Wheel Gauge Research Articles

Causes and failure forms of railway wheels

Railway wheels are a crucial part of the system, which provide necessary traction on railway tracks by carrying cyclic loads. Therefore, it is important to understand the various failure mechanisms of railway wheel sets and the causes to prevent the failure for safety issues. All various railway wheel failures such as crack and rim, crack at rim and disc interface, circumferential chipping-off, wheel tread shelling, thermal crack on wheel tread, wheel tread wear, fatigue, creep, wheel gauge widening, and wheel gauge condemning and their corresponding causes also discussed in this manuscript. Further, it gives detailed wheel failure scenarios in tread and disc braking of locomotive, wagon, and coach wheels. The in-depth details of various wheel failure sceneries observed and analyzed from the field, and case studies are also reviewed in detail.

Influence of wheel tread wear on Rolling Contact Fatigue and on the dynamics of railway vehicles

This paper evaluates the influence of railway tread wear on the occurrence of Rolling Contact Fatigue (RCF) as well as other dynamic parameters of the railway vehicle in order to propose a tread maintenance limit. Around 160 unworn and worn AAR-1/20wheel profiles were measured and simulated inside the commercial software UM® - Universal Mechanism on a representative track segment of a Brazilian railway. With the simulated dataset, RCF was evaluated using the Shakedown Diagram, the Energy Dissipation Model, and the Wheel Gauge Side False Flange Gradient. Vehicle dynamics were assessed using the Nadal Criterion, contact pressure, and Rolling Resistance. The results show when the tread wear depth exceeds 2.0 mm, RCF is very likely to occur due to larger contact pressures. However, no clear relationship between tread wear, safety (Nadal Criterion), and fuel expenditure were observed. Therefore, this study suggests keeping wheelsets in service until a tread wear depth of 2.0 mm occurs in order to avoid RCF.

Gauge widening failures of wagon wheels in Indian Railways: Finite element modeling and observed statistics

There were many gauge widening cases identified in wagon wheels of Indian Railways during the past decade, but no investigation was conducted to analyse the failures. The present work aims to investigate the main cause of failures in wagon wheels due to gauge widening. A train running model is used to estimate heat generation at wheel and brake block interface. A finite element model is used to estimate temperature and stress state in the wheel during heat treatment, wheel and axle fitment, and braking. Heat partition between brake blocks and wheel is considered for the analysis. Further, heat losses to the environment because of convection and radiation are also incorporated in the model. The wheel gauge reduces during the braking process and the permanent wheel gauge increases during the cooling process. Permanent wheel gauge increases with non-uniformity in braking and a higher frequency of braking.

Finite element modeling of railway wheel gauge change during braking: Effect of lateral shift of brake block

Finite element analysis is used to investigate the wheel gauge change in a new railway wheel under regular braking conditions and shifted brake block away from the flange. The FEM model used here accounts for residual stress development during manufacturing, thermal heat flux partitioning during braking, and heat dissipation to rail and ambient. The wheel gauge decreases while braking and increases once the wheel cools down in normal braking conditions. When the brake blocks are moved away from the wheel flange, a similar pattern emerges; however, the wheel gauge change is greater than in the previous case. The lateral displacement of brake blocks away from the flange side of the railway wheel during braking may result in a larger wheel gauge drop during braking and a larger wheel gauge increase after cooling.

Evaluation of the return of investments in transport route development

The network of Russian railways provides the movement of goods and passengers both within the country and in the context of international transport, through which goods from different countries go in transit. In Russia the railway lines are double-track and fully electrified on the main directions of the EastWest transport corridor. The modernization of the branches from the Trans-Siberian railway to the state border with China and Mongolia continues. The paper describes the business model of the project, the corresponding calculations for managerial decisions on the launch of a direct train route Novosibirsk – Urumqi and return. During the study, the monitoring of existing routes of passenger traffic was carried out: the capacity of railway routes, frequency, duration and capacity of alternative crossings. The result of the study is a developed model for launching a project of a direct connection between Novosibirsk and Urumqi and return. The paper describes the stations that are of particular importance for the route – the place of customs inspection, rearrangement of wheel sets of cars due to the different wheel gauge of neighboring countries. The result of the study is a multifunctional model of a transport route that allows analyzing the economic parameters of any route of a railway communication. According to the model, it is possible to analyze various parameters of the revenue side of the project, calculate the amount of investments and indicators for the assessment of the effectiveness of real investments.

