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Ralco Tyre Test Report

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Objective: To determine the 1.Wear resistance, 2. Road grip, 3. Load Dilation, 4. Bike handling ability and, 5. Stunting ability (wheelie / Stoppie / other stunts)RALCO  Tubed Tyres,

By carrying out Quantitative & Qualitative Tests on Ralco tubed tyres.

Two types of tests were done on the tyres by actually fitting on suitable bikes:

1.Static tests: INDENT-TEST & DiLATiON TEST, both quantified and objective.

2.Dynamic tests : in which wear measurements are quantitative & objective, while other results & conclusions are qualitative & subjective.

The following Static Measurements &Tests were done on various tyre sizes:

A. INDENT-TESTs:

<i> Round indentor ; 4.5 mm dia (round) indent point, increasing to 12.5 mm diameter over 50 mm (along hypotenuse), giving a slope angle of @ 20 degrees.

<ii>Hexagonal punch tapering into Flat Line indent point ;  1.5 mm thick edge X 14 mm long (blade type) indent point, increasing to 12.5 mm over 50 mm (along hypotenuse), giving a slope angle of @ 20 degrees.

Each indentor was held orthogonally at exactly 90 degrees to horizontal plane on the top of the exposed surface (front mudguard removed) of the front tyre, fitted on bike and inflated to 30 psi==2.06 kg / sq. cm. The indentor was subjected to a 30kg static load orthogonally downwards.

 B. DiLATiON TESTs:

<b>Tread Dilation measurements on two different size Ralco tyres: 2.75 X 18 front and 100/90 X 18 rear, having air pressure in tyres== 30 psi==2.06 kg / sq. cm. fitted on a Hero Honda Karizma of the time when today’s HeroMotoCorp was still Hero Honda.

Two readings of gap between treads were taken. One with bike off-stand with no load (no rider) on it, and another with 300 kg load of 4 riders on it.

 TYRE: Some Facts:

1>>>The first ever wheel was made of wood and the tyre was a steel belt wound around the wooden wheel. The American Stagecoach of the Cowboy times in Texas USA 150 years ago had wooden wheels with wooden spokes with a steel band (belt) around its circumference. Indeed, even today, the Indian bullock cart (bail-gaadi) has a steel tyre (belt) on wooden wheels.

2>>>The first practical pneumatic (air-filled) tube+tyre was made by John Dunlop in Ireland in 1887. Natural rubber (which comes as a sap from natural Rubber trees (in Kerala, Malaysia & Brazil) is VULCANiZED to withstand the rigors of road use. The Vulcanization process was invented by Charles Goodyear.

3>>>TYRE dimensions: Till the advent of the 150 cc Hero Honda CBZ (156.8 cc to be exact) in April-May 2000, almost all tyres on 100 cc bikes were 2.75 X 18 front and 3.oo X 18 rear. Some bikes, like the RX100 had even thinner tyres==2.5o X 18 front and 2.75 X 18 rear. In these tyre dimensions, 2.75, 3.oo and 2.5o indicate the WiDTH of the fully inflated tyre in inches, while 18 indicates the inner diameter of the tyre in inches (=0ne-and-a-half-feet), which would be the same as the diameter of the wheel rim in inches. 2.5o is probably the thinnest tyre ever used on any Indian geared motorcycle (except moped). Indeed, the TVS XL70 2-stroke moped uses 2.5o thickness tyres both front and rear, though of 16-inch diameter. The thinnest tyre ever used on any motorized two wheeler is probably the 2.oo inch wide, 17-inch diameter tyre used on the Enfield MOFA moped, which had a 22 cc engine and produced just 0.8 bhp of power at 5000 rpm. Another moped named Kinetic Luna WiNGs also used tyres of 2-inch thickness, though at 16-inches the diameter was an inch smaller than the 17 inch MOFA tyre diameter.

4>>>Hero Honda CBZ was the first Indian motorcycle to use a thicker / fatter tyre which was 100/90 X 18. These numbers mean that the tyre is 100 mm wide with and Aspect Ratio of 90%, which means, the height of the tyre is 90% of 100 mm, i.e. 90 mm, measured from where the tyre is touching the ground up to the wheel rim. 18 is the diameter of the tyre in inches.

