ran the 245/45 spare on the rear one day. I turned the ESP off and did lots of stops and starts. Sometimes the left wheel spun, and sometimes the rear wheel spun, but it was toss-up overall. There really didn't seem to be any difference in traction between the 245 & 265's.

The way things are at the moment, I'd be really happy with 265/40's all round, and I'm itching to try 275/40's all round.

This little experiment has been much more sucessful than I expected, and its something that anyone can do (except I don't think I'd try 285's at the front, though!).

Nick

wallyp

Styling is really important to some people. I still remember laughing out loud several years ago when I saw an Oldsmobile Toronado with little tires on the front and big tires on the rear.

For those not familiar with the Toronado, it was a big powerful (for the time) front-wheel-drive General Motors car. Oddly enough, that was the same day that I saw a Corvair with a cheesy bolt-on hood scoop sitting proudly on the front trunk...

Quadrobenz

Having owned 1971 and 1975 Toronado's I can see the humor in that. My dad once owned a 1960 Corvair, even in the correct rear location it would be a lost cause.
I have a 2006 S65, it is a W220. The 285x35's on the rear are not a problem. The front is the issue. The 255x40-19 are the largest that will fit in a stock wheel and fender setup. I can make them rub slightly if the wheel is turned full lock and then hit the brakes. Since the car came with 19" wheels stock I have not tried 18" combo's.

tusabes

275 40 18 will fit in the rear, not sure about the front

Welwynnick

I'm pretty confident of being able to fit 275/40/18 at both ends. The challenge was actually being able to fit 275/40 on 19 x 9.5, or 275/35 on 20 x 10's. The reason is there are lots of people with 2006-on ML63's selling their AMG wheels to upgrade to something tasteless.



The AMG wheels have a simple, bold design, which I think would suit the W220. I think the Difda design is perfect, but most larger wheels have fussy designs with spokes running right to the rim, which makes them look larger than they are. Relative to an understated and fine-featured car, that makes them look unbalanced and over-large to my eye. The spokes on the ML63 wheels stop short of the rims, and I think they'd look better. They're also 20x10, which would be a fine challenge to fit.

They're normally fitted with 295/40's, but the only tyres I could conceivably fit are 275/35's, or amybe 275/30's (which have about the same envelope as 275/40/18). Based on current experience, I'd be very happy with 265/40/18 or 275/40/18 all round, but my sights are set higher than I'd have thought possible a week ago.

My S600 has a history of ambition:

EDIT 2: The first to run 275-35-19 tires at the front
EDIT: The first with an engine cooling pump for the inter-cooler
The first with an engine radiator for the IC heat exchanger.
The first with a custom programmable IC pump controller.
The first with an IC header tank for filling, bleeding, air/water separation & inspection.
The first with compression-jointed ABC hoses - replaceable in situ.
The first with fire-sleeved ABC hoses.
The first with full-length coil pack heat shields.
The first with uprated front strut bushes.
The first with uprated steering rack bushes.
I also rebuilt both turbos without moving the engine (not aware anyone has done that before).

Nick :-)

Quadrobenz

That is a really interesting list of improvements and repairs on your S600.
We know that 285x35-19 tires on stock (I think 9.5") wheels fit in the rear, therefor 285x30-20's will fit as well. That assumes the ML wheels have the same offset as the S wheels. On the front it may be possible to use a 275x35-20 on a 10" wheel with the proper offset. Based on how little spare clearance exists on my 255x45-19" on stock ( I think 8.5") wheels I would expect some interference. I am not sure about the stock wheel offsets but the front and rear offsets for the S class staggered wheel fitment are different. So if 4 identical 10x20" wheels are used either the front or rear offset will be incorrect. It may be correctable with spacers. I hope you are able to make it work.

Welwynnick

Those are huge tyres, measuring 723mm nominal diameter, compared with 245/45/18 (689mm), 265/40/18 (682mm) or 285/35/19 (697mm). Are you sure you didn't mean 245/40/19 (690mm) instead?

My 18 x 8 front wheels have 44mm offset, and the rear 18 x 9 are 46mm. I think your 19's are the same. The ML63 wheels are 46mm - a seller sent me a picture on my phone. I saw some 20 x 10.5" Brabus with ET 45, and some 20 x 9.5 that were 50. I think it all hinges around quite precise dimensions, down to the last few mm.

Nick

Quadrobenz

I had a slip of the finger on the size. I have 255x40-19's on the front. The car was delivered with 245x40-19's, but they were an extended load range tire. The offsets should be the same as the 18" wheel, I was estimating the width so if the 18's are 8" and 9" the 19's should be the same.

Welwynnick

Well, it looks like I just scored a set of AMG 19's on the 'bay.
19 x 8.5 with 245/40
19 x 9.5 with 275/35
Can't wait to try those on back to front!