Review of Track Gauge for Trans-Sumatera Railway Revitalization and Development

The aim of this research is to comprehend in details how revitalization and development of railway infrastructure on the Trans-Sumatera line in Sumatera Island. The main problem in this research is that the use of railways in Sumatera Island is neither sustainable nor in all provinces. This research is both meta-analytical, by exploring the existing journals, and factual as a phenomenon in the utilization of spoor width that happens in the world today. It is completed by parameter or performance indicators as for benchmarking with other countries. From the result of this research, the data shows that almost 60 percent of existing railway tracks around the world have been installed with standard gauge of 1,435 mm and have been international standard. The benefit of this study is that the leaders or decision makers can take it into account to support the future transportation in Sumatera Island which must be oriented to bigger, faster, safer, cleaner, cheaper, affordable, and leisure. To keep exploiting the existing railway or track can be done by developing construction equipment of track gauge adjuster to change the wheel gauge from 1,435 mm to 1,067 mm. Subsequently re-gauging is done in stages, changing the track gauge from narrow gauge of 1,067 mm to standard gauge of 1,435 mm.

Effect of periodic wheel tread reprofiling on wheel gauge evolution in the wheelsets of tread-braked coaches: Finite element modeling and field observations

Field statistics of the wheelsets of gauge-widened coaches in the Indian Railways show higher tendency for excessive wheel gauge widening for lower diameter wheelsets. Additionally, the axial flange deflection in gauge-widened wheelsets increases nearly linearly with the radial distance. In this work, a finite element model is developed to investigate the reasons behind these field observations. The model considers heat generation during braking, heat loss to rail, brake blocks, ambient air, residual stresses generated during wheel manufacturing, and material removal during wheel reprofiling. Wheel gauge evolution is studied for different braking histories, including those that span the entire life period of the wheel, i.e. as the wheel diameter reduces from its initial to minimum allowable size. Simulations show that higher wheel rim temperatures and lower wheel stiffness, for lower diameter wheels, result in higher wheel gauge widening for these wheelsets. Wheel gauge widening occurs primarily due to bending at the hub–disc interface; consequently, the axial flange deflection increases linearly with the radial distance.

FEATURES OF STRESS-STRAIN STATE OF THE DUAL RAILWAY GAUGE

Purpose. The possibilities of railway transport for organizing transportation between the countries of the European Union and Ukraine are not fully utilized, since there are a number of technical differences in transport systems, namely: wheel gauge, characteristics of rolling stock, voltage in the contact network, dimensions, etc. One of the options in the organization of goods transportation in international traffic is the use of 1.435/1.520 mm dual gauge. The purpose of this study is to analyze the features of the stress-strain state of the combined construction of the track, first of all the changes in the operation of the under-sleeper base due to the use of a special design of reinforced concrete sleepers with simultaneous fastening of four rails. Methodology. To determine the stresses in the under-sleeper base, a spatial model of dynamic deformations of the railway track was chosen based on the elasticity theory. The movement on a railway track of a conventional construction (with sleepers Ш-1-1), accepted as a reference one, and along the track for combined movement, which differs from a standard using sleepers of type Ш2С-1, was considered. The main results of the calculations were the matrix of stresses in the under-sleeper base. Findings. The analysis of the results of the stresses simulation in the under-sleeper base of the dual gauge did not show their increase in absolute values, but revealed cyclical changes in the possible directions in deviation of ballast particles if there is a propensity for the occurrence of inelastic deformations in the ballast layer. Such a stress-strain state of the under-sleeper base, in turn, can lead to the appearance of deformations in the sleepers and the deterioration of the overall track geometry. Originality. The tasks of simulation got the further development of the track and rolling stock interaction, in particular to determine the stress-strain state of the under-sleeper base of the dual gauge. Practical value. The obtained results can be used to determine the timing of repair work on the sections with a combined track construction, justify the necessary degree of ballast consolidation, the feasibility of using the geogrids or special bonding materials.