5>>>Earlier Unique Tyre Sizes: The earliest Indian motorcycles were: Bullet, Yezdi (Jawa) and Rajdoot. While Bullet and Rajdoot used 19-inch diameter tyres, Yezdi 250 used 16-inch diameter tyres. Thickness varied from 3.oo inches in Rajdoot; 3.25 in Yezdi 250, and 3.25 (front) & 3.50 (rear) in Bullet.

6>>>Among the current modern bikes, the trend (started by Bajaj) is to have 17inch tyres. Why? People are getting shorter, so using 17inch tyres makes the seat height one inch lower, allowing shorties to ride more confidently.

7>>>Safety: The TWO factors which affect bike rider safety to the maximum are ROAD GRiP and handling-ability. Here, road grip matters 85% and handling-ability matters 15%. For road grip, softness matters 85% and tread pattern matters 15%. Obviously, softer tyres will wear out faster and have shorter life but rider life will be longer. Harder tyre lasts longer (save money) but is less safe.

8>>>Aspect Ratio: is the ratio of the depth of the tyre (measured vertically with the tyre fitted on the bike - depth is the measurement of distance measured from where the tyre is touching the ground up to the wheel rim), divided by the width of the tyre (measured horizontally with the tyre fitted on the bike). Thus: Aspect Ratio==Depth upon Width & always written on the tyre as a percentage.

9>>>In recent times there is a trend to have VERY WIDE tyres having LOW ASPECT RATiO, as low as 60%, which means a tyre size of (say) 130/60 X 17, and these are mostly tubeless. A 130/60 X 17 tyre has a width of 130 mm (measured horizontally) with an aspect ratio of 60%, which means depth of tyre is 60% of 130 mm, which is 130 X 0.6==78 mm.

10>>>Wide tyres having Low Aspect Ratio have a larger footprint (=more road contact area), due to which such tyres have better road holding and better braking.

ACTUAL MEASUREMENTS:

<i> Wear Resistance: This is an indication of LiFE of TYRE.  

Brand new Ralson tyres were fitted on a brand new Hero Karizma ZMR 223 cc bike. Ralson tyre of  size 100/90 X 18 was fitted on rear alloy wheel and Ralson tyre of size 2.75 X18 was fitted on front alloy wheel.

ROAD & LOAD CONDiTiONs: The bike was ridden from Pune to Ludhiana and back, single seat, by rider Devjeet Saha whose weight is 75 kg. The total distance covered from fitting brand new Ralson tyres till tread depth was measured again was 4472 km. Out of this distance, 4144 km was covered in the Pune – Ludhiana – Pune ride (mostly high speed highway riding) and 328 km was ridden in Pune city and environs, the rider always being 75 kg Devjeet Saha (no double seat at all) alone throughout.

Except for the last 20 km entering Pune on the return journey, there was no rain and the roads were totally dry throughout. For the purpose of this report, the wet condition of the road for 20 km out of a total of 4472 km is miniscule (less than half percent), and statistically insignificant. Thus this report gives TYRE WEAR for totally dry road conditions. This trip was done in the last week of September in temperatures ranging between 30 degrees Centigrade to 44 degrees Centigrade.

In the brand new Rear tyre, the TREAD DEPTH in the centre as measured by highly accurate Vernier Calipers was 7.5 mm, while the TREAD DEPTH at the side (edge) of the tyre was 6.5 mm.

After the 4472 km ride as per road, load & temperature conditions mentioned above, the central TREAD DEPTH of Rear tyre had reduced to 5.5 mm and at the side (edge) it had reduced to 6.1mm. Compared to the wear in the centre (2.5 mm), the wear at the side (edge) of 0.4 mm is very little, and statistically insignificant. Therefore, to determine wear-resistance (which gives an indication of tyre life) we shall consider only central tread depth wear.

The central groove depth in the Front tyre reduced from 4.65 mm to 4.35 mm, indicating a wear of 0.3 mm in 4472 km, which is very much less than rear tyre, and statistically insignificant, hence insignificant for wear calculation.

Firstly, out of the above total 4472 km, 4144 km (~93%) was done on highways at speeds averaging 80 kmph. The WEAR FACTOR therefore needs to be discounted for day-to-day use in city traffic by 99% bike users, who can hardly exceed 55 kmph on our crowded city roads. Since it is a proven fact that tyre wear increases EXPONENTiALLY with increase in road speed, we need to account for much LESS WEAR at 55 kmph than at 80 kmph.