Nick ;-)

Quadrobenz

Nick, outstanding! That is the stock S65 configuration. I just checked, the stock wheel widths are 8.5" front, 9.5" rear. Hopefully you will be pleased with the result.

Welwynnick

Well, looks who's feeling pleased with himself! Here in England we have lots of unfathomable expressions like smug, chuffed, happy as Larry, stoked. I don't know how well they translate to American, but you get the idea. I brought the AMG alloys home this morning and had them fitted almost before I got out the car.

To my surprise and delight, the 275/35 on 19/9.5 rears fitted perfectly both front and rear. They filled out the wheelarches brilliantly. I turned the wheels and jacked the car every way I could think of, and never got anything to foul. Then I took a few pictures to show the tighest clearance points, plus the tyre size - there's something very tangible about photographic evidence.

These wheels are 9.5" wide, and feeling my way around, I'd be pretty confident about fitting 10" wheels. If you look at the AlloyWheelsDirect website, you can see that Brabus realise you can fit 9.5's to both front and rear, but their front tyres only go up to 245/40/19 or 245/35/20. Could have tried harder.

http://www.alloywheelsdirect.net/inf.../mercedes-benz

So far, at the front I've fitted 245-45-18, 245-40-19, 265-40-18 and 275-35-19, so I think that means I can fit 275-30 on 20x10's as long as the offset is 45/46, but 275-35's may be too big. I took a short drive and felt a lot more rubber on the road (good and bad), the 35's extract a price in ride and refinement but I started to get back some of the old Lexus feeling. In particular, the extra grip made the difference between the ABC default and sport modes more pronounced; default was sloppy and poorly controlled, while sport kept proper control. I always thought you needed 245/45 tires to make the most of ABC, and 275's might make it even more worthwhile. Very worthwhile.

Nick

tusabes

Have you driven with those 275 35 19 on the front ?
Jacking the car up and looking for Interference is the first step but it's how the car settles down when loaded with passengers and going over bumps that will determine if it rubs while driving

Welwynnick

Sure have. I had quite a lot of mixed experience modding cars when I was younger, but based on lessons learned I tend to steer clear of that these days. One of the lessons was don't go overboard on wheel & tire sizes. It can be counter-productive, and you end up making a car worse rather than better.

I used to have a modded Rover 3500 - the bodyshell, propshaft and wiring loom were about the only original parts. It had a tuned V8 with Holley 390, heads, cams, headers, wheels, tyres and even a close-ratio gearbox. It also had lowered suspension, but still didn't handle too well. Frustrated by the mystery, I took it apart and found that the front struts had very long bump stops. They acted as progressive rate springs, but were spec'd for normal ride height. At my lower height, the car was riding on them all the time, so the front suspension was effectively much stiffer than it should have been. The result was the front end would wash out like an old front wheel drive car.

So I cut the bump stops in half, and the car was only riding on the springs again. This miraculously restored the front end grip, but now the corners of the tires started rubbing against the wheel arches, but not where you'd expect. Going round corners was never a problem, but they would rub in a straight line at high speed over dips and crests, simply by compressing the suspension. I didn't see that coming - its interesting what the whole package of a stock suspension system protects you against. Anyway, I rolled the front wheel arches and all was good. If a tire rubs, that's unacceptable, and I've made my mistakes (the V12TT keeps teaching some new ones though). But no, it didn't rub on the road.

A few observations though. I normally park wheels straight, but I went shopping and parallel parked in the street, leaving the car on full lock. Seeing 11" of rubber sticking out of the front wheel arch is quite a sight - SUVs aside very few cars have front tires that big - they usually stop at 245/255.

The other thing is the AMG wheels have a glossy paint finish all over. They're MUCH easier to clean than my old ones, and make the whole car look much cleaner and shinier. I wish I'd done this a long time ago.

Finally, I've just received a sheet of 15mm rubber to make some more front strut bushes. Last year I replaced the stock 5mm thick bushes with some new 10mm bushes, which took up the slack that worn strut top bushes had left, and the effect was to improve the damping performance over short bumps and broken surfaces. I didn't go quite far enough, and even the 10mm bushes were still slack. I'm going to cut some 15mm bushes today, and that should help control those big wheels over small bumps.

By the way, I also uprated the stock steering rack bushes with some very hard 95 Shore A bushes, which help to avoid that slight feeling of disconnected and uncontrolled steering. Most modern cars have hard-mounted racks, but I figured those bushes were there for a reason....



Nick

Welwynnick

Damn, gonna need another electric drill....