Gauge widening of passenger coach wheel sets in Indian Railways: Observed statistics and failure analysis

Abstract Several hundreds of gauge widening cases have been reported in coaching stock wheel sets of Indian Railways over the last two years. This work investigates the effect of non-uniformity in braking, brake load, braking frequency, wheel profile, and braking cycles on wheel gauge evolution in coach wheel sets with an aim to identify root cause of the problem. A validated finite element model considering heat generation at brake-wheel interface, heat partitioning at wheel-brake block and wheel-rail interfaces, and convective, radiative heat loss to ambient air is used to estimate wheel temperatures, stresses, and gauge change. Residual stresses generated during wheel manufacturing and fitment of wheel onto axle are considered in the study. It is found that wheel gauge reduces during braking and increases as wheels subsequently cool down. Magnitude of temporary gauge reduction and permanent gauge widening increases with increasing heat input. Thus, higher non-uniformity in braking – leading to overheating of some wheels – can cause wheel gauge widening. Interestingly, reduction in brake load reduces permanent gauge widening but increases temporary gauge reduction during braking. Nature of gauge change and effect of wheel profile, seen from gauge widening statistics, correlate well with findings from simulations.

Application of an on-line sensor to map soil packing density for site specific cultivation

Tillage is the most energy consuming operation in the primary production in agriculture. The majority of farmers worldwide adopt homogeneous tillage operations to optimise crop establishment, reduce weeds and compaction, where soil disturbance took place across the entire field including areas where no soil preparation is needed. This practice consumes high energy and leads to decrease soil resistance to water and air erosion. This paper investigates the potential of a previously developed on-line soil bulk density (BD) sensor to map packing density for the delineation of management zones for site specific tillage. The on-line sensor consisting of a multi-sensor platform pulled by a tractor was used to measure soil BD in two experimental fields with potato in East Anglia, UK. It consisted of a load cell to measure subsoiler draught, a wheel gauge to measure depth and a visible and near infrared (vis-NIR) spectrophotometer for the measurement of moisture content (MC). Based on these three on-line measured parameters, BD was calculated using a previously developed model with a hybrid numerical and multivariate statistical analysis. The packing density (PD) was then calculated for all on-line measured points as a function of BD and clay content (CC). Maps of soil BD and PD were produced, and both fields were divided into management zones with different tillage recommendations.Results, in the studied fields, showed that the on-line BD sensor can map not only the spatial distribution in BD but enable estimation of PD too. Classifying the PD into three compaction classes revealed that only 4.8% of the field needs aggressive tillage (primary and secondary tillage) and about 34.8% of the field requires harrowing or surface loosening with a cultivator (reduced tillage), while the remaining area of the field do not need any sort of tillage. Virtual calculations of fuel consumption and CO2 emission in one field based on the three PD classes confirmed that site specific tillage would significantly reduce energy consumption and CO2 emission, as compared to reduced and conventional tillage practices. By this it can be concluded that the on-line multi sensor platform for the assessment of PD holds a great potential for mapping and managing soil compaction site specifically. A future study is needed to relate soil compaction to actual plant growth and yield, and evaluate cost of production and practical limitations of this approach.

Locomotive wheel failure from gauge widening/condemning: Effect of wheel profile, brake block type, and braking conditions

A finite element model accounting for heat partitioning at brake block–wheel and rail–wheel interfaces is used to investigate the effect of locomotive wheel profile, wheel diameter, brake block type, nature of braking (independent, synchronized, and drag), braking frequency and braking cycles on wheel gauge for tread braked, locomotive wheel sets. A train running model estimates heat generation rates during braking for assumed operating and braking conditions. Wheel profiles and brake block types used in the work, match with that used by Indian Railways. Bending at hub–disc and disc–rim interfaces is seen to primarily control axial deflection of wheels. While gauge reduction is observed during braking, gauge increase is seen during subsequent cooling. Maximum gauge increase occurs as the wheels finally cool down to room temperature. S-shaped wheels are seen to be better suited than straight plate and parabolic profile wheels for avoiding excessive gauge change. Locomotive wheel failure from gauge widening and condemning, albeit at different times, is seen to occur with independent braking for locomotives fitted with straight plate, S-shaped as well as parabolic profile wheels.

