Bicycle tire with compression amplification

A solid, monolithic bicycle tire made of urethane rubber with a cured hardness of from 60 to 70 Durometer A. The tire is formed with a pair of laterally spaced bead shoulders that seat on the bead seats of the wheel rim, and is generally triangular in cross-section, with radially outwardly converging, slightly concave side walls that merge into a relatively narrow tread section. A circumferential, arch-shaped tunnel is formed in the inner side of the tire between the bead shoulders, and the material between the tunnel and the converging outer surfaces forms narrow, inwardly inclined side walls that are compressed when pressure is applied radially inwardly against the tread. The inclination of the side walls results in a substantial amplification of the deflection of the tire under impact loads, as compared to the deflection of similar-thickness side walls that are not inclined, but instead, are parallel to one another. As the tire is compressed under load, the side walls tend to collapse inwardly, causing the bead shoulders to grip the wheel rim with increasing force, thereby resisting any tendency of the bead shoulders to climb up over the edge of the wheel rim. The tire is also held firmly on the rim by means of a circumferential bead-locking insert that is placed in the bottom of the wheel rim before the tire is mounted. Foot extensions at the bottom edges of the tire side walls are then pressed down into the space between the wheel rim and the insert, and the insert acts to hold the foot extension and bead shoulder firmly against the wheel rim so as to resist any tendency of the foot extension or bead shoulder to climb.

BACKGROUND OF THE INVENTION 
The present invention pertains generally to vehicle tires, and more 
particularly to a new and improved form of tire of the type used primarily 
on bicycles, wheel chairs, and the like. 
Heretofore, the only type of bicycle tire available on the market has been 
the pneumatic tire, which is constructed much like an automobile tire, 
with a cord carcass and steel wire beads. Most bicycle tires are of the 
tube type, and generally, two types of tubes are available: the relatively 
thin, regular tube, and the considerably heavier, so-called thorn-proof 
tube. 
These pneumatic bicycle tires have a number of disadvantages. They are 
subject to blow-outs, which cause serious safety hazards. Because of the 
thin tread, they wear out quickly and have a relatively short service 
life. Also, as a result of the thin tread, they are readily punctured by 
thorns and/or small pieces of glass or nails. They lose air and become 
under-inflated, and as a result they become extremely difficult to ride. 
It is necessary to carry a tire pump to keep the tires properly inflated, 
or else make frequent trips to service stations to inflate the tires with 
their compressed air. The tires are easily cut, and cannot be repaired. 
They are expensive to manufacture because of the fact that a considerable 
amount of skilled labor and expensive tooling is required to make the 
tire. And finally, they do not contribute to the visibility of the 
bicycle, except when reflective strips are cemented to the side walls of 
the tires. 
There have been attempts to overcome some of the above disadvantages by 
filling the tires with a mixture of two liquid urethane resins, which 
react, or cure, to form a solid, resilient elastomeric tire. Such 
elastomeric tire fillings have been used successfully in automobile tires 
for a number of years, and two examples of this material are Permatire, 
made by Arnco, of Marina del Rey, Calif., and TireFill, made by Indpol, of 
Cucamonga, Calif. While bicycle tires filled solidly with urethane rubber 
eliminate some of the disadvantages of pneumatic tires, such as blow-outs, 
slow leaks, and underinflation, they have a number of disadvantages of 
their own. One serious disadvantage is that the urethane-filled tire is 
extremely heavy, weighing up to five or six pounds per tire, which makes a 
total weight penalty of 10 to 12 pounds for the bicycle. This is because 
it takes from 3 to 4 pounds of urethane rubber to fill the tire. Another 
disadvantage is that the ride is harder, and rolling resistance is 
increased. Ride comfort and rolling resistance are mutually antagonistic 
quantities, and it is necessary to make a compromise between them, which 
usually results in a fairly hard ride with a moderate amount of rolling 
resistance. 
A more serious problem with filled tires is that they cannot be removed 
from the wheel rims for spoke repairs or adjustment, without damaging the 
tire. This is because the tire is filled all the way to the full depth of 
the rim, which greatly reduces the minimum diameter that has to be pulled 
over the rim of the wheel. As a result, the only way the tire can be 
removed is by cutting it, and this destroys the tire. 
Another major problem with filled bicycle tires is that wheel rims are 
easily damaged on sharp impact, due to the incompressibility of the fill 
material, which extends directly to the rim. The solid fill material has 
no place to go, and therefore a sharp impact blow against the tire causes 
a highly concentrated stress to be applied directly to the rim, causing 
damage. 