Other than that I've had the best weekend ever. I bought my current S600TT three years ago at 147,000 miles (and no warranty of course). Its been nothing but trouble, but I took it on as a challenge. I've nearly got it running right now, but its had a noisy transmission all that time, and its getting worse. An auto transmission specialist confirmed my fears last week. It did occurr to me that the fault might be the ABC accumulator, but solutions like that only present themselves in fairy tales. Something told me I was dreaming. In real life you pay.

I wondered how to prove the cause one way or the other, and decided to remove the auxillary belt and start the engine with the ABC pump disconnected. I was fully expecting to hear the familiar tired groaning and whining sound, but instead was greeted by what sounded like an electric motor revving up. So the transmission had been good all along.

Meanwhile, I'm convinced that the torque convertor has failed, but I didn't think it worthwhile just repairing that while the rest of the transmission was shot. But if the tranny is good, I can justify the TQ. What I've been missing is the 2:1 torque multiplication from standstill; my car needs more revs to launch from standstill than you'd expect for something with 600 lb-ft torque. It uses 2000rpm just to pull away from standstill with other traffic. Apparently its not uncommon, and I bet there are many V12TT owners out there who don't realise their TQ has failed, and the engine's grunt covers the missing torque. I think I'd rather have that 1200 lb-ft from standstill if I can, plus the reduced fuel consumption.

I bought this car as a sort of masochistic experiment, and perhaps a stepping stone to "good" one, but now I'm actually thinking about keeping it. Its now up to 158,000 and I'm not thinking of that as being a problem any more. What a great weekend! Loving this car more and more.

Nick

Welwynnick

Actually I just needed a bigger fuse for the drill...

The 15mm bushes took no time to cut and fit, and I'm driving them now. Surprisingly, they didn't make that much difference from 10mm - that's where the gain was. I think the key benefit is avoiding having the strut bush go slack when the weight is off the wheel, especially momentarily. And 10mm does that.

Sadly I hit a pothole this morning and trashed one of my lovely new 19" wheels & tyres. A sobering reminder of the downside of over-ambition.

Nomatter, I collected and fitted my new ABC pulsation damper tonight. What a difference! I've been listening to a nasty whiring, whining, moaning sound that accompanies the engine revving all the time for nearly three years, and now its gone. What a revelation. Now I understand what everyone else has been going on about, how their cars are so quiet. Now it wafts when I want it to waft, and it goes whooosh the rest of the time. What a result.

This car has given the impression of fragility since I bought it, and that seemed kind of understandable given the 158k miles. But now it feels smooth, tight and solid, gives me more confidence than I'd have thought possible, and feels ready for many more miles. Its like having a new car. Tomorrow I'm looking into having the torque convertor reconditioned.

Regarding the wheels, I had been heading headlong towards 4x20x10" rims, but I'm tempering that somewhat. 4x19x9.5 may be as far as I'd want to go, and 4x18x9 is probably quite a good compromise. That way I could stick with those gorgeous Difda alloys, giving an elegant and unassuming stock appearance, while concealling a big tire upgrade with 265 or 275/40's all round. Sounds very tempting.

Happy Nick

tusabes

18s look small these days

I'd go big and go 20x9.5 all around

Welwynnick

That was how I started off - wondering whether I could fit enormous wheels all round. Now I know the answer is yes, I'm not sure I want to. What I found is that width isn't as much a problem as I thought - you just need the right offset. Front wheels don't have to be 20-30mm narrower than rear wheels, they can safely be the same size, and there isn't too much to fear from the dynamic aspect.

20's aren't a problem in themselves - you just need the right profile %. If you go big, wide & lot profile, you simply pay the price in ride, noise and durability. I've been looking at used 20" wheels on ebay for a while, and I've been struck by the high proportion that have welded crack repairs. If you run 20's, you can be pretty sure of breaking a wheel.

I'm running 19's at the moment - 245/40 and 275/35. They look great, and the road noise isn't too bad, but the ride is very surface dependant. Its OK on good surfaces, but they react badly to broken surfaces. I assume 245/35 & 275/30 on 20's would be even worse, and I'm not sure I could put up with that.

Here's the interesting bit, though. I'm interested in the dynamics, and 265/40/18x9 grips and steers better than 245/40/19x8.5 at the front. 275/35/19 at the front are even better, but at the rear they add NOTHING except looks. They add nothing to grip, nothing to ride, nothing to noise, nothing to traction and nothing to steering.

So I think having 265-40-18 all round would be better than staggered 19's, in every respect except maybe looks. Take another look at post 4, picture 3 - the wide rear wheels fill the front arches well, even though they're "only" 9x18's. If you can run 4x18x9 (or 9.5), then 275-40's would probably be a good choice dynamically and aesthetically.

So I think 4 x 275/40/18x9 is a good conservative choice - better than staggered 19's.
And 4 x 275/35/19x9.5 is a good ambitious choice - almost certainly better than staggered 20's.
4 x 275/30/20x10 may well work, but its starting to look a bit extreme to me. Bragging rights only, I suspect, and nothing wrong with that.