Secondly, temperature varies as per the seasons and regions in the huge geographical region that is India. While it may never fall below 35 degrees Centigrade in Chennai (Tamil Nadu), it may never go above 20 degrees Centigrade in Srinagar (J&K), though it is a fact that in J&K there are much more bikes in Jammu than in Srinagar. Thus it is statistically essential to equalize / normalize temperature for majority reasons where 90% of people live and use bikes.

Therefore for the purpose of this research, and for mathematical and statistical compatibility, we scientifically take WEAR FACTOR as 50% of our wear measurements above due to the fact that winter temperatures fall to FiVE degrees Centigrade in Jammu, Delhi, Pune and many other places in the country.

Thirdly: Rain. It is a fact that tyres wear MUCH LESS in wet conditions than in dry climate. Since Rainy season lasts from June to October (33% == one third of the year), we shall further reduce WEAR FACTOR by another 50% to account for wet season.

Now let us calculate tyre life as per WEAR actually measured by Devjeet Saha’s 4144 km high speed ride. On a straight line basis==high speed ride on highways at 40 degrees Centigrade: The wear was 2.5 mm in (say) 5000 km (actually 4472 km). So if SAFE TREAD DEPTH for replacement (as recommended by SAE) is 1.5 mm, then out of 7.5 mm tread depth of new tyre, we have 6.0 mm tread depth to use, tyre life (in high speed, hot, racing conditions of Devjeet Saha’s highway ride) would be 0.5 mm per 1000 km, which would be 12000 km till tread depth wore out to 1.5 mm, the safe limit set by SAE.

To account for day-to-day usage by normal rider in city conditions, as per the three factors mentioned above==speed (55 Vs 80); temperature (winter is much colder for four months in a year); and rainy season (four months), we can conclude that life of Ralson tubed tyre is 12000 X 3==36000 km, or (say) 40,000 km to round off.

<ii> Road Grip-Indent Test: Road Grip quality of tyre depends (among other factors) MAJORLY on softness / hardness of tyre, footprint area and tread design & depth. Of course, terrain surface quality, on which a bike tyre has to travel, is the MOST MAJOR FACTOR, but tyre manufacturers have absolutely no control on terrain surface quality. Therefore tyre makers design tyres based on the kind of terrain which a vehicle will be mostly used upon. A prime example of terrain specific tyres are the “knobby” tyres fitted on dirt bikes & ATVs which have to travel on loose soil / sand and “kuccha” surfaces. Needless to say, such knobby tyres would not be very suitable for use on tarmacadam roads or concrete expressways, which all of our urban roads and highways are made of.

While TREAD DESIGN is not a closed ended subject (new tread patterns keep evolving all the time), tread depth and tyre material hardness are key factors affecting road grip.

Footprint area though very important for road grip, also has a downside.  Even though larger footprint tremendously increases road grip & braking, larger footprint will increase friction and weight of tyre, both of which will adversely affect fuel consumption. Also there has to be some kind of limit on the width of the tyre. While a 0ne-foot wide tyre may make a bike almost skid proof, it would make the bike look like a road-roller and be almost impossible to steer and very difficult to handle. The sheer weight of a foot wide tyre would limit speed so much as to make it highly impractical. Thus there has to be a trade-off (balance) between grip requirement and handling ability as well as between weight and mileage requirement.

While it is a truism that deeper tread would give better road grip, it is also a fact that if the tread valley is too deep, the tread hill may tend to collapse in hard braking and/ or sharp turns, or even otherwise. Thus there is a limit to tread depth.

Then there is the question of  RAiN. Wet roads can lead to aquaplaning (also called hydroplaning), in which a film of water inhibits direct contact between tyre and road surface, resulting in skidding and loss of control.

Though tread depth and shape are a considerable factor in preventing hydro-planing / aqua-planing, in Hindustan 85% of the time we are on dry roads. Therefore for the purpose of this research, we shall consider only dry roads, which comprise 85% of the riding time in our riding life, for which, hardness / softness of the tyre material becomes critical.

To get an idea of the hardness / softness of the tyre material, we did the INDENT-TEST as mentioned above. The results of the 30 kg orthogonal Indent-test were as below:

The round indent, surface point area 16 sq.mm (=0.16 sq.cm), made an indent of 7.0 mm depth.

