Airless tires, what do you think ??

[Accumulator]

We don`t mind the harsher ride from low-profile tires, but the roads are just too bad and replacing/repairing wheels and tires got old.

There are higher-profile tires that have stiff sidwalls, but the ones I`m familiar with have some real shortcomings (e.g., Goodyear RSA ).

Yeah on the unsprung weight...the steel wheels on the Crown Vic weigh a ton and swapping them for alloys would improve some things dramatically (did on the last one). But it`s nice to have one vehicle that can simply go anywhere we want to go without having to worry about damaging a wheel or a tire (or being too low), well...two vehicles like that, counting the old Tahoe (75 series tires).

Same thing with suspensions...we don`t mind stiff, we simply need more ground clearance to be able to get around without scraping. The cars that couldn`t be used like normal vehicles were swell with their track day-level handling, and they sure looked neat, but they were so impractical that we simply don`t miss them. I`ll probably say the same thing about the S8 if/when I get rid of it, I never use the thing any more because it`s too extreme for running errands, even though it`s almost Camry-like-practical compared to so many cars. Heh heh, back when I had the Mallett, they assumed their customers would just replace the front airdam regularly!

 

[Dan]

Depending on the type of wheel you can loose weight or stay the same in weight thus being able to stop the same or quicker. Most stock wheels are made cheap as possible while still being sturdy (heavy). I went from a 18’ to a 20’ and they were lighter.

Modded suspension too to get better cornering. Same with those big SUV wheels. Unless their getting cheap not much difference in rotating mass. With those Lo pro tires the definetly ride rougher but still better than most cars.


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You certainly can get big wheels that are light, but most aftermarket wheels are big and heavy. It really varies by car, but some sportier cars actually come with some pretty light wheels. I know because I`ve priced out replacement and had to look at wheels north of $500 each to be lighter than the factory ones.

 

[The Driver]

You don’t need a sidewall to have a stiff tire on a airless tire.

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That was my point, you need some flex under extreme loads. The point over having a lower tire pressure (Besides the heat/expansion issue) when tracking is so when under load the tire shifts and puts more rubber to the road when pulling hard lateral G`s. You NEED give, otherwise, you`ll slide right off the track.

 

[Desertnate]

I think the break-even point for a passenger vehicle is around 19" before they start getting heavier.

My car comes with 18" wheels. When I was looking for my summer wheels, the significant weight savings was found by going down to 17". I could have made some crazy weight savings by going smaller. Finding a 19" wheel which was lighter than my OEM 18" was rather difficult. Most were equalt to, or heavier than OEM, but there were a few (very few!) very expensive wheels available from reputable brands. Going up to 20" and the wheels were all much heavier. I had no intentions to go over 19", but it was entertaining to look at 20"

In the end, I stayed at the OEM size and saved weight for a reasonable cost from a highly reputable brand. At my local autocross the only fast cars running anything over 18`s were those who had to go larger due to brake clearance issues.

 

[The Driver]

You don’t need a sidewall to have a stiff tire on a airless tire.

They have been around 15+ years in the AG and construction industry. We used them on projects that we where tearing up tires on and normal tires on other. We had issues with excessive tire hope when we where putting the tire under a height load situation on airless tires. Due to the ribs flexing and springing back.


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Yup, probably the dumbest thing you can do besides run crazy camber to look "Cool" as it were. Personally I`ll never run a bologna skin tire, I know someone who is a paraplegic because they ran 20 sidewalls on 20 inch rims, wound up, blowing out, sliding into a tree at high speed. 35+ sidewall for me not anything lower.

 

[Accumulator]

That was my point, you need some flex under extreme loads. The point over having a lower tire pressure (Besides the heat/expansion issue) when tracking is so when under load the tire shifts and puts more rubber to the road when pulling hard lateral G`s. You NEED give, otherwise, you`ll slide right off the track.

I find it interesting how some high-perf vehicles handle so great with lower pressures since that`s so foreign to my experiences with the vehicles I usually drive and completely opposite of how it works with the vehicles I was trained in.

IME, sidewall flex in big heavy vehicles is undesirable because of the risk of rim-to-pavement contact. Beyond "undesirable" really, as it`s a life/death issue.

When VDI was testing the effects of psi diffs in Crown Vics they had to suspend testing around 35psi because the sidewalls were flexing so much that the rim was gonna touch the pavement (with predictably fatal results). Looking at the pix, it was a hair`s breadth from contacting. When you track/AutoX those kind of cars and/or SUVs like my (old) Tahoe, anything below 42psi is a handicap, and when hard use raised that 42 up to something really high, it was never a problem and they never lowered the pressure to compensate. I can`t imagine how high the pressures got in the Suburbans we were running (especially the armored one, that thing weighed a *lot*), never thought to check them after they heated up.