The tire filling process is slow, difficult, expensive and unreliable when 
applied to bicycle tires. It requires equipment to handle liquid urethane 
and operators well-trained in handling the polymers to do this filling job 
right. Bike shops are not set up to do such jobs, and most of them would 
decline to go into the tire-filling business because of the many problems 
and relatively small volume of business. 
Recently, efforts have been made to develop a solid, monolithic tire of 
urethane elastomer having a tunnel on the inside to allow the tire to 
compress under impact loads. However, this has proved to be a difficult 
thing to achieve, as a tire made of a urethane soft enough to give a 
comfortable ride, turns out to have unsatisfactory resistance to wear and 
cuts, while urethane hard enough to give good resistance to wear and cuts 
gives a hard, uncomfortable ride. 
One of the more difficult problems with a solid, monolithic tire of 
urethane elastomer having a tunnel on the inside, is the tendency of the 
tires to come off the rims, even though they are glued to the rim with an 
adhesive. This is due, in part, to the fact that the only thing holding 
the tire bead shoulders against the rim is the adhesive bond, which is 
frequently less than perfect owing to the difficulty of getting a uniform 
film of adhesive on the mating surfaces. Another contributing factor is 
the elasticity of the unreinforced elastomer, which allows the tire to 
stretch under certain loading conditions. The problem is particularly 
acute when a side thrust is applied to the tire, as when cornering or 
bumping against a curb. 
SUMMARY OF THE INVENTION 
The primary object of the present invention is to provide a bicycle tire 
which overcomes all of the disadvantages of pneumatic bicycle tires, as 
well as the disadvantages of filled bicycle tires, and which has none of 
the shortcomings of prior solid urethane tires with a tunnel on the 
inside. 
More specifically, it is an object of the invention to provide a solid, 
monolithic bicycle tire of urethane elastomer of approximately 70 
Durometer A, with no tire bead or fabric reinforcement, which has 
excellent ride quality, comparable to a pneumatic tire, and rolling 
resistance equal to that of a properly inflated pneumatic tire. To obtain 
this superior ride quality, the tire is made with a novel cross-sectional 
configuration, including an arch-shaped tunnel and converging, slightly 
concave, side walls that provide a unique effect of compression 
amplification, that allows the tire to deflect under impact loads to a far 
greater extent than would otherwise be the case. 
Another important object of the invention is to provide a tire of the type 
described, together with an associated bead-locking insert, which 
cooperate to lock the tire to the wheel rim so that it is virtually 
impossible for the tire to come off the rim under any normal load 
condition. A flexible adhesive may also be used to bond the bead shoulders 
to the wheel rim so as to provide additional holding power, but the 
primary purpose of the adhesive is to prevent the tire from "growing" in 
diameter by centrifugal force at high speed. 
A further object of the invention is to provide a tire that is lightweight, 
long-lasting, easily removable and replaceable, fits most standard size 
wheel rims, and is easily repairable. The tread portion of the tire is 
relatively thick, and a substantial portion of the tread thickness can be 
utilized for wear purposes. The urethane elastomer can be pigmented with 
Day-Glo pigments for improved bicycle visibility, for safety. The tire is 
lighter in weight than a pneumatic tire with tube, and can easily be 
stretched over the wheel rim to mount the tire or remove it. This allows 
for easy removal of the tire for spoke adjustment and repair. 
Finally, the tire is easily manufactured with a minimum of hand labor, 
using liquid, room-temperature-curing elastomers. Automatic machinery can 
be used to make the tires, as there is no hand lay-up required. The 
room-temperature cure material requires little or no energy, and the tire 
can come out of the mold in as little as 3 to 5 minutes. 
These and other objects and advantages of the present invention will become 
apparent to those skilled in the art from the following detailed 
description of the preferred embodiment thereof, with reference to the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the drawings, a tire embodying the invention is shown in FIG. 1 and 
designated in its entirely by the reference numeral 10. The tire is shown 
mounted on a bicycle wheel rim 12. The wheel rim 12 is conventional, and 
is usually made of sheet-metal, roll-formed to the configuration shown in 
the drawings. The outer skin of the wheel rim forms flanks 14, which merge 
into a crown 16 that forms the inside periphery of the wheel. At their 
outer edges, the flanks 14 are rolled inwardly to form a bead flange 18, 
which merges into the inner side walls 20 of the rim. Sidewalls 20 
terminate in shoulders 22 which merge with a shallow channel 24 forming 
the bottom of the wheel rim. 
