Why isn't the Pneumatic Tyre used for suspension?

[some bloke]

TL;DR

to reduce unsprung weight, why isn't the pneumatic tyre developed for use in isolation?

I've been contemplating the design of a motorcycle, and I've been reading up on the sprung & unsprung weight thing, how you want to minimise unsprung weight (IE, the part of the vehicle which moves with the road, the wheel and lower half of the suspension) to improve handling.

This got me wondering on how to minimise unsprung weight, and the seemingly simple answer would be to use high-profile pneumatic tyres which are designed so that the only part of the "suspension" which moves is the rubber of the tyre, thus moving the entire weight of the wheel into the "sprung weight" category. It would also reduce wear (no suspension, no wear) and weight (no heavy springs).

I have a precedent for pneumatic tyre suspension, as I have a Harley and a Suzuki bandit, and the Harley has rubbish suspension and massively fat tyres, and yet it seems to soak up the bumps a lot nicer than the bandit. the tyres seem to absorb most of the impacts.

Is there any reason why pneumatic tyres have not been developed to account for 100% of a vehicles suspension?

Cheers,

 

[ChemAir]

One is the amount of heat generated in the tire sidewall. Rubber flexing a tremendous amount will get very hot. Tire failure due to overload (that causes excessive sidewall flex), on trailers is very common.

Another is reduced fuel efficiency. A soft, tall, tire sidewall has more rolling resistance than a rigid tire. This is also part of the heat problem above.

Usually, the tire is there to make controlled contact with the ground. Other suspension parts, that can have a larger, more controlled range of motion (springs, shocks) are better suited to controlling ride smoothness. Shock absorbers can have different rates of compression and extension, which is not really an option for a rolling tire, that will perform differently depending on how its inflated.

I have a precedent for pneumatic tyre suspension, as I have a Harley and a Suzuki bandit, and the Harley has rubbish suspension and massively fat tyres, and yet it seems to soak up the bumps a lot nicer than the bandit. the tyres seem to absorb most of the impacts.

Ride quality is a combination of a lot of things, including car weight , spring rate, and shock tuning. A heavier vehicle with lousy suspension may "feel" softer than another. Take the same vehicle and try and operate in a "panic mode", and attempt to make a rapid direction change, stop suddenly, etc... The softer the suspension, generally the less controlled a quick maneuver will feel. Most sport cars have a ride that could be considered harsh, but could also be called nimble, as they tend to be able to start, stop, and steer very quickly and accurately. This would be much more complicated with a mushy connection to the ground.

 

[OCR]

I have a precedent for pneumatic tyre suspension. . .

Yeah, so do I. . . .

Lol. . .

.

 

[Mark44]

I have a precedent for pneumatic tyre suspension, as I have a Harley and a Suzuki bandit, and the Harley has rubbish suspension

I'll go you one better.
No suspension on the rear wheel, and laughably little on the front, with a set of springs but no shock. Rear tire is fairly low pressure, at about 20 psi. The saving grace is that seatpost is sprung, and takes up a lot of the bumps. This is my 1948 Harley Davidson FL, common referred to as a Panhead.

 

[Ketch22]

As Chemair pointed out there is a lot more to vehicle comfort than just softness. I also rode a large Harley for many years. One of mine was a chopper that was converted to a "strut" rear suspension where the rear shocks were removed and replaced by a rigid post. It rode wonderful on a straight highway. I was even able to beat a friend on his early Kawasaki ninja from central California to Yuma Arizona. This was due to the large soft tire acting predictably at speed on the straight drive. The same two bikes with the same two drivers he always was faster in other areas where the highway was not straight. His bike was consistently more stable in the corners.