Locomotive wheel failure from gauge widening/condemning: Finite element modeling and identification of underlying mechanism

Gauge change in straight plate, locomotive, railway wheels is studied using finite element analysis. The study accounts for residual stresses generated during wheel manufacturing and fitment of the wheel on locomotive axle. A validated thermal model accounting for heat loss to rail, brake blocks and ambient air is considered for accurate prediction of wheel temperatures for a given train running and braking history. Results are obtained for low- and high-friction, composite brake blocks used by Indian Railways for two limiting braking scenarios: (i) synchronized braking where braking effort is uniformly distributed on all brake blocks and (ii) independent braking where braking effort to decelerate a train is provided solely by locomotive brake blocks. Results show that bending at hub–disc interface predominantly governs the gauge change. While compressive hoop stresses in the tread region, occurring from rim heating during braking, cause gauge reduction, tensile hoop stresses in the tread region, occurring during wheel cool down cause an increase in wheel gauge. Importantly, while gauge condemning is a transient phenomenon occurring only during braking, gauge widening is “permanent” as it exists even after the wheels cool to room temperature. Allowable reduction of wheel gauge of 0.5mm, currently used by Indian Railways, is found to be highly restrictive. In fact, in service wheel failure based on this criterion is observed in all braking scenarios considered.

Estimation of railway wheel running temperatures using a hybrid approach

Accurate prediction of railway wheel temperatures, for a given running and braking history, is crucial for estimation of service induced thermal stresses which can affect wheel gauge and fatigue crack growth, particularly in tread region. In this work, a three step approach is adopted for estimating wheel temperatures. Firstly, a train running model employing brake block friction, wheel–rail traction-slip, and train running resistance characteristics are used to estimate heat generation rates at brake block–wheel and wheel–rail interfaces. Next, a two dimensional boundary element method, proposed in this work, is used to estimate heat partitioning at the said interfaces as a function of brake block type, geometry, and thermal properties. Lastly, finite element method is used to estimate wheel temperatures taking inputs from the train running model and the boundary element method. The adopted methodology is validated using wheel temperatures, on rim and rim–disc interface, from field trials of a locomotive fitted with cast-iron brake blocks. A good match between simulation and field trial results was obtained despite highly complex speed and braking patterns encountered in the field trial. For periodic braking with no stopovers, heat lost to the rail, cast-iron brake blocks, via radiation, and convection are seen to be comparable to one another. Enhanced convective cooling of railway wheels and use of higher diffusivity brake blocks are seen to be effective ways of reducing the wheel temperatures and resulting thermal stresses.

Additional Yaw Moment Control of a 4WIS and 4WID Agricultural Data Acquisition Vehicle

A four-wheel independent steering (4WIS) and a four-wheel independent driving (4WID) agricultural data acquisition vehicle (ADAV) system was designed to monitor and manage the growing status of bio-energy crops. To avoid destroying crops, a changeable wheel gauge and high-clearance design was employed, which brought new problems to the ADAV system: reduced path-following precision and driving stability. Given the dynamic characteristics of the ADAV system, an additional yaw moment control (AYC) system was designed to achieve high path-following precision and stability of the ADAV system. Using the input steering wheel angle and driving speed, the desired yaw rate and sideslip angle were calculated. The difference between the desired and actual yaw rate and that between the desired and actual sideslip angle were employed as feedbacks to obtain an additional yaw moment executed on the ADAV system in real time. The effectiveness of the AYC system was verified in field tests. Experimental results show that the actual yaw rate, sideslip angle and path trajectory were close to the desired ones. Therefore, the stability and path-following accuracy of the ADAV system were improved.

Multiple on-line soil sensors and data fusion approach for delineation of water holding capacity zones for site specific irrigation