In my area, underinflated tires are responsible for countless rollovers...it happens *all the time*, especially with SUVs. When you see how the rim(s) gouged the pavement and the tire got peeled off, it`s obvious what happened. All those SUVs/CUVs on their roofs...on public streets with moderate speed limits too. The psi that give a comfortable ride and even wear isn`t high enough for emergency maneuvers.

 

[Desertnate]

I find it interesting how some high-perf vehicles handle so great with lower pressures since that`s so foreign to my experiences with the vehicles I usually drive and completely opposite of how it works with the vehicles I was trained in.

I think a lot of this comes down to how the suspension and the tire work together to keep the largest contact patch possible on the ground. With a large vehicle with tall, soft(ish) sidewalls, in order to keep the tire from squashing and rolling on the sidewall like you described, you`ll need to put quite a bit of air in the tire to ensure the the tire tread stays as flat as possible on the ground. Even at really high pressures, the tire is still going to flex due to the weight of the vehicle. In a smaller, lower, lighter, car the tires aren`t under nearly the same levels of stress and therefore, if you over-inflate them, they don`t deform properly under cornering loads and won`t get the needed amount of grip. It might actually make the contact patch smaller.

Example: Two weekends ago I was running in our local SCCA autocross. I ended up parked next to another, more experienced GTI owner on the grid. He and a couple other veterans of driving FWD cars were telling me how they could combat understeer by simply raising the rear tire pressure above normal levels. This made the tires deform/grip less and allow the back end to purposely slip around a bit and rotate quicker in turns.

Not sure if it would work in reverse for a RWD car, e.g. if an oversteer monster could be tamed by lowering the rear pressures and the raising the fronts to create a little more slip in the front.

 

[Dan]

I think a lot of this comes down to how the suspension and the tire work together to keep the largest contact patch possible on the ground. With a large vehicle with tall, soft(ish) sidewalls, in order to keep the tire from squashing and rolling on the sidewall like you described, you`ll need to put quite a bit of air in the tire to ensure the the tire tread stays as flat as possible on the ground. Even at really high pressures, the tire is still going to flex due to the weight of the vehicle. In a smaller, lower, lighter, car the tires aren`t under nearly the same levels of stress and therefore, if you over-inflate them, they don`t deform properly under cornering loads and won`t get the needed amount of grip. It might actually make the contact patch smaller.

Example: Two weekends ago I was running in our local SCCA autocross. I ended up parked next to another, more experienced GTI owner on the grid. He and a couple other veterans of driving FWD cars were telling me how they could combat understeer by simply raising the rear tire pressure above normal levels. This made the tires deform/grip less and allow the back end to purposely slip around a bit and rotate quicker in turns.

Not sure if it would work in reverse for a RWD car, e.g. if an oversteer monster could be tamed by lowering the rear pressures and the raising the fronts to create a little more slip in the front.

That`s part of the reason some cars have different pressure for different axles.

 

[RaskyR1]

Is that conjecture? Because I don`t see anything from Michelin that indicates that: https://michelinmedia.com/michelin-uptis/

This concept from Michelin has been around for 15 years or so.

You would also have major tire balance issues in states with freezing temps/snow if there were no side wall on the released version.

 

[Desertnate]

You would also have major tire balance issues in states with freezing temps/snow if there were no side wall on the released version.

That`s a great point I hadn`t even thought of!

I know how much my wheel well fill up with snow and ice, I couldn`t imagine that junk getting into the voids in that tire. Not only would it be a balance issue, but it would prevent the wheel from flexing properly as well. Those voids being open to the air would keep the tire from warming up too, so you couldn`t count on any sort of heat build up to melt anything that gets trapped. Some would break loose I`m sure through vibration on the road, but not all of it if things filled up and became really solid.

 

[Accumulator]

Desertnate- Right about the smaller/lighter vehicles using lower pressures. I ran lower pressures in the sports cars than I do in what I drive these days.

And yeah, as Dan said you can tweak handling characteristics a bit by playing with front-rear diffs, but if something *really* oversteers drastically (and I don`t mean just the way an old Porsche will) IMO it`s not set up right. As they say, "cars don`t oversteer, *drivers* do". Well, at least with remotely modern vehicles.

 

[The Driver]

Sway bar size and ratio will also dictate steering characteristics very heavily. Increasing the diameter Ie my car from 20mm to 25mm will increase handling but messing with the ratio can increase oversteer Ex.putting a ticker swaybar in the front over the rear and the opposite is also true. Drivetrain also has a role - FWD (Torque steer) AWD (Oversteer/ F&R Split ratios) 4WD and RWD.