30 kg load (=force) on 0.16 sq.cm translates to (30 divided by 0.16=187.5 kg/cm2), which divided by 1.03 (atmospheric pressure is 1.03 kg/cm2) gives a pressure of @182 atmospheres.

The flat indent, surface point area 28 sq.mm (=0.28 sq.cm), made an indent of 4.0 mm depth, which translates to a pressure of @ 104 atmospheres.

Now indentor area16 sq.mm divided by indentor area 28 sq. mm == 0.57.

And,

Indent depth 4.0 mm divided by indent depth 7.0 mm == 0.57.

The fact that indent depth ratio (4/7=0.57) is EXACTLY equal to the INVERSE of indentor point area (16/28=0.57) which is almost the same as the ratio of pressures (104/182=0.57) exerted by the two different indentors, shows that the material of is 100% uniformly distributed throughout the body of the tyre.

We shall define the figure 0.57 as the SOFTNESS COEFFiCiENT of  RALCO tyre material.

The ideal softness coefficient of tyre material would be 0.5, which would be an EXACT balance between desired softness (FOR BETTER GRiP AND RiDER SAFETY) and actual hardness (for LONGER TYRE LIFE, competitive price and greater profit to tyre maker).

The fact that RALCO tyres have a SOFTNESS COEFFiCiENT OF 0.57, shows that RALCO tyres are 14% softer than commercial mandate, and are therefore mathematically 14% more safe, because they have 14%  better ROAD GRiP, which makes for 14% GREATER SAFETY FOR RIDER.

<iii> LOAD DiLATiON TEST: Whenever a body is subjected to a load, the body dilates due to load & pressure. This is LAW OF NATURE. Even the human body dilates. Tyres also dilate. Our objective here is to MEASURE the dilation of tyre when load is applied, which in case of tyre is when Driver / Pillion / Triple seat / four people sit on the bike.

We took readings of TREAD GAP WiDTH measured by VERNiER CALiPERs on  2.75 X 18 front tyre and 100/90 X 18 rear tyre, having air pressure in tyres== 30 psi==2.06 kg / sq. cm.

The no-load gap in the central tread of both front and rear tyres was 5.35 mm. When subjected to 300 kg load (=4 adults sitting on it), the front tyre tread gap dilated to 6.35 mm (1.0 mm increase), and rear tyre tread gap dilated to 6.75 mm (1.4 mm increase). This is as per expectation because rear tyre takes more % of the total weight than the front tyre. If the weight was EQUAL on both wheels we could extrapolate that the mean increment in tread gap would be midway between 1.0 mm and 1.4 mm. That is 1.2 mm. Given that the tread depth at the centre is 7.5 mm, and mean tread gap is 1.2 mm, the ratio is almost 1:6.

1.6 seems the ideal ratio for a tyre having material quality as defined by Indent Test and Wear Test. Yet the road holding quality is greatly affected by the TREAD-SPREAD-ABiLiTY of the Tread pattern+Material quality defined by the ratio of 1:6 between increment in tread gap AND tread depth.  

In an extension of the same experiment, we applied WHiTE PAiNT on corresponding surfaces of both front and rear tyre and took its imprint on the ground and measured the width of the white paint imprint on the floor, without load and with load. These were measured at 2.55 cm wide Front tyre & 4.0 cm Rear tyre at No Load, AND 3.0 cm front tyre & 7.0 cm rear tyre at 300 kg Load, which gives a very visual picture of the effect of load on tyre dilation. You can see photos/ video of this experiment in the accompanying CD.

 <iv> Bike Handling Ability  

Bikeguru’s findings: There are no measureable parameters to define the above abilities. However bikeguru has extensively driven the Hero ZMR fitted with RALCO tyres in Pune city, on highways, and on EXTREMELY BAD ROADs such as the Tamini Ghat Road on the Pune-Roha-Pune (230 km) trip on 26.Oct.2012.

OVERALL behavior and performance of the RALCO tyres was EXCELLENT.

 

Ralco Tyres Analytic-Test: http://youtu.be/7jAe3_gY8sM

Ralco Tyres Action Test: http://youtu.be/-EcH9Gm5t9Q

Team bikeguru:

bikeguru Dilip Bam: www.facebook.com/bikegurudilipbam

Devjeet Saha: www.facebook.com/sahadevjeet

Hrishikesh Mandke: www.facebook.com/hrishikesh.mandke

Photo Credits: www.djclicks.com 

 

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