Soil water holding capacity (WHC) and available water (AW) are key parameters for water management and irrigation scheduling. Measurement of within field variation in WHC should account for affecting soil properties, namely organic matter (OM) or organic carbon (OC), clay content (CC), bulk density (BD) and plasticity index (PI). The aim of this paper is to implement on-line multi-sensor and data fusion approach for the delineation of management zones of WHC for site specific irrigation. A multi-sensor platform was used, which consisted of a load cell to measure subsoiler draught, a wheel gauge to measure depth and a visible and near infrared (vis–NIR) spectrophotometer for simultaneous measurement of moisture content (MC), OC, PI, CC and BD. An electromagnetic induction (EMI) sensor was implemented separately apart from the multi-sensor platform to measure apparent electrical conductivity (ECa) in three experimental fields with vegetable crop production in East Anglia, UK. Partial least squares (PLS) regression analysis with full-cross validation was adopted to establish vis–NIR calibration models of MC, OC, PI and CC, which were validated with prediction sets. Artificial neural network (ANN) and multiple linear regression (MLR) analyses were carried out on the six named soil properties to derive maps of WHC. The validation of the on-line measurement accuracy for OC and MC were good to excellent with root mean square error of prediction (RMSEP) values of 0.06–0.72% and 0.97–2.49% and residual prediction deviation (RPD) values of 2–2.57 and 1.94–2.1, respectively. For CC and PI, the measurement was of fair to moderate accuracy with RMSEP values of 1.4–3.94% and 2.43–2.77% and RPD values of 1.41–1.77 and 1.25–1.48, respectively. Accordingly each field was divided into four classes, with normalised ranges of WHC of 0–0.25, 0.26–0.50, 0.51–0.75 and 0.76–1. These were designated, respectively, as low, medium, high and very high WHC, with the low category being the most susceptible to water changes and entitled to accommodate the largest number of moisture sensors and receive the largest amount of water. A comparison between calculated WHC and measured AWC maps showed distinguished spatial similarity, to recommend the multi-sensors and data fusion as a new approach to optimise irrigation scheduling.

Calibration of an on-line sensor for measurement of topsoil bulk density in all soil textures

An on-line sensor for the prediction of bulk density (BD) has been previously developed, and calibrated for light textured soils. This study aims to expand the implementation of this sensor for all soil types, including clay soils. The on-line sensor consists of a single ended shear beam load cell to measure draught (D), a visible and near infrared (vis–NIR) sensor to measure moisture content (MC), and a wheel gauge equipped with a draw wire linear sensor to measure depth (d). This sensor was used to collect data from 14 fields across four European countries (Denmark, Czech Republic, the Netherlands and the UK) with different soil textures. The three measured parameters were substituted into a previously developed model to calculate BD. The calculated BD for 333 samples was compared with BD measured with a core sampling kit to validate the system and to calculate correction factors (CF) valid for each additional soil texture. A multiple linear regression (MLR), nonlinear multiple regression (NMR) and artificial neural network (ANN) analyses were carried out to establish models to predict CF, as a function of average field MC and soil texture fractions.For clay soils, the correlation between the measured and on-line predicted BD was satisfactory (R2=0.54–0.69), and suggested a large negative CF>−0.248Mgm−3. For other soil types with lighter soil textures, accuracy of measurements varied (R2=0.51–0.96), with lower CF values than those calculated for clay soils and ranged between negative and positive values (−0.007Mgm−3<CF<0.079Mgm−3). The ANN analysis resulted in the best model to predict CF as function of MC and soil texture fractions (R2=0.96), which allowed the utilisation of the on-line measurement system for any field having any texture and average MC. The on-line BD sensor was shown to be capable of predicting field dry BD rapidly for a large number of samples, as compared with traditional methods.

Development of the Reconfigurable Data Acquisition Vehicle for Bio-Energy Crop Sensing and Management

In this article, the development of the Reconfigurable Data Acquisition Vehicle (R-DAV) that has a high performance as a wheeled mobile robot is presented. The R-DAV is designed to monitor and manage the growing status of bio-energy crops, and the vehicle will be used for image collection, density measurements, and chemical applications. A theoretical model has been proposed to optimize the configuration. The 4-Wheel-Drive-4-Wheel-Steering (4WD4WS) locomotion was proposed as the essential base for high traffic conditions and maneuverability, and a prototype model was fabricated for this scenario. The chassis was uniquely reconfigured in two ways: (1) by adjusting the clearance and (2) by changing the wheel gauge. The reconfiguration of the clearance was necessary to operate the vehicle over a range of heights of bio-energy crops at different growing stages in the Miscanthus (Miscanthus is a genus of about 15 species of perennial grasses native to subtropical and tropical regions of Africa and southern Asia). The adjustable wheel gauge layout was designed to follow variable inter-row tracks in the Miscanthus field. Furthermore, a triangle-shaped guard was specifically considered to minimize the crop damage when the vehicle enters into the field.