 

[Accumulator]

The Driver- Heh heh, yeah...the original owner of my previous Crown Vic had totally [screwed] it up trying to "upgrade" it in just that way (HUGE rear bar with poly + a very small front one with rubber). Worked fine up to about 6/10ths but then it was simply a Drift Car, had to really back off in the wet. He freaked when I demonstrated (and controlled ) that, having never really pushed the car. A slightly bigger front bar with poly bushings fixed everything just fine. (I do like Crown Vics sorta "loose", hate when they just understeer like stock.)

And TBH, the way I like to set those cars up renders them less stable at >~130mph, but I don`t go there enough to care. Always some kind of trade-off.

Great point about how different AWD can be! My Audis and my Subies were totally different, and the 4WD Tahoe is different from how the AWD Yukon XLD was. I`ve never driven a FWD vehicle that I liked very much (handling-wise), but I hear some of today`s FWD cars are really good.

 

[Coleroad]

Then it also makes a difference what kind of track. A tight slow corner takes a different setup than fast flowing corners.

Take a car with McPherson struts, and stick a big front bar in will actually reduce understeer in tight corners. In fast flowing turns it increases understeer.

Its not not a static setup. It changes based on all parameters including driving style.

 

[Accumulator]

Coleroad- Yes indeed, sorta a case of finding the best overall compromise (at least for street cars).

 

[Desertnate]

I`ve never driven a FWD vehicle that I liked very much (handling-wise), but I hear some of today`s FWD cars are really good.

I own a GTI and have driven a few other "good handling" FWD cars and I`d still take a RWD over them without question. I also hear the Civic Type R is probably the best handling FWD car ever, but I haven`t had a chance to drive one and doubt it would change my mind.

I thought I had made peace with the idea of a good handling FWD car until I recently test drove an M2 Competition recently. Simply reminded me of how limited FWD really is when driven with enthusiasm. Not because of the power huge power difference, but on dynamics and balance alone. You could have put a lawn mower engine in the M2 and I`d still like it better than any FWD car.

 

[Accumulator]

Desertnate- Agree completely. And yeah, it does sound like that Honda is All That, but I could never live with the looks.

I bet your GTI is still a great car, as were my CRX`s. I gotta admit that whenever I found the "FWD limits" I was doing stupid [stuff] that I shouldn`t have been doing on the street. And FWIW, a pal of mine (Driving School instructor, serious SCCA competitor) used to *lap* cars like `vettes at MidOhio..in the same CRX he drove to work every day. As they say, "it`s not about the bike".

 

[Desertnate]

Great discussion...even if we`ve left airless tires behind. I love nerding out on these kinds of topics.

Desertnate- Agree completely. And yeah, it does sound like that Honda is All That, but I could never live with the looks.

I bet your GTI is still a great car, as were my CRX`s. I gotta admit that whenever I found the "FWD limits" I was doing stupid [stuff] that I shouldn`t have been doing on the street. And FWIW, a pal of mine (Driving School instructor, serious SCCA competitor) used to *lap* cars like `vettes at MidOhio..in the same CRX he drove to work every day. As they say, "it`s not about the bike".

CRX`s? Wow, those were great cars. I really wish I could have owned one in their prime.

Despite the GTI being a great handling car, I have come close enough to the limits on a remote backroad to dislike the understeer that starts to set in. On the track it wasn`t too bad, but at an autocross, I REALLY notice it on the tighter turns. Like your friend, there is a guy in our local SCCA Solo chapter driving a GTI who was in the top 10% based on raw score and killed everyone once the index was calculated. It`s amazing what can be accomplished with the right driver.

 

[Accumulator]

Great discussion...even if we`ve left airless tires behind. I love nerding out on these kinds of topics...

Heh heh, glad it`s not just me

CRX`s? Wow, those were great cars. I really wish I could have owned one in their prime.

MAYBE....but the early carb`ed one had vaporlock (or somesuch) issues that got really problematic, like..." it sat in the driveway while I borrowed a car" problematic and you had to turn off the A/C now and then when you needed power. The Si with FI was fine in those regards, and it was really fun. But it *had* to have good snows in the winter or it was terminal understeer at any speed in the snow.

But yeah, great cars for a young guy, same as today`s Sis undoubtedly are for today`s young folks.

Despite the GTI being a great handling car, I have come close enough to the limits on a remote backroad to dislike the understeer that starts to set in. On the track it wasn`t too bad, but at an autocross, I REALLY notice it on the tighter turns.

Heh heh, that sounds just like something I`d say

Like your friend, there is a guy in our local SCCA Solo chapter driving a GTI who was in the top 10% based on raw score and killed everyone once the index was calculated...

And I bet he loves every minute he spends in that car

Ya know, one of the most fun driving exercises for me was being pursued by somebody in a better car. Real sense of accomplishment stuff there.

It`s amazing what can be accomplished with the right driver.

Yes indeed.