The tire 10 is a solid, monolithic casting of urethane rubber, with a cured 
hardness of 70 Durometer A. The tire body is made by pouring liquid 
urethen resin into a mold, said resin being catalyzed to cure in 3 to 5 
minutes at room temperature (i.e. from 80.degree. to 100.degree. F.), 
after which the tire is removed from the mold as a finished product, with 
no further processing being required. 
The cross-sectional configuration of the tire is quite unconventional, as 
is immediately apparent from the drawings. Basically V-shaped in 
cross-section, the tire has sloping, outwardly converging side walls 26, 
the outer surfaces 28 of which are concave, and these side walls come 
together to form a narrow outer portion 30 having a tread pattern 32 on 
its outer peripheral surface. 
Formed in the inside of the tire body 10 is an arch-shaped tunnel 34, the 
lower side surfaces 36 of which are substantially parallel to one another. 
At the bottom extremity of the tunnel the sides turn outwardly to form the 
undersides of beads 38. 
At their lower ends, the side walls 26 thicken and divide, forming a 
shoulder 40 that juts out over the bead flange 18, and the bead 38 that 
extends down into the wheel rim 12 in contact with side wall 20. Between 
the shoulder 40 and bead 38 is a curved bead shoulder 42 that seats on the 
bead flange 18. Three concentric grooves 44 are formed in the outer 
surfaces of the beads 38, and these provide annular cavities between the 
side wall 20 and bead 38 to receive liquid adhesive cement so as to form 
cement rings of a predetermined thickness. The grooves 44 serve to prevent 
the cement from squeezing out, and relatively thick rings of elastic 
adhesive allow for a greater amount of stretch of the cement before it 
yields, and in the process of stretching, it spreads the load over a wider 
area. As a result, a low bonding strength adhesive can be used, which 
still exhibits an adequate overall bonding strength for bonding the tire 
to the rim. The cement may be applied after the tire has been mounted on 
the rim by merely pressing the sides of the tire inwardly to open up a 
slight gap between the bead 38 and side wall 20, and squeezing a liquid 
cement from a tube into the space, repeating the process all the way 
around the tire, on both sides thereof. The use of cement is primarily to 
prevent the tire from "growing" in diameter by centrifugal force at high 
speeds, and the majority of bike riders will not find it necessary to use 
cement, as the tire does not require the cement to hold it on the rim 
under normal conditions. 
The tire 10 is prevented from pulling off the rim 12 by means of a bead 
lock insert 46, which is placed in the bottom of the wheel rim before the 
tire is mounted. The insert 46 is preferably made of a resilient plastic, 
such as PVC, polypropylene, or nylon, and is preferably H-shaped in 
cross-section, with upper flanges 48, lower flanges 50, and a transverse 
web 52. Projecting laterally outward from the top edges of upper flanges 
48 on the outside thereof are ridges 54, which seat in shallow grooves 56 
formed in the tunnel sides 36. The top sides of the ridges 54 slope 
downwardly, as shown in FIG. 1, to facilitate pushing the beads 38 down 
into the space between the upper flanges 48 of the insert and the side 
walls 20 of the wheel rim. 
The insert 46 may conveniently be formed by extrusion to make a continuous 
helical coil which is then cut into lengths to form split rings, each of 
which is adapted to fit into a wheel rim, as shown, with its two ends 
spaced only a fraction of an inch apart. These ends are joined together by 
any suitable means (not shown) to hold the insert in the rim with the 
bottom edges of lower flanges 50 seated on the channel 24. 
To mount the tire on the wheel rim, the tire 10 is first lubricated with 
soft soap, or soapy water, and is then stretched over the rim, pulling the 
beads 38 down into the spaces between the upper flanges 48 and the side 
walls 20. The material of insert 46 is resilient, and upper flanges 48 
yield inwardly to allow the beads 38 to pass over the ridges 54, until the 
ridges 54 snap down into the grooves 56. The beads 38 are then held firmly 
against the side walls 20 by the upper flanges 48 of the insert, and this 
prevents the beads from climbing up over the bead flange 18. If it is 
desired to cement the beads to the side walls 20, this can be done after 
first rinsing the tire and rim and allowing it to dry. 