Expanding implementation of an on-line measurement system of topsoil compaction in loamy sand, loam, silt loam and silt soils

A previously developed model for on-line prediction of soil compaction indicated as bulk density (BD), was limited in use for a sandy loam field. This study was undertaken to investigate the possibility of modifying this model for new soil textures, namely loamy sand, loam, silt loam and silt soils. Using the on-line measurement system of BD, measurements were carried out in four fields with different average textures of loam, sandy loam and silt loam and silt loam/silt fields. The on-line measurement system used consisted of a subsoiler, whom draught ( D) was measured with a single shear beam load cell and depth ( d) was measured with a wheel gauge consisted of a swinging arm metal wheel equipped with a linear variable differential transducer (LVDT). The soil gravimetric moisture content (MC) was measured with the oven drying method. The on-line measured BD was compared with measured BD with Kopecki rings (core sampling method) (736 samples), to validate the potential use of this sensor in the new studied soil textures. Results showed that the BD model can be used for on-line measurement of soil compaction for the selected textures. It was found that the correction factor ( M) of this model was mainly sensitive to variable MC, and slightly sensitive to clay content. The M at field scale varied between 0.994 (silt loam/silt soil with an average MC of 0.279 kg kg −1) and 1.171 (loam soil with an average MC of 0.105 kg kg −1). At almost the same texture, M varied between 1.171 for an average MC of 0.105 kg kg −1 and 1.122 for an average MC of 0.186 kg kg −1, which proves the domination of MC effect on M. The multiple linear regression (MLR) analysis (analysis of variance (ANOVA)) performed between MC and clay and M retained MC as M predictor ( P < 0.001, R 2 = 0.86). This MLR resulted in similar prediction accuracy of compacted zones as compared to the linear regression model between MC and M. In a variable texture field, the corrected BD model resulted in remarkable spatial similarity of BD between the corrected on-line and core sampling method. Therefore, it can be concluded that the BD model with the new M can be used for on-line measurement of soil compaction in loamy sand, sandy loam, loam, silt loam, and silt soils at different MC, bearing in mind that the difference in clay content is minimal (83–175 g kg −1).

Development of on-line measurement system of bulk density based on on-line measured draught, depth and soil moisture content

On-line measurement of soil compaction is needed for site specific tillage management. The soil bulk density ( ρ) indicating soil compaction was measured on-line by means of a developed compaction sensor system that comprised several sensors for on-line measurement of the draught ( D) of a soil cutting tool (subsoiler), the soil cutting depth ( d) and the soil moisture content ( w ). The subsoiler D was measured with a single shear beam load cell, whereas d was measured with a wheel gauge that consisted of a swinging arm metal wheel and a linear variable differential transducer (LVDT). The soil w was measured with a near infrared fibre-type spectrophotometer sensor. These on-line three measured parameters were used to calculate ρ, by utilising a hybrid numerical–statistical mathematical model developed in a previous study. Punctual kriging was performed using the variogram estimation and spatial prediction with error (VESPER) 1.6 software to develop the field maps of ρ, soil w , subsoiler d and D, based on 10 m × 10 m grid. To verify the on-line measured ρ map, this map was compared with the map measured by the conventional core sampling method. The spherical semivariogram models, providing the best fit for all properties was used for kriging of different maps. Maps developed showed that no clear correlation could be detected between different parameters measured and subsoiler D. However, the D value was smaller at shallow penetration d, whereas large D coincided with large ρ values at few positions in the field. Maps of ρ measured with the core sampling and on-line methods were similar, with correlation coefficient ( r) and the standard error values of 0.75 and 0.054 Mg m −3, respectively. On-line measured ρ exhibited larger errors at very dry zones. The normal distribution of the ρ error between the two different measurement methods showed that about 72% of the errors were less than 0.05 Mg m −3 in absolute values. However, the overall mean error of on-line measured ρ was of a small value of 2.3%, which ensures the method accuracy for on-line measurement of ρ. Measurement under very dry conditions should be minimised, because it can lead to a relatively large error, and hence, compacted zones at dry zones cannot be detected correctly.

Development of Gauge Change Bogies

For the gauge-changeable EMUs (free-gauge train), we have been developing two types of new gauge change bogies, types A and B. The type A bogie adopts the direct drive motor system to mount a motor directly on the side of a wheel, independent wheel system, and wheel-set steering system. The type B bogie adopts the cardan drive system. Both bogies can change the wheel gauge between the narrow gauge and standard gauge sections. This paper discusses their construction and mechanism to change the wheel gauge.