The S600 isn't the ultimate luxury car, nor the ultimate sports saloon, but with the V12TT and ABC suspension, it gets unbeatably close to being both. So I think an iron fist in a velvet glove is it's raison d'etre - the best compromise between the two. I never realised how close it got until I replaced my pulsation damper this week, and upgrading the front wheels showed a little bit more of what ABC can do. With conventional passive suspension, the wider the tire and the lower the profile - the more the need to minimise camber angle change - paradoxical given the increased body roll. So bigger tires give dimishing returns - the more grip you provide, the less potential you can realise. Since ABC minimises dynamic camber change, it makes the most of all tyres - but especially wide tyres. Therefore I think an ABC car with say 4 x 275/40/18x9's may give better handling AND ride than ANY Airmatic car with ANY tires, or ANY ABC car with staggered tires. Get gready with the wheel size though - the brilliant compromise shifts too far, and that iron fist no longer wears a velvet glove.

Nick

Welwynnick

Right, this is where you think I'm going mad, but it's all in the name of science. I have two sets of staggered wheels - 18's and 19's. That gives me two rear 18x9's and two rear 19x9.5, so I don't have enough for four of anything. I could mix them with 18's at the front and 19's at the rear, but I wanted to prove the balanced front/rear configuration.

So I've done the only logical thing today, and fitted the 19x9.5's on one side and the 18x9's on the other. Yup, that's right, an asymmetric configuration. Bonkers or what? Downsides? The headlights pointed down a bit, but there was no pulling to the left or the right, and 275/35 had no traction advantage over 265/40, so I just wanted to try the handling. I'm the UK, and I like driving fast (clockwise!) round all the roundabouts we have here. The 19's were on the left so they could take the strain in clockwise turns.

Just considering the front wheels for the moment: 245/45/18 are a good compromise for a luxury car, but they feel overwhelmed by the weight of that V12 engine when pressing on. It can feel like a fight to get round fast corners. The 245/40/19's are a bit better - more grip but no better balance or agility. The 265/40/18's are better still, and feel like a good fit for the car's potential. They're still a bit soft and comfortable, but they make for a good compromise.

Having 275/35/19 FL & RL was a step forwards though. The chassis was improved, difficult to describe, but sort of coming alive. Grip was huge, but all the other subjective things were improved as well. The car felt lighter, like it had lost weight rather than gained grip. It was agile and changed direction better, but without being twitchy or unstable. There was less feeling of hauling the front end round the corner, so despite that big engine, it was less nose-heavy. Even cornering hard, the tires weren't overwhelmed, and didn't scrub or slide their way round. It kind of felt like carving a great turn on skis. You could say it was cornering on rails, but in a fluid and fun way. The tires just dug in and stuck to the line. For the first time, it reminded me of my wonderful old Lexus, with much of the talent but few of the downsides - the noise, harshness, bump-steer and tram-lining. Yes the ride was firm over broken surfaces, almost like the tires were solid rubber rather than pneumatic, but it wasn't too bad, and the road noise was reasonably low.

When driving fast down a heavily undulating road in a straight line, when the suspension goes from full bump to full rebound, I thought I heard the exhaust scrape for a second, but I now think I have a slight tire rub, so I'll investigate that in the daylight. That aside, I'm now officially smitten with this car. And I need two more 19x9.5's.

Nick

Edit:
Quick update. I took the wheels back off, had a good look round, and found the rubbing.
Guess where it was ....... front wheel arch? Nope.
It was the back of the rear wheel arch, at the corner of the bumper.
I think that's quite common, and was easily attended to with some side cutters.
My initial impression was that 275's had more room in the front arches than in the rear, and so it was.

Welwynnick

Some interesting stuff (for me anyway). The 19's drive as if they're heavier wheels, landing heavily into potholes, thumping and crashing around. So I weighted them all:

245/45 on 18x8: 23kg =50 lb
265/40 on 18x9: 23kg = 50 lb
245/40 on 19x8.5: 25kg = 55 lb
275/35 on 19x9.5: 25kg = 55 lb

That was interesting. Diameter makes all the difference, but width makes virtually none.
Now, the front brakes weigh about 30 lb, plus about 10 lb for the calipers and maybe 20 lb for the upright.
That means the 19" wheels increase the unsprung weight from approx 110 lb to 115 lb, which isn't that great a difference. The ride comfort seems to be a function of profile rather than anything else.

Nick

wallyp

Tire stiffness is a major factor, both sidewall and tread. Stiff tire=rough ride. Soft tire=high probability of tire/wheel damage on potholes and curbs.

Everything in life is a trade-off, but few things have more trade-offs than automobile tires.