What makes this tire design unique is the compression amplification that is 
obtained. The term "compression amplification" might be defined as the 
deflection of the tread surface 32 under load, as compared to the apparent 
compression of the side walls 26. Actually, urethane elastomer is not 
compressible, but instead, distorts under compression, and then regains 
its original shape when the load is removed. Thus, when the side walls 26 
are placed under a compressive load, the height of the side wall shortens, 
and its width thickens. FIGS. 2 and 3 illustrate this point. In FIG. 3, a 
triangle formed by sides A, B.sub.1 and C.sub.1 represents the force 
vectors involved. Side A is fixed in dimensions, by the essentially 
unyielding sides of the wheel rim. Side B.sub.1 represents the unloaded 
height of the tire, and side C.sub.1 represents the uncompressed sidewall 
26 of the tire. In FIG. 3, dimension B.sub.2 shows the height of the tire 
when heavily loaded, and side C.sub.2 represents the compressed sidewall 
26 of the tire. The difference between B.sub.1 and B.sub.2 represents the 
total deflection (i.e., compression) of the tire under load for an amount 
of compression of the side walls 26 represented by C.sub.1 -C.sub.2. 
The dimension B is not directly supported, but is actually supported at an 
angle by the two force vectors C, which are determined largely by the 
angle of the sidewalls 26. Movement of B is solely by compressing or 
distorting sidewalls 26. The total deflection of the tread under may be 
represented by .DELTA.B. By inspection of FIGS. 2 and 3, it is seen that 
B.sub.1 =.sqroot.(C.sub.1 -A)(C.sub.1 +A) and B.sub.2 =.sqroot.(C.sub.2 
-A)(C.sub.2 +A). With the present invention, tire flotation is controlled 
by the compression of the B dimension, and the percent change of B under 
load is governed by the percent of change equation: 
##EQU1## 
If C forms a 45.degree. angle with respect to A, then for 10% movement in 
C, B compresses a 22% of its original unloaded dimension. By lowering the 
angle, amplification is increased. Compression amplification allows the 
use of moderately compressible, high strength elastomers. These materials 
would be too hard to provide good ride with solid construction. With the 
tunnel construction and compression amplification, comfort and flotation 
similar to pneumatic construction is achieved. 
One factor that contributes to the effectiveness of the tunnel construction 
and compression amplification is the concave sides 28 of the tire. These 
concavities cause the side walls 26 to collapse inwardly as they compress, 
thereby lowering the angle between C and A and increasing the compression 
amplification. Another fortunate result is that the tire bead 38 and bead 
shoulder 42 press with increasing pressure against their respective rim 
surfaces as the compression load on the tread increases, thereby causing 
the tire to resist any tendency to climb over the bead flange 18. 
Variables that can be changed to vary the flotation quality of the tire 
are: (1) The elastomer can be made harder or softer to give a desired 
physical property, such as wear resistance, without sacrificing flotation; 
(2) The slope of C can be varied to increase or decrease the amount of 
compression amplification; and (3) The dimension A can be made variable by 
using spring-loaded restraint on the tire beads. 
The advantages of the invention are many. Probably most important to the 
bicycle owner is the fact that there is no possibility of blow-outs, flat 
tires, or underinflation. The tire has excellent ride quality, comparable 
to a pneumatic tire, with about the same rolling resistance as the latter. 
Cuts may be easily repaired with silicone bathtub caulk, or other suitable 
adhesive, which is needed merely to hold the cut edges together to prevent 
the cut from propagating further. No other tire can be repaired so easily. 
The tire has a thick usable tread surface for extended tire wear. It can 
be easily removed from the wheel rim for spoke adjustment and repair, and 
then replaced. The compression amplification principle allows the tire to 
absorb the energy of a severe impact over a much wider range than would be 
possible with a solid tire, and as a result, rim damage will be no greater 
than with conventional pneumatic bike tires. And finally, the bead-locking 
insert cooperates with the tire beads to hold the tire firmly on the rim 
at all times, despite excessive impact loads or severe side-thrust loads. 
While we have shown and described in considerable detail what we believe to 
be the preferred form of the invention, it will be understood by those 
skilled in the art that the invention is not limited to such details, but 
might take various other forms within the scope of the claims. For 
example, the invention has been described in particular as a bicycle tire, 
but it is not limited solely to bicycle tires, as it might be used with 
any other vehicle tire. In particular, tires used on wheel chairs or carts 
might be made in accordance with the invention, as well as industrial and 
agricultural tires.